Compact Photonic Integrated Chip for Tunable Microwave Generation

A tunable microwave generation is demonstrated by monolithically integrated photonic chip, which combines a mirror section and two distributed feedback (DFB) lasers. The focus ion beam technology was employed to achieve high-quality air/semiconductor slab for the mirror. Two DFB lasers (named slave and master lasers, respectively) can operate in a single fundamental mode when they are individually pumped. A microwave signal with the differential frequency between the two lasers can be obtained through optical heterodyning. A tunable microwave signal up to 25.5 GHz can be generated by adjusting the injected currents of the two DFB lasers. A four-wave mixing spectrum was measured and the linewidth of the generated radio frequency signal is 1.9 MHz.