ABSTRACT
Optical fiber communication system technology has been developed exten-
sively since the first system installation in the early 1980s, and the most
recent trunk lines run at a bit rate of 10 Gb s1; even 40 Gb s1 systems have been already prototyped and are expected to be commercialized soon. In
addition to such high-bit-rate time division multiplexing (TDM) systems,
wavelength division multiplexing (WDM) systems, which can involve hun-
dreds of different wavelength channels to support the overall throughput close
to 1 Tb s1, are used in recent systems, as illustrated in Figure 2.1 [1] . On the other hand, the most recent trend in the information transmission volume does
not show any sign of saturation, regardless of the recent worldwide recession
in the communication market at the very beginning of the new millenium [2].
This is thought to be caused by the ever increasing, strong demands for
transmitting multimedia information through global networks involving the
Internet and cellular phone services. Judging from an extrapolation of the
increasing rate of information volume, a breakthrough in optical communi-
cation technology is required to improve the throughput in the range between
1 and 10 Tb s1 within a decade. To achieve such an extremely high throughput in communication systems,
the WDM technique could be extensively used to further increase the system
