Fiber Optic Communications: Fundamentals and Applications

Chapter 7Transmission System Design

7.1 Introduction

So far, we have discussed photonic/optoelectronic components such as lasers, modulators, optical fibers, optical amplifiers, and receivers. In this chapter, we put together these components to form a fiber-optic transmission system. Critical system/signal parameters that affect the performance are identified and design guidelines are provided. In Section 7.2, the performance of a simple fiber-optic system consisting of a transmitter, a fiber, a preamplifier, and a receiver is analyzed. The transmission performance advantage of a coherent receiver over the direct detection receiver for this unrepeatered system is discussed. Section 7.3 covers the dispersion-induced limitations and provides a simple design rule relating the bit rate, dispersion coefficient, and reach. In Section 7.4, optical amplifier noise-induced limitations are discussed. For a long-haul fiber-optic system, optical amplifier noise is one of the dominant impairments. A design rule pertaining to amplifier spacing, number of amplifiers, and total reach is also discussed in Section 7.4.

7.2 Fiber Loss-Induced Limitations

Let us consider an unrepeatered direct detection system based on OOK, as shown in Fig. 7.1. Let be the transmitted power when ‘1’ is sent. The received power is

7.1

The variances of shot noise and thermal noise are given by Eqs. (5.72) and ...