A simple structure for a high-isolation polarization-independent optical circulator is proposed. A four-port circulator has been assembled for 1.3-μm single-mode fiber systems. Its insertion loss and isolation have been measured to be ≦2.0 and ≧44.0 dB, respectively, at a wavelength of 1.298 μm. The isolation, which is free from reflections, is measured to be ≧64.2 dB.
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