Wavelength Selective Switch (WSS)

The switching element inside a Reconfigurable Optical Add-Drop Multiplexer (ROADM).

A WSS typically comes in a 1xN format, with one fiber going in and going out. One of the outgoing fibers is an express lane, for the DWDM wavelengths that aren't being added or dropped by this particular ROADM. The remaining fibers can be used to add or drop wavelengths -- so, a 1x9 WSS creates a ROADM that can add or drop 8 wavelengths.

Vendors are starting work on 1x23 WSSs, but the most commonly used types are still the small ones, as small as 1x2.

WSSs are available with 100GHz and 50GHz ITU grid spacing, and some components vendors say they can also go "gridless," using software to assign wavelengths that aren't confined to one ITU grid assignment. (See OFC/NFOEC: For ROADMs, Less Is More.) JDSU and Finisar design their own WSSs. A handful of startups also deliver WSSs, including Capella Photonics Inc. , CoAdna Photonics Inc. , and Nistica .

phizaleo 12/5/2012 | 4:24:40 PM
re: Wavelength Selective Switch (WSS)

Craig, thanks for the note, i'm a fan.

The statement

"so, a 1x9 WSS creates a ROADM that can add or drop 8 wavelengths."  isn't 100% correct.  the 1x9 WSS makes this ROADM an 8 Degree ROADM.  Each degree/direction/fiber pair typically has several wavelengths (ie 80 or 88 in a 50Ghz spaced system or half that in a typical 100Ghz spaced system).  So a 1x9 WSS may be carrying 704 wavelengths.  My understanding is that the 1x23 WSS like we saw in action at OFC will be primarily used in colorless/directionless applications.


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