U.S. patent application number 11/696355 was filed with the patent office on 2007-10-11 for multi-unit planar lightwave circuit wavelength dispersive device.
Invention is credited to Paul Colbourne.
Application Number | 20070237451 11/696355 |
Document ID | / |
Family ID | 38561384 |
Filed Date | 2007-10-11 |
United States Patent
Application |
20070237451 |
Kind Code |
A1 |
Colbourne; Paul |
October 11, 2007 |
MULTI-UNIT PLANAR LIGHTWAVE CIRCUIT WAVELENGTH DISPERSIVE
DEVICE
Abstract
A multi-unit wavelength dispersive optical device includes a
plurality of independent planar lightwave circuit (PLC) wavelength
dispersive optical devices in a single device in which a plurality
of independent front and backend units can utilize the same
dispersion platform and share the same opto-mechanics and
packaging.
Inventors: |
Colbourne; Paul; (Ottawa,
CA) |
Correspondence
Address: |
TEITELBAUM & MACLEAN
280 SUNNYSIDE AVENUE
OTTAWA
ON
K1S 0R8
CA
|
Family ID: |
38561384 |
Appl. No.: |
11/696355 |
Filed: |
April 4, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60789564 |
Apr 6, 2006 |
|
|
|
Current U.S.
Class: |
385/18 ; 385/14;
385/37 |
Current CPC
Class: |
G02B 6/3512 20130101;
G02B 6/12007 20130101; G02B 6/29313 20130101; G02B 6/3524 20130101;
G02B 6/2931 20130101; G02B 6/29311 20130101; G02B 6/2938 20130101;
G02B 6/12021 20130101; G02B 6/29395 20130101; G02B 6/356 20130101;
G02B 26/0841 20130101 |
Class at
Publication: |
385/018 ;
385/014; 385/037 |
International
Class: |
G02B 6/26 20060101
G02B006/26 |
Claims
1. A multi-unit planar lightwave circuit device comprising: a first
planar lightwave circuit chip including a first input port, a first
input arrayed waveguide grating, a first plurality of output
arrayed waveguide gratings, and a first plurality of output ports,
wherein a first input optical signal launched into the first input
arrayed waveguide grating via the first input port is dispersed
into wavelength channels in a first dispersion plane upon exiting
the first input arrayed waveguide grating; a first cylindrical lens
for collimating the first input optical signal in a first direction
after exiting the first planar lightwave circuit; a first array of
switching elements for independently redirecting each of the
wavelength channels from the first input optical signal to selected
first output arrayed waveguide gratings forming a plurality of
first output optical signal for output respective first output
ports; a second planar lightwave circuit chip including a second
input port, a second input arrayed waveguide grating, at least one
second output arrayed waveguide gratings, and at least one second
output ports, wherein a second input optical signal launched into
the second input arrayed waveguide grating via the second input
port disperses according to wavelength into a second dispersion
plane parallel to the first dispersion plane upon exiting the
second input arrayed waveguide grating; a second cylindrical lens
for collimating the second input optical signal in the first
direction after exiting the second planar lightwave circuit; a
second array of switching elements, parallel to the first array of
switching elements, for independently redirecting each of the
wavelength channels from the second input optical signal to
selected second output arrayed waveguide gratings for output
respective second output ports; and a switching lens for focusing
the wavelength channels of the first input optical signal onto
respective switching elements from the first array of switching
elements, and for focusing the wavelength channels of the second
optical signal onto respective switching elements from the second
array of switching elements.
2. The device according to claim 1, wherein the first and second
array of switching elements comprise two parallel rows of MEMs
mirrors on a same substrate.
3. The device according to claim 1, further comprising a
photo-detector optically coupled to one of the second output
waveguide gratings; wherein the second array of switching elements
consecutively redirects each wavelength channel in the second input
optical signal to the one output waveguide grating, while directing
remaining wavelength channels to the second input waveguide for
output the second output port.
4. The device according to claim 3, wherein the second output port
is optically coupled to the first input port.
5. The device according to claim 3, further comprising: a third
planar lightwave circuit chip including a third input port, a third
input arrayed waveguide grating, a third plurality of output
arrayed waveguide gratings, and a third plurality of output ports,
wherein a third input optical signal launched into the third input
arrayed waveguide grating via the third input port disperses
according to wavelength into a third dispersion plane upon exiting
the third input arrayed waveguide grating; a third cylindrical lens
for collimating the third input optical signal in the first
direction after exiting the third planar lightwave circuit; and a
third array of switching elements for independently attenuating and
redirecting each of the wavelength channels from the third input
optical signal to selected third output arrayed waveguide gratings
for output respective third output ports; wherein the switching
lens focuses the wavelength channels of the third input optical
signal onto respective switching elements from the third array of
switching elements.
6. The device according to claim 5, wherein the first, second and
third array of switching elements comprise three parallel rows of
MEMs mirrors on a same substrate.
7. The device according to claim 5, wherein at least one of the
first output ports is optically coupled to the second input
port.
8. The device according to claim 7, wherein at least one of the
second output ports is optically coupled to the third input
port.
9. The device according to claim 5, wherein at least one of the
second output ports is optically coupled to the third input
port.
10. The device according to claim 5, wherein the second array of
switching elements independently attenuates and redirects each of
the wavelength channels from the second input optical signal to
selected second output arrayed waveguide gratings for output
respective second output ports.
11. The device according to claim 10, wherein at least one of the
first output ports is optically coupled to the second input
port.
12. The device according to claim 1, wherein the second array of
switching elements independently attenuates and redirects each of
the wavelength channels from the second input optical signal to
selected second output arrayed waveguide gratings for output
respective second output ports.
13. The device according to claim 1, further comprising: a third
planar lightwave circuit chip including a third input port, a third
input arrayed waveguide grating, a third plurality of output
arrayed waveguide gratings, and a third plurality of output ports,
wherein a third input optical signal launched into the third input
arrayed waveguide grating via the third input port disperses
according to wavelength into a third dispersion plane upon exiting
the third input arrayed waveguide grating; a third cylindrical lens
for collimating the third input optical signal in the first
direction after exiting the third planar lightwave circuit; and a
third array of switching elements for independently attenuating and
redirecting each of the wavelength channels from the third input
optical signal to selected third output arrayed waveguide gratings
for output respective third output ports; wherein the switching
lens focuses the wavelength channels of the third input optical
signal onto respective switching elements from the third array of
switching elements.
14. The device according to claim 13, wherein the first, second and
third array of switching elements comprise three parallel rows of
MEMs mirrors on a same substrate.
15. The device according to claim 1, further comprising: a fourth
planar lightwave circuit chip positioned adjacent and parallel to
the first planar lightwave circuit including a fourth plurality of
output arrayed waveguide gratings, and a fourth plurality of output
ports, wherein each of the switching elements in the first array of
switching elements pivots about a first axes for directing
wavelength channels back in the first dispersion plane to the first
plurality of output diffraction gratings, and about a second axis
perpendicular to the first axis for directing wavelength channels
at an acute angle to the first dispersion plane; and a fourth
cylindrical lens for receiving and focusing the wavelength channels
from the first input optical signal redirected out of the first
dispersion plane onto the fourth plurality of output arrayed
waveguides.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of U.S. Provisional Patent
Application No. 60/789,564 file Apr. 6, 2006, entitled "Wavelength
Switch With Multiple Units" which is incorporated herein by
reference for all purposes.
TECHNICAL FIELD
[0002] The present invention relates to a multi-unit wavelength
dispersive optical device, and in particular to the integration of
a plurality of independent planar lightwave circuit (PLC)
wavelength dispersive optical devices into a single device.
BACKGROUND OF THE INVENTION
[0003] Conventional optical wavelength dispersive devices, such as
those disclosed in U.S. Pat. No. 6,097,859 issued Aug. 1, 2000 to
Solgaard et al; U.S. Pat. No. 6,498,872 issued Dec. 24, 2002 to
Bouevitch et al; U.S. Pat. No. 6,707,959 issued Mar. 16, 2004 to
Ducellier et al; U.S. Pat. No. 6,810,169 issued Oct. 26, 2004 to
Bouevitch; and U.S. Pat. No. 7,014,326 issued Mar. 21, 2006 to
Danagher et al, separate a multiplexed optical beam into
constituent wavelengths, and then direct individual wavelengths or
groups of wavelengths, which may or may not have been modified,
back through the device to a desired output port. Typically the
back end of the device includes individually controllable devices,
such as a micro-mirror array, which are used to redirect selected
wavelengths back to one of several output ports, or an array of
liquid crystal cells, which are used to block or attenuate selected
wavelengths.
[0004] In the case of a wavelength blocker (WB), or a dynamic gain
equalizer (DGE) the front end unit can include a single
input/output port with a circulator or one input port and one
output port. Typically the front end unit will include a
polarization diversity unit for ensuring the beam of light has a
single state of polarization. The backend unit for a WB or a DGE
can be an array of liquid crystal cells, which independently rotate
the state of polarization of the wavelength channels to either
partially attenuate or completely block selected channels from
passing back through the polarization diversity unit in the front
end. Examples of WB and DGE backend units are disclosed in U.S.
Pat. No. 7,014,326 issued Mar. 21, 2006 to Danagher et al; U.S.
Pat. No. 6,498,872 issued Dec. 24, 2002 to Bouevitch et al; and
U.S. Pat. No. 6,810,169 issued Oct. 26, 2004 to Bouevitch, which
are incorporated herein by reference.
[0005] The arrayed waveguide diffraction grating (AWG) was invented
by Dragone (C. Dragone, IEEE Photonics Technology Letters, Vol. 3,
No. 9, pp. 812-815, September 1991) by combining a dispersive array
of waveguides (M. K. Smit, Electronics Letters, Vol. 24, pp.
385-386, 1988) with input and output "star couplers" on a planar
lightwave circuit chip. (C. Dragone, IEEE Photonics Technology
Letters, Vol. 1, No. 8, pp. 241-243, August 1989). The AWG can work
both as a DWDM demultiplexer and as a DWDM multiplexer, as taught
by Dragone in U.S. Pat. No. 5,002,350 (March 1991), which is
incorporated herein by reference.
[0006] U.S. Pat. No. 7,027,684 issued Apr. 11, 2006 to Ducellier et
al, and United States Patent Publication No. 2004/0252938 published
Dec. 16, 2004 to Ducellier et al relate to single and mulit-layer
planar lightwave circuit (PLC) wavelength selective switches (WSS),
respectively, which are illustrated in FIGS. 1 and 2. A single
level device 75, illustrated in FIG. 1, includes a PLC 74 with an
input diffraction grating in the middle, and a plurality of output
diffraction gratings on either side of the input diffraction
grating. An input optical signal launched into the input
diffraction grating is dispersed into constituent wavelengths,
which are directed at different angles through lensing 78 to an
array of tiltable mirrors 76. The light is collimated in one
direction, e.g. vertically, by a first cylindrical lens 77 adjacent
to the PLC 74, while a cylindrical switching lens 79 focuses the
output light in the horizontal direction onto the tiltable mirrors
76. Each wavelength channels falls onto a different one of the
tiltable mirrors 76, which redirect the individual wavelength
channels back through the lensing 78 to whichever output
diffraction grating is desired for recombination and output an
output port. For the single level device the tiltable mirrors 76
rotate about a single axis to redirect the wavelength channels
within the dispersion plane, i.e. the plane of the PLC 74.
[0007] A two level device 75', illustrated in FIG. 2, includes a
second PLC 74', similar to the PLC 74, superposed above the PLC 74
with a plurality of input or output diffraction gratings and ports.
A second cylindrical lens 77' is superposed above the first
cylindrical lens 77 for focusing the beams of light onto the output
diffraction gratings provided on the second PLC 74'. For the
two-level device, tiltable mirrors 76' rotate about two
perpendicular axes to redirect the wavelength channels within the
dispersion plane (as above) and at an acute angle to the dispersion
plane into a plane parallel to the dispersion plane, i.e. the plane
of the PLC 74'.
[0008] Unfortunately, each time a customer wishes to purchase a WB,
a DGE, a WSS or any form of monitor therefor, they must purchase a
separate dispersion platform, i.e. spherical lens and tiltable
mirror MEMS chip, along with associated opto-mechanics and
packaging. An object of the present invention is to overcome the
shortcomings of the prior art by providing a multi-unit wavelength
dispersive device, in which a plurality of independent front and
backend units can utilize the same dispersion platform and share
the same opto-mechanics and packaging.
SUMMARY OF THE INVENTION
[0009] Accordingly, the present invention relates to a multi-unit
planar lightwave circuit device comprising:
[0010] a first planar lightwave circuit chip including a first
input port, a first input arrayed waveguide grating, a first
plurality of output arrayed waveguide gratings, and a first
plurality of output ports, wherein a first input optical signal
launched into the first input arrayed waveguide grating via the
first input port is dispersed into wavelength channels in a first
dispersion plane upon exiting the first input arrayed waveguide
grating;
[0011] a first cylindrical lens for collimating the first input
optical signal in a first direction after exiting the first planar
lightwave circuit;
[0012] a first array of switching elements for independently
redirecting each of the wavelength channels from the first input
optical signal to selected first output arrayed waveguide gratings
forming a plurality of first output optical signal for output
respective first output ports;
[0013] a second planar lightwave circuit chip including a second
input port, a second input arrayed waveguide grating, at least one
second output arrayed waveguide gratings, and at least one second
output ports, wherein a second input optical signal launched into
the second input arrayed waveguide grating via the second input
port disperses according to wavelength into a second dispersion
plane upon exiting the second input arrayed waveguide grating;
[0014] a second cylindrical lens for collimating the second input
optical signal in the first direction after exiting the second
planar lightwave circuit;
[0015] a second array of switching elements for independently
redirecting each of the wavelength channels from the second input
optical signal to selected second output arrayed waveguide gratings
for output respective second output ports; and
[0016] a switching lens for focusing the wavelength channels of the
first input optical signal onto respective switching elements from
the first array of switching elements, and for focusing the
wavelength channels of the second optical signal onto respective
switching elements from the second array of switching elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention will be described in greater detail with
reference to the accompanying drawings which represent preferred
embodiments thereof, wherein:
[0018] FIG. 1 is a plan view of a conventional PLC WSS;
[0019] FIG. 2 is a side view of a conventional multi-layer PLC
WSS;
[0020] FIG. 3 is a side view of a multi-unit PLC wavelength
dispersive device according to the present invention; and
[0021] FIG. 4 is a top view of a first level of the device of FIG.
3;
[0022] FIG. 5 is a cross-sectional view of a second level of the
device of FIG. 3;
[0023] FIG. 6 is a side view of another embodiment of a multi-unit
PLC wavelength dispersive device according to the present
invention;
[0024] FIG. 7 is a cross-sectional view of a third level of the
device of FIG. 6;
[0025] FIG. 8 is a cross-sectional view of a second level of the
device of FIG. 6;
[0026] FIG. 9 is a cross-sectional view of a fourth level of the
device of FIG. 6; and
[0027] FIG. 10 is a top view of a first level of the device of FIG.
6;
DETAILED DESCRIPTION
[0028] With reference to FIGS. 3 to 5, a multiple independent unit,
planar lightwave circuit, (PLC) free-space, hybrid wavelength
selective switch (WSS) 11 operates on the same principle shown in
FIG. 1 above. A first wavelength multiplexed signal, including a
plurality of wavelength channels, enters a first input port 12,
e.g. the middle port, of a first PLC chip 13. The light exiting the
first PLC 13 angularly disperses, i.e. fans out, according to
wavelength in a first dispersion plane, as a result of an arrayed
waveguide grating (AWG) 14 on the PLC 13. The light is collimated
in one direction or plane, e.g. vertically or in the first
dispersion plane, by a first cylindrical lens 16 adjacent to the
PLC 13. The collimated wavelength channels pass through a
cylindrical switching lens 17 on one side of a central OA thereof,
which focuses the output light in the other direction or plane,
e.g. a horizontal direction perpendicular to the dispersion plane,
onto a first array or switching elements 18, e.g. a MEMS array of
tiltable mirrors or an array of liquid crystal cells for
redirecting, attenuating or blocking all or a portion of selected
wavelength channels. Each wavelength channel falls onto a different
switching element 19a to 19f in the switching element array 18,
which independently redirect each of the individual wavelength
channels back through the switching lens 17 and the first
cylindrical lens 16 to whichever output diffraction grating 21a to
21d is desired or back to the input diffraction grating 14. The
first array of switching elements 18 may also perform partial
attenuation or full wavelength channel blocking, as is well known
in the art. The output diffraction gratings 21a to 21d recombine
the wavelength channels directed thereto and output the recombined
output signals to respective output ports 22a to 22d. Preferably,
the input port 12 and the output ports 22a to 22d are optically
coupled to waveguides, e.g. optical fibers, for transmission to and
from an optical network. In a one dimensional system with MEMS
mirrors, each MEMS mirror 19a to 19f can rotate about a single axis
to redirect the wavelength channels within the first dispersion
plane, i.e. the plane of the PLC 13, and do not redirect any of the
channels to other PLCs.
[0029] The illustrated embodiment of FIG. 4 provides a 1.times.4
switch, but any number of output diffraction gratings and output
ports within suitable optical and mechanical parameters is within
the scope of the present invention. Furthermore, converting some of
the output ports to input ports or input/output ports is also
possible to provide additional functionality, e.g. add/drop
multiplexer, cross-connect multiplexer.
[0030] With reference to FIG. 5, a second PLC chip 23 is positioned
parallel to, i.e. superposed under or on top of, the first PLC chip
13 with a second cylindrical lens 26 adjacent thereto. The second
PLC chip 23 can be identical to the first PLC chip 13 or can
include more or less diffraction gratings, input ports and output
ports, as desired. As above, a second input optical signal,
including a plurality of constituent wavelength channels, is
launched via a second input port 22 into a second input diffraction
grating 24, which disperses the wavelength channels at an angle
according to wavelength. The second cylindrical lens 26 collimates
the dispersed light in one direction or plane, e.g. vertically or
in the second dispersion plane.
[0031] The wavelength channels from the second input beam pass
through the same cylindrical switching lens 17, on an opposite side
of the central axis to the wavelength channels from the first input
optical signal. The cylindrical switching lens 17 focuses the
output light in the other direction or plane, e.g. horizontal
direction and perpendicular to the second dispersion plane, onto a
second array of switching elements 28, e.g. a MEMS array of
tiltable mirrors 29a to 29f or an array of liquid crystal cells for
redirecting, attenuating or blocking all or a portion of selected
wavelength channels, which are parallel to the first array of
switching elements 18, but independently controlled. Each
wavelength channel falls onto a different switching element 29a to
29f (only one of which is shown) in the second switching element
array 28, which independently redirect each of the individual
wavelength channels back through the switching lens 17 and the
second cylindrical lens 26 to whichever output diffraction grating
31a to 31d is desired or back to the input diffraction grating 24.
The second array of switching elements 28 may also perform partial
attenuation or full wavelength channel blocking, as is well known
in the art. The output diffraction gratings 31a to 31d recombine
the wavelength channels directed thereto and output the recombined
output signals to respective output ports. As above, in a one
dimensional system with MEMS mirrors, each MEMS mirror 29a to 29d
is the second array of switching elements 28 can rotate about a
single axis to redirect the wavelength channels within the second
dispersion plane, i.e. the plane of the PLC 23, and do not redirect
any channels to other PLCs.
[0032] Accordingly, the device 11 of the present invention provides
two fully functioning and independent 1.times.4 switching (or
attenuating or blocking) devices within a single package 35, with
virtually the same optics size as a single 1.times.4 device, by
adding a second row of switching elements 28 and by adjusting the
alignment of the cylinder collimating lenses 16 and 26 in front of
the PLC's 13 and 23, respectively, as shown in FIG. 3. Ideally, the
independent rows of switching elements 18 and 28, e.g. MEMS
mirrors, are fabricated on the same substrate 30 to reduce size and
cost, but are independent of each other, i.e. the first row of
switching elements 19a to 19f only directs light to the first
plurality of output waveguide gratings 21a to 21d and 14, while the
second row of switching elements 29a to 19f only directs light to
the second plurality of output waveguides 31a to 31d and 24.
[0033] In an exemplary embodiment, the first array of switching
elements 18 comprises MEMS mirror 19a to 19f, while the second
array of switching elements 28 comprises a different wavelength
channel adjusting means, e.g. an attenuator or a blocker, whereby
at least one of output signals from output ports 22a to 22d is
input the input port 22 of the second PLC 23 and undergoes
wavelength selective attenuation, equalization or blocking in
accordance with desired power levels or wavelength selections.
[0034] For channel monitoring, a plurality of wavelength channels,
e.g. .lamda..sub.1m to .lamda..sub.11m, are launched via the second
input port 22, and one wavelength channel, .lamda..sub.nm, at a
time is redirected by the array of MEMs mirrors 28 to the output
port 32a, which is optically coupled to a photodetector for
measuring the output optical power of the selected wavelength
channel as each wavelength channel is selected sequentially. The
remaining wavelength channels are redirected back to the second
input port 22 or another one of the output ports 32b to 32d.
[0035] FIGS. 6 to 10 illustrates a multiple independent unit,
planar lightwave circuit (PLC), free-space, hybrid wavelength
selective switch (WSS) 41 with a more complex combination of
devices within a single package 42. The second and third levels
comprise a 1.times.9 wavelength switch, the fourth or bottom layer
comprises a 1.times.3 DGE or WB, and the first or top layer
comprise a 1.times.1 wavelength switch, which could be operated as
a wavelength monitor. Accordingly, multiple PLC, free-space, hybrid
wavelength switch devices incorporated into a single free-space
optics block, by adding additional PLCs, cylindrical collimating
lens, and rows of switching elements, whereby the independent
devices share the same cylinder focusing lens 47, MEMS substrate
50, and package 42.
[0036] With reference to FIGS. 7 and 8, the double layer 1.times.9
WSS includes a first PLC 43 and an second PLC 63. In use, a first
wavelength multiplexed signal, including a plurality of wavelength
channels, enters a first input port 42, e.g. the middle port, of
the first PLC chip 43. The light exiting the first PLC 43 angularly
disperses, i.e. fans out, according to wavelength in a first
dispersion plane, as a result of an arrayed waveguide grating (AWG)
44 on the first PLC 43. The light is collimated in one direction or
plane, e.g. vertically or in the first dispersion plane, by a first
cylindrical lens 46 adjacent to the PLC 43. The collimated
wavelength channels pass through a cylindrical switching lens 47 on
one side of an optical axis OA thereof, which focuses the output
light in the other direction or plane, e.g. horizontal direction
perpendicular to the first dispersion plane, onto a first array or
switching elements 48, e.g. a MEMS array of tiltable mirrors 49a to
49f or an array of liquid crystal cells for redirecting,
attenuating or blocking all or a portion of selected wavelength
channels. The tiltable mirrors 49a to 49f rotate about two
perpendicular axes to redirect the wavelength channels within the
first dispersion plane, i.e. the plane of the PLC 43, and at an
acute angle to the first dispersion plane into a plane parallel to
the first dispersion plane, i.e. the plane of the PLC 63. Each
wavelength channel falls onto a different switching element 49a to
49f, which independently redirect each of the individual wavelength
channels back through the switching lens 47 and either the first
cylindrical lens 46 or a second cylindrical lens 66 to whichever
output diffraction grating 51a to 51d and 71a to 71e is desired or
back to the input diffraction grating 44. In the illustrated
embodiment, mirrors 49c, 49d and 49e rotate about both axes for
directing their respective wavelength channels out of the first
dispersion plane to the second cylindrical lens 66 for output the
output gratings 71b and 71c, but not to any other PLC, i.e. PLC 83
or 103. Simultaneously, the mirrors 49b and 49f rotate about a
single axis, which is perpendicular to the first dispersion plane,
to switch their respective wavelength channels within the first
dispersion plane to output gratings 51a and 51d, i.e. not to any
other output gratings on other PLCs. The array of first switching
elements 48 may also perform partial attenuation or full wavelength
channel blocking, as is well known in the art. The first output
diffraction gratings 51a to 51d and 71a to 71e recombine the
wavelength channels directed thereto and output the recombined
output signals to respective output ports 52a to 52d and 72a to
72e. Preferably, the input port 42 and the output ports 52a to 52d
and 72a to 72e are optically coupled to waveguides, e.g. optical
fibers, for transmission to and from an optical network.
[0037] With reference to FIG. 9, the bottom level of the device 41
includes a third PLC 83 with an input port 82 and a plurality of
output ports 92a to 92c. In use, a second wavelength multiplexed
signal, including a plurality of wavelength channels, enters the
second input port 82, e.g. the middle port, of the third PLC chip
83. The light exiting the third PLC 83 angularly disperses, i.e.
fans out, according to wavelength in a second dispersion plane
parallel to the first dispersion plane, as a result of an arrayed
waveguide grating (AWG) 84 on the third PLC 83. The light is
collimated in one direction or plane, e.g. vertically or in the
second dispersion plane, by a third cylindrical lens 86 adjacent to
the third PLC 83. The collimated wavelength channels pass through
the cylindrical switching lens 47 on the other side of an optical
axis OA thereof, which focuses the output light in the other
direction or plane, e.g. horizontal direction perpendicular to the
third dispersion plane, onto a third array of switching elements
88, e.g. an array of liquid crystal cells 89a to 89f for
redirecting, attenuating or blocking all or a portion of selected
wavelength channels. An example of a suitable liquid crystal device
is a liquid crystal on silicon (LCoS) phased array, such as those
disclosed in United States Patent Publication No. 2006/0067611
published Mar. 30, 2006 to Frisken et al, which is incorporated
herein by reference.
[0038] Each wavelength channel falls onto a different switching
element 89a to 89f, which independently attenuates, either
partially or entirely, and redirects each of the individual
wavelength channels back through the switching lens 47 and the
third cylindrical lens 86 to whichever output diffraction grating
91a to 91c is desired or back to the input diffraction grating 84,
i.e. not to any other output gratings on other PLCs. The output
diffraction gratings 91a to 91c recombine the wavelength channels
directed thereto and output the recombined output signals to
respective output ports 92a to 92c. Preferably, the input port 92
and the output ports 92a to 92c are optically coupled to
waveguides, e.g. optical fibers, for transmission to and from an
optical network.
[0039] For channel monitoring, a plurality of wavelength channels,
e.g. .lamda..sub.1m to .lamda..sub.11m, are launched via a third
input port 102 into a fourth PLC 103, superposed on the second PLC
63. The light exiting the fourth PLC 103 angularly disperses, i.e.
fans out, according to wavelength in a third dispersion plane
parallel to the first dispersion plane, as a result of an arrayed
waveguide grating (AWG) 104 on the fourth PLC 103. The light is
collimated in one direction or plane, e.g. vertically or in the
third dispersion plane, by a fourth cylindrical lens 106 adjacent
to the fourth PLC 103. The collimated wavelength channels pass
through a cylindrical switching lens 47 on the one side of an
optical axis OA thereof, which focuses the output light in the
other direction or plane, e.g. horizontal direction perpendicular
to the third dispersion plane, onto a third array of switching
elements 108, e.g. an MEMS mirrors 109a to 109f for redirecting,
attenuating or blocking all or a portion of selected wavelength
channels. One wavelength channel, .lamda..sub.nm, at a time is
redirected by the third array of MEMs mirrors 108 through the
switching lens 47 and the fourth cylindrical lens 106 to an output
port 112 via an output grating 111 i.e. not to any other output
gratings on other PLCs. The output port 106 is optically coupled to
a photodetector 115 for measuring the output optical power of the
selected wavelength channel as each wavelength channel is selected
sequentially. The remaining wavelength channels are redirected by
the array of switching elements 108 back to the third input port
102 via the input grating 104 or to a different output port via an
additional grating (not shown). Accordingly, the third input port
102 may include a circulator for directing the output wavelength
channels to a separate output port.
[0040] In use the output ports of one of the PLC's may be optically
coupled to the input ports of the other PLC's to provide cascaded
functionality, e.g. one of the signals output the WWS formed by
PLC's 43 and 63 can be output to the channel monitor formed by PLC
103 and/or the signal output the channel monitor (PLC 103) can be
then output to an attenuator/WB formed by PLC 83. Alternatively,
all of the channels can be sent to the channel monitor (PLC 103)
initially and then passed to the WSS (PLC 43 and 63) and/or to the
attenuator/WB (PLC 83).
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