In an optical communications network, an optical signal is modulated with digital information and transmitted over a length of optical fiber from a source location to a destination location. An optical cross-connect module allows switching of optical signals from one optical fiber to another. A multicasting optical switch allows one to switch optical signals from one optical fiber to not one but, simultaneously, to a plurality of optical fibers, or to switch optical signals from a plurality of input optical fibers to a plurality of output optical fibers, such that optical signals in any of the input optical fibers can be multicast into non-overlapping subsets of the plurality of the output optical fibers.
By way of example, referring to FIG. 1A, a 8×8 multicast optical switch 100 of the prior art includes eight input fibers 102, eight optical amplifiers 104, eight 1:8 optical splitters 106, eight 8×1 optical switches 108, and eight channel filters 110 coupled to output fibers 112. Each 1:8 splitter 106 connects an output of each amplifier 104 to an input of each 8×1 switch 108. A crossover region 107 includes a plurality of optical fibers connecting each of the eight outputs of each 1:8 splitter 106 to an input of each 8×1 switch 108. In operation, the amplifiers 104 boost multi-wavelength optical signals in the input fibers 102 to compensate for subsequent optical power splitting by the 1:8 splitters 106. Multi-wavelength signals from each of the eight input fibers 102 are present at the eight inputs of each 8×1 switch 108, which function to select multi-wavelength signals from only one of the input fibers 102. Since the 8×1 switches 108 operate independently on each other, the optical signals from any of the input fibers 102 can be multicast into any subset of the channel filters 110. The channel filters 110 select a channel of interest, that is, an optical signal at a particular center wavelength, to be outputted at the output fibers 112. The amplifiers 104 and the channel filters 110 are optional, and are included in FIG. 1A by way of an example. If the channel filters 110 are not included, the entire multi-wavelength signals will be present in the output fibers 112. Without the amplifiers 104, the signal will appear attenuated at the output fibers 112.
One drawback of the multicast optical switch 100 is complexity. The 1:8 splitters 106 and the 8×1 switches 108 are separate devices connected with a multitude of optical fibers in the crossover region 107, which complicates assembly, increases outer dimensions, and heightens optical losses. Since the 1:8 splitters 106 and the 8×1 switches 108 can both be fabricated using planar lightwave circuit (PLC) technology, one can integrate these components together onto a single substrate to obtain a relatively compact and inexpensive device, as compared with separate splitter and switch components of the multicast optical switch 100. At least two vendors—Enablence of Toronto, Canada; and Neophotonics of San Jose, USA—are offering such products. However, one challenge with the PLC implementation is the large number of waveguide crossovers involved. Referring now to FIG. 1B, a waveguide crossover region 117 of a 8×16 PLC multicast optical switch is shown. The example waveguide layout in FIG. 1B illustrates the large number of the waveguide crossovers. Even in a simpler case of an 8×12 multicast switch, a single waveguide has to cross up to 83 other waveguides before exiting the PLC. Each waveguide crossing adds loss and creates a possibility for unwanted crosstalk.
Accordingly, it is an object of the invention to provide a less complex multicast optical switch, which would not require waveguide or fiber crossovers.