Ultra-low-phase-noise photonic microwave generation and high-precision laser frequency determination with an NPRO...

Ultra-low-phase-noise photonic microwave generation and high-precision laser frequency determination are critical for advanced applications, such as radar, communication, and spectroscopy. Here, we demonstrate a monolithic nonplanar ring oscillator dual-frequency laser (NPRO-DFL) at 1064 nm that simultaneously generates ultra-stable photonic microwaves and enables sub-MHz laser frequency readout. By actively phase-locking the laser intracavity dual-frequency beat signal (equal to cavity free spectral range) to an ultra-stable oscillator via piezo control, we suppress the phase noise of the 5.6-GHz microwave signal to -40 dBc/Hz at 1 Hz offset, maintaining -105 dBc/Hz at 10 kHz offset. Leveraging this stabilized frequency as a precision ruler, we calibrate the cavity's longitudinal mode number through simultaneous monitoring of the locked microwave frequency and laser frequency. This approach achieves high-precision laser frequency readout with sub-MHz uncertainty, meeting the stringent 1 × 10^-8 scale factor requirement for inter-satellite metrology.