U.S. patent application number 10/439071 was filed with the patent office on 2003-10-23 for optoelectronic device having a direct patch mask formed thereon and a method of manufacture therefor.
This patent application is currently assigned to Lucent Technologies Inc.. Invention is credited to Pafchek, Robert M., Salama, John.
Application Number | 20030198450 10/439071 |
Document ID | / |
Family ID | 29216022 |
Filed Date | 2003-10-23 |
United States Patent
Application |
20030198450 |
Kind Code |
A1 |
Pafchek, Robert M. ; et
al. |
October 23, 2003 |
Optoelectronic device having a direct patch mask formed thereon and
a method of manufacture therefor
Abstract
The present invention provides an optoelectronic device with
superior qualities. The optoelectronic device includes an optical
core feature located over a substrate, an outer cladding layer
located over the optical core feature and a direct patch mask
formed on an outer cladding layer. In an exemplary embodiment of
the invention, the direct patch mask has a light source passed
therethrough that corrects birefringence in the optical core
feature and the outer cladding layer.
Inventors: |
Pafchek, Robert M.;
(Blandon, PA) ; Salama, John; (Macungie,
PA) |
Correspondence
Address: |
HITT GAINES P.C.
P.O. BOX 832570
RICHARDSON
TX
75083
US
|
Assignee: |
Lucent Technologies Inc.
Murray Hill
NJ
|
Family ID: |
29216022 |
Appl. No.: |
10/439071 |
Filed: |
May 15, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10439071 |
May 15, 2003 |
|
|
|
09651543 |
Aug 29, 2000 |
|
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Current U.S.
Class: |
385/129 |
Current CPC
Class: |
G02B 6/126 20130101;
G02B 6/122 20130101; G02B 6/136 20130101 |
Class at
Publication: |
385/129 |
International
Class: |
G02B 006/10 |
Claims
What is claimed is:
1. An optoelectronic device, comprising: an optical core feature
located over a substrate; an outer cladding layer located over the
optical core feature; and a direct patch mask formed on an outer
cladding layer.
2. The optoelectronic device as recited in claim 1 wherein the
direct patch mask comprises an essentially opaque material.
3. The optoelectronic device as recited in claim 2 wherein the
opaque material is a metal.
4. The optoelectronic device as recited in claim 3 wherein the
metal is selected from the group consisting of molybdenum,
tantalum, tungsten, chrome, gold and titanium.
5. The optoelectronic device as recited in claim 1 wherein the
direct patch mask has a thickness ranging from about 10 nm to about
500 nm.
6. The optoelectronic device as recited in claim 5 wherein the
direct patch mask has a thickness ranging from about 50 nm to about
200 nm.
7. The optoelectronic device as recited in claim 1 further
including multiple optical core features.
8. The optoelectronic device as recited in claim 7 wherein the
direct patch mask has openings located therein and over the optical
core features.
9. The optoelectronic device as recited in claim 1 further
including an inner cladding layer located between the substrate and
the outer cladding layer.
10. The optoelectronic device as recited in claim 9 wherein the
inner cladding layer has a thickness of up to about 35000 nm, the
optical core feature has a thickness ranging from about 1000 nm to
about 10000 nm and the outer cladding layer has a thickness ranging
from about 5000 nm to about 25000 nm.
11. The optoelectronic device as recited in claim 10 wherein the
optical core feature has a thickness of about 6800 nm.
12. The optoelectronic device as recited in claim 9 wherein the
substrate is a silicon substrate, the inner cladding layer is an
undoped silica inner cladding layer, the optical core feature is a
phosphorous doped silica optical core feature and the outer
cladding layer is a boron phosphorous doped tetraethylorthosilicate
(TEOS) outer cladding layer.
13. A method of manufacturing an optoelectronic device, comprising:
forming an optical core feature over a substrate; forming an outer
cladding layer over the optical core feature; forming a direct
patch mask on the outer cladding layer; and exposing the core
structure and the outer cladding layer to a light source.
14. The method as recited in claim 13 wherein forming a direct
patch mask include forming an essentially opaque direct patch
mask.
15. The method as recited in claim 14 wherein forming an opaque
direct patch mask includes forming a metal direct patch mask.
16. The method as recited in claim 15 wherein forming a metal
direct patch mask includes forming a metal direct patch mask from a
metal selected from the group consisting of molybdenum, tantalum,
tungsten, chrome, gold and titanium.
17. The method as recited in claim 13 wherein forming a direct
patch mask includes forming a direct patch mask having a thickness
ranging from about 10 nm to about 500 nm.
18. The method as recited in claim 17 wherein forming a direct
patch mask having a thickness ranging from about 10 nm to about 500
nm includes forming a direct patch mask having a thickness ranging
from about 50 nm to about 200 nm.
19. The method as recited in claim 13 wherein forming an optical
core feature includes forming multiple optical core features.
20. The method as recited in claim 19 wherein forming a direct
patch mask includes forming a direct patch mask having openings
located therein and over the optical core features.
21. The method as recited in claim 20 wherein forming a direct
patch mask having openings located therein includes forming a
direct patch mask having openings located therein using
photolithography.
22. The method as recited in claim 13 wherein exposing the core
structure and the outer cladding layer to a light source includes
exposing the core structure and the outer cladding layer to an
ultraviolet (UV) light source.
23. The method as recited in claim 22 wherein exposing the core
structure and the outer cladding layer to an ultraviolet (UV) light
source includes exposing the core structure and the outer cladding
layer to an ultraviolet (UV) light source to correct a
birefringence.
24. The method as recited in 13 further including removing the
direct patch mask subsequent to exposing the core structure and the
outer cladding layer to a light source.
25. An optical fiber communications system, comprising: an optical
fiber; a transmitter and a receiver connected by the optical fiber;
and an optoelectronic device including: an optical core feature
located over a substrate; an outer cladding layer located over the
optical core feature; and a direct patch mask formed on the outer
cladding layer.
26. The optical fiber communication system as recited in claim 25
wherein the direct patch mask comprises an opaque material.
27. The optical fiber communication system as recited in claim 26
wherein the opaque material is a metal.
28. The optical fiber communication system as recited in claim 27
wherein the metal is selected from the group consisting of
molybdenum, tantalum, tungsten, chrome, gold and titanium.
29. The optical fiber communication system as recited in claim 25
wherein the direct patch mask has a thickness ranging from about 10
nm to about 500 nm.
30. The optical fiber communication system as recited in claim 29
wherein the direct patch mask has a thickness ranging from about 50
nm to about 200 nm.
31. The optical fiber communication system as recited in claim 25
further including multiple optical core features.
32. The optical fiber communication system as recited in claim 31
wherein the direct patch mask has openings located therein and over
the optical core features.
33. The optical fiber communication system as recited in claim 25
further including an inner cladding layer located between the
substrate and the outer cladding layer.
34. The optical fiber communication system recited in claim 25
wherein the transmitter includes the optoelectronic device.
35. The optical fiber communication system recited in claim 25
wherein the receiver includes the optoelectronic device.
36. The optical fiber communication system recited in claim 25
further including a source.
37. The optical fiber communication system recited in claim 36
wherein the source is a laser or a diode.
38. The optical fiber communication system recited in claim 25
further including a repeater.
39. A method of manufacturing an optical fiber communications
system, comprising: forming an optical fiber; forming a transmitter
and a receiver connected by the optical fiber; and forming an
optoelectronic device including: forming an optical core feature
over a substrate; forming an outer cladding layer over the optical
core feature; forming a direct patch mask on the outer cladding
layer; and exposing the core structure and the outer cladding layer
to a light source.
40. The method as recited in claim 39 wherein forming a direct
patch mask include forming an opaque direct patch mask.
41. The method as recited in claim 40 wherein forming an opaque
direct patch mask includes forming a metal direct patch mask.
42. The method as recited in claim 41 wherein forming a metal
direct patch mask includes forming a metal direct patch mask from a
metal selected from the group consisting of molybdenum, tantalum,
tungsten, chrome, gold and titanium.
43. The method as recited in claim 39 wherein forming a direct
patch mask includes forming a direct patch mask having a thickness
ranging from 10 nm to 500 nm.
44. The method as recited in claim 43 wherein forming a direct
patch mask having a thickness ranging from 10 nm to 500 nm includes
forming a direct patch mask having a thickness ranging from about
50 nm to about 200 nm.
45. The method as recited in claim 39 wherein forming an optical
core feature includes forming multiple optical core features.
46. The method as recited in claim 45 wherein forming a direct
patch mask includes forming a direct patch mask having openings
located therein and over the optical core features.
47. The method as recited in claim 39 further including forming an
inner cladding layer between the substrate and the outer cladding
layer.
48. The method as recited in claim 39 wherein exposing the core
structure and the outer cladding layer to a light source includes
exposing the core structure and the outer cladding layer to an
ultraviolet (UV) light source.
49. The method as recited in claim 48 wherein exposing the core
structure and the outer cladding layer to an ultraviolet (UV) light
source includes exposing the core structure and the outer cladding
layer to an ultraviolet (UV) light source to correct a
birefringence.
50. The method as recited in 39 further including removing the
direct patch mask subsequent to exposing the core structure and the
outer cladding layer to a light source.
51. The method as recited in claim 39 wherein forming a transmitter
includes forming a transmitter having the optoelectronic
device.
52. The method as recited in claim 39 wherein forming a receiver
includes forming a receiver having the optoelectronic device.
53. The method as recited in claim 39 further including forming a
source.
54. The method as recited in claim 53 wherein forming a source
includes forming a laser or a diode.
55. The method as recited in claim 39 further including forming a
repeater.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention is directed, in general, to an optical
device and, more specifically, to an optoelectronic device having a
direct patch mask formed thereon, and a method of manufacture
therefor.
BACKGROUND OF THE INVENTION
[0002] As optical communications advance, more and more passive
optical components are needed, e.g., broadband multiplexors are
needed for delivering voice and video to the home, for combining
pump and signals in an optical amplifier and for adding a
monitoring signal to the traffic on optical fibers. Dense
wavelength division multiplexing (WDM) systems need multiplexers to
combine and separate channels of different wavelengths and also
need add-drop filters to partially alter the traffic. Splitters and
star couplers are used in broadcast applications. Low speed optical
switches are needed for sparing applications and network
reconfiguration.
[0003] Currently, silica-based integrated optical waveguide
technology is well known and used in the industry for the above
mentioned devices. A typical silica-based integrated optical
waveguide may comprise a silicon substrate having an undoped silica
base layer located thereon. Also, a phosphorous doped and/or
germanium core layer is typically located over the base layer. The
core layer is patterned and etched to form individual cores. A
boron/phosphorous doped silica glass cladding layer may also be
blanket deposited over the individual cores.
[0004] One problem associated with current optical waveguide
technology is birefringence. Since core layers and cladding layers
are typically made of different materials, they often have
different refractive indices. For example, the core material may
comprise a phosphorous doped silica layer and the cladding may
comprise a borosilicate glass. The two layers have different
thermal expansion coefficients, such that when the molten fiber
solidifies after deposition and annealing, stresses are introduced
and frozen into the materials. These stresses tend to cause
birefringence of the transverse electric mode (TE) and the
transverse magnetic mode (TM). Birefringence often results in
polarization dependent wavelength (PDW). PDW is a shift in the
center wavelength between the TE and TM modes. For most
applications, and especially system applications, this polarization
is undesirable because it generally requires that the two modes be
matched.
[0005] Currently, one technique used by optoelectronics suppliers
uses ultraviolet light and an independent patch mask to correct
birefringence. The patch mask commonly comprises a glass substrate
having a patterned metal layer formed thereon. The pattern in the
metal layer typically mirrors the location of the previously
discussed cores, i.e., the metal layer has been patterned and
etched to leave unprotected areas over where the cores are located.
After the patch mask has been manufactured, the patch mask is
visually placed over the device. Ultra violet (UV) light is then
projected through the mask, which alters the properties of the
film.
[0006] Using the patch mask to correct birefringence, as previously
described, currently encounters certain problems. One problem
results from manual placement of the patch mask over the device.
Currently, a window in the patch mask is used to manually align a
cross hair in the window with an alignment mark previously
manufactured in the device. This manual aspect tends to cause
distortion, and furthermore, requires additional unwanted wafer
real estate to form such alignment marks.
[0007] Another problem is UV intensity variations across the
waveguide. This is assumed to be a result of inconsistencies in the
glass substrate as the UV light passes through the glass. Another
problem is dispersion of the UV light. As with any process
requiring passing particles through a pattern to affect a separate
surface, the further the pattern is away from the separate surface,
the more the dispersion of the particles that results. Inherent in
the conventional patch mask process is the glass substrate, on
which the patterned metal layer is formed. The glass substrate,
located between the patterned metal layer and the separate surface,
typically causes such dispersion.
[0008] Accordingly, what is needed in the art is a passive optical
component that does not experience the prior art's problems
associated with correcting birefringence, and a method of
manufacture thereof.
SUMMARY OF THE INVENTION
[0009] To address the above-discussed deficiencies of the prior
art, the present invention provides an optoelectronic device with
superior qualities. The optoelectronic device includes an optical
core feature located over a substrate, an outer cladding layer
located over the optical core feature and a direct patch mask
located and formed on an outer cladding layer. In an exemplary
embodiment of the invention, the direct patch mask has a light
source passed therethrough that corrects birefringence in the
optical core feature and the outer cladding layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention is best understood from the following detailed
description when read with the accompanying FIGUREs. It is
emphasized that in accordance with the standard practice in the
optoelectronic industry, various features are not drawn to scale.
In fact, the dimensions of the various features may be arbitrarily
increased or reduced for clarity of discussion. Reference is now
made to the following descriptions taken in conjunction with the
accompanying drawings, in which:
[0011] FIG. 1 illustrates one embodiment of a completed
optoelectronic device, taught herein;
[0012] FIG. 2 illustrates a partially completed optoelectronic
device, including a substrate, an inner cladding layer, optical
core features and an outer cladding layer;
[0013] FIG. 3 illustrates the device illustrated in FIG. 2 after
formation of a direct patch mask layer;
[0014] FIG. 4 illustrates the device illustrated in FIG. 3 after
formation and patterning of a photoresist layer;
[0015] FIG. 5 illustrates the device illustrated in FIG. 4 after
etching the direct patch mask layer and removal of photoresist
portions;
[0016] FIG. 6 illustrates the device shown in FIG. 5 being
subjected to a light source, wherein the light source is attempting
to correct birefringence;
[0017] FIG. 7 illustrates an alternative embodiment of the
completed optoelectronic device illustrated in FIG. 1, wherein the
direct patch mask is removed subsequent to exposure to the light
source;
[0018] FIG. 8 illustrates an optical fiber communication system,
which forms one environment where the completed optoelectronic
device may be used; and
[0019] FIG. 9 illustrates an alternative embodiment optical fiber
communication system, including a repeater.
DETAILED DESCRIPTION
[0020] Referring initially to FIG. 1, illustrated is a
cross-sectional view of an exemplary embodiment of a completed
optoelectronic device 100. In the illustrative embodiment shown in
FIG. 1, the completed optoelectronic device 100 includes an inner
cladding layer 120 formed over a substrate 110, optical core
features 130 formed over the inner cladding layer 120 and an outer
cladding layer 140 formed over the optical core features 130.
Likewise, in contrast to the prior art optical waveguide
technologies, the completed optoelectronic device 100 includes a
direct patch mask 150 formed on the outer cladding layer 140.
[0021] The direct patch mask 150 substantially corrects many of the
problems associated with using the prior art independent patch
masks. Since the direct patch mask 150 is directly formed on the
outer cladding layer 140, rather than being formed on a glass
substrate which then is manually laid upon the outer cladding
layer, the direct patch mask 150 can be used more accurately and in
a much less labor intensive manner. Also, since the direct patch
mask 150 is formed on the layer, rather than being formed on the
glass substrate, substantially no dispersion of light occurs during
UV illumination. Additional benefits are that substantially no
distortion occurs due to improper alignment of the direct patch
mask 150, and substantially no UV intensity variations occur across
the optical core features 130 and outer cladding layer 140.
[0022] Thus, one aspect of the invention provides an optoelectronic
device that does not experience the disadvantages experienced by
the prior art optoelectronic devices during correction of the
birefringence. Moreover, since the direct patch mask is formed on
the outer cladding layer and has no glass substrate located there
between, the optoelectronic device does not experience UV intensity
variations caused by the glass substrate, distortion and dispersion
of the light source. Since the direct patch mask is formed on the
outer cladding, it may be accurately aligned using conventional
photolithographic processes, which can save wafer real estate by
substituting the large visual alignment features with small
photolithography alignment marks and thus, save both time and
money.
[0023] Turning to FIGS. 2-6, with continued reference to FIG. 1,
illustrated are detailed manufacturing steps instructing how one
might, in a preferred embodiment, manufacture the completed
optoelectronic device 100 depicted in FIG. 1. FIG. 2 illustrates a
cross-sectional view of a partially completed optoelectronic device
200. The partially completed optoelectronic device illustrated in
FIG. 2, includes an inner cladding layer 220, which in a previous
step, was formed over a substrate 210. The inner cladding layer
220, in an exemplary embodiment, forms a lower cladding layer. The
substrate 210 may be any layer located in an optoelectronic device,
including a layer located at the wafer level or a layer located
above or below wafer level. The substrate 210, in an exemplary
embodiment, is a silicon substrate. However, it should be
understood that other materials, doped or undoped, may also be
used.
[0024] In an exemplary embodiment, the inner cladding layer 220,
which is commonly referred to as a base layer, is an undoped silica
inner cladding layer having an index of refraction of about 1.4575.
Typically, the inner cladding layer 220 is the most rigid layer and
keeps the optical core features from moving after it is formed and
patterned. Likewise, a common thickness for the inner cladding
layer 220 is about 35000 nm. The inner cladding layer 220 tends to
isolate the fundamental mode from the silicon substrate and thereby
attempts to reduce leakage through the inner cladding layer 220 to
substrate 210 interface, which may not be completely reflective.
Even though specifics have been given for the material used,
thicknesses, and index of refraction of the inner cladding layer
220, they have only been given as examples, and it should be
understood that other materials, thicknesses, and indices are
within the scope of the present invention.
[0025] Formed over the inner cladding layer 220 are one or more
optical core features 230. The formation of the optical core
features 230 are conventional. In the illustrative embodiment, the
optical core features 230 comprise a phosphorous doped silica
material; however, one skilled in the art understands that the
optical core features 230 could comprise any material consistent
with optoelectronic devices. The optical core features 230 may have
a thickness ranging from about 1000 nm to about 10000 and a width
ranging from about 1000 nm to about 15000 nm. However, the
thickness of the optical core features 230 depends on the delta of
the optoelectronic device it is included within, and in an
exemplary embodiment is about 6800 nm. To achieve optical
confinement, the optical core feature's 230 refractive index is
typically increased by a small amount over the refractive index of
the inner cladding layer 220. For example, where the refractive
index of the inner cladding layer 220 is about 1.4575, as discussed
above, the refractive index of the optical core features may be
about 1.4664.
[0026] Formed over the optical core features 230 is an outer
cladding layer 240. In an exemplary embodiment, the thickness of
the outer cladding layer 240 may range from about 5000 nm to about
25000 nm. To promote filling in between the closely spaced optical
core features 230, the outer cladding should flow readily, while
the optical core features 230 and inner cladding layer 220 remain
rigid. Likewise, the outer cladding layer's 240 refractive index
should match the inner cladding layer's 220 refractive index. These
demanding requirements may be met by using an outer cladding layer
240 comprising a boron phosphorous doped tetraethylorthosilicate
glass. In such an exemplary embodiment, the addition of boron to
the outer cladding layer 240 lowers both the flow temperature and
the refractive index, which may compensate for the increase in
refractive index caused by the addition of phosphorous.
[0027] The completed structure shown in FIG. 2 illustrates a
conventional waveguide after fabrication but prior to UV
illumination to correct birefringence. Thus, the structure shown in
FIG. 2 might have polarization dependent wavelength (PDW), which is
a shift in the center wavelength between the transverse electric
mode (TE) and the transverse magnetic mode (TM).
[0028] Turning to FIG. 3, illustrated is the formation of a
structure to correct this PDW. FIG. 3 illustrates the formation of
a patch mask layer 310, located and formed on the optical core
feature 240. The patch mask layer 310, in the illustrative
embodiment, comprises an essentially opaque material. For example,
in an exemplary embodiment, the opaque material is a metal, which
may in a more exemplary embodiment, be selected from the group
consisting of molybdenum, tantalum, tungsten, chrome, gold,
titanium, or another similar material. It should be understood that
the thickness of the patch mask layer 310 may vary, but should be
thick enough to be sufficiently opaque. In one advantageous
embodiment, the thickness of the patch mask layer 310 ranges from
about 10 nm to about 500 nm, and in another exemplary embodiment
the thickness of the patch mask layer 310 ranges from about 50 nm
to about 200 nm. However, one having skill in the art understands
that the effectiveness of the direct patch mask 510 (FIG. 5) is
partially dependent on the thickness thereof and the material
composition therefor. The patch mask layer 310 may be formed using
many manufacturing processes. For example, it is common to form
such layers using a physical vapor deposition (PVD) process, an
evaporation process, or another similar process. It should also be
noted that an adhesion layer, depending on the design or type of
metal used, might be present between the patch mask layer 310 and
the optical core feature 240.
[0029] Turning to FIG. 4, illustrated is the partially completed
optoelectronic device 200 illustrated in FIG. 3, after conventional
formation of photoresist portions 410. As illustrated, the
photoresist layer is patterned and developed to leave unprotected
portions 420 over the optical core features 230.
[0030] Turning to FIG. 5, illustrated is the partially completed
optoelectronic device 200 illustrated in FIG. 4, after etching the
unprotected portions 420 of the patch mask layer 310, and removal
of the photoresist portions 410. In an exemplary embodiment, a
conventional wet etch is used to remove the unprotected portions;
however, one skilled in the art understands that other removal
processes may be used. What results, is a direct patch mask 510,
having openings 520 formed therein directly over the optical core
features 230 through which light may pass to change the refractive
index of the underlying layers. Since the direct patch mask 510 is
formed using conventional techniques, the mask can be very
accurately formed having the openings 520 directly over the optical
core features 230, as opposed to prior art processes.
[0031] Turning to FIG. 6, illustrated is the partially completed
optoelectronic device 200 illustrated in FIG. 5, while being
exposed to a light source 610. The light source 610, which
typically is an ultraviolet light source, attempts to bring the
center wavelength for the TE mode in line with the center
wavelength for the TM mode. What results, are optical devices
wherein birefringence is substantially eliminated. The specifics of
using a light source to correct birefringence, and thus correct
polarization dependent wavelength (PDW), is well known in the art.
After completely subjecting the partially completed optoelectronic
device 200 to the light source 610, the light source 610 may be
removed resulting in the completed optoelectronic device 100
illustrated in FIG. 1.
[0032] Turning to FIG. 7, illustrated is an optional exemplary
embodiment of the completed optoelectronic device 700, where the
direct patch mask 510 illustrated in FIG. 6, is removed subsequent
to exposure to the light source 610. In such an exemplary
embodiment, the direct patch mask 510 may be removed using any
removal technique, such as a reactive ion etch or wet etch, that is
consistent with the present invention. It should be noted that
removal of the direct patch mask 510 subsequent to exposure to the
light source 610 is an optional step, and should not be construed
to limit the scope of the present invention. Thus, if so desired,
the direct patch mask 510 may be left on the device.
[0033] Turning briefly to FIG. 8, illustrated is an optical fiber
communication systems 800, which may form one environment where the
completed optoelectronic device 100 may be included. The optical
fiber communication system 800, in the illustrative embodiment,
includes an initial signal 810 entering a receiver 820. The
receiver 820, receives the initial signal 810, addresses the signal
810, and sends the resulting information across an optical fiber
830 to a transmitter 840. The transmitter 840 receives the
information from the optical fiber 830, addresses the information,
and sends an ultimate signal 850. As illustrated in FIG. 8, the
completed optoelectronic device 100 may be included within the
receiver 820. However, one having skill in the art understands that
the completed optoelectronic device 100 may be included anywhere in
the optical fiber communication system 800, including the
transmitter 840. The optical fiber communication system 800 is not
limited to the devices previously mentioned. For example, the
optical fiber communication system 800 may include a source 860,
such as a laser or a diode, or many other similar devices. Turning
briefly to FIG. 9, illustrated is an alternative optical fiber
communication system 900 in which the optoelectronic device 100 may
be employed. In the illustrated embodiment, the optical fiber
communication system 900 has a repeater 910 that includes a second
receiver 920 and a second transmitter 930 located between the
receiver 820 and the transmitter 840.
[0034] Although the present invention has been described in detail,
those skilled in the art should understand that they can make
various changes, substitutions and alterations herein without
departing from the spirit and scope of the invention in its
broadest form.
* * * * *