Study On Resonant Cavity Of Single Frequency Fiber Laser

Single frequency fiber lasers, as one of the research directions of fiber lasers, because of their advantages of narrow line width output and good coherence, have widely potential applications in many fields such as data storage, optical fiber sensing, high precision spectral analysis, coherent optical communication and so on.In the basic structure of optical fiber laser, the characteristic of resonant cavity plays a vital role in single frequency output. This thesis is mainly concentrated on the theory analysis and simulation of the mode selection devices-Fiber Bragg Grating (FBG) and resonant cavity structures in single frequency fiber lasers. The main research contents and achievements are listed as follows:1. The basic structure of fiber lasers is obtained based on the conditions of laser produces. The working principle of fiber lasers is illustrated in depth, and the role of each component is analyzed. The mode selection theory of fiber lasers is introduced in detail. The common methods of single frequency output and common resonant cavity structures are presented, whose advantages and disadvantages are discussed at the same time.2. Different kinds of writing methods and classification of fiber gratings are introduced simply based on the phototoxic of optical fibers. Coupled-mode equations of FBG are derived from the classical coupled-mode theory, and then the reflective characteristics can be obtained. The influences of different parameters on the peak reflectivity and bandwidth are simulated, and the corresponding conclusion is obtained. Base on all above, ordinary Fabry-Perot (F-P) cavity composed of high reflectors and F-P cavity composed of FBGs are simulated respectively and then compared. Contrasted with the ordinary F-P cavity, FBG has an effective length, which can be a part of the effective cavity length. F-P cavity based on FBGs has more excellent mode selection characteristics; single frequency output can be realized by choosing proper L (cavity length) and Lg(length of FBG) in the case of keeping the peak reflectivity unchanged.3. A FBG is written in the single mode optical fiber successfully with phase mask technique in the laboratory. By observing transmission spectrum, the conclusion proves that the good performance of the FBG enables it suit to single frequency fiber lasers well. 4. The characteristic of Er3+-Yb3+ co-doped optical fibers is analyzed in detail base on the energy level system of Er3+-Yb3+ ion pair. F-P cavity base on FBG is used as resonant cavity, and the system model of Er3+-Yb3+ co-doped fiber lasers is established combining rate equations. According to the model, Er3+-Yb3+ co-doped fiber lasers are simulated and analyzed further; at the same time, the influences of different parameters on the output characteristic are obtained.