Crystal-based Devices — High-power Optical Isolators

The research and application of fiber lasers flourish in recent years. Optical isolators are important devices to ensure the reliability of fiber lasers. Depending on the actual applications, different types of optical isolator are employed. For some applications under relatively low optical power, wedge-type in-line optical isolator is employed, just with more consideration on heat dissipation. While for some applications under high optical power, BD-type in-line optical isolator is employed instead of wedge-type. The reason is that the FR for telecom applications can’t be used anymore.

Crystal-based Devices— Basics for Crystal Optics

Birefringent crystals are widely used to fabricate optical passive devices such as optical isolator, optical circulator, polarization beam combiner/splitter, optical interleaver. The mostly used crystals are uniaxial, such as YVO4 and LiNbO3.

Birefringence in Uniaxial Crystal
Wave normal K is the normal of equalphase surface which describes the transmission of wave phase. Ray S is the normal of wave front which describes the transmission of optical energy. When light incidents on the air-crystal (uniaxial) interface, there are usually two refractive rays, o-ray So and e-ray Se. The direction of each ray depends on the direction of corresponding wave normal.