Investigation On Linearized Optical Transmission Technology Of Microwave Fiber Link

With the development of optical fiber communication technology,the advantages of optical fiber over radio frequency(RF)cables are increasingly prominent,and thereby the scheme of employing fiber-optic links to transmit microwave signals has gradually entered the minds of scientific researchers.The key to measuring the performance of the microwave photonic links(MPL)is how to transmit the signal with low loss and no distortion,and severe nonlinear distortion could disrupt a system's normal operation during MPL transmission.Therefore,it is crucial to research linearization techniques for MPLs to secure the transmission of modulated signals without distortion,and the spurious-free dynamic range(SFDR)is an important indicator of the nonlinear characteristics of MPLs.Consequently,this thesis aimed to improve the dynamic range of the MPL.In the practical application,the needs of modern optical wireless communication could not always be met by a single function of the MPL.Therefore,this thesis aimed to implement multifunctional integration of the MPL while also dealing with its linearization.The main contents of this thesis are stated as follows.Firstly,the applications and advantages of the MPL were outlined,and relevant research on technologies of the MPL conducted at home and abroad,including linearization,phase shifting,and frequency conversion,was summarized to analyze the key performance indicators and key devices of the MPL.Additionally,the key parameters of the MPL were examined to investigate the connection between noise factor and dynamic range.Moreover,the way to apply suitable two-tone signals to eliminate third-order intermodulation distortion(IMD₃)was theoretically explored,when the upper and lower two sub-Mach-Zehnder modulators(MZM)of dual-parallel Mach-Zehnder modulator(DPMZM)were at the orthogonal bias point,and finally multiple sets of RF signals that could eliminate IMD₃ were obtained.Secondly,a scheme of suppressing nonlinear distortion based on a dual-drive DPMZM and bandpass filter was investigated.The seventh-order nonlinear distortion(IMD₇)was the main reason affecting the nonlinear distortion of the MPL,allowing the seventh-order SFDR to attain a dynamic range of 130.3 d B·Hz^6/7.Founded on the assumption,a type of MPL with simultaneous frequency conversion,phase shifting,and linearization was proposed that could make the dynamic range of seventh-order SFDR reach 125.6 d B·Hz^6/7.Therefore,frequency conversion and phase-shifting could be achieved by MPL while suppressing IMD₃.Thirdly,a linearization strategy based on a single-drive DPMZM cascaded Mach-Zehnder modulator(MZM),as well as a dual-drive DPMZM cascaded MZM,were studied.The single-drive DPMZM could suppress IMD₃ to generate a variable-frequency signal,resulting in a third-order SFDR of 121.53 d B·Hz^2/3;the dual-drive DPMZM suppressed IMD₃ while suppressing second-order intermodulation distortion(IMD₂)to generate a variable-frequency signal,yielding a second-order SFDR of 80.49d B·Hz^2/3 and a third-order SFDR of 118.21 d B·Hz^2/3.Fourthly,a linearized MPL based on dual-drive DPMZM and a balanced detector was explored,which could eliminate IMD₂ and second harmonic distortion(SHD)while effectively suppressing IMD₃ and third-order harmonic components.Based on IMD₃,the third-order SFDR was 120.1 d B·Hz^2/3,while the third-order SFDR based on third-order harmonic components was 106.85 d B·Hz^2/3.At broadband signal input,the scheme outperformed the common single-drive DPMZM linearized link.