Abstract: An optical circulator having reduced size and low polarization mode dispersion is disclosed. A transparent optical circulator comprises a first birefringent crystal, a first pair of Faraday polarization rotators having two Faraday polarization rotators aligned in parallel with the propagation direction of an optical signal, a second birefringent crystal, a second pair of Faraday polarization rotators similar to the first pair of Faraday polarization rotators, and a third birefringent crystal. The optical circulator with a reflector or an input/output device and the Faraday rotators together reduce the total size of the circulator, increase the number of input/output ports, and improve the propagation quality of the optical signal by decreasing the polarization mode dispersion. A reflective optical circulator is also presented.

Abstract: An optical isolator is placed in the path of an input optical fiber and an output optical fiber, the optical isolator comprises: a first GRIN lens for receiving rays emitted from the input optical fiber and converging into parallel rays; a first birefringent crystal wedge for splitting the parallel rays into a first ray polarized along the birefringent crystal's optical axis and a second ray polarized perpendicularly to the optical axis; a second birefringent crystal wedge for recombining the first ray and the second ray wherein at least one of the first birefringent crystal wedge and the second birefringent crystal wedge comprises a birefringent crystal of YVO.sub.

Abstract: A system for measuring the strength of fiber optical current in an AC magnetic field by adopting Faraday effect and temperature compensation. In general, the current measurement systems that adopt Faraday effect have the structure including a Faraday element, a polarizer and an analyzer. When a light beam is directed through the Faraday element, the plane of polarization rotates according to the strength of induced magnetic field and Verdet constant in the Faraday element. The rotation affects the optical intensity sensed by the analyzer. The variation on light intensity after passing through the analyzer is converted into an electric current by a optical-electric transducer. But the accuracy of this system this system always affected by the ambient environment, wherein the major factor is the thermal effect of Verdet constant.