Large Core Diameter Erbium-doped Fiber Pulse Amplifier Theory And Simulation

To achieve diffraction-limited beam quality laser, single mode fiber is used as waveguide in both fiber amplifier and fiber laser in the past. However, in the pulse application fields, the output pulse energy from single mode fiber lasers or amplifiers is limited by amplified spontaneous emission(ASE), nonlinear effect and facet damage. To increase the energy storage and reduce fiber nonlinearities, the feasibility of multimode fiber being a waveguide in fiber amplifiers and fiber lasers have been discussed.Based on the theories of bend loss and mode coupling, a model to analyze the characteristics of distributed spatial filtering of bend multimode fiber is given in this paper. Then we made numerical simulation by the means of stepwise scan, dichotomy and the Four Orders Runge-Kutta. Numerical simulation indicated that the distributed spatial filtering of the bend multimode fiber can improve the beam quality.However, to suppress high order modes, bending multimode fiber will bring additional power wastage, which will affect the output characteristics of fiber amplifiers and fiber lasers, such as the Gain and pulse energy. In this paper, we analyzed bend loss of multimode fiber and calculated the equivalent wastage coefficient of LP01. Added the equivalent wastage coefficient into the model of fiber amplifier, we attain a equivalent fiber amplifier model in present of bend loss. The model can be use to analyze the effect of the characteristics of fiber amplifier caused by bend loss.Two models were given to analyze the characteristics of distributed spatial filtering of bend multimode fiber and the multimode fiber amplifier in this paper. The models'simulation show that single mode operate in fiber amplifier at the core radii is 32μm ,when the output pulse energy is to 2.69mJ .Compared with single mode fiber amplifier, the output pulse energy is more than 2 orders.