ELECTRO-OPTICAL FILTERS.

This article presents information on electro-optical filters. An optical filter that can be electrically tuned to a desired wavelength is known as an electro-optical filter. There are various types of electro-optical filters that have been reported so far. Typical filters are based on directional couplers, distributed Bragg reflectors, Fahry-Perot resonators, Mach-Zehnder interferometers, and polarization mode converters. Among them, the directional coupler- type filter has a single passband in transmission and can send the selected wavelength to the other port without inherent light reflection. This makes it possible to integrate other components into the coupler structure and to prevent optical noise from entering the system.