Incoherent optical CDMA systems

Since the initial efforts (Prucnal, Santoro, Fan [1986]; Salehi [1989]; Hui [1985]) toward CDMA in the optical domain (OCDMA), different approaches have been proposed for its implementation. The demonstrated systems can be classified into two main categories: coherent and incoherent. These two categories differ primarily in the signal modulation and detection. Incoherent schemes use the simpler, more standard techniques of intensity modulation with direct detection while coherent schemes are based on the modulation and detection of optical phase (Lam [2000]). Coherent approaches have been reviewed in Chapter 5 and are also the topic for discussion in many review papers (Salehi, Weiner, Heritage [1990]; Marhic [1993]; Griffin, Sampson, Jackson [1995]; Sardesai, Chang, Weiner [1998]; Huang, Nizam, Andonovic, Tur [2000]). The most common approaches to incoherent OCDMA are based on spectral-amplitude coding, spatial coding, temporal (time) spreading, and two-dimensional (2D) wavelength-hopping time-spreading (WHTS). This chapter will give a brief overview of all these approaches and will focus in particular on WHTS.