In Chapter 4, various types of digital modulation schemes such as PSK, OOK, and FSK were introduced and in Chapter 5, different receiver architectures such as direct detection, homodyne, and heterodyne detections were discussed. In this chapter, the performances of these modulation schemes with the different receiver architectures are investigated. Firstly, the concept of a matched filter is introduced in Section 8.2. In practice, optical matched filters are rarely used in optical communication systems due to the difficulties involved in fabricating such a matched filter. Nevertheless, the performance is optimum when the matched filters are used, and the expressions for the error probability developed in this Chapter using the matched filters provide a lower bound on the achievable BER.
8.2 Optimum Binary Receiver for Coherent Systems
In this section, we consider the generalized model for the optimum binary receivers (See Fig. 8.1) and later, we apply this model to various detection schemes. Let and be the real optical signals used to transmit bits ‘1’ and ‘0’, ...