U.S. patent application number 09/768828 was filed with the patent office on 2001-07-12 for compact optical amplifier with integrated optical waveguide and pump source.
This patent application is currently assigned to Molecular OptoElectronics Corporation. Invention is credited to Lawrence, Brian L..
Application Number | 20010007607 09/768828 |
Document ID | / |
Family ID | 23227476 |
Filed Date | 2001-07-12 |
United States Patent
Application |
20010007607 |
Kind Code |
A1 |
Lawrence, Brian L. |
July 12, 2001 |
Compact optical amplifier with integrated optical waveguide and
pump source
Abstract
An optical amplifier with integrated optical waveguide, pump
source and other, optional components for amplifying an input
optical signal coupled from a fiber optic. The amplifier includes a
housing having these components mounted therein, and appropriate
optics for coupling the input and output optical signals to and
from the appropriate ports, and for carrying an optical pump signal
from its source to the waveguide. The optical waveguide disclosed
is a channel waveguide amplification chip, having a relatively
small size; and the pump source disclosed is a laser diode capable
of generating the optical pump signal internal to the housing with
only electrical (e.g., power) signals applied thereto from outside
of the housing. Other optional components may be provided for
cooperative optical processing in the amplifier housing. The
disclosed optical amplifier offers size and cost advantages over
other known systems.
Inventors: |
Lawrence, Brian L.;
(Watervliet, NY) |
Correspondence
Address: |
HESLIN & ROTHENBERG, PC
5 COLUMBIA CIRCLE
ALBANY
NY
12203
|
Assignee: |
Molecular OptoElectronics
Corporation
Watervliet
NY
|
Family ID: |
23227476 |
Appl. No.: |
09/768828 |
Filed: |
January 23, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09768828 |
Jan 23, 2001 |
|
|
|
09316102 |
May 24, 1999 |
|
|
|
6208456 |
|
|
|
|
Current U.S.
Class: |
385/132 |
Current CPC
Class: |
H01S 3/063 20130101;
H01S 3/025 20130101 |
Class at
Publication: |
385/132 |
International
Class: |
G02B 006/10 |
Claims
What is claimed is:
1. An optical amplifier, comprising: a housing having optical
signal input and output ports; a channel waveguide chip in said
housing for optically amplifying an input optical signal from said
input port using an optical pump signal applied thereto; and an
optical pump source in said housing for generating the optical pump
signal.
2. The optical amplifier of claim 1, further comprising: input
coupling optics for transmitting the input optical signal into the
channel waveguide chip from the input port; and output coupling
optics for carrying an output optical signal from the channel
waveguide chip to the output port.
3. The optical amplifier of claim 1, wherein the channel waveguide
chip comprises: a linear core having an input end for receiving an
input optical signal, and an output end for producing an output
optical signal; and a surface through which the optical pump signal
is received.
4. The optical amplifier of claim 3, wherein the surface of the
waveguide amplification chip is arranged at an approximately 45
degree angle with the linear core thereof, the optical pump source
transmits the optical pump signal at approximately a 90 degree
angle with the core, the channel waveguide chip further comprising:
a reflective coating applied over the surface to reflect the
optical pump signal into the linear core.
5. The optical amplifier of claim 4, wherein the channel waveguide
chip further comprises: a prism applied over the surface for
directing the input optical signal colinearly into the linear
core.
6. The optical amplifier of claim 1, wherein the optical pump
source is a laser diode which generates the optical pump signal
internal to the housing, and wherein the only optical ports of the
amplifier are the optical signal input and output ports.
7. The optical amplifier of claim 1, wherein the housing has at
least one planar dimension less than about 3 inches.
8. The optical amplifier of claim 1, further comprising: an
additional optical component in the housing in cooperative
operation with the channel waveguide chip.
9. A method for optically amplifying an input optical signal
applied to an amplifier housing, the method comprising: generating
an optical pump signal in the housing; applying the optical pump
signal to a channel waveguide chip in the housing to facilitate
amplification of the input optical signal into an amplified, output
optical signal.
10. The method of claim 9, wherein said generating includes using a
laser diode in said housing.
11. The method of claim 9, further comprising coupling as optical
signals to the housing only the input optical signal and the output
optical signal.
12. The method of claim 9, further comprising: coupling, using
input coupling optics, the input optical signal from a first fiber
optic to the channel waveguide chip; and coupling, using output
coupling optics, an amplified, output optical signal from the
channel waveguide chip to a second fiber optic.
13. The method of claim 9, wherein the channel waveguide chip
comprises: a linear core having an input end for receiving an input
optical signal, and an output end for producing an output optical
signal; and a surface through which the optical pump signal is
received.
14. The method of claim 13, wherein the surface of the channel
waveguide chip is arranged at an approximately 45 degree angle with
the linear core thereof, the optical pump source transmits the
optical pump signal at approximately a 90 degree angle with the
core, the channel waveguide chip further comprising: a reflective
coating applied over the surface to reflect the optical pump signal
into the linear core.
15. The method of claim 14, wherein the channel waveguide chip
further comprises: a prism applied over the surface for directing
the input optical signal colinearly into the linear core.
16. A method for fabricating an optical amplifier, comprising:
providing a housing having optical signal input and output ports;
positioning a channel waveguide chip in said housing for optically
amplifying an input optical signal from said input port using an
optical pump signal applied thereto; and positioning an optical
pump source in said housing for generating the optical pump
signal.
17. The method of claim 16, further comprising: providing input
coupling optics for transmitting the input optical signal into the
channel waveguide chip from the input port; and providing output
coupling optics for carrying an output optical signal from the
channel waveguide chip to the output port.
18. The method of claim 16, wherein the channel waveguide chip
comprises: a linear core having an input end for receiving an input
optical signal, and an output end for producing an output optical
signal; and a surface through which the optical pump signal is
received.
19. The method of claim 18, wherein the surface of the waveguide
amplification chip is arranged at an approximately 45 degree angle
with the linear core thereof, the optical pump source transmits the
optical pump signal at approximately a 90 degree angle with the
core, the channel waveguide chip further comprising: a reflective
coating applied over the surface to reflect the optical pump signal
into the linear core.
20. The method of claim 19, wherein the channel waveguide chip
further comprises: a prism applied over the surface for directing
the input optical signal colinearly into the linear core.
21. The method claim 16, wherein the optical pump source is a laser
diode which generates the optical pump signal internal to the
housing, and wherein the only optical ports of the amplifier are
the optical signal input and output ports.
22. The method of claim 16, wherein the housing has at least one
planar dimension less than about 3 inches.
23. The method of claim 16, further comprising: providing an
additional optical component in the housing for cooperative
operation with the channel waveguide chip.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This Application relates to the following commonly assigned,
previously filed, co-pending U.S. patent applications:
[0002] 1. U.S. patent application Ser. No. 09/121,455, filed Jul.
23, 1998 and entitled "Method for Fabricating an Optical
Waveguide;" and
[0003] 2. U.S. patent application Ser. No. 09/159,012, filed Sep.
23, 1998 and entitled "Optical Channel Waveguide Amplifier."
[0004] Each of these previously filed U.S. patent applications is
hereby incorporated by reference herein in its entirety.
TECHNICAL FIELD
[0005] The present invention relates to optical amplifiers, and
more particularly to a compact, low cost optical amplifier package
having a small optical waveguide amplifier chip and an optical pump
integrated therein.
BACKGROUND OF THE INVENTION
[0006] The field of optical telecommunications has experienced
phenomenal growth over the past several years, fueled in large part
by the development and deployment of erbium-doped fiber amplifiers
("EDFAs").
[0007] Prior to optical amplifiers, fiber optic communication
systems required electronic repeaters to amplify signals and offset
the losses associated with long distance optical transmission.
These electronic devices converted the transmitted optical signal
into the electrical domain, amplified and reshaped the electrical
signal, and converted the electrical signal back into an optical
signal, and onto the next leg of the fiber system.
[0008] Electronic detectors are incapable of discriminating between
different wavelengths, therefore, multi-wavelength systems require
an independent repeater for each wavelength in the system, as well
as the necessary filtering components to isolate each of the
wavelengths into their respective repeaters. FIG. 1a is a
representative bock diagram of a 16 channel repeater system 10. The
large amount of equipment needed made multi-wavelength
communications systems using repeaters prohibitively expensive.
[0009] The deployment of the EDFA, however, changed the topology of
fiber-optic communication networks. Because the optical amplifier
was capable of amplifying multiple wavelengths independently in a
single unit, a multi-wavelength system could use a single optical
amplifier. The 16 channel repeater system of FIG. 1a requires a
wavelength de-multiplexer 12 to break the 16 channels out onto
individual fibers 14, 16 repeaters 18, and a wavelength multiplexer
16 to recombine the 16 individual wavelengths. All of this was
replaced by the single EDFA 20 shown in FIG. 1b.
[0010] This ability to add multiple channels to a single fiber with
minimal additional amplifier costs created an explosion in the
bandwidth of optical fiber communication systems. Deployed systems
went from single channel sub-gigabit per second operation to 128
channel, multi-gigabit per second per channel operation.
[0011] The continuing growth in the bandwidth of optical
communication systems has also led to a new demand for more complex
functionality in optical networks. To satisfy this demand,
manufacturers are desirous of devices in increasingly smaller and
more compact packages, while at the same time integrating multiple
functions into a single device. In sharp contrast to the
ever-shrinking size of many optical network components, the EDFA
faces a hard limit because of the fixed value of the minimum bend
radius of the fiber. Bend losses are proportional to the bend
radius, and hence the radius must be kept large. A nominal radius
for such fiber is about 3.75 cm, resulting in a coil diameter of
about 7.5 cm (about 3 inches) which in turn results in an minimum
package planar dimension of at least 31/2.times.31/2inches.
Consequently, though many components such as the isolators,
980/1550 nm multiplexers, and monitor taps and photodiodes can be
integrated into the package, the footprint remains constrained by
the minimum diameter of the erbium-doped fiber coil. Nominal
package dimensions are now about 6.times.6 inches.
[0012] Semiconductor optical amplifiers (SOAs) are also available,
and rely on electrical (rather than optical) pump sources for
amplification. However, their performance characteristics are known
to be deficient in many areas, compared to EDFAs.
[0013] The demand for more compact devices with greater integrated
functionality is accompanied by the need to reduce the cost of
these devices. As optical system designers increase the complexity
of their networks, the number of optoelectronic components required
grows substantially. For the very same reasons that
multi-wavelength systems with electronic repeaters were
prohibitively expensive, more complex networks begin to face the
same cost issues. Thus, not only is "real estate" within the system
at a premium requiring smaller, integrated devices, but cost also
plays a significant role requiring less expensive components as
well.
[0014] The EDFA was the critical enabling technology that gave rise
to the recent boom in optical communications known as WDM. As
communications systems continue to grow and expand, system
designers find themselves in need of new devices, amplifiers in
particular, that are smaller and less expensive than their current
counterparts. A compact, low cost optical amplifier with the
ability to incorporate additional devices for added functionality
is therefore required.
SUMMARY OF THE INVENTION
[0015] The shortcomings of the prior approaches are overcome, and
additional advantages are provided, by the present invention which
in one aspect is an optical amplifier having a housing with optical
signal input and output ports; a channel waveguide chip in said
housing for optically amplifying an input optical signal from the
input port using an optical pump signal applied thereto; and an
optical pump source in the housing for generating the optical pump
signal.
[0016] The amplifier may also include input coupling optics for
transmitting the input optical signal into the channel waveguide
chip from the input port; and output coupling optics for carrying
an output optical signal from the channel waveguide chip to the
output port.
[0017] In one embodiment, the channel waveguide chip includes a
linear core having an input end for receiving an input optical
signal, and an output end for producing an output optical signal;
and a surface through which the optical pump signal is received.
The surface of the channel waveguide chip may be arranged at an
approximately 45 degree angle with the linear core thereof. The
optical pump source transmits the optical pump signal at
approximately a 90 degree angle with the core. The chip may also
include a reflective coating applied over the surface to reflect
the optical pump signal into the linear core. A prism may be
applied over the surface for directing the input optical signal
colinearly into the core.
[0018] The optical pump source may be a laser diode which generates
the optical pump signal internal to the housing, wherein the only
optical ports of the amplifier are the optical signal input and
output ports.
[0019] Based on the types of components used, the present invention
attains a package dimension of less than about 3 inches in at least
one planar dimension.
[0020] The amplifier disclosed herein provides, in a compact,
cost-effective package, a channel waveguide amplifier chip,
appropriate optics to couple the signal into and out of the
waveguide, a pump laser diode, and appropriate optics to focus the
light from the pump laser diode into the waveguide. In addition,
the amplifier may also be constructed to integrate additional
optical components for added functionality. This invention
therefore provides significant optical amplification in a low-cost,
compact package that can minimize the space required within a
communications system to provide signal amplification, and be
integrated with additional components, such as splitters,
wavelength multiplexers or demultiplexers, or optical add/drop
multiplexers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] 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:
[0022] FIG. 1a depicts in schematic form an electrical repeater
approach to amplifying a multi-channel optical signal;
[0023] FIG. 1b depicts in schematic form an EDFA approach to
amplifying a multi-channel optical signal;
[0024] FIG. 2a is a top plan view of an optical amplifier in
accordance with the present invention, partially in schematic form
and with the cover of the housing removed;
[0025] FIG. 2b is a top plan view of another embodiment of an
optical amplifier in accordance with the present invention,
partially in schematic form and with the cover of the housing
removed;
[0026] FIG. 3 is a perspective view of a channel waveguide
amplification chip employed in the amplifiers of FIGS. 2a-b, in
accordance with the present invention; and
[0027] FIG. 4 is a front sectional view of an alternate embodiment
of the channel waveguide chip of FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0028] With reference to FIGS. 2a-b, compact waveguide amplifiers
100 and 100' in accordance with the present invention include a
channel waveguide amplifier chip 110, signal input coupling optics
120 (to couple the optical input signal from input fiber 122),
signal output coupling optics 130 (to couple the optical output
signal to output fiber 132), a pump laser 140, and pump coupling
optics 150 (to couple the optical pump signal between pump laser
140 and chip 110). Certain components may be aligned on alignment
bench 190. Optional components such as planar lightwave circuit 170
and its associated coupling lens 180 can also be easily integrated
into amplifier 100 of FIG. 2a, but are omitted from the smaller
version thereof 100' of FIG. 2b.
[0029] The compact size of the housing 160 (e.g., nickel/gold
plated) results from the small waveguide chip 110, coupled with the
ability to use an integrated diode pump 140, discussed further
below.
[0030] Exemplary channel waveguide chip 110, shown in detail in
FIGS. 3-4, may be of the type disclosed in the above-incorporated
U.S. patent application 09/159,012 entitled "Optical Channel
Waveguide Amplifier," and may be fabricated using the procedures
disclosed in the above-incorporated U.S. patent application
09/121,455 entitled "Method for Fabricating an Optical Waveguide".
The waveguide chip 110 may be composed of a linear core 212 doped
with an active ion such as Nd:YAG, Er:glass, or Nd:glass, among
others. The compact nature of the waveguide is enabled by the use
of high-gain materials. Of particular applicability is the family
of Erbium/Ytterbium(Er/Yb) co-doped phosphate glasses which have
nearly 100 times the number density of atoms, do not suffer
quenching effects, and have twice the emission cross-section
relative to their silica counterparts typically used in EDFAs . The
core 212 may be nominally square in cross-section and of size from
10 .mu.m to 30 .mu.m on a side. The surrounding cladding 214 may be
an undoped material of lower refractive index. One end of the
waveguide chip 216 may be polished at an angle (.alpha.) of 45
degrees with respect to the waveguide axis. The angle-polished end
is then coated 220 to reflect the applied pump signal 211, and
overlaid with a prism 230 matched in index to the core (and bonded
to the waveguide with an ultraviolet(UV)-cured optical adhesive)
for directing the input optical signal colinearly into the core as
signal 213.
[0031] The opposing end of the waveguide may be prepared in one of
two ways. The first design (shown in FIG. 4) utilizes a
perpendicular end-face 218 with an anti-reflection (AR) coating 222
to minimize back-reflections. If, however, the AR coating is
insufficient, the second design option (shown in FIGS. 2a-b)
involves polishing the opposing end at 45 degrees and bonding an
index-matched right-angle prism with UV-cured adhesive to further
mitigate reflections.
[0032] Channel waveguide chip 110 in one embodiment is about 10-30
mm in length (L), and the overall planar dimensions of the
amplifier housing of amplifier 100'(i.e., the length and width of
the view of FIG. 2b without the optional PLC 170 and coupling lens
180 of amplifier 100 of FIG. 2a), can therefore be about
11/2inches.times.about 21/2inches. (The package thickness is about
3/4inch.) This smaller, overall planar dimension stands in contrast
to that of a functionally equivalent EDFA amplifier of 6.times.6
inches, at the 1530 - 1565 nm bandwidth of interest, and in fact is
even better than the absolute, theoretically planar dimensions of
EDFAs discussed above of 3.times.3 inches, based on the minimum
bend radius. The present invention therefore provides at least one
(and in fact both) planar dimensions of less than about 3 inches.
Waveguide chip 110 of amplifiers 100 and 100' provides high gain in
a relatively short device (when compared to the several meters of
erbium-doped fiber typical in EDFAs), and therefore results in a
smaller size of the amplifier housings.
[0033] Waveguide 110 requires a pump source to provide a source of
the optical pump signal 211 for waveguide gain. With reference to
FIG. 2a, exemplary pump source 140 disclosed herein is a single or
multi-mode laser diode on a submount and maintained at constant
temperature with a thermoelectric cooler (TEC) 142. One exemplary
diode is an Open Heat Sink Packaged Laser Diode available from High
Power Devices, Inc., model number HPD1005C. Power is provided to
both the laser diode and the TEC through external pins 144.
Additional pins may also be included to incorporate a monitor
photodiode to monitor pump laser power, a thermistor to monitor
pump laser temperature, and gain monitoring sensors (not shown). To
couple the signal 211 from the pump laser diode into the waveguide
110, lenses 150 are used to focus the power into the waveguide off
of the 45-degree coated end-face of the waveguide. The pump source
may therefore be arranged to transmit the optical pump signal at an
angle of 90 degrees relative the longitudinal axis of the
waveguide. Notably, the optical pump signal is generated internal
to the amplifier housing, and no additional optical input ports are
required for the pump signal. This feature adds to the cost and
space savings provided by the amplifier disclosed herein.
[0034] Amplifiers 100 and 100' also include the optics used to
couple the optical signal into and out of the waveguide 110. The
input side of the waveguide is typically buried behind a prism 230
(FIG. 4) and thus requires a set of optics 120 to image the
single-mode fiber 122 output into the waveguide chip 110. At a
minimum, a low numerical aperture (NA) matched pair of lenses may
be used to image the fiber output with a 1:1 magnification ratio
into the waveguide. Other options include lenses that can expand
the beam to fill the waveguide core. In any case, the goal of the
input optics is to couple the signal light from the input fiber 122
into the waveguide with as little loss as possible. For core
dimensions larger than approximately 10 .mu.m on a side, 1:1
imaging lenses work very well.
[0035] Coupling optics 130 recover the signal from the waveguide
and return it to the optical fiber 132. For waveguides not much
larger than 10-15 .mu.m on a side, 1:1 imaging lenses can effect
coupling with as little as 2-3 dB of total coupling loss. To reduce
the coupling losses further may require lenses that provide image
reduction. Similarly, for larger waveguides some form of imaging
reduction may also be necessary.
[0036] The compact nature of the amplifier disclosed herein
facilitates integration of additional components therein. For
example, as shown in FIG. 2a, an optional planar lightwave circuit
(PLC) 170 may, for example, be a silica waveguide splitter (e.g.,
Gould Fiber Optics, model number 47-10335-18-05631) or an arrayed
waveguide grating (AWG) multiplexer (e.g., Photonic Integration
Research, Inc., model number AWG-WB-1.times.8-200G-1.5-M-FC). Each
of these devices, because of its performance in a filter capacity,
has high insertion loss associated therewith. However, when
integrated with the compact, low-cost amplifier discussed above in
a small package, the intrinsic losses are offset to create
so-called "lossless" versions. Many benefits result from a small,
inexpensive amplifier integrated with one, or even several,
additional optoelectronic components, such as PLC 170.
[0037] The amplifiers discussed herein, based on a channel
waveguide chip, provide compact, low cost optical solutions for use
in fiber optic systems. Their primary application is optical
amplification in communication systems where space is at a premium,
and smaller devices are required. In addition, these amplifiers are
ideal for use in systems where the design requires large numbers of
low-cost devices to achieve the desired performance. Finally,
because of their compact nature, the amplifiers can be integrated
with other devices such as splitters or multiplexers and
de-multiplexers. When adding additional components into the
package, the insertion loss associated with the components can be
offset by the optical amplification, allowing for the development
of "lossless" versions of these very same optical components.
[0038] 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.
* * * * *