We propose and experimentally demonstrate the programmable photonic radio frequency (RF) filters based on an integrated Fabry–Pérot laser with a saturable absorber (FP-SA). Owing to the high output power and the relative flatness spectrum of the FP-SA laser, only a waveshaper and an erbium-doped fiber amplifier (EDFA) were needed, which can greatly reduce the complexity of the system. The sinc filter employed 87 taps, representing a record-high tap number and resulting in a 3-dB bandwidth of 0.27 GHz and a quality factor of 148. Furthermore, Gaussian apodization enabled the out-of-band rejection of the filter to reach 34 dB and the center frequency to be finely tuned over a wide range, spanning from 4 to 14 GHz. These results indicate that the proposed scheme could provide a promising guideline for the photonic RF filters that demand both high reconfigurability and greatly reduced size and complexity.

The stable long-distance transmission of radio-frequency (RF) signals holds significant importance from various aspects, including the comparison of optical frequency standards, remote monitoring and control, scientific research and experiments, and RF spectrum management. We demonstrate a scheme where an ultrastable frequency signal was transmitted over a 50 km coiled fiber. The optical RF signal is generated using a two-section distributed feedback (DFB) laser for direct modulation based on the reconstruction equivalent chirp (REC) technique. The 3-dB modulation bandwidth of the two-section DFB laser is 18 GHz and the residual phase noise of -122.87dBc/Hz is achieved at 10-Hz offset frequency. We report a short-term stability of 1.62×10-14 at an average time of 1 s and a long-term stability of 6.55×10-18 at the measurement time of 62,000 s when applying current to the front section of the DFB laser. By applying power to both sections, the stability of the system improves to 4.42×10-18 within a testing period of 56,737 s. Despite applying temperature variations to the transmission link, long-term stability of 8.63×10-18 at 23.9 h can still be achieved.