4. Conclusion In conclusion, a compact and widely tunable OEO configuration based on directly-modulated dual-mode laser has been proposed and experimentally demonstrated. The functions of the laser source, intensity modulator, and tunable narrow-band RF filter are realized by a single AFL chip, which significantly simplifies the configuration and reduces the power consumption and cost. Stable microwave signals continuously tunable from 28 to 41GHz with signal-side-band (SSB) phase noise below −106 dBc/Hz (@ 10-kHz frequency offset) and threshold electronic gain