Yasunori IGASAKI,¹ Fanghong LI,² Narihiro YOSHIDA,¹ Haruyoshi TOYODA,¹ Takashi INOUE,¹ Naohisa MUKOHZAKA,¹ Yuji KOBAYASHI¹ and Tsutomu HARA¹

¹Central Research Laboratory, Hamamatsu Photonics K.K., 5000, Hirakuchi, Hamakita, 434-8601 Japan, ²State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027, China

(Received January 13, 1999; Accepted February 25, 1999)

To realize a high efficiency electrically addressable phase-only modulator, we have coupled a liquid crystal display (LCD) to an optically addressed parallel-aligned nematic liquid crystal spatial light modulator (PAL-SLM) with a set of lenses. Phase modulation exceeding 3π at 532 nm wavelength was obtained. We obtained linear transfer characteristics for phase modulation at various desired phase levels after calibration and adjustment of the transfer characteristics of the PAL-SLM and the LCD. Diffraction efficiency of 40% for binary phase grating and of 90% for 8-level blazed phase grating, which were very close to the simulation values, were observed. The power loss of the readout light was caused when passed through a half mirror, therefore, we examined a setup using an oblique readout light at the modulator. Very high diffraction efficiency was obtained from the setup by optimizing the polarization direction and optical path for this light, and the orientation of liquid crystals. Since the modulator can perform at better than 90% diffraction efficiency and at nearly 100% reflectivity, various high efficiency systems utilizing such modulators are expected.

Key words : spatial light modulator, liquid crystal display, phase-only modulator, diffraction efficiency, oblique incident, phase modulation, amorphous silicon, liquid crystal

igasaki@crl.hpk.co.jp