ROADM Architecture for Wide Spectrum Channels

Abstract

A Reconfigurable Optical Add/Drop Multiplexer (ROADM) node architecture is disclosed that supports wide-spectrum channel operation. The ROADM includes a plurality of degrees, each degree comprising a Wavelength Selective Switch (WSS) configured to define variable-width spectral slices and perform spectral shaping or equalization. A central fiber/space switch interconnects slice ports of the WSSs and provides programmable partial-mesh connectivity. Local add/drop is achieved through direct connection of optical modems, including Full-Spectrum-Transponders (FSTs) that integrate multiple modems and internal multiplexing to provide wide-spectrum outputs spanning all or part of an amplified band. The fiber/space switch treats the FST as an add/drop degree, simplifying operations by eliminating intervening multiplexers and reducing external fiber connections. This architecture enables efficient end-to-end transport of wide spectral slices, reduces insertion loss, and allows scalable, cost-effective deployment of high-capacity ROADM nodes using existing optical components.

Claims

1. A Reconfigurable Optical Add/Drop Multiplexer (ROADM) node comprising: a plurality of degrees, each degree including a Wavelength Selective Switch (WSS) having common ports facing a network and a plurality of slice ports; and a fiber/space switch configured to interconnect the plurality of slice ports of the WSSs, wherein one or more modems connect directly to the fiber/space switch for local add/drop of spectrum without an intervening add/drop WSS.

2. The ROADM node of claim 1, wherein each spectral slice comprises a contiguous swath of optical spectrum and the variable width is programmable per slice.

3. The ROADM node of claim 1, wherein the variable width is selectable among widths including at least approximately 600 GHz and approximately 1.2 THz.

4. The ROADM node of claim 1, wherein the WSS performs spectral shaping or equalization to flatten or tailor power spectral density of a slice prior to interconnection by the fiber/space switch.

5. The ROADM node of claim 1, wherein the fiber/space switch dynamically interconnects only degrees requiring connectivity for current traffic, providing partial-mesh interconnection between degrees.

6. The ROADM node of claim 1, further comprising control circuitry configured to (i) program slice definitions at the WSSs; and (ii) program the fiber/space switch to route the defined slices between degrees and to the one or more modems.

7. The ROADM node of claim 6, wherein the control circuitry is further configured to adjust slice width in response to measured traffic demand or optical performance.

8. The ROADM node of claim 1, wherein the fiber/space switch comprises a plurality of central fabrics arranged in a 1:N protection configuration and the ROADM node is configured to switch a slice to a protected fabric responsive to a detected fault.

9. The ROADM node of claim 1, wherein the one or more modems provide a wide-spectrum output spanning at least a substantial portion of an amplified band.

10. The ROADM node of claim 1, wherein the fiber/space switch treats a wide-spectrum modem connection as an add/drop degree corresponding to at least one of: substantially an entire band, more than one band, or a fraction of a band.

11. The ROADM node of claim 1, wherein each degree WSS is a 1M WSS with M slice ports, and M is selected based on a number of spectral slices provisioned for a supported spectrum.

12. The ROADM node of claim 11, wherein M8 per degree for C+L operation and the fiber/space switch has at least 128128 ports.

13. The ROADM node of claim 1, wherein the ROADM node supports switching of up to about 9.6 THz of spectrum in a plurality of spectral slices.

14. The ROADM node of claim 1, wherein the fiber/space switch is configured to route spectral slices for both express degree-to-degree connections and direct local add/drop to the one or more modems.

15. The ROADM node of claim 1, wherein the spectral slices are routed without individual wavelength selection within a slice by the WSS, the WSS being configured to operate at slice granularity.

16. The ROADM node of claim 1, wherein the ROADM node further comprises add/drop equipment coupled to the fiber/space switch for channel-level grooming, and wherein the WSSs operate at slice level while channel-level grooming is performed by subtending equipment.

17. The ROADM node of claim 1, wherein the ROADM node employs space-division multiplexing internally to interconnect WSS modules via the fiber/space switch so as to scale degree count without increasing WSS port fan-out.

18. A method of operating a Reconfigurable Optical Add/Drop Multiplexer (ROADM) node comprising: providing a plurality of degrees, each degree including a Wavelength Selective Switch (WSS) having common ports facing a network and a plurality of slice ports; interconnecting the plurality of slice ports of the WSSs via a fiber/space switch; and routing the spectral slices through the fiber/space switch between the plurality of degrees and one or more modems connected directly to the fiber/space switch for local add/drop of spectrum without an intervening add/drop WSS.

19. The method of claim 18 further comprising dynamically adjusting slice width at the WSSs in response to one of traffic demand or optical performance measurements.

20. A Reconfigurable Optical Add/Drop Multiplexer (ROADM) node comprising: a plurality of degrees, each degree including a Wavelength Selective Switch (WSS) having common ports facing a network and a plurality of slice ports; and a fiber/space switch configured to interconnect the plurality of slice ports of the WSSs, wherein the fiber/space switch is further configured to connect directly to a Full-Spectrum-Transponder (FST) that includes a plurality of optical modems and internal multiplexing functionality, the FST providing a wide-spectrum output corresponding to at least a substantial portion of an amplified band, and wherein the fiber/space switch treats the FST as an add/drop degree.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present disclosure is illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like system components/method steps, as appropriate, and in which:

[0011] FIG. 1 is a diagram of an example 9-degree ROADM with optical add/drop and with degree-to-degree and optical add/drop switching based on superchannels or media channels.

[0012] FIG. 2 is a diagram of additional detail and connectivity of an N-degree ROADM.

[0013] FIG. 3 is a diagram of additional detail and connectivity of an N-degree ROADM with a Colorless-Directionless (CD) architecture.

[0014] FIG. 4 is a block diagram of an implementation of a Colorless Channel Multiplexer/Demultiplexer (CCMD) utilizing Multicast Switches (MCS).

[0015] FIG. 5 is a block diagram of an implementation of a CCMD utilizing Contentionless Wavelength Selective Switches (CWSS).

[0016] FIG. 6 is a block diagram of a CWSS-based MxN CCMD with channel pre-combiners.

[0017] FIG. 7 is a flowchart of a process of operating a ROADM.

[0018] FIG. 8 is a diagram of the ROADM of FIG. 2 illustrating inline optical processing.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0019] Again, the present disclosure relates to systems and methods for a Reconfigurable Optical Add/Drop Multiplexer (ROADM) architecture for wide spectrum channels. The present disclosure describes a new ROADM architecture that is tailored to address future photonic layer connectivity requirements. In particular, the present disclosure views a ROADM from the perspective of slices of spectrum (i.e., media channels, super channels, etc.) as opposed to channels (e.g., 50 GHz, 100 GHz spaced channels, etc.). The number of spectral slices is less than or equal to the number of channels, e.g., both the C-band and L-band includes 9.6 THz and having spectral slices of 1.2 THz yields only 8 slices, far less than 192 channels (i.e., using 50 GHz spaced channels) between the combined C and L-band. Of course, 1.2 THz is an example value, and other values are contemplated. The spectral slice represents aggregate optical capacity requirements between two end points. In this manner, high-degree ROADMs are possible as the number of ports is significantly reduced. Also, the present disclosure includes the use of an optical switch between the degrees, instead of fixed fiber connectivity. The advantages of the present disclosure include the ability to build high-capacity, high-degree ROADM nodes with current optical component technology, without having to dedicate switching planes, such as in Space Division Multiplexing (SDM), etc. That is, the ROADM can be constructed with 18, 124, or 132 WSSs and 6464, 128128, etc. optical switches which are readily available. Stated differently, ROADM sizes, in terms of number of degrees, are no longer defined or constrained by available WSS technology (1N). WSS technology now only defines the granularity at which the spectrum is switched. For instance, 19WSS can be used to construct any size of ROADM. The central space switch now defines nodal capacities. There is no need to continue to scale the optical component technology to achieve this architecture.

[0020] Also, the present disclosure includes additional possibilities for degrees besides an ingress and egress fiber. One example includes the so-called single fiber working where a single fiber carries both the transmit and receive light. Another example is multi-core, wherein multiple waveguides are used within the same fiber strand. Multi-core may be very useful in terms of supporting the SDM applications. A third example is hollow core fiber which presents an even wider transmission window then current silica-based fiber technology. Those skilled in the art will recognize the term degree used herein contemplates any physical implementation and is not confined to two fibersone ingress and one egress. Also, the architecture described herein can be viewed as replacing conventional ROADM degrees and may even include different terminology such as ingress/egress waveguides. Again, the term degree used herein contemplates such different terminology.

[0021] Given that network connection bandwidth requirements are forecasted to continue growing at a high Compound Annual Growth Rate (CAGR) and future gains in spectral transmission efficiency are expected to diminish, it can be ascertained that:

[0022] 1) Site-to-site capacity requirements (A-Z connections) will require increasing amounts of spectrum to deliver the required traffic data rate.

[0023] 2) More spectrum per connection will result in fewer unique A-Z connections per fiber pair. Of note, higher-capacity optical modems utilized larger amounts of spectrum than traditional 50 GHz spaced channels.

[0024] 3) Larger ROADMs (higher degree count/more fiber pairs) will be required to meet aggregate nodal traffic requirements.

[0025] To date, ROADMs have predominantly been architected to support any-any switching of wavelengths between ROADM degrees. Since ROADMs typically terminate relatively few fiber pairs (typically 8 or fewer fiber pairs), and wavelength channel count per fiber pair is high (up to 9650 GHz channels per C-band), an any-any switching architecture was sensible since there was a high probability that at least one wavelength per degree would need to connect to each of the 7 or fewer other ROADM degrees.

[0026] In the current approach, a ROADM is constructed to support full interconnect between degrees with a high channel count per fiber pair9650 GHz channels per C-band and 9650 GHz channels per L-band for a total of 19250 GHz channels for C+L band for a total of 9.6 THz of optical spectrum. With coherent optical modems, flexible grid spacing, and Media Channels (MC) (also referred to as superchannels), the channel count significantly decreases (although each channel has significantly more bandwidth). A media channel is a defined slice of optical spectrum which can include multiple Network Media Channels (NMCs) and which has the same A-Z routing in the network. Of note, every new generation of coherent modem operates at progressively higher baud rate and consumes correspondingly more spectrum, thereby reducing the number of channels that can be carried on a fiber. MC constructs allowing several NMC to be treated as a single wider channel further reduce total channel count. Note that older 50 GHz channel modems were also for the most part coherent modems.

[0027] However, the anticipated reduction in channel count per fiber, and the need to support increasing numbers of ROADM degrees per node will result in a change in ROADM nodal connectivity requirements whereby, individual ROADM degrees will only need to connect to a few other degrees or drop ports. To illustrate this point, if we assume that the average channel requirements per A-Z connection is 1.2 THz, then a fiber degree supporting C&L bands (9.6 THz of spectrum), will carry a maximum of 8 unique A-Z connections, i.e., 8 media channels. In large ROADMs of 16 degrees or more, this means that any individual degree will only need to connect a fraction of the other ROADM degrees.

[0028] This change in ROADM connectivity requirements paves the way for a new architecture that is outlined below. Specifically, the present disclosure contemplates architecting a ROADM based on media channels instead of based on individual channels. In this manner, a much larger ROADM can be constructed in terms of degrees, directions, and add/drop, all with existing optical components. That is, this solves the issue of scaling 1N WSS technology, avoids ROADM planes in SDM, or needing to deploy parallel ROADM planes that risk stranding capacity.

[0029] The key components of this approach are fiber/space switches 12 to provide interconnectivity between degrees and to add/drop, and channels defined as large swaths of spectrum (e.g., 600 GHz, 1.2 THz, etc.). With this approach, there is not a need to connect every degree to every other degree, rather the fiber/space switches 12 can be used for interconnect. Of note, the fiber/space switches 12 can allow any degree to connect to any other degree and add/drop, but there is not a need to dedicate ports on the degrees for full interconnect, allowing less ports.

[0030] The new ROADM architecture has the following characteristics:

[0031] 1) Utilizes less complex and lower cost ROADM WSS technology to build large nodes.

[0032] 2) Replaces the fixed fiber interconnect modules, known as fiber shuffles or Fiber Interconnect Modules (FIMs), or alternately, the large quantity of optical cables used for interconnecting ROADM degrees with optical space switches (used as optical spine switches), i.e., the fiber/space switches 12. This enables any interconnect without the disadvantage of dedicating ports between every degree.

[0033] 3) Includes a control system allowing ROADM degrees to be dynamically interconnected through the central optical switch fabric as required based on channel connectivity needs.

[0034] 4) Employs a mechanism by which central switch fabrics can provide path redundancy through the ROADM node to avoid single points of failure, i.e., dual fiber/space switches 12.

[0035] The envisaged ROADM architecture looks at photonic layer connectivity in a different perspective which enables new levels of optimization and scaling, The new approach:

[0036] 1) is designed to switch wide spectrum media channels that are sized to meet the aggregate capacity requirements of A-Z connections. These media channels can be occupied by a single very high baud rate NMC or multiple co-routed NMCs (superchannel). Contrary to existing ROADM architectures, this solution is not intended or capable of switching individual wavelengths of relatively low bandwidth (e.g., 50 GHz-100 GHz). The switching of individual wavelengths is still possible with subtending equipment, such as pre-combiners, multiplexers/demultiplexers, subtending optical switches, WSSs, etc.

[0037] 2) Replaces the static full mesh interconnect of ROADM degrees, which becomes progressively more complex and costly as ROADM nodes are scaled up, with a programmable interconnect, i.e., the fiber/space switches 12, tailored to the connectivity requirements of the node.

[0038] Additionally, this new architecture introduces intra-nodal data path protection providing a new level of redundancy not available in existing architectures, i.e., dual fiber/space switches 12.

[0039] FIG. 1 is a diagram of an example 9-degree ROADM 10 with optical add/drop and with degree-to-degree and optical add/drop switching based on superchannels or media channels. The ROADM 10 includes one or more fiber/space switches 12. In this example, there are two switches 12 for protection/redundancy. The ROADM 10 also includes degree devices 14, such as 1N WSSs, other wavelength selective switching devices, etc. In this example, for illustration purposes, there are 9-degrees formed by the degree devices 14. Also, there can be optical add/drop devices 16 to support local add/drop. The degree devices 14 and the optical add/drop devices 16 can be the same or different type of devices. That is, the local add/drop can be treated as another degree.

[0040] The switches 12 can be NN cross-point switches. For example, it is envisaged that the switches 12 can be 128128 ports which is currently available. Of note, the switches 12 provide degree-to-degree connectivity. In the conventional approach, the degree-to-degree connectivity and the local add/drop is fixed, through fixed fiber connections such as a fiber interconnect module or fiber shuffler. In contrast, the present disclosure replaces such fixed connectivity with intermediate fiber/space switches 12.

[0041] Each of the degree devices 14 can include two common ports, facing the network for transmit and receive and M ports connecting to the switches 12. Of course, those skilled in the art will appreciate other components are also used such as amplifiers, etc., which are omitted for simplicity. The M ports are based on the spectral slicing. For example, assuming each superchannel is 1.2 THz, M would equal 8 to support all 9.6 THz across the C+L band. Of course, other numbers are contemplated, e.g., would be 16 for 600 GHz channels, 32 for 300 GHz channels, etc. Also, the present disclosure contemplates additional bands as well, besides the C+L band, such as the S-band, O-band, or any other future band. Those skilled in the art will recognize the approach described herein can be used in one band, in multiple bands, etc.

[0042] The switches 12 are configured to switch the superchannels between the degree 14 for express connections, degree to degrees, and the optical add/drop devices 16 for local add/drop.

[0043] FIG. 2 is a diagram of additional detail and connectivity of an N-degree ROADM 10. The ROADM node can be part of an optical network and is responsible for local add/drop channels and node bypass. In the example of FIG. 2, the ROADM 10 includes a number of degrees equal to N, N is an integer, each degree being formed by a 1M WSS 14, M is an integer, such as M=8, 24, 32, etc. Each degree includes a 1M WSS 14, labeled as 1M WSS #1, #2, . . . , #N. The degrees are input/output connectivity between the ROADM 10 and other nodes in an optical network. In this example, the ROADM node 10 can connect to N adjacent nodes in the optical network. For illustration clarity, FIG. 2 shows bidirectional connectivity. Thus, each of the degrees have a transmit (TX) and receive (RX) fiber. Also, those skilled in the art will recognize the ROADM 10 can include various other components such as pre/post amplifiers, Optical Channel Monitors (OCMs), Optical Service Channels (OSCs), and the like which are omitted for illustration purposes.

[0044] The ROADM 10 includes a 1P WSS 16 for local add/drop of spectrum. In the ROADM 10, the local add/drop can be viewed as another degree. The degree 1M WSSs 14 include two common ports that face the network and M individual ports facing inward, such as via an SS switch 12. The local add/drop 1P WSSs 16 can be the same devices as the degree 1M WSSs 14, but include two common ports connecting to the SS switch 12 and the remaining P ports connecting to subtending equipment, such as for sub-media channel grooming.

[0045] Again, the SS switch 12 provides flexibility connectivity at the spectral slice level between the degree 1M WSSs 14 and the local add/drop 1P WSSs 16. In another embodiment, it is possible to exclude the SS switch 12 and fiber cable the degree 1M WSSs 14 and the local add/drop 1P WSSs 16. Of note, this is less efficient relative to the SS switch 12. For the size of the SS switch 12, it is expected a modest port count will suffice, e.g., 128128. For example, 128128 would allow 8 spectral slices across up to 32 degrees while only having 18 WSS's for the degree WSSs 14, i.e., M=8. This seems sufficient, and is a significant advantage as it allows construction of a large degree site (32 degrees) with full add/drop with conventional optical components. If we start using switch ports for add/drop then we correspondingly reduce the number of degrees (8 add/drop ports is equivalent to one degree in this case).

[0046] Also, for example, 328 slices require a 256256 port central switch. However, this can also be achieved with 2128 port switches configured if connections are not protected (half the capacity through each spine switch). Note, as described herein, the SS switch 12 can be referred to interchangeably as a spine switch, central switch, fiber/space switch, port switch, etc. The switches 12 can also be configured in 1:N (one protection for N working switches) central fabric spines as a mechanism not only to scale interconnect but also to provide redundancy, if required. In this example, 3128 port switches in a 1:2 configuration would provide 8 slices+redundancy. 464 port switches is another configuration that would deliver 8 slices to 32 degrees (5 in a 1:4 config, if protection is required).

[0047] If the spectral slices were fixed, we could use thin film filters or Arrayed Waveguide Grating (AWGs) as this stage, as was done in many conventional ROADMs before the advent of the WSS. The reason to use the WSSs is that we can change the width of each spectral slice to account for differences in the data flow between pairs of degrees/add-drops. It is advantageous using the WSS for spectral shaping and equalization using the WSS. Intra-channel spectral shaping is of increasing importance as channel widths increase.

[0048] For the local add/drop, it is possible to omit the local add/drop 1P WSSs 16. For example, it is possible to connect ports of the SS switch 12 for direct local add/drop. In another embodiment, we could use a simple splitter/combiner, sometimes called a pre-combiner, along with the coherent transponders to allow more than one transponder per space switch port. For example, pre-combiners are described in commonly-assigned U.S. patent application Ser. No. 16/567,023, filed Sep. 11, 2019, and entitled Upgradeable colorless, directionless, and contentionless optical architectures, the contents of which are incorporated by reference in their entirety. For example, the pre-combiners can be directly connected to the SS switch 12.

[0049] Those of ordinary skill in the art will recognize other configurations are also possible to support the architecture of the ROADM 10. Further, the selection of M, N, P, S are implementation specific, and various values are contemplated. The selection of these values is generally a function of component availability, insertion loss, performance, etc. An advantage of the present disclosure is the ability to use conventional optical components. There is no need for a large port count WSS or other advanced switching components.

[0050] The local add/drop 1P WSSs 16 in FIG. 2 are selectively connected to the degree of interest by the space SS switch 12. This is why you could use the common ports of the WSS rather than the switch ports. The common ports can be connected to only one degree in this case (there is only one set of commons). Once connected, the add/drop 1P WSSs 16 can select any slices which are to be sent to/from that degree. It could be the whole spectrum in the extreme. Of course, the ROADM 10 can include multiple add/drop 1P WSSs 16, such as one for each degree.

[0051] FIG. 3 is a diagram of additional detail and connectivity of an N-degree ROADM 10 with a Colorless-Directionless (CD) architecture. The CD architecture includes MN Colorless Channel Multiplexer/Demultiplexer (CCMD) 18. The ROADM 10 includes the MN CCMD 18, labeled as MN CCMD #1, #2, . . . , #(D-X), for local add/drop of channels in a colorless, directionless, and contentionless manner. The number of degrees, X, can be any value between 1 and M. The ROADM 10 includes up to D-X MN CCMDs 18. The MN CCMD is an optical add/drop device that supports M degrees and N channels (optical modems). The MN CCMDs 18 can be implemented using Multicast Switches (MCS) or Contentionless WSS (CWSS), and additional detail of the MN CCMDs 18 is shown in FIGS. 4 and 5. The MN CCMDs 18 are optical add/drop devices that generally include optical amplifiers, Multicast Optical Switches (MCS), etc. and are configured to support colorless multiplexing/demultiplexing in the ROADM 10. The MN CCMDs 18 are directionless meaning any channel can be sent to any degree and contentionless as well, supporting more than one instance of a specific channel in the same MN CCMD 18. Each of the MN CCMDs 18 is connected to up to N optical modems 20. To support directionless operation, each of the MN CCMDs 18 is connected to each of the 1D WSSs 14, such as via the SS switch 16.

[0052] FIG. 4 is a block diagram of an implementation of a Colorless Channel Multiplexer/Demultiplexer (CCMD) 18A utilizing Multicast Switches (MCS). FIG. 5 is a block diagram of an implementation of a CCMD 18B utilizing Contentionless Wavelength Selective Switches (CWSS). Both the CCMDs 18A, 18B are MN devices supporting connectivity to M degrees and N channels/ports per device. The CCMD 18A includes an M-array of 1N splitters/combiners 22, and an N-array of M1 switches 24. The CCMD 18B includes an M-array of 1N WSSs 26 and an N-array of M1 switches 24. Thus the CCMD 18B is a CWSS-based MN CCMD (optical add/drop device). On the channel side (facing the optical modems 20), both the CCMDs 18A, 18B utilize the M1 switches 24 to direct a given channel/wavelength to a specific degree. The fundamental difference is that an MCS (CCMD 18A) uses a combiner to multiplex the channel ports whereas the Contentionless WSS uses a WSS.

[0053] For the MCS (CCMD 18A), when channels are multiplexed with a combiner, the out-of-band Amplified Spontaneous Emission (ASE) from all those channels add up (i.e., noise funneling). This is mitigated in newer optical modems by adding tunable filters at the output to remove the out-of-band ASE. This is because higher order modulation formats cannot afford the Optical Signal-to-Noise Ratio (OSNR) penalty from noise funneling.

[0054] The systems and methods described herein utilize the CWSS (CCMD 18B) with pre-combining of channels to improve channel/port scaling and cost. Conventional CDC architectures generally use the MCS (CCMD 18A), and it is expected that next-generation CDC architectures will move predominantly towards the CWSS (CCMD 18B) approach. Advantageously, the CWSS has a significantly lower loss (e.g., about 7 dB for a 132 WSS versus 13 dB for a 116 splitter), the potential to scale to higher port counts (than the MCS implementation) and channel filtering is built-in in the multiplexing direction to reduce noise funneling. The systems and methods herein address one of the adoption challenges for the CWSS in CDC architectures, namely port scaling and cost per port.

[0055] The CWSS requires two switching elements, namely the M-array of 1N WSS 26 and the N-array of 1M switches 24 (whereas the MCS has a single switching element with combiners/splitters). The M-array of 1N WSS 26 can be realized with a single Liquid Crystal on Silicon (LCoS) chip, and each WSS 26 creates different diffraction angles for individual channels pointing at any of the N channel ports. The N-array of 1M switches 24 can be realized with a Microelectromechanical system (MEMS) mirror array (a Planar Lightwave Circuit (PLC) design also possible) and is configured to point a particular channel port to one of the M-array of 1N WSS 26.

[0056] The MN CCMD 18 can be used for add/drop with programmable interconnect selected by the space switch. This could be accomplished by having the normal 2-stage add drop structure that we'd use for a CD ROADM where there is a WSS with the switch ports connected to the space switch 16 and a MUX/DEMUX element (which could be a fixed filter, a set of power combiners/splitters, or another WSS) connected to the common of the degree WSS. The difference here is that instead of needing the degree facing WSS to have as many ports as there are degrees, one only needs as many ports as supported transponders on that add/drop. In our case this is max 8. Let's assume that we use splitters and combiners and decide that 2 is enough. Then we need only two ports on the degree side and the space switch takes care of directing those 2 spectral slices to which ever degrees we wish. Furthermore, we could replace the WSS and MUX/DEMUX portion with an MN WSS where the M and N are substantially reduced from typical CDC architectures today. We could also use only splitters and combiners and use the wavelength selectivity on the degree WSS to pass only the needed spectral slices on the degree(s) of interest.

[0057] FIG. 6 is a block diagram of a CWSS-based MN CCMD 30 with channel pre-combiners 32, 34. The channel pre-combiners 32, 34 mitigate the limitations of the ROADM architecture by pre-combining channels being added through the CDC ROADM, thus allowing the multiplication of channels per port when they are co-routed (originate and terminate at the same nodes). Of note, the channel pre-combiners 32, 34 can be used to form media channels, spectral slices.

[0058] FIG. 6 illustrates three approaches for channel add/drop with the CWSS-based MN CCMD 30, namely a direct connection with an optical modem 20A, a passive combination of two optical modems 20B with a passive pre-combiner 32, and an amplified combination of four optical modems 20C with an amplified pre-combiner 34. The optical modem 20A directly connects to the CWSS-based MN CCMD 30. Thus one of the N ports of the CWSS-based MN CCMD 30 is used for a single channel. The channel pre-combiners 32, 34 connect in a similar manner as the optical modem 20A, each taking up a port of the N ports of the CWSS-based MN CCMD 30, but the channel pre-combiners 32, 34 have multiple ports on an add/drop side. In this example, the passive pre-combiner 32 has two ports, thus it operates as to double the port it connects to on the CWSS-based MN CCMD 30. The amplified pre-combiner 34 has four ports, thus it operates to quadruple the port it connects to on the CWSS-based MN CCMD 30.

[0059] The channel pre-combiners 32, 34 include couplers 50 in the transmit direction to combine the channels from the optical modems 20B, 20C before they are coupled to the CWSS-based MN CCMD 30. The channel pre-combiners 32, 34 include splitters 52 in the receive direction to split the channels to the optical modems 20B, 20C from the CWSS-based MN CCMD 30. The channel pre-combiners 34 can also include an amplifier 54 in the transmit direction and an amplifier 56 in the receive direction.

[0060] The channel pre-combiners 32, 34 act as a local add/drop port multiplier. Thus, cost/port and the maximum number of ports per CWSS-based MN CCMD 30 scales with the pre-combining. The approach can pre-combine any number of channels (e.g., 2, 3, 4, 5 . . . ) depending on the channel pre-combiners 32, 34. In the example shown here, the pre-combiner 32 supports 2 channels, and the channel pre-combiner 34 supports 4 channels. Those of ordinary skill in the art will recognize any number C, C being an integer, can be supported for pre-combining. However, routing granularity also scales with the number of pre-combined channels, the objective is in finding balance in terms of channels to the group routed. Further, as described herein, a channel is formed by a single physical optical modem 20. The optical modem 20 could support multiple wavelengths, flexible grid spectrum, advanced modulation formats, etc. That is, a port/channel represents a physical connection to the channel pre-combiners 32, 34 connects to a physical port on the CWSS-based MN CCMD 30. Of note, the systems and methods work for different baud rates (e.g., 37, 56, 75, 90GBaud, etc.) as long as the amplifiers factor in the total power required to maintain the power spectral density.

[0061] Of note, there is a need for inter-channel and, especially for the very large spectral slices we contemplate, intra-channel equalization. The most efficient device to do this is the WSS and the simplest implementation of that is to tie it to the degree/direction being equalized. There is an argument that one could use the layer of WSS's to perform these functions, but the complexity of the joint control of the space switch and the WSS shared across channels and degrees makes this more complex and without any benefit of reduced equipment.

[0062] SDM has been proposed as a mechanism to construct larger ROADM nodes by interconnecting multiple ROADM network elements, whereas we are using SDM internal to the ROADM network element to create one large node. That is, the present disclosure utilizes the fiber/space switches 12 for a mechanism to dynamically interconnect WSS modules, i.e., the degrees. Our SDM block replaces the interconnect lines between the WSS modules. The disclosure is about a new method of constructing a wavelength switch based on the premise that future wavelengths with very wide spectral widths can be switched using a different architecture which uses a programmable, partial mesh interconnect of WSS modules (which can be implemented with a space switch), rather than a static, full mesh WSS interconnect (which requires more costly WSS modules that have more ports). This new ROADM architecture could be deployed with or without an external space switch.

[0063] In an embodiment, a ROADM node 10 includes a plurality of degrees 14; one or more add/drop components 16; and one or more fiber/space switches 12, wherein each of the plurality of degrees 14 and the one or more add/drop components 16 connect to the one or more fiber/space switches 12, and the one or more fiber/space switches 12 are configured to interconnect any of the plurality of degrees 14 and the one or more add/drop components 16.

[0064] The plurality of degrees 14 are partially interconnected to one another, while supporting any-to-any interconnect based on a configuration of the one or more fiber/space switches 12. This advantageously enables construction of a large ROADM node 10 with conventional components, namely removing the requirement for higher port count WSSs to support high degree ROADMs.

[0065] Capacity of ports on the plurality of degrees 14 can be defined in terms of spectrum including any of superchannels and media channels. Capacity of ports on the plurality of degrees 14 can be defined in spectral slices including any of 1.2 THz and 600 GHz. A number of ports on a Wavelength Selective Switch (WSS) for each of the plurality of degrees 14 can be equal to or less than a number of spectral slices, each spectral slice including a swath of spectrum switchable in the ROADM node.

[0066] In some examples, the plurality of degrees 14 can include a 1N Wavelength Selective Switch (WSS), N32. The plurality of degrees 14 can include a 18 Wavelength Selective Switch (WSS), for up to 32 degrees and support for 8 spectral slices, each spectral slice including a swath of spectrum switchable in the ROADM node 10, and the one or more fiber/space switches 12 are 128128, or less.

[0067] The one or more add/drop components can include Wavelength Selective Switches (WSSs), thin film filters, Arrayed Waveguide Grating (AWGs), and/or one or more pre-combiners connected to the one or more fiber/space switches. Also, the one or more add/drop components can include direct connectivity between transceiver and the one or more fiber/space switches. This approach is advantageous on new builds or low add/drop counts.

[0068] The ROADM 10 can include control configured to selectively set connectivity of the one or more fiber/space switches. The ROADM node can support switching of up to 9.6 THz of spectrum in a plurality of spectral slices. Also, it is expected that the spectrum band can be in excess of 9.6 THz with the use of other bands, expansion of the C and/or L band, etc., and these embodiments are contemplated with the present disclosure.

[0069] In another embodiment, a ROADM 10 includes one or more fiber/space switches 12 configured to selective interconnect a plurality of degrees 14 and one or more add/drop components 16 such that the plurality of degrees 14 are partially interconnected to one another, while supporting any-to-any interconnect based on a configuration of the one or more fiber/space switches 12, wherein the one or more fiber/space switches 12 switch at a spectral slice level, each spectral slice including a swath of spectrum switchable in the ROADM 10.

[0070] The spectral slice can be greater than or equal to 600 GHz. The ROADM 10 can support switching of up to 9.6 THz of spectrum in a plurality of spectral slices.

[0071] FIG. 7 is a flowchart of a process 100 of operating a ROADM 10. The process 100 includes selectively interconnecting a plurality of degrees and/or one or more add/drop components via one or more fiber/space switches, such that there is a partial interconnect while supporting any-to-any interconnect based on a configuration of the one or more fiber/space switches (step 102); and switching spectral slices via the one or more fiber/space switches between the plurality of degrees and/or the one or more add/drop components, each spectral slice including a swath of spectrum switchable in the ROADM node (step 104).

[0072] The process 100 can include adjusting the interconnecting of the plurality of degrees and/or the one or more add/drop components via the one or more fiber/space switches (step 106). The process 100 can include with the one or more fiber/space switches including two fiber/space switches, selectively switching between the two fiber/space switches based on failures (step 108).

[0073] FIG. 8 is a diagram of the ROADM 10 illustrating inline optical processing, such as with an example all-optical frequency translator 150. Also, this architecture supports inline patching. Imagine there is a useful optical processing function that could be in the optical chain. Today it is really not practical, as interconnect fibers always have more than one channel potentially on them. In this architecture, it is possible to only have a single superchannel on each fiber and therefore each OXC port. These functions could be simple like filtering or amplification, or they could be more complex like optical wavelength conversion or optical regeneration (2R or 3R). One of the main reasons all optical wavelength conversion is not employed today is it is best used with a single channel whereas the architecture described herein is given to that naturally. One could connect these facilities to port-pairs the OXC and use them to process a superchannel through it before Add, Drop or even Passthrough. Optical wavelength conversion would allow the equivalent to Time-Slot-Interchange (TSI) in SONET switching and could be used to unblock optical paths and allow higher spectral utilization in mesh networks.

[0074] FIG. 8 shows a channel routed from one degree to an inline function (optical in/optical out). This example is an all-optical frequency translator which uses optical processing to change the frequency of the light without affecting the modulation. This could be achieved by creating a copy of the input signal using non-linear processes like four-wave mixing. Only one path is shown where a frequency 152 light ingresses at degree one, is translated to frequency 154 and then egresses at degree N. There is a complementary reverse path the flows from degree N to degree 1 and is translated from frequency 154 to frequency 152 which is not shown for clarity. This allows for programmable frequency translation in the optical domain which can reduce frequency blocking in a mesh network. Other optional in-line functions are contemplated as described above.

[0075] In some embodiments, the direct connectivity of the optical modems 20 to the fiber/space switch 12 can include what hyperscale operators refer to, for exemplary purposes, as a Full-Spectrum-Transponder (FST). As used herein, the term transponder encompasses implementations that include one or more modems 20 (e.g., line-side modem functions with associated optics/DSP), and the terms modem and transponder may be used together where context permits. An FST is an integrated transponder unit that contains sufficient modem capacity to light up a wide range of spectrum via a single line-fiber interface. In certain examples, this may correspond to substantially an entire amplified band (e.g., C-band or L-band), more than a single band, or less than a full band. The key aspect is that the FST, or an equivalent device, provides wide-spectrum channel outputs that can be advantageously utilized with the ROADM architecture described herein. For example, a single FST may support on the order of 25.6 Tbps across approximately 4800 GHz of spectrum in one band.

[0076] The FST may be physically realized in many configurations, including but not limited to multiple modems 20, optical components, client optics, and associated circuitry co-packaged into a single unit, device, chassis, module, or other form factor. In some embodiments, the FST is implemented as a rack-mounted chassis with redundant power and cooling, while in other embodiments it may be realized as a field-replaceable module or card integrated into a larger optical transport platform. Those skilled in the art will recognize that the particular physical packaging is implementation-specific and can vary based on operator needs, equipment footprint, integration strategy, technology, etc.

[0077] The key aspect of the FST in the context of the ROADM architecture described herein is that the service hand-off can occur through a highly aggregated set of client interfaces (e.g., 64400GE, 32800GE, or other combinations) with line-side transport delivered via a single wide-spectrum line port. The wide-spectrum line port may carry substantially an entire band, more than one band, or a large fraction of a band, depending on system design and traffic requirements. This architecture simplifies operations compared with traditional systems that typically require multiple line interfaces, e.g., often one per channel, resulting in a large number of external fiber connections. By contrast, the FST architecture aggregates capacity into a single or small number of wide-spectrum outputs, thereby significantly reducing external fiber management complexity, lowering operational risk, and streamlining provisioning. In effect, the line-side of the FST provides a single logical connection with wide-spectrum transport capability, which aligns advantageously with the spectral-slice-based ROADM node described herein.

[0078] Because the FST terminates a wide spectrum on its line side, it is particularly well suited for direct connection to the fiber/space switch 12 in the ROADM node 10, thereby eliminating the need for intermediate add/drop WSS stages that would otherwise be required for per-channel or per-slice add/drop. In this configuration, the fiber/space switch 12 can treat the FST as an add/drop degree corresponding to an entire spectral band, more than one band, or a large fraction of a band, depending on the implementation. The WSS elements 14 in the ROADM node can then be utilized to define the slice granularity, apply variable-width spectral slicing, and perform functions such as spectral shaping or equalization prior to or after routing through the fiber/space switch 12.

[0079] This arrangement enables efficient end-to-end transport of very wide spectral slices in a manner that significantly reduces operational complexity and insertion loss compared with architectures that rely on channel-level add/drop. By collapsing what would otherwise require dozens or even hundreds of discrete line-side ports into a single wide-spectrum connection, the ROADM architecture benefits from reduced port consumption on the fiber/space switch 12, simplified fiber management, and improved optical performance. This also allows network operators to more easily scale capacity while maintaining flexibility in traffic grooming, since the WSS elements 14 continue to provide per-slice programmability even when the FST is treated as a full-band add/drop device.

[0080] The FST can further include redundant and field-replaceable subsystems, such as power modules, fan modules, and control processors, to maintain high availability and resiliency in carrier-class deployments. In operation, individual optical modems 20 within the FST may fail gracefully while the chassis continues to transport the remaining modems 20 and associated spectrum. Spare or backup capacity can be utilized to protect against such failures, and the FST chassis may be replaced when thresholds of channel or modem failures are reached. This approach provides a cost-, power-, and space-optimized package for scaling nodal capacity in large ROADM deployments, while aligning well with the partial-mesh and spectral-slice switching architecture described herein.

[0081] Referring back to FIG. 1, each degree is formed by the WSS14 interfacing with network fibers, shown here as Fiber OMS sections. The degree WSSs 14 provide slice ports that are interconnected via the fiber/space switch 12, which may be deployed in a protected configuration with dual switch fabrics. In conventional implementations, local add/drop functionality is realized through separate channel add/drop modules that connect into the fiber/space switch 12. These modules can be treated as an additional degree of the node, in the same manner as network-facing degrees. In the configuration of FIG. 1, add/drop ports are therefore logically represented as another degree coupled through the central switch fabric.

[0082] In some embodiments, the add/drop function is provided by the FST which connects directly to the fiber/space switch 12. Unlike traditional arrangements where an add/drop path includes intervening multiplexers/demultiplexers, the FST integrates these functions internally and provides a single wide-spectrum line-side connection. As such, the FST can be directly switched by the fiber/space switch 12 without requiring external multiplexing equipment. This simplifies the optical interconnect, reduces insertion loss, and collapses what would otherwise be multiple line-side connections into one wide-spectrum connection. Because the FST terminates wide spectrum, the fiber/space switch 12 can treat the FST as an add/drop degree, similar to any other ROADM degree. The degree WSSs 14 in the node may continue to define the granularity of spectral slices, providing variable slice widths and performing shaping or equalization prior to routing through the switch fabric. In this way, wide-spectrum outputs from the FST are advantageously combined with spectral-slice switching in the ROADM to enable efficient high-capacity add/drop.

[0083] For control of the ROADM node and the fiber/space switches 12, it will be appreciated that some embodiments described herein may include or utilize one or more generic or specialized processors (one or more processors) such as microprocessors; Central Processing Units (CPUs); Digital Signal Processors (DSPs): customized processors such as Network Processors (NPs) or Network Processing Units (NPUs), Graphics Processing Units (GPUs), or the like; Field-Programmable Gate Arrays (FPGAs); and the like along with unique stored program instructions (including both software and firmware) for control thereof to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the methods and/or systems described herein. Alternatively, some or all functions may be implemented by a state machine that has no stored program instructions, or in one or more Application-Specific Integrated Circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic or circuitry. Of course, a combination of the aforementioned approaches may be used. For some of the embodiments described herein, a corresponding device in hardware and optionally with software, firmware, and a combination thereof can be referred to as circuitry configured to, logic configured to, etc. perform a set of operations, steps, methods, processes, algorithms, functions, techniques, etc. on digital and/or analog signals as described herein for the various embodiments.

[0084] Moreover, some embodiments may include a non-transitory computer-readable medium having instructions stored thereon for programming a computer, server, appliance, device, at least one processor, circuit/circuitry, etc. to perform functions as described and claimed herein. Examples of such non-transitory computer-readable medium include, but are not limited to, a hard disk, an optical storage device, a magnetic storage device, a Read-Only Memory (ROM), a Programmable ROM (PROM), an Erasable PROM (EPROM), an Electrically EPROM (EEPROM), Flash memory, and the like. When stored in the non-transitory computer-readable medium, software can include instructions executable by one or more processors (e.g., any type of programmable circuitry or logic) that, in response to such execution, cause the one or more processors to perform a set of operations, steps, methods, processes, algorithms, functions, techniques, etc. as described herein for the various embodiments.

[0085] Although the present disclosure has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present disclosure, are contemplated thereby, and are intended to be covered by the following claims. Moreover, it is noted that the various elements, operations, steps, methods, processes, algorithms, functions, techniques, etc. described herein can be used in any and all combinations with each other.