Optical code-division multiple access (OCDMA)

Petropoulos, P. (2004) Optical code-division multiple access (OCDMA). Optical Architectures for RF Signal Processing and Signal Mixing, Panticosa, Spain.

Record type: Conference or Workshop Item (Other)

Abstract

Optical Code Division Multiple Access (OCDMA) is an alternative multiplexing scheme to the more conventional Wavelength Division Multiple Access (WDMA) and Time Division Multiple Access (TDMA). It has recently attracted significant research interest because of the advantages it offers in terms of network granularity and the flexibility in the management of the system resources. In addition, it is attractive for applications where secrecy in the transmission is important, and also has the potential of supporting burst IP traffic and multi-protocol-based networks

OCDMA is based on allocating each user of the network one particular code; the codes are assigned to the data pulses before transmission; at the receiver the users rely on correctly decoding the signal intended for them in order to establish communication, while rejecting all other coded data intended for other users at the same time. Thus, unlike WDMA and TDMA, in general, each user is allowed to use the entire available spectrum for all of the time. The earliest pulse encoding implementations used arrays of discrete optical fibres of different path lengths appropriately coupled together using fibre couplers, in order to temporally split the input pulses in a predefined manner. The decoder used the same configuration, which served as a correlator for the encoded signals. However, this simplified scheme introduces several issues associated to its scalability as well as its sensitivity to environmental conditions. Since then several other technologies have been investigated, which apply encoding/decoding either in the time (direct-sequence-) or the frequency domain (frequency-encoded-OCDMA). Hybrid (also called two-dimensional or frequency-hopping) approaches have also been demonstrated.

This lecture will review some of the most promising all-optical encoding/decoding schemes and will explore the implications involved in the OCDMA system design. Apart from multiple access, pulse encoding can be applied to other communication scenarios too, such as for providing the header information in packet switched networks. These applications of pulse encoded systems will also be discussed.

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