Abstract: An apparatus and method for converting a signal of arbitrary polarization one of preselected polarization, e.g. for use by a sensor, transducer, etc. A signal splitter divides the input signal into its orthogonal linearly polarized components, and launches the components from a pair of output ports. The signals counterpropagate to the opposite port, and, while counterpropagating, are rotated into the same linear polarization state. In one embodiment, the rotation is done by a pair of complementary 45.degree. Faraday rotators; in another, by one 90.degree. rotator. In the former, the signal is recombined at the splitter in the initial state of polarization that in which the signal initially entered the splitter; in the latter, the recombined signal is of orthoconjugate polarization to the input signal.