Research On Nonlinear Distortion Of RoF Link Based On DPMZM

With the rapid development of modern communication technology and the continuous change of Internet application scenarios,high-speed and large-bandwidth network requirements have put tremendous pressure on the communication network infrastructure.Radio over fiber?RoF?is a communication system that can provide wireless signal services in the millimeter wave band.This system uses optical fiber to transmit data between base stations,bringing high bandwidth and faster data transmission experience to users.Despite the rapid development of RoF system,the distortion caused by the nonlinearity of the electro-optical devices in the link seriously affects the effective transmission of signal,reducing the spurious free dynamic range?SFDR?and linearity of the system link.Therefore,how to suppress or eliminate the nonlinear distortion and improve the SFDR and linearity of the link has become one of the research focuses.In this thesis,we mainly study the linear optimization technology in RoFsystem link based on dual drive Dual Parallel Mach Zehnder modulator?DPMZM?.Firstly,the structure,advantages and application of RoF system link are introduced,and the domestic and foreign linearization technical solutions are classified and analyzed in detail.Second,the structure and working principle of the core devices in the link are analyzed,and the mathematical model of the working mechanism of the electro-optic modulator is established.Finally,the generation mechanism of non-linear distortion and various parameters affecting the performance of the SFDR system are analyzed in detail.Three linearization methods of RoFsystem link based on DPMZM are proposed to suppress the second-and third-order nonlinear distortion in RoF system link and enhance SFDR.A dynamic range improve scheme for ROF link based on DPMZM was proposed.The third-order intermodulation distortion?IMD3?is suppressed by adjusting the phase of the radio frequency signal and the bias voltage of sub modulator.The inhibition mechanism of IMD3 was theoretically analyzed,and verified and discussed by simulation.Simulation results show that IMD3 is completely suppressed below the noise floor,IMD3 carrier-to-interference ratio?CIR?is as high as 65.5d B,and the third-order spurious-free dynamic range?SFDR3?is increased to 127.8d B·Hz2/3.A high linear RoF link based on DPMZM was proposed to suppress IMD2 and IMD3 simultaneously.By changing the driving signal loaded on the DPMZM and optimizing the bias voltage,the two-tone signals are separately modulated in the two sub-modulators of the DPMZM,thereby suppressing the IMD2 and IMD3components generated at the beat frequency.The inhibition mechanism of IMD2 and IMD3 was theoretically analyzed,and simulation verification and discussion were performed.Simulation results show that IMD2 and IMD3 are completely suppressed below the noise floor,and the second-order spurious free dynamic range?SFDR2?and SFDR3 are 90.86d B·Hz^1/2and 114.53d B·Hz^2/3,respectively.A high linear RoF link schemebased on DPMZM and balanced detector?BPD?is proposed to suppress SHD,IMD2 and IMD3 simultaneously.The IMD3 components are eliminated by phase control and optimizing the bias point of two DPMZMs.The second order distortion can be eliminated by balanced differential detection of orthogonally polarization optical signals from two DPMZMs.Meanwhile,in order to study the digital signal transmission capability of the linearized link,the DPMZM is loaded with a 28-Gbit/s 16QAM signal for vector modulation.The inhibition mechanisms of SHD,IMD2 and IMD3 was theoretically analyzed,and simulation verification and discussion were performed.Simulation results show that SFDR2 and SFDR3 are 91.3d B·Hz^1/2and 123.2 d B·Hz^2/3,respectively,and theerror vector magnitude?EVM?reaches 4.05%after digital signal demodulation.The linearized RoF link can be used in both.The linearized RoF link achieves high dynamic range and has good adjustability.It can be applied to both single-octave communication system and multi-octavecommunication system.