Research On Multi-waveform Generation Technology Based On Optical Frequency Domain Processing

Although the microwave waveform generation technology based on electronic technology is relatively mature and has been widely used in satellite communication,instrument measurement,radar detection and other fields,it still faces the speed bottleneck problem of electronic system,which is difficult to meet the rapid increase of bandwidth and frequency requirements in its application fields.Microwave photonics technology,which combines photonics and microwave millimeter wave technology,can generate,process and transmit signals with higher speed and larger bandwidth,which is expected to break through the rate bottleneck of traditional electronics and provide a new solution for the generation of large bandwidth and high frequency waveforms.The waveform generation technology based on microwave photonics can generate user-defined arbitrary waveforms,such as triangular,rectangular and sawtooth waveforms,and the generated waveforms have the advantages of convenient tuning,high frequency,wide bandwidth and strong anti-interference ability.In this paper,three waveform generation schemes based on microwave photonics technology are proposed:(1)Based on the study of the decisive factors of the accuracy of photonic microwave waveform,a high-accuracy waveform generation scheme based on dual-parallel Mach-Zehnder modulator(DP-MZM)is proposed.Based on the modulation characteristics of DP-MZM,the optical carrier and±4th-order siderbands are generated via a DP-MZM in the upper branch,and the±1st and±3rd-order siderbands are generated via a MZM in the lower branch.After the polarization orthogonal coupling of the two modulated optical signals,the PC and PBS are used to reconstruct the two modulated optical signals with equal amplitude and inverse phase,then the photoelectric conversion is carried out by a light balance detector to output multiple harmonic components contained in the photoelectric current.By adjusting the RF driving voltage of DP-MZM and changing the modulation index,the amplitude of the output harmonics can be close to the first,third,fifth and seventh order Fourier expansion coefficients of ideal triangular and rectangular waveforms,and then the required triangular and rectangular waveforms can be generated.This scheme can generate more harmonic orders,improve the accuracy of the generated waveform,and eliminate the interference caused by unnecessary harmonic components.The simulation results show that the full duty cycle triangular and rectangular waveforms with repetition rate of 10GHz are generated.The root mean square error(RMSE)of the two waveforms and the ideal waveform is reduced to 0.0217 and 0.264 respectively,which has higher waveform fidelity.(2)Based on the study of tunability of photonic microwave waveform,a tunable and frequency doubling waveform generation scheme based on dual-polarization Mach-Zehnder modulator(DPol-MZM)is proposed.After the MZM generates a dual frequency optical signal containing±lst-order sidebands,it is divided into two channels.The upper channel generates ± 1st and±3rd-order sidebands by the modulation of a DPol-MZM,and the lower channel generates±2nd-order sidebands by another MZM.The two optical signals generate 2nd,4th and 6th-order harmonics by the photoelectric conversion and current difference of BPD,and the microwave waveform is synthesized.The relative amplitude of each order harmonics can be adjusted by adjusting the DC bias volltage of DPol-MZM and the relative power of the upper and lower optical paths.The triangular,rectangular and sawtooth waveforms with repetition rate of 20GHz are generated by simulation,and the tuning symmetry of the triangular waveform is realized.The harmonic amplitude in the electric spectrum is consistent with the theoretical analysis.(3)A scheme for simultaneous generation of waveform(rectangular,triangular and sawtooth waveforms)based on parallel MZM is proposed.On the basis of the rectangular waveform generated by the original modulator,different modulated optical signals are introduced through another modulator in parallel.After orthogonal coupling with the optical signal corresponding to the rectangular waveform,the harmonic components for correction is added to the original output optical current of the rectangular waveform through high-speed PD,so that the rectangular waveform is transformed into triangular and sawtooth waveforms.In the case of only using a set of waveform generators with fixed parameters,this scheme outputs three kinds of waveforms in parallel:rectangular,triangular and sawtooth waveforms,and does not use a filter in the structure,so it has wide frequency adjustability.Rectangular,triangular and sawtooth waveforms with the repetition rate of 10 GHz are generated in the simulation,which changes the realization mode of producing different waveforms by repeatedly changing the structural parameters.