Study On The Linewidth Control Mechanism And Technology Of Single-frequency Fiber Laser

Single-frequencyfiber lasers(SFFLs) have broad application prospectsinthe area of scientific research, industry, and national defense due to their promisingperformances of narrowlinewidth, low intensity noise, high efficient, compact all-fiber configuration and simple thermal management. On the one hand, narrow linewidth SFFL can improve the detection range of Lidar, the sound pressure resolution of hydrophone and reduce the error rate of coherent optical communication system. On the other hand, wider laser linewidth is needed in the high power laser operation in order to suppress the stimulated Brillouin scattering. Therefore, it is of great significance to control the laser linewidth to meet the requirements of different applications. The linewidth control of the SFFL is investigated theoretically and experimentally. The specific research contents and results are as follows:(1) The linewidth control model of the self-injection locking SFFL is derived from the two-level rate equation and the the linewidth of the SFFL, which reveals the relation of the linewidth before and after the self-injection locking process. According to the model, the laser linewidth can be controlled by means of changing the length of the external cavity, self-injection frequency modulation and noise injection.(2) The experiment of linewidth suppression is conducted based on the self-injection locking. By optimizing the length of the external cavity, the linewidth of the polarization-maintaining SFFL reduces from 1.5 k Hz 200 Hz by using an external cavity with a length of 101 m. In addition, in the experiment of self-injection locking SFFL, the polarization splitting is vanished by the injection locking polarization dragging effect. The linewidth suppression is also achivevd based on the slow light effect of fiber grating filter, from which a compact SFFL with a linewidth of 780 Hz is obtained.(3) The experiment of linewidth broading is conducted based on the noise injection, where the relation of noise frequency bandwidth and noise intensity with the linewidth broadening is investigated. A linewidth more than 131 k Hz is achieved with a noise intensity of 500 m Vpp and noise bandwith of 20 k Hz, from which a linewidth broadening of 22.1 d B is obtained.