Simulation of a digital micromirror device to characterize optical performance in SAMOS: a DMD-based spectrograph

Abstract

We present a 3D electromagnetic simulation of a digital micromirror device (DMD) to characterize the device efficiency and contrast ratio when used in a spectrograph configuration. A DMD is a spatial light modulator with a wide range of applications, including projection displays, 3D printing, and imaging spectroscopy. In astronomical instrumentation, DMDs are commonly used as reconfigurable slit masks in multi-object spectrographs, such as SAMOS: the SOAR Adaptive-Module Optical Spectrograph. The micromirror array structure of the DMD induces wavelength-dependent diffraction and scatter effects that impact stray light, optical throughput, and the pupil illumination function of an optical system. We simulate the far-field intensity distribution reflected by a DMD and propagate it through an optical model of SAMOS. The results of our simulation are compared to measurements taken with SAMOS in the lab using a controlled source. We further analyze the far-field intensity at the collecting aperture to construct a pupil illumination function. This function is Fourier transformed to determine the diffraction-limited point spread function (PSF) when using a DMD as a field stop. SAMOS measurements are taken using a 656 nm narrow bandpass filter and simulations cover the entire bandpass of SAMOS from 400 nm to 950 nm. Our results inform the design of astronomical instruments using DMDs as reconfigurable slit masks.