U.S. patent application number 13/595645 was filed with the patent office on 2012-12-20 for photonic crystal fibers having a preferred bending plane and systems that use such fibers.
This patent application is currently assigned to OmniGuide, Inc.. Invention is credited to James Goell, Steven A. Jacobs, Steven G. Johnson, Marin Soljacic, Burak Temelkuran, Gokhan Ulu, Tairan Wang.
Application Number | 20120321262 13/595645 |
Document ID | / |
Family ID | 36603625 |
Filed Date | 2012-12-20 |
United States Patent
Application |
20120321262 |
Kind Code |
A1 |
Goell; James ; et
al. |
December 20, 2012 |
PHOTONIC CRYSTAL FIBERS HAVING A PREFERRED BENDING PLANE AND
SYSTEMS THAT USE SUCH FIBERS
Abstract
In general, in a first aspect the invention features photonic
crystal fibers that include a core extending along a waveguide
axis, a confinement region extending along the waveguide axis
surrounding the core, and a cladding extending along the waveguide
axis surrounding the confinement region, wherein the cladding has
an asymmetric cross-section.
Inventors: |
Goell; James; (Lexington,
MA) ; Soljacic; Marin; (Belmont, MA) ; Jacobs;
Steven A.; (Needham, MA) ; Wang; Tairan;
(Chelmsford, MA) ; Ulu; Gokhan; (Roslindale,
MA) ; Temelkuran; Burak; (Boston, MA) ;
Johnson; Steven G.; (Cambridge, MA) |
Assignee: |
OmniGuide, Inc.
|
Family ID: |
36603625 |
Appl. No.: |
13/595645 |
Filed: |
August 27, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11366345 |
Mar 2, 2006 |
8280212 |
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13595645 |
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11101915 |
Apr 8, 2005 |
7167622 |
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11366345 |
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60658531 |
Mar 4, 2005 |
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Current U.S.
Class: |
385/123 ;
385/134 |
Current CPC
Class: |
C03B 2203/42 20130101;
A61B 2018/2272 20130101; G02B 6/03638 20130101; A61F 9/00825
20130101; A61B 1/018 20130101; C03B 2203/18 20130101; A61B
2018/2238 20130101; C03B 2203/14 20130101; C03B 2203/12 20130101;
G02B 6/023 20130101; G02B 6/02385 20130101; A61F 2009/00863
20130101; A61B 18/22 20130101; C03B 2203/16 20130101; A61B 18/201
20130101; A61B 2018/00982 20130101; A61F 9/008 20130101; C03B
2201/86 20130101; A61F 9/00802 20130101; G02B 6/03694 20130101;
G02B 6/03622 20130101; Y02P 40/57 20151101; A61F 2009/00891
20130101; A61F 9/00821 20130101; G02B 6/02304 20130101 |
Class at
Publication: |
385/123 ;
385/134 |
International
Class: |
G02B 6/02 20060101
G02B006/02; G02B 6/00 20060101 G02B006/00 |
Claims
1.-25. (canceled)
26. A waveguide fiber, comprising: a core extending along a
waveguide axis; a confinement region extending along the waveguide
axis, the confinement region surrounding the core; and a cladding
extending along the waveguide axis, the cladding surrounding the
confinement region, wherein the waveguide fiber bends preferably in
a bend plane relative to other planes, and the cladding includes a
first portion extending along the waveguide axis and a second
portion extending along the waveguide axis, the first portion being
composed of a first material having a first stiffness and the
second portion being composed of a second material having a second
stiffness, the first stiffness being different from the second
stiffness.
27. (canceled)
28. The waveguide fiber of claim 26 wherein the cladding further
comprises a third portion being composed of a third material having
a third stiffness, the third stiffness being different from the
first stiffness.
29. The waveguide fiber of claim 28 wherein, in cross-section, the
core is positioned between the second portion and the third
portion.
30. The waveguide fiber of claim 26 wherein the first portion
surrounds the second portion.
31.-33. (canceled)
34. The waveguide fiber of claim 26, wherein the first stiffness is
greater than the second stiffness.
35. The waveguide fiber of claim 26, wherein the first stiffness is
lower than the second stiffness.
36. The waveguide fiber of claim 26, wherein the waveguide fiber
comprises a photonic crystal fiber.
37. A system, comprising: a CO.sub.2 laser; and a waveguide fiber,
the waveguide fiber having an input end positioned relative to the
CO.sub.2 laser to receive radiation from the CO.sub.2 laser and the
waveguide fiber is adapted to deliver the radiation to a target,
wherein the waveguide fiber comprises: a core extending along a
waveguide axis; a confinement region extending along the waveguide
axis, the confinement region surrounding the core; and a cladding
extending along the waveguide axis, the cladding surrounding the
confinement region, wherein the cladding has an asymmetric
cross-section that extends along a length of the waveguide
fiber.
38. The system of claim 37, wherein the waveguide fiber comprises a
photonic crystal fiber.
39. A system, comprising: a waveguide fiber having an input end and
an output end; and a handpiece attached to the waveguide fiber,
wherein the handpiece allows an operator to control the orientation
of the output end to direct the radiation to a target location of a
patient and the waveguide fiber comprises: a core extending along a
waveguide axis; a confinement region extending along the waveguide
axis; the confinement region surrounding the core; and a cladding
extending along the waveguide axis, the cladding surrounding the
confinement region, wherein the cladding has an asymmetric
cross-section that extends along a length of the waveguide
fiber.
40. The system of claim 39 wherein the handpiece comprises an
endoscope.
41. The system of claim 40 wherein the endoscope comprises a
flexible conduit and a portion of the waveguide fiber is threaded
through a channel in the flexible conduit.
42. The system of claim 41 wherein the endoscope comprises an
actuator mechanically coupled to the flexible conduit configured to
bend a portion of the flexible conduit in at least one plane
thereby allowing the operator to vary the orientation of the output
end.
43. The system of claim 42 wherein the waveguide fiber is attached
to the endoscope so that the at least one plane corresponds to the
bend plane of the waveguide fiber.
44. The system of claim 39, wherein the waveguide fiber comprises a
photonic crystal fiber.
45. A fiber assembly comprising: a jacket adapted to surround a
waveguide fiber having a waveguide axis, the jacket exhibiting a
preferential bend plane.
46. The fiber assembly of claim 45, wherein the jacket comprises an
asymmetric cross-sectional profile about the waveguide axis.
47. The fiber assembly of claim 46, wherein the cross-sectional
profile is elliptical.
48. The fiber assembly of claim 45, further comprising: the
waveguide fiber disposed within the jacket.
49. The fiber assembly of claim 48, wherein the waveguide fiber
comprises a core extending along the waveguide axis.
50. The fiber assembly of claim 49, wherein the waveguide fiber
comprises a confinement region extending along the waveguide axis,
the confinement region surrounding the core.
51. The fiber assembly of claim 50, wherein the confinement region
comprises a seam.
52. The fiber assembly of claim 51, the waveguide fiber further
comprises a cladding extending along the waveguide axis, the
cladding surrounding the confinement region.
53. The fiber assembly of claim 52, wherein the cladding is
adhesively bonded to the jacket.
54. The fiber assembly of claim 53, wherein the jacket and cladding
are consolidated.
55. The fiber assembly of claim 48, wherein the waveguide fiber
comprises a photonic crystal fiber.
56. A system comprising: a CO.sub.2 laser; and the fiber assembly
comprising: a waveguide fiber having a waveguide axis, and a jacket
surrounding the waveguide fiber, the jacket exhibiting a
preferential bend plane, wherein the fiber assembly has an input
end positioned relative to the CO.sub.2 laser to receive radiation
from the CO.sub.2 laser and the laser assembly is adapted to
deliver the radiation to a target.
57. The system of claim 50, wherein the jacket comprises an
asymmetric cross-sectional profile about the waveguide axis.
58. The system of claim 56, wherein the waveguide fiber comprises a
photonic crystal fiber.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part application of
and claims priority under 35 U.S.C. .sctn.120 to U.S. application
Ser. No. 11/101,915. entitled "PHOTONIC CRYSTAL FIBERS AND MEDICAL
SYSTEMS INCLUDING PHOTONIC CRYSTAL FIBERS," filed on Apr. 8, 2005.
This application also claims priority under 35 U.S.C.
.sctn.119(e)(1) to Provisional Patent Application No. 60/658,531,
entitled "PHOTONIC CRYSTAL FIBERS," filed on Mar. 4, 2005. The
entire contents of both, of the above-mentioned applications are
incorporated herein by reference.
BACKGROUND
[0002] This invention relates to the field of photonic crystal
waveguides and systems using photonic crystal waveguides.
[0003] Waveguides play important roles in numerous industries. For
example, optical waveguides are widely used in telecommunications
networks, where fiber waveguides such as optical fibers are used to
carry information between different locations as optical signals.
Such waveguides substantially confine the optical signals to
propagation along a preferred path or paths. Other applications of
optical waveguides include imaging applications, such as in an
endoscope, and in optical detection. Optical waveguides can also be
used to guide laser radiation (e.g., high intensity laser
radiation) from a source to a target in medical (e.g., eye surgery)
and manufacturing (e.g., laser machining and forming)
applications.
[0004] The most prevalent type of fiber waveguide is an optical
fiber, which utilizes index guiding to confine an optical signal to
a preferred path. Such fibers include a core region extending along
a waveguide axis and a cladding region surrounding the core about
the waveguide axis and having a refractive index less than that of
the core region. Because of the index-contrast, optical, rays
propagating substantially along the waveguide axis in the
higher-index core can undergo total internal reflection (TIR) from
the core-cladding interface. As a result, the optical fiber guides
one or more modes of electromagnetic (EM) radiation to propagate in
the core along the waveguide axis. The number of such guided modes
increases with core diameter. Notably, the index-guiding mechanism
precludes the preserve of any cladding modes lying below the
lowest-frequency guided mode for a given wavevector parallel to the
waveguide axis. Almost all index-guided optical fibers in use
commercially are silica-based in which one or both of the core and
cladding are doped with impurities to produce the index contrast
and generate the core-cladding interface. For example, commonly
used silica optical fibers have indices of about 1.45 and index
contrasts ranging from about 0.2% to 3% for wavelengths in the
range of 1.5 mm, depending on the application.
[0005] Another type of waveguide fiber, one that is not based on
TIR index-guiding, is a Bragg fiber, which includes multiple
alternating dielectric layers surrounding a core about a waveguide
axis. The multiple layers form a cylindrical mirror that confines
light to the core over a range of frequencies. The alternating
layers are analogous to the alternating layers of a planar
dielectric stack reflector (which is also known as a Bragg mirror).
The multiple layers form what is known as a photonic crystal, and
the Bragg fiber is an example of a photonic crystal fiber, Photonic
crystal structures, are described generally in Photonic Crystals by
John D, Joannopoulos et al. (Princeton University Press, Princeton
N.J., 1995).
[0006] Drawing a fiber from a preform is the most commonly used
method for making fiber waveguides. A preform is a short rod (e.g.,
10 to 20 inches long) having the precise form and composition of
the desired fiber. The diameter of the preform, however, is much
larger than the fiber diameter (e.g., 100's to 1000's of times
larger). Typically when drawing an optical fiber, the material
composition of a preform includes a single glass having varying
levels of one or more dopants provided in the preform core to
increase the core's refractive index relative to the cladding
refractive index. This ensures that the material forming the core
and cladding are theologically and chemically similar to he drawn,
while still providing sufficient index contrast to support guided
modes in the core. To form the fiber from the preform a furnace
heats the preform to a temperature at which the glass viscosity is
sufficiently low (e.g., less than 10.sup.8 Poise) to draw fiber
from the preform. Upon drawing, the preform necks down to a fiber
that has the same cross-sectional composition and structure as the
preform. The diameter of the fiber is determined by the specific
rehological properties of the fiber and the rate at which it is
drawn.
[0007] Preforms can be made using many techniques known to those
skilled in the art, including modified chemical vapor deposition
(MOVD), outside vapor deposition (OVD), plasma activated chemical
vapor deposition (PCVD) and vapor axial deposition (VAD). Each
process typically involves depositing layers of vaporized raw
materials onto a wall of a pre-made tube or rod in the form of
soot. Each soot layer is fused shortly after deposition. This
results in a preform tube that is subsequently collapsed into a
solid rod, over jacketed, and then drawn into fiber.
[0008] Optical fibers applications can be limited by wavelength and
signal power. Preferably, fibers should be formed from materials
that have low absorption of energy at guided wavelengths and should
have minimal defects. Where absorption is high, it can reduce
signal strength to levels indistinguishable from noise for
transmission over long fibers. Even for relatively low absorption
materials, absorption by the core and/or cladding beats the fiber.
Detects ears scatter guided radiation out of the core, which can
also lead to heating of the fiber. Above a certain power density,
this heating can irreparably damage the fiber. Accordingly, many
applications that utilize high power radiation sources use
apparatus other than optical fibers to guide the radiation from the
source to its destination.
SUMMARY
[0009] In general, in a first aspect, the invention features a
photonic crystal fiber that includes a core extending along a
waveguide axis, a confinement region extending along the waveguide
axis, the confinement region surrounding the core, and a cladding
extending along the waveguide axis, where the cladding surrounds
the confinement region. The cladding has an asymmetric
cross-section that extends along a length of the photonic crystal
fiber.
[0010] Embodiments of the-photonic crystal fiber can include one or
more of the following features. For example, the confinement region
can include a layer of a first material arranged in a spiral
structure that extends along the waveguide axis and the asymmetric
cross-section causes the photonic crystal fiber to bend preferably
in a plane that does not intersect an end of the spiral structure
that is adjacent the core. The photonic crystal fiber can be
configured to guide radiation at a wavelength .lamda. along the
waveguide axis where the confinement region includes a periodic
structure that substantially confines the radiation to the core.
The cladding can include a layer of a first material surrounding
the confinement region, the layer having a thickness along a
direction normal to the waveguide axis that is larger than the
period of the periodic structure of the confinement region (e.g.
the layer thickness can he about 10 times larger than the period,
about 20 times larger, about 50 times larger, about 100 times
larger, about 200 times larger, about 400 times larger).
[0011] In certain, embodiments, the asymmetric cross-section causes
the photonic crystal fiber to bend preferably in a bend plane
relative to other planes.
[0012] The confinement region can include a seam extending along
the waveguide axis. In some embodiments, the confinement region
includes a layer of a first material that is arranged in a spiral
around the waveguide axis and the seam is the end of the layer that
is adjacent the core. The cladding can have a short cross-sectional
dimension, a, non-coincident with the seam. The seam can be located
in a range from about 80 degrees to about 110 degrees from, the
short cross-sectional dimension. The cladding can have a short
cross-sectional dimension, a, and a long cross-sectional dimension,
b, and an ellipticity, .epsilon., given by the formula:
= ( b - a ) 1 2 ( b + a ) , ##EQU00001##
that is in a range from about 0.05 to about 0.5 (e.g., about 0.08
or more, about 0.1 or more, about 0.12 or more, about 0.15 or more,
about 0.2 or more, about 0.4 or less, about 0.3 or less, such as
about 0.25).
[0013] The confinement region can include a layer of a first
dielectric material arranged in a spiral around the waveguide axis.
The confinement region can further include a layer of a second
dielectric material arranged in a spiral around the waveguide axis,
the second dielectric material having a different refractive index
from the first dielectric material. The first dielectric material
can be an inorganic dielectric material, such as a glass (e.g., a
chalcogenide glass). The second dielectric material can be an
inorganic dielectric material, such as a polymer.
[0014] In some embodiments, the confinement region includes at
least one layer of a chalcogenide glass. In certain embodiments,
the dielectric confinement region includes at least one layer of a
polymeric material. The core can be a hollow core.
[0015] In some embodiments, the photonic crystal fiber is
configured to guide radiation at about 10. 6 .mu.m along the
waveguide axis.
[0016] In another aspect, the invention features a system that
includes a CO.sub.2 laser and the foregoing photonic crystal fiber.
The photonic crystal fiber has an input end that is positioned
relative to the CO.sub.2 laser to receive radiation from the
CO.sub.2 laser and the photonic crystal fiber being arranged to
deliver the radiation to a target.
[0017] In a further aspect, the invention features a system that
includes the foregoing photonic crystal fiber which has an input
end and an output end, and a handpiece attached to the photonic
crystal fiber. The handpiece allows an operator to control the
orientation of the output end to direct the radiation to a target
location of a patient. In some embodiments, the handpiece includes
an endoscope. The endoscope can include a flexible conduit and a
portion of the photonic crystal fiber is threaded through a channel
in the flexible conduit. The endoscope can include an actuator
mechanically coupled to the flexible conduit configured to bend a
portion of the flexible conduit in at least one plane thereby
allowing the operator to vary the orientation of the output end.
The photonic crystal fiber can be attached to the endoscope so that
the at least one plane corresponds to the bend plane of the
photonic crystal fiber.
[0018] In general, in another aspect, the invention features a
photonic crystal fiber that includes a core extending along a
waveguide axis, a confinement region extending along the waveguide
axis, the confinement region surrounding the core, and a cladding
extending along the waveguide axis, the cladding surrounding the
confinement region. The photonic crystal fiber bends preferably in
a bend plane relative to other planes.
[0019] Embodiments of the photonic crystal fiber can include one or
more of the following features and/or one or more features of other
aspects.
[0020] For example, in some embodiments, the cladding includes a
first portion extending along the waveguide axis and a second
portion extending along the waveguide axis, the first portion being
composed of a first material and the second portion being composed
of a second material having a greater stiffness than the first
material. The cladding can further include a third portion being
composed of a third material having a greater stiffness than the
first material. In cross-section, the core can be positioned
between the second portion and the third portion. The first portion
can surround the second portion.
[0021] In general, in a further aspect, the invention features a
fiber waveguide that includes a core extending along a waveguide
axis, a first portion extending along the waveguide axis, the first
portion, surrounding the core, and a cladding extending along the
waveguide axis, the cladding surrounding the first portion region.
An interface between the core and the first portion includes a
defect (e.g., a seam) that extends along the waveguide axis and the
fiber waveguide bends preferably in a bend plane relative to other
planes. Embodiments of the photonic crystal fiber can include one
or more features of other aspects.
[0022] In general, in a further aspect, the invention features a
fiber waveguide that includes a core extending along a waveguide
axis, a first portion extending along the waveguide axis, the first
portion surrounding the core, and a cladding extending along the
waveguide axis, the cladding surrounding the first portion, wherein
an interface between the core and the first portion includes a
defect (e.g., a seam) that extends along the waveguide axis and the
cladding has an asymmetric cross-section that extends along a
length of the photonic crystal fiber. Embodiments of the photonic
crystal fiber can include one or more features of other
aspects.
[0023] In general, in a further aspect, the invention features a
fiber waveguide that includes a core extending along a waveguide
axis, and a first portion extending along the waveguide axis, the
first portion surrounding the core, wherein the first portion has
an asymmetric cross-section that extends along a length of the
photonic crystal fiber. Embodiments of the photonic crystal fiber
can include one or more features of other aspects.
[0024] In general in another aspect, the invention features
photonic crystal fibers that include a core extending along a
waveguide axis, a confinement region extending along the waveguide
axis surrounding the core, and a cladding extending along the
waveguide axis surrounding the confinement region, wherein the
cladding has an asymmetric cross-section.
[0025] In general, in another aspect, the invention features
photonic crystal fibers that include a core extending along a
waveguide axis, a confinement region extending along the waveguide
axis surrounding the core, and a cladding extending along the
waveguide axis surrounding the confinement region, wherein the
photonic crystal fiber bends preferably in a first plane compared
to other planes.
[0026] In general, in a further aspect, the invention features
photonic crystal fibers that include a core extending along a
waveguide axis, a confinement region extending along the waveguide
axis surrounding the core, and a cladding extending along the
waveguide axis surrounding the confinement region, the cladding
having a first diameter of a first size and a second diameter of a
second size different from the first size.
[0027] In general, in another aspect, the invention features
photonic crystal fibers that include a core extending along a
waveguide axis, a confinement region extending along the waveguide
axis surrounding the core, and a cladding extending along the
waveguide axis surrounding the confinement region, the cladding
having a surface with a cross-section having portions with
differing radii of curvature.
[0028] Embodiments of the photonic crystal fibers can include one
or more of the following features. The confinement region can
include a seam. The seam can he non-coincident with the first
plane. The seam can be adjacent the core. The cladding can have a
short cross-sectional dimension non-coincident with the seam. The
seam can be located about 80 degrees or more from the
cross-sectional dimension. The seam can be located about 85 degrees
or more from the cross-sectional dimension. The seam can be located
about 90 degrees from the cross-sectional dimension. The
confinement region can have a spiral cross-section. The confinement
region can include a chalcogenide glass.
[0029] Among other advantages, the photonic crystal fibers can
control which portion of a fiber is on the inside or outside of a
bend in the fiber. For example, fibers can be designed so that the
fiber preferably bends in a way that a seam (or other defect) in
the fiber is not positioned on the outside of the bend. Positioning
a defect away from the outside of a bend cm reduce loss of guided
radiation due to the bend, and can reduce fiber failure due to,
e.g., heating of the fiber at the defect when the defect is
positioned on the outside of a bend.
[0030] Accordingly, fibers can be provided that have improved loss
characteristics compared with fibers that don't have a preferred
bend plane. Improved loss characteristics can result in higher
working powers, greater efficiency, and/or longer working
lifetimes. Improved loss characteristics can also allow fibers to
he used in applications not previously appropriate for the fibers,
such as certain high power applications (e.g., high power medical
applications).
[0031] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features and advantages of the invention will be apparent
from the description and drawings, and from the claims.
DESCRIPTION OF DRAWINGS
[0032] FIG. 1A is a cross-sectional view of an embodiment of a
photonic crystal fiber.
[0033] FIG. 1B is a perspective view of the embodiment of the
photonic crystal fiber shown in FIG. 1A.
[0034] FIGS. 2A-2E are schematic diagrams showing stages in a
method for forming the photonic crystal fiber shown in FIG. 1.
[0035] FIG. 3 is a cross-sectional view of an embodiment of a
photonic crystal fiber.
[0036] FIGS. 4A-4D are cross-sectional views of embodiments of
photonic crystal fibers.
[0037] FIG. 5 is a schematic diagram of a medical laser system that
includes a photonic crystal fiber.
[0038] FIG. 6A is a schematic diagram of a medical laser system
that includes a photonic crystal fiber and an endoscope.
[0039] FIG. 6B is a schematic diagram of the endoscope shown in
FIG. 6A.
[0040] FIG. 7 is a schematic diagram of an optical
telecommunication system that implements photonic crystal fibers
described herein.
[0041] FIG. 8 is a schematic diagram of a laser system that
implements photonic crystal fibers described herein.
[0042] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0043] Referring to FIGS. 1A and 1B, a photonic crystal fiber 100
includes a core 120 extending along an axis 199, and a confinement
region 110 surrounding the core. A cladding 160 surrounds the
confinement region. Photonic crystal fiber 100 is configured to
guide radiation at a guiding wavelength .lamda. along axis 199. As
discussed below, confinement region 110 substantially confines
guided radiation at 1 to core 120. Cladding 160 serves primarily to
protect and mechanically support, confinement region 110.
[0044] Cladding 160 has an asymmetric cross-section with a larger
diameter along a major axis 161 compared to its diameter along a
minor axis 162 orthogonal to the major axis. The major and minor
axes are orthogonal to axis 199. The asymmetric cross-section is
also manifested in the shape of the cladding's outer surface. In
particular, the outer surface of cladding 160 includes portions of
differing curvature. In particular, cladding 160 includes arcuate
portions 131 and 132 and two straight portions 133 and 134. Arcuate
portions 131 and 132 are on opposite sides of the cladding along
major axis 121. Straight portions 133 and 134 are on opposite sides
of the cladding along minor axis 122. Cladding 160 is co-drawn with
confinement region 110 when the fiber is produced.
[0045] In general, the asymmetry of the cross-sectional profile of
cladding 160 is sufficient to cause fiber 100 to preferably bend in
a plane 101 defined by fiber axis 199 and the minor axis 162 during
normal use of the fiber. In general, where a fiber has a plane in
which the resistance to bending is less than other planes, the
plane is referred to as a "bend plane."
[0046] The ratio of cladding 160's outer diameter, b.sub.160, along
the major axis to its outer diameter, a.sub.160, along the minor
axis can vary. Typically, this ratio is selected so that fiber 100
bends preferably in the bend plane, while cladding 100 still
provides the desired mechanical support or other function(s) for
which it is designed (e.g., optical function-thermal management),
in some embodiments, this ratio can he relatively low, soon as
about 1.5:1 or less (e.g., about 1.4:1 or less, about 1.3:1 or
less, about 1.2:1 or less, about 1.1:1 or less). Alternatively, in
certain embodiments, this ratio can be larger than about 1.5:1.
(e.g., about 1.6:1 or more, about 1.7:1 or more, about 1.8:1 or
more, about 1.9:1 or more, about 2:1 or more).
[0047] The ratio of b.sub.160 to a.sub.160 can be characterized as
an ellipticity; .epsilon., which is mathematically expressed
as:
= ( b 160 - a 160 ) 1 2 ( b 160 + a 160 ) . ##EQU00002##
[0048] Typically, .epsilon. is selected so that fiber 100 has
desired mechanical properties, .epsilon. is generally sufficient
large so that fiber 100 has a preferred bend plane. For example,
.epsilon. can be about 0.05 or more (e.g., about 0.08 or more,
about 0.10 or more, about 0.12, or more, about 0.15 or more, about
0.1.8 or more, about 0.20 or more, about 0.22 or more), .epsilon.
should not he so large that if introduces unwanted ellipticity into
other parts of the fiber, such as the core. In some embodiments,
.epsilon. is less than 0.50 (e.g., about 0.40 or less, about 0.30
or less, about 0.25 or less, about 0.20 or less). In certain
embodiments, .epsilon. is in a range that provides a preferred bend
plane, but does not entirely prevent the fiber bending in the plane
orthogonal to the preferred bend plane. .epsilon. can be in a range
from about 0.08 to about 0.25 (e.g., from about 0.1.0 to about
0.20, from about 0.12 to about 0.18).
[0049] Typically, sis substantially constant along the length of
fiber 100, However, in certain embodiments, e can vary along the
length of the fiber. For example, in some embodiments. It may be
desirable to have a bend plane in one section of a fiber but not in
another. In such cases, .epsilon. can he relatively large in the
section where a bend plane is desired, but small or zero in other
sections. Further, in certain embodiments, a and b can be oriented
differently with respect to a reference co-ordinate system for
different portions of a fiber. For example, in some embodiments, it
may be desirable to have a bend plane in one orientation in one
section of a fiber, while having a bend plane with a different
orientation at another section. This can be achieved by having a
and b oriented differently in the different sections of the fiber.
Vary .epsilon. and/or a and b orientation can be achieved
introducing the asymmetry into the preform, while drawing fiber
from the preform, or after the fiber has been drawn.
[0050] In some embodiments, two or more lengths of fibers having
differing .epsilon.'s and/or differing orientations of a and b may
be connected to provide a concatenated fiber that has different
mechanical properties along its length.
[0051] In general, the actual dimensions of a.sub.160 and b.sub.160
can vary depending on the operational wavelength of operation of
fiber 100 and other constraints imposed by the application for
which the fiber is used. For example, a.sub.160 and b.sub.160
should be sufficiently larger to provide adequate mechanical
support and protection for core 120 and confinement region 110,
However, a.sub.160 and b.sub.160 should be small enough so that the
fiber is sufficiently flexible and/or capable in fitting in fiber
conduits of a particular size (e.g., in an endoscope conduit). In
some embodiments, a.sub.160 and/or b.sub.160 are about 500 .mu.m or
more (e.g., about 750 .mu.m or more, about 1,000 .mu.m or more,
about 1,250 .mu.m or more, about 1,500 .mu.m or more, about 1,750
.mu.m or more, about 2,000 .mu.m or more). a.sub.160 and/or
b.sub.160 can be about 10,000 .mu.m or less (e.g., about 7,000
.mu.m or less, about 5,000 .mu.m or less, about 3,000 .mu.m or
less, about 2,000 .mu.m or less).
[0052] Confinement region 110 includes continuous layers 130, 140,
and 150 of dielectric material (e.g., polymer, glass) having
different refractive indices, as opposed to multiple discrete,
concentric layers that form confinement regions in other
embodiments. Continuous layers 130, 140, and 150 form a spiral
around an axis 199 along which the photonic crystal fiber waveguide
guides electromagnetic radiation. One or more of the layers, e.g.,
layer 140 and/or layer 150, is a high-index layer having an index
n.sub.H and a thickness d.sub.H, and the layer, e.g., layer 130, is
a low-index layer having an index n.sub.L and a thickness d.sub.L,
where n.sub.H>n.sub.L (e.g., n.sub.H-n.sub.L can be greater than
or equal to or greater than 0.01, 0.05, 0.1, 0.2, 0.5 or more).
[0053] Because layers 130, 140, and 150 spiral around axis 109, a
radial section extending from axis 199 intersects each of the
layers more than once, providing a radial profile that includes
alternating high index and low index layers. In some embodiments,
layers 140 and 150 have the same refractive index. In such cases,
for all hut the innermost spiral of layer 140 and the outermost
spiral of layer 150, adjacent layers 140 and 150 effectively create
a single layer (e.g., a single high index or low index layer) along
a radial section.
[0054] Confinement region 110 has an inner seam 121 and an outer
seam 122 corresponding to the edges of the continuous layers from
which the confinement region is formed. Inner seam 121 is located
along an azimuth 123 that is displaced by an angle a from minor
axis 162. .alpha. can be in a range from about 10.degree. to about
170.degree. (e.g., from about 20.degree. to about 160.degree., from
about 30.degree. to about 150.degree. from about 40.degree. to
about 140.degree., from about 50.degree. to about 130.degree., from
about 60.degree. to about 120.degree., from about 70.degree. to
about 110.degree., from about 80.degree. to about 100.degree.). in
some embodiments, .alpha. is about 90.degree..
[0055] The inner seam does not lie in bend plane 101 of the fiber.
In fiber 100, this, is achieved by locating inner seam 121 away
from the minor axis. Locating the inner seam away from the bend
plane can be advantageous since it is believed that losses (e.g.,
due to scattering, and/or absorption) of guided radiation is higher
at the seam compared to other portions of the confinement region.
Further, it is believed that the energy density of guided radiation
in the core is higher towards the outside of a bend in the fiber
relative to the energy density at other parts of the core. By
locating the inner seam relative to the minor axis so that the seam
is unlikely to lie in the bend plane (e.g., where .alpha. is about
90.degree.), the probability that the inner seam will lie towards
the outside of a fiber bend is reduced. Accordingly, the
compounding effect of having a relatively high loss portion of the
confinement region at the region, where the energy density of
guided radiation is high can be avoided, reducing the loss
associated with bends in the fiber.
[0056] Although inner seam 121 and outer seam 122 are positioned at
the same azimuthal position with respect to axis 199 in fiber 100,
its other embodiments the inner and outer seams can be located
along at different relative azimuthal positions with respect to the
fiber's axis.
[0057] The spiraled layers in confinement region 110 provide a
periodic variation in the index of refraction along a radial
section, with a period corresponding to the optical thickness of
layers 130, 140, and 150. Is general, the radial periodic variation
has an optical period corresponding to
n.sub.130d.sub.130+n.sub.140d.sub.140+n.sub.150d.sub.150.
[0058] In embodiments where layers 140 and 150 have the same
refractive index, n.sub.H, and a combined thickness d.sub.H, layer
130 has a refractive index n.sub.L and thickness d.sub.L,
confinement region 110 has an optical period
n.sub.Hd.sub.H+n.sub.Ld.sub.L. The thickness (d.sub.H and d.sub.L)
and optical thickness (n.sub.Hd.sub.H and n.sub.Ld.sub.L) of layers
140 and 150 and of layer 140 can vary. In some embodiments, the
optical n.sub.Hd.sub.H=n.sub.Ld.sub.L. Layer thickness is usually
selected based on the desired optical performance of the fiber
(e.g., according to the wavelength radiation to be guided). The
relationship between layer thickness and optical performance is
discussed below. Typically, layer thickness is in the sub-micron to
tens of micron range. For example, d.sub.L and/or d.sub.H can be
between about 0.1 .mu.m to 20 .mu.m thick (e.g., about 0.5 to 5
.mu.m thick).
[0059] For the embodiment shown in FIG. 1, confinement region 110
is 5 optical periods thick. In practice, however, confinement
region 110 may include many more optical periods (e.g., more than
about 8 optical periods, 10 optical periods, 15 optical periods, 20
optical periods, 25 optical periods, such as 40 or more optical
periods).
[0060] Layer 140 and 150 include a material that has a high
refractive index, such as a chalcogenide glass. Layer 130 includes
a material having a refractive index lower than the high index
material of layers 140 and 150, and is typically mechanically
flexible. For example, layer 130 often includes a polymer.
Preferably, the materials forming layers 130, 140, and 150 can be
co-drawn. Criteria for selecting materials that can be co-drawn are
discussed below.
[0061] In the present embodiment, core 120 is hollow. Optionally,
the hollow core can be filled with a fluid, such as a gas (e.g.,
air, nitrogen, and/or a noble gas) or liquid (e.g., an isotropic
liquid or a liquid crystal). Alternatively, core 120 can include
any material or combination of materials that are ideologically
compatible with the materials forming confinement region 110. In
certain embodiments, core 120 can include one or more dopant
materials, such as those described in U.S. patent application Ser.
No. 10/121,452, entitled "HIGH INDEX-CONTRAST FIBER WAVEGUIDES AMD
APPLICATIONS," filed Apr. 12, 2002 and now published under Pub. No.
US-2003-0044158-A1, the entire contents of which, are hereby
incorporated by reference.
[0062] Core and confinement regions 120 and 110 may include
multiple dielectric materials having different refractive indices.
In such cases, we may refer to an "average refractive index" of a
given region, which refers to the sum of the weighted indices for
the constituents of the region, where each index is weighted by the
fractional area in the region of its constituent. The boundary
between layers 130 and 140 and layers 130 and 150, however, are
defined by a change in index. The change may be caused by the
interface of two different dielectric materials or by different
dopant concentrations in the same dielectric material (e.g.,
different dopant concentrations in silica).
[0063] Dielectric confinement region 110 guides EM radiation in a
first range of wavelengths to propagate in dielectric core 120
along waveguide axis 199. The confinement mechanism is based on a
photonic crystal structure in region 110 that forms a bandgap
including the first range of wavelengths. Because the confinement
mechanism is hot index-guiding, it is not necessary for the core to
have a higher index than that of the portion of the confinement
region immediately adjacent the core. To the contrary, core 120 may
have a lower average index than that of confinement region 110. For
example, core 120 may be air, some other gas, such as nitrogen, or
substantially evacuated. In such a case, EM radiation guided in the
core will have much smaller losses and much smaller nonlinear
interactions than EM radiation guided in a silica core, reflecting
the smaller absorption and nonlinear interaction constants of many
gases relative to silica or other such solid material. In
additional embodiments, for example, core 120 may include a porous
dielectric material to provide some structural support for the
surrounding confinement region while still defining a core that is
largely air. Accordingly, core 120 need not have a uniform index,
profile.
[0064] Layers 130, 140 and 150 of confinement region 110 form what,
is known as a Bragg fiber. The periodic optical structure of the
spirally wound layers are analogous to the alternating layers of a
planar dielectric stack reflector (which is also known as a Bragg
mirror). The layers of confinement region 110 and the alternating
planar layers of a dielectric stack reflector are both examples of
a photonic crystal structure. Photonic crystal structures are
described generally in Photonic Crystals by John D. Joannopoulos et
al. (Princeton University Press, Princeton N.J. 1995).
[0065] As used herein, a photonic crystal is a dielectric structure
with a refractive index modulation that produces a photonic bandgap
in the photonic crystal. A photonic bandgap, as used herein, is a
range of wavelengths (or inversely, frequencies) in Which there are
no accessible extended (i.e., propagating, non-localized) states in
the dielectric structure. Typically the structure is a periodic
dielectric structure, but it may also include, e.g., more complex
"quasi-crystals." The bandgap can be used to confine, guide, and/or
focalize light by combining the photonic crystal with "defect"
regions that deviate from the bandgap structure. Moreover, there
are accessible extended states for wavelengths both below and above
the gap, allowing light to be confined even in lower-index regions
(in contrast to index-guided the structures, such as those
described above). The term "accessible" states means those states
with which coupling is not already forbidden by some symmetry or
conservation law of the system. For example, in two-dimensional
systems, polarization is conserved, so only states of a similar
polarization need to be excluded from the bandgap. In a waveguide
with uniform, cross-section (such as a typical fiber), the
wavevector .beta. is conserved, so only states with a given .beta.
need to be excluded from the bandgap to support photonic crystal
guided modes. Moreover, in a waveguide with cylindrical symmetry,
the "angular momentum" index m is conserved, so only modes with the
same m need to be excluded front the bandgap. In short, for
high-symmetry systems the requirements for photonic bandgaps are
considerably relaxed compared to "complete" bandgaps in which all
states, regardless of symmetry, are excluded.
[0066] Accordingly, the dielectric stack reflector is highly
reflective in the photonic, bandgap because EM radiation cannot
propagate through the stack. Similarly, the layers in confinement
region 110 provide confinement because they are highly reflective
for incident rays in the bandgap. Strictly speaking, a photonic
crystal is only completely reflective in the bandgap when the index
modulation in the photonic crystal has an infinite extent.
Otherwise, incident radiation, can "tunnel" through the photonic
crystal via an evanescent mode that couples propagating modes on
either side of the photonic crystal. In practice, however, the rate
of such tunneling decreases exponentially with photonic crystal
thickness (e.g., the number of alternating layers). It also
decreases with the magnitude of the index-contrast in the
confinement region.
[0067] Furthermore, a photonic bandgap may extend over only a
relatively small region of propagation vectors. For example, a
dielectric stack may he highly reflective for a normally incident
ray and yet only partially reflective for an obliquely incident
ray. A "complete photonic bandgap" is a bandgap that extends over
all possible wavevectors and all polarizations. Generally, a
complete photonic bandgap is only associated with a photonic
crystal having index modulations along three dimensions. However,
in the context of EM radiation incident on a photonic crystal from
an adjacent dielectric material, we can also define an
"omidirectional photonic bandgap," which is a photonic bandgap for
all possible wavevectors and polarizations for which the adjacent
dielectric material supports propagating EM modes, Equivalently, an
omnidirectional photonic bandgap can be defined as a photonic hand
gap for all EM modes above the light line, wherein the light line
defines the lowest frequency propagating mode supported fey the
material adjacent the photonic crystal. For example, in air the
light line is approximately given by .omega.=c.beta., where .omega.
is the angular frequency of the radiation, .beta. is the
wavevector, and c is the speed of light. A description of an
omnidirectional planar reflector is disclosed in U.S. Pat. No.
6,130,780, the contents of which are incorporated herein by
reference. Furthermore, the use of alternating dielectric layers to
provide omnidirectional reflection (in a planar limit) for a
cylindrical waveguide geometry is disclosed in U.S. Pat. No.
6,463,200, entitled "OMNIDIRECTIONAL MULTILAYER DEVICE FOR ENHANCED
OPTICAL WAVEGUIDING" to Yoel Fink et al., the contents of which are
incorporated herein by reference.
[0068] When alternating the layers in confinement region 110 give
rise to an omnidirectional bandgap with, respect to core 120, the
guided modes are strongly confined because, in principle, any EM
radiation incident on the confinement region from the core is
completely reflected. However, such complete reflection only occurs
when there are an infinite number of layers. For a finite number of
layers (e.g., about 10 optical periods), an omnidirectional
photonic bandgap may correspond to a reflection in a planar
geometry of at least 95% for all angles of incidence ranging from
0.degree. to 80.degree. and for all polarisations of EM radiation
having frequency in the omnidirectional bandgap. Furthermore, even
when photonic crystal fiber 100 has a confinement region with a
bandgap that is not omnidirectional, it may still support a
strongly guided mode, e.g., a mode with radiation losses of less
than 0.1 dB/km for a range of frequencies in the bandgap.
Generally, whether or not the bandgap is omnidirectional will
depend on the size of the bandgap produced by the alternating layer
(which generally scales with index-contrast of the two layers) and
the lowest-index constituent of the photonic crystal.
[0069] In a Bragg-like configuration, the high-index layers may
vary in index and thickness, and/or the low-index layers may vary
in index and thickness. The confinement region may also include a
periodic structure including more than three layers per period
(e.g., four or more layers per period). Alternatively, in some
embodiments, the confinement region can include only two layers per
period. Moreover, the refractive index modulation may vary
continuously or discontinuously as a function of fiber radius
within the confinement region. In general, the confinement region
may be based on any index modulation that creates a photonic
bandgap.
[0070] In the present embodiment, multilayer structure 110 forms a
Bragg reflector because it has a periodic index variation with
respect to the radial axis. A suitable index variation is an
approximate quarter-wave condition. It is well-known that, for
normal incidence, a maximum band gap is obtained for a
"quarter-wave" stack in which each, layer has equal optical
thickness .lamda./4, or equivalently
d.sub.8/d.sub.L=n.sub.L/n.sub.H, where d and n refer to the
thickness and index, respectively, of the high-index and low-index
layers in a fiber including two layers per period. Normal incidence
corresponds to .beta.=0. For a cylindrical waveguide, the desired
modes typically lie near the light line .omega.=c.beta. (in the
large core radius limit, the lowest-order modes are essentially
plane waves propagating along z-axis, i.e., the waveguide axis). In
this case, the quarter-wave condition becomes:
d H d L = n L 2 - 1 n H 2 - 1 ##EQU00003##
[0071] Strictly speaking, this equation may not be exactly optimal
because the quarter-wave condition is modified by the cylindrical
geometry, which may require the optical thickness of each layer to
vary smoothly with its radial coordinate. Nonetheless, we find that
this equation provides an excellent guideline for optimizing many
desirable properties, especially for core radii larger than the
mid-bandgap wavelength.
[0072] The radius of core 120 can vary depending on the end-use
application of fiber 120. The core radius can depend on the
wavelength or wavelength range of the energy to be guided by the
fiber, and on whether the fiber is a single or multimode fiber. For
example, where the fiber is a single mode fiber for guiding visible
wavelengths (e.g., between about 400 nm and 800 nm) the core radius
can be in the sub-micron to several micron range (e.g., from about
0.5 .mu.m to 5 .mu.m). However, where the fiber is a multimode
fiber for guiding IR wavelengths (e.g., from about 2 .mu.m to 15
.mu.m, such as 10.6 .mu.m), the core radius can be in the tens to
thousands of microns range (e.g., from about 10 .mu.m to about
5,000 .mu.m, such-as about 500 .mu.m to about 2,000 .mu.m). The
core radius can be greater than about 5.lamda.. (e.g., more than
about 10 .lamda., more than about 20 .lamda., more than about 30
.lamda., more than about 50 .lamda., more than about 100 .lamda.),
where a is the wavelength of the guided energy.
[0073] As discussed previously, cladding 160 provides mechanical
support for confinement region 110. The thickness of cladding 160
can vary as desired along major axis 161. The thickness of cladding
160 along minor axis 162 can also vary but is generally less than
the thickness along the major axis. In some embodiments, cladding
160 is substantially thicker along the major axis than confinement
region 110. For example, cladding 160 can be about 10 or more times
thicker than confinement region. 110 (e.g., more than about 20,
more than about 30, more than about 50 times thicker) along the
major axis.
[0074] The composition of cladding 160 is usually selected to
provide the desired mechanical support and protection for
confinement region 110. In many embodiments, cladding 160 is formed
from, materials that can be co-drawn with the confinement region
110. Criteria for selecting materials suitable for co-drawing are
discussed, below. In some embodiments, cladding 160 can be formed
from the same material(s) as used to form at least part of
confinement region 110. For example, where layer 130 is formed from
a polymer, cladding 160 can be formed from the same polymer.
[0075] Turning now to the composition of layers 130, 140 and 150 in
confinement region 110, materials with a suitably high index of
refraction to form a high index portion (e.g., layers 140 and 150)
include chalcogenide glasses (e.g., glasses containing a chalcogen
element, such as sulfur, selenium, and/or tellurium), heavy metal
oxide glasses, amorphous alloys, and combinations thereof.
[0076] In addition to a chalcogen element, chalcogenide glasses may
include one or more of the following elements: boron, aluminum,
silicon, phosphorus, sulfur, gallium, germanium, arsenic, indium,
tin, antimony, thallium, lead, bismuth, cadmium, lanthanum and the
halides (fluorine, chlorine, bromide, iodine).
[0077] Chalcogenide glasses can be binary or ternary glasses, e.g.,
As--S, As--Se, Ge--S, Ge--Se, As--Te, Sb--Se, As--S--Se, S--Se--Te,
As--Se--Ta, As--Te, Ge--S--Te, Ge--Se--Te, Ge--S--Se, As--Ge--Se,
As--Ge--Te, As--Se--Pb, As--S--Tl, As--Se--Tl, As--Te--Tl,
As--Se--Ga, Ga--La--S, Ge--Sb--Se or complex, multi-component
glasses based on these elements such as As--Ga--Ge--S,
Pb--Ga--Ge--S, etc. The ratio of each element in a chalcogenide
glass can be varied. For example, a chalcogenide glass with a
suitably high refractive index may be formed, with 5-30 mole %
Arsenic, 20-40 mole % Germanium, and 30-60 mole % Selenium. As
another example, As.sub.2Se.sub.3 can be used.
[0078] Examples of heavy metal oxide glasses with high refractive
indices include Bi.sub.2O.sub.3-, PbO-, Tl.sub.2O.sub.3-,
Ta.sub.2O.sub.3-, TiO.sub.2-, and TeO.sub.2-containing glasses.
[0079] Amorphous alloys with suitably high indices of refraction
include Al--Te, R--Te(Se) (R=alkali).
[0080] Suitable materials for high and low index layers can include
inorganic materials such as inorganic glasses or amorphous alloys.
Examples of inorganic glasses include oxide glasses (e.g., heavy
metal oxide glasses), halide glasses and/or chalcogenide glasses,
and organic materials, such as polymers. Examples of polymers
include acrylonitrile-butadienc-styrene (ABS), poly
methylmethacrylate (PMMA), cellulose acetate butyrate (CAB),
polycarbonates (PC), polystyrenes (PS) (including, e.g., copolymers
styrene-butadiene (SBC), methylestyrene-acrylonitrile,
styrene-xylylene, styrene-ethylene, styrene-propylene,
styrene-acylonitrile (SAN)), polyetherimide (PES), polyvinyl
acetate (PVAC), polyvinyl alcohol (PVA), polyvinyl chloride (PVC),
pelyoxymethylene; polyformaldehyde (polyacetal) (POM), ethylene
vinyl acetate copolymer (EVAC), polyamide (PA), polyethylene
terephthalate (PBTP), fluoropolymers (including, e.g.,
polytetrafluoroethylene (PTFE), polyperfluoroalkoxythylene (PFA),
fluorinated ethylene propylene (FEP)), polybutylene terephthalate
(PBTP), low density polyethylene (PB), polypropylene (PP), poly
methyl pentenes (PMP) (and other polyolefins, including cyclic
polyoleflns), polytetrafluoroethylene (PTFE), polysulfides
(including, e.g., polyphenylene sulfide (PPS), and polysulfones
(including, e.g., polysulfone (PSU), polyehtersulfone (PES),
polyphenylsulpbone (PPSU), polyarylalkylsufone, and
polysulfonates). Polymers can be homopolymers or copolymers (e.g.,
(Co)poly(acrylamide-acrylonltrile) and/or acrylonitrile stytene
copolymers). Polymers can include polymer blends, such as blends of
polyamides-polyolefins, polyamides-polycarbonates, and/or
PBS-polyolefins, for example.
[0081] Further examples of polymers that can be used include cyclic
olefin polymers (COPs) and cyclic olefin copolymers (COGs). In some
embodiments, COPs and COGs can be prepared by polymerizing norbomen
monomers or copolymerization norbomen monomers and other
polyolefins (polyethylene, polypropylene). Commercially-available
COPs and/or COCs can he used, including, for example, Zeonex.RTM.
polymers (e.g., Zeonex.RTM. E48R) and Zeonor.RTM. copolymers (e.g.,
Zeonor.RTM. 1600), both available from Zeon Chemicals L.P.
(Louisville, Ky.). COCs can also be obtained from Promerus LLC
(Brecksville, Ohio) (e.g., such as FS1700).
[0082] Suitable oxide glasses may include glasses that contain one
or more of the following compounds: 0-40 mole % of M.sub.2O where M
is Li, Na, K, Rb, or Cs; 0-40 mole % of M'O where M' is Mg, Ca, Sr,
Ba, Zn, or Pb; 0-40 mole % of M''.sub.2O.sub.3 where M'' is B, Al,
Ga, In, Sn, or Bi; 0-60 mole % P.sub.2O.sub.5; and 0-40 mole %
SiO.sub.2.
[0083] Portions of photonic crystal fiber waveguides (e.g., layers
in confinement region 110) can optionally include other materials.
For example, any portion can include one or more materials that
change the index of refraction of the portion. A portion can
include a material that increases the refractive index of the
portion. Such materials include, for example, germanium oxide,
which can increase the refractive index of a portion containing a
bore-silicate glass. Alternatively, a portion can include a
material that decreases the refractive index of the portion. For
example, heron oxide can decrease the refractive index of a portion
containing a borosilicate glass.
[0084] Portions of photonic crystal fiber waveguides can he
homogeneous or inhomogeneous. For example, one or more portions can
include nano-particles (e.g., particles sufficiently small to
minimally scatter light at guided wavelengths) of one material
embedded in a host material to form an inhomogeneons portion. An
example of this is a high-index polymer composite formed, by
embedding a high-index chalcogenide glass nano-particles in a
polymer host. Further examples include CdSe and or PbSe
nano-particles in an inorganic glass matrix.
[0085] Portions of photonic crystal fiber waveguides can include
materials that alter the mechanical, rheological and/or
thermodynamic behavior of those portions of the fiber. For example,
one or more of the portions can include a plasticizer. Portions may
include materials that suppress crystallization, or other
undesirable phase behavior within the fiber. For example,
crystallization in polymers may he suppressed by including a
cross-linking agent (e.g., a photosensitive cross-linking agent).
In other examples, if a glass-ceramic material was desired, a
nucleating agent, such as TiO.sub.2 or ZrO.sub.2, can be included
in the material.
[0086] Portions can also include compounds designed to affect the
interface between adjacent portions in the fiber (e.g., between the
low index and high index layers). Such compounds include adhesion
promoters and compatibilizers. For example, an organo-silane
compound can he used to promote adhesion between a silica-based
glass portion and a polymer portion. For example, phosphorus or
P.sub.2O.sub.5 is compatible with both chalcogenide and oxide
glasses, and may promote adhesion between portions formed from
these glasses.
[0087] Fiber waveguides can include additional materials specific
to particular fiber waveguide applications. In fiber amplifiers,
for example, any of the portions can be formed of any dopant or
combination of dopants capable of interacting with an optical
signal in the fiber to enhance absorption or emission of one or
more wavelengths of light by the fiber, e.g., at least one rare
earth ion, such as erbium ions, ytterbium ions neodymium ions,
holmium ions, dysprosium ions, and/or thulium ions.
[0088] Portions of high index-contrast waveguides can include one
or more nonlinear materials. Nonlinear materials are materials that
enhance the nonlinear response of the waveguide. In particular,
nonlinear materials have a larger nonlinear response than silica.
For example, nonlinear materials have a Kerr nonlinear index,
n.sup.(2), larger than the Kerr nonlinear index of silica (i.e.,
greater than 3.5.times.10.sup.-20 m/W, such as greater than
5.times.10.sup.-20 m.sup.2/W, greater than 10.times.10 .sup.-20
m.sup.2/W, greater than 20.times.10.sup.-20 m.sup.2/W, greater than
100.times.10.sup.-20 m.sup.2/W, greater than 200.times.10.sup.-20
m.sup.2/W).
[0089] When making a robust fiber waveguides using a drawing
process, not every combination of materials with desired optical
properties is necessarily suitable. Typically, one should select
materials that are theologically, thermo-mechanically, and
physico-chemically compatible. Several criteria for selecting
compatible materials will now be discussed.
[0090] A first criterion is to select materials that are
theologically compatible. In other words, one should select
materials that have similar viscosities over a broad temperature
range, corresponding to the temperatures experience during the
different stages of fiber drawing and operation. Viscosity is the
resistance of a fluid to flow under an applied shear stress. Here,
viscosities are quoted in units of Poise. Before elaborating on
rheological compatibility, it is useful define a set of
characteristic temperatures for a given material, which are
temperatures at which the given material has a specific
viscosity.
[0091] The annealing point, T.sub.a, is the temperature at which a
material has a viscosity 10.sup.13 Poise. T.sub.a can be measured
using a Model SP-2A System fro. Orion Ceramic Foundation
(Westerville, Ohio). Typically T.sub.a is the temperature at which
the viscosity of a piece of glass is low enough to allow for relief
of residual stresses.
[0092] The softening point, T.sub.s, is the temperature at which a
material has a viscosity 10.sup.7.65 Poise, T.sub.s can be measured
using a softening point instrument, e.g., Model SP-3A from Orton
Ceramic Foundation (Westerville, Ohio). The softening point is
related to the temperature at which the materials flow changes from
plastic to viscous in nature.
[0093] The working point, T.sub.w, is the temperature at which a
material has a viscosity 10.sup.4 Poise. T.sub.w can be measured
using a glass viscometer, e.g., Model SP-4A from Orton Ceramic
Foundation (Westervilie, Ohio). The working point is related to the
temperature at which a glass can be easily drawn into a fiber. In
some embodiments, for example, where the material is an inorganic
glass, the material's working point temperature can be greater than
250.degree. C., such as about 300.degree. C., 400.degree. C.,
500.degree. C. or more.
[0094] The melting point, T.sub.m, is the temperature at which a
material has a viscosity 10.sup.2 Poise. T.sub.m can also be
measured using a glass viscometer, e.g., Model SP-4A from Orton
Ceramic Foundation (Westerville, Ohio), The melting point is
related to the temperature at which a glass becomes a liquid and
control of the fiber drawing process with respect to geometrical
maintenance of the fiber becomes very difficult
[0095] To be rheologically compatible, two materials should have
similar viscosities over a broad temperature range, e.g., from the
temperature at which the fiber is drawn down to the temperature at
winch the fiber can no longer release stress at a discernible rates
(e.g., at T.sub.a) or lower. Accordingly, the working temperature
of two compatible materials should be similar, so that the two
materials How at similar rates when drawn. For example, if one
measures the viscosity of the first material, .eta..sub.1(T) at the
working temperature of the second material, T.sub.w2,
.eta..sub.1(T.sub.w2) should he at least 10.sup.3 Poise, e.g.,
10.sup.4 Poise or 10.sup.5 Posse, and no more than 10.sup.6 Poise.
Moreover, as the drawn; fiber cools the behavior of both materials
should change front viscous to elastic at similar temperatures. In
Oliver words, the softening temperature of the two materials should
be similar. For example, at the softening temperature of the second
material, T.sub.s2, the viscosity of the first material,
.eta..sub.1(T.sub.s2) should be at least 10.sup.6 Poise, e.g.,
10.sup.7 Poise or 10.sup.8 Poise and no more than 10.sup.9 Poise.
In preferred embodiments, it should be possible to anneal both
materials together, so at the annealing temperature of the second
material, T.sub.a2, the viscosity of the first material
.eta..sub.1(T.sub.a2) should be at least 10.sup.8 Poise (e.g., at
least 10.sup.6 Poise, at least 10.sup.10 Poise, at least 10.sup.11
Poise, at least 10.sup.12 Poise, at least 10.sup.13 Poise, at least
10.sup.14 Poise).
[0096] Additionally, to be rheologically compatible, the change in
viscosity as a function of temperature (i.e., the viscosity slope)
for both materials, should preferably match as close as
possible.
[0097] A second selection criterion is that the thermal expansion
coefficients (TEC) of each material should be similar at
temperatures between the annealing temperatures and room
temperature. In other words, as the fiber cools and its rheology
changes from liquid-like to solid-like, both materials' volume
should change by similar amounts. If the two materials TEC's are
not sufficiently matched, a large differential volume change
between two fiber portions can result in a large amount of residual
stress buildup, which can cause one or more portions to crack
and/or delaminate. Residual stress may also cause delayed fracture
even at stresses well below the material's fracture stress.
[0098] The TEC is a measure of the fractional change in sample
length with a change in temperature. This parameter can he
calculated for a given material from the slope of a
temperature-length (or equivalently, temperature-volume) curve. The
temperature-length curve of a material can be measured using e.g.,
a dilatometer, such, as a Model 1200D dilatometer from Orton
Ceramic Foundation (Westerville, Ohio). The TEC can be measured
either over a chosen temperature range or as the instantaneous
change at a given temperature. This quantity has the units .degree.
C..sup.-1.
[0099] For many materials, there are two linear regions in the
temperature-length curve that have different slopes. There is a
transition region where the curve changes from the first to the
second linear region. This region is associated with a glass
transition, where the behavior of a glass sample transitions from
that normally associated with a solid material to that normally
associated with a viscous fluid. This is a continuous transition
and is characterized by a gradual change in the slope of the
temperature-volume curve as opposed to a discontinuous change in
slope. A glass transition temperature, T.sub.g, can be defined as
the temperature at which the extrapolated glass solid and viscous
fluid lines intersect. The glass transition, temperature is a
temperature associated with a change in the materials rheology from
a brittle solid to a solid that can flow. Physically, the glass
transition temperature is related to the thermal energy required,
to excite various molecular translational and rotational modes in
the material. The glass transition temperature is often taken as
the approximate annealing point, where the viscosity is 10.sup.13
Poise, but in fact, the measured T.sub.g is a relative value and is
dependent upon the measurement technique.
[0100] A dilatometer can also be used to measure a dilatometric
softening point, T.sub.ds. A dilatometer works by exerting a small
compressive load on a sample and heating the sample. When the
sample temperature becomes sufficiently high, the material starts
to soften and the compressive load causes a deflection in the
sample, when is observed as a decrease in volume or length. This
relative value is called the dilalometric softening point and
usually occurs when the materials viscosity is between 10.sup.10
and 10.sup.12.5 Poise. The exact T.sub.ds value for a material is
usually dependent upon the instrument and measurement parameters.
When similar instruments and measurement parameters are used, this
temperature provides a useful measure of different materials
theological compatibility in this viscosity regime.
[0101] As mentioned above, matching the TEC is an important
consideration for obtaining fiber that is tree from excessive
residual stress, which can develop in the fiber during the draw
process. Typically, when the TEC's of the two materials are not
sufficiently matched, residual stress arises as elastic stress. The
elastic stress component stems from the difference in volume
contraction between different materials in the fiber as it cools
from the glass transition temperature to room temperature (e.g.,
25.degree. C.). The volume change is determined by the TEC and the
change in temperature. For embodiments in which the materials in
the fiber become fused or bonded at any interface during the draw
process, a difference in their respective TEC's will result in
stress at the interface. One material will be in tension (positive
stress) and the other in compression (negative stress), so that the
total stress is zero. Moderate compressive stresses themselves are
not usually a major concern for glass fibers, but tensile stresses
are undesirable and may lead to failure over time. Hence, it is
desirable to minimize the difference in TEC's of component
materials to minimise elastic stress generation in a fiber during
drawing, for example, in a composite fiber formed from two
different materials, the absolute difference between, the TEC's of
each glass between T.sub.g and room temperature measured with a
dilatometer with a heating rate of 3.degree. C./min, should be no
more than 5.times.10.sup.-6 .degree. C..sup.-1 (e.g., no more than
4.times.10.sup.-6 .degree. C..sup.-1, no more than
3.times.10.sup.-6 .degree. C..sup.-1, no more than
2.times.10.sup.-6 .degree. C..sup.-1, no more than
1.times.10.sup.-6 .degree. C..sup.-1, no more than
5.times.10.sup.-7 .degree. C..sup.-1, no more than
4.times.10.sup.-7 .degree. C..sup.-1, no more than
3.times.10.sup.-7 .degree. C..sup.-1, no more than
2.times.10.sup.-7 .degree. C..sup.-1).
[0102] While selecting materials having similar TEC's can minimize
an. elastic stress component, residual stress can also develop from
viseoelastic stress components. A viseoelastic stress component
arises when there is sufficient difference between strain point or
glass transition temperatures of the component materials. As a
material cools below T.sub.g it undergoes a sizeable volume
contraction. As the viscosity changes in this transition upon
cooling, the time needed to relax stress increases from aero
(instantaneous) to minutes. For example, consider a composite
preform made of a glass and a polymer having different glass
transition ranges (and different T.sub.g's). During initial
drawing, the glass and polymer behave as viscous fluids and
stresses due to drawing strain are relaxed instantly. After leaving
the hottest part of the draw furnace, the fiber rapidly loses heat,
causing the viscosities of the fiber materials to increase
exponentially, along with the stress relaxation time. Upon cooling
to its T.sub.g, the glass and polymer cannot practically release
any more stress since the stress relaxation time has become very
large compared with the draw rate. So, assuming the component
materials possess different T.sub.g values, the first material to
cool to its T.sub.g can no longer reduce stress, while the second
material is still above its T.sub.g and can release stress
developed between the materials. Once the second material cools to
its T.sub.g, stresses that arise between the materials can no
longer be effectively relaxed. Moreover, at this point the volume
contraction of the second glass is much greater than the volume
contraction of the first material (which is now below its T.sub.g
and behaving as a brittle solid). Such a situation can result
sufficient stress buildup between the glass and polymer so that one
or both of the portions mechanically fail. This leads us to a third
selection criterion for choosing fiber materials: it is desirable
to minimize the difference in T.sub.g's of component materials to
minimise viseoelastic stress generation in a fiber during drawing.
Preferably, the glass transition temperature of a first material,
T.sub.g1, should, be within 100.degree. C. of the glass transition
temperature of a second material, T.sub.g2 (e.g.,
|T.sub.g1-T.sub.g2| should be less than 90.degree. C., less than
80.degree. C., less than 70.degree. C., less than 60.degree. C.,
less than 50.degree. C., less than 40.degree. C., less than
30.degree. C., less than 20.degree. C., less than 10.degree.
C.).
[0103] Since there are two mechanisms (i.e., elastic and
viseoelastic) to develop permanent stress in drawn fibers due to
differences between constituent, materials, these mechanisms may be
employed to offset one another. For example, materials constituting
a fiber may naturally offset the stress caused by thermal expansion
mismatch if mismatch in the materials, T.sub.g's results in stress
of the opposite sign. Conversely; a greater difference in T.sub.g
between materials is acceptable if the materials' thermal
expansion, will reduce the overall permanent stress. One way to
assess the combined effect of thermal expansion and glass
transition temperature difference is to compare each
component-materials' temperature-length curve. After finding
T.sub.g for each material using the foregoing slope-tangent method,
one of the curves is displaced along the ordinate axis such that
the curves coincide at the tower T.sub.g temperature value. The
difference in y-axis intercepts at room temperature yields the
strain, .epsilon., expected if the glasses were not conjoined. The
expected tensile stress, .sigma., for the material showing the
greater amount of contraction over the temperature range from
T.sub.g to room temperature, can be computed, simply from the
following equation:
.sigma.=E.epsilon.,
[0104] where E is the elastic modulus for that material. Typically,
residual stress values less than 100 MPa (e.g., less than 50 MPa,
less than 30 MPa), are sufficiently small to indicate that two
materials are compatible.
[0105] A fourth selection criterion is to match the thermal
stability of candidate materials. A measure of the thermal
stability is given by the temperature interval (T.sub.x-T.sub.g),
where T.sub.x is the temperature at the onset of the
crystallisation, as a material cools slowly enough that each
molecule can find its lowest energy state. Accordingly, a
crystalline phase is a more energetically favorable state for a
material than a glassy phase. However, a material's glassy phase
typically has performance and/or manufacturing advantages over the
crystalline phase when it comes to fiber waveguide applications.
The closer the crystallization temperature is to the glass
transition temperature, the more likely the material is to
crystallise during drawing, which can be detrimental to the fiber
(e.g., by introducing optical inhomogeneities into the fiber, which
can increase transmission losses). Usually a thermal stability
interval, (T.sub.x-T.sub.g) of at least about 80.degree. C. (e.g.,
at least about 100.degree. C.) is sufficient to permit fiberization
of a material by drawing fiber from a preform. In preferred
embodiments, the thermal stability interval is at least about
120.degree. C., such as about 150.degree. C. or more, such as about
200.degree. C. or more. T.sub.x can be measured using a thermal
analysis instrument, such as a differential thermal analyser (DTA)
or a differential scanning calorimeter (DSC).
[0106] A further consideration when selecting materials that can be
co-drawn are the materials' melting temperatures, T.sub.m. At the
melting temperature, the viscosity of the material becomes too low
to successfully maintain precise geometries during the fiber draw
process. Accordingly, in preferred embodiments the melting
temperature of one material is higher than the working temperature
of a second, rheologlcally compatible material in other words, when
heating a preform, the preterm reaches a temperature at it can be
successfully drawn before either material in the preform melts.
[0107] One example of a pair of materials which can be co-drawn and
which provide a photonic crystal fiber waveguide with high index
contrast between layers of the confinement region are
As.sub.2Se.sub.3 and the polymer PES, As.sub.2Se.sub.3 has a glass
transition temperature (T.sub.g) of about 180.degree. C. and a
thermal expansion coefficient (TEC) of about
24.times.10.sup.-6/.degree. C. At 10.6 .mu.m, As.sub.2Se.sub.3 has
a refractive index of 2.7775, as measured by Hartouni and coworkers
and described in Proc. SPIE, 505, 11 (1984), and an absorption
coefficient, .alpha., of 5.8 dB/m, as measured by Voigt and Linke
and described in "Physics and Applications of Non-Crystalline
Semiconductors in Optoelectronics," Ed. A. Andriesh and M.
Bertolotti, NATO ASI Series, 3. High Technology, Vol. 36, p. 155
(1996). Both of these references are hereby Incorporated by
reference in their entirety. PES has a TEC of about
55.times.10.sup.-6/.degree. C. and has a refractive index of about
1.65.
[0108] In some embodiments, photonic crystal fibers, such as fiber
100, can be made by rolling a planar multilayer article into a
spiral structure and drawing a fiber from a preform derived from
the spiral structure.
[0109] Referring to FIG. 2A, to prepare a preform, one or more
glasses are deposited 220 on opposing surfaces 211 and 212 of a
polymer film 210. The glass can be deposited by methods including
thermal evaporation, chemical vapor deposition, or sputtering.
Referring to FIG. 2B, the deposition process provides a multilayer
article 240 composed of layers 230 and 231 of glass on polymer film
210.
[0110] Referring, to FIG. 2C, following the deposition step,
multilayer film 240 is roiled around a mandrel 255 (e.g., a hollow
glass, such as a borosilicate glass, or polymer tube) to form a
spiral tube. A number (e.g., about three to ten) of polymer films
are then wrapped around the spiral tube to form a preform wrap. In
some embodiments, the polymer films are made from the same polymer
or glass used to form multilayer article. Under vacuum, the preform
wrap is heated to a temperature above the glass transition
temperature of the polymer(s) and glass(es) forming multilayer film
240 and the films wrapped around the spiral tube. The preform wrap
is heated for sufficient time for the layers of the spiral tube to
fuse to each other and for the spiral tube to fuse to polymer films
wrapped around it. The temperature and length of time of heating
depends on the preform wrap composition. Where the multilayer is
composed of As.sub.2Se.sub.3 and PES and the wrapping films are
composed of PES, for example, heating for 15-20 minutes (e.g.,
about 18 minutes) at about 200-300.degree. C. (e.g., about
250.degree. C.) is typically sufficient. The heating fuses the
various layers to each other, consolidating the spiral tube and
wrapping films. The consolidated structure is shown in FIG. 2D. The
spiral tube consolidates to a multilayer region 200 corresponding
to rolled multilayer film 240, The wrapped polymer films
consolidate to a monolithic support cladding 270, The consolidated
structure retains a hollow core 250 of mandrel 255.
[0111] As an alternative to wrapping polymer films around the
spiral tube to provide support cladding 270, the spiral tube can be
inserted into a hollow tube with inner diameter matching the outer
diameter of the spiral tube.
[0112] Referring to FIG. 2E, portions at opposing sides 271 and 272
of cladding 270 are removed to provide a perform 280 having an
asymmetric cross-sectional shape. The portions can be removed by
cutting, or shaving the perform (e.g., with a blade or milling
cutter) or by grinding (e.g., with a grinding wheel) and polishing
the sides of the perform.
[0113] Mandrel 255 is removed from the consolidated structure to
provide a hollow preform that is then drawn into a fiber. The
preform has the same composition and relative dimensions (e.g.,
core radius to thickness of layers in the confinement region) of
the final fiber. The absolute dimensions of the fiber depend on the
draw ratio used. Long lengths of fiber can be drawn (e.g., up to
thousands of meters). The drawn fiber can then be cut to the
desired length.
[0114] Preferably, consolidation occurs at temperatures below the
glass transition for the mandrel so that the mandrel provides a
rigid support for the spiral tube. This ensures that the multilayer
film does .not collapse on itself under the vacuum. The mandrel's
composition can fee selected so that it releases from the innermost
layer of the multilayer tube after consolidation. Alternatively,
where the mandrel adheres to the innermost layer of the multilayer
tube during consolidation, it can be removed chemically, e.g., by
etching. For example, in embodiments where the mandrel is a glass
capillary tube, it can be etched, e.g., using hydrofluoric acid, to
yield the preform.
[0115] In embodiments where a solid core is desired, the multilayer
tube can be consolidated around a solid mandrel that is co-drawn
with the other parts of lire fiber. Alternatively, in other
embodiments, the multilayer film can be rolled without a mandrel to
provide a self-supporting spiral tube.
[0116] In some embodiments, the fiber asymmetry can be introduced
after the fiber is drawn from a perform. For example, a fiber can
be shaved or ground as part of the production process after being
drawn but before being spooled. In certain embodiments, the preform
can be shaved, and then the fiber can he shaved further after if
has been drawn.
[0117] Photonic crystal fiber waveguides prepared using the
previously discussed technique can be made with a low defect
density. For example, waveguides can have less than about one
defect per 5 meters of fiber (e.g., less than about, one defect per
10 meters, 20 meters, 50 meters, 100 meters of fiber), Defects
include both material defects (e.g., impurities) and structural
defects (e.g.,, delamination between layers, cracks with layers),
both of which can scatter guided radiation from the core resulting
in signal, loss and can cause local heating of the fiber.
Accordingly, reducing fiber defects is desirable in applications
sensitive to signal loss (e.g., in high power applications where
radiation absorbed, by the fiber can cause damage to the
fiber).
[0118] In fiber 100, only the outer surface of the cladding has an
asymmetric cross-section. More generally, however, other portions
of photonic crystal fibers can have an asymmetric cross-section. In
certain, embodiments, the confinement region and/or core can also
have an asymmetric cross-section. For example, referring to FIG. 3,
a photonic crystal fiber 300 has a confinement region 310 having an
asymmetric cross-section surrounded by an asymmetric cladding 330.
The core 320 of fiber 300 also has an asymmetric cross-section.
Confinement region 310, core 320, and cladding 330 have an
elliptical cross-sectional shape. The confinement region includes
an inner seam 315 that is located on the major axis of the ellipse,
although, more generally, the inner seam can he located at other
orientations with respect to the elliptical axes.
[0119] In some embodiments, the asymmetry of the core anchor
confinement region can affect the guiding properties of the fiber.
For example, in certain embodiments, asymmetric fibers can maintain
the polarization state of guided radiation (i.e., can be
polarisation maintaining fibers).
[0120] Cladding 330 and core 320 have dimensions b.sub.330 and
b.sub.320, respectively, along the major axis. Correspondingly,
cladding 330 and core 320 have dimensions a.sub.330 and a.sub.320
along the minor axis. Respective ellipticities for the cladding and
core can be expressed mathematically as:
330 = ( b 330 - a 330 ) 1 2 ( b 330 - a 330 ) , and ##EQU00004##
320 = ( b 320 - a 320 ) 1 2 ( b 320 - a 320 ) . ##EQU00004.2##
[0121] In general, .epsilon..sub.330 and .epsilon..sub.320 can he
the same or different. In some embodiments,
.quadrature..sub.320>.epsilon..sub.330. For example, in
embodiments where an asymmetric core is desired, such as in a
polarization-maintaining fiber, a high core ellipticity may be
desired. Alternatively, in other embodiments,
.epsilon..sub.330>.epsilon..sub.320.
[0122] Fiber 300 can be made by applying a force (e.g., a
compressive force) to opposing sides of the fiber or fiber perform.
The force can be applied while the fiber or perform is at an
elevated temperature (e.g., at a temperature where components of
the fiber have a softened) to facilitate the deformation. The
deformation sets once the fiber or fiber perform cools.
[0123] Furthermore, while fiber 300 has an elliptical
cross-sectional, shape, and fiber 100 has a shape composed of two
circular arcs and two straight lines, in general, fibers can have
other shapes. For example, fibers can have asymmetric polygonal
shapes, can be formed from arcuate portions having different radii
of curvature, and/or from arcuate portions that curve in opposite
directions. Generally, the shape should provide the fiber with a
preferred bending plane.
[0124] While the foregoing fibers are asymmetric with respect to
their cross-sectional shape, in general, fibers can be asymmetric
in a variety of ways in order to provide a preferred bend plane.
For example, in some embodiments, fibers can include material
asymmetries that give rise to a preferred bend plane. Material
asymmetries refer to variations between the material properties of
different portions of a fiber that cause the fiber to bend
preferably in a particular way. For example, a portion of a fiber
cladding can be formed from a material that is mechanically less
rigid that other portions, causing the fiber to bend preferably at
that portion. Mechanical variations can be caused by compositional
changes or by physical differences in portions having the same
composition. Compositional differences can be introduced, e.g., by
doping portions of a fiber or fiber-preform with a dopant, that
alters the mechanical properties of a fiber. As another example,
compositional differences can he introduced by forming different
portions of a fiber from different compounds. Physical differences
refer to, e.g., differences in the degree of crystallinity in
different portions of a fiber. Physical differences, such as
differences in crystallinity, can be introduced by selectively
heating and/or cooling portions of a fiber during fiber
fabrication, and/or using different, rates of heating/cooling on
different fiber portions.
[0125] Referring to FIG. 4A, another example of a photonic crystal
400 includes a confinement region 410 surrounding a core 420, and a
cladding 430 surrounding confinement region 410. Confinement region
410 includes a seam 415. Cladding 430 includes two portions 431 and
432 that are composed of different materials than the rest of the
cladding. For example, in some embodiments, portions 431 and 432
are formed from a material that has a higher mechanical stiffness
than the rest of cladding 430. As an example, portions 431 and 432
can be formed from a polymer that has a higher density of
cross-linking than a polymer forming the rest of cladding 430. In
embodiments where portions 431 and 433 are stiffer than the rest of
the cladding, fiber 400 includes a preferred bend plane that is
perpendicular to the plane that includes a diameter that intersects
portions 431 and 432. Alternatively, in certain embodiments,
portions 431 and 432 are formed from materials that are less stiff
than the material forming the rest of cladding 430. In snob cases,
fiber 400 has a preferred bend plane that corresponds to the plane
that includes a diameter that intersects portions 431 and 432.
Portions 431 and 432 can ran substantially along the entire length
of fiber 400, or just along segments of the fiber.
[0126] Referring to FIG. 4B, a further example of a photonic
crystal fiber 440 includes a confinement region 450 surrounding a
core 460. A cladding 470 surrounds confinement region 450.
Confinement region 460 includes a seam 455. Embedded in cladding
470 are two stiffening elements 451 and 452, which are formed from
materials having higher mechanical stiffness than the rest of
cladding 470. For example, stiffening elements 451 and 452 can be
formed from wires (e.g., steel wires) that are inserted into holes
that run the length of fiber 440. As an example, forming photonic
crystal fiber can include machining grooves into the preform
cladding on opposite sides of the preform core. The fiber is drawn
at a temperature and tension such that the grooves are preserved in
the drawn fiber. Finally, wires are inserted into the grooves and
an adhesive (e.g., an epoxy) is used to fix the wires in place.
[0127] Stiffening elements 451 and 452 create a bend plane
orthogonal to the diagonal connecting the two stiffening elements.
Other embodiments can include more than two stiffening elements.
Further, in certain embodiments, claddings can included embedded
elements that are of lower mechanical stiffness than the rest of
the cladding, providing a bend plane in the same plane as the
diagonal intersecting the elements. For example, a cladding can
include two or more holes that run along the length of the
fiber.
[0128] In some embodiments, asymmetry can be introduced on one side
of the fiber only, rather than on opposing sides as for the
embodiments described above. For example, referring to FIG. 4C, a
photonic crystal fiber 470 includes a confinement region 480 that
surrounds a core 490. Confinement region 480 includes a seam 485.
Confinement region 480 is surrounded by a cladding 495, that, in
cross-section, includes a circular portion 496 and a flat portion
497. Flat portion 497 can be formed by shaving or grinding the
fiber or fiber preform on one side only. Flat portion 497 is
positioned so that seam 485 lies between it and core 490 in a
radial direction from the fiber axis. Fiber 470 has a bend plane
that intersects portion 497. Moreover, fiber 470 bends preferably
so that seam 385 is on the inside of the bond.
[0129] In some embodiments, fibers can include a symmetric first
cladding, but can include additional structure outside of the
cladding that cause the fiber to bend preferably in a particular
plane. For example, fibers can be placed in one or more jackets
that are asymmetric when it comes to allowing the fiber to bend.
Referring to FIG. 4D, for example, a photonic crystal fiber
includes a jacket 4050 that surrounds a cladding 4040. Cladding
4040, in turn, surrounds, a confinement region 4030, which
surrounds a core 4020. Confinement region 4030 includes a seam
4010. Jacket 4050 has an elliptical cross-section that provides a
bend plane. Cladding 4040 has a circular cross-section. In certain
embodiments, cladding 4040, confinement region 4030, and core 4020
are formed by drawing a preform structure. The drawn fiber is then
inserted into a hole in jacket 4050. The orientation of the jacket
with respect, to the rest of the fiber can be secured by, for
example, applying an adhesive to the interface of the jacket and
the cladding, or by consolidating the jacket, onto the cladding
(e.g., using heat).
[0130] Although the fibers described, above include confinement
regions that have a seam, in general, embodiments of fibers with a
bend plane can be designed to position other features in or away
from the bend plane. For example, in some embodiments, fibers can
include extended defects (e.g., structural or compositional
defects) other than a seam that is desirably positioned away from
the bend plane. Moreover, embodiments can include confinement
regions with no seams (e.g., confinement regions that are formed
from a number of annular layers).
[0131] A number of embodiments of photonic crystal fibers have been
described. However, further embodiments can include other types of
photonic crystal fibers. For example, while the foregoing
description relates to photonic crystal fibers having spiral
confinement regions, the principles described herein can be applied
to non-spiral photonic crystal fibers. In general, these principles
can be applied to fibers composed of a confinement region with one
or more concentric layers. Embodiments of photonic crystal fibers
are described in the following patents, patent applications, and
provisional patent applications: U.S. Pat. No. 6,625,364, entitled
"LOW-LOSS PHOTONIC CRYSTAL WAVEGUIDE HAVING LARGE CORE RADIUS;"U.S.
Pat. No. 6,563,98.1, entitled "ELECTROMAGNETIC MODE CONVERSION IN
PHOTONIC CRYSTAL MULTIMODE WAVEGUIDES;" U.S. patent application
Ser. No. 10/057,440, entitled "PHOTONIC CRYSTAL OPTICAL WAVEGUIDES
HAVING TAILORED DISPERSION PROFILES," and filed on Jan. 25, 2002;
U.S. patent application Ser. No. 10/121,452, entitled "HIGH
INDEX-CONTRAST FIBER WAVEGUIDES AMD APPLICATIONS," and filed on
Apr. 12, 2002; U.S. Pat. No. 6,463,200, entitled "OMNIDIRECTIONAL
MULTILAYER DEVICE FOR ENHANCED OPTICAL WAVEGUIDING;" Provisional
60/428,382, entitled "HIGH POWER/WAVEGUIDE," and filed on Nov. 22,
2002; U.S. patent application Ser. No. 10/196,403, entitled "METHOD
OF FORMING REFLECTING DIELECTRIC MIRRORS," and filed on Jul. 16,
2002; U.S. patent application Ser. No. 10/720,606, entitled
"DIELECTRIC WAVEGUIDE AND METHOD OP MAKING THE SAME," and filed on
Nov. 24, 2003; U.S. patent application Ser. No. 10/733,873,
entitled "FIBER WAVEGUIDES AND METHODS OF MAKING SAME," and filed
on Dec. 10, 2003; Provisional Patent Application No. 60/603,067,
entitled "PHOTONIC CRYSTAL WAVEGUIDES AND SYSTEMS USING SUCH
WAVEGUIDES," and filed on Aug. 20, 2004. The contents of each, of
the above mentioned patents, patent applications, and provisional
patent applications are hereby incorporated by reference in their
entirety.
[0132] Moreover, while the foregoing embodiments pertain to
photonic crystal fibers having solid confinement regions, photonic
crystal fibers can also include confinement regions with portions
that are not solid, such as holey fibers.
[0133] The photonic crystal fibers described herein may be used in
a variety of applications. For example, the photonic crystal fibers
can be used in medical laser systems. Referring to FIG. 5, an
example of a medical laser system 500 includes a CO.sub.2 laser
510, and a photonic crystal fiber 520 having a hollow core to guide
radiation 512 from the laser to a target location 99 of a patient.
Radiation 512 has a wavelength of 10.6 microns. Laser radiation 512
is coupled by a coupling assembly 530 into the hollow core of
photonic crystal fiber 520, which delivers the radiation through a
handpiece 540 to target location 599. During use, an operator
(e.g., a medical practitioner, such as a surgeon, a dentist, an
ophthalmologist, or a veterinarian) grips a portion. 542 of
handpiece 540, and manipulates the handpiece to direct laser
radiation 513 emitted from an output end of photonic crystal fiber
520 to target location 599 in order to perform a therapeutic
function at the target location. For example, the radiation can be
used to excise, incise, ablate, or vaporise tissue at the target
location.
[0134] CO.sub.2 laser 510 is controlled by an electronic controller
550 for setting and displaying operating parameters of the system.
The operator controls delivery of the laser radiation using a
remote control 552, such as a foot pedal. In some embodiments, the
remote control is a component of handpiece 540, allowing the
operator to control the direction of emitted laser radiation and
delivery of the laser radiation with one hand or both hands.
[0135] In addition to grip portion 542, handpiece 540 includes a
stand off tip 544, which maintains a desired distance (e.g., from
about 0.1 millimeters to about 30 millimeters) between the output
end of fiber 520 and target tissue 599. The stand off tip assist
the operator in positioning the output end of photonic crystal
fiber 520 from target location 599, and can also reduce clogging of
the output end due to debris at the target location. In some
embodiments, handpiece 540 includes optical components (e.g., a
lens or lenses), which focus the beam emitted from the fiber to a
desired spot size. The waist of the focused beam can be located at
or near the distal end of the stand off tip.
[0136] In some embodiments, fiber 520 can be easily installed and
removed from-coupling-assembly 530, and from handpiece 540 (e.g.,
using conventional fiber optic connectors). This can facilitate
ease of use of the system in single-use applications, where the
fiber is replaced after each procedure.
[0137] Typically, CO.sub.2 laser 510 has an average output power of
about 5 Watts to about 80 Watts at 10.6 microns (e.g., about 10
Watts or more, about 20 Watts or more). In many applications, laser
powers of about 5 Watts to about 30 Watts are sufficient for the
system to perform its intended function. For example, where system
500 is being used to excise or incise tissue, the radiation is
confined to a small spot size and a laser having an average output
power in this range is sufficient.
[0138] In certain embodiments, however, laser 510 can have an
output power as high as about 100 Watts or more (e.g., up to about
500 Watts). For example, in applications where system 500 is used
to vaporize tissue over a relatively large area (e.g., several
square millimeters or centimeters), extremely high power lasers may
he desirable.
[0139] Photonic crystal fiber cars deliver the radiation from laser
510 to the target location with relatively high efficiency. For
example, the fiber average output power can be about 50% or more of
the fiber input energy (e.g., about 60% or more, about 70% or more,
about 80% or more). Accordingly the fiber's output power can be
about 3 Watts or more (e.g., about 8 Watts or more, about 10 Watts
or more, about 15 Watts or more). In certain embodiments, however,
the average output power from the fiber can be less than 50% of the
laser power, and still be sufficiently high to perform the intended
procedure. For example, in some embodiments, the fiber average
output power can be from about 20% to about 50% of the laser
average output power.
[0140] The length of photonic crystal fiber 520 can vary as
desired. In some embodiments, the fiber is about 1.2 meters long or
more (e.g., about 1.5 meters or more, about 3 meters or more, about
3 meters or more, about 5 meters or more). The length is typically
dependent on the specific be application tor which the laser system
is used. In applications where laser 510 can be positioned close to
the patient, and or where the range of motion of the handpiece
desired for the application is relatively small, the length of the
fiber can be relatively short (e.g., about 1.5 meters or less,
about 1.2 meters or less, about 1 meter or less). In certain
applications, the length of fiber 520 can be very short (e.g.,
about 50 centimeters or less, about 20 centimeters or less, about
10 centimeters or less). For example, very short lengths of
photonic crystal fiber may be useful in procedures where the system
can deliver radiation from the laser to the fiber by some other
means (e.g., a different waveguide or an articulated arm). Very
short fiber lengths maybe useful for nose and ear procedures, for
example.
[0141] However, in applications where it is inconvenient for the
laser to be placed in close proximity to the patient and/or where a
large range of motion of the handpiece is desired, the length of
the fiber is longer (e.g., about 2 meters or more, about 5 meters
or more, about 8 meters or more). For example, in surgical
applications, where a large team of medical practitioners is needed
in close proximity to the patient, it may be desirable to place the
laser away from, the operating table (e.g., in the corner of the
operating room, or in a different room entirely). In such,
situations, a longer fiber may be desirable.
[0142] In general photonic crystal fiber 520 is flexible, has a
bend plane, and can be bent in relatively small radii of curvature
over relatively large angles without significantly impacting its
performance (e.g., without causing the fiber to fail, or without
reducing the fiber transmission to a level where the system cannot
be used for its intended use while the fiber is bent). In some
embodiments, an operator can bend photonic crystal fiber 520 to
have a relatively small radius of curvature, such as about 15 cm or
less (e.g., about 10 cm or less, about 8 cm or less, about 5 cm, or
less, about 3 cm or less) while still delivering sufficient power
to the target location for the system to perform its function.
[0143] In general, the angle through which the fiber is bent can
vary, and usually depends on the procedure being performed. For
example, in some embodiments, the fiber can be bent through about
90.degree. or more (e.g., about 120.degree. or more, about
150.degree. or more),
[0144] Losses of transmitted power due to the operator bending
photonic crystal fiber 520 may be relatively small. In general,
losses due to bends should not significantly damage the fiber,
e.g., causing it to fail, or reduce the fiber output power to a
level where the system can no longer perform the function, for
which it is designed. Embodiments of photonic crystal fiber 520
(e.g., about 1 meter or more in length) can be bent through
90.degree. with a bend radius of about 5 centimeters or less, and
still transmit about 30% or more (e.g., about 50% or more, about
70% or more) of radiation coupled into the fiber at the guided
wavelength. These fibers can provide such transmission
characteristics and provide average output power of about 3 Watts
or more (e.g., about 5 Watts or more, about 8 Watts or more, about
10 Watts or more).
[0145] The qualify of the beam of the laser radiation emitted
from-the output end of fiber 520 cache relatively good. For
example, the beam can have a low M.sup.2 value, such as about 4 or
less (e.g., about 3 or less, about 2.5 or less, about 2 or less),
M.sup.2 is a parameter commonly used lo describe laser beam
quality, where an M.sup.2 value of about 1 corresponds to a
TEM.sub.00 beam emitted from a laser, which has a perfect Gaussian
profile. The M.sup.2 value is related to the minimum spot size that
can be formed from the beam according to the formula:
d.sub.s=1.27f.lamda.M.sup.2/d.sub.b
where d.sub.s is the minimum spot diameter, d.sub.b is the beam
diameter prior to being focused to the spot by a lens having focal
length f. Accordingly, the minimum, possible spot size a beam can
he focused is proportional to the M.sup.2 value for the beam.
Practically, beams having smaller values of M.sup.2 can provide
higher radiation power densities to the target area, with less
damage to surrounding tissue due to the decreased spot size.
[0146] The spot size of radiation delivered by photonic crystal
fiber 520 to the target tissue can be relatively small. For
example, in certain embodiments, the spot can have a diameter of
about 500 microns or less (e.g., about 300 microns or less, about
200 microns or less, such as about 100 microns) at a desired
working distance from the fiber's output end (e.g., from about 0.1
mm. to about 3 mm), As discussed previously, a small spot size is
desirable where system 500 is being used to excise or incise tissue
or in other applications where substantial precision in the
delivery of the radiation is desired. Alternatively, in
applications where tissue is to be ablated or vaporized, and/or a
lesser level of precision is sufficient, the spot size can be
relatively large (e.g., having a diameter of about 2 millimeters or
more, about 3 millimeters or more, about 4 millimeters or
more).
[0147] While laser 510 is a CO.sub.2 laser, photonic crystal fibers
can be used in medical laser systems that use other types or
lasers, operating at wavelengths different from 10.6 microns. In
general, medical laser systems can provide radiation at ultraviolet
(UV), visible, or infrared (IR) Wavelengths. Lasers delivering IR
radiation,, for example, emit radiation having a wavelength between
about 0.7 microns and about 20 microns (e.g., between about 2 to
about 5 microns or between about 8 to about 12 microns). Waveguides
having hollow cores, such as photonic crystal fiber 520, are
well-suited for use with laser systems having wavelengths of about
2 microns or more, since gases that commonly occupy the core have
relatively low absorptions at these wavelengths compared to many
dielectric materials (e.g. silica-based glasses and various
polymers). In addition, to CO.sub.2 lasers, other examples of
lasers which can emit IR radiation, include Nd:YAG lasers (e.g., at
1.064 microns), Er:YAG lasers (e.g., at 2.94 microns), Er, Cr: YSGG
(Erbium, Chromium doped Yttrium Scandium Gallium Garnet) lasers
(e.g., at 2.796 microns), Ho:YAG lasers (e.g., at 2.1 microns),
free electron lasers (e.g., in the 6 to 7 micron range), and
quantum, cascade lasers (e.g., in the 3 to 5 micron range).
[0148] In general, the type of laser used in a medical laser system
depends on the purpose for which the system is designed. The type
of laser can be selected depending on whether the system is to be
used in surgical procedures, in diagnosis, or in physiologic
studies. For example, an argon laser, which delivers in the blue
and green regions of the visible light spectrum, with two energy
peaks, at 488 nm and 514 nm, can be used for photocoagulation. A
dye laser, which is a laser with organic dye dissolved in a solvent
as the active medium whose beam is in the visible light spectrum,
can be used in photodynamic therapy. Excimer lasers provide
radiation in the ultraviolet spectrum, penetrates tissues only a
small distance, can he used to break chemical bonds of molecules in
tissue instead of generating heat to destroy tissue. Such lasers
can be used in ophthalmological procedures and laser angioplasty.
Ho:YAG lasers can provide radiation in the near infrared spectrum
and can be used for photocoagulation and photoablation. Krypton
lasers provide radiation in the yellow-red visible light spectrum,
and can be used for photocoagulation. Radiation from KTP lasers can
be frequency-doubled to provide radiation in the green visible
light spectrum and can be used for photoablation and
photocoagulation. Nd:YAG lasers can be for photocoagulation and
photoablation. Pulsed dye lasers can be used to provide in the
yellow visible light spectrum (e.g., with a wavelength of 577 nm or
585 nm), with alternating on and off phases of a few microseconds
each, and can be used to decolorise pigmented lesions.
[0149] In general, laser systems can use continuous wave or pulsed
lasers. Furthermore, while CO.sub.2 lasers are typically used at
average output powers of about 5 Watts to about 100 Watts, photonic
crystal fibers can generally be used with a variety of laser
powers. For example, average laser power can be in the milliWatt
range in certain systems, up to as much as several hundred Watts
(e.g., about 200 Watts or more) in extremely high power
systems.
[0150] In general, for high power systems, the average power
density guided by fiber 520 can be extremely high. For example,
power density in the fiber, or exiting the fiber's core) can be
about 10.sup.3 W/cm.sup.2 or more (e.g., about 10.sup.4 W/cm.sup.2
or more, about 10.sup.5 W/cm.sup.2 or more, 10.sup.6 W/cm.sup.2 or
more).
[0151] In certain embodiments, handpieces can include actuators
that allow the operator to bend the fiber remotely, e.g., during
operation of the system. For example, referring to FIG. 6A, in some
embodiments, laser radiation 512 can be delivered to target tissue
699 within a patient 601 using an endoscope 610. Endoscope 610
includes a gripping portion 611 and a flexible conduit 615
connected to each other by an endoscope body 616. An imaging cable
622 housing a bundle of optical fibers is threaded through a
channel in gripping portion 611 and flexible conduit 615. Imaging
cable 622 provide illumination to target tissue 699 via flexible
conduit 615. The imaging cable also guides light reflected from the
target tissue to a controller 620, where it is imaged and displayed
providing visual information to the operator. Alternatively, or
additionally, the endoscope can include an eyepiece lens that
allows the operator to view the target area directly through the
imaging cable.
[0152] Endoscope 610 also includes an actuator 640 that allow the
operator to bend or straighten flexible conduit 615. In some
embodiments, actuator 640 allows flexible conduit 615 to bend in
one plane only, e.g., in the bend plane of fiber 520,
Alternatively, in certain embodiments, the actuator allow the
flexible conduit to bend in more than one plane.
[0153] Endoscope 610 further includes an auxiliary conduit 630
(e.g., a detachable conduit) that includes a channel through, which
fiber 520 is threaded. The channel connects to a second channel in
flexible conduit 615, allowing fiber 520 to be threaded through the
auxiliary conduit into flexible conduit 615. Fiber 520 is attached
to auxiliary conduit in a matter than maintains the orientation of
the fiber with respect the channel through flexible conduit 615,
thereby minimizing twisting of the photonic crystal fiber about its
waveguide axis within, the flexible conduit. In embodiments where
photonic crystal fiber 520 has a confinement region, that includes
a seam, the fiber can be attached to the auxiliary conduit so that
the seam is not coincident with a bend plane of the flexible
conduit.
[0154] In general, photonic crystal fibers can be used in
conjunction with commercially available endoscopes, such as
endoscopes available from PENTAX Medical Company (Montvale, N.J.)
and Olympus Surgical & Industrial America, Inc. (Orangeburg,
N.Y.).
[0155] Auxiliary conduit 630 can be configured to allow the user to
extend and/or retract the output end of the photonic crystal fiber
within flexible conduit 615. For example, referring to FIG. 6B, in
some embodiments, auxiliary conduit 630 of endoscope 610 can
include two portions 631 and 632 that are moveable with respect to
each other Portion 632 is attached to endoscope body 616, while
portion 631 telescopes with respect to portion 632. Portion 632
includes a connector 636 that connects to a fiber connector 638
attached to fiber 520. The mating mechanism of connector 636 and
fiber connector 638 can allow for quick and simple removal and
attachment of the photonic crystal fiber to the endoscope. When
attached, connector 636 and fiber connector 638 substantially
prevent fiber 520 from twisting, maintaining its orientation about
the fiber axis within flexible conduit 615. The connectors can
maintain the orientation of the fiber in the conduit with a seam in
the fiber oriented away from a bend plane of the conduit, for
example. Furthermore, when portion 631 extends or retracts with
respect to portion 632, it extends or retracts the output end 645
of fiber 520 with respect to the distal end 618 of flexible conduit
615. Auxiliary conduit 630 also includes a locking mechanism 634
(e.g., a latch or clamp) that allows the user to lock the portion
631 with respect to portion 632. The locking mechanism prevents
unwanted movement of fiber 520 within flexible conduit 615 while
radiation is being delivered to the patient. The channel in body
616 through which fiber 520 is threaded includes a kink 650.
Connector 638 can be configured so that a seam in the fiber has a
particular orientation with respect to kink 650. For example, the
seam can be positioned so that it is not on the outside of the bend
that the fiber experiences at kink 650. In some embodiments, the
connectors can orient the seam on the inside of the bend at kink
650.
[0156] In general, laser systems that utilise photonic crystal
fibers can be used in a number of different medical procedures. For
example, laser systems can be used in aesthetic medical procedures,
surgical medical procedures, ophthalmic procedures, veterinary
procedures, and/or dental procedures.
[0157] Aesthetic procedures include treatment for; hair removal;
pulsed light skin treatments for reducing fine wrinkle lines, sun
damage, age spots, freckles, some birthmarks, rosacea, irregular
pigmentation, broken capillaries, benign brown pigment and
pigmentation; skin resurfacing; leg veins; vascular lesions;
pigmented lesions; acne; psoriasis & vitiligo; and/or cosmetic
repigmentation.
[0158] Surgical procedures include procedures for gynecology,
laparoscopy, condylomas and lesions of the external genitalia,
and/or leukoplakia. Surgical applications can also include
ear/hose/throat (ENT) procedures, such as laser assisted uvula
palatoplasty (LAUP) (i.e., to stop snoring); procedures to remove
nasal obstruction; stapedotomy; tracheobronchial endoscopy; tonsil
ablation; and/or removal of benign laryngeal lesions. Surgical
applications can also include breast biopsy, cytoreduction for
metastatic disease, treatment of decubitus or stalls ulcers,
hemorrhoidectomy, laparoscopic surgery, mastectomy, and/or
reduction mammoplasty. Surgical procedures can also include
procedures in the field of podiatry, such as treatment of neuromas,
periungual, subungual and plantar warts, porokeratoma ablation,
and/or radical nail excision. Other fields of surgery in which
lasers may be used include orthopedics, urology, gastroenterology,
and thoracic & pulmonary surgery.
[0159] Ophthalmic uses include treatment of glaucoma, age-related
macular degeneration (AMD), proliferative diabetic retinopathy,
retinopathy of prematurity, retinal tear and detachment, retinal
vein occlusion, and/or refractive surgery treatment to reduce or
eliminate refractive errors.
[0160] Veterinary uses include both small animal and large animal
procedures,
[0161] Examples of dental applications include hard tissue, soft
tissue, and endodontic procedures. Hard tissue dental procedures
include caries removal & cavity preparation and laser etching.
Soft tissue dental procedures include incision, excision &
vaporization, treatment of gummy smile, coagulation (hemostasis),
exposure of unerupted teeth, aphthous ulcers, giogivopiasty,
gingivectomy, gingival troughing for crown impressions, implant
exposure, frenectomy, flap surgery, fibroma removal, operculectomy,
incision & drainage of abscesses, oral papilectomy, reduction
of gingival hypertrophy, pre-prosthetic surgery, pericoronitis,
peri implantitis, oral, lesions, and sulcular debridement.
Endodontic procedures include pulpotomy, root canal debridement,
and cleaning. Dental procedures also include tooth whitening.
[0162] Generally, the type of laser, wavelength, fiber length,
fiber outer diameter, and fiber inner diameter, among other system
parameters, are selected according to the application. For example,
embodiments in which laser 510 is a CO.sub.2 laser, laser systems
500 or 600 can be used for surgical procedures requiring the
ablation, vaporization, excision, incision, and coagulation of soft
tissue. CO.sub.2 laser systems can be used for surgical
applications in a variety of medical specialties including
aesthetic specialties (e.g., dermatology and/or plastic surgery),
podiatry, otolaryngology (e.g., ENT), gynecology (including
laparoscopy). neurosurgery orthopedics (e.g., soft tissue
orthopedics), arthroscopy (e.g., knee arthroscopy), general and
thoracic surgery (including open surgery and endoscopic surgery),
dental and oral surgery, ophthalmology, genitourinary surgery, and
veterinary surgery.
[0163] In some embodiments, CO.sub.2 laser systems can be used in
the ablation, vaporization, excision, incision, and/or coagulation
of tissue (e.g., soft tissue) in dermatology and/or plastic surgery
in the performance of laser skin resurfacing, laser derm-abrasion,
and/or laser hum debridement. Laser skin resurfacing (e.g., by
ablation and/or vaporization) can be performed, for example, in the
treatment of wrinkles, rhytids, and/or furrows (including fine
lines and texture irregularities). Laser skin resurfacing can be
performed for the reduction, removal, and/or treatment of:
keratoses (including actinic keratosis), seborrhoecae vulgares,
seborrheic wart, and/or verruca seborrheica; vermillionectomy of
the lip; cutaneous horns; solar/actinic elastosis; cheilitis
(including actinic cheilitis); lentigines (including lentigo
maligna or Hutchinson's malignant freckle); uneven
pigmentation/dyschromia; acne scars; surgical scars; keloids
(including acne keloidalis nuchae); hemangiomas (including Buccal,
port wine and/or pyogenic granulomas/granuloma pyogenicum/granuloma
telagiectaticum); tattoos; telangiectasia; removal of skin tumors
(including periungual and/or subungual fibromas); superficial
pigmented lesions; adenosebaceous hypertrophy and/or sebaceous
hyperplasia; rhinophyma reduction; cutaneous papilloma; mills;
debridement of eczematous and/or infected skin; basal and squamous
cel carcinoma (including keratoacanthomas, Bowen's disease, and/or
Bowenoid Papulosis lesions); nevi (including spider, epidermal,
and/or protruding); neurofibromas; laser de-epithelialization;
tricoepitheliomas; xanthelasma palpebrarum; and/or syringoma.
CO.sub.2 laser systems can be used for laser ablation, vaporization
and/or excision for complete and/or partial nail matrixectomy, for
vaporization and/or coagulation of skin lesions (e.g., benign
aid/or malignant, vascular and/or avascular), and/or for Moh's
surgery; for lipectomy. Further examples include using laser system
1300 for laser incision and/or excision of soft tissue for the
performance of upper and/or lower eyelid blepharoplasty, and/or for
the creation of recipient sites for hair transplantation.
[0164] In certain embodiments, CO.sub.2 laser systems is used in
the laser ablation, vaporization, and/or excision of soft tissue
during podiatry procedures for the reduction, removal, and/or
treatment of: verrucae vulgares/plantar warts (including
paronychial, periungual, and subungual warts); porokeratoma
ablation; ingrown nail treatment; neuromas/fibromas (including
Morton's neuroma): debridement of ulcers; and/or other soft tissue
lesions. CO.sub.2 laser systems can also be used for the laser
ablation, vaporisation, author excision in podiatry for complete
and/or partial matrixectomy.
[0165] CO.sub.2 laser systems can be used for laser incision,
excision, ablation, and/or vaporization of soft tissue in
otolaryngology for treatment of: choanal atresia; leukoplakia
(including oral, larynx, uvula, palatal, upper lateral pharyngeal
tissue); nasal obstruction; adult and/or juvenile papillomatosis
polyps; polypectomy of nose and/or nasal passages, lymphangioma
removal; removal of vocal cord/fold nodules, polyps and cysts;
removal of recurrent papillomas in the oral cavity, nasal cavity,
larynx, pharynx and trachea (including the uvula, palatal, upper
lateral pharyngeal tissue, tongue and vocal cords); laser/tumor
surgery in the larynx, pharynx, nasal, car and oral structures and
tissue; Zenker diverticulum/pharynoesopltageal diverticulum (e.g.,
endoscopic laser-assisted esophagodiverticulestomy); stenosis
(including subglottic stenosis); tonsillectomy (including tonsillar
cryptolysis, neoplasms) and tonsil ablation/tonsillotomy; pulmonary
bronchial and tracheal lesion removal; benign and malignant
nodules, tumors and fibromas (e.g., of the larynx, pharynx,
trachea, tracheobronchial/endobronchial); benign and/or malignant
lesions and/or fibromas (e.g., of the nose or nasal passages);
benign and/or malignant tumors and/or fibromas (e.g., oral);
stapedotomy/stapedectomy; acoustic neuroma in the ear; superficial
lesions of the ear (including chondrodermatitis nondularis chronica
helices/Winkler's disease); telangiectasia/hemangioma of larynx,
pharynx, and/or trachea (including uvula, palatal, and/or upper
lateral pharyngeal tissue); cordectomy, cordotomy (e.g., for the
treatment of vocal cord paralysis/vocal fold motion impairment),
and/or cordal lesions of larynx, pharynx, and/or trachea;
myringotomy/tympanostomy (e.g., tympanic membrane fenestration);
uvulopalastoplasty (e.g., LAUP); turbinectomy and/or turbinate
reduction/ablation; septal spur ablation/reduction and/or
septoplasty; partial glossectomy; tumor resection on oral,
subfacial and/or neck tissues; rhinophyma; verrucae vulgares;
and/or gingivoplasty/gingivectomy.
[0166] In some embodiments, CO.sub.2 laser systems can be used for
the laser incision, excision, ablation, and/or vaporization of soft
tissue in gynecology for treatment of: conizaton of the cervix
(including cervical intraepithelial neoplasia, vulvar and/or
vaginal intraepithelial neoplasia); condyloma acuminata (including
cervical, genital, vulvar, preineal, and/or Bowen's disease, and/or
Bowenoid papulosa lesions); leukoplakia (e.g., vulvar dystrophies);
incision and drainage of Bartholin's and/or nuhuthlan cysts; herpes
vaporization; urethral caruncle vaporisation; cervical dysplasia;
benign and/or malignant tumors; and/or hemangiomas.
[0167] CO.sub.2 laser systems can he used for the vaporisation,
incision, excision, ablation and/or coagulation of soft tisane in
endoscopic and/or laparoscopic surgery, including gynecology
laparoscopy, for treatment of: endometrial lesions (inclosing
ablation of endometriosis); excision/lysis of adhesions;
salpingostomy; oophorectomy/ovariectomy; fimbroplasty; metroplasty;
tubal microsurgery; uterine myomas and/or fibroids; ovarian
fibromas and/or follicle cysts; uterosacral ligament ablation;
and/or hysterectomy.
[0168] In certain embodiments, CO.sub.2 laser systems are used for
the laser incision, excision, ablation, and/or vaporization of soft
tissue in neurosurgery for the treatment of cranial conditions,
including; posterior fossa tumors; peripheral neurectomy; benign
and/or malignant tumors and/or cysts (e.g., gliomos, menigiomas,
acoustic neuromas, lipomas, and/or large tumors); arteriovenous
malformation; and/or pituitary gland tumors. In some embodiments,
CO.sub.2 laser systems are used for the laser incision, excision,
ablation, and/or vaporization of soft tissue in neurosurgery for
the treatment of spinal cord conditions, including:
incision/excision and/or vaporization of benign and/or malignant
tumors and/or cysts; intra- and/or extradural lesions; and/or
laminectomy/laminotomy/micordisectomy.
[0169] CO.sub.2 laser systems cars be used for the incision,
excision, and/or vaporization of soft tissue in orthopedic surgery
in applications that include arthroscopic and/or general surgery.
Arthroscopic applications include; menisectomy; chondromalacia;
chondroplasty; ligament release (e.g., lateral ligament release);
excision of plica; and/or partial synovectomy. General surgery
applications include: debridement of traumatic wounds; debridement
of decubitus and/or diabetic ulcers; microsurgery; artificial joint
revision; and/or polymer (e.g., polymethylmethacrylate)
removal.
[0170] CO.sub.2 laser systems can also be used for incision,
excision, and/or vaporization of soil tissue in general and/or
thoracic surgery, including endoscopic and/or open procedures. Such
applications include: debridement of decubitus ulcers, stasis,
diabetic and other ulcers; mastectomy; debridement of burns; rectal
and/or anal hemorrhoidectomy; breast biopsy; reduction mammoplasty;
cytoreduction for metastatic disease; laparotomy and/or
laparoscopic applications; mediastinal and/or thoracis lesions
and/or abnormalities; skin tag vaporization; atheroma; cysts
(including sebaceous cysts, pilar cysts, and/or mucous cysts of the
lips); pilonidal cyst removal and/or repair; abscesses; and/or
other soft tissue applications.
[0171] In certain embodiments, CO.sub.2 laser systems can be used
for the incision, excision, and/or vaporization of soft tissue in
dentistry and/or oral surgery, including for: gingivectomy;
gingivoplasty; incisional and/or excisional biopsy; treatment of
ulcerous lesions (including aphthous ulcers); incision of infection
when used with, antibiotic therapy; frenectomy; excision and/or
ablation of benign and/or malignant lesions; homeostasis;
operculectomy; crown lengthening; removal of soft tissue, cysts,
and/or tumors; oral cavity tumors and/or hemangiomas; abscesses;
extraction site hemostasis; salivary gland pathologies;
preprosthetic gum preparation; leukoplakia; partial glosseotomy;
and/or periodontal gum resection.
[0172] In some embodiments, CO.sub.2 laser systems can be used for
incision, excision, and/or vaporization of soft tissue in
genitourinary procedures, including for: benign and/or malignant
lesions of external genitalia; condyloma; phimosis; and/or
erythroplasia.
[0173] In addition to medical applications, photonic crystal fibers
such as those described herein can be used in other applications as
well. In some embodiments, photonic crystal fibers can be used to
guide radiation between a source and a detector. FIG. 7 shows a
schematic diagram of a system 700 including a source 710 and a
detector 720, which are coupled to one another by a photonic
crystal fiber 730. In certain embodiments, system 700 is an optical
telecommunication system and photonic crystal fiber 730 serves as
an optical transmission line to guide optical signals between
source 710 and detection system 720. In general, the optical
transmission line may include one or more other segments in
addition to photonic crystal fiber 730. Source 710 may be the
original source of an optical, signal directed along the
transmission line or it may be an intermediate node that redirects
the optical signal to the transmission line, optically amplifies
it, and/or electronically detects it and optically regenerates it.
Furthermore, source 710 may include components for multiplexing or
demultiplexing multiple optical signals at different wavelengths.
Similarly, detector 720 may be the final destination for the
optical signal transmitted along the transmission line, or it may
be an intermediate node that redirects, optically amplifies, and/or
electrically detects and optically regenerates the optical signal.
In addition, defector 720 may also include components for
multiplexing or demultiplexing multiple optical signals at
different wavelengths. The optical signal transmitted along the
transmission line may be a WDM signal that includes multiple
signals at corresponding wavelengths. Suitable wavelengths for the
system include those within a range of about 1.2 microns to about
1.7 microns, which corresponds to many long-haul, systems in use
today, as well those within a range of about 0.7 microns to about
0.9 microns, which corresponds to some metro systems currently
being considered.
[0174] Because of their small losses, the photonic crystal fibers
described herein may provide one or more advantages when used as
the transmission fiber in an optical telecommunications system.
Because the losses are small, the lengths of the transmission line
can be made larger as periodic amplification is less necessary. For
example, the losses may be smaller than 1 dB/km, smaller than 0.1
dB/km, or even, smaller than 0.01 dB/km. Moreover, because FWM is
reduced, WDM channel spacing in the fiber can be made smaller.
[0175] In some embodiments, system 700 may be a diagnostic tool For
example, photonic crystal fiber 730 can be used as a sample cell in
a gas-phase spectrometer, where the hollow core of fiber 730 is
filled with a sample gas. Radiation launched into fiber 730
interacts with the gas. Typically, the amount of radiation at
different wavelengths depends on rite composition of the gas in the
core. Thus, by monitoring the intensity of radiation exiting the
fiber at different wavelengths, one can determine the composition
of the gas. In such embodiments, detector 720 can be connected to a
processor (e.g., a computer), which performs an analysis of a
signal generated by detector 720 in response to radiation from the
source. An example of a gas phase spectrometer utilizing a hollow
fiber is described by C. Charlton et al, in IEEE
Proc.-Optoelectron., Vol. 150, No. 4, pp. 306-309.
[0176] In some embodiments, a photonic crystal fiber, such as those
described above, can be used to deliver laser radiation to a
target. For example, referring to FIG. 8, a laser system 800
includes a laser 810 and a photonic crystal fiber 820 for guiding
electromagnetic (EM) energy from the laser to a target 830 (e.g., a
sheet of steel or a patient) remote from the laser. Radiation is
coupled from laser 810 into fiber 820 using a coupler 840. Laser
system 800 also includes a focusing element 850 (e.g., a lens or
combination of lenses) that focuses radiation 801 emerging from
photonic crystal fiber 820 onto target 830. The radiation can, for
example, be used to cut, clean, ablate, coagulate, form, liquefy,
engrave and/or weld material at target 830. For example, in forming
applications, laser radiation can be directed to a metal sheet in
order to thermal stress a portion of the sheet, which causes the
sheet to bend.
[0177] Laser 810 can be a continuous wave or pulsed laser. The
distance between laser 810 and target 830 can vary depending on the
specific application, and can be on the order of several meters or
more (e.g., about 10 m or more, about 20 m or more, about 50 m or
more, about 100 m or more).
[0178] Laser system 800 can operate at UV, visible, or infrared
(IR) wavelengths. In some embodiments, photonic crystal fiber 820
is configured to guide IR energy emitted by laser 810, and the
energy has a wavelength between about 0.7 microns and 20 microns
(e.g., between about 2 to 5 microns or between about 8 to 12
microns). In some embodiments, laser 1210 is a CO.sub.2 laser and
the radiation has a wavelength of about 6.5 microns or 10.6
microns. Other examples of lasers which can emit IR. energy include
Nd:YAG lasers (e.g., at 1.064 microns) Er:YAG lasers (e.g., at 2.94
microns), Er, Cr: YSGG (Erbium, Chromium doped Yttrium Scandium
Gallium Garnet) lasers (e.g., at 2.796 microns), Ho:YAG lasers
(e.g., at 2.1 microns), free electron lasers (e.g., in the 6 to 7
micron range), and quantum cascade lasers (e.g., in the 3 to 5
micron range).
[0179] The power emitted from laser 810 at the guided wavelength
can vary. Although the laser power can be relatively low, e.g., mW,
in many applications the laser system is operated at high powers.
For example, the laser output intensity can be about one Watt or
more (e.g., about five Watts or more, about 10 Watts or more, about
20 Watts or more). In some applications, the laser output energy
can be about 100 Watts or more (e.g., about 200 Watts or more,
about 300 Watts or more, about 500 Watts or more, about 1 kilowatt
or more).
[0180] For high, power systems, the power density guided by fiber
820 can be relatively high. For example, power density in the fiber
can be about 10.sup.5 W/cm.sup.2 or more, such as about 10.sup.6
W/cm.sup.2 or more, about 10.sup.7 W/cm.sup.2 or more, about
10.sup.8 W/cm.sup.2 or more, about 10.sup.9 W/cm.sup.2 or more,
about 10.sup.10 W/cm.sup.2 or more.
[0181] Fiber 1820 can have relatively low losses at the guided
wavelength (e.g., about 10 dB/m or less, about 5 dB/m or less,
about 2 dB/m or less, about 1 dB/m or less, about 0.5 dB/m or less,
about 0.2 dB/m or less). Due to the low loss, only a relatively
small amount of the guided energy is absorbed by the fiber,
allowing the fiber to guide high power radiation, without
substantial damage due to heating.
[0182] Coupler 840 can be any coupler suitable for the wavelength
and intensity at which the laser system operates. One type of a
coupler is described by R. Nubling and J Harrington in
"Hollow-waveguide rich very systems for high-power, industrial
CO.sub.2 lasers," Applied Optics, 34, No. 3, pp. 372-380 (1996).
Other examples of couplers include one or more focusing elements,
such as one or more lenses. Coupling efficiency can be high. For
example, coupler 140 can couple about 70% or more of the laser
output into a guided mode in the fiber (e.g., about 80% or more,
about 90% or more, about 95% or more, about 98% or more). Coupling
efficiency refers to the ratio of power guided away by the desired
mode to the total power incident on the fiber.
[0183] Other embodiments are within the scope of the following
claims.
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