Optical characterization of liquid-crystal-on-silicon displays

摘要

Electronically addressed spatial light modulators (SLMs) are key elements for the reconstruction of digital holograms. Reflective liquid-crystal-on-silicon displays (LCOS) have great potential to fulfill this task due to their high fill factors of over 90% and their small pixel sizes of less than 15 μm. In order to obtain maximum diffraction efficiency of the holographic reconstruction, analog phase holograms have to be implemented making a maximum phase shift of 2π in each LCOS pixel necessary. Therefore, each LCOS display has to be thoroughly characterized prior to its use as a holographic element. In this publication, we report on a specially designed LCOS test bench. Here, displays can be characterized with respect to their phase and amplitude modulation (i.e. the complex transmittance) under a varying angle of the incident linearly polarized light. Additionally, the Jones matrix of the displays can be measured, which allows computation of the response of the displays to light of arbitrary polarization. The measurement of panel flatness is also possible which is necessary to compensate wave front aberrations. Results of measurements of two LCOS displays are presented and a comparison to other measurement methods is given.