The use of raised cosine shaped symbols has been proposed for optical digital communications. The raised cosine pulse shape reduces the receiver signal bandwidth to that of the data rate while simultaneously minimizing inter-symbol interference. This has the effect of increasing receiver sensitivity due to the noise density characteristics of transimpedance amplifiers when bandwidth is reduced. Receiver sensitivity is an essential criteria for free space laser communication. An optical communications experiment was conducted consisting of a laser transmitter modulated by a 20 megabit per second bipolar coded raised cosine bit stream and a matched filter receiver utilizing an APD detector and a transimpedance amplifier. Pulse shaping and matched filter circuits were implemented using a tapped delay line filter type topology. The bit error rate of the receiver as a function of incident optical power was measured and is compared to predicted performance. Implementation losses are accounted for in terms of matched filter mismatch loss, inter-symbol interference, sample time uncertainties, and system nonlinearities.

Date Published: 1 July 1990
PDF: 11 pages
Proc. SPIE 1218, Free-Space Laser Communication Technologies II, (1 July 1990); doi: 10.1117/12.18203

Published in SPIE Proceedings Vol. 1218:
Free-Space Laser Communication Technologies II
David L. Begley; Bernard D. Seery, Editor(s)