The study of diffractive lenses displayed in a phase-only liquid crystal spatial light modulator

Abstract

Phase-only spatial light modulator (SLM) based on liquid crystal on silicon (LCOS) is a kind of device based on electrically controlled birefringence effect to realize phase modulation. Due to its low cost, programmable, high resolution, fast response time, LCOS has been widely used in multi-channel imaging, adaptive optics, diffraction optical elements (DOEs), dynamic holographic, optical tweezers and other fields. It is necessary to numerically evaluate the modulation characterization of LCOS before application. Firstly, the phase modulation characterization of the LCOS (PLUTO HED6010XXX by Holoeye Company) was measured based on the Twyman-Green interferometer, and the curves of both phase shift and normalized intensity as grey level functions were obtained. Experimental results indicated that phase modulation of the LCOS could be achieved to 3.99π, and the root-mean-square value (RMS) of normalized intensity was less than 0.01, which demonstrated that LCOS could be regarded as a phase-only modulation device. This method is also suitable for the evaluation of modulation characterization of other LCOS devices. Secondly, a phase pattern of thin lens written onto LCOS was demonstrated. Because of the pixel structure of LCOS, the theory of discretization of lenses was studied. Both simulation and experimental results were obtained. The experimental results proved that the convergence character of the lens written onto LCOS was similar to optical lenses. In the experiment, the measured focal length was in a good agreement to the theoretical deduction, and the relative error (RE) of which was below 1%. Both simulation and experimental results showed that LCOS could be used as lens to converge the plane wave, and replace the optical lens successfully.