Optical CDMA Networks: Principles, Analysis and Applications

Chapter 4

Spectrally Encoded OCDMA Networks

4.1 Introduction

In Chapter 3, we introduced different kinds of OCDMA schemes alongside various transceiver structures composed of lenses, masks and gratings for spectral-encoded systems. However, as pointed out earlier, for this system the basic transceiver structure is too complex which makes it too expensive to build.

An important requirement for transceiver design in a practical OCDMA system is the address reconfiguration ability. The transmitter structure which was introduced in Section 3.4.4 is composed of gratings and a mask. In such a transmitter, we need to mechanically change the amplitude mask to generate a different sequence. In doing so, every user needs a set of the same masks, which makes the transmitter tremendously expensive.

To overcome these disadvantages, many encoder/decoder structures have been proposed based on the present optical devices. For example, arrayed waveguide gratings (AWG) have been employed to construct a spectral-amplitude-coding (SAC) OCDMA system in [1]. This chapter is devoted to a discussion of various system implementation methods using different optical devices.

Fibre Bragg gratings (FBGs) have also been used to implement the encoder/decoder in OCDMA [2]. A coherent spectral phase-encoder composed of FBGs has been proposed in [3]. In a similar approach, we have designed both the transmitter and the receiver structures for a SAC system based on the SAC-appropriate modified quadratic congruence ...