Infrared Isolator Using Yttrium Iron Garnet

摘要

Infrared isolators using the Faraday rotation in a single crystal Yttrium Iron Garnet (YIG) and calcite dichroic polarizers have been built. By using the YIG crystal with thorium fluoride antireflection coating the authors obtained isolation better than 32 dB and the insertion loss smaller than 1.8 Db and 1.3 dB at He-Xe 3.5 micron and He-Ne 3.39 micron gas laser lines, respectively. The basic principles of isolators, theory of magneto-optical effect, and Faraday effect in various magnetic materials are surveyed. The optical and magnetic properties of single crystal YIG are examined. The design and performance of infrared isolaters using 45-degree Faraday rotation in a single crystal YIG (6mm long, 3mm diameter) with a small permanent magnet and calcite dichroic polarizers is described. The isolation of the YIG isolator is practically limited by the induced ellipticity due to internal multiple reflections, boundary effect, and magnetic birefringence produced in YIG. Improvement of isolation due to the antireflection coating is discussed. A few representative applications of YIG isolator to unilateral laser amplifiers systems to decoupling a laser from a Fabry-Perot interferometer and also to the ring laser gyroscopy are described. (Author)