Hybrid optical circulator using garnet-quartz composite embedded in planar waveguides

A novel hybrid configuration of optical circulator is presented. A Garnet-Quartz composite (GQC), which is comprised of four quarter-wave plates and Faraday rotator, is embedded into a groove formed across the branching waveguides pair of Mach-Zehnder interferometer. Optical path difference of the pair is 0 rad for forward path, whereas /spl pi/ for backward path with the GQC, realizing nonreciprocal operation. The forward-to-reverse isolation of 16.2-29.8 dB and the insertion loss of 8.8-9.4 dB are obtained.