Low-noise x-band tunable microwave generator based on external cavity lasers

Abstract

A relatively simple and stable microwave oscillator tunable across the full X-band is achieved. The microwave oscillations are self-generated limit-cycles produced by a laser diode subjected to optical feedback from a mirror. Further, the oscillations are stabilized utilizing two techniques in tandem, the first being a resonance effect based on locking the two inherent timescales of the laser, and the second being optoelectronic feedback. The resulting stable oscillations are fully tunable across the X-band from 5.5 to 12.1 GHz with typical phase noise performance of -107 dBc/Hz at 10 kHz offset. Further, the system is relatively simple by not requiring multiple lasers, radio-frequency filters, external RF sources, or any specialized equipment, thus, enabling a compact and low-cost microwave oscillator for applications in radar, radio over fiber, and telecommunications.