All-fiber-optic polarization state azimuth control: application to Faraday rotation

An all fiber-optic system for the control and modulation of the azimuth of a linearly polarized beam is described. The experimental configuration is basically that of a Mach-Zehnder interferometer but with the birefringence of the two fiber arms controlled to produce orthogonal circular states of polarization which recombine in the final directional coupler. Azimuth control is then achieved by relative phase modulation using a piezo-electric element. The system has required the use of monomode fiber directional couplers of accurately characterized polarization properties, and the development of fiber linear retarders. The application of the system in the measurement of electric currents via Faraday rotation is described, although extensions to other types of optical instrument are equally feasible