MEMS-Based Tracking for an Indoor Optical Wireless Communication Bidirectional Link

We report on the development of a free space, line of sight bidirectional optical wireless communication system for personal area networking. The system includes several transmitters mounted at the ceilings and attached directly to the optical communications cable. Each transmitter contains up to eight outlets connected to eight receivers through an infrared laser beam. Using a transmitted power of 5 dBm, the system transmits at 1.25 and 10 Gb/s and bit-error rates better than 10-12 over the distance range of 2-12 m. To provide robustness against the environmental distortions, such as shock, vibration, and temperature fluctuations, an active repositioning is implemented by a closed-loop controlled steering of the laser beam by electrostatically actuated microelectro-mechanical system mirrors mounted within each of the outlets and allowing up to ±2° optical scanning angle. An algorithm based on the maximization of the transmitted optical power has been developed for automatic alignment between the central station and each of the user modules, enabling certain mobility of the system.