DMD Optical Efficiency for Visible Wavelengths

Abstract

The purpose of this document is to summarize the optical properties that are most important in estimating the efficiency of a Digital Micromirror Device (DMD) in a projection system.

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1 Purpose and Scope

The next three sections discuss the fill factor, window optical properties, and the active mirror array properties, respectively. This report concludes with a discussion on calculating the overall efficiency.

As discussed in more detail in Section 6, overall optical efficiency can be estimated using
Equation 1.

Equation 1. Efficiency_DMD = transmission_window × efficiency_fillfactor × efficiency_diffraction × reflectivity_mirror × transmission_window

where

transmission_window is single-pass window transmission including two anti-reflection surfaces. This term is accounted for twice because light travels through the window twice.
efficiency_fillfactor is the fractional mirror coverage (on-state mirrors) as viewed from the illumination direction
efficiency_diffraction is the mirror array diffraction efficiency which can include effects of non-flat mirrors
reflectivity_mirror is the mirror reflectivity including mirror scatter

Overall DMD efficiency is generally a product of fill factor, window transmission, diffraction efficiency, and mirror reflectivity, which are described in more detail in the following sections.