An optical 90 degrees hybrid comprising a single-mode fiber coupler and a polarization beam splitter was made at 0.82 microm. It relies on the phase retardation intentionally induced in one of the input fiber leads of the coupler. By properly choosing the transmission/coupling coefficient as well as the orientation of the polarization beam splitter following the coupler, optimum distribution of the available optical fields can be obtained in a Costas loop.