Magneto-optic circulator for optical fiber transmission (abstract)

We have developed a polarization-independent optical circulator for optical transmission systems whose overall dimensions are 25×18×18 mm. The configuration of the circulator is shown in Fig. 1. The insertion losses and the isolations of the circulator are about 2.0–2.2 and 20–21 dB, respectively, at 1.3 μm wavelength. The circulator has four ports. The nonreciprocal paths of the circulator are 1–3, 2–4, 3–2, and 4–1. The prisms of the polarization separator of the circulator were pestered with a kind of estersil. The refraction index of the estersil is 1.46 at 1.3 μm wavelength. The polarization separator separates the incident beam into two polarized beams with polarization planes perpendicular to each other. The distance of the two beams is 3.2 mm. A Faraday rotator consists of an 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) thickness. The two polarized beams are transmitted along the longitudinal direction of the YIG crystal block. The applied magnetic field of the YIG crystal is produced by Sm-Co permanent magnets. The half-wave plate of the circulator is made of a white mica.