Faraday rotation variable attenuator

摘要

A variable optical attenuator comprises a Faraday rotator including a ferromagnetic garnet film disposed input/output single mode optical signal paths. A collimating/lensing arrangement is used to focus the optical signal between the input/output signal paths and the ferromagnetic garnet film. The ferromagnetic material exhibits multiple types of magnetic domain such that an optical signal will experience ±rotation as its passes through the film. A 90° garnet film thus provides ±90° rotation, resulting in a fill 180° directional difference between the optical signal components. The amplitudes of these signals will thus cancel, providing an essential "full" attenuation of the optical signal. The application and adjustment of a magnetic field to the garnet film controls the strength (i.e., size and area) of each type of magnetic domain within the ferromagnetic material so as to control the amount of optical signal cancellation and, therefore, the degree of attenuation at the output of the arrangement.