选模型光子灯笼的模式演化机理及其控制技术研究

With the popularization of the Internet, the demand of network bandwidth is increasing rapidly. The available capacity of traditional single-mode fiber is already approaching its limit. An effective solution is utilizing mode-division-multiplexing technology. The key problem of mode-division-multiplexing technology is how to realize effective mode multiplexing/de-multiplexing. The invention of mode-selective photonic lantern provides a completely new train to break through this bottleneck. However, mode evolution mechanism of mode-selective photonic lantern has not been research thoroughly, which lead to a lack of effective theoretical guidance for increasing the port number of a photonic lantern. The project aims at discovering mode evolution mechanism of mode-selective photonic lantern. Based on our previous research about tapered multi-core fiber and traditional photonic lantern, the project plans to study mode evolution properties of mode-selective photonic lantern. Firstly, we will build a mode evolution model of a mode-selective photonic lantern and deduce a quantitative calculation method for adiabatic tapering criterion based on taper angle. Then, we will optimal design mode-selective photonic lantern with more port number. At last, manufacture and measurement technique of mode-selective photonic lantern will be conduct based on theoretical results. Research achievement will provide a theoretical guidance for increasing the port number of a photonic lantern. It will also be helpful to further exploit the application potentialities of mode-selective photonic lantern and provide technical support for capacity scaling of fiber communication system.

随着互联网应用的广泛普及，人们对网络带宽的需求急剧增长，传统单模光纤的传输容量已接近极限，解决途径之一是采用模分复用技术。如何实现有效的模式复用/解复用是该技术的关键，选模型光子灯笼的出现为突破该瓶颈提供了崭新思路。然而，目前人们对选模型光子灯笼的模式演化机理还缺乏深入研究，使得在对光子灯笼进行端口数目扩展时缺乏有效的理论指导。本项目以揭示选模型光子灯笼的模式演化机理为目标，基于前期对锥形多芯光纤和传统型光子灯笼的研究成果，开展选模型光子灯笼模式演化特性研究，探索建立选模型光子灯笼的模式演化模型，提出一种基于拉锥角度的绝热拉锥条件定量计算方法，优化设计具有更多端口的选模型光子灯笼，并据此开展选模型光子灯笼的制作及测试技术研究。预期研究成果将为选模型光子灯笼的端口数目扩展提供理论依据，有助于进一步挖掘选模型光子灯笼的应用潜力，为光纤通信系统容量的大幅度提升提供技术支撑。

选模型光子灯笼在光纤通信模式复用、光纤激光功率合成和计算光成像等多个领域都有重要应用。目前对于选模型光子灯笼的一个重要研究方向是如何扩展光子灯笼的端口数目。为此，必须首先弄清选模型光子灯笼的模式演化机理，并有针对性地提出有效的模式控制技术。本项目以揭示选模型光子灯笼的模式演化机理为主要目标，以锥形光纤和多芯光纤中的模式求解为基础，提出了一种基于局域耦合模理论的模式演化过程定量求解方法。该方法在计算过程中可以沿轴向自适应地调整网格大小以提高模式求解精度，并且还能够给出任意轴向位置处的模式比重，为选模型光子灯笼的模式演化过程提供了清晰的物理图像。在此基础上，利用局域模耦合理论和光束传播法相结合的手段探索基于结构优化设计的模式控制技术，主要从拉锥特性和截面特性两方面对选模型光子灯笼的结构进行优化，在保持低传输损耗的条件下提高选模能力、扩展端口数目。结合激光合成的应用需求，提出了一种哑铃型结构的光纤功率合束器，实现了合成激光的亮度优化。项目成果可以支持模分复用光纤通信系统容量的进一步提升，为提高选模型光子灯笼的实用效能和扩展应用领域提供理论支持。

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