Beam steering with spatial light modulators: Quantisation effects

Abstract

Beam steering can be achieved by sending holograms to a phase-only spatial light modulator (SLM). The use of holograms, defined by linear phases, induce a one dimensional transverse shift of the beam spot at the focal plane of a lens. An SLM is formed by N pixels and uses a limited number of grey levels, M. These limitations produce the quantisation of the phase values introduced on the incoming beam and decrease the accuracy on spot positioning. We have built a system in which a laser beam is focused by a lens after being reflected by an SLM. Different positions of the focal spot have been captured by a camera and accurately determined by image processing. Measurements were done with N=100 and M=16. We proved that quantisation effects are not relevant in most of the positions, except for certain locations, which produce such errors on spot positioning that need to be avoided.