This paper introduces a simple O(N) algorithm that decomposes BPC (bit-permutecomplement) permutations into semi-permutations for avoiding crosstalk when realizing them in N × N optical multistage interconnection networks (OMINs). Crosstalk means that two optical signals, sharing an optical switch, undergo a kind of undesired coupling. A semipermutation is a partial permutation which meets the requirement for each switch in an input and output stages of the network to be used with only one optical signal at a time. It provides avoiding ...