WO2014141281A1 - Routing in an sdm optical communication network - Google Patents

Abstract

A technique for routing of SDM data traffic in an optical communication network, based on SDM (spatial) superchannels, by using SDM-adapted optical switching devices, for example SDM-adapted Wavelength Selective Switches.

Description

Routing in an SDM optical communication network

Field of the invention

The present invention relates to the field of routing and switching in optical communication networks utilizing the principle of Space Division Multiplexing (SDM) of optical channels.

Background of the invention

The increasing data capacity that optical networks are transporting implies that within a few years we may reach the maximal attainable capacity over a single mode fiber (SMF).

WDM (Wavelength Division Multiplexing) is one of the presently known techniques which allows transmission of different informational channels through one single mode fiber (SMF), by carrying data of the informational channels using different optical wavelengths, thus forming different optical channels in the SMF fiber.

One of the key elements of existing, SMF- based optical networks supporting WDM traffic and WDM-based routing is a wavelength- selective switch (WSS). One conventional WSS type is configurable to obtain a group of WDM multiplexed optical channels at its single (1) input port, and to individually switch each optical channel of the group to one of multiple (K) output ports, or conversely: to switch a single WDM channel from one of the multiple (K) input ports of such a WSS to a single output port. This functionality is summarized as lxK WSS and Kxl WSS, respectively, and is based on K+l SMF fibers at the WSS interfaces. When a WSS is configured as a K*l, it will have K input fibers carrying WDM channels (any number from 0 to the full count) and the WSS will combine them all to the single output fiber.

Initial designs of WSS offered K-count multiple input or output ports of 5 and 9. The K value of modern commercial WSS devices can now reach 24 and 40, and the research community is demonstrating even higher values.

It should also be noted that a conventional WSS is bound to operate with a single input port or a single output port on account of its relatively simple realization which images all the input and output fibers to a common point in space, but being dispersed in wavelength (or channel). Since each spectral component is imaged to the same location, one cannot switch independently more than one path of WDM optical channels. Since only one path is permissible, it is assigned to one unique path from the input to the output port in the lxK WSS or Kxl WSS realizations.

Physical limitations on the number of simultaneously transmitted WDM optical channels on SMF exist and manifest themselves, for example, via nonlinear cross-talk effects between neighbor channels. Thus, we are presently approaching saturation in the capacity of a single-mode fiber [1], notwithstanding the fact that we fill the fiber's operational bandwidth (determined from the fiber amplifiers) with data encoded using sophisticated modulation formats with near-optimal forward error correction (FEC) [2,3].

The incessantly increasing demand for more and more communication channels in a single fiber & higher and higher data rates demonstrates that neither WDM nor DWDM (dense Wavelength Division Multiplexing) can satisfy future optical communication capacity requirements, if such multiplexing techniques are used alone.

Consequently, researchers are turning to space-division multiplexing (SDM), in which multiple data streams are carried in multiple parallel spatial modes along each network link, for example by a multi mode fiber MMF (also called a few mode fiber FMF), a multi-core fiber MCF or by multiple SMF fibers operating in parallel [4]. Space -division multiplexing (SDM) is seen as a contemporary means to overcome the transmission capacity exhaust of SMF by introducing additional conduits of information. SDM may be implemented with few-mode (multi-mode) fibers (FMFs or MMFs) [5-7], multi-core fibers (MCF) [8-10], by parallel conventional single mode fibers (SMF), or by multiple modes in multiple cores [11- 12]. The entire optical network will have to be redesigned for the age of SDM, including the hardware and software components that are required for its realization.

However, capacity is only part of the picture; to sustain the future of the information economy, SDM must offer lower cost-per-bit through higher component integration, must offer a smooth transition from existing WDM networks on SMF, and must support optical channel switching at reconfigurable optical add/drop nodes as well (such nodes being based on for example wavelength selective switches WSS or reconfigurable optical add drop multiplexors ROADM which may be based on WSS).

Spatial superchannels are known in the prior art as those in which data streams (e.g., high-rate data streams, for example of about lTb/s) are transported as groups of subchannels occupying the same wavelength in separate modes/cores/fibers of the SDM network link. Such spatial superchannels may help simplifying both transceiver hardware at the optical signal transmitter and receiver and the optical routing equipment at the optical network switching nodes [13].

Various solutions have been proposed in the prior art to handle multi-mode optical channels in SDM optical networks, for example:

US2012207470A [25] describes an optical transport network based on multimode/multicore fibers, which includes a mode-multiplexer to multiplex independent data streams from one or more transmitters; a multimode erbium-doped fiber amplifier (MM EDFA) to compensate for MMF loss; a multimode optical add- drop multiplexer (MM OADM) to add and/or drop multimode channels in multimode networks; a multimode optical cross-connect; and a mode-demultiplexer to separate various mode streams to one or more receivers.

US2013236175A [26] describes a space division multiplexed (SDM) transmission system that includes at least two segments of transmission media in which a spatial assignment of the two segments is different. For example, the SDM transmission may include a first segment of transmission media having a first spatial assignment and a second segment of transmission media having a second spatial assignment, wherein the first spatial assignment differs from the second spatial assignment. An example method obtains an optical signal on a first segment of transmission media having a first spatial assignment and forwards the optical signal on a second segment of transmission media with a different spatial assignment. The transmission media may be a multi-core fiber (MCF), a multi-mode fiber (MMF), a few-mode fiber (FMF), or a ribbon cable comprising nominally uncoupled single- mode fiber (SMF).

To the best of the Applicant's knowledge, prior art does not teach how the ideas for switching/routing of SDM traffic in optical network can be practically implemented, and does not propose cost-effective and robust solutions for switching (and routing) such traffic in SDM-enabled optical networks.

Object and Summary of the Invention

It is therefore one object of the present invention to provide practical solutions and cost-effective implementations for routing/switching of SDM traffic in SDM- enabled optical networks.

In the present patent description, some specific terms are used and should be understood as follows:

SDM modes - SDM data conduits in the form of fiber modes, fiber cores, separate SMFs, or a combination thereof; a multimode fiber ( see below) is characterized by more than one SDM modes.

Multimode fiber (MMF) - a fiber capable of accommodating "M" (where M>1) SDM conduits (SDM modes). The present description also uses SDM fiber as a general term for the multimode fiber, and few mode fiber FMF as a specific term thereof.

Spatial (SDM) sup er channel - a group of M (M>1) subchannels occupying the same wavelength in separate M optical modes/cores/SMFs, for transporting a respective group of data streams. N superchannels may be transported simultaneously, using N different wavelengths.

SDM link (also referred in the description as SDM path) - a group comprising "M" SDM modes; the SDM link may carry data (optical signals) along one to N spatial superchannels, along M subchannels thereof . The term SDM link/path may be used, for example, to indicate a multimode input (an SDM input link/path) or a multimode output (an SDM output link/path) at an optical switching device.

Network supporting SDM - network operable for SDM, i.e. capable of transporting data via multimode fibers, whether in the form of FMF, MCF, parallel SMFs, or a mixture thereof. The main concept of the solution proposed by the Inventor is

to perform routing of SDM data traffic in an optical communication network, based on SDM (spatial) superchannels, by using at least one SDM-adapted optical switching device (for example an SDM-adapted Wavelength Selective Switch), and to ensure that the network is provided with suitable means comprising at least one such device (for example, SDM-adapted Wavelength Selective Switch) for performing that type of routing.

As a result of the routing, all subchannels of a spatial superchannel upon switching thereof , may be routed together, or jointly, through the network. It should be noted, however, that though the switching is performed per spatial superchannel, the subchannels must not be further transported together, and one or more subchannels of the superchannel may be split out from the superchannel upon the switching (routing) operation, so as to be utilized/routed separately.

The above may take place in some certain situations where no mode mixing occurred. One example of such a case is an SMF array/bunch. So while it is advantageous to jointly switch all spatial modes of superchannels due to the newly proposed switching hardware which will further be described, one could also break up one or more of the superchannels in other places of the network. The proposed routing is performed per spatial superchannel ( i.e., per wavelength spanning all spatial modes), by using at least one said SDM-adapted switching device, at a network node.

The SDM-adapted Wavelength Selective Switch WSS may be based on a conventional WSS. It may form part of an SDM-adapted ROADM, or another SDM- adapted optical switching element. In one specific example, the SDM-adapted switching device may be implemented as proposed by the Inventor and described later below.

The proposed method of routing SDM traffic presented at least by an input SDM path and an output SDM path, each carrying at least one spatial superchannel; the method may, for example, comprise:

providing a conventional WSS (for example, but not only lxK or Kxl WSS), adapting said conventional WSS to switching a spatial superchannel, according to its wavelength, between an input SDM path and an output SDM path, by assigning a first group of fiber ports of said conventional WSS to respective separate SDM modes of the input SDM path, and

assigning a second group of fiber ports to respective separate SDM modes of the output SDM path intended for said spatial superchannel,

applying the input SDM path carrying said superchannel in the form of optical signals of said wavelength, transported along preliminarily separated said SDM modes, to respectively assigned first group of fiber ports of said WSS, (wherein said input SDM path carrying at least said superchannel);

switching all optical signals of said superchannel, according to its wavelength, by feeding said optical signals from the first group of fiber ports to the second group of fiber ports, thereby switching the input SDM path to the output SDM path. To implement the proposed routing per spatial superchannel, there is further provided an SDM-adapted switching device comprising a conventional Wavelength Selective Switch WSS which is adapted/configured for switching spatial

superchannels.

In other words, such a specific solution describes the use of today's high port count WSS configured to be operable for SDM, whether in the form of FMF, MCF, or parallel SMF, and a modification of existing WSS to better support this function.

The SDM-adapted WSS device may comprise a conventional WSS provided with an adapter interfacing the conventional WSS with an input SDM link (i.e., input fiber) and an output SDM link (i.e, output fiber), the adapter being capable of

-providing separated SDM modes (conduits) from the input SDM link (which should be understood as a variety comprising for example MCF, FMF, a bundle of SMF, any combinations thereof), said separated SDM modes forming an input SDM path;

- combining separated SDM modes of an output SDM path, for combining thereof into the output SDM link; - adapting said conventional WSS to switching a spatial superchannel, according to its wavelength, between the input SDM path and the output SDM path, by connecting a first group of fiber ports of said conventional WSS to respective separate SDM modes of the input SDM path, and a second group of fiber ports to respective separate SDM modes of the output SDM path intended for said spatial superchannel,

- ensuring applying the input SDM path possibly carrying at least said superchannel in the form of optical signals of said wavelength, transported along preliminarily separated said SDM modes, to respectively assigned first group of fiber ports of said WSS;

said conventional WSS thereby being adapted to switching all optical signals of said superchannel, according to its wavelength, by feeding said optical signals from the first group of fiber ports to the second group of fiber ports. One specific implementation of the proposed optical switching device is a

Reconfigurable Optical Add Drop Multiplexor (ROADM) comprising two or more conventional WSS devices adapted for switching of SDM data traffic per spatial superchannel (for example in the manner described above).

There is also provided a network node in an optical communication network, for routing SDM traffic; the network node may comprise the proposed optical switching device, for example in the form of the above-mentioned ROADM.

According to a further aspect of the invention, there is provided an adapter for adapting a conventional WWS to switching of SDM superchannels.

The adapter (the interface designed to modify the conventional WSS) may comprise:

one or more SDM splitter devices ( or "mode splitters", say, mode demultiplexer for MMF or FMF, multi-core demultiplexer or breakout device for MCF) for separating SDM modes/conduits from SDM input path, one or more SDM coupler (mode compler or multiplexer) devices for combining separated SDM modes/conduits into a SDM output path,

single-mode fibers SMF for interconnecting the fiber ports of the conventional WSS with said SDM splitter and SDM coupler devices.

The coupler and the splitter device preferably form a combined block, for example in the form of a MCF mux/demux, MMF(FMF) mux/demux, etc.

As mentioned above, the conventional WSS may, for example, be a IxK or Kxl WSS having high count of fiber ports among those available in the market. In one specific embodiment, where the SDM- adapted switching device comprises a conventional IxK or Kxl WSS and the adapter for modifying said WSS for switching between at least one input SDM path carrying N spatial superchannels at M modes, and "k" output SDM paths each carrying one or more of said N spatial superchannels at M modes,

said adapter, per each of said at least one input SDM paths, is operative to:

obtain M split modes and assign (connect) thereof to respective M input fiber ports of said conventional WSS, and

assign/connect k* M output fiber ports of said conventional WSS to "k" SDM output paths, wherein each of the "k" SDM output paths being supposed to carry M split modes of one or more of said N superchannels,

wherein the total number of fiber ports (M + k*M)=M(l+k) required for assigning one input SDM path and k output SDM paths of size M being not greater than the total number (K+l) of fiber ports of the conventional IxK or Kxl WSS.

Technically, multiple input SDM links and multiple output SDM links can be applied to a conventional WSS provided with a suitable adaptor, as long as a single wavelength appears only once on the input ports. Otherwise the two channels having the same wavelength will be superimposed (imaged to the same position at the output). More than one ("p") input SDM paths (for example, each composed of M modes), may be applied to the SDM-adapted switching device and similarly switched to k output SDM paths per spatial superchannel, provided that the common wavelength set of said "p" paths comprises only different wavelengths, and

provided that the total number of fiber ports (M*p + k*M)=M(p+k) required for assigning p input SDM paths and k output SDM paths being not greater than the total number (K+l) of fiber ports of the conventional lxK or Kxl WSS.

Presently, possibility of 1x100 WSS has been demonstrated.

The above allows converting a conventional lxK or Kxl WSS switch into an SDM-adapted (p*M)x(k*M) or (k*M) x(p*M) Wavelength Selective Switch having real practical capacity.

Alternatively, " p" separate input SDM paths may be first merged into one common input path, by "multiplexing" their superchannels ( with the same condition that the wavelengths are not overlapping)

In practice, the adapter may be designed so as:

to obtain M separate modes/conduits split out of each of the input SDM paths that together carry N spatial superchannels,

to assign (and connect) the demultiplexed M modes to respective M input fiber ports of said conventional WSS, for each input SDM path,

to assign k* M output fiber ports of said conventional WSS to "k" SDM output paths, wherein each of the "k" SDM output paths is supposed to carry one or more of the total number of N superchannels.

It should be noted, however, that different SDM paths (for example different input SDM paths or different output SDM paths) may alter by the nature and the number of SDM modes/conduits. In other words, the SDM conduits may be different in different MMF fibers/SDM paths, which in turn may comprise different number of their conduits. However, since it is problematic to switch from a large SDM group into a smaller one, the same size groups will be preferable. Assignment of the fiber ports ( and the adapter ) should take the above issues into account. Finally, there is provided a software and/or a firmware product, forming part of the new SDM-adapted WSS. The software embedded/firmware product allows providing the new functionality of the adapter to enable assigning SDM modes of input and output SDM links to various fiber ports of the WSS.

Preferably, the newly proposed software/firmware product is a modification of the internal embedded software (firmware) of a conventional WSS, that

communicates to the outside world and operates the internal switching elements. The internal software embedded/firmware should be modified to be aware of the outside fiber adaptation, and thus may be considered to form part of the adapter.

In other words, the software/firmware of the WSS ( or of the adapter) should be configurable to serve as a communication interface between an outside fiber arrangement and internal switching elements of the optical switching device.

The firmware/software is modified to suit to a new outside fiber arrangement with fiber ports respectively assigned to at least one SDM input path and at least one SDM output path.

Based on the above description and definitions, the newly proposed technique allows:

creating a new optical switching device for performing this type of routing; creating an adapter that allows conversion of a conventional optical switching device into an SDM-adapted switching device;

creating a network node comprising the new optical switching device; in particular, creating an ROADM node.

performing data routing in optical communication networks supporting SDM, based on spatial superchannels and using the new optical switching device;

building a new, SDM supporting network, capable of performing this type of routing;

creating a software/firmware product enabling conversion of a conventional optical switching device into the SDM-adapted one.

The invention will be further described in details as the description proceeds. Brief description of preferred embodiments

The invention will be further described with reference to the following non- limiting drawings, in which:

Fig. 1 shows the proposed principle of routing in an SDM-supporting network, based on spatial superchannels and by utilizing an SDM-adapted optical switching device.

Figs. 2A, 2B - schematically illustrate how the principle of the SDM routing can be implemented by adapting a conventional Kxl WSS. The SDM mode of the input and output fibers is shown as MCF for example only.

Fig. 3 schematically shows that different types of SDM modes/conduits can be used for data routing in the same SDM-adapted switching device. (The SMF fibers used for connecting the SDM conduits to fiber ports of the switching device can be interleaved, for example similarly to that shown in Fig. 2B).

Figs. 4A, 4B, 4C schematically shows an improved , array-like arrangement of fiber ports of the proposed SDM-adapted WSS.

Fig. 5 schematically illustrates how a network node being ROADM can be built based on the proposed SDM-adapted WSS devices.

Detailed description of the invention

One practical version of routing of spatial superchannels via an SDM-adapted ROADM is illustrated in Fig. 1.

Fig. 1 shows that an incoming SDM link 10 accommodates three SDM modes/ cores/ SMF fibers (the number of SDM modes M=3, but can be any integer greater than 1), and that each of the SDM modes carries a set of four optical

wavelengths/channels (different wavelengths are indicated by different patterns of thick lines; different modes are distinguished by the line dashing). It can be seen that the set of wavelengths is the same in all of the three SDM modes. Fig. 1 also illustrates that an SDM-ROADM device 12 should be capable of switching/routing the incoming optical channels in such a manner that one spatial superchannel (data transmitted by three different subchannels/SDM modes at the same wavelength (in this case marked by the homogeneous black color) is routed to an SDM link 14, while three remaining spatial superchannels (marked by the three remaining patterns), out of those incoming the device, are transferred to another, SDM link 16. The spatial superchannel routing is performed on all spatial subchannels at once (solid line, dashed line, and dotted line).

As long as a spatial superchannel comprises all of the spatial modes present at the given wavelength, the scheme should guarantee that the receiver at the end of the link will have all the information it needs to correct for possible mode mixing using digital signal processing (DSP).

The SDM-ROADM device 12 can be built using newly proposed SDM- adapted WSS devices examples of which will be described below.

Figs. 2-5 will describe the use of today's high port count WSS configured to be operable for SDM (whether in the form of FMF, MCF, or parallel SMF), and modified to better support the SDM switching/routing function in various implementations.

Fig. 2A. The Inventor 's solution to realize the principle of data routing by switching spatial superchannels will be now demonstrated on an example of 1x20 WSS , by describing various implementations.

The number of conventional WSS ports K required to support simultaneous switching from one input M conduit SDM route to one of "k" SDM routes each with M conduits is K=(l+k)xM. For example, it is possible to switch from a single 7 conduit SDM route to one of two output SDM routes with one today's conventional 1x20 WSS (The functionality we'll call 7x(lx2) WSS which should be understood as one input SDM link of size 7 to two output SDM links also of size 7. It is readily understood that the number of fiber ports on the WSS required to support 7x(lx2) switching functionality is 7*(1+2)=21 , which is exactly equal to the number of fiber ports of a conventional 1x20 WSS (being equal to 1+20=21).

Fig. 2A demonstrates one realization for 7x(lx2) WSS ( marked as 20) with MCF as its SDM solution. It should be noted that instead of MCF, the input and output fibers may be all MMF(FMF) fibers, may comprise cables of parallel conventional SMF fibers, or may present any combination of the above. Each input and output MCF is shown separated to its constituent SDM conduits (cores) with a MCF

breakout(demux) device 22 . In case of using FMF fibers, FMF mux/demux blocks should be used instead of devices 22. In case of using parallel SMFs, no intermediate breakouts/blocks are needed.

The description will be continued by using MCF as an example of SDM mode. The M separated SDM conduits (M=7) are connected by single mode fibers 24 to the conventional WSS, with their fibers grouped contiguously. Each group of 7 fibers transports a specific SDM path carrying several spatial superchannels, each at its wavelength and along 7 subchannels transmitted along 7 SDM conduits. Each group of 7 fibers is connected to a corresponding group of fiber ports (arranged along line 26) of the WSS 20. It should be understood that any of the groups may be used either as an input SDM path or as an output SDM path.

In the figure, the elements located to the right of the line 26 belong to the

conventional WSS 20, while the elements situated to the left from the line 26 are considered as part of SDM adapter 27 of the WSS 20.

Let an input SDM path is obtained from the input MCF fiber 28 ( in the middle) . The optical beams from its corresponding input fiber ports pass an optical lens 30 of the WSS and arrive to its internal switching element 32. Fig. 2A is quite schematic and thus does not show some additional elements required to build a WSS. The important element to note is a diffraction grating used to separate the beams by wavelength on the switching element (e.g. mirror, not being a mirror but a mirror array with one per wavelength channel, or other switching technologies such as spatial light modulators configured for phase modulation). The grating will be schematically shown as 46 in Fig. 3.

The wavelength/channel switching element 32 (say, a mirror or a phase blazed grating) jointly tilts the M=7 input beams of the input SDM path and reflects those beams as M output beams to locations (i.e., to output fiber ports found at the upper or lower portion of line 26) where switching will occur to these subchannels. The output fiber ports are connected to M output conduits of a selected output MCF fiber, which may be 34 or 36 depending on the mirror tilt applied to the specific superchannel. This same switching operation is performed to each wavelength channel independently, and is not shown in the figures as this is well understood by experts in this field.

As can be seen, the fibers 24 are grouped and interconnected by the groups with the fiber ports at the adaptation I/O 26 of the WSS. The WSS is configured so that, for example, upon switching (i.e., upon reflection from the mirror 32), outputs of the incoming beam originating from fiber 1 ( indication in a circle) must be found at either fiber la or lb ( similar indications), depending on switching state. To provide that, quite a great tilt of the mirror is required. Fig. 2B illustrates the arrangement similar to that shown in Fig. 2 A, where

SMF fibers of all input and output SDM paths (groups) are interleaved. The advantage of this realization (with interleaved fibers) over the previous one with the grouped fibers is that the beam tilt ( the mirror tilt) required for the WSS switching functionality is greatly reduced.

Fig. 3 demonstrates yet another realization for the SDM adapted 7x(lx2) WSS , with different types of the SDM modes at its I/O interface. Let SDM path 40 carried by 7 SMF fibers connected to an FMF (MMF) fiber via an FMF mux/demux. Let the SDM path 42 ( input path in this example) is similarly created from an MCF fiber, while the SDM path 44 is always carried by parallel SMFs. No interfacing device is required between the parallel SMF and the conventional WSS. The input M=7 parallel SMF conduits of each of the SDM paths are connected to the conventional WSS; in this example, the fibers are interleaved. The

wavelength/channel switching element (mirror or phase blazed grating 32) jointly tilts the input beams ( say, from the SDM path 42) to locations where switching will occur to each of them according to the wavelength of each specific spatial superchannel. We keep in mind that each superchannel should be routed to one or another SDM output path, in this example selected from the output parallel SMF array 42 or 44.

In all the above-described configurations (Figures 2-3), fibers were either grouped contiguously or interleaved between SDM routes/paths and WSS interfaces. Note that other connectivity options are permissible, such as interleaved pairs, to anyone well versed in the design of WSS.

Figs. 4A, B, C show modifications of the I/O interface of an SDM adapted WSS. It is known that conventional WSS devices are designed with SMF input/output interfaces and configured to switch from one input fiber port to one of K output fiber ports, or vice versa. In either case, there are K+1 input/output fiber ports interfaced to the WSS, typically configured as a linear array (see Fig. 4A).

The linear array distribution facilitates switching, as the beam tilt is prescribed in one direction only. Since there is an interest in joint switching between a number of fiber groups in support of SDM, the SMF input/output can be configured to span a two dimensional array. One example would have the array configured to be M wide and k+1 tall (see Fig. 4B), allowing for the realization of a Mx(lxk) WSS. The M conduits of each SDM path/route are connected to the individual rows (M wide). Switching from the single input SDM route to the selected output SDM route is achieved by simultaneously tilting the beams from the input row to the output row (see Fig. 4C). Such a new arrangement of the fiber ports at the I/O interface (actually, at the WSS adapter) allows a greater number of SDM paths (links) to be switched by the WSS, as it better utilizes the lens aperture.

The Inventors thus propose such an SDM-adapted optical switching device, wherein fiber ports of the device are arranged in a two-dimensional array. For example, the array may have M columns and k+1 rows, wherein M is a number of SDM conduits of an SDM path, and k+1 is a number of input and output SDM paths; and wherein M conduits of each SDM path are connected to an individual row in the array, to thereby allow switching from a single input SDM path to a selected output SDM path by simultaneously tilting optical beams in said device from one row to another row in the array.

The above arrangement may actually be part of the SDM-adapter for a conventional WSS device. There is an additional alternative, and that is to divide the M spatial channels to several rows (say two) and then jointly switch from two rows of the input to two corresponding rows attached to an output. Fig. 5 shows an exemplary arrangement for an SDM-adapted ROADM system, which may form a network node in an SDM operable optical communication network.

The main functions of the ROADM node 50 will be described below.

In this example, the ROADM system 50 comprises five SDM-adapted WSS switches:

Input WSS 52; in this example performing the routing of input SDM link(s) 54 into SDM Express (through) links 56 and 58 and an SDM drop link 60;

Output WSS 62, in this example configured for routing the through link 56 into an SDM output link 64.

Another output WSS 66, is presently configured to route the through link 58 and an add link 68 into an output SDM link 70.

An add WSS 72 receives three input SDM links from respective three transmitters 74, and routes them into one common add SDM path/link 68.

A drop WSS 76 receives the drop SDM path 60 and routes if to three output SDM paths forwarded to three respective receivers 78.

In practice, such an ROADM system may comprise more WSS devices, as one needs to support communications in both directions on each path. Fig. 5 just shows traffic originating at 80.

Each of the above-mentioned WSS devices (52, 62, 66, 72, 76) is SDM-adapted, for example by using the means described in Figures 2-4.

The inputs and the outputs of the ROADM 50 are connected to SDM links with SDM- breakout or mux/demux devices. For example, in case the SDM link is an MCF fiber, such a device may be an MCF breakout 80 splitting cores of the MCF input fibers for applying them to the interface of the WSS 52. Fig. 5 shows that, if the input SDM link is of an FMF type, the SDM breakout device may be in the form of an FMF mux demux 80A. In case the input is transmitted via parallel SMF fibers, these fibers will be connected to the WSS just as an SMF array 80B. Additional MCF breakout/multiplexer devices 82 and 84 are shown at the output of the ROADM, for combining the output SDM links into respective output MCF cables 86 and 88.

Though the invention has been described with reference to specific embodiments, it should be appreciated that other versions of the method may be proposed, as well as additional embodiments of the SDM-adapted WSS, the adapter, the network node and the network can be found, which should be considered part of the invention whenever defined by the clams which follow.

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Claims

Claims:

1. A method for routing of SDM data traffic in an optical communication network, by providing a network node with an optical switching device comprising at least one SDM-adapted Wavelength Selective Switch WSS, and by performing said routing per spatial superchannel, using said SDM-adapted WSS.

2. An optical switching device comprising at least one SDM-adapted

Wavelength Selective Switch WSS, configurable for switching SDM data traffic per spatial superchannel.

3. An optical communication network, wherein at least one network node thereof is equipped with an optical switching device comprising at least one SDM-adapted Wavelength Selective Switch WSS capable of switching of SDM data traffic per spatial superchannel

4. The method for routing of SDM data traffic according to Claim 1, wherein the SDM data traffic is represented at least by an input SDM path and an output SDM path, each carrying at least one spatial superchannel; the method comprises:

providing a conventional WSS having fiber ports,

adapting said conventional WSS for switching a spatial superchannel, according to its wavelength, between an input SDM path and an output SDM path, by assigning a first group of fiber ports of said conventional WSS to respective separate SDM modes of the input SDM path, and a second group of fiber ports to respective separate SDM modes of the output SDM path intended for said spatial superchannel, applying the input SDM path carrying said superchannel in the form of optical signals of said wavelength, transported along preliminarily separated said SDM modes, to respectively assigned first group of fiber ports of said conventional WSS; switching all optical signals of said superchannel, according to its wavelength, by feeding said optical signals from the first group of fiber ports to the second group of fiber ports by said conventional WSS.

5. The optical switching device according to Claim 2, wherein said SDM- adapted WSS comprises a conventional Wavelength Selective Switch WSS, configured for switching SDM traffic.

6. The optical switching device according to Claim 5, comprising the conventional WSS provided with an adapter interfacing said conventional WSS with an input SDM fiber and an output SDM fiber, the adapter being capable of

-providing separated SDM modes from the input SDM fiber, said separated SDM modes forming an input SDM path;

- combining separated SDM modes of an output SDM path, for combining thereof into the output SDM fiber;

- adapting said conventional WSS to switching a spatial superchannel, according to its wavelength, between the input SDM path and the output SDM path, by connecting a first group of fiber ports of said conventional WSS to respective separate SDM modes of the input SDM path, and a second group of fiber ports to respective separate SDM modes of the output SDM path intended for said spatial superchannel,

- ensuring applying the input SDM path possibly carrying at least said superchannel in the form of optical signals of said wavelength, transported along preliminarily separated said SDM modes, to respectively assigned first group of fiber ports of said WSS ;

said conventional WSS thereby being adapted to switching all optical signals of said superchannel, according to its wavelength, by feeding said optical signals from the first group of fiber ports to the second group of fiber ports.

7. The optical switching device according to any one of Claims 5 or 6, comprising the conventional lxK or Kxl WSS having high count of fiber ports among those available in the market.

8. The optical switching device according to any one of Claims 6 or 7, comprising the conventional lxK or Kxl WSS and the adapter for modifying said WSS for switching between at least one input SDM path carrying N spatial superchannels at M modes, and "k" output SDM paths each carrying one or more of said N spatial superchannels at M modes,

said adapter, per each of said at least one input SDM paths, is operative to:

obtain M split modes and assign thereof to respective M input fiber ports of said conventional WSS, and assign k* M output fiber ports of said conventional WSS to "k" SDM output paths, wherein each of the "k" SDM output paths being supposed to carry one or more of said N superchannels,

wherein the total number of fiber ports (M + k*M)=M(l+k) required for assigning one input SDM path and k output SDM paths being not greater than the total number (K+1) of fiber ports of the conventional lxK or Kxl WSS.

9. The optical switching device according to Claim 8, allowing more than one, p input SDM paths to be applied there-to and switched to k output SDM paths per spatial superchannel,

provided that the common wavelength set of said p paths comprises only different wavelengths, and

provided that the total number of fiber ports (M*p + k*M)=M(p+k) required for assigning p input SDM paths and k output SDM paths is not greater than the total number (K+1) of fiber ports of the conventional lxK or Kxl WSS.

10. The optical switching device according to any one of claims 2, 5-9, wherein its fiber ports are arranged in a two-dimensional array having M columns and k+1 rows, wherein M is a number of SDM conduits of an SDM path, and k+1 is a number of input and output SDM paths; and

wherein M conduits of each SDM path are connected to an individual row in the array, to thereby allow switching from a single input SDM path to a selected output SDM path by simultaneously tilting optical beams in said device from one row to another row in the array.

11. An adapter for a conventional Wavelength Selective Switch WSS, enabling conversion thereof to become said optical switching device according to any one of claims 2, 5-10.

12. The adapter according to Claim 11 , comprising:

one or more mode demultiplexing devices for separating SDM conduits from a multimode input SDM fiber,

one or more multiplexing devices for combining separated SDM conduits into a multimode output SDM fiber, single-mode fibers SMF for interconnecting the fiber ports of the conventional WSS with said mode splitter and mode coupler devices.

13. The adapter according to Claim 12, wherein the mode demultiplexer device and the mode multiplexer device form a combined block in the form selected from the following non-exhaustive list comprising: MCF mux/demux, MMF mux/demux.

14. The adapter according to Claim 11 , designed so as:

to obtain M separate modes/conduits demultiplexed out of each of input SDM paths together carrying N spatial superchannels,

to assign and connect the demultiplexed M modes to respective M input fiber ports of said conventional WSS, for each input SDM path,

to assign k* M output fiber ports of said conventional WSS to "k" SDM output paths, wherein each of the "k" SDM output paths is supposed to carry one or more of said N spatial superchannels.

15. The adapter according to Claim 11 , designed so as to re-arrange fiber ports of the conventional WSS in a two-dimensional array.

16. The adapter according to Claim 15, wherein the array has M columns and k+1 rows, wherein M is a number of SDM conduits of an SDM path, and k+1 is a number of input and output SDM paths; and

wherein M conduits of each SDM path are connected to an individual row in the array, to thereby allow switching from a single input SDM path to a selected output SDM path by simultaneously tilting optical beams by said conventional WSS device from one row to another row in the array.

17. The adapter according to any one of Claims 11 to 16, comprising a firmware configurable to serve as a communication interface between internal switching elements of the optical switching device and an outside fiber arrangement with fiber ports respectively assigned to at least one SDM input path and at least one SDM output path

18. The optical switching device according to any one of claims 2, 5-10, in the form of a Reconfigurable Optical Add Drop multiplexor ROADM comprising two or more conventional WSS devices adapted for switching of SDM data traffic per spatial superchannel.

19. A network node in the network according to Claim 3, for routing SDM traffic; the network node comprising the optical switching device in the form of an ROADM built from two or more conventional WSS devices adapted for switching of SDM data traffic per spatial superchannel.