Research On Large Dynamic Range Microwave Photonic Links And Nonlinear Distortion

Benefitting from the inherent ultra-wideband,low loss and long distance transmission characteristics,microwave photonic links are widely applied in military radar,aerospace,commercial communication and next-generation radio access networks.However,there are still many problems to be overcome in microwave photonic area.Due to the intrinsic nonlinear transfer characteristic of devices such as MZM modulator and photo-detector,a lot of nonlinear distortions occur in(electro-optic)E/O and(opto-electronic)conversion based analog photonic link(APL).It includes harmonic distortion,inter-modulation distortion and cross-modulation distortion,these distortions seriously limit the lineartity in APL,lower the spurious-free dynamic range(SFDR),and it also enhances difficulties to obtain high signal fidelity.In this paper,main research content focus on nonlinear distortions in microwave photonic links,and propose a new methoad to reduce nonlinear distortions impact.This paper mainly contains two part contents.The first part content is about a new digital linearization technique to enhance spurious-free dynamic range in analog photonic link.This paper proposes and demonstrates an innovative digital linearization algorithm to eliminate the nonlinear distortions existing in RF photonic link.Experimentally,more than 29dB suppression of IMD3 has been achieved and a spurious-free dynamic range increases from 104.1 to 128.8dB within a 1-Hz bandwidth.On the other hand,the second content of this paper is about amplitude modulation to phase distortion conversion in photonic bandpass sampling link.Under high peak optical power working at photo-detector,PD is easily entering saturation area,resulting in nonlinear distortions such as amplitude modulation to phase modulation(AM-PM)distortion.This paper validates AM-PM distortion exisiting in saturated PD by experimental and theoretical analysis.In experiment,the phase difference between fundamental signal and the second harmonic distortion is 90 degrees,this is orthogonal,so adjusting the MZM operational point is no use eliminating the AM-PM distortion.In the future,only when MZM modulator nonlinearities and PD AM-PM distortion are eliminated in bandpass photonic link,high linearity bandpass photonic link can be achieved.