Fig. 1. Schematic diagram of modulator. (a) Schematic diagram of 2×2 MZM; (b) transmission spectra of 2×2 MZM; (c) schematic diagram of modulator based on coupling modulation with racetrack ring resonator; (d) transmission spectra of modulator based on coupling modulation with racetrack ring resonator; (e) enlarged view of transmission spectra in critical-coupled region

Fig. 2. Schematic and microscope images of modulator. (a) Schematic diagram of modulator based on the coupling modulation of racetrack ring resonators; (b) schematic diagram of tapered waveguide; (c) microscope view of modulator

Fig. 3. Transmission spectra of modulator. (a) 1556-1559 nm; (b) enlarged view of spectrum around 1558.8 nm

Fig. 4. EO responses of modulator. (a) EO S₂₁ response; (b) S₁₁ response

Fig. 5. Measured large signal transmission eye diagrams. (a)(b) 56 Gbit/s OOK optical eye diagrams at different driving voltages 0.8 V and 1.2 V; (c)-(f) 112 Gbit/s PAM4 optical eye diagrams at different driving voltages 0.4, 0.6, 1.0, 1.2 V

Fig. 6. Thermal stability of modulator. (a) Responses of the modulator transmission spectrum to temperature; (b) variations of modulator wavelength shift and temperature sensitivity with temperature

Fig. 7. 112 Gbit/s PAM4 optical eye diagrams at different temperature. (a) 20 ℃; (b) 25 ℃; (c) 30 ℃; (d) 35 ℃; (e) 40 ℃; (f) 45 ℃