Methods and apparatus for constructing large wavelength selective switches using parallelism
View Patent ↗Optical networks are increasingly employing optical network nodes having multiple interfaces to allow a node to direct optical signals received at any interface to any other interface connected to the node. Constructing a larger wavelength selective switching (WSS) module used in such a node can be complex and expensive. A method an apparatus for constructing a large WSS using parallelism is provided. In example embodiments, a larger WSS may include multiple parallel non-cascaded smaller WSSs and an optical coupler configured to optically couple the multiple parallel, non-cascaded smaller WSSs. This technique may be used to construct both N×1 and 1×N WSSs. Because the technique employs multiple parallel, non-cascaded WSSs, all inputs of a larger N×1 WSS and all outputs of a larger 1×N WSS are available receive or transmit external signals rather than being rather than being unavailable due to, for example, cascading smaller WSS devices together.
1. An optical network node, comprising:
at least two multi-degree reconfigurable optical add/drop modules (ROADMs), each ROADM including a wavelength-selective switch (WSS), the WSS including multiple parallel non-cascaded sub-WSSs; and
intra-network node paths configured to interconnect the at least two ROADMs to enable a given ROADM to direct optical signals received at the given ROADM to any other interconnected ROADM.
2. The node as claimed in claim 1 , further comprising:
add paths configured to add optical signals from tributary paths to inter-node network paths;
drop paths configured to drop optical signals from the inter-node network paths to tributary paths; and
express paths configured to pass optical signals to the inter-node network paths, wherein an insertion loss for the express paths is lower than an insertion loss of the add paths or drop paths.
3. The node as claimed in claim 2 wherein the drop paths include dedicated drop paths and express drop paths, the express drop paths being output from the WSS.
4. The node as claimed in claim 2 wherein at least a subset of the drop paths are coupled to an output of a sub-WSS and selectively configured to be drop paths or express paths.
5. The node as claimed in claim 2 further comprising an optical amplifier configured to amplify signals travelling along the drop paths, the drop paths including dedicated drop paths and express drop paths configurable to be both dedicated drop paths or express drop paths.
6. The node as claimed in claim 2 further comprising an optical amplifier disposed along an add path.
7. The node as claimed in claim 6 wherein the optical amplifier is coupled to the output of a sub-WSS.
8. The node as claimed in claim 6 wherein the optical amplifier is coupled to an input of a sub-WSS.
9. The node as claimed in claim 2 further comprising a tunable filter array disposed along the drop paths.
10. The node as claimed in claim 2 further comprising an optical coupler disposed along the add paths.
11. A method for processing optical signals in an optical network node having at least two multi-degree reconfigurable optical add/drop modules (ROADMs), the method comprising:
performing parallel non-cascaded wavelength selective switching of optical signals having multiple wavelengths;
directing wavelengths in a selective manner from a first ROADM to a second ROADM in the optical network node via the intra-network node network paths and to other optical network nodes.
12. The method as claimed in claim 11 , further comprising:
adding optical signals from tributary paths;
dropping optical signals to the tributary paths;
interconnecting express paths of each ROADM in the optical node via intra-network node network paths;
coupling multiple optical paths associated with the parallel non-cascaded wavelength selective switching to a common optical path wherein coupling the multiple optical paths includes performing cascaded optical coupling.
13. The method as claimed in claim 12 wherein performing the wavelength-selective switching includes coupling an output expansion path associated with a wavelength-selective switching group to the common optical path.
14. The method as claimed in claim 13 , further comprising:
amplifying the optical signals in the output expansion path.
15. The method as claimed in claim 12 wherein coupling the multiple optical paths includes:
coupling multiple optical path groups, wherein each group is associated with respective multiple parallel non-cascaded wavelength selective switching; and
combining the coupled groups onto the common optical path via a combining WSS.
16. A reconfigurable optical add/drop module (ROADM), comprising:
at least two multi-degree wavelength filtering devices, each filtering device including:
a light distributor configured to receive a first optical signal along a subtending input and to distribute the optical signal received along a plurality of subtending outputs; and
a light combiner configured to receive second optical signals along a plurality of subtending inputs, to combine the second optical signals received into
a combined signal, and to output the combined signal; and
a parallel non-cascaded wavelength selective switch (WSS) coupled to at least one of the multi-degree wavelength filtering devices.
17. The ROADM of claim 16 wherein the at least two wavelength filtering devices are WSSs.
18. The ROADM of claim 17 wherein a first WSS is configured to forward wavelengths to the at least one dedicated express port, and a second WSS is used to forward wavelengths to the at least one dedicated drop port and the at least one express drop port.
19. The ROADM of claim 16 wherein at least one wavelength filtering device is a WSS and at least one wavelength filtering device is a tunable filter array.
20. The ROADM of claim 19 , wherein each filtering device includes:
a first set of add ports configured to add signals only;
a second set of add ports configurable to add signals or to transmit signals to second ROADM;
a first set of drop ports configured to drop signals only; and
a second set of drop ports configurable to drop signals or to transmit signals to the second ROADM; and
wherein each WSS is configured to forward wavelengths to the at least one dedicated express port and the at least one express drop port, and the tunable filter array is configured to forward wavelengths to the at least one dedicated drop port.