Polarization-based technique for separating copropagating waves of different wavelengths

Abstract

A polarization-based technique is described that splits two copropagating waves of different wavelengths into separate monochromatic waves that travel in orthogonal directions. The technique uses a simple modular optical train that consists of a linear polarizer, a birefringent-plate linear retarder, and a polarizing beamsplitter cube. The birefringent plate is a key element and must operate, simultaneously, as a full-wave (virtually absent) plate at one wavelength and as a half-wave plate at the other. Examples of such plates that use crystalline quartz and mica are presented. The minimum wavelength separation of two channels that can be split apart using this method is given. It is also shown how three or more wavelength channels can be separated by cascading modules of this kind.