U.S. patent application number 10/686126 was filed with the patent office on 2006-08-24 for optical terminator.
Invention is credited to Ariela Donval, Sharon Goldstein, Moshe Oron, Ram Oron, Anatoly Patlakh.
Application Number | 20060188212 10/686126 |
Document ID | / |
Family ID | 32912278 |
Filed Date | 2006-08-24 |
United States Patent
Application |
20060188212 |
Kind Code |
A1 |
Oron; Ram ; et al. |
August 24, 2006 |
OPTICAL TERMINATOR
Abstract
The disclosure relates to an optical terminator device suitable
for terminating high energy optical signals. The device includes a
heat sink cap having an internal surface. An optical absorbing
layer is positioned on the internal surface of the heat sink cap. A
scattering core having a fiber or waveguide connection is
positioned within the heat sink cap such that a thermal barrier is
maintained between the optical absorbing layer and the scattering
core.
Inventors: |
Oron; Ram; (Rehovot, IL)
; Donval; Ariela; (Ramat Gan, IL) ; Patlakh;
Anatoly; (Holon, IL) ; Goldstein; Sharon; (Tel
Aviv, IL) ; Oron; Moshe; (Rehovot, IL) |
Correspondence
Address: |
JENKENS & GILCHRIST, P.C.
225 WEST WASHINGTON
SUITE 2600
CHICAGO
IL
60606
US
|
Family ID: |
32912278 |
Appl. No.: |
10/686126 |
Filed: |
October 15, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60448023 |
Feb 18, 2003 |
|
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|
Current U.S.
Class: |
385/139 |
Current CPC
Class: |
G02B 6/032 20130101;
G02B 6/262 20130101; G02B 6/02033 20130101; G02B 6/4471 20130101;
G02B 6/3849 20130101; G02B 6/243 20130101 |
Class at
Publication: |
385/139 |
International
Class: |
G02B 6/00 20060101
G02B006/00 |
Claims
1. An optical terminator for absorbing high power optical energy
traveling along a fiber or waveguide, comprising: a scattering core
that receives the high power optical energy at an end of the
scattering core and scatters the high powered optical energy along
a length of the scattering core within the optical terminator; an
absorbing layer at least partially surrounding the scattering core
to absorb the high power optical energy scattered by the scattering
core; and a thermal barrier between the scattering core and the
surrounding absorbing layer.
2. The optical terminator of claim 1 further including a heat sink
for the absorbing layer.
3. The optical terminator of claim 1 wherein the thermal barrier is
an air barrier.
4. The optical terminator of claim 1 wherein the absorbing layer
absorbs optical energy of a broad spectrum of wavelengths.
5. The optical terminator of claim 1 as presented in a connector
configuration.
6. The optical terminator of claim 1 as presented in a plug
configuration.
7. The optical terminator of claim 1 as presented in a bare fiber,
in line connection configuration.
8. The optical terminator of claim 1 as presented in a waveguide,
in line connection configuration.
9. The optical terminator of claim 1 as presented in an in line
configuration with an angled splice connection.
10. The optical terminator of claim 1 wherein the scattering core
comprises a fiber fuse-type core.
11. The optical terminator of claim 1 wherein the scattering core
comprises a filled capillary-type core.
12. The optical terminator of claim 1 wherein the scattering core
comprises an enlarged-type core.
13. The optical terminator of claim 1 as presented in an in line
configuration with a tapered splice connection.
14. The optical terminator of claim 1 wherein the scattering core
comprises an enlarged-type core having an angled end.
15. The optical terminator of claim 14 as presented in an in line
configuration with an angled splice connection to the enlarged-type
core.
16. The optical terminator of claim 1 wherein the scattering core
comprises an enlarged-type core with a conical shape.
17. The optical terminator of claim 16 wherein the enlarged-type
core with the conical shape is an extended fiber.
18. The optical terminator of claim 1 wherein the absorbing layer
includes an angled absorbing face.
19. The optical terminator of claim 1 further including an axial
distance adjustment mechanism for selectively choosing an axial
distance relationship between the scattering core and the absorbing
layer.
20. A method for producing a scattering core, comprising: emitting
high-energy laser light into a large core fiber/waveguide; flowing
the emitted light into a narrowed fiber/waveguide to increase its
power per unit area to a level above a fiber fuse threshold; and
impinging the increased power, emitted light on a contaminating
deposition which initiates a fiber fuse backward effect along the
narrowed fiber/waveguide to damage the narrowed fiber/waveguide
through the production of bubbles along a core of the narrowed
fiber/waveguide.
21. The method of claim 20 wherein the foregoing steps are
performed in situ with respect to the assembly of an optical
terminator device.
22. The method of claim 20 wherein the foregoing steps are
performed as an external production method to assembly of an
optical terminator device
23. A method for producing a scattering core, comprising: emitting
high-energy laser light into a fiber/waveguide at a power per unit
area level above a fiber fuse threshold; impinging the emitted
light on a contaminating deposition which initiates a fiber fuse
backward effect along the fiber/waveguide to damage the narrowed
fiber/waveguide through the production of bubbles along a core of
the fiber/waveguide; and reverse splitting energy from the
fiber/waveguide to terminate the fiber fuse backward effect.
24. The method of claim 23 wherein the foregoing steps are
performed in situ with respect to the assembly of an optical
terminator device.
25. The method of claim 23 wherein the foregoing steps are
performed as an external production method to assembly of an
optical terminator device.
26. A method for producing a scattering core, comprising: drawing a
liquid, which shrinks in volume when solidified, into a capillary
to substantially fill its inner volume; and solidifying the liquid
within the capillary to produce bubbles along the inner volume due
to shrinkage in volume.
27. The method of claim 26 wherein the foregoing steps are
performed in situ with respect to the assembly of an optical
terminator device.
28. The method of claim 26 wherein the foregoing steps are
performed as an external production method to assembly of an
optical terminator device.
29. The method of claim 26 wherein the liquid is glass in liquid
form at room temperature, and solidifying comprises heating the
liquid within the capillary.
30. The method of claim 26 wherein the liquid is a polymer primer
that when solidified within the capillary releases adsorbed gases
to create the bubbles.
31. An optical terminator, comprising: a heat sink cap having an
internal surface; an optical absorbing layer on the internal
surface of the heat sink cap; a fiber having a scattering core and
a transparent cladding, the fiber being positioned within the heat
sink cap such that a thermal barrier is maintained between the
optical absorbing layer and the cladding of the fiber.
32. The optical terminator of claim 31 further including an axial
distance adjustment mechanism for selectively choosing an axial
distance relationship between the fiber and the optical absorbing
layer.
33. The optical terminator of claim 31 wherein the fiber includes a
splice for in line connection to another fiber.
34. The optical terminator of claim 33 wherein the splice is an
angled splice.
35. The optical terminator of claim 33 wherein the splice is
positioned within the heat sink cap.
36. The optical terminator of claim 33 wherein the splice includes
a funnel region.
37. The optical terminator of claim 31 wherein the optical
absorbing layer on a surface of the heat sink cap adjacent an end
of the fiber is angled.
38. The optical terminator of claim 31 wherein the fiber within the
heat sink cap has a conical shape.
39-50. (canceled)
51. An optical terminator, comprising: a heat sink cap having an
internal surface; an optical energy absorbing layer on the internal
surface of the heat sink cap for absorbing optical energy; a
scattering core for scattering the optical energy; a transparent
cladding on the scattering core; and a thermal barrier positioned
between the optical energy absorbing layer and the transparent
cladding.
Description
PRIORITY CLAIM AND CROSS REFERENCE
[0001] The present application claims priority from co-pending U.S.
Provisional Application for Patent Ser. No. 60/448,023, filed Feb.
18, 2003, the disclosure of which is hereby incorporated by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to optical
terminator devices used for fiber optics or optical waveguides. The
present invention further relates to methods of producing such
optical terminator devices. In addition, the present invention more
particularly relates to optical terminator devices which are useful
in terminating both low and high power optical signals. Still more
particularly, the present invention relates to the use of small
volume scattering media along with large area and volume absorbing
optical media in an optical terminator application.
BACKGROUND OF THE INVENTION
[0003] It is not unusual for optical systems (such as fiber lasers,
fiber optic communications, and medical, industrial and remote
sensing applications which utilize light delivery means) to handle
high optical power signals. For example, it is common for such
systems to utilize optical signals in a single fiber or waveguide
having optical signal power of up to several Watts. These fibers
and waveguides support a large variety of operating modes, for
example, single-mode, multi-mode and polarization maintaining
mode.
[0004] These optical systems suffer from noise which is commonly
caused by optical reflections resulting from discontinuities. As an
example, the end of an optical fiber may cause an optical signal to
reflect and travel back towards the source. This reflected signal
may interfere with the source operation. Additionally, the
generated noise may limit the ability of system components to
detect transmitted signals. It is known in the art to control
reflection through the use of optical terminators which possess low
reflection characteristics. These optical terminators typically
utilize thin film coatings, optical absorbing polymers and
adhesives, and optical black coatings. However, when the specific
intensity or power per unit area of the terminated optical signal
is relatively high, these prior art terminators are exposed to
light fluxes beyond their damage thresholds and eventually fail. A
need accordingly exists for an optical terminator that is capable
of terminating or dumping optical signals having high intensities
or powers. There would be an advantage if such an optical
terminator could be placed at the end of the fiber line or
integrated within an optical device.
[0005] It is further recognized that many optical systems are being
designed to carry optical signals over a relatively broad spectral
range. Unfortunately, many prior art optical terminators, in
addition to being limited in terms of power, are further restricted
to providing effective termination to a limited range of
wavelengths. There is accordingly a need for an optical terminator
that is capable of terminating a wide range of wavelengths (for
example, from the visible at about 400 nm to the infrared at about
2000 nm).
[0006] It is further recognized that transmitted optical signals
can utilize any one of a number of selected transverse modes. The
variety of mode choices include, for example, single-mode of
various numerical apertures, multi-modes of various numerical
apertures and polarization maintaining waveguides of various
geometries. It would be an advantage if the optical terminator were
configured to be capable of terminating a wide range of numerical
apertures and mode structures.
[0007] There exist a number of known ways for realizing an optical
terminator.
[0008] In accordance with one method, one or more highly absorbing
materials are attached to the end of a fiber or a waveguide thus
creating a spot of high temperature at the point of optical signal
impingement. This solution puts the maximal limit of operation at
the damage threshold of the chosen absorbing material. The damage
threshold is limited since heat transfer times are slow, and in
many cases not sufficiently fast to cool down the hot spot before
damage, like melting or phase change, occurs to the absorbing
media.
[0009] In another method, a higher power optical terminator is
realized by using long volume absorbers in the core (for example,
core absorbing fibers ATN-FB by CorActive Inc. Quebec, Canada).
This solution is relatively expensive, and undesirably leaves the
heat in the core volume which is generally small compared to the
clad and cover cap volume. Additionally, these fibers usually can
perform an absorbing function within a limited wavelength
region.
[0010] Yet another method performs the absorbing function in a
tight clad coated with polymer. Here, the core is non-absorbing
core, with absorption occurring in a tight clad coated with polymer
solutions. Undesirably, the core can nonetheless become heated by
heat conduction from the absorbing tight clad, thus limiting the
useful power range of the terminator to low powers. This solution
requires a very precise matching of the core indexes (so as to
prevent back reflection at the interface). Matching in this manner
is a difficult task at a wide range of temperatures of operation
since different materials used possess different dn/dT values
(index change with temperature).
[0011] In summary, optical terminators which are better at handling
higher power signals without damage, are capable of handling wider
spectral ranges and further support many mode structures
simultaneously, are needed. The present invention addresses these
and other needs in the art.
SUMMARY OF THE INVENTION
[0012] In accordance with an embodiment of the present invention,
an optical terminating device comprises a light transmitting medium
having an input end leading to a scattering core and an absorbing
area heat sink, terminating scattered light, which is thermally
insulated from the core area.
[0013] In accordance with another embodiment of the present
invention, an optical terminating device comprises a light
transmitting medium having an input end leading to a scattering
outer clad, or an enlarged core, and an absorbing area heat sink,
terminating scattered light, which is thermally insulated from the
core area.
[0014] More generally speaking, the present invention involves
scattering received light (either away from the inner parts of a
core or away from an outer part of an enlarged core), and then
absorbing the scattered light in a thermally insulated heat sinking
area.
[0015] Embodiments of the present invention possess a number of
advantages in comparison to prior art optical terminator designs.
The optical terminators of the present invention are broadband in
operation and thus can be applied to all light bands of the
communication needs (for example, at regions of 0.8, 1.3, 1.5
micrometers), and can serve as a terminator to a multitude of
different light sources at the same time. The optical terminators
of the present invention possess a very high damage threshold and
can withstand high input powers for long periods of time. The
optical terminators of the present invention dissipate power in a
large area and volume heat sink which is isolated thermally from
the light transmitting fiber, thus enabling the device to withstand
high average powers. The optical terminators of the present
invention can be applied to single-mode, multi-mode and
polarization maintaining fibers as well as waveguides having
similar properties. Some designs for the optical terminators of the
present invention are capable of terminating all the mode
structures in a single terminator unit. Certain embodiments of the
optical terminator of the present invention have a scattering core
manufactured based on a "fiber fuse" phenomenon, and thus can be
advantageously manufactured in the optical waveguide or fiber using
external laser light. Certain embodiments of the optical terminator
of the present invention have a scattering core manufactured based
on filled capillaries including scattering bubbles wherein the
filler material is advantageously solidified using heat or UV
(ultra-violet) radiation in either external or in situ
positions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] A more complete understanding of the invention and its
advantages will become apparent upon reading the following detailed
description in conjunction with the following drawings wherein:
[0017] FIGS. 1a and 1b are lateral and longitudinal, respectively,
cross-sectional schematic views of an optical terminator on a
fiber;
[0018] FIGS. 2a and 2b are lateral and longitudinal, respectively,
cross-sectional schematic views of an optical terminator in a
waveguide;
[0019] FIG. 3 is a cross-sectional view of a package for the
terminator in a connector-like assembly;
[0020] FIG. 4 is a cross-sectional view of a package for the
terminator in a bare fiber assembly;
[0021] FIG. 5 is a cross-sectional view of a package for the
terminator in a bare fiber assembly, where two different core
diameters are used;
[0022] FIG. 6 is a cross-sectional view of a package for the
terminator in a bare fiber assembly having angled spliced
faces;
[0023] FIG. 7 illustrates a set up used to prepare the scattering
core using the "fiber fuse" method (with a funnel);
[0024] FIG. 8 illustrates a set up used to prepare the scattering
core using the "fiber fuse" method (with a splitter);
[0025] FIG. 9 is a photographic picture of a fiber possessing a
scattering core formed/produced by use of the "fiber fuse"
method;
[0026] FIG. 10 illustrates a capillary filling process used to
manufacture a scattering core;
[0027] FIG. 11 is a cross-sectional schematic view of an alternate
embodiment optical terminator on a fiber;
[0028] FIG. 12 is a graph illustrating the performance of the
scattering core terminator at a large spectral band and at high
power;
[0029] FIGS. 13a and 13b are cross-sectional schematic views of
additional optical terminator embodiments;
[0030] FIG. 14 is a cross-sectional view of a package for the
terminator in a connector-like assembly which utilizes an angled
absorber cap;
[0031] FIG. 15 is a cross-sectional view of a package for the
terminator in a connector-like assembly which utilizes a variable
reflectance terminator;
[0032] FIG. 16 is a cross-sectional view of a package for the
terminator in a connector-like assembly which utilizes a scattering
conic core terminator; and
[0033] FIG. 17 is a cross-sectional view of a package for the
terminator in a connector-like assembly which utilizes a scattering
conic core terminator.
DETAILED DESCRIPTION OF THE DRAWINGS
[0034] Reference is now made to FIGS. 1a and 1b wherein there are
shown lateral and longitudinal, respectively, cross-sectional
schematic views of an optical terminator 2 on a fiber 3. The fiber
3 includes a light conducting core 4 and a cladding 6. The fiber 3
may, for example, comprise a single mode silica SMF 28 fiber. Light
(indicated by an arrow path) propagates through the core 4 of the
fiber 3. Within the terminator 2 is affixed an optical fiber 7
having similar dimensions to the non-terminator fiber 3. The fiber
7 within the terminator 2, however, has a scattering core 8 as
opposed to a light conducting core 4. Any suitable scattering fiber
may be used within the terminator 2. The scattering core 8 of the
fiber 7 may be produced using any selected one of a number of
techniques. For example, the scattering core 8 may be produced by a
"fiber fuse" method as described herein (see, also, FIGS. 7 and 8).
Alternatively, the scattering core 8 may be produced using a filled
capillary method as described herein (see, also, FIG. 10). Still
further, the scattering core 8 may comprise a scattering enlarged
core as described herein (see, also, FIGS. 11, 13, 16 and 17).
Light, again represented by arrow paths, is scattered by the
scattering core 8, and propagates through the silica cladding 6
(and a surrounding air barrier 9) into an absorber area layer 10 of
the terminator 2. The absorber layer 10 is configured to
substantially surround the silica cladding 6 and cover the entire
internal area of a heat sink cap 11 which provides an enclosure for
the terminator 2. The absorber layer 10 functions to, absorb the
scattered light from the scattering core 8 over a much larger area
(between about 1,000 and 10,000 times) than the core 8
cross-section. This significantly larger area of absorption
provided by the absorber layer 10 allows for better heat conduction
outwards and the air barrier 9 maintains the thermally insulated
core 8 at temperatures which are below its damage or melting
temperature. The absorber layer 10 may be made of any suitable
material which allows for wide range of wavelengths to be absorbed,
and in particular may comprise an optical black paint or epoxy
paint.
[0035] Reference is now made to FIGS. 2a and 2b, wherein there are
shown lateral and longitudinal, respectively, cross-sectional
schematic views of an optical terminator 12 in a waveguide 13. The
terminator 12 is similar in configuration and operation to the
terminator 2 of FIGS. 1a and 1b, with the exception that the
terminator 12 is built on the waveguide 13. The waveguide 13
propagates light (indicated by an arrow path) within a guide core
18 having dimensions of few microns by few microns (for example,
10.times.10 microns) which is built on a substrate 14 and covered
by a cladding 16. The cladding 16 may comprise, for example, spin
on glass (SOG). Within the terminator 12 is a waveguide 15 having
similar dimensions to the waveguide 13. The waveguide 15 within the
terminator 12, however, has a scattering guide core 22 as opposed
to a light conducting core 18. Any suitable scattering fiber may be
used within the terminator 12. The scattering core 22 of the
waveguide 15 may be produced using any selected one of a number of
techniques. For example, the scattering core 22 may be produced by
a "fiber fuse" method as described herein (see, also, FIGS. 7 and
8). Alternatively, the scattering core 22 may be produced using a
filled capillary method as described herein (see, also, FIG. 10).
Still further, the scattering core 22 may comprise a scattering
enlarged core as described herein (see, also, FIGS. 11, 13, 16 and
17). Light, again represented by arrow paths, is scattered by the
scattering core 22, and propagates through the cladding 24 (and a
surrounding air barrier 19) into an absorber layer 20 of the
terminator 12. The absorber layer 20 is configured to substantially
surround the cladding 24 and cover the entire internal area of a
heat sink cap 21 which provides an enclosure for the terminator 12.
The absorber layer 20 functions to absorb the scattered light from
the scattering core 22 over a much larger area (between about 1,000
and 10,000 times) than the core 22 cross-section. This
significantly larger area of absorption provided by the absorber
layer 20 allows for better heat conduction outwards and the air
barrier 19 maintains the thermally insulated core 22 at
temperatures which are below its damage or melting temperature. The
absorber layer 20 may be made of any suitable material which allows
for wide range of wavelengths to be absorbed, and in particular may
comprise an optical black paint or epoxy paint.
[0036] Reference is now made to FIG. 3, wherein there is shown a
cross-sectional view of a package for the terminator in a
connector-like assembly. A ferrule 32 contains an insertion part of
the terminator which may comprise, for example, a SMF 28 fiber or a
high numerical aperture HNA fiber. This is connected optically (for
example, by fusion splicing 28) to a fiber 30 within the terminator
which functions as a scatter. An absorber cap 31 surrounds the
fiber 30. The cap 31 may comprise a terminator of the type
described above and illustrated in FIGS. 1a, 1b, 2a and 2b. Again,
the fiber 30 may be produced by using "fiber fuse" process, the
"filled capillary" process or the scattering enlarged core
process.
[0037] An alternative embodiment for the terminator of FIG. 3 is
shown in FIG. 14. The terminator in this instance includes an
angled absorber cap 66 surrounding the fiber 30. In this instance,
the fiber 30 preferably, but need not necessarily, comprises a
scatterer. Light 88 exiting from the fiber 30 impinges on the
angled absorbing cap 66, more specifically on an angled insert 90
portion thereof. The inner surface of the cap 66, including the
angled insert 90, is covered with absorber layer 68 (like the layer
10/20 described above). The angled insert 90 may possess an angles
of about 4-10 degrees. This angle assists is minimizing mirror-like
reflections of the light 88 from the absorber layer 68 (which exist
in every absorber to a certain extent) from re-entering the central
(scattering) fiber 30. This serves to additionally reduce the
amount of light that is back reflected through ferrule and fiber
32.
[0038] A further alternative embodiment of the terminator of FIG. 3
is shown in FIG. 15. The terminator in this instance includes a
variable reflectance cap 66 surrounding the fiber 30. In this
instance, the fiber 30 preferably, but need not necessarily,
comprises a scatterer. The absorbing cap 66 is threaded 94 such
that its axial position with respect to the fiber 30 can be
changed. More specifically, by rotating the cap 66, a distance
between the end of the cap and an end of the fiber 30 changes. When
the distance is too short, some scattered light from the absorber
layer 68 (like layer 10/20 described above) may re-enter the fiber
30 thus giving rise to a small amount of back reflection into the
system through fiber and ferrule 32. Controlling the distance
through clockwise or counter-clockwise rotation of the cap 66
allows for precise control to be exercised over reflection
characteristics.
[0039] Yet another alternative embodiment of the terminator of FIG.
3 is shown in FIG. 16. In this embodiment, the terminator includes
a conic enlarged scattering core 96. The connecting fiber is
preferably cut at an angle 52 (for example, of about 4-10 degrees)
and then spliced or glued to a transparent conic volume which
comprise the core 96. The volume has a scattering external surface
72. The core 96 volume can be viewed as an enlarged or extended
core which has a cone base with dimensions similar to that of the
fiber clad in diameter and a length of about 5-10 mm. The angle
splicing allows for a wide selection of materials, not being
confined to materials with matching indexes of refraction to the
fiber. Light entering the core 96 is not confined within the conic
volume 96. This light spreads to the outer surface 72 where it is
partially scattered 98 at each instance where it hits the external
surface. Light leaving the conic scattering core is absorbed by the
absorbing layer 68 (like layer 10/20 as described above) on the
inside surface of the cap 66.
[0040] It is recognized that the external surface of an extended
core 96 regularly looses light by scattering due to surface
irregularities. Etching, mechanical sanding or sand blasting can
create the scattering surface on, for example, glass or glass-like
materials of the extended core. Maintaining a large index of
refraction difference (.DELTA.n) at the scattering surface enhances
the scattering ability of the surface proportionally to (.DELTA.n).
In the preferred embodiment, .DELTA.n is a relatively large value
of about 0.5 (the difference between glass and air which surrounds
the volume). The conic shape further advantageously enlarges the
number of times the light hits the scattering surface, thus
enabling more efficient scattering to occur.
[0041] An alternative embodiment of the terminator of FIG. 16 is
shown in FIG. 17. In this embodiment, the conic scattering core 96
is prepared using a method wherein the fiber is pulled when hot to
create a transparent extended conic volume 100 having a diminishing
size core 104. This smaller size core cannot transmit the light
mode which enters into it and instead scatters the light out into
the clad 102. Light, which is not being confined at core 104,
spreads to the outer surface of clad 102 where it is partially
scattered 106 at each instance where it hits the external surface
of the clad. This additional volume has a cone base dimension
similar to the core in diameter and length of about 5-10 mm. Light
leaving the clad 102 of the conic extended scattering core 96 is
absorbed by the absorbing layer 68 (like layer 10/20 as described
above) on the inside surface of the cap 66.
[0042] Again, it is recognized that the external surface of an
extended core 96 regularly looses light by scattering due to
surface irregularities. Etching, mechanical sanding or sand
blasting can create the scattering surface on, for example, glass
or glass-like materials of the extended core. Maintaining a large
index of refraction difference (.DELTA.n) at the scattering surface
enhances the scattering ability of the surface proportionally to
(.DELTA.n). In the preferred embodiment, .DELTA.n is a relatively
large value of about 0.5 (the difference between glass and air
which surrounds the volume). The conic shape further advantageously
enlarges the number of times the light hits the scattering surface,
thus enabling more efficient scattering to occur.
[0043] With reference now to FIG. 4, a cross-sectional view is
presented of a package for the terminator 2 in a bare fiber
assembly. Here, the light impinging from core 4 on scattering core
8 is scattered (passing through thermal air barrier 9) and absorbed
in the absorber layer 10 of a heat sink cap that covers the whole
assembly. In this configuration the fibers having cores 4 and 8 are
fusion spliced together at plane 26 which is located within the
area of the heat sink cap.
[0044] In FIG. 5, a cross-sectional view is presented of a package
for the terminator 2 in a bare fiber assembly, where two different
core diameters are used. Here, the light impinging from core 4 on
scattering core 8 is scattered and absorbed in the absorber layer
10 of the heat sink that covers the whole assembly. In this
configuration, the core 4 is larger in diameter than scattering
core 8 (for example, an SMA fiber for core 4 with an HNA fiber for
core 8). In a preferred implementation, the "fiber fuse"
manufacturing method is utilized because it is simpler and
resembles the geometry described in FIG. 7. The cores 4 and 8 are
fusion spliced together at 26 to produce a funnel region 32 in the
diameter transition between the cores. This geometry works also
with normal fusion splicing of the input fiber having core 4 with a
pre-processed (for example, by the "fiber fuse" method or the
filled capillary method) fiber having core 8. As discussed above,
an air barrier 9 is provided for thermally insulating the cores 4/8
from heat dissipated in the layer 10 of the heat sink cap.
[0045] With reference to FIG. 6, there is shown a cross-sectional
view of a package for the terminator 2 in a bare fiber assembly
having angled spliced faces. Here, the light impinging from core 4
on scattering core 8 is scattered (passing through an air barrier
9) and absorbed in the absorber layer 10 of the heat sink that
covers the whole assembly. In this configuration the fibers having
cores 4 and 8 are fusion spliced 26 together in an angled
connection having an angle 52 (which, for example, may be chosen as
about 8 degrees). This angled splice tends to eliminating back
reflection from surface at the fusion splice 26 of the impinging
radiation into core 4.
[0046] Reference is now made to FIG. 7 wherein there is shown a set
up used to prepare the scattering core using the "fiber fuse"
method. A high-energy laser 46 (for example, providing 30-35 dBm CW
power) emits light which is fed into a large core fiber/waveguide
48. The power per unit area of this light is lower than a "fiber
fuse" threshold. The laser power flows in the fiber/waveguide 48
toward a narrowing funnel box 32. The funnel box is sized and
shaped to fit the core size of a fiber/waveguide 34. On its way
forward, the light impinges into end box 38 where a contaminating
deposition 36 creates a "fiber fuse" backward (toward the laser
46). This effect damages the fiber/waveguide 34 to include bubbles
along its core up to the location of the funnel 32 where the damage
stops since the area is larger and the power per unit area is lower
than needed for "fiber fuse" to occur/continue. The fiber 34 may
then be utilized as the scattering core of the optical
terminator.
[0047] FIG. 8 describes a fiber fuse method similar to that of FIG.
7. Again, a high-energy laser 46 (for example, providing 30-35 dBm
CW power) emits light which is fed into regular core
fiber/waveguide 44. The laser power flows in the fiber/waveguide 44
toward an energy splitter 42 and continues to propagate in
fiber/waveguide 34. On its way forward the light impinges into end
box 38, where a contaminating deposition 36 creates a "fiber fuse"
backward (toward the laser 46). This effect damages the
fiber/waveguide 34 to include bubbles along its core up to the
location of the splitter 42 where the damage stops since the split
increases the area (by bleeding off energy) and the power per unit
area is lower than needed for the "fiber fuse" to continue. The
fiber 34 may then be utilized as the scattering core of the optical
terminator.
[0048] It will be noted that these fiber fuse processes can be
performed externally on a dedicated set up, with the scattering
core then being fitted into its place within the terminator.
Alternatively, the processes can be performed internally (in situ)
on the finished product.
[0049] The "fiber fuse" is a phenomenon that results in the
destruction of an optical fiber core creating a string of highly
scattering empty bubbles in the core. This "fiber fuse" effect has
been observed at laser powers on the order of
3.times.10.sub.J.sup.6 watts/cm.sup.2 in the core. The "fiber fuse"
effect is characterized by the propagation of a bright visible
light from the point of initiation toward the laser source. The
term "fiber fuse" has been adopted to refer to the phenomenon
because of the similarity in appearance to a burning fuse. The
fiber fuse has been shown to occur when the end of the fiber is
contaminated, and it has also been initiated spontaneously from
splices and in-core fiber gratings. Examination of the fiber core
after the "fiber fuse" effect occurs reveals extensive damage. The
silica core is melted and refused, and bubbles are formed
throughout its length. The damaged regions, or bubbles, observed in
the core after "fiber fuse" propagation, have been the subject of a
number of investigations. Atomic force microscope tests show that
the bubbles are hollow, indicating vaporization of the silica. The
structure of the bubbles is in many cases a periodic structure. The
"fiber fuse" phenomenon is used here to create scattering, or
change of direction of the impinging light by the bubbles, thus
creating an angularly spread light source at the terminator that
does not reflect the light back into the input fiber. Instead,
scattered light passes into and through the cladding.
[0050] Study of this effect by the inventors indicates that the
"fiber fuse" effect is readily initiated in most fibers. It appears
as a brilliant white visible spot that propagates from the point of
initiation at the fiber end towards the laser source. The spectrum
of the light emitted from the fuse corresponds approximately to a
temperature of 5400.degree. K., indicating that the "fiber fuse"
may consist of plasma. The speed of the "fiber fuse" propagation is
about 1 meter per second in most fibers. The "fiber fuse" can
travel through many meters of fiber. The fiber gets non-transparent
and scattering thus serving as a good scatterer for high power
terminators.
[0051] The high-energy laser light (for example, providing 30-35
dBm CW power at 1550 nm wavelength) is fed into large core
fiber/waveguide, where its power per unit area is lower than the
"fiber fuse" threshold. The laser power flows in the fiber toward a
narrowing funnel where its size is fit to a smaller core size of
fiber/waveguide. A contaminating deposition at the end of this
fiber creates a "fiber fuse" effect travelling backward (toward the
laser) and damaging the fiber/waveguide up to the funnel. At this
point, it stops since the area gets larger and the power per unit
area is lower than needed for the "fiber fuse" effect to continue.
The damaged fiber the "fiber fuse" is then a processed scatterer,
having bubbles along its core.
[0052] FIG. 9 is a microscope photographic picture of a fiber
possessing a scattering core formed/produced by use of the "fiber
fuse" method (as described herein). The picture clearly shows the
fiber with bubbles present in the core region. These bubbles act to
scatter light which is traveling in the core.
[0053] Reference is now made to FIG. 10 wherein there is shown a
capillary filling process used to manufacture a scattering core. A
silica capillary 56 (for example, having a 125 micrometer external
diameter and a 10 micrometer internal diameter) is connected at one
end to a vacuum pump 54. The other end of the capillary 56 is
dipped in a liquid container 60. When the vacuum pump 54 is
activated, a suction draws the liquid into the capillary 56 to
fills its inner volume. The liquid may comprise, for example,
Sol-Gel (which is glass in liquid form, at room temperature). This
liquid solidifies when heated by heat source 62. When solidifying,
the liquid shrinks in volume to create bubbles (whose location is
generally indicated at 58) within the internal diameter. The liquid
may alternatively comprise a polymer primer. This liquid solidifies
in response to a UV radiation source or a heat source
(alternatively referenced as 62). In this case, solidification
releases adsorbed gases which create bubbles 58 within the internal
diameter. The filled capillary 56 may then be used as the
scattering core of the optical terminator. As with the fiber fuse
method, the included bubbles in the core act to scatter light.
[0054] Reference is now made to FIG. 11 wherein there is shown an
alternate embodiment cross-sectional schematic view of an optical
terminator on a fiber. The fiber 3 is cut in an angle 52 (for
example, of about 4-10 degrees) and is spliced or glued to a
transparent volume 64 having a scattering external surface 72. The
angle splicing of the fiber 3 allows for a wide selection of
materials which are not confined to materials having matching
indices of refraction to the that of the fiber 3 core. The light
traveling in the core of fiber 3 enters the volume 64, but is not
confined therein. The light spreads by refraction to the outer
surface 72 of the volume 64 where it is partially scattered 74 at
each instance of reflection/refraction with the external surface. A
far end of the volume 64 away from attachment to the fiber 3 is cut
at an angle 66 (for example, of about 4-10 degrees). The volume 64
can be viewed as an enlarged or extended core of the fiber 3 which
possesses dimensions similar to the cladding in diameter and with a
length of about 5-10 mm. Scattered light leaving the volume 64,
passing through air insulation 9, is absorbed by the absorbing
layer 68. As discussed above, this layer 68 absorbs light over a
much larger area (between 1,000 and 10,000 times) than that of the
core cross-section. Heat from absorption is conducted by convection
outwards using the heat sink 70 to the ambient environment. The
larger area of the absorbing layer 68 allows for better heat
conduction outwards and maintains the thermally insulated core
region at temperatures below its damage or melting temperature. The
absorbing layer 68 may be made of any suitable material which
allows for wide range of wavelengths to be absorbed, and in
particular may comprise an optical black paint or epoxy paint.
[0055] It is recognized that the external surface of an optical
fiber regularly looses light by scattering due to surface
irregularities. Etching, mechanical sanding or sand blasting can
create the scattering surface on, for example, glass or glass-like
materials of the extended core comprising the volume 64.
Maintaining a large index of refraction difference (.DELTA.n) at
the scattering surface enhances the scattering ability of the
surface proportionally to (.DELTA.n). In the preferred embodiment,
.DELTA.n is a relatively large value of about 0.5 (the difference
between glass and air which surrounds the volume 64).
[0056] Reference is now made to FIG. 12 wherein there is shown a
graph illustrating the performance of the scattering core
terminator, in this case the terminator appearing in FIG. 11,
(similar behavior and curves were generated using terminators of
FIGS. 1 and 4 as well). at a large spectral band and at high power.
The terminator was simulated with a goal of optimizing its
dimensions and materials. The tests included experiments where
terminators were exposed to CW laser light as well as short pulses.
The optimization goals were: minimal back reflection and high power
operation. The terminators worked in the same way in both CW and
pulsed cases. The achieved results are presented in FIG. 12 which
shows broad-spectrum operation with low back reflection of -55 dB
at the wavelength spectral range of 1500 to 1600 nm, and high power
performance that is not degraded. Endurance tests of terminators
over many hours with powers of 33 dBm were conducted without
negative result. These results show that the described terminator
design can work at high powers of 2 watts of light without
compromising its performance due to heating by the light. The low
back reflection and the wide absorption band, -55 dB at the
wavelength spectral range of 1500 to 1600 nm show the
performance.
[0057] Reference is now made to FIGS. 13a and 13b wherein there are
shown cross-sectional schematic views of additional optical
terminator embodiments. These embodiments relate to an "input mode
independent, enlarged scattering core" type of terminator. In this
optical terminator, a ferrule 80 (for example, of a standard
diameter of 1.25 or 2.5 mm) serves as an enlarged scattering core.
This ferrule 80 may, for example, comprise quartz (or other
material which possesses similar optical properties as the feed
fiber 76). Light passes through fiber 76 (having its ferrule 78)
and impinges into the enlarged scattering core ferrule 80. The
feeding fiber 76 can be of any suitable kind (for example,
SMF-Single Mode Fiber, HNA-High Numerical Aperture fiber, MM-Multi
Mode or PM-Polarization Maintaining). The impinging light is spread
by refraction in the enlarged scattering core ferrule 80 until the
scattered light reaches the outer surface 86 of the ferrule. This
outer surface 86 is naturally scattering or is alternatively
treated for providing a scattering surface. At that point, the
scattered light impinges on an air gap within an isolation cap 66
having an inside surface which is covered by an absorber area 68
(like the area 10/20 described above). In a preferred embodiment,
an end face of the scattering core ferrule 80 is angled 55 (for
example, of about 4-10 degrees) in order to avoid mirror like
reflections of the scattered light in the ferrule from entering
back into the feed fiber 76. In order to minimize back reflection
from the interface between the ferrules 78 and 80, the interface 96
therebetween, being normally perpendicular as shown in FIG. 13a
can, alternatively, be angled as shown in FIG. 13b (with that angle
98 being from about 4 to 10 degrees).
[0058] As shown herein, optical terminator devices can be packaged
in at least two ways. A first way uses optical fiber connectors. In
this packaging technique, an input fiber leads to the terminator
which includes a scattering-absorbing fiber all placed inside a
connector like assembly. A second way uses a bare fiber
configuration. In this packaging technique, two bare fibers, one
that is in its original form and the other that has scattering
characteristics (for example, from a "fiber fuse" damaging event, a
"filled capillary" process or possessing a "scattering enlarged
core") are fusion-spliced or inserted into an aligning sleeve or
large diameter capillary and are fixed in position relative to each
other. This assembly is then packaged in an outer protective
sleeve.
[0059] A number of advantages and benefits accrue from use of
optical terminator embodiments of the present invention.
[0060] The present invention provides a high damage threshold
terminator for waveguides or fiber optics which can be used
internally in optical systems or at the output port of an optical
device or system.
[0061] The present invention further provides a terminator for use
in a waveguide or optical fiber system, where the fabrication of
the terminator can be executed using only optical means or optical
laser radiation. This allows for the optical terminator to
fabricated inside a waveguide assembly (in situ) after the
waveguide and all other components are already manufactured.
[0062] The present invention still further provides an optical
terminator suitable for use in a waveguide or optical fiber and
operable over a broad range of wavelengths.
[0063] The present invention additionally provides an optical
terminator suitable for use in a waveguide or optical fiber wherein
the core or central portion of the terminator scatters light
impinging on it and absorption of that scattered light occurs at a
heat sink isolated thermally from the fiber core and clad area.
This implementation enables high power operation without extreme
heating of the optical fiber or waveguide part.
[0064] While the invention is susceptible to various modifications
and alternative forms, specific embodiments have been shown by way
of example in the drawings and will be described in detail herein.
It should be understood, however, that the invention is not
intended to be limited to the particular forms disclosed. Rather,
the invention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
* * * * *