Research On The Linear Transmission Of RF Signals VIA Optical Fiber

Linear transmission of RF signals via optical fiber belongs to the research scope of analog photonic link?APL?which is an essential part of microwave photonics?MWP?.Due to the advantages offered by optical fiber including low loss and large bandwidth,it has been considered as the key technology for the transmission of RF signals over long distances and drawed great attention from many research areas including radars,antenna remoting,radio astronomy and the next generation wireless communication systems.However,the linearity and dynamic range of conventional intensity modulation-direct detection?IM-DD?links and phase modulation-coherent detection?PM-CD?links are strictly limited by the nonlinear transfer function at their transmitter side and receiver side respectively,which seriously hinders the practical application of APL.Numbers of linearization schemes have been proposed and a huge part of them only focus on the transmitter side of the IM-DD link.PM-CD link is inherently linear and bias-free at the transmitter,which makes its remote unit be with simpler structure and more adaptive to the adverse working conditions.Thus PM-CD link has been considered as the most promising technique to transmit the RF signals.The challenge lies in the linearization of the interferometer-based reveiver.There are mainly two methods.One is based on the digital signal processing technique which however is severely limited by the sampling rate and quantization noise.The other is the linear coherent phase demodulation?LCPD?technique based on optical phase-locked loop?OPLL?.LCPD is a fundamental linear technique with the ability to suppress the overall distortions,thus it could support multi-octave RF signals and has become a hotspot for the past few years.The realization of OPLL with ultra wide loop bandwith is the most difficult part in LCPD construction.The loop bandwith directly limited the bandwith of the linear receiver.In recent years,several foreign research groups have taken the advantage of integration techniques,mitigated the fundamental limit induced by the loop delay and demonstrated LCPD modules with 1.4GHz bandwidth and a spur-free dynamic range?SFDR?of125dB/Hz^2/3 at 300MHz.In contrast,domestic researches on this direction are almost blank.In this context,this thesis gives deeply theoretical analysis and experimental invetigations on the LCPD technique.Basing on the innovative improvement of LCPD,this thesis successfully realizes the highly linear transmission of RF signals.In other word,a highly linear APL based on composite OPLL,i.e.phase modulation-linear coherent phase demodulation?PM-LCPD?link,is demonstrated,which lays a solid foundation for the futher research and application of LCPD technique.In theory,this thesis derives key formulas of LCPD which clearly characterize the operation theory and system performances.Moreover,for the first time,this thesis presents accurate mathematical expressions of link gain,noise figure,third-order intercept point and SFDR for the PM-LCPD link under open loop and close loop condition respectively,which is of great importance for the design and realization of PM-LCPD link.In the experiment,by using discrete optoelectronic components,this thesis designs and implements a LCPD module with a loop delay of 4.5ns corresponding a loop bandwidth of near 32MHz.Futhermore,basing on composite OPLL,the thesis finally succeeds in constructing PM-LCPD link with sufficient stability and realizing linear transmission of RF signals with5km long link length and SFDR over 126dB/Hz^2/3 within the effective bandwidth.