A short cavity fiber laser for microwave and radio-wave generation

Broadband and low loss capability of photonics has led to increasing interests in its use for generating, processing, controlling and distributing of microwave and radio-wave signals with low phase noise for applications such as Radio over Fiber systems (RoF), broadband wireless access networks, sensor networks and satellite communitarians. In this thesis, I have introduced and demonstrated a short cavity Distributed Bragg Reflector (DBR) laser operating in two stable longitudinal modes to generate microwave and radio-wave frequency signals. In the laser, Er/Yb core doped fiber has been used as the gain medium and two wavelength matching fiber Bragg gratings (FBGs) of 99.9% and 90% reflectivity in C-band were used as end reflectors. The dual mode operation was achieved by reducing the cavity length of the fiber laser to 8 mm. It was pumped with a 980 nm pump laser and the laser output has an optical signal-to-noise ratio (SNR) larger than 65 dB at 1533 nm. Due to the birefringence introduced during FBG fabrication two orthogonal polarization modes were observed for each longitudinal mode. Microwave and radio-wave signals were generated by beating these longitudinal polarization laser modes on a fast photo detector. The generated microwave signals were at 1.2687 GHz, 1.2828 GHz, 14.6962 GHz and 14.7103 GHz with a SNR of 45 dB. The generated radio-wave signals were at 14.1 MHz with a SNR of 30 dB. The 3dB bandwidth of microwave and radio-wave signals were measured to be less than 30 kHz and the Allan variance measurements indicate that the signals are highly stable for temperature variations while the generated microwave signals demonstrated a linear relationship with temperature at 1 MHz/Celsius. Due to high stability of the generated radio-wave signal and low complexity of the overall system this short cavity fiber laser has potential applications such as ultrasonic sensors and optical clocks