ABSTRACT
This chapter provides an overview of various optical codes for optical code-division multiple-access (OCDMA). It reviews the constructions of three common families of bipolar codes, maximal-length sequences, Walsh codes, and Gold sequences and then two well-known families of unipolar codes, OOCs and prime codes. The chapter analyses and compares the performance of these codes. It also analyses the developed extended carrier-hopping prime code. To support multiple users in OCDMA systems, one-dimensional unipolar codes, such as OOCs and prime codes, were originally designed to provide thumbtack-shape autocorrelation and very low cross-correlation functions in order to optimize the discrimination between the correct sequence and interference. Walsh codes are employed to improve the bandwidth efficiency of wireless CDMA since they have zero cross-correlation functions when they are all synchronized in time. Most studies on two-dimensional wavelength-time codes were based on the assumption that there is only one type of media in OCDMA systems with single-data-rate services.
