We proposed and demonstrated 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 dielectric material as the core, the response time was reduced to 105 μs (rise time) and 15 μs (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 wavelength selective switch will be introduced.
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