8.1 OVERVIEW

Spatial light modulators (SLMs) are devices that produce an output light distribution that results from modulating an input light distribution either optically or by electrical addressing. SLMs may be single-pixel, one-dimensional (1-D), two-dimensional (2-D), or three-dimensional (3-D). We will focus primarily on 1-D and 2-D SLMs, but 3-D SLMs (volume holographic elements) may play an increasingly important role in the future. Figure 8.1 illustrates in very simple terms the typical generic structure of 2-D SLMs. Note that in general, SLMs can be signal multiplying, self-emissive, signal amplifying, or self-modulating. Volume holographic devices consist of photorefractive or nonlinear optical materials. Self-modulating devices include bistable optical devices and passive self-pumped phase-conjugate mirrors. Self-emissive SLMs consist of cathode ray tubes (CRTs) and image intensifiers, both of which employ phosphor screens for image display.

Figure 8.1: Generic 2-D SLM structure showing basic features of most reflective-type devices. Polarizers are especially useful when the modulating material rotates the plane of polarization is a function of bias voltage as in electrically addressed liquid crystal SLMs.

Signal multiplying SLMs are generally three-port devices where the amplitude at each point in the output image is multiplied by an effective transmittance or reflectance of the modulating element or pixel. The amount of modulation may be determined by the write image intensity or by an electrical write signal at the corresponding pixel on the SLM. Electrical addressing requires a means of reading-in a 2-D spatial image usually from a 1-D serial signal.

Some examples of the more common...