Digitally tunable MOEMS diffraction gratings

Abstract

The angles of diffraction of a grating are a function of the incident wavelength and the period of the grating. The ability to vary the period of a grating is of interest in a variety of applications, as this in effect provides tunability of the diffraction angles. Most tunable gratings vary the period in an analog fashion. This is achieved by pulling the grating beams apart, which varies the gap between the beams, and hence the period. Changing the period in this way usually does not alter the width of each beam. Although this provides tunability with a high resolution, the ratio of the width of each grating beam to the period changes for each period. This in turn changes the efficiency for each grating period. In this work, we present a design of a MOEMS grating that changes the period between two values, i.e., from 12 to 24 μm and 48 μm, while keeping the efficiency constant. Electrostatic attraction is used to selectively pull down beams in order to achieve this. Simulation and experimental results show a variation of about 1% in efficiency between the two grating states. The measured efficiencies in the first order of the 24- and 48-μm period gratings were found to be 6.5% and 7% compared to the simulated values of 9% and 10%, respectively. The gratings were fabricated using surface micromachining. The process flow is