U.S. patent application number 09/450472 was filed with the patent office on 2001-08-16 for use of a laser to fusion-splice optical components of substantially different cross-sectional areas.
This patent application is currently assigned to LIGHTPATH TECHNOLOGIES, INC.. Invention is credited to BERNARD, PIERRE, FITCH, MARK A., FOURNIER, PAUL, HARRIS, MARC FARRELL, WALTERS, WILLIAM P..
Application Number | 20010014198 09/450472 |
Document ID | / |
Family ID | 22376140 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010014198 |
Kind Code |
A1 |
WALTERS, WILLIAM P. ; et
al. |
August 16, 2001 |
USE OF A LASER TO FUSION-SPLICE OPTICAL COMPONENTS OF SUBSTANTIALLY
DIFFERENT CROSS-SECTIONAL AREAS
Abstract
A method is provided for fusion-splicing with a laser beam two
optical components, one of the optical components (e.g., an optical
element such as a lens) having a surface that has a comparatively
larger cross-sectional area than a surface of the other optical
component (e.g., an optical fiber). The method comprises: (a)
aligning the two optical components along one axis; (b) turning on
a directional laser heat source to form the laser beam; (c)
directing the laser beam to be collinear with that optical
component having a smaller cross-sectional area; (d) ensuring that
the laser beam strikes the surface of the optical component having
the larger cross-sectional area at normal or near normal incidence
so that absorption of the laser beam is much more efficient on the
surface; (e) adjusting the power level of the laser beam to reach a
temperature equal to or higher than the softening temperature of
the surface of the optical component having the larger
cross-sectional area to form a softening region thereon, thereby
achieving the fusion-splicing; and (f) turning off the laser.
Inventors: |
WALTERS, WILLIAM P.;
(PERALTA, NM) ; FITCH, MARK A.; (ALBUQUERQUE,
NM) ; FOURNIER, PAUL; (ALBUQUERQUE, NM) ;
HARRIS, MARC FARRELL; (TIJERAS, NM) ; BERNARD,
PIERRE; (ST-AUGUSTIN-DE-DESMAURES, CA) |
Correspondence
Address: |
DAVID W COLLINS
75 WEST CALLE DE LAS TIENDAS
SUITE 125B
GREEN VALLEY
AZ
85614
|
Assignee: |
LIGHTPATH TECHNOLOGIES,
INC.
|
Family ID: |
22376140 |
Appl. No.: |
09/450472 |
Filed: |
November 29, 1999 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09450472 |
Nov 29, 1999 |
|
|
|
09118033 |
Jul 17, 1998 |
|
|
|
6033515 |
|
|
|
|
Current U.S.
Class: |
385/96 |
Current CPC
Class: |
G02B 6/32 20130101; G02B
6/4204 20130101; G02B 6/2551 20130101; G02B 6/24 20130101 |
Class at
Publication: |
385/96 |
International
Class: |
G02B 006/255 |
Claims
What is claimed is:
1. A method for fusion-splicing two optical components with a laser
beam, one of said optical components having a surface that has a
comparatively larger cross-sectional area than a surface of the
other optical component, comprising: (a) aligning said two optical
components along one axis; (b) turning on a directional laser heat
source to form said laser beam; (c) directing said laser beam to be
collinear with that optical component having a smaller
cross-sectional area; (d) ensuring that said laser beam strikes
said surface of said optical component having said larger
cross-sectional area at normal or near normal incidence so that
absorption of said laser beam is much more efficient on said
surface; (e) adjusting the power level of said laser beam to reach
a temperature equal to or higher than the softening temperature of
said surface of said optical component having said larger
cross-sectional area to form a softening region thereon, thereby
achieving said fusion-splicing; and (f) turning off said laser heat
source.
2. The method of claim 1 wherein said larger cross-sectional area
is at least two times larger than said smaller cross-sectional
area.
3. The method of claim 2 wherein said larger cross-sectional area
is at least ten times larger than said smaller cross-sectional
area.
4. The method of claim 1 wherein said two optical components
comprise silica-based glasses.
5. The method of claim 4 wherein said laser operates in a
wavelength region of about 9 to 11 .mu.m.
6. The method of claim 5 wherein said laser is a CO.sub.2
laser.
7. The method of claim 1 wherein said optical component having said
larger cross-sectional area is an optical element.
8. The method of claim 1 wherein said optical component having said
smaller cross-sectional area is an optical fiber.
9. The method of claim 8 wherein said directing of said laser beam
to be collinear with said optical component having said smaller
cross-sectional area is achieved by providing a mirror having a
hole therethrough, through which said optical fiber passes.
10. The method of claim 9 wherein said mirror is inclined at
45-degrees with respect to said optical fiber.
11. The method of claim 1 wherein said two components are aligned
but separated by a space, said laser beam is turned on to form said
softening region, and said surface of said optical component having
said smaller cross-sectional area is brought in contact with said
softening region of said optical component having said larger
cross-sectional area, said contact resulting in heat transfer to
said surface of said optical component having said smaller
cross-sectional area, which then softens, thereby achieving said
fusion-splicing.
12. The method of claim 1 wherein said two components are first
brought into contact and said laser beam is then turned on to form
said softening region where said two components are in contact to
achieve said fusion-splicing.
13. The method of claim 1 wherein said two components are aligned,
then brought into contact, then separated by a space, said laser
beam is turned on to form said softening region, and said surface
of said optical component having said smaller cross-sectional area
is brought in contact with said softening region of said optical
component having said larger cross-sectional area, said contact
resulting in heat transfer to said surface of said optical
component having said smaller cross-sectional area, which then
softens, thereby achieving said fusion-splicing.
14. A method for fusion-splicing an optical fiber and an optical
element with a laser beam, said optical element having a surface
that has a comparatively larger cross-sectional area than a surface
of said optical fiber, comprising: (a) aligning said optical fiber
and said optical element along one axis; (b) turning on a
directional laser heat source to form said laser beam; (c)
directing said laser beam to be collinear with said optical fiber;
(d) ensuring that said laser beam strikes said surface of said
optical element at normal or near normal incidence so that
absorption of said laser beam is much more efficient on said
surface; (e) adjusting the power level of said laser beam to reach
a temperature equal to or higher than the softening temperature of
said surface of said optical element to form a softening region
thereon, thereby achieving said fusion-splicing; and (f) turning
off said laser heat source.
15. The method of claim 14 wherein said cross-sectional area of
said optical element is at least two times larger than that of said
optical fiber.
16. The method of claim 15 wherein said cross-sectional area of
said optical element is at least ten times larger than that of said
optical fiber.
17. The method of claim 14 wherein said optical element and said
optical fiber each comprise silica-based glasses.
18. The method of claim 17 wherein said laser operates in a
wavelength region of about 9 to 11 .mu.m.
19. The method of claim 18 wherein said laser is a CO.sub.2
laser.
20. The method of claim 14 wherein said directing of said laser
beam to be colinear with said optical fiber is achieved by
providing a mirror having a hole therethrough, through which said
optical fiber passes.
21. The method of claim 20 wherein said mirror is inclined at
45-degrees with respect to said optical fiber.
22. The method of claim 14 wherein both said optical element and
said optical fiber have similar thermal and mechanical
properties.
23. The method of claim 14 wherein said optical element is selected
from the group consisting of lenses, filters, gratings, prisms, and
wavelength division multiplexer devices.
24. The method of claim 14 wherein said optical element and said
optical fiber are aligned but separated by a space, said laser beam
is turned on to form said softening region, and said surface of
said optical fiber is brought in contact with said softening region
of said optical element, said contact resulting in heat transfer to
said surface of said optical fiber, which then softens, thereby
achieving said fusion-splicing.
25. The method of claim 14 wherein said optical element and said
optical fiber are first brought into contact and said laser beam is
then turned on to form said softening region where said optical
fiber contacts said optical element to achieve said
fusion-splicing.
26. The method of claim 14 wherein said optical element and said
optical fiber are aligned, then brought into contact, then
separated by a space, said laser beam is then turned on to form
said softening region, and said surface of said optical fiber is
brought in contact with said softening region of said optical
element, said contact resulting in heat transfer to said surface of
said optical fiber, which then softens, thereby achieving said
fusion-splicing.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to optoelectronics
involving optical components and, more particularly, to coupling
optical components together of significantly different
cross-sectional areas, such as coupling optical fibers to optical
elements such as lenses, filters, gratings, prisms, and the
like.
BACKGROUND ART
[0002] Splicing of one optical fiber to another or of one optical
fiber to an optical waveguide is known. Such splicing can be done
by a variety of techniques, including fusion-splicing, which
involves localized melting in the region of the splice.
[0003] The following references disclose fusion-splicing of fiber
to fiber or fiber to silica-waveguide: (1) R. Rivoallan et al,
"Monomode fibre fusion-splicing with CO.sub.2 laser", Electronics
Letters, Vol. 19, No. 2, pp.54-55, 1983; (2) R. Rivoallan et al,
"Fusion-splicing of fluoride glass optical fibre with CO.sub.2
laser", Electronics Letters, Vol. 24, No. 12, pp.756-757, 1988; (3)
N. Shimizu et al, "Fusion-splicing between optical circuits and
optical fibres", Electronics Letters, Vol. 19, No. 3, pp.96-97,
1983; (4) T. Shiota et al, "Improved optical coupling between
silica-based waveguides and optical fibers", OFC'94 Technical
Digest, pp.282-283; and (5) H. Uetsuka et al, "Unique optical
bidirectional module using a guided-wave
multiplexer/demultiplexer", OFC'93 Technical Digest, p. 248-249. In
both cases (fiber-fiber or fiber-waveguide), the masses to fuse are
very small and of similar size. The fusion does not require careful
thermal balance between the two components involved and can be done
with a laser beam impinging from the side.
[0004] U.S. Pat. No. 4,737,006 entitled "Optical Fiber Termination
Including Pure Silica Lens And Method Of Making Same", issued to K.
J. Warbrick on Apr. 12, 1988, discloses fusion-splicing an undoped
(pure) silica rod to a single mode fiber to fabricate a collimator,
employing an electric arc. However, this is an extremely
complicated method and has limited applications.
[0005] The present practice in the art often requires the
attachment of optical fibers to other optical elements such as
lenses, filters, gratings, prisms, and other components which have
a much larger cross-sectional area than the optical fibers. The
most often utilized processes for attaching optical fibers to the
larger optical elements include (1) bonding the fiber faces
directly to the optical element with adhesives or (2) engineering a
complex mechanical housing which provides stable positioning of
air-spaced fibers and optical elements throughout large changes in
environmental conditions.
[0006] The use of adhesives in the optical path of such devices is
undesirable due to the chance of degradation of the adhesive over
time. On the other hand, spacing the fibers a fixed distance away
from the optical elements by utilizing complex mechanical housings
requires the use of anti-reflection coatings at all air-glass
interfaces in order to minimize losses of optical energy through
the device. The presence of air-glass interfaces also provides a
source of back-reflected light into the optical fibers. This
back-reflected light is a source of noise in many communication
networks, and effectively limits transmission bandwidth of such
communication networks.
[0007] In previous art, it has been shown that positioning an angle
cleaved fiber or polished fiber in proximity to the angle polished
face of a collimating lens results in excellent collimation and
excellent performance characteristics. However, these existing
technologies for assembling collimators require very labor
intensive active alignment techniques. The alignment techniques
include manipulating the position of the fiber relative to the lens
in three linear axes and three rotational axes during final
assembly. If a collimator can be built that effectively makes the
fiber and the lens a single piece, then alignment can be reduced to
two linear and two rotational axes during the fusion process and
there is no need for alignment during final assembly, thereby
reducing costs dramatically.
[0008] A key performance parameter to be minimized in collimator
assemblies is back reflection of light down the fiber. By
butt-coupling or fusion-splicing a fiber to a lens of the same
refractive index, there is no apparent interface to cause back
reflection. The beam is then allowed to diverge in the lens and
does not see an index break surface until it exits the lens. By
then, the beam is so diffused that the amount of light that can
return to the fiber core is extremely small.
[0009] Many advances can be made in the optoelectronics and
telecommunications markets if one is able to fusion-splice a single
mode optical fiber directly to a collimating lens, a filter, a
grating, a prism, a wavelength division multiplexer (WDM) device,
or any other optical component of comparatively larger
cross-sectional area. More generally, these advances can be made if
one is able to fuse optical components of substantially different
cross-sectional areas.
[0010] Thus, a need remains for a method of fusion-splicing optical
components of significantly different cross-sectional areas.
DISCLOSURE OF INVENTION
[0011] In accordance with the present invention, such a method is
provided for fusion-splicing optical components with significantly
different cross-sectional areas using a laser. By "significantly
different" is meant a difference of at least two times.
[0012] The method of the present invention for fusion-splicing with
a laser beam two optical components, one of the optical components
having a surface that has a comparatively larger cross-sectional
area than a surface of the other optical component, comprises:
[0013] (a) aligning the two optical components along one axis;
[0014] (b) turning on a directional laser heat source to form the
laser beam;
[0015] (c) directing the laser beam to be collinear with that
optical component having a smaller cross-sectional area;
[0016] (d) ensuring that the laser beam strikes the surface of the
optical component having the larger cross-sectional area at normal
or near normal incidence so that absorption of the laser beam is
much more efficient on the surface;
[0017] (e) adjusting the power level of the laser beam to reach a
temperature equal to or higher than the softening temperature of
the surface of the optical component having the larger
cross-sectional area to form a softening region thereon, which then
softens, thereby achieving the fusion-splicing; and
[0018] (f) turning off the laser heat source.
[0019] The method of the invention is particularly useful for
fusion-splicing an optical fiber to an optical element, such as a
lens, having a much larger cross-sectional area. In the case of the
present invention, the difference in cross-sectional areas between
the optical fiber and the optical element is at least about two
times, and typically at least about ten times, although the present
invention is not so limited.
[0020] Seamlessly fusing the optical fibers to the optical
elements, as defined herein, negates the need for both adhesives
and complicated housings. Additionally, such fusing eliminates the
source of back-reflected light, and requires no additional
antireflective coatings between optical fibers and optical
elements. The present invention represents a substantial
improvement to optoelectronic assembly, and allows such devices to
be manufactured at significantly lower costs than currently
achievable.
[0021] Other objects, features, and advantages of the present
invention will become apparent upon consideration of the following
detailed description and accompanying drawings, in which like
reference designations represent like features throughout the
FIGURES.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The drawings referred to in this description should be
understood as not being drawn to scale except if specifically
noted.
[0023] FIG. 1 is a side elevational view, showing schematically the
apparatus employed in the practice of the present invention;
and
[0024] FIG. 2 is a view of an annular laser beam as it appears on
the surface of a mirror through which the optical fiber is
passed.
BEST MODES FOR CARRYING OUT THE INVENTION
[0025] Reference is now made in detail to a specific embodiment of
the present invention, which illustrates the best mode presently
contemplated by the inventors for practicing the invention.
Alternative embodiments are also briefly described as
applicable.
[0026] Localized heat has been effectively used in a variety of
glass processing operations including surface polishing, fiber
drawing, and fusion-splicing. The heat source used is frequently a
simple resistance heater or a controlled arc. All of the
aforementioned processes can also be performed using a laser as a
heat source.
[0027] Prior to the present invention, however, a method for
splicing optical components of substantially different
cross-sectional areas had not been developed, to the knowledge of
the inventors. The present invention is directed to a method to
form seamlessly fused monolithic pieces.
[0028] To fuse optical components of substantially different
cross-sectional areas, in one embodiment, the larger surface is
first pre-heated by the laser. The pre-heat temperature is just
sufficient to polish and melt the surface of the larger component
at the location one desires to fuse the smaller component.
Depending upon the size, it may be a heating of the entire surface
or only a localized heating. The second surface is then brought
into contact with the preheated surface and, once the thermal
exchange is established (by conduction of heat), the two components
are heated simultaneously. If both surfaces are large (large with
respect to the localized heating zone), then both may need
preheating. Once the surfaces are in contact at the appropriate
elevated temperatures, fusion occurs. The fusion temperature is
just enough above the softening temperature to ensure a good flow
of thermal energy between the two components.
[0029] In a second embodiment, the fusion occurs starting with
contact of the two optical components and the components are never
separated during the fusion-splicing.
[0030] In a third embodiment, the optical components are brought
into contact, then pulled back after alignment, and then
fusion-spliced as in the first embodiment.
[0031] Qualification of the interface is accomplished by measuring
the back reflection of light through the system as well as
mechanical testing.
[0032] There are no practical limitations in using this technique
with respect to size mismatch, or the absence of a mismatch, or in
cross-sectional geometry.
[0033] Any two pieces of optical elements, whether comprising an
inorganic glass or an organic polymer, can be fused using the
method of the present invention. The most common application will
be fusion of single mode fibers to optoelectronic or
telecommunications devices. Fusion-splicing in accordance with the
teachings herein virtually eliminates back-reflection and the
associated losses. It is also very cost-effective, with a splice
requiring a few seconds or less and the process can be fully
automated. Splicing eliminates the need for active alignment in
many instances. Splicing also ablates contaminants and precludes
the need for foreign materials, such as adhesives and other organic
materials, in the optical path.
[0034] Optical inorganic glasses, such as silicas, borosilicates,
borates, phosphates, aluminates, chalcogenides and chalco-halides,
halides, etc., and optical organic polymers, such as acrylates,
methacrylates, vinyl acetates, acrylonitriles, styrenes, etc., may
be beneficially employed in the practice of the present invention,
although the invention is not limited to the specific classes of
materials listed.
[0035] Because the heating is quick and localized, components can
be anti-reflection-coated on surfaces other than the surface to be
fused prior to fusion. The process of the present invention also
minimizes the number of coated surfaces. Typical assembly
techniques leave a minimum of three surfaces to be coated: the
fiber face and both the input and output faces of the lens.
However, the process of the present invention leaves as few as one
surface because two surfaces are combined into a monolithic fused
piece. Every surface, even when coated, contributes losses to the
system because there is no perfect antireflection coating. Thus,
reducing the number of surfaces to be coated reduces losses to the
system.
[0036] Pointing accuracy and beam quality can be monitored prior to
fusion and locked in due to fusion. Because the part count and the
labor intensity of the process is minimized, costs are very
low.
[0037] Elimination of angled surface index breaks reduces
polarization effects such as polarization-dependent losses (PDL)
and polarization mode dispersion (PMD) in fabricated components.
Current methods employ optical surfaces which are angled relative
to the optical axis in order to control back reflection, thereby
inducing PDL and PMD above those inherent in the materials.
[0038] Another distinct advantage of the present invention is the
thermal stability of the system. Because the parts are seamlessly
fused into a monolithic piece, there is no dependence on the
housing for maintaining sub-micron spacing tolerances as there is
with other prior art approaches in optoelectronic and
telecommunications devices.
[0039] The present invention makes possible a very high quality and
low cost product for the optoelectronics/telecommunications
industry. Without this technology, one would be forced to use the
prior art techniques known in the telecommunications industry,
which are very costly, cannot perform as well, and/or use
undesirable materials in the optical path.
[0040] The novel method of the present invention for splicing small
cross-sectional area optical component (e.g., optical fiber) to
larger cross-sectional area optical component (e.g., optical
element) comprises:
[0041] 1. aligning the optical fiber and the optical element on the
same axis;
[0042] 2. turning on a directional laser heat source (such as an
infrared laser) to form a laser beam;
[0043] 3. directing the laser beam to be collinear with the fiber
(this way, most of the laser light is not absorbed by the small
fiber but is reflected off surface because the reflection
coefficient is very high at grazing incidence);
[0044] 4. ensuring that the laser beam strikes the larger
cross-sectional area optical element at normal or near normal
incidence so that absorption of the laser is much more efficient on
the larger surface;
[0045] 5. adjusting the laser power level to reach a temperature
equal to or higher than the softening temperature on the surface of
the element to achieve fusion-splicing (and simultaneously achieve
polishing and contamination ablation); and
[0046] 6. turning off the laser.
[0047] In the first embodiment, the two components are aligned but
separated by a space (typically a few millimeters), the laser beam
is turned on to form the softening region, and the surface of the
optical component having the smaller cross-sectional area is
brought in contact with the softening region of the optical
component having the larger cross-sectional area, the contact
resulting in heat transfer to the surface of the optical component
having the smaller cross-sectional area, which then softens,
thereby achieving the fusion-splicing.
[0048] In the second embodiment, the two components are first
brought into contact and the laser beam is then turned on to form
the softening region where the two components are in contact to
achieve the fusion-splicing.
[0049] In the third embodiment, the two components are aligned,
then brought into contact, then separated by a space (typically a
few millimeters), the laser beam is turned on to form the softening
region, and the surface of the optical component having the smaller
cross-sectional area is brought in contact with the softening
region of the optical component having the larger cross-sectional
area, the contact resulting in heat transfer to the surface of the
optical component having the smaller cross-sectional area, which
then softens, thereby achieving the fusion-splicing.
[0050] For fusion-splicing typical inorganic glasses, such as
silica, a CO.sub.2 laser, which operates in the range 9 to 11
.mu.m, is preferred, since silica-based glasses have very large
absorption coefficient. Other optical materials typically have a
large absorption in the infrared, and accordingly, lasers operating
in another region of the IR spectrum may be used with such other
optical materials.
[0051] The laser beam is collinear and grazes the fiber. This can
be accomplished in many ways. For example, a 45-degree mirror with
a central hole is used to redirect the laser beam along the axis of
the fiber (the fiber passes through the hole). Other methods that
direct the laser beam along the axis of the fiber may also be
employed; such methods are well-known to those skilled in this art.
The laser beam itself can be (but not necessarily) annular in
shape. This last requirement is accomplished by different
techniques: scanning system, special optical components (axicon),
TEM.sub.01 laser mode, central obstruction, diffractive optical
element, etc. The same effect could be accomplished by using two or
more laser beams, all collinear with the optical fiber.
[0052] The two optical components being fusion-spliced preferably
have similar thermal and/or mechanical properties. However, this is
not a necessary requirement, since dissimilar optical components
can be fusion-spliced employing the teachings of the present
invention. In such cases, the possibility of strain due to the
process may cause the splice to break if the conditions are not
right, and thus must be taken into account. However, such a
consideration is well within the experience of the person skilled
in this art, and no undue experimentation is required.
[0053] FIG. 1 depicts the laser beam 10 impinging on the mirror 12,
which has a hole 12a therethrough. The optical fiber 14 passes
through the hole 12a in the mirror 12 and is fusion-spliced to the
optical element 16. FIG. 1 depicts the optical fiber 14 just prior
to fusion-splicing to the lens 16. FIG. 2 depicts an annular laser
beam 10a in cross-section. The optical element 16 may be a lens,
filter, grating, prism, WDM device, or other such optical component
to which it is desired to secure the optical fiber 14.
[0054] The technology disclosed herein can be applied to
conventional fiber collimators, expanded beam collimators, WDM
products, and any other device that has a glass or polymer
attachment site. One is no longer limited to fusing components that
only have substantially similar diameters.
INDUSTRIAL APPLICABILITY
[0055] The method of the invention is expected to find use in
fusion-splicing two optical components together of dissimilar
cross-sectional areas, such as splicing an optical fiber to an
optical lens.
[0056] Thus, there has been disclosed a method for fusion-splicing
two optical components together of dissimilar cross-sectional
areas, such as splicing an optical fiber to an optical element. It
will be readily apparent to those skilled in this art that various
changes and modifications of an obvious nature may be made, and all
such changes and modifications are considered to fall within the
scope of the present invention, as defined by the appended
claims.
* * * * *