Silica Optical Fiber Technology for Devices and Components: Design, Fabrication, and International Standards

CHAPTER FOUR

Dispersion-Managed Single-Mode Fibers for Wavelength Division Multiplexing

4.1  WAVELENGTH ALLOCATIONS IN SINGLE-MODE FIBERS FOR WDM APPLICATIONS

In Chapter 2, standard specifications for single-mode fibers have been reviewed. In recent optical communications, signals in conventional band (C band) have expanded to neighboring optical bands to cover almost entire available optical window in single-mode optical fiber. The band allocation in International Telecommunication Union (ITU) is summarized in Table 2.8.

In transmission of signals through optical fiber, two major fundamental limitations were and have been optical loss and chromatic dispersion. With the advent of fiber amplifiers, the limitation imposed by optical loss has been virtually removed but within a finite range of gain bandwidth. In other words, previous loss limit has been changed to bandwidth limit of optical amplifiers. Among the above communication bands, S, C, and L bands are widely used due to availability of efficient fiber optical amplifiers.

The optical amplifiers in S, C, and L bands are schematically shown in Figure 4.1, along with an optical loss spectrum of conventional single-mode fiber. Since the successful deployment of EDFA for C band in both terrestrial and submarine cables, erbium ions in silica glass have been further studied to find that lower population inversion in a longer EDF length could provide a sufficient optical gain in L band [1]. Instead of using erbium, thulium ions also ...