Fig. 1. Diagram of the cross-sectional structure.

Fig. 2. Microwave electrical mode distribution of the TWMZM cross section (a) before and (b) after the silicon substrate is removed.

Fig. 3. Microwave attenuation based on finite element method (FEM) simulations on unloaded CPS transmission lines before and after substrate removing of the wafer used in our design.

Fig. 4. Simulated EO S21 before and after substrate removal of the wafer used in our design.

Fig. 5. Fabrication process of the substrate removed modulator based on IME’s silicon photonics platform.

Fig. 6. Micrograph of the fabricated substrate removed silicon modulator viewed from above and the enlarged picture of the (a) edge couple, (b) phase shifter, and (c) the electrode region.

Fig. 7. (a) Measured EE S21 of the substrate removed modulator under various bias voltages. (b) Microwave index of the modulator before and after the silicon substrate is removed, which is extracted from the tested EE S21 at −4  V bias voltage. (c) Electrode characteristic impedance of the modulator before and after the silicon substrate is removed, which is calculated from the tested EE S21 and S11 at −4  V bias voltage.

Fig. 8. Measured EO S21 response under various bias voltages after the silicon substrate is removed.

Fig. 9. Experimental setup for the substrate removed TWMZM OOK eye-diagram measurements.

Fig. 10. Optical eye diagrams at the different rates of 70  GBaud/s, 80  GBaud/s, and 90  GBaud/s under the driving voltage of 5 V Vpp without any pre-emphasis under bias voltage of −6  V. The extinction ratios are 3.6 dB, 2.7 dB, and 3.3 dB, respectively.

Fig. 11. Experimental setup for the substrate removed TWMZM PAM-4 eye-diagram measurements.

Fig. 12. Measured PAM-4 modulation optical eye diagrams at 28  GBaud/s, 50  GBaud/s, and 56  GBaud/s without any pre-emphasis under bias voltage of −6  V. The extinction ratios are 3.6 dB, 2.5 dB, and 2.7 dB, respectively.

Fig. 13. Experimental setup for the PAM-4 signal transmission based on the substrate removed silicon modulator even different distances.

Fig. 14. Measured curve of BER versus the received optical power for 56  GBaud/s (112  Gb/s) PAM-4 signal transmission under bias voltage of −6  V.

Fig. 15. Measured curve of BER versus the received optical power for 64  GBaud/s (128  Gb/s) PAM-4 signal transmission under bias voltage of −6  V.