U.S. patent application number 09/789093 was filed with the patent office on 2001-08-23 for blockless fiber optic attenuators and attenuation systems employing dispersion tailored polymers.
This patent application is currently assigned to Molecular OptoElectronics Corporation. Invention is credited to Chan, Kwok P., Gascoyne, David G., McCallion, Kevin J., Wagoner, Gregory A..
Application Number | 20010016106 09/789093 |
Document ID | / |
Family ID | 22488296 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010016106 |
Kind Code |
A1 |
Wagoner, Gregory A. ; et
al. |
August 23, 2001 |
Blockless fiber optic attenuators and attenuation systems employing
dispersion tailored polymers
Abstract
Controllable fiber optic attenuators and attenuation systems are
disclosed for controllably extracting optical energy from a fiber
optic, and therefore attenuating the optical signal being
transmitted through the fiber optic. In one aspect, material is
removed from a portion of the fiber optic, thereby exposing a
surface through which optical energy can be extracted. The portion
of the fiber is suspended between two support points, and a
controllable material is formed over the surface for controllably
extracting optical energy according to a changeable stimulus
applied thereto, which affects the refractive index thereof. In one
embodiment, the changeable stimulus is temperature, and a
controllable heating/cooling source can be provided in the
attenuator for control of the attenuation. The limited amount of
thermal contact between the suspended, side-polished portion of the
fiber optic and the controllable material to surrounding structures
offers a more predictable response, and improved response time. The
controllable material, in one embodiment, may be a dispersion
controlled (e.g., matched) polymer, offering uniform spectral
characteristics of attenuation across a wavelength band of
interest.
Inventors: |
Wagoner, Gregory A.;
(Watervliet, NY) ; McCallion, Kevin J.; (Boston,
MA) ; Chan, Kwok P.; (Troy, NY) ; Gascoyne,
David G.; (Schenectady, NY) |
Correspondence
Address: |
HESLIN & ROTHENBERG, PC
5 COLUMBIA CIRCLE
ALBANY
NY
12203
|
Assignee: |
Molecular OptoElectronics
Corporation
877 25th Street
Watervliet
NY
12189
|
Family ID: |
22488296 |
Appl. No.: |
09/789093 |
Filed: |
February 20, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09789093 |
Feb 20, 2001 |
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09139787 |
Aug 25, 1998 |
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6205280 |
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Current U.S.
Class: |
385/140 |
Current CPC
Class: |
C02F 2101/30 20130101;
G02B 6/266 20130101; C11D 3/3953 20130101; C11D 3/0031 20130101;
C11D 7/12 20130101; G02B 6/02219 20130101; C11D 7/14 20130101; C02F
2101/32 20130101 |
Class at
Publication: |
385/140 |
International
Class: |
G02B 006/26 |
Claims
What is claimed is:
1. An attenuator for attenuating optical energy, comprising: a
portion of a fiber optic through which the optical energy is
transmitted, having an exposed surface through which at least some
of said optical energy can be controllably extracted; a support
structure suspending the portion of the fiber optic; and a
controllable material formed over the exposed surface of the fiber
optic for controllably extracting said optical energy.
2. The attenuator of claim 1, wherein the controllable material
controllably extracts the optical energy according to a changeable
stimulus applied thereto.
3. The attenuator of claim 2, wherein the changeable stimulus
comprises temperature, the portion of the fiber optic and the
controllable material are both positioned to be substantially
thermally insulated from any surrounding structures, and wherein
the attenuator further comprises: a controllable heating/cooling
source in operative contact with the controllable material to
change the temperature thereof.
4. The attenuator of claim 3, further comprising: a housing,
including the support structure, and enclosing the portion of the
fiber optic, the controllable material and the controllable
heating/cooling source.
5. The attenuator of claim 4, wherein the controllable
heating/cooling source is mounted in the housing, and projects
toward the suspended portion of the fiber optic, such that a
control surface of the controllable heating/cooling source is in
operative contact with the controllable material.
6. The attenuator of claim 3, further comprising: a thermal sensor
for sensing the temperature of the controllable material.
7. The attenuator of claim 6, further comprising: at least one
control lead emanating from the controllable heating/cooling source
for control thereof; and at least one sense lead emanating from the
thermal sensor for transmitting a signal representative of the
temperature of the controllable material as sensed by the
sensor.
8. The attenuator of claim 1, wherein the controllable material has
its optical dispersion properties controlled in accordance with
those of the fiber in a given wavelength band.
9. The attenuator of claim 8, wherein the controllable material has
its optical dispersion properties substantially matched to those of
the fiber in the given wavelength band of interest.
10. The attenuator of claim 9, wherein the controllable material
comprises about 0.82% by weight bis[1,2-[4-ethyl heptyl
amino)phenyl]-1,2-ethylened- ithiolate]nickel and about 99.18%
weight of a polymer formed from about 60% by weight
pentafluorophenyl acrylate and about 40% by weight
tetrafluoropropyl methacrylate; or about 1.9% by weight
bis[1,2-[4-(ethyl heptyl
amino)phenyl]-1,2-ethylenedithiolate]platinum and about 98.1% by
weight polar olefin polymer comprising monomeric units derived from
about 80% by weight pentafluorophenyl acrylate and about 20% by
weight tetrafluoropropyl methacrylate.
11. The attenuator of claim 1, wherein the portion of the fiber
optic is suspended between two support points within the housing
and is substantially thermally insulated by surrounding air in the
housing.
12. An attenuator for attenuating optical energy transmitted
through a fiber optic, comprising: a housing enclosing a portion of
the fiber optic, the portion of the fiber optic having an exposed
surface through which at least some of the optical energy can be
controllably extracted; the portion of the fiber optic being
suspended within the housing; a controllable material formed over
the exposed surface of the fiber optic for controllably extracting
optical energy in accordance with a changeable stimulus applied
thereto; and a stimulus source mounted in the housing, projecting
towards the suspended portion of the fiber optic, and in operative
contact with the controllable material to apply the changeable
stimulus thereto.
13. The attenuator of claim 12, wherein the changeable stimulus
comprises temperature, the portion of the fiber optic and the
controllable material are both positioned within the housing to be
substantially thermally insulated from any surrounding structures,
and the stimulus source comprises a controllable heating/cooling
source.
14. The attenuator of claim 13, further comprising: a thermal
sensor for sensing the temperature of the controllable
material.
15. The attenuator of claim 14, further comprising: at least one
control lead emanating from the controllable heating/cooling source
for control thereof; and at least one sense lead emanating from the
thermal sensor for transmitting a signal representative of the
temperature of the controllable material as sensed by the
sensor.
16. The attenuator of claim 12, wherein the controllable material
has its optical dispersion properties controlled in accordance with
those of the fiber in a given wavelength band.
17. The attenuator of claim 16, wherein the controllable material
has its optical dispersion properties substantially matched to
those of the fiber in the given wavelength band of interest.
18. The attenuator of claim 17, wherein the controllable material
comprises about 0.82% by weight bis[1,2-[4-ethyl heptyl
amino)phenyl]-1,2-ethylenedithiolate]nickel and about 99.18% weight
of a polymer formed from about 60% by weight pentafluorophenyl
acrylate and about 40% by weight tetrafluoropropyl methacrylate; or
about 1.9% by weight bis[1,2-[4-(ethyl heptyl
amino)phenyl]-1,2-ethylenedithiolate]plat- inum and about 98.1% by
weight polar olefin polymer comprising monomeric units derived from
about 80% by weight pentafluorophenyl acrylate and about 20% by
weight tetrafluoropropyl methacrylate.
19. A method for attenuating optical energy transmitted in a fiber
optic, comprising: providing a portion of the fiber optic through
which the optical energy is transmitted, having an exposed surface
through which at least some of said optical energy can be
controllably extracted; suspending the portion of the fiber optic
within a support structure; forming a controllable material over
said exposed surface of the fiber optic for controllably extracting
said optical energy; and attenuating the optical energy by applying
a changeable stimulus to the controllable material thereby
controllably extracting said optical energy.
20. The method of claim 18, wherein the changeable stimulus is
temperature, and said suspending includes suspending the portion of
the fiber optic to be substantially thermally insulated from any
surrounding structures, and said forming includes positioning the
controllable material to be substantially thermally insulated from
any surrounding structures.
21. The method of claim 20, further, comprising: sensing the
temperature of the controllable material.
22. The method of claim 19, wherein the controllable material has
its optical dispersion properties controlled in accordance with
those of the fiber in a given wavelength band.
23. The method of claim 22, wherein the controllable material has
its optical dispersion properties substantially matched to those of
the fiber in the given wavelength band of interest.
24. The method of claim 23, wherein the controllable material
comprises about 0.82% by weight bis[1,2-[4-ethyl heptyl
amino)phenyl]-1,2-ethylened- ithiolate]nickel and about 99.18%
weight of a polymer formed from about 60% by weight
pentafluorophenyl acrylate and about 40% by weight
tetrafluoropropyl methacrylate; or about 1.9% by weight
bis[1,2-[4-(ethyl heptyl
amino)phenyl]-1,2-ethylenedithiolate]platinum and about 98.1% by
weight polar olefin polymer comprising monomeric units derived from
about 80% by weight pentafluorophenyl acrylate and about 20% by
weight tetrafluoropropyl methacrylate.
25. A method for forming an attenuator in relation to a portion of
a fiber optic through which optical energy is to be transmitted,
comprising: exposing a surface of a portion of the fiber optic
through which at least some of the optical energy can be
controllably extracted; suspending the portion of the fiber optic
in a housing; mounting a stimulus source in the housing; forming a
controllable material on a control surface of the stimulus source,
the controllable material for controllably extracting the optical
energy according to a stimulus from the stimulus source; and
bringing the portion of the fiber optic into contact with the
controllable material by assembling the housing such that the
exposed surface of the portion of the fiber optic is substantially
covered by the controllable material.
26. The method of claim 25, wherein the stimulus comprises
temperature, the portion of the fiber optic and the controllable
material are positioned to be substantially thermally insulated,
and the stimulus source comprises a controllable heating/cooling
source.
27. The method of claim 25, wherein the controllable material has
its optical dispersion properties controlled in accordance with
those of the fiber in a given wavelength band.
28. The method of claim 27, wherein the controllable material has
its optical dispersion properties substantially matched to those of
the fiber in the given wavelength band of interest.
29. The method of claim 28, wherein the controllable material
comprises about 0.82% by weight bis[1,2-[4-ethyl heptyl
amino)phenyl]-1,2-ethylened- ithiolate]nickel and about 99.18%
weight of a polymer formed from about 60% by weight
pentafluorophenyl acrylate and about 40% by weight
tetrafluoropropyl methacrylate; or about 1.9% by weight
bis[1,2-[4-(ethyl heptyl
amino)phenyl]-1,2-ethylenedithiolate]platinum and about 98.1% by
weight polar olefin polymer comprising monomeric units derived from
about 80% by weight pentafluorophenyl acrylate and about 20% by
weight tetrafluoropropyl methacrylate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This Application is related to U.S. patent application Ser.
No. 09/026,755, filed Feb. 20, 1998, and entitled "FIBER OPTIC
ATTENUATORS AND ATTENUATION SYSTEMS;" and U.S. patent application
Ser. No. ______ , filed concurrently herewith, and entitled
"DISPERSION CONTROLLED POLYMERS FOR BROADBAND FIBER OPTIC DEVICES";
and U.S. patent application Ser. No. ______, filed concurrently
herewith, and entitled "BLOCKLESS TECHNIQUES FOR SIMULTANEOUS
POLISHING OF MULTIPLE FIBER OPTICS."
[0002] Each of these Applications is hereby incorporated by
reference herein in its entirety.
TECHNICAL FIELD
[0003] The present invention relates to controllable attenuators
and attenuation systems for attenuating optical energy transmitted
through a fiber optic.
BACKGROUND OF THE INVENTION
[0004] There are requirements in fiber optic systems for precise
control of optical signal levels entering various system
components. This is particularly true for systems at test and
characterization stages of deployment. A controllable optical
attenuator can be used, for example, to characterize and optimize
the optoelectronic response of high-speed photoreceivers, wherein
the detection responsivity is dependent on the average optical
power incident on the photodiode.
[0005] The majority of controllable fiber optic attenuators
currently commercially available rely on thin-film absorption
filters, which require breaking the fiber and placing the filters
in-line. Controllable attenuation is then achieved by mechanical
means such as rotating or sliding the filter to change the optical
path length within the absorptive material. This adversely impacts
the response speed of the device, the overall mechanical stability,
zero attenuation insertion loss and optical back reflection. In
general, broken fiber designs suffer numerous disadvantages such as
high insertion loss, significant back reflection, and large size.
These factors can be minimized, although such corrective measures
typically result in added cost and/or size.
[0006] Additional issues have impeded the development of
thermo-optic variable attenuators, including: (i) the thermal mass
of surrounding materials and/or structures which significantly
degrades device response time; and (ii) spectrally non-uniform
attenuation, resulting from a dispersion mis-match between the
optical mode index of the underlying transmission media and a
controllable overlay material.
[0007] Improved controllable fiber optic attenuators and
attenuation systems are therefore required which keep the optical
fiber core intact, which achieve controllable attenuation via
control of radiative loss from the fiber, and which offer improved
response time and spectral uniformity over the wavelength bands of
interest.
SUMMARY OF THE INVENTION
[0008] The shortcomings of the prior approaches are overcome, and
additional advantages are provided, by the present invention, which
in one aspect relates to an attenuator for attenuating optical
energy transmitted through a portion of a fiber optic. The portion
of the fiber optic has an exposed surface through which at least
some of the optical energy can be controllably extracted. This
portion of the fiber optic is suspended within a support structure,
and a controllable material is formed over the exposed surface of
the fiber optic for controllably extracting the optical energy. The
controllable material controllably extracts the energy according to
a changeable stimulus, e.g., temperature. The portion of the fiber
optic and the controllable material are both positioned to be
substantially thermally insulated from any surrounding
structures.
[0009] The attenuator may also include a controllable
heating/cooling source in operative contact with the controllable
material to change the temperature thereof, and therefore the
attenuating effects thereof. A substantially cylindrical housing
may be provided, which includes the support structure, and encloses
the portion of the fiber optic, the controllable material and the
controllable heating/cooling source. A sensor may also be provided
for sensing the temperature of the controllable material, and
control leads for both the controllable heating/cooling source and
the temperature sensor are provided.
[0010] By suspending the fiber optic, and substantially thermally
insulating the fiber optic and the controllable material from any
surrounding support structures, device size is reduced, and
thermo-optic response time is improved.
[0011] To improve spectral uniformity of the response of the
attenuator across a given wavelength band (e.g., 1520 nm to 1580
nm), the controllable material may have its optical dispersion
properties controlled (e.g., matched) in accordance with those of
the fiber in this band. Preferably, the controllable material has
its optical dispersion properties substantially matched to those of
the fiber in the band of interest. The control of the dispersion
properties is effected using, for example, polymers with added
dyes, discussed in detail in the co-filed Application entitled
"DISPERSION CONTROLLED POLYMERS FOR BROADBAND FIBER OPTIC
DEVICES."
[0012] The present invention, in another aspect, relates to methods
for attenuating optical energy in a fiber optic using the
attenuator discussed above, as well as methods for forming the
attenuator discussed above.
[0013] The "blockless," dispersion controlled attenuator of the
present invention provides a high performance design with wide
flexibility. The simplicity of the design permits low-cost,
high-volume manufacturing without sacrificing optical
performance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The subject matter which is regarded as the invention is
particularly pointed out and distinctly claimed in the concluding
portion of the specification. The invention, however, both as to
organization and method of practice, together with further objects
and advantages thereof, may best be understood by reference to the
following detailed description of the preferred embodiment(s) and
the accompanying drawings in which:
[0015] FIG. 1 is a front elevational view of a controllable fiber
optic attenuator in accordance with the present invention;
[0016] FIG. 2 is a central, cross-sectional view of the attenuator
of FIG. 1;
[0017] FIG. 3 is an enlarged view of certain features of the
attenuator of FIGS. 1 and 2;
[0018] FIG. 4 is a top plan view of a side-polished fiber optic
showing the exposed surface and an exemplary optical interaction
area;
[0019] FIG. 5 is a system within which the attenuator of FIGS. 1-3
can be employed;
[0020] FIG. 6 is a graph depicting, in percentage, the loss
characterization versus the refractive index of an overlay material
for three exemplary levels of fiber side-polishing; and
[0021] FIGS. 7a-b are spectral plots of the attenuation obtained
using a standard overlay material, and a dispersion-matched overlay
material, respectively.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0022] In accordance with the elevational view of FIG. 1, an
attenuator 100 is provided in accordance with the present invention
for attenuating optical energy transmitted in fiber optic 30.
Attenuator 100 includes a housing comprising, for example, strain
reliefs 120a and 120b, shell pieces 110a and 110b, and end caps
130a and 130b. Control leads 105a and 105b may also be provided for
attenuator control.
[0023] As discussed further below, the attenuator is formed with
respect to a portion of the fiber optic having material removed
therefrom, thereby exposing a surface thereof, through which
optical energy can be controllably extracted. By maintaining the
integrity of the fiber optic within this attenuator, unnecessary
losses due to interruption of the fiber can be controlled. In one
exemplary embodiment, the entire housing, including the strain
reliefs, is 2.375 inches in length, and about 0.5 inches in
diameter. Therefore, the attenuator of the present invention can be
implemented in a relatively small package suitable for many types
of system and/or field uses.
[0024] Internal details of attenuator 100 are shown in the central
cross-sectional view thereof of FIG. 2. As discussed above, a
housing comprising, in one example, strain reliefs 120a and 120b,
end caps 130a and 130b, and shell pieces 110a and 110b is provided
to accommodate the input and output sections of the fiber, as well
as additional, internal components. Another exemplary portion of
the housing, i.e., fiber support structure 140, is also shown in
FIG. 2 having two support points 142a and 142b between which the
fiber is suspended. These support points are at the ends of
longitudinal notches 144a and 144b formed in structure 140 to
accommodate the input and output portions of the fiber.
[0025] In accordance with the previously filed U.S. application
Ser. No. 09/026,755 entitled "FIBER OPTIC ATTENUATORS AND
ATTENUATION SYSTEMS," a bulk material, here designated 160, can be
formed over a side-polished surface of the fiber to controllably
remove optical energy therefrom. Either electro-optic or
thermo-optic materials are appropriate for this purpose, whose
refractive indices, and therefore their attenuation effects, vary
with applied electrical or thermal stimuli, respectively. Shown in
FIG. 2 is an exemplary thermo-optic material 160 in contact with
the suspended, side-polished portion of fiber optic 30, and with an
underlying controllable heating/cooling (heating and/or cooling)
source 170 which is mounted, via a thermally conductive epoxy 172,
to an inside wall 112 of shell piece 110b.
[0026] The suspension of the portion of the fiber 30 and material
160, without any other significant thermal contacts, results in an
efficient, thermally insulated attenuation device such that any
changes in temperature induced by the controllable heating/cooling
source 170 are transferred solely, and quickly, to the thermo-optic
material 160, but to no other surrounding structures. This
"blockless" technique stands in contrast to the prior technique
described in the above-mentioned, previously filed U.S.
Application, wherein the fiber is mounted in a block, and any
thermal changes in the material are also affected by the heat sink
characteristics of the block within which the side-polished fiber
is mounted, and on which the material is formed. In the approach
disclosed herein, since the fiber is suspended in a thermally
insulative environment (e.g., air or any other effective thermal
insulator), and is in thermal contact with only material 160 (also
thermally insulated except for its contact with source 170), the
heat sink effect of surrounding structures is minimized, and faster
and more predictable control of the temperature, and therefore the
optical attenuating effects, are provided.
[0027] With reference to the enlarged view of FIG. 3, as discussed
above, controllable heating/cooling source 170 is mounted to an
inside housing wall 112, using epoxy 172, and projects toward fiber
optic 30. Source 170 supports a controllable material 160 on its
active control surface 174. As discussed herein, a portion 30' of
fiber optic 30 has material removed therefrom thereby exposing the
evanescent field of the optical energy transmitted therein such
that at least some of the optical energy can be controllably
extracted therefrom, using controllable material 160. With
reference to FIG. 4, this portion 30' of fiber optic 30 is shown in
greater detail. Fiber optic 30, for example, is polished into its
cladding, approaching the core, thereby exposing a surface 32
having, in one example, a width 34 dimension of 100 .mu.m, and a
length 36 dimension of 7-10 mm. This substantially flat surface may
be formed by polishing the cladding of the fiber optic in
accordance with the techniques disclosed in the above-incorporated,
concurrently filed, U.S. patent application entitled "BLOCKLESS
TECHNIQUES FOR SIMULTANEOUS POLISHING OF MULTIPLE FIBER OPTICS."
Though the cladding is polished to this surface 32, the actual
evanescent optical interaction area 33 is much smaller, i.e.,
having a width 35 of 10 .mu.m and a length 37 of 2 mm. In general,
this optical interaction area 33 must be substantially covered by
the controllable material 160, but the material can actually extend
beyond this optical interaction area 33 to encompass the entire
polished surface 32.
[0028] Referring to FIGS. 1-4, one exemplary fabrication technique
for the attenuator includes:
[0029] a) polishing a portion 30' of the fiber (FIGS. 3 and 4);
[0030] b) suspending the polished portion of the fiber between two
support points 142a and 142b of a fiber support structure (e.g.,
140, FIG. 2) and gluing the adjacent input and output portions of
the fiber in respective, preformed, longitudinal notches running
outward toward the distal ends of the support structure;
[0031] c) affixing the controllable heating/cooling source 170 to
an inner wall 112 of an outer shell piece 110b of a housing using a
thermally conductive epoxy 172;
[0032] d) forming the controllable material 160 on a control
surface 172 of the controllable heating/cooling source 170 such
that it retains some softness (at least temporarily); and
[0033] e) bringing the fiber support structure 140 and the shell
piece 110b into their assembled relationship wherein the suspended
fiber portion 30' is immersed in the softened controllable material
160 such that at least the interaction area 33 thereof is covered
by a portion of material 160.
[0034] As discussed above with reference to FIGS. 1-3, material 160
may be controlled using a controllable heating/cooling source 170.
Further, a sensor 180 can be placed (FIG. 3) in material 160, to
measure the resultant temperature thereof. The signal representing
the temperature can be carried from the attenuator using sense
leads 105b, and the controllable heating/cooling source can be
operated using control leads 105a.
[0035] FIG. 5 depicts an exemplary system 500 employing attenuator
100, and its electrical control leads 105a and sense leads 105b.
Sense leads 105b can be operated by a temperature sensing unit 200,
which provides a result thereof to control circuit 300. (It should
be noted that attenuator 100 normally requires calibration
subsequent to its fabrication so that its optical response to
changes in the temperature of the controllable material can be
accurately predicted, and therefore used for accurate control, in
an operational system, such as system 500.)
[0036] In one exemplary embodiment, the controllable
heating/cooling source is a thermoelectric cooler (Melcor part
number FC0.45-4-05); the thermal sensor is a thermistor (Fenwell
Electronics part number 112-503JAJ-B01), and the fiber is a single
mode fiber, (Corning part number SMF-28).
[0037] Improvement in the spectral uniformity of the device can be
obtained through proper choice of the controllable material 160.
More particularly, dispersion controlled polymers such as any of
those disclosed in the above-incorporated, concurrently filed U.S.
patent application entitled "DISPERSION CONTROLLED POLYMERS FOR
BROADBAND FIBER OPTIC DEVICES," can be used as the controllable
material 160 to improve spectral uniformity.
[0038] A mis-match between the dispersion characteristics of the
material and the dispersion characteristics of the fiber may result
in spectrally non-uniform attenuation across a band of interest
(e.g., 1520-1580 nm). By controlling the dispersion of material
160, spectral uniformity can be improved. Preferably, the
dispersion of material 160 should be controlled to be matched to
that of the mode index of the fiber, thereby providing optimum
spectral uniformity.
[0039] As explained in detail in the co-filed Application, polymers
with added dyes provide the required dispersion control, and are
also thermo-optically active. One preferred material comprises
about 0.82% by weight bis[1,2-[4-ethyl heptyl
amino)phenyl]-1,2-ethylenedithiolate]nicke- l and about 99.18%
weight of a polymer formed from about 60% by weight
pentafluorophenyl acrylate and about 40% by weight
tetrafluoropropyl methacrylate; another comprises about 1.9% by
weight bis[1,2-[4-(ethyl heptyl
amino)phenyl]-1,2-ethylenedithiolate]platinum and about 98.1% by
weight polar olefin polymer comprising monomeric units derived from
about 80% by weight pentafluorophenyl acrylate and about 20% by
weight tetrafluoropropyl methacrylate.
[0040] In the previously filed U.S. Application, a cladding-driven
approach was disclosed in which a thin, controllable cladding layer
is placed between a high index bulk overlay and the surface of the
fiber. The high index bulk material has an index significantly
greater than the effective mode index of the fiber (n.sub.ef). By
using a higher overlay index, the spectrally non-uniform
characteristics of the device were avoided, such as those along
curve 99 depicted in FIG. 6 (reproduced from FIG. 2a of the
previously filed Application, and explained in greater detail
therein). However, by using materials having their dispersion
controlled relative to the dispersion of the fiber mode index,
operation along curve 99, with the refractive index of the overlay
approximating that of the fiber, is possible with spectral
uniformity.
[0041] The spectral attenuation characteristics of a non-dispersion
controlled material (Cargille oil, n.sub.D=1.456 at 27.degree. C.
on a 95% polished fiber) are shown in FIG. 7a in the range of
1520-1580 nm. The spectral attenuation characteristics of the same
device using an approximately dispersion matched polymer (40% DMMA,
60% TFPMA and 0.9 mole % Ni (ethyl, heptyl) dye at 19.degree. C.)
are shown in FIG. 7b. As is evident from a comparison of the
spectra of 7a and 7b, using dispersion matched polymers greatly
increases the spectral uniformity in a given wavelength band of
interest. In this example, the attenuation level remains constant
to within about 0.5 dB over this spectral range.
[0042] The disclosed "blockless" side-polished fiber approach, and
the dispersion-matched thermo-optic materials, have permitted the
development of the disclosed high performance, low cost broad-band
compact variable attenuator. The blockless approach allows fiber
components to be produced with minimal size, weight and thermal
mass. This dramatically reduces device size and thermo-optic
response time (to possibly about one second). Further, the
incorporation of dispersion matched materials yields devices which
have a spectrally uniform response, which is especially desirable
for broadband applications.
[0043] In addition to these benefits, the blockless approach also
retains the intrinsic performance characteristics of continuous
fiber devices: low insertion loss, low back reflection (return
loss), and low polarization-dependent loss ("PDL"). Exemplary
performance levels of the disclosed attenuator are shown below in
Table 1.
1 TABLE 1 QUANTITY VALUE UNIT Dynamic Range 50 dB Spectral Variance
(1500-1600 nm) 0.5 dB Excess Loss 0.05 dB PDL 0.5 dB Return Loss
-55 dB Optical Power Handling 20 dBm DC Power Consumption <200
mW
[0044] In accordance with the present invention, it is also
possible to develop more sophisticated designs such as ovenized
and/or multiple thermoelectric cooling devices to improve device
stability. Further, because of the design flexibility afforded by
the dispersion-matched polymers (i.e., control of the refractive
index), it is possible to design custom applications which exhibit
minimal power consumption and varying operating temperatures.
[0045] In summary, the blockless, dispersion matched fiber optic
attenuator of the present invention is a high performance design
with wide flexibility. The simplicity of the design permits
low-cost, high-volume manufacturing without sacrificing
performance.
[0046] While the invention has been particularly shown and
described with reference to preferred embodiment(s) thereof, it
will be understood by those skilled in the art that various changes
in form and details may be made therein without departing from the
spirit and scope of the invention.
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