Fig. 1. Schematic diagram of the proposed RF signal detection (EDFA, erbium-doped fiber amplifier; SMF, single mode fiber; OTDL, optical tunable delay line; PD, photodetector; EC, electrical coupler; ES, electrical splitter; ESA, electrical spectrum analyzer).

Fig. 2. Illustration of the RF signal detection. (a) Modulation response of the laser with a relaxation oscillation at f_m. (b) Optical signal from the DFB laser after modulation. (c) Multi-mode oscillation state around f_m after closing the loop when there is no input RF signal. (d) The RF signal f_m is amplified when it matches with the oscillation mode. (e) The RF signal f_m^′ has loss when it mismatches with the oscillation mode. (f) The RF signal f_m^′ is amplified after tuning the delay time of the OTDL.

Fig. 3. Simulation for the max G_sys with G_open.

Fig. 4. Noise power with different photocurrents.

Fig. 5. Sidemode power at different frequencies.

Fig. 6. Electrical spectra of the output RF signal: (a) span is 2 GHz, (b) span is 500 kHz.

Fig. 7. RF signals at different frequencies are amplified.

Fig. 8. Electrical spectra at 2.61825 GHz when the delay time is different.

Fig. 9. Electrical spectra of the detected RF signal at different frequencies with corresponding delay time when acquiring the max gain.

Fig. 10. Electrical spectra of the detected signals at 2.618255 GHz with different input power.

Fig. 11. Stability of the detected signal. (a) 4.499963 GHz signal with different power. (b) Power fluctuation of the signal with −75 dBm at different frequencies.

Fig. 12. QPSK constellation with different modulation rates at the power of −75 dBm with the center frequency of 2.618255 GHz.