Design of wavelength cross-connects based on permutations among fibers

A wavelength cross-connect (WXC) is an optical cross-connect with external stage of wavelength converters. It is a crucial element in a wavelength division multiplexing (WDM) network. A new type of WXC, namely wavelength-exchanging cross-connect (WEX), was recently proposed. Because WEX can simultaneously perform switching and wavelength converting, it has low hardware complexity. To achieve switching nonblocking, the designs of current WXCs (including WEXs) are based on full-permutation switching, which provides any permutation of input signals at the output of the cross-connect. This may result in routing of various wavelengths originating from a fiber to a particular fiber; and they may also perform wavelength converting. Such permutations may not be necessary in a WDM network. We propose a novel concept to design WEXs, which is based on the permutations among output fibers, but not among output ports. This leads to the reduction of the number of permutations, as well as the complexity of WEXs. In designing such WEXs, we propose the following method: (i) using a permutation matrix to describe the operation of a 2x2 element in a WEX; and (ii) applying a permutation matrix product rule to simplify the architecture of the WEX.