Fig. 1. (a) Schematic diagram of the proposed photonic microwave harmonic down-converter (OFCG: optical frequency comb generator; SSA: sideband selective amplification; ML: master laser; PC: polarization controller; OC: optical circulator; SL1/2: slave laser 1/2; ATT: optical attenuator; PD: photodetector; PM: optical phase modulator; WSS: wavelength selective switch; EDFA: erbium-doped fiber amplifier; OSA: optical spectrum analyzer; ESA: electrical spectrum analyzer). (b) Illustration of the high-efficiency PMHDC based on the self-oscillation OFC and the SSA effect.

Fig. 2. (a) Optical spectra for the generated OFC under different conditions. (b) Corresponding electrical spectra. (c) The electrical spectrum of the signal at 5.63 GHz. (d) The phase noise of the signal at 5.63 GHz with/without OI.

Fig. 3. OFCs generated for a varying OI strength.

Fig. 4. OFCs generated for a varying ML wavelength at the same power of -10.5 dBm.

Fig. 5. Change in the OFCs when the wavelength of the ML is adjusted in the locking condition.

Fig. 6. Generation of the 2nd–12th harmonic locked OFC.

Fig. 7. (a) Output optical spectra for SL2: free-running SL2 with no OI (black), injection locking state with a gain spectrum (red), and when the RF signal is modulated to the ML (blue). (b) Optical spectra with different frequency spacings of 100 GHz and 190 GHz.

Fig. 8. (a) Optical spectrum for the combined output. (b) Electrical spectra for the down-converted signal with/without the SSA effect.

Fig. 9. (a) Phase noise of the input RF signal and output IF signal. (b) Corresponding phase jitter of the signals.

Fig. 10. (a) Optical spectra when the frequency of the input RF signal is varied from 11 to 40 GHz. (b) Electrical spectra for the corresponding IF signals. (c) Conversion efficiency of the system for the RF signals with different frequencies.

Fig. 11. Corresponding IF signals with high conversion efficiency are obtained when adjusting the FSR.

Fig. 12. (a) Electrical spectrum measured for the IF signals (span = 1 MHz, RBW = 1 kHz). (b) Measured fundamental and IMD3 components as a function of the input RF signal power.

Fig. 13. (a)–(c) Constellation of the IF signal with different data rates. (d) EVMs for the IF signals when the data rate and carrier frequency are different. (e) Change in the EVM and SNR with output optical power.