F-P Cavity And DFB Yb～(3+)-doped Fiber Laser Research

Yb-doped fiber lasers have many advantages such as wide gain and absorption band, long upper level lifetime, high pump efficiency, large select wide at pumping wavelength and suitable for being pumped by LD. Next ,fiber lasers have exhibited a lot of good characteristics, for example, low threshold, small volume , bendable agilely structure and so on. Thus, Yb-doped fiber lasers attract people attention In this paper, characteristics of F-P cavity and distributed-feedback~ FB Yb-doped fiber lasers were researched. At the same time, formula describing threshold of DFB fiber lasers and describing saturable absorption of unpumped Yb-doped fiber in F-P cavity fiber laser were obtained. In the first chapter, the basic configuration and characteristics of fiber laser were introduced. Because of fiber grating was an important device in fiber laser, fiber grating was also introduced in detail. In the second chapter, characteristics of mode configuration and threshold in distributed-feedback-FB fiber grating lasers were analyzed. At the same time, formula describing threshold of both uniform DFB and phase-shift DFB fiber lasers were firstly obtained. 4 In the third chapter, characteristics of F-P cavity fiber laser under the condition of free run were researched experimentally. According to the experimental result, we can have conclusion that multiple laser hills will appear owing to wide gain band in Yb-doped fiber and gain spatial hole burning of F-P cavity. The space between laser hills was about 1 Onm In the fourth chapter, a fiber grating was used in Yb-doped F-P cavity fiber laser, narrow band lasers were obtained, bands of which were such narrow as the band of fiber grating. However, multiple laser hills still were observed. The space between laser hills was about 0.1 5nm. In the fifth chapter, Formula describing saturable absorption of unpumped Yb-doped fiber were obtained. The conclusion can be obtained according to the formula that the stronger the signal laser was, the less the saturable absorption coefficient was. What more, the relationship between temperature and the saturable absorption to which signal lasers were subjected from quasi-four-level medium was firstly obtained, the saturable absorption coefficient will rise as temperature rises. Finally, the previous conclusions were proved by experiment. Single frequency lasers play an important role in a lot of fields, thus, single frequency Yb-doped fiber lasers were deeply researched in this paper. At first, single frequency lasers with an output power of about 5mW were obtained in a F-P cavity Yb-doped fiber laser with a length of 2m 5 Yb-doped fiber. The above experiment results were obtained thanks to following phenomena: There were saturable absorption spatial hole burning in unpumped Yb- doped fiber of F-P cavity, which can compensate gain spatial hole burning in pumped Yb-doped fiber. In the experiment, the appearing possibility single frequency relates to adequate pump power. Besides, the length of Yb-doped fiber can also affect the possibility. Secondly, single frequency lasers were realized once again in uniform DFB Yb-doped fiber lasers near pump threshold.