Fig. 1. Concept of the proposed photonic-frequency-interleaving (PFI)-enabled broadband receiver. (a) Schematic diagram of the PFI-enabled receiver. LD, laser diode; EOM electro-optic modulator; BPD, balanced photodetector; OLO, optical local oscillator; LPF, low-pass filter; ADC, analog-to-digital converter; DSP, digital signal processing; CH, channel. (b) The relative spectral positions among the optical carrier, the incoming signal, and the OLOs. (c) The digitized baseband spectral slices of the incoming signal in each channel after IQ combination. Overlap n, the overlap region between channel n and channel n+1.

Fig. 2. Experimental setup of demonstration of the PFI-enabled broadband receiver. (a) Experimental hardware setup. AWG, arbitrary waveform generator; MSG, microwave signal generator; BPF, band-pass filter; RF chain, the RF filter-amplifier-filter chain; EA, electrical attenuator; TCR, trihedral corner reflectors; EC, electrical coupler; CW laser, continuous-wave laser; DFB lasers, distributed feedback lasers; MZM, Mach–Zehnder modulator; CR, optical coherent receiver; LPF, low-pass filter; ADC, analog-to-digital converter; DSP, digital signal processing; EA, electrical amplifier; IF, intermediate frequency. Inset 1: structure of the RF chain. Inset 2: structure of the optical coherent receiver. (b) The relative spectrum positions setting of the signal reconstruction experiment (Ku-band region) and the dual-band microwave imaging. (c) The relative spectrum positions setting for the experiment of scalability demonstration.

Fig. 3. System frequency-response measurements. (a) The amplitude-frequency response of the first channel. (b) The phase-frequency response of the first channel. (c) The amplitude-frequency response of the second channel. (d) The phase-frequency response of the second channel. The gray “background” is the superposition of 20 results curves measured by feeding 20 pulses with a known waveform into the system at the T0 moment. The red curve is the averaged result of the gray curves and is adopted as the reliable system response. The blue and green curves are the averaged response recorded at the moments of the T0+5  min and T0+30  min.

Fig. 4. The experiment results of multi-format broadband signals reconstruction, which are widely used in radar and communication applications. RmsPD, root-mean-square phase difference; EVM, error vector magnitude. (a) The results and analyses of the reconstructed LFM signals. (i) The temporal waveform of the reconstructed signal compared to the original signal; (ii) the power spectra of the compensated signal for two channels; (iii) the time-frequency plot of the reconstructed signal; (iv) the pulse-compression curve of the reconstructed signal; (v) the inter-channel phase difference in the overlap region. (b) The results and analyses of the reconstructed NLFM signals. (i) The temporal waveform of the reconstructed signal compared to the original signal; (ii) the power spectra of the compensated signal for two channels; (iii) the time-frequency plot of the reconstructed signal; (iv) the pulse-compression curve of the reconstructed signal; (v) the inter-channel phase difference in the overlap region. (c) The results and analyses of the reconstructed QPSK signals. (i) The temporal waveform of the reconstructed signal compared to the original signal; (ii) the power spectra of the compensated signal for two channels; (iii) the constellation diagram of the reconstructed signal. (d) The results and analyses of the reconstructed 16QAM signals. (i) The temporal waveform of the reconstructed signal compared to the original signal; (ii) the power spectra of the compensated signal for two channels; (iii) the constellation diagram of the reconstructed signal.

Fig. 5. The experiment results of the dual-band microwave imaging of two TCRs. (a) LFM signal experiment results. (i) The spectra of the compensated signals of three channels. (ii) The range profiles of the two bands. (iii) The azimuth slice of one TCR. (iv) The ISAR image of C-band. (v) The ISAR image of Ku-band. (b) NLFM signal experiment results. (i) The spectra of the compensated signals of three channels. (ii) The range profiles of the two bands. (iii) The azimuth slice of one TCR. (iv) The ISAR image of C-band. (v) The ISAR image of Ku-band.

Fig. 6. The results of the image interference suppression in the second channel. (a) The spectrum slices of the received LFM echo in the second channel with (red) and without (blue) image suppression after a time-frequency 2D filtering. (b) The time-frequency diagram of the LFM echoes with (left) and without (right) image suppression. (c) The time-frequency diagram of the NLFM echoes with (left) and without (right) image suppression.

Fig. 7. The experiment results of the system’s scalability demonstration. (a) LFM signal experiment results. (i) The power spectra of the compensated signals of three channels. (ii) The range profiles after pulse compression utilizing the reconstructed broadband signal and the signal slice in first channel. (iii) The ISAR image of the signal slice in first channel. (iv) The ISAR image of the reconstructed signal. (b) NLFM signal experiment results. (i) The power spectra of the compensated signals of three channels. (ii) The range profiles after pulse compression utilizing the reconstructed broadband signal and the signal slice in first channel. (iii) The ISAR image of the signal slice in first channel. (iv) The ISAR image of the reconstructed signal.