Research On The Nonlinearity Suppression And Temperature Stability Of Radio Over Fiber Links

Radio over fiber(RoF)link plays an important role in the applications like 5G telecommunication,deepspace network,high definition video signal transmission etc.,meanwhile,as the key but also fundamental element in the microwave photonics,the performance of the RoF link also determins the performance of its based applications,including optoelectronic oscillator,phase stable dissemination of radio frequency signal.RoF link successfully solves the loss and weight problem that exist in the electronic systems,meanwhile,RoF link has a very large bandwidth and is immune to the electromagnetic interference.However,there are some key elements in the RoF link that is not ideal,e.g.the electro-optic modulator has nonlinear transfunction and therefore generates nonlinear distortion after RoF link,and the optical fiber is sensitive to the temperature change which will make the signal transfer over RoF link has an uncertain phase or time delay.How to solve those nonideal problem is the key to improve those RoF based application,which makes it of great significance to investigate the nonlinear distortion suppression and the temperature stability problem.The maj or research work is listed as follows:1.The analysis and suppression of the nonlinearity of the RoF linkThis thesis presents three methods to suppress the nonlinear IMD3 signal,two of them are realized by manipulating the phase of the optical spectrum components,so that the IMD3 generated by differents origins have opposite phase but with the same amplitude,so that they can cancel with each other,the two methods for manipulating the optical phase are achieved by stimulated Brillouin scattering and the Sagnac interferometer,with these methods,the spurious free dynamic range(SFDR)can be improved by more than 10 dB.The rest one is based on the destructive combination of the nonlinear distortion,where we use a fiber Bragg gratting to suppress the optical carrier and the first optical sideband of the phase modulated signal,then a highly nonlinear electrical signal could be generated.By matching the phase of this highly nonlinear electrical signal with another electrical signal output from a normal RoF link,then the IMD3 can be well cancelled while the fundamental not surffering from the power loss,the experimental results show that the SFDR can be improved by 14 dB,reaching 109.6 dB·Hz2/3.2.Thermal coefficient measurement of single mode fiber and hollow core fiberThe signal delay in RoF normally influenced by the optical fiber,recently,hollow core fiber(HCF)is proved to have a very low thermal sensitivity as compared with standard single mode fiber,as the light is guided in the atmosphere filled core,then the thermal sensitivity is limited by the thermal expansion of fused silica material,make the thermal sensitivity reaching 2 ps/km/K.Considering that cryogenic temperature is very common in the polar region and some physical experiments,while the thermal sensitivity of the optical fiber at such low temperature is still unknow yet.Here,we present for the first time,the thermal sensitivities of SMF and HCF from cryogenic to room temperature.A liquid nitrogen cooling system is used to create the cryogenic environment,the thermal sensitivities of both SMF and HCF with and without coating are measured,providing significant reference for the RoF's application in those extreme environment.Meanwhile,we also realized thermally insensitive property in HCF,which is important for the optical metrology related application.3.High precision positioning in 5G with HCF based RoF linkBenefiting from the low thermal sensitivity of the HCF,we tried to use the HCF in high precision positioning in 5G.We found that when the hollow core photonic bandgap fiber works at its thermally insensitive wavelength,it is the the polarization mode dispersion that influence the propagation delay.Considering the polarization mode dispersion,chromatic dispersion and the loss,we believe that the fiber should work at the C band at present.In the experiment,we prove that by using HCF based RoF link,the basestation can be passively synchronized,even when the fiber optic link in 5G experiences the temperature fluctuation over ±10?,the calculated maximimum positioning error based on observed time difference of arrival(OTDoA)is 1 cm,which is more than 20 times better than the SMF based 5G network.