SLM-based sinusoidal fringe projection under coherent illumination

The paper is dedicated to SLM implementation of a sinusoidal phase grating for fringe projection profilometry with sinusoidal fringes. A low-contrast sinusoidal phase grating is capable of projecting focused sinusoidal fringes with satisfactory visibility in a large spatial region under coherent divergent illumination. The paper presents analysis of distortions in the projected fringes due to phase quantization when the phase grating is generated by a phase-only 8-bit SLM. We showed by simulation of propagation in the free space that the spread of intensity fluctuations of the projected fringes comprises 4-5 gray levels if an SLM with a 2π phase span is used and is much lower for an SLM with π/2 phase span. In addition, we proved that distortion due to the phase encoding of the grating complex amplitude can be modeled as gamma distortion with an invariable behavior in time at small values of the modulation parameter and removed by a proper correction of fringes after polyspectral analysis. The experiments we made with an 8-bit SLM of π/2 phase span confirmed the ability of this optical element to project sinusoidal fringes with a high spectral purity.