Research On The Generation Of Parabolic Pulses Based On Time-domain Envelope Operations And Nonlinear Interferometers

Parabolic pulses have attracted widespread attention because of its excellent characteristics,which mainly include two aspects.First,the parabolic pulse can output from gain fiber with linear chirp and without waveform distortion.Therefore,it is widely applied in fiber lasers and optical amplifiers to generate ultra-fast and ultra-high power pulses.Second,parabolic pulse can make signal with linear chirp through modulate processes such as cross-phase modulation(XPM)and electro-optic phase modulation,so it has wide applications in time lens,all-optical signal processing and so on.There are two kinds of parabolic pulse generation schemes in general.The first one is based on the self-similar propagation theory to control the parameters of the initial light field and optical fiber.The second one is based on the spectrum shaping to match the spectrum characteristic of parabolic pulse.These two kinds of methods both have the problem of strict parameter requirement.In this paper,we discuss the parabolic pulse generation based on time-domain envelope operation and nonlinear interferometer.The main research work includes the following two parts:We propose and demonstrate a new and simple scheme for accuracy parabolic pulses generation.Mathematically,a parabola can be expressed as a quadratic function,which is equivalent to the product of two linear functions.According to this concept,since a triangular pulse natively has a linear rising edge and a linear falling edge,and the intensity modulation has the feature of multiply operation,a parabolic pulse with full duty cycle can be consequently obtained if a triangular pulse is carved by an identical triangular time window.In experiment,2-GHz dark parabolic pulses and double-frequency bright parabolic pulses are obtained.The flexibility of this system is demonstrated by adjusting the triangular pulse frequency,the dark parabolic pulses with frequency of 1 GHz,3 GHz and the corresponding double-frequency bright parabolic pulses are obtained.This method avoids complex spectral line manipulation and strict parameter control,meantime the system is stable.A new parabolic pulse generation scheme based on nonlinear optical fiber loop mirror(NOLM)is proposed.Some desired waveforms can be obtained by interference process because the intensity of an optical interference field is the function determined by the amplitudes and phase of two coherent light fields.Therefore,if the interference field can be expressed as a quadratic function by properly controlling the amplitudes and phase of the coherent beams,parabolic pulses can be consequently generated.Based on the NOLM,the experimental system can obtain 8 GHz bright and dark parabolic pulses at the same time.In order to show the tunability of this system,triangular waveforms with frequencies of 9 GHz and 10 GHz are sent to nonlinear interferometer structure.Consequently,parabolic pulses at 9 GHz and 10 GHz are achieved.The nonlinear modulation process of this method has no bandwidth limitation,furthermore the bright and dark parabolic pulses can be obtained simultaneously,and the whole system is easy to operate.The research work of this paper not only provides new methods for how to generate parabolic pulses,but also provides new ideas for how to obtain pulses of other shapes.