Phase modulation using the silicon backplane spatial light modulator and transmissive glass

Spatial Light Modulators (SLMs) are very important components in optical systems. SLMs using arrays of phase modulating pixels are the basis of many new system proposals in adaptive optics(1), image processing(2) and switching(3). Ferroelectric Liquid Crystals (FLCs) are especially well suited to devices requiring binary phase gratings and have been widely used(4). Many of the above applications have been pioneered and demonstrated using 'all glass' multiplexed FLC SLMs (128 by 128 pixels)(5) operating in transmission mode(1, 2, 3). More compact and integrated system will be built using FLC and Silicon SLMs6.7 and much work is now focused in this area due to the interest in polarization insensitive FLC8 binary phase modulation for beamsteering application(3) and arrays of intensity modulator for microdisplays(6.7). Here we examine the advantages and disadvantages of a range of different implementations of FLC SLMs for applications requiring arrays of phase modulating pixels. The basis of our comparison is the spatial and temporal distribution of light in the far field diffraction pattern formed by the SLMs. The spatial field is influenced by the flatness and pixel structure of the SLMs, its topology, the surface finish of pixels, the liquid crystal alignment and so forth. Temporal variations arise because of the electronic addressing schemes used to address pixels. Both are important in most applications discussed. The devices considered are all-glass multiplexed FLC SLMs operating in transmissive mode and non-planarised silicon backplane FLC SLM with the mirror flat down on the silicon.