Suppression of Zeroth-Order Diffraction in Phase-Only Spatial Light Modulator

Abstract

A correction beam is created using a spatial light modulator (SLM) to suppress the zeroth-order diffraction (ZOD) that is produced by the unmodulated light coming from the dead areas of the said SLM. The correction beam is designed to interfere destructively with the undesirable ZOD that degrades the overall quality of the propagated SLM signal. Two possible techniques are developed and tested for correction-beam generation: aperture division and field addition. With a properly-calibrated SLM, ZOD suppression is demonstrated numerically and experimentally at sufficiently high area factor (AF) values where suitable matching is achieved between the correction beam and the ZOD profiles to result in a \(39\%\) reduction of the ZOD intensity via angular aperture division, \(32\%\) reduction via annular aperture division, and \(24\%\) reduction via vertical aperture division. At low AF values however, meaningful ZOD suppression is not obtained. With the field addition method, a ZOD reduction as high as \(99\%\) is gained numerically which was not realized experimentally using an SLM with a fill factor of 0.81 due to limitations posed by an iterative phase-recovery algorithm (ghost image) as well as unwanted signal contributions from the SLM anti-reflection coating, SLM surface variations, optical misalignment and aberrations.