基于非线性耦合机理的少模光纤传导模式控制方法研究

Reconfigurable photonic devices capable of manipulating the optical modes are important devices for the future mode-division multiplexing (MDM) optical fiber communications. In the project, a scheme has been presented based on the nonlinear coupling effect between optical modes in the few-mode fibers (FMFs), by which an optical signal input with any intensity pattern could be controlled to output with any desired optical profile. The key problem for it is to control and compensate for the phase mismatching between interacting optical modes occurred in the nonlinear process. To do so, a complex numerical model has been firstly constructed to have a deep insight into the physical mechanism upon nonlinear mode coupling in FMFs. Based on the model, we can find the ways how to realize the phase-matching conditions (PMC) involved in the mode nonlinear coupling. Secondly, all the possible nonlinear processes and input variable parameters are analyzed and optimized to determine the best ones for the efficient generation of nonlinear coupling according to the law of momentum conservation. Thirdly, we have investigated the amplitude- and phase-frequency response characteristics of stimulated Brillouin scattering (SBS) in FMFs, the latter of which has been utilized to compensate for the phase mismatching in the nonlinear mode coupling process. Fourthly, a structure with a combination of Brillouin gain and Brillouin loss has been provided to cancel out the disturbance on the PMC caused by the amplitude-frequency response of SBS. Lastly, an optimum design of the nonlinear coupling system has been finished. The successful implementation of the project will provide theoretic and technical supports to develop mode-related all-optical signal processing devices for future MDM systems.

具有可重构性的模式操控光子器件是未来模式复用光纤通信的关键器件。本项目提出基于少模光纤模式非线性耦合机理的模式控制方法，使任意模态输入的信号光以指定模式输出。非线性耦合过程的核心在于控制和补偿少模光纤传导模式的相位失配。为此，本项目将构建少模光纤模式非线性耦合的复杂物理模型，揭示影响模式非线性耦合的深层次物理机理，掌握模式非线性耦合的相位匹配方法；基于动量守恒原则优化模式非线性耦合过程和自变量参数，探索高效的模式操控新途径；针对相位匹配条件控制问题，研究少模光纤受激布里渊散射效应（SBS）的幅频特性和相频特性，提出基于SBS相频特性补偿模式非线性耦合相位失配；针对SBS幅频特性对相位匹配的扰动问题，研究布里渊增益和布里渊损耗互补结构，使之相互抵消；最后，完成模式控制最佳工作性能设计。本项目研究成果将为未来模式复用光纤通信发展高性能的模式相关全光信号处理功能器件提供新的设计思路和方法支撑。

具有可重构性的模式操控光子器件预期在未来光通信、光子传感等领域具备较好应用前景。本项目提出基于少模光纤模式非线性耦合机理的模式控制方法，使指定模态输入的信号光以特定模式输出，实现模态转换。非线性耦合过程的核心在于控制和补偿少模光纤传导模式非线性过程的相位失配。. 本项目通过详尽研究，结果表明：（1）渐变折射率少模光纤可以通过布拉格散射型或者相位共轭型四波混频实现LP01模向LP11模的模态转换；（2）针对阶跃折射率少模光纤，当LP01模和LP02模的群速度倒数关于输入泵浦光的平均波长对称分布时，可通过相位共轭型四波混频实现两者的模态转换；（3）当渐变折射率或者阶跃折射率少模光纤实现非线性模态转换存在相位失配时，可通过少模光纤中受激布里渊散射效应的相频响应特性进行适当的补偿，或者通过引入泵浦光的自相位调制或者交叉相位调制产生的非线性相位进行相移补偿，能一定程度提高模态转换效率或者模态转换3dB带宽。. 本项目研究工作的成功实施，将为发展高性能的模式相关全光信号处理功能器件提供新的设计思路与方法支撑。