Abstract
This chapter reviews the development of planar lightwave circuits (PLC)-type thermo-optic (TO) switches for wavelength-division multiplexing (WDM)-based photonic networks. The PLC device family includes optical couplers, 1/N optical power splitters, thermo-optic switches (TOSW), arrayed waveguide grating (AWG)-type multi/demultiplexers, and lattice filters for high-speed transmission systems. PLC-type optical switches consist of a Mach-Zehnder interferometer (MZI) with a phase shifter. The MZI is an extremely effective circuit for achieving a variety of optical functions in an optical waveguide circuit. The MZIs are realized by using silica-based PLC technology, and their circuit functions are classified according to the difference in optical path length of the waveguide arms. The TO effect is a phenomenon by which the refractive index of a substance changes with temperature. In silica glass, this effect is characterized by an increase in the refractive index as the temperature rises. The MZI-type TO switch can be used as a gate switch, and its extinction ratio should be as high as possible. The optical performance, insertion loss, extinction ratio, crosstalk, polarization-dependent loss, and wavelength dependence are also reviewed for PLC-type switches.
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