Measurement of additional phase modulation of an amplitude liquid crystal spatial light modulator HoloEye LC 2002 by dual-beam interferometric method

Abstract

The majority of liquid crystal amplitude spatial light modulators (SLM) in addition to amplitude modulation also produce phase modulation. This additional phase shift depends on a signal value addressed to each SLM pixel. Knowledge of additional phase shift is often necessary for coherent optical systems design. If dependency of phase shift on signal value is known, then the accounting for this additional phase shift during experiments is possible. The results of phase shift measurements of HoloEye LC 2002 SLM, performed by a dual-beam interferometric method are presented. The processing method is based on summation of lines of images of interferometric fringes. Maximum phase shift value detected in experiments was about 0.6π. It was observed with signal value equal to 219. The measurement error is about 0.05π. Implemented techniques can also be used for other amplitude and phase SLMs. The results of using measured dependency of phase shift on signal value in invariant coherent optical correlator design to decrease pattern recognition errors by addition of phase to the output correlation filter in order to compensate for undesired SLM phase shift are presented.