Fig. 1. Model diagram of DPMZ IQ silicon-based optical modulator

Fig. 2. Equivalent circuit model of push-pull modulation in silicon-based optical modulator (common cathode)

Fig. 3. Bias points control flowchart of channel I, channel Q, and channel Phase. (a) Initialization search; (b) closed loop locking control

Fig. 4. Simulation results of MPD feedback signal spectra after channel I and channel Q applied different bias voltages. (a) Amplitude spectra; (b) phase spectra

Fig. 5. Simulation waveforms of MPD feedback signals at time domain after channel I and channel Q applied different bias voltages

Fig. 6. Simulation results of MPD feedback signal spectra after channel Phase applied different bias voltages. (a) Amplitude spectra at sum frequency; (b) phase spectra at sum frequency

Fig. 7. Simulation waveforms of MPD feedback signals at time domain after channel Phase applied different bias voltages

Fig. 8. Test platform for direct current bias voltage closed-loop control of IQ silicon-based optical modulator

Fig. 9. Test results of MPD feedback signal spectra after channel I and channel Q applied different bias voltages. (a) Amplitude spectra; (b) phase spectra

Fig. 10. Test waveforms of MPD feedback signals at time domain after channel I and channel Q applied different bias voltages

Fig. 11. Test results of MPD feedback signal spectra after channel Phase applied different bias voltages. (a) Amplitude spectra; (b) phase spectra

Fig. 12. Test waveforms of MPD feedback signals at time domain after channel Phase applied different bias voltages

Fig. 13. Constellation diagrams of optical signals in QPSK modulation after channel I, channel Q, and channel Phase applied different bias voltages. (a) Revised by algorithm; (b) 0.96Vπ, 1.04Vπ and 0.96Vπ/2 ; (c) 0.96Vπ, 0.96Vπ and 0.96Vπ/2; (d) 1.04Vπ, 1.04Vπ and 0.96Vπ/2; (e) 1.04Vπ, 0.96Vπ and 0.96Vπ/2; (f) 0.96Vπ, 1.04Vπ and 1.04Vπ/2; (g) 0.96Vπ, 0.96Vπ and 1.04Vπ/2; (h) 1.04Vπ, 1.04Vπ and 1.04Vπ/2 ; (i) 1.04Vπ, 0.96Vπ and 1.04Vπ/2

Table 1. Sine dither signal parameters

Table 2. Relevant indexes test results of channel I, channel Q, and channel Phase with different bias voltages