High-efficiency diffraction performance of LCoS-SLMs at ultra-large incident angles

Liquid crystal on silicon spatial light modulators (LCoS-SLMs) are widely used for wavefront shaping through spatial phase modulation, owing to their high resolution, high diffraction efficiency and multi-level phase programmability. Conventional LCoS systems are operated at normal incidence, as oblique illumination suffers from a well-known problem of degradation in diffraction efficiency, limiting its applicability in beam steering. In this work, we utilize a cascaded coordinate-transformed Jones-matrix model to analyze light propagation in the LCoS device under oblique incidence. Optimization approaches are further introduced to improve diffraction efficiency, including polarization controlling and phase pre-compensation. Experiments demonstrate that with the proposed approaches the operating range in the angle of incidence is extended from around 10° to 50° and beyond, while maintaining diffraction efficiency close to that under normal incidence. Moreover, the approaches significantly improve diffraction performance at large diffraction angles, resulting in the 1st-order efficiency more than 40% at a diffraction angle of 10° with an incident angle of 50°. Our findings enable practical oblique-incidence operation of LCoS-SLMs, expanding their applicability in high-efficiency and large-angle beam steering architectures.