We propose and demonstrate an efficient and fast thermo-optic phase shifter for integrated silicon photonics. By inserting a small AlN block between the TiN heater and Si waveguide, both the phase-shifting efficiency and the modulation speed are improved from ~9.4 to ~8.2 mW/π and from ~26 to ~32 kHz, respectively, as compared to the counterpart without the AlN block. The improvement can be attributed to the very large thermal conductivity of AlN (~285 W/m-K), which makes the waveguide has almost similar temperature as the heater upon it is heated. Numerical simulation shows that the proposed method is also applicable for the Si3N4 waveguide.
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