The Reasearch Of Photonic Generation And Pulse Compression For Linear Frequency Modulation Signal

Linear frequency modulation signal(LFM)has been widely used in modern radar systems,wireless communications and medical imaging,which has been highly concerned by researchers.Due to the the limited sampling rate,the generation of the linear frequency modulation signal in the electrical domain is limited to a low frequency and small bandwidth.But photonic generation of linear frequency modulation signal can break through these limitations,which provides a new direction for solving the electronic bottleneck.At present,the techniques proposed in the optical domain have the ability to generate linear frequency modulation signal with bandwidth as high as tens of GHz,tunable characteristics and low phase noise.The research on photonic generation and pulse compression of linear frequency modulation signal has been done in this thesis.Main work are as follows:1.Photonic generation of LFM signal based on a polarization maintaining fiber-incorporated Sagnac loop mirror is studied.The central frequency and the chirp profile of the generated chirped microwave pulse can be controlled by the time delay in the Sagnac loop mirror,and dispersion in the dispersive element.Simulation work and experimental investigations are carried out,and the results are in good agreement.The measured LFM signal in experiment with bandwidth of4.3GHz,chirp rate of-0.62GHz/ns,the time bandwidth product of 30 is generated,corresponding to pulse compression ratios of 141.2 for the LFM signal by simulation.2.Photonic generation of widely LFM signal with more tuning flexibility based on optically heterodyne beating between two laser sources is studied.The central frequency,the bandwidth and the chirp profile of the generated chirped microwave pulses can be flexibly controlled by tuning CW laser,optical filter,and dispersion in the dispersive element.Linearly chirped microwave pulses with bandwidth of50 GHz,chirp rate of m 125GHz/ns,and time bandwidth product of 40 are generated in our simulation,corresponding to pulse compression ratios of 61.5.3.Photonic generation of widely LFM signal with more tuning flexibility based on the Mach-Zehnder interference is studied,that avoids unexpected instability due to the phase irrelevance of two independent lasers.Simulation work and experimental investigations are carried out,and the results are in good agreement.The measured microwave signals in experiment with the bandwidth of 6.1GHz,chirp rate ofm 5.8GHz/ns,the time bandwidth product of 12.8 are observed,corresponding to compression ratio of 16.7 for the LFM signal by simulation.Our approaches show the promise to generate widely tunable linear frequency modulation microwave signal with bandwidth as high as tens of GHz,even up to THz.It is rather more competitive than other schemes,and more suitable for modern microwave systems than electronic methods.