Chapter 11
Basics of Optical Amplifiers
Abstract The creation and development of optical amplifiers has provided significant increases in information capacity in applications ranging from ultra-long
undersea links to short links in access networks. This chapter describes the three
main optical amplifier types, which are semiconductor optical amplifiers, active fiber
or doped-fiber amplifiers, and Raman amplifiers. The topics include noise effects
generated in the amplification process, the concept of optical signal-to-noise ratio
and its relation to bit-error rate, the operation and use of optical amplifiers based on
the Raman scattering mechanism, and wideband optical amplifiers that operate over
several wavelength bands simultaneously.
Traditionally, when setting up an optical link, one formulates a power budget and
adds repeaters when the path loss exceeds the available power margin. To amplify
an optical signal with a conventional repeater, it is necessary to perform photonto-electron conversion, electrical amplification, retiming, pulse shaping, and then
electron-to-photon conversion. Although this process works well for moderatespeed single-wavelength operation, it can present a data transmission bottleneck for
high-speed multiple-wavelength systems. Thus, to eliminate the transmission delay
problem a great deal of effort has been expended to develop all-optical amplifiers.
These devices operate completely in the optical domain to boost the power levels of
multiple lightwave signals over spectral bands of 30 nm and more [1–5].
The three fundamental amplifier types are semiconductor optical amplifiers
(SOAs), doped-fiber amplifiers (DFAs), and Raman amplifiers. In addition, the literature uses the term hybrid optical amplifier (HOA), which is the combination of more
than one optical amplifier in any type of configuration. This chapter first classifies
the three basic types and usage of optical amplifiers in Sect. 11.1. Then Sect. 11.2
discusses SOAs, which are based on the same operating principles as laser diodes.
This discussion includes external pumping principles and signal gain mechanisms.
Next, Sect. 11.3 gives details on erbium-doped fiber amplifiers (EDFAs), which are
widely used in the C-band (1530–1565 nm) for optical communication networks.
Noise effects generated in the amplification process are discussed in Sect. 11.4.
The concept of optical signal-to-noise ratio (OSNR) and its relation to bit-error rate
is discussed in Sect. 11.5. The topic of Sect. 11.6 concerns system applications of
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
G. Keiser, Fiber Optic Communications,
https://doi.org/10.1007/978-981-33-4665-9_11
437
Basics of Optical Amplifiers
Abstract The creation and development of optical amplifiers has provided significant increases in information capacity in applications ranging from ultra-long
undersea links to short links in access networks. This chapter describes the three
main optical amplifier types, which are semiconductor optical amplifiers, active fiber
or doped-fiber amplifiers, and Raman amplifiers. The topics include noise effects
generated in the amplification process, the concept of optical signal-to-noise ratio
and its relation to bit-error rate, the operation and use of optical amplifiers based on
the Raman scattering mechanism, and wideband optical amplifiers that operate over
several wavelength bands simultaneously.
Traditionally, when setting up an optical link, one formulates a power budget and
adds repeaters when the path loss exceeds the available power margin. To amplify
an optical signal with a conventional repeater, it is necessary to perform photonto-electron conversion, electrical amplification, retiming, pulse shaping, and then
electron-to-photon conversion. Although this process works well for moderatespeed single-wavelength operation, it can present a data transmission bottleneck for
high-speed multiple-wavelength systems. Thus, to eliminate the transmission delay
problem a great deal of effort has been expended to develop all-optical amplifiers.
These devices operate completely in the optical domain to boost the power levels of
multiple lightwave signals over spectral bands of 30 nm and more [1–5].
The three fundamental amplifier types are semiconductor optical amplifiers
(SOAs), doped-fiber amplifiers (DFAs), and Raman amplifiers. In addition, the literature uses the term hybrid optical amplifier (HOA), which is the combination of more
than one optical amplifier in any type of configuration. This chapter first classifies
the three basic types and usage of optical amplifiers in Sect. 11.1. Then Sect. 11.2
discusses SOAs, which are based on the same operating principles as laser diodes.
This discussion includes external pumping principles and signal gain mechanisms.
Next, Sect. 11.3 gives details on erbium-doped fiber amplifiers (EDFAs), which are
widely used in the C-band (1530–1565 nm) for optical communication networks.
Noise effects generated in the amplification process are discussed in Sect. 11.4.
The concept of optical signal-to-noise ratio (OSNR) and its relation to bit-error rate
is discussed in Sect. 11.5. The topic of Sect. 11.6 concerns system applications of
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
G. Keiser, Fiber Optic Communications,
https://doi.org/10.1007/978-981-33-4665-9_11
437