Electrically addressed spatial light phase modulator

A nonpixelized electrically addressable spatial light phase-only modulator has been developed. The device consists of an optically addressed parallel aligned nematic liquid crystal spatial light modulator (PAL-SLM), coupling optics, an XGA liquid crystal display (LCD) which serves as an accurate addressable mask for the PAL-SLM, a laser diode (LD) for illuminating the LCD and collimating optics for the LD. The device has a phase modulation capability of over 2pi radians and a high diffraction efficiency of greater than 35% at a spatial frequency of 10 1p/mm of binary (0,pi) grating. Also when a multilevel (0, 0.5pi, pi, 1.5pi) grating was written in the device, a diffraction efficiency of greater than 70% at a spatial frequency of 10 1p/mm was obtained. Moreover, surplus diffraction light (diffraction noise) caused by the pixelized structure was reduced to less than 3% by the coupling optics, compared with almost 50% occurring in the LCD by itself.