Magneto-optic circulator for optical fiber transmission

We have developed a polarization-independent optical circulator for optical transmission systems whose overall dimensions are 25×18×18 mm3. The insertion losses and the isolations of the circulator are about 2.0–2.2 and 20–21 dB, respectively, at a 1.3-μm wavelength. The circulator consists of ‘‘polarization separators’’ on either side of a Faraday rotator and a λ/2 retardation plate. The polarization separator separates the incident beam into two polarized parallel beams with orthogonal linear polarizations. The separation of the two beams is 3.2 mm. The Faraday rotator consists of a yttrium-iron-garnet (YIG) crystal and Sm-Co permanent magnets. The size of the YIG block is 2.25 mm length×4.5 mm width×1.5 mm thick. The half-wave plate of the circulator is made of a white mica.