Waveguide Filters and Related Technologies:Issues and Solutions for Practical Use in Transmission Systems

Passive waveguide devices have been utilized for many applications such as optical communication, optical sensing, and so forth. Owing to the intrinsic small footprint of passive waveguide devices, they can realize many functional devices in an integrated form, such as a waveguide branch, directional coupler, Mach-Zehnder interferometer, arrayed waveguide grating (AWG) filter, microring resonator filter, and so forth. Among them, the most successful application of passive waveguide devices is the wavelength filter, as typified by an AWG wavelength multi/demultiplexer. However, for the practical use of these waveguide-type wavelength filters, many issues should be solved, such as the polarization dependence, ambient temperature dependence, the tailoring of characteristics, and sometimes trimming. In this tutorial, waveguide-type wavelength filters are reviewed from the viewpoint of functionality realized by solving such issues with ingenuity, because the most widely used functions are the wavelength filter and wavelength multi/demultiplexer.