Self-injection locking dual-DFB lasers based on a micro-resonator for ultra-low noise microwave generation

A novel scheme for generating ultra-narrow linewidth and ultra-low noise photonic microwave based on simultaneous self-injection locking of dual DFB lasers is proposed and demonstrated. Herein, two narrow linewidth DFB lasers can be independently achieved by Rayleigh backscattering excited in a micro-resonator as feedback for self-injection locking. The 3-dB linewidth of the DFB laser is compressed from 320 kHz to 1.5 kHz, which is narrowed by 2 orders of magnitude. Based on dual narrow linewidth lasers locked to the same micro-resonator, an all-optical high-performance photonic microwave signal is generated by using the optical heterodyne method. The photonic microwave signal with the single sideband phase noise of −102 dBc/Hz and frequency noise of 600 Hz²/Hz is obtained at a frequency offset of 1 MHz for the generated 5.42 GHz microwave. The proposed scheme is also applicable to any other type of lasers such as VCSEL, fiber lasers et al, which provides a new perspective for the generation of ultra-low noise microwave signals.