Chapter 14 - Semiconductor Optical Amplifiers for Metro and Access Networks

Abstract

In 1990s, semiconductor optical amplifiers (SOAs) were expected to emerge as a compact and low-cost alternative to erbium-doped fiber amplifiers (EDFAs). However, because of the short time constant of their gain dynamics, the SOAs caused unacceptable levels of inter- and intra-channel distortions making them unsuitable for in-line amplification in dense wavelength division multiplexing (DWDM) systems. Schemes such as laser cavity formation to clamp the amplifier gain led to many years of research and development activity without significant commercial success. The ability of SOAs to amplify signals in the wavelength regions beyond the C- and L-band covered by the EDFAs did not give them much benefit because the commercial DWDM systems remain confined to these bands. The other proposed applications of SOAs such as switching, non-linear signal processing, and wavelength conversion have also been confined to academic research. With the advent of PONs for access applications in recent years, however, there is renewed interest in SOAs to extend the total loss budget of such networks. This chapter addresses the architecture issues of PONs to show the benefits of including SOAs for network reach extension, for example. The standards of gigabit passive optical network (GPON), for example, specify a loss budget of 28 dB to be used in a combination of splitting loss and fiber loss. This limitation can be overcome by the inclusion of SOAs at the splitter as a mid-span amplifier. It also discusses the ability of SOAs to amplify signals at the wavelengths 1550, 1310, and 1490 nm in PON standard.