Fig. 1. Schematic structure of the ML-MZM.

Fig. 2. (a) Operating principle of the proposed modulator; (b) cross section structure of the modulator arms.

Fig. 3. (a) Top view of the designed ADC mode converter; (b) simulated electric field of ADC; (c) calculated CE and XT of the mode converter.

Fig. 4. (a) Refractive index variations for TE0 and TE1 modes as a function of reverse bias for lateral PN junction. TE0 mode overlap with lateral PN junction of (b) single-mode waveguide and (c) two-mode waveguide. (d) Refractive index variations for TE0 and TE1 modes as a function of reverse bias for L-shaped PN junction. TE0 mode overlap with L-shaped PN junction of (e) single-mode waveguide and (f) two-mode waveguide.

Fig. 5. Optical microscope image of (a) the fabricated ML-MZM, (b) the mode converter, (c) MMI.

Fig. 6. (a) Transmission spectra of the ML-MZM under different reverse voltages; (b) extracted phase change as a function of bias voltage.

Fig. 7. (a) Microscope image of the ML-MZM with 1 mm phase shifter; (b) microscope image of the normal MZM with 2 mm phase shifter; (c) normal MZM transmission spectrum under various reverse voltages.

Fig. 8. Measured EO-S21 response at −3  V bias voltage.

Fig. 9. (a) Schematic diagram of the high-speed measurement setup; (b) OOK eye diagram at 10 Gb/s; (c) OOK eye diagram at 15 Gb/s; (d) measured SNR response and bit allocation of 40 Gb/s DMT signal; (e) measured BER curve of 40 Gb/s DMT signal; (f) received constellations of four typical subcarriers of the DMT signal.

Fig. 10. Optical modulation spectra of the modulator at different RF sinusoidal frequencies.

Fig. 11. Calculated EO response of ML-MZM with 1 and 0.5 mm phase shifter length.