Fiber Optic Communications: Fundamentals and Applications

Chapter 9Channel Multiplexing Techniques

9.1 Introduction

Typically, the single-channel symbol rates range from 10 Gsym/s to 40 Gsym/s. A symbol rate beyond 40 Gsym/s is hard to achieve in practice because of the speed of electronic components in transmitter and receiver circuits. In the low-loss region of the fiber (1530–1620 nm), it has a bandwidth greater than 10 THz. To utilize the full bandwidth of the fiber, several channels can be multiplexed and they can share the same fiber channel. An EDFA operating in C-band (1530–1565 nm) has a bandwidth of about 4.3 THz and, therefore, several channels can be amplified simultaneously by a single amplifier. The multiplexing techniques can be divided into three types: (i) polarization division multiplexing (PDM) or polarization multiplexing (PM), (ii) frequency or wavelength-division multiplexing (WDM), (iii) time-division multiplexing (TDM).

9.2 Polarization-Division Multiplexing

PDM is an effective technique to double the capacity. Commercial coherent systems make use of PDM and WDM to enhance the capacity. A single-mode fiber supports two polarization modes–one with the electric field aligned with the -axis and the other aligned with the -axis (see Section 2.7.5). Therefore, it is possible to transmit information using each of these ...