Abstract

A variety of planar lightwave circuits (PLCs) that consist of low- loss silica waveguides on silicon substrates have been developed.¹ These PLCs can be grouped into four generations, as shown in Fig. 1. The first generation includes simple Y branches and directional couplers, which can be used as optical splitters and taps. The second generation includes Mach-Zehnder interferometers and ring resonators, which find many applications, such as optical switches and WDM/FDM filters. The third generation includes N × N star couplers and arrayed-waveguide grating multiplexers, which are associated with radiative slab waveguides. The fourth generation, the main concern of this paper, includes optical transversal filters and lattice filters, in which thermo-optic (TO) phase shifters on the waveguides are controlled (programmed) to perform different lightwave functions.

© 1994 Optical Society of America