Research On Arbitrary Waveform Generation And Wavelength Conversion Based On Chirped Fiber Bragg Grating And Frequency-Time Mapping

Arbitrary waveform generation(AWG)technology is widely used in UWB communication and other fields.Compared with other AWG schemes,the optical AWG technology has the advantages of small size,light weight,strong anti-electromagnetic interference ability,which can generate signals with ultra-high speed and ultra-large bandwidth.As one of the hot technologies of the optical AWG,the scheme based on space spectral shaper and frequency to time mapping theory has good reconfigurability.In recent years,the AWG scheme based on the chirped fiber Bragg grating to realize spectral shaping and frequency-time mapping simultaneously has attracted much attention,which can break the limitations of high insertion loss,low stability and high cost of space spectral shaper.In the reported AWG scheme based on chirped fiber grating and frequency to time mapping theory,the design method of grating reflection spectrum is complex,and it is only used to generate chirped microwave pulse and pulse-coded signal,which is difficult to achieve arbitrary waveform generation.In this paper,a simplified design method of chirped fiber Bragg grating with arbitrary reflection spectrum shape is proposed.Based on the dispersion characteristics of chirped fiber Bragg grating,frequency-time mapping is introduced to generate user-defined arbitrary waveform pulse.The all-optical wavelength conversion of triangular and sawtooth pulse is studied combined with the fiber nonlinear effect.The all-optical wavelength conversion technology is widely used in code conversion,time-division multiplexing system and other fields.The reported wavelength conversion systems have complex structure,large volume and high cost.In this paper,the method of AWG based on chirped fiber Bragg grating and frequency to time mapping theory,combined with the fiber nonlinear effect to realize all-optical wavelength conversion has the advantages of simple system structure,easy integration and low cost.The main research contents and innovations are as follows:(1)The system structure and implementation principle of AWG scheme based on frequency to time mapping theory are studied,and the relevant formulas of frequency-time mapping theory are theoretically deduced.The feasibility of using chirped fiber Bragg grating to realize spectral shaping and frequency-time mapping simultaneously is analyzed.The results show that chirped fiber Bragg gratings can be used as spectral shaping and dispersion element because of its reflection and dispersion characteristics.When satisfying the frequency-time mapping condition,the shape of the output pulse can be designed by changing the shape of the chirped fiber Bragg grating reflection spectrum.(2)User-defined AWG is realized based on the simplified design of arbitrary shape of chirped fiber Bragg grating reflection spectrum and the frequency-time mapping theory.Firstly,a simplified design scheme of arbitrary shape reflection spectrum of chirped fiber Bragg grating is proposed based on the transmission loss formula.Variable factors are introduced to optimize the shape of the chirped fiber Bragg grating reflection spectrum,and the design error was reduced to less than 10% with high reflectivity(?0.9).The AWG is realized combining with the dispersion characteristics of chirped fiber Bragg grating.The feasibility of the scheme is verified by the successful generation of various waveforms(triangular,sawtooth,rectangular,trapezoidal,Gaussian,and parabolic).In addition,the influence of system parameters on the output pulse is analyzed.The results show that the output pulse with controllable pulse width and adjustable frequency can be obtained by changing the grating length and pulse source frequency.(3)In this paper,the all-optical wavelength conversion scheme is studied by combining the AWG with the nonlinear effect of fiber and the design of the AWG is based on the chirped fiber Bragg grating and frequent-time mapping.Triangular pulse is used as the pump pulse,and wavelength conversion results of the triangular pulse generated by intensity modulated single-frequency continuous light source and arbitrary waveform generator designed in this paper are compared.The wavelength conversion based on self-phase modulation and cross-phase modulation is studied theoretically,and the influence of various parameters on wavelength conversion is analyzed by simulation.The results show that the self-phase modulated wavelength conversion results of the designed arbitrary waveform generator are larger than that of the intensity modulated single-frequency continuous light source under the same conditions.In addition,the effects of pump pulses with different shapes(Gaussian,triangular and sawtooth)on the wavelength conversion of cross-phase modulation are also studied.The results show that the signal-to-noise ratio of the wavelength conversion sideband of the triangular and sawtooth pulses is higher than that of the Gaussian pulse.