Halftone Wave Front Control: Numerical Simulation and Laboratory Demonstration

High-contrast instruments are required for direct imaging of faint exoplanets around bright host stars. In high-contrast instruments, a wave front control system is needed to generate a dark hole by suppressing residual stellar speckles. However, the achievable contrast is limited by the phase quantization error (i.e., finite phase resolution) of wave front control devices, such as deformable mirrors or spatial light modulators. In this paper, we propose a halftone method for wave front control to improve the contrast using a wave front control device with quantized phase modulation. In a numerical simulation, the contrast was improved from 1.4 × 10 −9 to 3.8 × 10 −10 by halftone wave front control. In addition, we performed a laboratory demonstration in which a spatial light modulator was used for wave front control, and the contrast was improved from 2.2 × 10 −7 to 6.0 × 10 −8 for a phase resolution of 2 π /256.