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

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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).