Optical Amplifiers As seen in Chapter 5, the transmission distance of any fiber-optic communication system is eventually limited by fiber losses. For long-haul systems, the loss limitation has traditionally been overcome using optoelectronic repeaters in which the optical signal is first converted into an electric current and then regenerated using a transmitter. Such regenerators become quite complex and expensive for wavelength-division multiplexed (WDM) lightwave systems. An alternative approach to loss management makes use of optical amplifiers, which amplify the optical signal directly without requiring its conversion to the electric domain. Several kinds of optical amplifiers were developed during the 1980s, and. | Fiber-Optic Communications Systems Third Edition. Govind P. Agrawal Copyright 2002 John Wiley Sons Inc. ISBNs 0-471-21571-6 Hardback 0-471-22114-7 Electronic Chapter 6 Optical Amplifiers As seen in Chapter 5 the transmission distance of any fiber-optic communication system is eventually limited by fiber losses. For long-haul systems the loss limitation has traditionally been overcome using optoelectronic repeaters in which the optical signal is first converted into an electric current and then regenerated using a transmitter. Such regenerators become quite complex and expensive for wavelength-division multiplexed WDM lightwave systems. An alternative approach to loss management makes use of optical amplifiers which amplify the optical signal directly without requiring its conversion to the electric domain. Several kinds of optical amplifiers were developed during the 1980s and the use of optical amplifiers for long-haul lightwave systems became widespread during the 1990s. By 1996 optical amplifiers were a part of the fiber-optic cables laid across the Atlantic and Pacific oceans. This chapter is devoted to optical amplifiers. In Section we discuss general concepts common to all optical amplifiers. Semiconductor optical amplifiers are considered in Section while Section focuses on Raman amplifiers. Section is devoted to fiber amplifiers made by doping the fiber core with a rare-earth element. The emphasis is on the erbium-doped fiber amplifiers used almost exclusively for m lightwave systems. System applications of optical amplifiers are discussed in Section . Basic Concepts Most optical amplifiers amplify incident light through stimulated emission the same mechanism that is used by lasers see Section . Indeed an optical amplifier is nothing but a laser without feedback. Its main ingredient is the optical gain realized when the amplifier is pumped optically or electrically to achieve population inversion. The optical gain in general
