To convert an optical isolator to a high performance optical circulator having high cost effectiveness by arranging optical elements adjacently to first and third ports in such a manner that the desired orientation is established with respect to the polarized light components of parallel first and third light beams introduced via the ports.

The first two optical elements 18 and 20 at the front end of an assembly 10 form a polarized light mixer. The light beams are propagated through the polarized light mixer forward from the first and third fibers 12 and 14, by which the two beams respectively having the polarized light components are generated. The steps for the polarized light combiner formed by the third and fourth optical elements 26 and 28 in the assembly 10 are set by this 'mixing' of the polarized light components. The polarized light combiner recouples the two polarized light components of the first beam from the first fiber 12 and shifts the two polarized light components of the third beam from the third fiber 14 to both sides of the recoupled first beam.