Compact high-efficiency electrically-addressable phase-only spatial light modulator

A compact electrically-addressable spatial light phase modulator module is described. The module consists of an electrically-addressed liquid crystal display (LCD), an optically-addressed phase-only spatial light modulator (SLM), one of which substrates is a fiber optic plate (FOP), a laser diode, and collimating optics for it. The module size is 95 mm long 55 mm wide, and 90 mm high. The module had a nearly 100% reflectivity and a diffraction efficiency close to the theoretical maximum. Surplus diffraction light caused by the pixelized structure was reduced to approximately 3%, almost 50% of which was in the LCD alone. A reflection type of SLM would cause another power loss of the readout light by a half mirror, which was set up so as to separate the incident and reflected lights. An oblique incidence readout method was evaluated in the module, instead of the half mirror scheme, for the readout. We have found adequate alignments among the polarization and incident directions of the readout light, and the corresponding liquid crystal orientation. Consequently, almost no degradation in diffraction efficiency was observed for the incident angle within 45 degrees.