【作者】 杨硕；

【导师】 薄方；

【作者基本信息】 南开大学 ， 光学， 2021， 硕士

【摘要】 脉冲进入三阶非线性介质之后会产生极大且平坦的光学频谱,这类频谱被称为超连续谱,它的每个频率分量都有固定的相位关系,可以应用于超高精度的频率测量。近年来,集成光学平台上的非线性光学效应研究迅速发展,在波导中超连续谱产生作为集成光学和光谱学领域的重要课题引起了广泛关注。非线性材料铌酸锂以其倍频转换特性在超连续谱产生中受到了新的关注,人们利用铌酸锂优异的二阶、三阶非线性在紧束缚波导中产生了丰富多样的非线性效应。本文就铌酸锂波导中超连续谱的产生及相关非线性效应展开研究。具体研究工作主要分为三个部分:第一部分工作主要是波导结构设计和色散调控。以铌酸锂厚度、刻蚀深度、波导宽度和楔角为变量分析了不同结构下的TE模式色散曲线。本文在对比了多种结构的色散曲线之后,选择了Z切的厚度700 nm、刻蚀深度350 nm、宽度700nm、楔角65~o的铌酸锂脊波导结构,开展超连续研究。第二部分工作是理论模拟超连续谱的产生。本文基于非线性薛定谔方程描述脉冲在铌酸锂波导中传输的现象,方程中包括了自相位调制、拉曼效应、自陡直效应、级联二阶效应等非线性效应和群速度色散对脉冲的影响,并分析了每种非线性作用的原理与产生的效果。在求解非线性薛定谔方程时运用了分步傅里叶法和有限差分法等方法,模拟得到了与理论相符的超连续谱现象。第三部分工作是在实验上产生超连续谱。首先根据设计的波导结构制备出了铌酸锂脊波导,之后将1550 nm中心波长,脉冲宽度330 fs(频谱宽度约10nm)的飞秒脉冲激光通过光纤端面耦合的方式进入波导。在实验上,观察到了18 nm的光谱展宽。与理论模拟结果相符频谱展宽的现象。本文理论模拟了铌酸锂波导中各种非线性效应的产生,并且为铌酸锂波导超连续谱的产生提供了理论支撑。初步实验结果,为后续实验开展打下了基础。更多还原

【Abstract】 After passing through a third-order nonlinear medium,light pulses could have a very large and flat optical spectrum.This type of spectrum is called a supercontinuum.Each of its frequency components has a fixed phase relationship and can be used for ultra-high-precision frequency measurement.In recent years,the research of nonlinear optical effects on integrated optical platforms has been developed rapidly,and the generation of supercontinuum in waveguides has attracted widespread attention as an important subject in the fields of integrated optics and spectroscopy.Lithium niobate,a second-order nonlinear material,has received attention in supercontinuum generation due to its frequency-doubling conversion characteristics.Researchers use excellent second-order and third-order nonlinearities of lithium niobite to produce a rich variety of nonlinear effects in tightly bound waveguides.This article focuses on the generation of supercontinuum and related nonlinear effects in lithium niobate waveguide.The specific research work is mainly divided into three parts:The first part of the work is mainly about waveguide structure design and dispersion control.The TE mode dispersion curves of different structures are analyzed with the thickness of lithium niobate,the depth of etching,the width of the waveguide and the wedge angle as variables.After comparing the dispersion curves of various structures,this thesis selects a Z-cut lithium niobate ridge waveguide structure with a thickness of 700 nm,an etching depth of 350 nm,a width of 700 nm,and a wedge angle of 65~o to carry out the supercontinuum study.The second part of the work is the theoretical simulation of the generation of supercontinuum.This thesis analysis the phenomenon of pulse propagation in a lithium niobate waveguide based on the nonlinear Schrodinger equation.The equation includes the nonlinear effects such as self-phase modulation,Raman effect,self-steepening effect and cascade second-order effect,and group velocity dispersion on the pulse,and this thesis analyzes the principle and influence of each nonlinear effect.When solving the nonlinear Schrodinger equation,methods such as split-step Fourier and finite difference method are used to simulate the supercontinuum phenomenon consistent with the theory.The third part of the work is to experimentally generate supercontinuum.First,a lithium niobate ridge waveguide was prepared according to the designed waveguide structure,and then a femtosecond pulse laser with a center wavelength of 1550 nm and a pulse width of 330 fs was pumped into the waveguide through fiber end-face coupling.It is observed experimentally that the spectrum broadening width is 18 nm,which is consistent with the simulation results.This paper simulates the generation of various nonlinear effects in lithium niobate waveguides,and provides theoretical support for the generation of supercontinuum in lithium niobate waveguides.The preliminary experimental results laid the foundation for subsequent experiments.更多还原