Optical combiner for a ring laser gyro

Abstract

The apparatus of this invention is a composite combining prism for combining the beams of a ring laser gyro. It uses a composite prism whose trunk is fabricated of two substantially identical juxtaposed sub-prisms having beam splitters in the region where laser beams cross their common boundary. The beam splitter regions are very thin dielectric films, typically no thicker than a fraction of a wavelength of the laser light. Dielectric films, such as titanium dioxide, are used for the splitters so that the geometrical path lengths of interfering beams are almost exactly the same. To make the path lengths optically the same, the two sub-prisms and the substrate of the partly transmitting corner mirror of the ring laser preferably have the same index of refraction. In a first embodiment, the outwardly-extending trunk of the assembled composite prism is substantially rectangular in cross-section. It is split into two identical sub-prisms with negligible-thickness beam splitters at the common interface of the sub-prisms. It has a slanted outward end carrying two combining light heterodyne sensors. To reduce the outward extension of the prism from the ring laser gyro another embodiment has the composite prism lying flat on the substrate of the partly transmitting corner mirror. It uses a forty five degree prism surface to turn the laser light through a right angle to deliver the outwardly directed laser beams into a direction parallel to the surface of the mirror substrate.