# Patent

## Title
Multipoint, contentionless wavelength selective switch (WSS)

## Abstract

An optical device includes a plurality of optical input ports, a plurality of optical output ports, a wavelength dispersion arrangement and at least one optical beam steering arrangement. The plurality of optical input ports is configured to receive optical beams each having a plurality of wavelength components. The wavelength dispersion arrangement receives the optical beams and spatially separates each of the optical beams into a plurality of wavelengths components. The optical beam steering arrangement has a first region onto which the spatially separated wavelength components are directed and a second region onto which any subset of the plurality of wavelength components of each of the optical beams is selectively directed after the wavelength components in each of the subsets are spatially recombined with one another. The optical beam steering arrangement selectively directs each of subset of the plurality of wavelength components to a different one of the optical output ports.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. Provisional Application Ser. No. 62/113,738, filed Feb. 9, 2015 entitled “Multipoint, Contentionless Wavelength Selective Switch (WSS)”, the contents of which are incorporated herein by reference.


BACKGROUND
In an optical communication network, optical signals having a plurality of optical channels at individual wavelengths (i.e., channels), are transmitted from one location to another, typically through a length of optical fiber. Various types of optical switches are available which allow switching of optical signals from one optical fiber to another. A wavelength-selective switch (WSS), allows reconfigurable wavelength-dependent switching, that is, it allows certain wavelength channels to be switched from a first optical fiber to a second optical fiber while letting the other wavelength channels propagate in the first optical fiber, or it allows certain wavelength channels to be switched to a third optical fiber. An optical network architecture based on wavelength-selective optical switching has many attractive features due to the ability to automatically create or re-route optical paths of individual wavelength channels. It accelerates service deployment, accelerates rerouting around points of failure of an optical network, and reduces capital and operating expenses for a service provider, as well as creating a future-proof topology of the network.
Different switching architectures offer different degrees of flexibility with respect to the allocation and routing of individual wavelengths. FIG. 1 shows a functional block diagram of an N×M optical switch 12 illustrating one routing function that is sometimes desired. The N×M optical switch 10 has N input ports 101, 102, 103 . . . 10N (“10”) and M output ports 151, 152, 153, . . . 15M (“15”). The input ports 10 are WDM ports that are able to receive a wavelength division multiplexed (WDM) signal that includes multiple wavelengths or channels. As explained below, the routing function that is desired is sometimes referred to as contentionless routing.
In contentionless routing, if, as shown in FIG. 1, a signal 1 of wavelength λ1 received on one input port is sent to a given output port and signal 2 of the same wavelength λ1 (but with different data content) is received on a different input port, then signal 2 can be sent to any output port except to the output port to which signal is sent. In other words, optical switch 12 is able to establish a connection from one input port to one output at one wavelength without preventing a second connection from being established at that same wavelength between a second input port and a second output port.
Wavelength selective switches having the functionality shown in FIG. 1 have been demonstrated. Such wavelength selective switches have a relatively small number of input and output ports and are not easily scaled up to provide significantly more ports. For example, U.S. Patent Publication No. 2014/0294346 to Neilson et al. shows one WSS that employs an LCOS array as the switching element. In this device each WDM signal received on an input port is imaged and spectrally dispersed along a separate row of the LCOS array. Because of its design, this WSS requires M physically separate rows to be allocated on the LCOS array to provide the functionality of an N×M switch, where M>N. This becomes impractical for devices with a relatively large number of ports because of the large amount of space that needs to be allocated on the surface of the LCOS array.
SUMMARY
In accordance with one aspect of the invention, an optical device is provided which includes a plurality of optical input ports, a plurality of optical output ports, a wavelength dispersion arrangement and at least one optical beam steering arrangement. The plurality of optical input ports is configured to receive optical beams each having a plurality of wavelength components. The wavelength dispersion arrangement receives the optical beams and spatially separates each of the optical beams into a plurality of wavelengths components. The optical beam steering arrangement has a first region onto which the spatially separated wavelength components are directed and a second region onto which any subset of the plurality of wavelength components of each of the optical beams is selectively directed after the wavelength components in each of the subsets are spatially recombined with one another. The optical beam steering arrangement selectively directs each of the subsets of the plurality of wavelength components to a different one of the optical output ports.
In accordance with another aspect of the invention, an optical device is provided that includes a plurality of optical input ports, a plurality of optical output ports, a wavelength dispersion element and a switching arrangement. The plurality of optical input ports is configured to receive optical beams each having a plurality of wavelength components. The wavelength dispersion element receives the optical beams and spatially separates each of the optical beams into a plurality of wavelengths components. The switching arrangement receives the wavelength components of the optical beams and selectively directs any subset of the plurality of wavelength components of each of the optical beams to a different one of the optical output ports, provided that wavelength components of optical beams received by two of the input ports cannot be simultaneously directed to a common one of the output ports.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a functional block diagram of one example of a wavelength selective switch.
FIGS. 2A and 2B are top and side views respectively, of one example of a simplified optical device such as a multipoint contentionless wavelength selective switch.
FIG. 3 is a plan view of the first switching element employed in the wavelength selective switch of FIGS. 2A and 2B onto which the input beams are imaged.
FIG. 4 is a plan view of the second switching element employed in the wavelength selective switch of FIGS. 2A and 2B onto which non-dispersed optical beams are imaged.
FIG. 5 is a side view of the optical device of FIGS. 2A and 2B showing various subsets of wavelengths that are received on the input ports being directed to various ones of the output ports.
FIG. 6 is a side view of the optical device of FIGS. 2A and 2B illustrating a manner of switching two wavelengths components which the switching arrangement is incapable of performing.
FIG. 7 is a plan view of the switching element employed in an alternative embodiment of the wavelength selective switch in which only a single switching element is employed.
FIG. 8 is a plan view of the first switching element employed in an alternative embodiment of the wavelength selective switch of FIGS. 2A and 2B.



DETAILED DESCRIPTION
FIGS. 2A and 2B are top and side views respectively, of one example of a simplified optical device such as a multipoint contentionless wavelength selective switch (WSS) 100 that may be used in conjunction with embodiments of the present invention. The top view of FIG. 2A is also referred to herein as the dispersion plane view and the side view of FIG. 2B is also referred to herein as the switching plane view. Light is input and output to the WSS 100 through optical waveguides such as optical fibers which serve as input and output ports. As best seen in FIG. 2B, an input port array 101 may comprise a plurality of individual input fibers 1011, 1012, 1013 . . . 101m respectively coupled to collimators 1021, 1022 1023 . . . 102m. Light from one or more of the input fibers 101 is converted to a free-space beam by the collimators 102. The light exiting from input port array 101 is parallel to the z-axis. While the input port array 101 only shows four optical fiber/collimator pairs in FIG. 1B, more generally any suitable number of optical fiber/collimator pairs may be employed.
In FIGS. 2A and 2B, optical elements which affect the light in two axes are illustrated with solid lines as bi-convex optics in both views. On the other hand, optical elements which only affect the light in one axis are illustrated with solid lines in the axis that is affected. The optical elements which only affect light in one axis are also illustrated by dashed lines in the axis which they do not affect. For instance, in FIGS. 2A and 2B the optical elements 102, 106, 109 and 111 are depicted with solid lines in both figures. On the other hand, optical elements 103, 104, 105, 107 and 110 are depicted with solid lines in FIG. 1A (since they have focusing power in the dispersion plane) and with dashed lines in FIG. 1B (since they leave the beams unaffected in the switching plane). Optical element 108 is depicted with solid lines in FIG. 2B (since it affects the beams in the switching plane) and with dashed lines in FIG. 2A (since it leaves the beams unaffected in the dispersion plane).
The beams exiting the input port array 101 are directed to the collimators 102, which are cylinder lenses that collimate the beams along one axis in the switching plane and allow the beams to continue diverging in the dispersion plane. A cylinder lens 103 receives the beams from the collimators 102 and collimates the beams in the dispersion plane. The lens 103 has no significant effect on the beams in the switching plane. The beams are now collimated in both dispersion plane and the switching plane.
After being collimated in the dispersion plane by the cylinder lens 103, the beams are directed to a first wavelength dispersion element 104 (e.g., a diffraction grating or prism), which separates the free space light beams into their constituent wavelength components (or simply “wavelengths”) or channels in the dispersion plane. Due to the configuration of the first wavelength dispersion element 104 (e.g., the orientation of the grating), it has no significant effect on the beams in the switching plane. The dispersed wavelengths are then directed to a cylinder lens 105, which focuses the wavelengths in the dispersion plane onto a first transmissive switching element 106. The cylinder lens 105 leaves the wavelengths largely unaffected in the switching plane.
At this point, the input beams are spatially separated from one another, but each is dispersed on the switching element 106. This is illustrated in FIG. 3, which is a plan view, also known as an optical footprint view, of the first switching element 106 on which the input beams are imaged. Each one of the inputs beams 2021, 2022, 2023 . . . 202m is received from one of the fibers 1011, 1012, 1013 . . . 101m in the input array 101. As shown, any specific input beam 2021, 2022, 2023 . . . 202n is dispersed into its constituent wavelength components along the x-axis and spatially separated from the other input beams along the y-axis.
The first switching element 106 then steers the input beams in a wavelength dependent manner in the switching plane. The switching by the first switching element is performed in coordination with a second switching element 109. The manner in which this switching is performed will be explained below after specifying the remaining optical elements in the example of the optical device shown in FIGS. 2A and 2B.
After being steered by the first switching element 106, some or all of the constituent wavelengths components of each of the input beams are re-collimated in the dispersion plane by a cylinder lens 107. A second wavelength dispersion element 108 (e.g., a diffraction grating or prism), is then used to combine or un-disperse the collimated, constituent components of the beams in the dispersion plane. Cylinder lens 107 and second wavelength dispersion element 108 have no significant effect in the switching plane.
A second switching element 109 receives the recombined beams from the dispersion element 108. The location at which each of the beams is received on the second switching element 109 is determined by the switching performed by the first switching element 106. Specifically, the recombined beams are each selectively directed to one of the locations A, B, C, . . . shown in FIG. 2B. FIG. 4 shows the beams 2041, 2042, 2043 . . . 204n arriving on the second switching element 109 at the various locations A, B, C . . . , which although not dispersed, are physically separated from the other input beams 2041, 2042, 2043 . . . 204n on the second switching element 109
Cylinder lens 110, cylinder lenslet array 111 and fiber array 112 form the output optical couplings in a similar way to the input optics 101,102 and 103. In particular, the cylinder lens 110 collimates the beams in the switching plane and directs the beams to respective ones of the cylinder lenses 1111, 1112, 1113, . . . 111n in the cylinder lenslet array 111. Each cylinder lens 1111, 1112, 1113, . . . 111n directs its respective beam to a corresponding one of the output ports 1121, 1122, 1113 . . . 112n in the output fiber port array 112.
As shown in FIG. 2B, there is a one-to-one relationship between the locations A, B, C . . . on the second switching element 109 and the output ports 1121, 1122, 1123 . . . 112n. That is, any subset of recombined wavelengths in each beam that is directed from any of the input ports to say, location A on the second switching element 109 will always be directed by the second switching element 109 to the same predefined one of the output ports. More generally, any subset of recombined wavelengths in each beam that is directed by any of the input ports to any particular location A, B, C . . . on the second switching element 109 will always be directed by the second switching element 109 to the same predefined one of the output ports corresponding to the particular location A, B, C . . . on the second switching element 109.
In operation, first and second switching elements 106 and 109 cooperate so that any subset of wavelengths of an optical beam received by any given input port 101 may be routed to any given output port 112, provided that any given output port can only accept a subset of wavelengths from a single input port at any one time. That is, switching elements 106 and 109 are arranged so that the output ports are restricted in that they only support a connection to one input at any given time, not multiple inputs at the same time. This switching behavior will be illustrated with reference to FIGS. 5 and 6.
FIG. 5 shows various subsets of wavelengths that are received on the input ports 101 being directed to various ones of the output ports. Each input port receives a WDM optical beam that includes wavelength components λ1-λn. For example, in FIG. 5 the wavelength components λ1 and λ5-λ7 of the optical beam received by input port 1011 are directed to output port 1129, the wavelength component λ1 of the optical beam received by input port 1012 is directed to output port 1121, the wavelength components λ1-λn of the optical beam received by input port 1013 are directed to output port 1125 and the wavelength components λ3-λ4, λ6 and λ10-λn of the optical beam received by input port 101n are directed to output port 1127.
In contrast to FIG. 5, FIG. 6 shows a hypothetical and impermissible situation in which wavelength components are routed from the first switching element 106 to the second switching element 109. Specifically, the switching behavior shown in FIG. 6 is impermissible because it shows location D on the second switching element 109 simultaneously receiving wavelength components from both input port 1011 and input port 1013.
The first and second switching elements 106 and 109 may be based on any of a variety of different technology platforms. For example, the first and second switching elements may be beam-steering elements such as programmable optical phase modulators or micro-electromechanical (MEMS) based devices, for instance. One example of a suitable programmable optical phase modulator is a liquid crystal on silicon (LCoS) device. One example of a MEMs-based device is a digital micromirror device (DMD). In some embodiments both the first and second switching elements 106 and 109 are based on the same technology platform or different technology platforms. For instance, in the latter case the first switching element 106 may be a programmable optical phase modulator and the second switching element 109 may be a MEMs-based device.
In one alternative implementation, a single switching element is employed instead of the two switching elements shown in FIGS. 2-6. That is, the functions of both the first and second switching elements shown in FIGS. 2-6 are accomplished with one physical switching element. FIG. 7 shows an optical footprint view of such a combined switching element 301. The dispersed beams 302 and the non-dispersed beams 303 are physically separated and could be oriented or laid out in multiple ways. For example, although both the dispersed beams 302 and the non-dispersed beams 303 extend in the horizontal direction in FIG. 4, in other embodiments they may extend in different directions from one another (e.g., the dispersed beams 302 may extend in the horizontal direction and the non-dispersed beams 303 may extend in the vertical direction).
In another alternative implementation, crosstalk may be reduced by orienting the input ports so that that the spatially separated input beams are imaged onto the switching element 106 so that the input beams are misaligned with respect to one another. This is shown in FIG. 8, which is plan view of the switching element 106 similar to the plan view of FIG. 3. In FIG. 8, however, the input beams are staggered along the x-axis so that the same wavelengths in any two different input beams are not aligned along the y-axis.
It should be noted that the optical switch described herein may operate in a reciprocal manner such that the input ports may serve as output ports and the output ports may serve as input ports. Accordingly, the terms input and output are used interchangeably herein.

## Claims

1. An optical device, comprising:
a plurality of optical input ports configured to receive optical beams each having a plurality of wavelength components;
a plurality of optical output ports;
a wavelength dispersion element for receiving the optical beams and spatially separating each of the optical beams into a plurality of wavelengths components; and
a switching arrangement for receiving the wavelength components of the optical beams and selectively directing any subset of the plurality of wavelength components of each of the optical beams to a different one of the optical output ports, provided that wavelength components of optical beams received by two of the input ports cannot be simultaneously directed to a common one of the output ports.

2. The optical device of claim 1, wherein the subset of wavelength components of a first of the optical beams selectively directed by the switching arrangement and the subset of wavelength components of a second of the optical beams selectively directed by the switching arrangement include wavelength components having the same wavelength.

3. The optical device of claim 1, wherein the switching arrangement includes at least one optical beam steering arrangement having a first region onto which the spatially separated wavelength components are directed and a second region onto which each of the selectively directed subset of wavelength components are directed after the wavelength components in each of the subsets are spatially recombined with one another.

4. The optical device of claim 3, wherein the at least one optical beam steering arrangement includes a single optical beam steering arrangement on which the first and second regions are located.

5. The optical device of claim 3, wherein the optical beam steering arrangement includes first and second optical beam steering arrangements, the first region being located on the first optical beam steering arrangement and the second region being located on the second optical beam steering arrangement.

6. The optical device of claim 5, wherein the first and second optical beam steering arrangements include first and second programmable optical phase modulators.

7. The optical device of claim 5, wherein the first and second optical beam steering arrangements include a programmable optical phase modulator and a MEMs-based device.

8. The optical device of claim 5, wherein the first optical beam steering arrangement is programmable optical phase modulator and the second optical beam steering arrangement is a MEMs-based device.

9. The optical device of claim 3, wherein the wavelength dispersion element spatially separates each of the optical beams in a first plane and the switching arrangement selectively directs the spatially received subset of the plurality of wavelength components of each of the optical beams in a second plane orthogonal to the first plane.

10. The optical device of claim 3, wherein the at least one optical beam steering arrangement includes a programmable optical phase modulator.

11. The optical device of claim 1, wherein the switching arrangement is configured to switch selected ones of the wavelength components while they are dispersed into spatially separated wavelength component and also when they are non-dispersed.

12. The optical device of claim 1, wherein the switching arrangement switches spatially separated ones of the wavelength components and wavelength components that have been spatially recombined with one another.

13. An optical device, comprising:
a plurality of optical input ports configured to receive optical beams each having a plurality of wavelength components;
a wavelength dispersion arrangement for receiving the optical beams and spatially separating each of the optical beams into a plurality of wavelengths components; and
at least one optical beam steering arrangement having a first region onto which the spatially separated wavelength components are directed and a second region onto which any subset of the plurality of wavelength components of each of the optical beams is selectively directed after the wavelength components in each of the subsets are spatially recombined with one another, the at least one optical beam steering arrangement selectively directing each of the subsets of the plurality of wavelength components to a different one of the optical output ports.

14. The optical device of claim 13, wherein the at least one optical beam steering arrangement includes a single programmable optical phase modulator on which the first and second regions are located.

15. The optical device of claim 13, wherein the at least optical beam steering arrangement includes first and second programmable optical phase modulators, the first region being located on the first programmable optical phase modulator and the second region being located on the second programmable optical phase modulator.

16. The optical device of claim 13, wherein the second region includes a plurality of locations on which the spatially recombined subsets of wavelength components are selectively directable by the at least one optical beam steering arrangement, each of the locations being associated with a different one of the optical output ports such that any of the subsets that are directed to a given one of the locations is received by the optical output port associated with the given location.

17. The optical device of claim 16, wherein the wavelength dispersion element spatially separates each of the optical beams in a first plane and the at least one optical beam steering arrangement selectively directs the spatially recombined subset of the plurality of wavelength components of each of the optical beams in a second plane orthogonal to the first plane.

18. The optical device of claim 13, wherein the at least optical beam steering arrangement includes a programmable optical phase modulator and a MEMs-based device, the first region being located on the programmable optical phase modulator and the second region being located on the MEMs based device.

19. The optical device of claim 13, wherein at least two of the optical beams having wavelength components located at a common wavelength.