Research On Microwave Waveform Signal Generation Technology Based On Optical Modulation And Filtering

Microwave photonics is a new interdisciplinary subject which combines the advantages of microwave technology and photon technology.It can realize the generation,processing,transmission and control of high-frequency microwave signal by optical means.Photogenerated microwave signal is an important research branch of microwave photonics.Compared with the microwave signal generated by traditional electrical methods,it can not only overcome the constraints of "electronic bottleneck",but also has the characteristics of large bandwidth,high frequency,strong reconfigurability,anti electromagnetic interference,light volume,small weight and so on,therefore widely used in optical wireless communication system,digital satellite communication system,radar systems and other fields.This paper focuses on the microwave waveform signal generation technology based on optical modulation and filtering.The main contents include the following aspects:(1)The research background and significance of microwave photonics and photogenerated microwave waveform signal are introduced.According to the different structure and principle,and combined with the related research status at home and abroad,we classify and summarize the photogenerated arbitrary waveform microwave signals.(2)The modulator of photogenerated microwave waveform signal is described in detail,and the modulator of three kinds of Mach-Zehnder modulator is simulated.The theory of microwave signal arbitrary waveform generation based on optical filtering is deduced from the perspective of mathematical model,and the synthesis results of triangular wave,square wave and sawtooth wave under different Fourier components are analyzed by MATLAB software according to Fourier series theory,which lays a foundation for the following research content.(3)A scheme of microwave waveform signal photon generation based on Mach Zehnder modulator is proposed.Firstly,the theoretical derivation of the scheme is carried out,and then the simulation is carried out by optisystem software.In this scheme,the output optical signal is divided into two channels,one is modulated by Mach Zehnder modulator,and the other is phase shifted by optical delay line.The two optical signals are combined at the coupler,and a band-pass filter is used as a spectrum shaper to filter the coupled optical signal.After photoelectric detection,the microwave waveform signal can be obtained.By changing the parameters of the modulator and the phase shift generated by the optical delay line,the triangular wave,square wave,sawtooth wave and mirror sawtooth wave with the repetition rate of10 GHz can be generated;by changing the repetition rate of the driving signal and adjusting the filtering range of the filter,the triangular wave,square wave and sawtooth wave with the repetition rate of 5GHz and 20 GHz can also be obtained.Generally speaking,the microwave waveform of this scheme can be reconstructed and the repetition rate of microwave signal can be tuned easily.(4)A scheme of microwave waveform signal photon generation based on phase modulator is proposed.Firstly,the triangular wave signal generation scheme of shaping and filtering phase modulated optical signal through inverse rectangular filter is simulated and analyzed by optisystem software.The simulation results show that the triangular wave with repetition rate of 10 GHz can be generated,and the scheme is theoretically deduced.Secondly,the inverse rectangular filter is improved,and an improved scheme is proposed,which selects the sinusoidal wave filter based on polarization maintaining fiber as a spectrum shaper,the sinusoidal wave filter structure has the advantages of adjusting the length of polarization maintaining fiber and controlling the state of polarization controller,so it can flexibly tune the filter curve,and analyze the influence of the length of polarization maintaining fiber and the rotation of polarization controller on the adjacent transmission peaks in sine wave filter structure.Finally,the improved scheme is verified by experiments,and the repetition rate of 1 0 GHz triangle wave,square wave and a pair of opposite polarity pulse sequence,the switching between waveforms is flexible and agile.