Spatially resolved contrast measurement of diffractive micromirror arrays

Abstract

Diffractive micromirror arrays (MMA) are a special class of optical MEMS, serving as spatial light modulators (SLM) that control the phase of reflected light. Since the surface profile is the determining factor for an accurate phase modulation, high-precision topographic characterization techniques are essential to reach highest optical performance. While optical profiling techniques such as white-light interferometry are still considered to be most suitable to this task, the practical limits of interferometric techniques start to become apparent with the current state of optical MEMS technology. Light scatter from structured surfaces carries information about their topography, making scatter techniques a promising alternative. Therefore, a spatially resolved scatter measurement technique, which takes advantage of the MMA’s diffractive principle, has been implemented experimentally. Spectral measurements show very high contrast ratios (up to 10 000 in selected samples), which are consistent with calculations from micromirror roughness parameters obtained by white-light interferometry, and demonstrate a high sensitivity to changes in the surface topography. The technique thus seems promising for the fast and highly sensitive characterization of diffractive MMAs

Spatially resolved scatter measurement of diffractive micromirror arrays

“…From an application perspective, this corresponds to global contrast ratios up to 10,000 and above, since the contrast ratio is simply the reciprocal of the relative scatter as defined in Eq. ( 1) [23]. As an example the scatter map of a device with a particularly low scatter is shown in Fig.…”

“…In this paper we focus on a new scatter technique that is specialized for diffractive MMAs. It is partially based on our previous work on MMA contrast [23]. Here we present for the first time a self-contained description of spatially resolved scatter.…”