Study On Er-doped Random Fiber Laser With Random Distributed Bragg Gratings

Random fiber laser is a novel type laser. Rare earth doped random fiber laser with random distributed Bragg gratings is an important kind of random fiber laser. This kind of laser has the advantage of low lasing threshold, short fiber length and narrow linewidth and so on. However, multiple light localization modes arises in the randomly spaced fiber Bragg grating array. Due to mode competition, the time domain characteristics is not stable, mode jump can be observed in the output spectrum. Laser output characteristics especially its single-mode laser output and the selection of mode is a problem urgently needed research.In this thesis, we proposes a new way to control lasing modes of a Er-doped RFL by heating different position of the disordered FBG array. Besides, a tunable point reflector is introduced to optimize output characteristics of the RFLs. The experimental results show that, several stable lasing modes can be selected by heating different position of the disordered FBG array. The proposed method provides a dynamical and flexible way of laser mode control in RFLs. The location dependent mode selection mechanism could also be a potential way for laser mode switching in application of information optics. The main job as follows:Firstly, take advantage of the transfer matrix method, we obtain the transfer matrix and reflectivity expression of a single fiber bragg grating. Through Giles rate equations, we receive the relation between gain and pump, and the put up the EDF gain model; The release method is introduced to solve the problem of insufficient boundary conditions, realizing the numerical simulation of random fiber laser with random distributed Bragg gratings recorded in Er-doped fiber. Results can reflect the RFL characteristics, such as output spectrum when different locations are heated, which consistent with the experimental results.Secondly, we give the simulation of reflection and transmission spectrum based on the product of a series of transfer matrix of fiber bragg gratings and Er-doped fiber segments. We also measure the real reflection and transmission spectrum in the experiment, then we compare the result of simulation and experiment.And then, we proposed a way to realize Er-doped random fiber laser(RFL) with a disordered fiber Bragg gratings(FBG) array, as well as to control the lasing mode of the RFL by heating specific locations of the disordered FBG array. The disordered FBG array performs as both the gain medium and random distributed reflectors, which together with a tunable point reflector forms the RFL. Coherent multi-mode random lasing is obtained with threshold of between 7.5-10 m W and power efficiency between 13%-19% when reflectivity of the point reflector changes from 4% to 50%. To control lasing mode of random emission, specific point of the disordered FBG array is heated so as to shift wavelength of FBG(s) at this point away from the other FBGs. Thus, different resonance cavities are formed, and the lasing mode can be controlled by changing location of the heating point.