We report the use of an experimental ferroelectric liquid crystal material called CDRR8 in bistable optically addressed spatial light modulators for both amplitude- and phase-modulating devices. First, the methods used to improve the alignment and obtain truly bistable switching with CDRR8 are described. The diffraction efficiency and switching characteristics of a bistable CDRR8 optically addressed spatial light modulator used as an amplitude-modulating device and then as a phase-modulating device for encoding high-resolution patterns are compared. The CDRR8 devices exhibit bistability when driven by alternating monopolar pulses. The results show that the use of a device as a phase-modulating rather than an amplitude-modulating device, increases the diffraction efficiency by 10 times. Resolution is better than 100 lp/mm, as measured by the fall in diffraction efficiency by 50% compared with the diffraction efficiency at low spatial frequencies. © 2005 Society of Photo-Optical Instrumentation Engineers.