Introduction

Optical communication systems employ lightwaves to transmit information from one place to another separated by a few kilometers to thousands of kilometers for delivery to homes and from central exchanges between major cities. Furthermore, the reach can now be extended to transoceanic distances covering several thousands of kilometers as shown in Figure 1.1. Figure 1.2 depicts a map from KDD Submarine Cable Systems, Inc. that shows the submarine cable infrastructure in the Asian region in 1996. This reveals more details of the fi ber cable networks in Southeast Asia and the Australia Oceania region. The connection and cable from Australia to America and Europe is the longest and most extensive layout of the optical transmission systems. The lightwave frequency is in the range of nearly 200 THz for 1550 nm wavelength and several wavelength channels can be multiplexed so as to take the total capacity over this spectral band to a few tens of terabytes per second. This band is only a very small part of the optical spectrum. Fortunately, this region is the lowest attenuation spectral window of silica fi ber, which is the critical guiding medium with minimum broadening effects on the transmitted data pulse sequences. This electromagnetic spectrum for communications is shown in Figure 1.3. As observed, the spectrum of optical communication based on silica fi ber occupies only a small fraction of the electromagnetic spectrum but extensive bandwidth and capacity can be made available for years to come.