Simulation Research On The Performance Of Microwave Photonic Broadband Phase Shifting System

With the development of microwave photonics,the important application goal of microwave photonics in recent years is to use optical fiber for the transmission of microwave carrier signals for wireless communication,so that microwaves can achieve low-loss transmission in optical fibers.However,due to the influence of fiber dispersion in the microwave photonic link,the modulated optical signal will have periodic power fading after it is transmitted through the fiber,so that the output RF signal will have serious power fading at certain specific frequency points.which seriously affects the performance of the microwave photonic broadband phase-shifting system.Therefore,how to suppress the dispersion generated in the optical fiber is an important research direction.This article proposes three broadband dispersion immunity schemes starting from how to avoid the periodic power fading caused by fiber dispersion.Mathematical analysis of its working principle was carried out,and the corresponding experimental system was built and the performance test was carried out.The first two schemes were verified by simulation experiments,and the last scheme was to build a microwave photonic link and conduct experimental verification.The main research work of this paper are as follows:(1)Broadband chromatic-dispersion-induced power-fading compensation for radio-over-fiber links based on Hilbert transform is proposed.In the range of 2-24GHz,it is not affected by periodic power fading,and it has achieved stable amplitude-frequency response,and the performance will not Affected by the length of the fiber.Ideally,when the phase difference between the input RF signals deviates from the ideal bias point by ± 15°,the power fluctuation of the output RF signal will not exceed±2dB.When the DC bias voltage of one of the MZM deviates from the ideal bias point When the set point is±20°,the power fluctuation of the output RF signal will not exceed±2dB.When there is a delay difference between two MZMs and while the delay difference is 0.05ms,the maximum power fluctuation is only 9.3dB.The measurement of the two-tone signal proves that the ratio of the fundamental to the third-order intermodulation distortion(IMD3)of this scheme is improved by 18.75dB compared with the traditional scheme,and the spurious-free dynamic range(SFDR3)of the final output of the system is also improved by 16.19dB.(2)Chromatic dispersion immune microwave photonic phase shifter based on double-sideband modulation is proposed.The scheme is based on scheme 1 to continue in-depth research,The MZM1 and MZM2 are both realize DSB modulation,The scheme realizes the control of the phase of the output RF signal by use Optical Spectrum Processor(OSP),and it can realize 0-360° full range phase shift and stable amplitude-frequency response output in the frequency range of 14-25GHz,and its frequency fluctuation does not exceed±0.5dB.The OSP is a special notch filter,the optical signal processed by the OSP is analyzed by Pol,its positive and negative first-order sidebands are beat to generate a frequency-doubling signal.This solution greatly improves the flexibility of the system.(3)Wideband and Dispersion Immune Microwave Photonic Phase Shifter with Tunable Optical Carrier to Sideband Ratio is proposed.This scheme uses DP-DPMZM,it can achieve a stable amplitude-frequency response output by use dual-channel superposition technology,By adjusting the DC bias voltage of the main modulators of x-DPMZM and y-DPMZM,the output RF signal can achieve 0-360°full range phase shift,and in the frequency range of 5-2 5 GHz,its relative amplitude-frequency response fluctuation does not exceed±2dB.By adjusting the DC bias voltage of MZM2 and MZM4 from 0-V? under the premise of ensuring V2=V4,the carrier can be converted from-34.91 dB to-1.51dB,therefore,it can control the Optical Carrier to Sideband Radio(OCSR)of the system and further control the power of the output RF signal of the system.Compared with the traditional DSB modulation scheme,this scheme achieves a relatively stable amplitude-frequency response output.Through two-tone signal measurement,the ratio of the fundamental to the third-order intermodulation distortion(IMD3)of this scheme is improved by 10dB,Compared with the power fading point of the traditional scheme,the ratio of the fundamental to the third-order intermodulation distortion(IMD3)is improved by 18.75dB.