Research On Generation Of Microwave Signal And Bias Control Technology Based On External Modulator

In recent years,with the increase of radio frequency band,radar system is developing towards the direction of ultra-wide operating frequency band,re-configuration,multi-function integration and so on.The generation and processing of radar signal in the electric domain are affected by the low bandwidth of key electrical components and the serious electromagnetic interference(EMI).However,photonic generation technology of microwave signal has the advantages of high carrier frequency,large frequency tunable range,large time broadband width product and so on,which is effectively immune to the EMI.As a key component in photonic generation technology of microwave signal,the stability of electro-optic modulator affects the quality of generated microwave signals.However,due to the material characteristics,bias drift occurs when the modulator works for a long time,resulting in unstable work and seriously affecting the system performance.Therefore,it is necessary to study the bias control technology of electro-optic modulator.Aiming at the above two kinds of problems,this paper mainly studies photonic generation technology of microwave signal and bias control technology based on electro-optic modulator,respectively:1.A photonic approach to generate phase-coded microwave signal based on a dual-polarization Mach-Zehnder modulator(DPol-MZM)is proposed and experimentally demonstrated.Compared with other schemes,this system has a simple structure and only use an integrated modulator,which can improve the stability of the photonic link and has a good frequency tunability.Phase-coded microwave signals with carrier frequencies of 5 GHz and 11 GHz are generated experimentally.The pulse compression capability of phase-coded signal with a length of 16 bits is verified.The pulse compression ratios are 12.3 and 14.5,respectively,which is close to the theoretical value.Besides,the peak-to-side ratios are 5.38 dB and 6.20 dB,respectively.2.A photonic approach to generate phase-coded microwave signal with frequency doubling based on Mach-Zehnder modulator(MZM)and wavelength division multiplexer(WDM)is theoretically proposed and studied by simulation.In this scheme,although the link is not stable enough,it has a simple structure and low cost.What's more,this approach can effectively reduce the frequency requirement of the local oscillator signal.The phase-coded signals with carrier frequencies of 10 GHz and 20 GHz are generated by using the local oscillator signals of 5 GHz and 10 GHz,respectively.The pulse compression capability is also studied and the result accords well with theoretical analysis.3.A photonic approach to generate phase-coded microwave signal with frequency doubling based on dual-parallel quadrature phase shift keying modulator(DP-QPSK)and polarization modulator(PolM)is theoretically proposed and studied by simulation.Its integration and availability are very high and optical filter is not used in the entire link.Besides,this scheme can effectively reduce the requirements of the local oscillator signal.4.The bias control technology of electro-optic modulator is studied in depth.Firstly,the bias control technology of MZM in special and arbitrary bias point of transmission function are introduced,respectively.Then,two kinds of bias control methods of dual-parallel Mach-Zehnder modulator(DPMZM)in special bias point based on single pilot signal and two pilot signal are analyzed by theoretical derivation and simulation.Finally,a novel bias control approach is proposed in arbitrary bias point of DPMZM.High precision bias control is implemented in the simulation.