Characterization and Modeling of SAGCM InP/InGaAs Avalanche Photodiodes for Multigigabit Optical Fiber Communications

This chapter describes extensive characterization and modeling of a specific type of state-of-the-art InGaAs/InP avalanche photodiode (APD), utilized in current and future multigigabit optical fiber communication systems. A short introduction to optical fiber communications is presented by considering the general system architecture, the major advantages over other technologies, and the historical developments of the technology. The general design requirements for optical receivers are discussed. An optical fiber communication system as presented is similar in its basic concept to any type of communication systems (i.e, its purpose is to convey the signal from the information source to the destination). In an optical fiber communication system, the information signal is converted from electrical form to optical form (E/O) by modulating an optical carrier of an optical source, such as laser or light-emitting diode (LED). Then the signal is transmitted through an optical fiber that can be as long as a few hundred kilometers; finally it is converted back into electrical form (O/E) by an optical receiver. In long-haul digital optical fiber communication systems, repeaters are used along the communication route to regenerate optical pulses to extend the communication distance. The chapter discusses the major advantages of optical fibers over metallic media. Low-frequency noise (LFN) in dark currents is discussed. An extensive investigation on a state-of-art photodetector—namely, planar separate absorption, grading, charge, and multiplication (SAGCM) InP/lnGaAs avalanche photodiode (APD) with partial charge sheet in device periphery has been conducted.