Aberration and coherence effects with a micromirror array

Abstract

Micro mirror arrays, such as the Digital Micromirror Device (DMD) from Texas Instruments, are amplitude modulating spatial light modulators. Binary holograms write spatial amplitude modulations to the device and with coherent sources can be used to control reflected beams through controlled diffraction. In this paper the inherent aberrations within the DMD device have been identified and corrected through the use of Zernike modes written to the array allowing a device profile to be used as a foundation characteristic upon which other applications can be improved. The approach used coopts a technique used for wavelength measurement using a DMD which focusses onto a camera. The tilting action of the mirrors means the device acts as a mixture of a lens and 2D blazed grating. In this case it also allows assessments of coherence length to be made based on a dual dispersion capability. A model for producing the Fresnel diffraction pattern from a specific DMD pattern is produced using Fresnel diffraction theory and shows good agreement with measured results.