Correcting Fabrication-Induced Curvature in Micromirror-Based Spatial Light Modulators with a Microlens Array

TL;DR

This paper presents an optical compensation technique using a microlens array to correct curvature artifacts in high-fill-factor micromirror SLMs, significantly improving phase accuracy and brightness for holography applications.

Contribution

Introducing a microlens array-based method to mitigate fabrication-induced curvature in micromirror SLMs, enhancing optical fill factor and phase fidelity without altering the mechanical design.

Findings

Pearson correlation coefficient improved from 0.11 to 0.85

Holographic spot brightness increased by 8 times

Nearly 100% optical fill factor achieved

Abstract

Computer generated holography requires high-speed spatial light modulators (SLMs) for dynamically patterning light in 3D. Piston-motion micromirror-based SLMs support high-speed ($\geq$ 10 kHz) phase modulation; however, fabricating micromirror arrays with sufficient fill factor necessary for high diffraction efficiency is challenging. In particular, the larger mirrors of high fill factor designs are susceptible to stress-induced curvature that significantly degrades optical performance. In this work, we introduce an optical compensation method using a pitch-matched microlens array (MLA) to focus light onto just the center of each mirror. Our approach thus avoids curvature-induced artifacts and improves optical fill factor to nearly 100$\%$, independent of the original mechanical fill factor. Through simulations and experiments on a fabricated micromirror array with bowed mirrors, we show that the Pearson correlation coefficient of the imparted phase profile is improved from 0.11 to 0.85 and the brightness of a holographically-generated single spot is enhanced by 8$\times$ with our microlens array in place. Our hybrid optical-electromechanical strategy thus provides a scalable path toward high-speed, high-fidelity wavefront control for applications such as adaptive optics, holographic displays, and optogenetics.