Research On Wavelength Conversion Of Mg-doped Lithium Niobate Crystals Based On Nonuniform Periodic Polarization

Wavelength conversion technology based on lithium niobate crystals plays an important role in biomedical fields,optical signal processing and optical communication with the development of nonlinear optical technology.In this paper,we build a wavelength conversion system based on the transfer function method,and carries out research from the perspective of experiment and numerical simulation to achieve high conversion efficiency and wide band wavelength conversion.The specific research contents are as follows:1.This paper describes the research significance,background and current status of wavelength conversion,and introduces the wavelength conversion method and quasi-phase matching technology.The coupled wave equation describing the wavelength conversion process is derived theoretically and the approximate plane wave coupled wave equation is obtained,and the numerical simulation methods for solving the coupled wave equation,such as the step-Fourier algorithm and the transfer function method,are analyzed.The transfer function method is simpler and more suitable for numerical solution of coupled wave equation.2.The wavelength conversion system is constructed based on the transfer function method,which is divided into three modules: input fundamental wave,transfer function and output wave.The bandwidth,waveform and efficiency of output wavelengths are studied by using Gaussian beam and chirped Gaussian beam as input base,and uniform periodic grating and chirped periodic grating as transfer function.Chirped Gaussian beams and chirped gratings can get better bandwidth but lower efficiency.The waveforms corresponding to the narrower bandwidth of the input fundamental and transfer function determine the waveforms of the output.The conversion efficiency can be improved by increasing the crystal length.3.A wavelength tuning system based on multiperiod grating is designed.A multi-period grating with a period range of 19.5 ～21.3μm and a temperature range of25 ℃ ～150 ℃ are selected for theoretical analysis and experimental verification of wavelength tuning.The wide spectrum output of about 42 nm can be realized,and the conversion efficiency can reach up to 12.3%,that is,high conversion efficiency and wide spectrum can be realized at the same time.In addition,the non-central phase matched harmonics,which are generated by the combination of summing and frequency doubling effects,are studied,and the central and non-central phase matched continuous wide spectrum are obtained under certain conditions.