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Abstract

With the advanced development of fiber-optics, the large bandwidth-expansion required by spread spectrum code-division multiple-access (CDMA) can now be accomodated by using a fiber-optic channel for transmission and incoherent optical signal processing for code generation and correlation. Optical synchronous CDMA (S/CDMA), a synchronous transmission format, is introduced and compared with optical (asynchronous) CDMA. Using modified prime sequence codes, S/CDMA is shown to accomodate a larger number of subscribers and more simultaneous users than CDMA. A two-user experiment demonstrating the feasibility of optical S/CDMA is performed at 10 Mbit/s (500 Mchip/s), using optical signal processing. (A chip is a bit-representation component; please see Section 2.) An environment in which S/CDMA would be particularly suited is also discussed. In addition, recent research shows that the feasibility of optical CDMA is also determined by the architecture of the optical encoders/decoders. The coding architecture affects, for example, the amount of power loss and length of optical delays associated with code sequence generation and correlation, which, in turn, affect the power budget, size, and cost of an optical CDMA system. Therefore, a new, modified 2n coding architecture is proposed and compared with prime and 2n coding architectures. Study shows that the modified 2n architecture performs the best and is particularly suitable for ultrafast all-optical processing and waveguides implementation for the future all-optical CDMA networks. A 100 Mbit/s optical CDMA experiment in free space demonstrating the feasibility of the modified 2n coding architecture, using a serial combination of 50/50 beam splitters and retroreflectors, at 10 Tchip/s (i.e., 100,000 chip/bit) with 100 fs laser pulses is also reported.