Abstract

Asynchronous multiplexing schemes are most applicable when the traffic on the network is characterized by relatively long idle periods between the transmitted packets of data. An asynchronous system that provides random access makes the most efficient use of the channel. However, when the intensity of the traffic increases (i.e., the channel is being accessed by many users at the same time), collisions between packets become unavoidable and the throughput of the channel is greatly degraded. To alleviate this problem, spread spectrum multiplexing techniques, commonly known as code division multiple access (CDMA), can be applied. Application of CDMA requires a channel with a large bandwidth, such as an optical channel. Processing the received coded data requires a correlator. If high data rates are used, because of the bandwidth expansion of CDMA, a fast correlator must be implemented. Although for conventional systems this correlation requires sophisticated electronics, optical correlators could handle this fast processing with less complexity. Therefore, the CDMA scheme proposed here was implemented by optically correlating the incoming coded data. One set of codes that show promise for our application are prime sequences obtained from a Galois field GF(P) where P is a prime number and N = P**2. An experiment is described employing a P = 5 code sequence on a 100-Mbps fiber-optic link using 32 chips per bit. This optical CDMA system can potentially allow many more chips per bit, and therefore more users, than conventional systems.

© 1985 Optical Society of America