**1. Introduction**

Generally, communication network systems provide data transfer services for customers. Further requirements such as performance, security, and reliability characterize the quality of the transfer service. Network and information security refer to confidence that information and services existing on a network cannot be accessed by unauthorized users (eavesdropper). However, these service requirements affect each other such that a decision has to be made for cases in which all or some of these requirements are desired but cannot be fulfilled (Zorkadis 1994).

In secure communication networks, tradeoff considerations between system performance and security necessities have not been mentioned widely in many researches. Actually, it has been known that security is of main concern in both wireless and optical communications networks, security mechanisms employed often have implication on the performance of the system (Imai et al. 2005). For some application environments, such as military or enterprise networks, security and system capacity in communications transmission media could become a critical issue. Optical code-division multiple-access (optical CDMA) technology, a multiplexing technique adapted from the successful implementation in wireless networks, is an attractive solution for these applications because it presents security in the physical layer while providing significantly wide bandwidth (Chung et al. 2008).

Optical CDMA systems are getting more and more attractive in the field of all optical communications as multiple users can access the network asynchronously and simultaneously with high level of security (Salehi 1989, Salehi & Brackett 1989) compared to other multiplexing techniques such as Wavelength Division Multiplexing WDM and Time Division Multiplexing TOM.

The potential provided by optical CDMA for enhanced security is frequently mentioned in several studies using different techniques and approaches such as quantum cryptography and chaotic encryption systems (Castro et al. 2006). Other approaches to enhance security have been proposed using optical encoding techniques such as fiber bragg gratings (FBG) to implement optical CDMA systems (Shake 2005a,2005b). Their degree of security depends on code dimensions being used.

In this chapter, security limitations of spectral amplitude coding Optical CDMA are presented and investigated. The tradeoffs between security and system performance have been investigated for a specific eavesdropper interception situation. Section II briefly presents some network security services and assumptions required for optical CDMA confidentiality analysis in the physical layer. Security and performance tradeoffs, based on MQC code system, are presented in section III. Performance analysis is given in section IV. Finally, a conclusion is given in section V.
