Components, Modules, and Subsystems

Abstract

In this chapter, basic components, modules, and subsystems relevant in both optical and wireless communications are described. In the first half of the chapter, key optical components, modules, and subsystems are described. After describing optical communication basic, focus is changed to optical transmitters. The following classes of lasers are introduced: Fabry-Perot, distributed feedback (DFB), and distributed Bragg reflector (DBR) lasers. Regarding the external modulators, both Mach-Zehnder modulator and electroabsorption modulator are described. Regarding the external modulator for multilevel modulation schemes, phase modulator, I/Q modulator, and polar modulator are described. In subsection on optical receivers, after the photodetection principle, the p-i-n photodiode, avalanche photodiode (APD), and metal-semiconductor-metal (MSM) photodetectors are briefly described. In the same subsection, both optical receiver high-impedance front end and transimpedance front end are described. In section on optical fibers, both single-mode fiber (SMF) and multimode fiber (MMF) are introduced. In subsection on optical amplifiers, after describing optical amplification principles, the following classes of optical amplifiers are described: semiconductor optical amplifier (SOA), Raman amplifier, and Erbium-doped fiber amplifier (EDFA). In subsection on optical processing components and modules, the following components/modules are described: optical couplers, optical filters, and WDM multiplexers/demultiplexers. After that, the principles of coherent optical detection are introduced, followed by the description of optical hybrids. In subsection on coherent optical balanced detectors, both homodyne and heterodyne optical balanced detectors for both binary and multilevel (QAM, PSK, APSK) modulations are described. In the second half of the chapter, basic components and modules of relevance to modern wireless communications are described. First, the DSP basics, including various discrete-time realizations, are provided. Then the direct digital synthesizer (DDS), relevant in discrete-time (DT) wireless communications systems, is described. In subsection on multirate DSP and resampling, various upsampling, downsampling, and resampling schemes/modules are described. In the same subsection, the polyphase decomposition of the system (transfer) function is introduced and employed in resampling. In subsection on antenna array antennas, the linear array antennas are described. Finally, in subsection on automatic gain control (AGC), the AGC schemes operating in passband and baseband are described.