Study On The Characteristics Of Hybrid-gains Random Distributed Feedback Fiber Laser

Random distributed feedback fiber laser(RDF-FL) is a novel type of random laser reported by Turistsyn et al based on a roll of single-mode fiber(SMF) in 2010, which is based on random distributed Rayleigh scattering(RS) in single mode fiber(SMF) and Raman amplification gain. Thanks to its stable and continuous output, high photon degeneracy and low spatial coherence, RDF-FL can be applied to the laser source, optical communication and optical sensors. In addition, it has important influence in some basic subjects, such as laser physics, disordered system theory and nonlinear optics, etc.Now, the gain of RDF-FL based on SMF is provided by Raman amplification, so that the threshold is really high, the length of cavity is long, and output spectrum depends on the SMF’s gain, such as with the increase of pump power, the laser spectrum will appear bimodal structure, the peak will move. Furthermore, the gain of RDF-FL also could be provided by active fibers doped with rare-earth elements. The threshold of RDF-FL based active fiber is low and the output spectral is fixed. However, Rayleigh scattering in short active fiber is weak enough to emit random lasing(RL).We could emit the RL of high efficiency and low threshold with the help of combination of two fibers and feedback strengthen process. The main job as follows:Firstly, through adding the Raman gain, fiber loss and RS to the nonlinear Schrodinger equations, we obtain the stable transmission equations of Raman amplification system; through Giles rate equations, we receive the relation between gain and pump, and the put up the EDF gain model; With the help of boundary conditions, we realize the numerical simulation of hybrid structure through combination of two transmission equations. Results can reflect the RDF-FL characteristics, such as power distribution, the threshold and the evolution of spectrum, which consistent with the experimental results.Secondly, we study the random laser emission of EDF. With the 1480 nm bump solely, narrow spikes appear randomly above the ASE spectrum. After adding SMF, ASE is suppressed and a narrow lasing peak generates at 1569 nm.And then, we analyze the output characteristics in asymmetric RDF-FL structure. When EDF acted as a part of the laser cavity, it can provide gain for the backward lasing. There are no obvious threshold and no change with increase of 1480 nm pump power at the left side, while we can observe threshold at right side, and the curve moves upward when 1480 nm bump power increases. When EDF not acted as a part of the laser cavity, only provide seed light, the broad output spectrum are got at both side, and 1480 nm pump power can control the transmission efficiency of the backward light.Finally, experimental setup with symmetry pumping and optical fiber configuration is realized. Taking advantages of combination of EDF and Raman amplifications, random lasing with novel output characteristics,(i.g., stable single-peak random lasing and transitional variation between chaotic and stable states) are observed. At the stable state, the output is single peak and modeless RL, whose linewidth is about 1 nm and spectral contrast is larger than 25 dB. What’s more, centre wavelength is not change with the pump power.