A compact optical isolator with a plano-convex YIG lens for laser-to-fiber coupling

An optical isolator for laser-to-single-mode fiber coupling is discussed. The coupling unit consists of a confocal two-lens system with a spherical glass lens and a planoconvex lens which is made of yttrium iron garnet (YIG). To minimize the number of elements, the YIG lens is used as a Faraday rotator as well as a coupling lens. Nevertheless, the planoconvex YIG lens satisfies the requirements of high coupling efficiency, high isolation, and low optical feedback from the Faraday rotator. The arrangement is theoretically and experimentally investigated. At a coupling efficiency of 34%, the total optical feedback into the laser diode was measured to be about -60 dB