Patent Application
20240369774
The disclosure relates to optical circuit switches.
In an optical fiber network, data encoded in modulated pulses of light is transported between nodes on fiber-optic cables. Because the capacity of this technology for carrying information is extremely high, it has become critical for telecommunication networks of various kinds and at various scales. One important feature in the operation of an optical fiber network is the fast switching of connections between nodes. All-optical switching is one of several possible approaches to network switching. Advantages of all-optical switching include high bandwidth and transparency to network protocols. All-optical switches can also be non-blocking.
An optical cross-connect (OXC) is a device that can implement all-optical switching between different optical fibers of an optical network. The OXC may include optical interfaces for individual optical fiber or for pairs of optical fiber(s), which carry incoming or outgoing optical signals. Within the OXC each connection is effectuated by controllably establishing an optical path between an optical fiber for input and an optical fiber for output. These optical paths are reconfigurable at high speed through the use of, for example, MEMS mirrors or LCOS arrays under suitable digital control.
Recent growth in the scale of core optical networks, among others, has begun to challenge the capacity of existing infrastructure. As a consequence, there has been interest in increasing the port counts of switching devices such as OXCs, as network requirements increase.
Various embodiments provide non-blocking, scalable OXC switch architectures that allow the port count to be extended by adding optical circuit switch (OCS) modules to an OXC node. Each OCS module can independently operate to establish connections between its own inputs and outputs. The modularity of these embodiments offers the further advantage of creating independent failure regions, so that single point of failure can often be avoided.
In various implementations, the OCS modules include modular sub-matrix switch cards. The port count of an OXC switch node to which the OCS modules belong can be extended by adding OCS modules to the OXC node. The additional OCS modules can be added to the OXC without affecting existing light paths. Intermediate optical reflectors situated within the OCS modules may be used to direct incoming light to an intended module's input or output steering matrix. The intermediate optical reflectors may be active or passive. In embodiments, an optical reflector may be, e.g., a mirror.
Each OCS module has an array of input optical fiber ports and an array of output optical fiber ports. Each OCS module may include imaging optics, input and output steering matrices or an input/output steering matrix, and an intermediate optical reflector section that interfaces the input and output matrices.
The intermediate optical reflectors can route an input light beam to a destination OCS module that is different from the OCS module where the beam originally entered. In some cases, the input light beam could be routed directly to an output optical fiber port of the destination module. In other cases, the beam could be routed to subcomponents within the destination OCS module that act on the beam before it reaches an output optical fiber port. For example, the beam could be routed first to an output steering matrix of the destination OCS module, which, in turn, routes the beam to the output optical fiber port of the destination OCS module. Another example of a subcomponent of the destination OCS module that could usefully act on the beam before it reaches an output optical fiber port is an optic element or mirror set that reduces the angle of incidence of the beam on the output steering matrix.
Accordingly, the present disclosure relates, in a first aspect, to apparatus that comprises an electronic device having on it a plurality of module connectors and a plurality of optical circuit switch (OCS) modules that are removably mechanically affixed to the electronic device by the module connectors. The OCS modules each have a plurality of input optical fiber ports and a plurality of output optical fiber ports.
Each one of the OCS modules has a reconfigurable arrangement of optical reflectors capable of selectively optically cross-connecting ones of the input optical fiber ports of the same one of the OCS modules to ones of the output optical fiber ports of the same one of the OCS modules. Further, each particular one of the OCS modules is selectively configurable to route light received from ones of its optical input optical fiber ports, via its arrangement of optical reflectors, to one or more others of the OCS modules.
In embodiments, the routing of light from particular ones to others of the OCS modules is via one more free-space optical paths connecting the particular ones to the one or more others of the OCS modules.
In embodiments, at least one of the OCS modules is configurable to route light from ones of its own input optical fiber ports to a second one of the OCS modules via a free-space optical path traversing an intervening third one of the OCS modules.
In embodiments, the electronic device comprises an electronic controller communicatively connected to operate the reconfigurable arrangements of optical reflectors of the OCS modules.
In embodiments, the reconfigurable arrangement of optical reflectors within each of the OCS modules comprises an input optical reflector arranged to receive light from the input optical fiber ports, an output optical reflector arranged to transmit light to the output optical fiber ports, and an intermediate optical reflector array comprising an intermediate reflector that can reflectively couple the input optical reflector to the output optical reflector.
In embodiments, the input optical reflector is configurable to selectively direct light, via the intermediate optical reflector array, to one or more others of the OCS modules. In some embodiments, the intermediate optical reflector array comprises a configurable reflector that can be configured to act jointly with the input optical reflector for selectively directing light to one or more others of the OCS modules.
In embodiments, the electronic device comprises an electronic controller communicatively connected to operate the reconfigurable arrangements of optical reflectors of the OCS modules.
In embodiments, the reconfigurable arrangement of optical reflectors within each specific one of the OCS modules is configurable to direct light received from a different one of the OCS modules to one or more of the output optical fiber ports of the specific one of the OCS modules.
In embodiments, the input optical reflector and the output optical reflector are MEMS mirror arrays.
In embodiments, the intermediate optical reflector array comprises an intramodular intermediate reflector that can reflectively couple the input optical reflector of the particular one of the OCS modules to the output optical reflector of the particular one of the OCS modules, and the intermediate optical reflector array further comprises at least one intermodular intermediate reflector that can reflectively couple the input optical reflector of the particular one of the OCS modules to a different one or different ones of the OCS modules. In some embodiments, each of the intermodular intermediate reflectors is a static mirror. In other embodiments, each of the intermodular intermediate reflectors is a reconfigurable mirror.
In a second aspect, the present disclosure relates to a method that comprises causing an optical signal from a first input optical fiber port of a first optical circuit switch (OCS) module to be received by a second OCS module by reconfiguring at least one optical reflector of the first OCS module to reflect the optical signal onto an optical path terminating at the second OCS module.
The method further comprises causing the received optical signal to be output by the second OCS module by reconfiguring an optical reflector of the second OCS module to direct the received optical signal to an output optical fiber port of the second OCS module, thereby to make an intermodular connection.
The method further comprises causing an optical signal from a second input optical fiber port of the first OCS module to be output by said first OCS module by reconfiguring at least one optical reflector of the first OCS module to direct the optical signal from said second input optical fiber port to an output optical fiber port of the first OCS module, thereby to make an intramodular connection.
In embodiments, the optical path terminating at the second OCS module is a free-space optical path.
In embodiments, the making of the intramodular connection comprises reconfiguring an input optical reflector and reconfiguring an output optical reflector of the first OCS module, the making of the intermodular connection comprises reconfiguring an input optical reflector of the first OCS module and reconfiguring an output optical reflector of the second OCS module, and within each said OCS module, the respective input and output optical reflectors are reflectively coupled via an intermediate optical reflector. In embodiments, the making of the intermodular connection further comprises reconfiguring the intermediate optical reflector of the first OCS module.
In embodiments, the intramodular connection and the intermodular connection are made concurrently with a plurality of other intramodular and intermodular connections. The making of the plural, concurrent connections in such embodiments comprises selecting an input OCS module and an output OCS module for implementing each connection from a set of desired connections, the selection being made from a plurality of OCS modules that includes said first and second OCS modules.
The making of the plural, concurrent connections further comprises selecting a respective input optical fiber port and a respective output optical fiber port of the selected OCS modules for implementing each desired connection, obtaining a set of optical reflector configurations for implementing each desired connection, and reconfiguring at least some of the input and output optical reflectors of the selected input and output OCS modules according to the obtained configurations to make the desired connections.
In embodiments, the making of the plural concurrent connections further comprises reconfiguring at least some of the intermediate optical reflectors of the selected input and output OCS modules according to the obtained configurations.
An example of beam steering using MEMS mirrors is provided in R. Ryf et al., “1296-port MEMS transparent optical crossconnect with 2.07 petabit/s switch capacity, “OFC 2001 Optical Fiber Communication Conference and Exhibit Technical Digest Postconference Edition, Anaheim, CA, USA (2001) pages PD28-PD28, hereinafter cited as “RYF 2001” and hereby incorporated herein in entirety by reference.
MEMS-based optical switching is also discussed in the following publications, each of which is hereby incorporated herein by reference in entirety: J. Leuthold et al., “All-optical nonblocking terabit/s crossconnect based on low power all-optical wavelength converter and MEMS switch fabric,” OFC 2001 Optical Fiber Communication Conference and Exhibit Technical Digest Postconference Edition (IEEE Cat. 01CH37171), Anaheim, CA, USA (2001) pages PD16-PD16, and R. Urata, R. et al., “Mission Apollo: Landing Optical Circuit Switching at Datacenter Scale,” ArXiv, abs/2208.10041 (2022), hereinafter cited as “URATA 2022”.
For the intermediate optical reflector array, one possible alternative to mirrors is afforded by a Liquid Crystal On Silicon (LOCOS) array. With a LOCOS array, special holograms could be used to control the directional distribution of optical power. Typical LOCOS arrays have relatively small angular excursions, but the effective angular range could be extended, using imaging optics. Reducing the pixel pitch of the LOCOS arrays could also increase the angular excursion.
With further reference to the figure, it will be seen that the OCS module 100 includes an array 110 of input optical fiber ports 115, an array 120 of output optical fiber ports 125, an input steering matrix 130 of beam steering elements 135, and an output steering matrix 140 of beam steering elements 145. The OCS module further includes imaging optics 150, 155, for conditioning input and output beams, respectively.
Although the embodiment of
The imaging optics are the optical components required for the optical signal to be properly routed and aligned to the steering optical reflectors and to and from the input and output optical fiber ports. Typical examples of imaging optics include, without limitation, collimator lens arrays, double telecentric lenses, polarization diversity elements, and Fourier lenses.
The OCS module further includes an array 160 of intermediate optical reflectors, best seen in the inset to the figure.
In the non-limiting example shown in
In some example embodiments, the input 135 and output 140 steering matrices may be implemented as arrays of MEMS mirrors. In other example embodiments, they may be implemented as arrays of LCOS pixels.
In embodiments, the intermediate optical reflectors of array 160 may be fixed reflectors such as mirrors oriented at suitable incidence angles for coupling light beams incident from the local input steering matrix 130 to the output steering matrices or other elements of the home OCS module or of respective destination OCS modules. In other embodiments, the intermediate optical reflectors of array 160 may be, e.g., MEMS mirrors, having variable incidence angles. In some embodiments, the same steering intermediate optical reflector could support either intramodular or intermodular connections, depending on how its incidence angle has been set.
It is noteworthy in this regard that to facilitate intermodular coupling, it may be necessary for the optical reflector elements of the steering arrays to have relatively large angular ranges, so that they can reach fully into the intermediate optical reflector region. However, a reconfigurable, rather than a fixed, intermediate optical reflector can potentially relax this requirement. That is, a suitably oriented intermediate optical reflector could reflect an incoming beam to a destination OCS module even when the beam impinges the same spot on the intermediate optical reflector that is used for making intramodular connections.
The OCS module of
It is noteworthy in this regard that input and output optical fiber ports are not necessarily limited to one fiber each. Various types of space multiplexing can be used as known in the art, including the use of multicore fibers. The OCS modules described here would more typically be used in space-division multiplexing, where all wavelengths belonging to a core would be switched together. using the two dimensions of the steering matrix for space switching. However, it is also noteworthy that in embodiments, the imaging optics subcomponent of the OCS module could be used for wavelength demultiplexing. That is, it could be used to separate the different wavelengths present in a core, so that wavelength channels can be switched independently. Such an approach would leave one dimension of the steering matrix for space switching, while using the other for wavelength switching. Alternatively, an additional steering layer could be used for wavelength switching.
In the example of
As represented in
In example embodiments, the intermodular propagation is free-space propagation. In embodiments, the intermodular free-space propagation could be limited to propagation between adjacent OCS modules. In other embodiments, however, free-space propagation could be permitted from source modules to non-adjacent destination modules. Direct forwarding from the source module to the destination module would be beneficial, because it would be immune to failures of elements along the propagation path that would otherwise be used to relay the beam to its destination. For certain system sizes, however, it could still be advantageous to use intermediate relay elements. In some cases, intermodular propagation may take place wholly or partly within waveguiding media such as optical fibers or planar waveguides.
Imaging optics 150, 155 will typically include lenses for collimation or focusing. Although optics 150 and 155 are shown in the figure as separate elements, it should be noted that optical designs are feasible in which at least some subcomponents of the imaging optics can be shared between the input and output light beams.
With further reference to
It will be understood from the above discussion that the optical reflectors for optical steering in an OCS module as described here should have enough angular range to impinge those portions of intermediate array 160 that direct the reflected light beam to optical fiber ports located in other OCS modules. This intermodular coupling makes it possible to increase the port count of the optical switch by adding more OCS modules to the same OXC node, and it makes it possible to do so without affecting existing light paths. Two-dimensional MEMS mirror arrays, for example, can offer an angular range above ±6°, and further magnification optics can be used to extend the angular reach, if needed. The utilization of an active intermediate optical reflector can substantially reduce the angular reach needed from the input/output steering optical reflectors, since the same intermediate optical reflector spot can be reconfigured to be used for intramodular and intermodular links.
One of the design constraints on an example OCS module of the kind described here is that there should typically be enough space for an intermediate optical reflector array that includes optical reflectors for intermodular coupling. Another constraint is that the steering optical reflectors have enough tilt-angle capacity to reach the portions of the intermediate optical reflector array that effectuate the intermodular coupling. Yet another constraint is that there typically be optical propagation paths between interconnected OCS modules. As mentioned above, these paths can be paths in free space or, alternatively, they can be achieved with optical waveguiding media such as optical fiber or planar waveguides. We believe that all of these constraints can feasibly be met using current capabilities in optical system design.
Two light beams 320, 325 are also shown to illustrate the potential for intermodular coupling. In a first example, light beam 320 enters OCS module 301 through one of its input optical fiber ports of input array 110.1, reflects from the input steering matrix 130.1 of the same OCS module 301, and impinges optical reflector 341 of the intermediate optical reflector array of the same OCS module 301. Due to the particular orientation of optical reflector 341, light beam 320, after reflecting from optical reflector 341, exits module 301 and enters module 302 through respective intermodular gates. Within OCS module 302, light beam 320 impinges output steering matrix 140.2 of OCS module 302 and is reflected from there to a selected output optical fiber port of output array 120.2.
In a second example, light beam 325 enters OCS module 303 through one of its input optical fiber ports of input array 110.3 and impinges the input steering matrix 130.3 of the same OCS module 303. Due to the particular configuration of steering matrix 130.3, light beam 325, upon reflection from the steering matrix, bypasses the intermediate optical reflector array of OCS module 303, exits OCS module 303 and enters OCS module 302 through respective gates thereof. Light beam 325 passes through OCS module 302 and exits OCS module 302 to enter OCS module 301 through respective gates of these OCS modules 302, 301. Within module 301, light beam 325 impinges on optical reflector 342 of the intermediate optical reflector array therein. Due to the particular orientation of optical reflector 342, light beam 325, after reflecting from optical reflector 342, impinges on output steering matrix 140.1 of the same OCS module 301 and is reflected from there to a selected output optical fiber port of output array 120.1. A feature of light beam 325 is that to connect OCS module 303, which is the first OCS module in the propagation path, to OCS module 301, which is the last module in the propagation path, the input steering matrix 130.3 of the first OCS module 303 reflects the incoming light beam into an intermediate optical reflector of the last OCS module 301.
The example of light beams 320 and 325 is provided to illustrate the more general point that with suitable arrangements of the intermediate optical reflectors, any input optical fiber port in an ensemble of several OCS modules could, in principle, connect to any output optical fiber port in the same ensemble.
On inspection of
In
As briefly noted above, embodiments can be designed with fixed passive intermodular routing, in which each OCS module has an intermediate optical reflector array with reflective elements dedicated to interconnect to output steering matrices of respective OCS modules. Alternative embodiments can be designed with active intermodular routing, in which the tilt angles of intermediate optical reflectors can be adjusted to reach desired destination OCS modules.
As also noted above, input and output steering matrices, as well as intermediate optical reflectors, can be implemented in various technologies, including MEMS and LCOS. MEMS mirrors for optical switching have been reported in the technical literature. As reported, for example, in J. I. Dadap et al., “Modular MEMS-based optical cross-connect with large port-count,” in IEEE Photonics Technology Letters, vol. 15, no. 12, (December 2003) 1773-1775, cited hereinafter as “DADAP 2003”, an example MEMS mirror is an electrostatically actuated, double-gimbaled tilting mirror of gold-plated single-crystal silicon, suspended by torsional springs. Closed loop servo control may be provided, e.g., by a digital signal processor (DSP) with ADC and DAC interfaces. Reference in this regard may also usefully be made to R. Ryf et al., “1296-port MEMS transparent optical cross-connect with 2.07 petabit/s switch capacity,” OFC 2001. Optical Fiber Communication Conference and Exhibit. Technical Digest Postconference Edition (IEEE Cat. 01CH37171), Anaheim, CA, USA, (2001) pages PD28-PD28, hereinafter cited as “RYF 2001”. DADAP 2003 and RYF 2001 are hereby incorporated herein by reference in their respective entireties.
Suitable controller techniques are known. Nonlinear servo control techniques that may be useful in this regard are reported in, e.g., I. Brener et al., “Nonlinear servo control of MEMS mirrors and their performance in a large port-count optical switch,” in OFC 2003, Atlanta, GA, March 2003, pp. 385-386, the entirety of which is hereby incorporated herein by reference. Additional information on controller techniques that may be useful in this regard may be found in G. F. Franklin, J. D. Powell, and M. L. Workman, Digital Control of Dynamic Systems. Reading, MA: Addison-Wesley, 1998, particularly at pages 323-325, which are hereby incorporated herein by reference.
LCOS for optical switching has also been reported in the technical literature. Reference may usefully be made, for example, to N. K. Fontaine et al., “Few-Mode Fiber Wavelength Selective Switch with Spatial-Diversity and Reduced-Steering Angle,” in Optical Fiber Communication Conference, OSA Technical Digest (online) (Optica Publishing Group, 2014), paper Th4A.7, the entirety of which is hereby incorporated herein by reference. For LCOS steering matrices or other types of reconfigurable steering matrix, it is noteworthy that the matrix transfer function of a hologram or grating type reflector can be adapted to decrease losses and crosstalk according to the angular reach required for the number of OCS modules that are in place. This may be significant, particularly because the tilt angle that is required increases with the number of OCS modules that are connected.
As illustrated in
Precise optical reflector angle tuning can be used to correct residual position deviations through monitoring channels. By way of example, URATA 2022, cited above, describes the use of camera modules operating at an out-of-band wavelength to provide monitor signals.
Mirror switching controller 535 may also be operable to minimize the impact on already-established connections when a new optical path is being established.
In at least some embodiments, connecting additional modules to the system will leave the relative positions of the steering matrices and intermediate optical reflectors unchanged in OCS modules that were already in place. In such cases, additional training may be unnecessary for internal connectivity within the pre-existing OCS modules. However, training would generally be needed for intermodular connectivity with the newly inserted OCS modules of the ensemble 505. For example, the training could be used to identify the spots in an intermediate optical reflector, or to identify the configuration angles of a reconfigurable intermediate optical reflector, that optimize the signal quality of intermodular connections.
At block 601, input and output OCS module(s) are selected for each optical beam connection(s).
At block 602, input and output optical fiber ports of the OCS module(s), selected at block 601, are selected for each optical beam connection.
At block 603, steering optical reflector and intermediate optical reflector positions are determined for the respective connections. In embodiments, instead of making a fresh determination of the optical reflector positions, some or all of the desired optical reflector positions may be obtained by consulting a look-up table.
At block 604, respective optical signal(s) are received at the selected optical fiber port(s). If intermodular connections have been designated, this will result in one or more beams of light being transmitted from an intermediate optical reflector array of a source module to an element of a destination module, and ultimately to an output optical fiber port of the destination module. The intermodular transmission may, in example embodiments, include free-space transmission through free-space optical ports or gates between respective modules.
Each switch module 705 has a plurality 715 of input optical fiber ports and a plurality 720 of output optical fiber ports. Each switch module 705 also has a reconfigurable optical reflector array 725 that, as explained above, is capable of selectively making optical cross-connections between ones of the input optical fiber ports of its own switch module and ones of the output optical fiber ports of its own switch module. Each switch module 705 is also selectively reconfigurable to route light received from one of its own input optical fiber ports, via its own optical reflector array 725, to one or more others of the optical switch modules.
Free-space optical ports 730 in the switch modules 705 permit the routing of light between switch modules.
