Retro-reflective Communications over a kilometre range using a MEMS-based optical tag

摘要

We report on a laser communications experiment over a kilometre optical range where we have used a retro-reflective transponder incorporating an optical modulator based on silicon micro-electro-mechanical systems (MEMS) device. This employs interference to provide modulation and relies on performing as a coherent array to modulate incident light in the near-IR band (1550nm) over a wide angular range (120 degrees). Modulation is achieved by tuning a large array of Fabry-Perot cavities via the application of an electrostatic force to adjust the gap between a moveable mirror and the underlying silicon substrate.rnThe micro-mirrors have a strong mechanical resonance, and modulate light by adjusting the spacing between the micro-mirrors and the substrate. We use a 'release and catch' technique to exploit the mechanical resonance, and we time the motion of the micro-mirrors to be synchronised with the arrival of an interrogator pulse to ensure that the etalon spacing provides the required modulation, whatever the angle of incidence.rnWe describe experiments over a one kilometre path where simple strings were sent at 200kbit per second. We also discuss approaches to adapting the link to a given angle of incidence.