Numerical evaluation of commercial amplitude spatial light modulator for synthesis of general complex fields

Abstract

In this work we present the numerical analysis of fully complex fields employing computer generated holograms, implemented with a commercial amplitude liquid-crystal spatial light modulator (SLM). The hologram transmittance is obtained by adding an appropriate bias function to the real cosine computer hologram of the encoded signal. For the purpose of this work, we consider an appropriated bias function for a modulator in which the amplitude transmittance is coupled with a phase modulation. This type of coupled phase appears in a commercial Twisted Nematic Liquid Crystal Display (TNLCD), configured to provide amplitude modulation, with only two polarizers as external components. This modulation curve was experimentally obtained and adjusted to a mathematical function. The numerical evaluation is done by calculating the signal to noise ratio of the reconstructed complex fields for the real modulation curve. Results show that for a good behavior for complex fields a constant bias function should be implemented. As a particular interesting case we generate propagation invariant complex beams with high accuracy and simplicity.