Study On Output Characteristic Of Multiwavelength Erbium-doped Fiber Laser Based On Four-wave Mixing

Multiwavelength Erbium-doped fiber laser based on four-wave mixing (FWM) is a technic that can get stable multiwavelength laser output at room temperature. It utilizes FWM effect to mitigate mode competition in erbium-doped fiber (EDF). In this paper, a theoretical study on this type of laser is taken. The output characteristic is analyzed, and the influence of some structure parameters is discussed.Firstly, the theory foundation of multiwavelength erbium-doped fiber laser based on FWM is introduced. Gain characteristic of EDF is demonstrated, as well as the energy exchange among different wavelengths caused by FWM. The output characteristic of an erbium-doped fiber laser without FWM medium is analyzed, on condition of different structure parameters. The energy transfer effect caused by FWM is investigated.Secondly, a theoretical model of multiwavelength erbium-doped fiber laser based on FWM is established. A ring fiber laser pumped by 980 nm laser diode is studied. The laser's gain medium and FWM medium are respectively EDF and highly nonlinear fiber. The model is based on Giles model and couple-wave equations.Finally, the model of multiwavelength erbium-doped fiber laser based on FWM is stimulated. The output spectrum obtained with different pump power and different nonlinear fiber's lengths is compared and analyzed. The reason for the differences of the output is discussed, and the relationship between the output and the two parameters (pump power and length of nonlinear fiber) is summarized.The results show that the two parameters notably affect output spectrum. With a certain pump power, the output is related to the nonlinear fiber's length. Excessive short or long fiber is harmful to the output spectrum's flatness. To get a flat spectrum, an appropriate length of nonlinear fiber is necessary. Multiwavelength output can't be formed when pump power is lower than a threshold, and only can be formed with an enough long nonlinear fiber when pump power is low. Higher pump power can get flat output spectrum with shorter nonlinear fiber. As a result, the nonlinear fiber's length and the pump power should be optimized in design of multiwavelength fiber laser based on FWM.