Design of a compact optical isolator

Reports on a compact optical isolator design in which the (Faraday) rotator is composed of a wafer of bismuth substituted gadolinium iron garnet in a saturating magnetic field produced by miniature high energy cylindrical rare-earth magnets. The Faraday rotator is introduced into the optical path using single-mode birefringent fibre tapers, which expand the propagating mode-field radius and enable efficient coupling through the garnet wafer whilst maintaining the linear polarisation state necessary for good isolation; High isolation values can be maintained in the presence of errors in the nonreciprocal rotation, using a simple relative adjustment of the fibre birefringence axes