Phase optimization for tiled spatial light modulators

Abstract

Optical phase conjugation using computer generated holograms takes advantage of the ability to tailor a wavefront for specific applications. This includes directing laser beams through obscuring or distorting media, holographic image projection, and beam tracking of various targets. These techniques employ spatial light modulators (SLM) which tend to be the limiting component in terms of resolution, response time, efficiency and cost. For beam tracking, system field of regard and target spot size depend directly on SLM resolution. We are investigating techniques to tile multiple SLMs to provide increased resolution using existing devices. Cost and complexity are a major focus. We use a ferroelectric liquid crystal SLM (Forth Dimension Displays Ltd) due to their low cost, high resolution (1024x1280) and the ability to generate phase-only binary holograms. Even with relatively inexpensive SLMs, we develop techniques to compensate for SLM non-uniformities and distortions introduced by system optics. Our approach uses a simple algorithm to measure the cumulative phase error introduced by the SLM, system optics and geometry and then to subtract that error from any ideal pattern imposed on the SLM. We present results showing the effectiveness of this technique.