Research On Suppression Of Nonlinear Distortion In Microwave Photonic Frequency Conversion Link

Microwave photonic frequency conversion is an important technology in signal processing of microwave photonic.It combines the advantages of flexible and precise in microwave processing and broadband and low loss in optical processing,which greatly increase the performance of the conversion system.This paper mainly studies the photonic conversion technology and its performance improvement method.Firstly,this paper introduces the development need,significance of research,research sta-tus,and application scenarios of microwave photonics and microwave photonic frequency conversion technology.Secondly,the related knowledge of microwave photonic devices and performance indicators of link is introduced,which provides theoretical support for the measurement of link.Then,by studying the existing photonic frequency conversion link and their nonlinear suppression method,we found the most conversion link suppress the nonlin-ear distortion successfully but they sacrifice a part of link gain.In order to solve this problem,this paper presents a photonic downconversion link base on optical linearization and full spectrum utilization.By utilizing the different electro-optic coefficients of the z-cut LiNbO₃phase modulator and controlling the polarization angle at the optimal point,we realized the suppression of the nonlinear distortion.One this basis,the link gain is improved by reusing the optical carrier and lower sideband.And then,this scheme is proved by detailed formula deduction,the link gain is improved 12dB through the theoretical calculation.We established the simulation model and completed the parameter setting according to the link structure.According to the simulation,the nonlinear distortion suppressed?23dB com-pared with the single polarization state link,the link gain is improved?13.42dB compared to the linearized downconversion link without full spectrum utilization.The SFDR of the link can be up to 104.7 dB·Hz^4/5,and it is 7.4dB better than the case of conventional TM-link.Finally,the stability and wide applicability of the link are verified by simulation.The simu-lation results show,in the range of RF frequency covered 10?41GHz and RF power covered-10?10dBm,the link can work as usual,and the link gain is stable with the fluctuation of conversion gain is less than±0.94dB.Furthermore,the frequency adaptability of the link can be further optimized by adjusting the bandwidth of FBG.In multi-channel tests,this link also shows good applicability.In three-tones,five-tones and nine-tones tests with fre-quency spacing greater than 50MHz,this link can almost perfectly restore the required IF signal,and they ensure that the power of IF is significantly different from the undesired signal.Especially in the nine-tones test with the frequency spacing is 50MHz,it is almost unable to get the IF signal from the output signal before the nonlinear suppression.And the desired IF signal has been completely recovered after using this link.However,in the17-tones test with the frequency spacing is 25MHz,although the IF signal is recovered from completely unavailable to the basic recognition,but the power difference of IF signal and undesired signal is small,it can be further optimization.Generally,this photonic conversion link has a good applicability for multi-channel situation.