High-speed photonic switching networks can switch optical signals at the rate of several terabits per second. However, they suffer from an intrinsic crosstalk problem when two optical signals cross at the same switch element. To avoid crosstalk, active connections must be node disjoint in the switching network. In this paper, a sequence of decomposition and merge operations, called conjugate transformation, performed on each switch element to tackle this problem, is proposed. The network resulting from this transformation is called the conjugate network. By using the numbering schemes of networks, the authors prove that if the route assignments in the original network are link disjoint, their corresponding ones in the conjugate network would be node disjoint. Thus, traditional nonblocking switching networks can be transformed into crosstalk-free optical switches in a routine manner. Furthermore, it has been shown that crosstalk-free multicast switches can also be obtained from existing nonblocking multicast switches via the same conjugate transformation.
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