Implementation of phase-only modulation utilizing a twisted nematic liquid crystal spatial light modulator

Twisted nematic liquid crystal spatial light modulators (SLM) are widely used for amplitude modulation of light. The technique for measuring phase and amplitude modulation introduced by a twisted nematic cell is not new but the novelty here is that, after characterization of a Holoeye LC2002 TNLC device, we were able to identify specific conditions that allow for its use as a pure 180° or more phase modulator with little or no amplitude modulation at 514.5nm laser wavelength. The phase shift introduced by the SLM was measured using a near common-path Mach-Zehnder interferometer. The experimentally measured and the theoretically predicted intensity transmission and phase shift as functions of gray levels are compared. Finally, the effects of errors in the angular settings of the polarizers and quarter waveplates on the intensity transmission and phase shift are studied.