摘要
随着光通信技术的发展,基于SOI (silicon-on-insulator)结构的硅纳米线波导因其相对低成本的制作工艺,较高的非线性系数以及对光束的强束缚作用,被广泛应用于非线性光学领域。本论文主要研究了硅纳米线波导中基于四波混频效应的波长转换原理,并对应用于波长转换的硅纳米线波导进行了优化设计。
本论文首先简单介绍了硅光子学在光通信领域的发展以及硅纳米线波导中基于四波混频效应的波长转换的研究情况。
通过对光波导的基本理论的回顾,本论文简要阐述了分析光波导中模场分布的解析方法和近似方法,以及有限差分法、光束传播方法等常用且有效的数值计算方法。
本论文对SOI硅纳米线矩形波导中基于四波混频效应的宽带波长转换进行了理论研究,并分析了波导中损耗以及吸收效应对于相位匹配条件的影响。数值模拟了波导芯层横截面尺寸对于调节波导色散的作用,通过对波导横截面尺寸、波导长度以及泵浦光入射功率的优化设计扩展了波长转换的带宽并在波导的出射端得到了最大波长转换效率。
在常规矩形波导结构的基础上,本论文提出了一种多层结构的条形波导。这种波导是在硅材料芯层的上、下两个方向依次沉积折射率一低一高的两层介质膜,形成一种多层结构。论文分析了芯层宽度、高度以及两层覆盖层的厚度四个几何结构参数对零色散波长位置以及色散曲线斜率的影响,经数值计算在理论上提出了对该多层结构条形波导横截面尺寸的优化设计方案,实现了宽带的波长转换。
四波混频波长转换的效率与入射信号光相对泵浦光的偏振态有密切关系。而在实际传输系统中,信号光的偏振态总是会因为时间或者传输距离等原因而发生波动,因此研究偏振不敏感的波长转换方案变得十分必要。本论文从理论上研究了在SOI硅纳米线矩形波导中利用具有一定偏振角度的泵浦光实现基于四波混频效应的偏振无关波长转换的方案,并对入射泵浦光的偏振角度进行了优化。更进一步研究了因波导芯层横截面尺寸调整引起TE和TM模式的色散改变对波长转换带宽的影响。
With the development of optical communication technology, silicon nanowire waveguides base on the SOI (silicon-on-insulator) structure have been widely used in the fields of nonlinear optics due to their relative low-cost fabrication process, large third-order nonlinearity and tight confinement of optical waves. The theory of four-wave mixing-based wavelength conversion in a SOI waveguide is investigated and the waveguides used to realize the wavelength conversion are optimized.
Firstly, the development of silicon photonics for optical communication is introduced, and the research progress of four-wave mixing-based wavelength conversion in the silicon nanowire waveguides is summarized.
The basic theory of optical waveguides is then introduced. The analytical and approximate methods to analyze the modal field of optical waveguides are briefly described, and the numerical methods such as the finite difference method and the beam propagation method are discussed.
The theory of four-wave mixing-based broadband wavelength conversion in a SOI nanowire waveguide is investigated, and the influence of loss and absorption in the waveguide on the phase-matching condition is analyzed. The dispersion tailoring by the adjustment of the cross-section size of the waveguide core is numerically simulated. The conversion band is enhanced and the maximum conversion efficiency is achieved at the end of the waveguide by optimizing the cross-section size, the waveguide length and the input power of the pump light.
A new structure of multi-layered silicon nanowire waveguide is presented, where two overlayers with lower and higher refractive indices are sequentially added underneath and on top of the silicon core. The impact of the core width and the thicknesses of core and two overlayers on the zero-dispersion wavelength and the dispersion slope are analyzed, respectively. The optimal design of the multi-layered nanowire waveguides for the broadband conversion is proposed based on the numerical simulation.
The conversion efficiency is tightly determined by the state of polarization (SOP) of the input signal with respect to the pump. Since the SOP of the signal in a real transmission system may fluctuate with time and distance, it is necessary to realize polarization insensitive wavelength conversion schemes. A proposal for polarization-independent wavelength conversion is presented based on the four-wave mixing in a SOI nanowire waveguide by using an angled-polarization pump. The basic theory of the polarization-independent wavelength conversion is analyzed and the polarization angle of pump is optimized. The influence of the dispersion change of TE and TM modes induced by the adjustment of the core cross-section size on the wavelength conversion band is investigated.
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