Microwave signal generation with a dual-frequency self-injection-locked DFB laser

Abstract

Low-noise lasers are a powerful tool in precision spectroscopy, displacement measurements, and the development of advanced optical atomic clocks. All applications benefit from lower frequency noise and robust design, however, the generation of microwave signals additionally requires narrowband lasing at two frequencies. Here, we introduce a simple optoelectronic oscillator enabling the generation of a stable ultra-narrow microwave carrier signal with low phase noise based on stimulated Brillouin scattering. A cost-effective sub-kilohertz Brillouin fiber ring laser with stabilized selfinjection locked pump DFB (Distributed Feedback Laser) laser is used for this purpose. The system is supplied by a low-bandwidth active optoelectronic feedback controlled by a low-cost USB-DAQ card. The full-width of generated microwave signal at -3 dB level is approximately equal to 300 Hz with a peak maximum at ~10.946 GHz. The strongest parasitic harmonics shifted from carrier signal peak by ±50 kHz, ±450 kHz, and ±900 kHz are below the main peak by 45-50 dB. A phase noise below −90 dBc/Hz for a frequency offset above 10 kHz from the carrier after passing the 20 km length test fiber has been achieved.