Optical switch

PURPOSE:To drive an optical switch easily by a small magnetic field by using a 45 deg. Faraday rotator thin plate with a phase matching film and a 45 deg. rotary polarizer in combination as a polarization plane converting element. CONSTITUTION:Incident light beams 1 and 2 are separated by a polarizing and separating element 3, and the transmitted and reflected beams are passed through Faraday rotators 4 and 4' to rotate their planes of polarization by +45 deg. or -45 deg.; and they are passed through 45 deg. rotary polarizers 5 and 5' to further rotate the planes of polarization by 45 deg., and then caused to illuminate wedge- shaped polarizing and separating elements 6 and 6' which reflect two orthogonal polarized beams in slightly different directions. Since the reflected light beams pass through the 45 deg. rotary polarizers 5 and 5' and 45 deg. Faraday rotators 4 and 4', they are polarized light beam crossing the original light beams at right angles. Therefore, the light 7 from the rotator 4 is transmitted and the light 8 from the rotator 4' is reflected, eliminating polarization dependency. The magnetization of the Faraday rotators is inverted, and thus the switching of luminous flux to A or B is possible.