Methodology for the fabrication of novel mode selective fiber couplers using fused biconical taper process and UV induced grating structures

本文的目的是研究一种新型模式选择性光纤融合耦合器的制造方法。耦合概念基于单模光纤，包括光栅结构和相邻的多模光纤。其工作原理是利用光栅结构实现单模和多模光纤之间的倏逝波耦合。根据光栅周期的不同，多模光纤的任意模式可以耦合到单模光纤上。与现有技术相比，新型融合耦合器的主要优点是结构坚固、通过光栅结构实现高模式选择性耦合以及多模光纤相邻模式通道之间的低串扰。本研究项目的科学目标和挑战是耦合原理的建模和仿真，新制造技术的研究和模式选择融合耦合器的表征。为了确定和优化所需的耦合器长度、两个光波导之间的距离以及光栅结构的周期和折射率调制，必须对耦合器结构进行建模和仿真。新型光纤耦合器的制造技术研究包括合适的双锥熔锥工艺和光栅刻字技术的探索。根据其光学特性，新型融合耦合器可能在多个研究领域开辟新的道路，例如在多模光纤通信网络中关于模式复用和光纤MIMO（多输入多输出）概念，或者在激光技术中，即通过大模区光纤（LMAF）中的模式选择耦合来提高光纤激光器的输出。

The aim of this proposal is to investigate the manufacturing method for a novel mode selective fibre optic fusion coupler. The coupling concept is based on a single-mode fibre comprising a grating structure and an adjacent multi-mode fibre. The working principle relies on evanescence wave coupling between the single mode and the multi-mode fibre by utilising the grating structure. Depending on the grating period an arbitrary mode of the multi-mode fibre can be coupled to the single-mode fibre.Compared to state of the art, the main advantages of the novel fusion coupler are the robust structure, the highly mode selective coupling realised by the grating structure as well as the low cross-talk between adjacent mode channels of the multi-mode fibre. The scientific objectives and challenges of this research project are the modelling and simulation of the coupling principle, the investigation of the new manufacturing technique and the characterization of the mode selective fusion coupler. Modelling and simulation of the coupler structure is necessary in order to determine and optimise the required coupler length, the distance between the two optical waveguides as well as the period and refractive index modulation of the grating structure. The investigation of the manufacturing technique of the novel fibre coupler includes the exploration of an appropriate fused biconical taper process and grating inscription technique.Depending on the optical properties the novel fusion coupler may open new routes in various research fields, for example in multi-mode fibre optic communication networks with regard to mode multiplexing and fiber optic MIMO (Multiple Input Multiple Output) concepts or in laser technology, i.e. for improving the output of fibre lasers by mode selective coupling in Large Mode Area Fibers (LMAF).