Alignment and performance analysis of free-space optical communications for broadband video transmission.

We describe a free-space optical communications system operating with an externally modulated infrared carrier signal at 1550 nm. The purpose of the system is to explore an alternative to radio-frequency wireless communications, which are subject to spectral congestion and bandwidth limitations. We provide details of the optical alignment procedure and a means for extrapolating the obtained results to larger transmission distances. To illustrate the versatility of the system, a relatively wideband signal was chosen for transmission: an NTSC analog video signal, whose instantaneous bandwidth was 6 MHz. We describe the performance of the system by examining its output image quality and signal-to-noise ratio.