ABSTRACT
The rapid and global spread of the Internet is accelerating the growth of optical communication networks. Optical networks based on wavelength division multiplexing (WDM) systems have played a key role in increasing the capacity and flexibility of these networks. Thermo-optic (TO) effects, which are refractive index changes caused by temperature variations in a material, have been used when constructing optical switches. This chapter reviews the development of TO devices for WDM-based photonic networks. There are two main kinds of TO switch; one is composed of silica-based planar lightwave circuits (PLC), and the other of polymer waveguides. The chapter reviews these two kinds of TO device, which were developed for optical communication networks. PLC-type devices have been playing an important role because of their suitability for large-scale integration and mass production. Variable optical attenuators are playing a more important role in the gain control of linear repeaters for WDM networks and channel power equalization in WDM optical add/drop multiplexing nodes.
