Numerical Analysis Of High Repetition Rate Ultrashort Pulse Train Generation Based On Modulation Instability In Optical Fiber

As the main light source of high speed fiber communication system, high-repetition-rate ultra-short pulse train arises people's attention. Because the repetition rate and width of pulse train can impact the bandwidth and transmission speed of high speed fiber communication system, and furthermore impact the quality of communication. Therefore, it becomes more and more important to supply the method of producing high quality, high repetition rate ultra-short pulse train. Although using adiabatic soliton compression effect and higher order soliton compression effect can compress pulse from the laser, the repetion rate is not high enough.Based on the demand of high-repetition-rate ultra-short pulse train, this paper proposes a method to produce high-repetition-rate ultra-short pulse with modulation instability in optical fiber. The pulse is generated by shaping and compressing dual frequency beat signal with the effect between dispersion and self-phase modulation in nonlinear fiber. Details are as follows:(1) A scheme to generate high-repetition-rate ultra-short pulse train with beat signal is proposed. The beat signal is produced by coupling two continuous wave lasers and the power is amplified with fiber amplifier. Then, the beat signal is transmitted in high nonlinear fiber. At the output port of the fiber, a high-repetition-rate ultra-short pulse train with repetition rate equal to the frequency interval of the beat signal is generated.(2) The width of pulse train depends on the parameters in the proposed scheme. In order to get the optimal pulse train, we analyze the parameters and get the conclusion that the dispersion coefficient, the nonlinear coefficient, the interval of beat signal and the input power will impact the produced pulse train together.(3) Based on the Schrodinger equation, by simulating the evolvement process of double frequency beat signal in fiber, we get pulse trains with repetition rate of 100GHz, 200GHz,300GHz and 500GHz and pulse width of 1.56ps,830fs,526fs and 312fs, respectively.(4) In order to enhance the quality of pulse, we can get a 500GHz 234fs pulse train without pedestal based on the switching characteristics of fiber loop mirror. The pulse train generated from fiber loop mirror with beat signal incidence has better performance than that from fiber directly with the same incidence.