h' r.times.h optical switches each being connected to said h h'.times.n/h' optical switches; an i-th h'.times.m/h' optical switch, i being an integer between 1 and h, including 1 and h, in each ofsaid n/h' input optical switch groups of each of said r/h input matrix switches is connected to an i-th n/h'.times.h' optical switch of each of said m/h' nh/h'.times.h'r optical switches of the r/h input