Fig. 1. (Color online) The proposed multi-channel FWI system architecture based on the silicon photonic MMW generator.

Fig. 2. (Color online) (a) Micrograph of the fabricated chip. (b) Schematic diagrams of the polarization tuning units. (c) Normalized P_M(Δϕ₁, Δϕ₂) with different optical power ratios and initial phase differences between the two inputs of the first MMI. (d) Photograph of the polarization control sub-system. (e) Schematic diagram of the control sub-system.

Fig. 3. (Color online) Pseudo-code of the global minimum-power searching algorithm.

Fig. 4. (Color online) Progresses of the proposed algorithm and the algorithm in Ref. [22] when a local minima exists in the normalized P_M(Δϕ1, Δϕ2) with a 75% to 25% power ratio and a π/2 phase difference between the two inputs of the first MMI.

Fig. 5. (Color online) Experimental setup of the multi-channel MMW signals generation base on the proposed silicon photonic MMW generator.

Fig. 6. (Color online) On-chip automated polarization-tuning progresses of the 7-channel signal lights.

Fig. 7. (Color online) (a) Waveforms and the demodulated constellation diagrams of the generated 7-channel QPSK MMW signals. (b) Optical spectrum of channel-1 of the MMW signal before the heterodyne beating. (c) Electrical spectrum of channel-1 of the MMW signal after the heterodyne beating. (d) Measured SNRs of the 7 channels of demodulated QPSK signal.