Hybrid wavelength hopping/time spreading code division multiple access systems

The capacity of local area networks (LAN) can be increased substantially by amalgamating different access techniques. Wavelength division multiplexing (WDM) and code division multiple access (CDMA) can both offer an asynchronous mode of communication and can be integrated into a hybrid system. Here, the characteristics of one particular approach to achieving a hybrid system, analogous to hybrid systems used in electrical CDMA are examined. An optical CDMA concept using wavelength hopping and time spreading is described employing prime sequences for both the hopping and the spreading pattern (prime-hop sequences), and proofs are given that the autocorrelation function has zero side lobes and that the cross-correlation function is at most 1. In such systems, the number of possible stations is greatly increased as is the number of simultaneous users. Code generation and correlation are described in detail and networks for efficient code generation are analysed. It is shown that the system offers increased security levels leading to a very secure transmission. The system is suitable for truly asynchronous highly secure LAN applications.