a Perspective view of the thermally tunable MDR. b Cross-sectional view of the MDR along the dashed line AA’ shown in (a). c Micrograph of the fabricated MDR. d Spectral response of the MDR from the drop port. e Zoom-in view of the WGM1,107, the 3-dB bandwidth is 72 pm. f Spectrum tuning of the MDR by applying a voltage to the micro-heater.