The Oretical And Numerical Analysis On Cascade SHG/SPDC In Nonlinear Waveguides

In recent years,quantum communication has been highly valued,and entangled photon pairs have been the source of communication.A large number of studies have been initiated.Quantum entangled photons can be realized by nonlinear effects such as spontaneous parametric down conversion(SPDC)or cascaded SHG/SPDC.The production of the pair has been studied by a large number of domestic and foreign laboratories.Based on the theory of quantum theory,based on the research of SPDC process theory and more precise model setting,the wave function and conversion efficiency of the cascaded SHG/SPDC process are derived,and the simulation results are compared with the experimental results.Finally,the wave function and conversion efficiency formula of the entangled photon pair of the process are obtained.In this paper,we first analyze the photon conditions and related wave functions of the second harmonic(SHG),SPDC and cascade SHG/SPDC processes,and obtain the necessary theoretical basis.The cascade SHG/SPDC process can improve the SPDC process.The inconvenience is due to the fact that the pump light can be multiplied by SHG to convert to the pump light frequency under the phase matching condition required by SPDC,so that the device with the same optical frequency can be realized for the incident portion and the outgoing portion.However,this process requires a more accurate analysis,because the conversion of SHG and the conversion of SPDC occur at the same time,and the traditional analysis only analyzes the nonlinear waveguide as a whole,so this paper needs to be re-established.The waveguide model performs an accurate analysis.Based on the quantum theory model of the SPDC process wave function,the wave function and its spectral distribution of the cascaded SHG/SPDC process are obtained.By establishing an n-segment subdivision mathematical model,the nonlinear waveguide is segmented step by step,and the wave function in each case is obtained.Finally,when n tends to infinity,the continuous integral function is used to obtain the nonlinear wave derivation.The process wave function is then compared with the experimental results of foreign scholars based on the theoretical results.It is found that the images are basically consistent,which shows that the cascaded SHG/SPDC wave function obtained by the mathematical model is correct.Finally,based on the quantum theory model of SPDC process conversion efficiency,the conversion efficiency of the cascaded SHG/SPDC process is obtained,and the theoretical cascaded SHG/SPDC process conversion efficiency is combined into the nonlinear waveguide to obtain the cascade of nonlinear waveguides.The conversion efficiency of SHG/SPDC,using the same segmentation model,verified the conversion efficiency of cascaded SHG/SPDC in nonlinear waveguides and obtained the conversion efficiency of AlGaAs optical waveguides in this process.In this paper,the conversion efficiency function of nonlinear waveguides under general conditions is obtained,which has a guiding role for the subsequent entangled photons.Through the established mathematical model,a more accurate wave function and conversion efficiency are obtained to provide a theoretical basis for design integration,high photon generation efficiency,and high entanglement polarization entangled light source.