Optical modeling of MEMS corner cube retroreflectors with misalignment and nonflatness

Micromachined corner cube retroreflectors (CCRs) can be employed as transmitters in free-space optical communication links. In this application, a CCR is illuminated by an unmodulated beam, and one mirror of the CCR is intentionally misaligned to modulate the intensity of the retroreflected beam. The low power consumption, small size, and ease of operation of a CCR makes it an attractive option for certain types of optical links. However, curvature and misalignment of the micromachined mirrors can cause CCRs to perform far from theoretical limits. In this paper, we develop two methods to predict the optical performance of CCRs having ideal or nonideal mirrors. We first introduce a discretized analysis method based on ray tracing and scalar diffraction theory. We then propose a simpler phase-shift model under the assumptions that the misalignment and surface nonflatness are small and that they do not alter the optical topology of the CCR. These assumptions are satisfied by typical CCRs to be used in free-space optical links. Using our two methods, we determine tolerances on mirror curvature and misalignment for representative micromachined CCRs.