Optical Transponder Components

Zusammenfassung

This chapter introduces the general architecture of an optical transponder and describes the three critical optical components that comprise the transponder, the laser, the optical modulator, and the photodetector. Following this, the subsystem consisting of the optical transmitter and the coherent receiver that are typically used for generating and detecting dual-polarization complex-modulated signals are explained. The typical characteristics of the components used in the transponder are presented both from current-generation products, as well as from more recent research demonstrations.

In this chapter, we focus on the line-side optics, as they are the key to understanding the components in a transponder. The transmitter at the line side consists of a number of high-performance optical components, such as narrow-linewidth lasers, and high-speed modulators with linear driver amplifiers. The receiver at the line side consists of $90^{\circ}$ optical hybrids, high-dynamic-range linear balanced photodetectors (s), and high-gain low-noise transimpedance amplifiers (s). The digital electronic functions are in application-specific integrated circuits (s), which include digital-to-analog converters (s) for the transmitter to generate optical signals, analog-to-digital converters (s) for the receiver to recover the optical signals. Both ends need digital signal processing () engines to condition and process the signals. The client side optics, which are not covered in this chapter, are usually a subset or a simpler version of those used in the line-side part of the transponder.