System and Circuit Design for Time-Wavelength Optical CDMA Networks

Code Division Multiple Access (CDMA) was first proposed in the context of Wire-less Communications to achieve high-speed connectivity, random asynchronous operation and network control simplification. Recent developments in optical networks have led to growing interest on the adoption of the same technique in the optical domain to develop new generations of access and Local Area Networks [1]. One of the main practical difficulties is the implementation of the encoding and decoding hardware [2]. Traditionally, all-optical devices have been proposed to implement encoders and correlators of the OCDMA networks. Such approaches rely on the use of Fiber Bragg Gratings (FBGs) [3, 4] or optical delay lines [5]. Although many OCDMA systems have been successfully demonstrated and implemented, the migration from laboratory to real world has been slower than expected. This is mainly due to the thermal variability of the FBGs and the difficulty to achieve good spectral characteristics such as flat group delay and low ripple in the reflection spectrum. The designs relying on optical delay lines suffer from lack of tunability since, with the existing techniques, it is impossible to achieve accurate time delays for high speeds [6].