Abstract: A compact high quality and lightweight symbol generator for projecting symbolic information into the field of view of a viewfinder is provided. The symbol generator comprises at least one ESBG device sandwiched between a pair of transparent plates which together function as a total internal reflection lightguide, switching electrodes and means for coupling illumination into the lightguide. Each ESBG device contains information encoded in a multiplicity of separately switchable grating regions. A plurality of independently switchable transparent electrodes elements, substantially overlay the separately switchable grating regions. When no electric field is applied, the ESBG device is in its diffracting state and projects images of said information towards the viewer. The projected images are surimposed onto an image of the external scene. When an electric field is applied the ESBG no longer diffracts and hence3 no information is displayed.

Abstract: A polarization rotating optical device is provided. The device comprises a prism configured to accept an input collimated optical beam and redirect the beam by means of total internal reflection at three or more faces of the prism. The first face reflects an incident collimated beam at an angle of 90 degrees with respect to the original beam direction. The incident and reflected beams are comprised of orthogonal s and p polarized components, where the s and p directions are defined with respect to the plane containing the incident and reflected beam directions in the conventional manner. One or more prism faces then reflect the beam within the plane normal to the incident beam. The sum of the included angles of these reflections must total an odd multiple of 90 degrees. The final prism face reflects the beam by 90 degrees in a third plane orthogonal to the planes of the preceding reflection.