Fig. 1. Schematic structure of the TFLN thermo-optical modulator with an NbN superconducting heater. (a) Cross-sectional view of the waveguide and heater (the schematics are not drawn to scale); (b) SEM image of the detail of the heater.

Fig. 2. (a) Measured transmission of the modulator under varying applied current; (b) Current-resistance curves measured at 293 and 3.45 K, respectively.

Fig. 3. (a) Time response of the TFLN thermo-optical modulator with an NbN superconducting heater at 293 and 3.45 K, respectively; (b) details of the time response; the red curve is the waveform measured at 293 K, and the blue curve is the waveform measured at 3.45 K.

Fig. 4. Measured transmission spectra of the device under zero bias at 293 and 3.45 K, respectively.