High index contrast optical waveguides and their applications to microring filter circuit and wavelength selective swich

Utilizing the small bending radius of high index contrast optical waveguides, ultra-compact optical devices such as waveguide branch, Mach-Zehnder interferometer, arrayed waveguide grating filter, microring resonator filter, and so on can be realized. We have proposed and demonstrated a vertically coupled microring resonator as an Add/Drop filter, and recently realized a hitless wavelength channel selective switch (hitless tunable Add/Drop filter) using Thermo-Optic (TO) effect of double series coupled dielectric microring resonator. Using a high-index dielectric material as the core, the response time was reduced to 105μs (rise time) and 15μs (fall time), which are fifteen-fold and hundred-fold faster than that of polymer material, and the reproducibility by the heat cycle test was also improved to less than 0.01nm. The tuning range of wavelength selective switch was expanded to 13.3nm using the Vernier effect, and a large extinction ratio of more than 20dB was realized. In this review, the principle and recent progress of microring resonator based wavelength selective switch will be introduced and some basic switching circuits required to optical cross connect will be discussed