Single-mode Bragg gratings in tapered few-modes and multimode fibers

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Optical Society of America (OSA)
We propose the implementation of fiber Bragg gratings in tapered few-modes, and multimode fibers to accomplish single-mode operation by reducing the core diameter while preserving the core-cladding structure. Gratings present a single reflection band and the device show low insertion losses after the taper fabrication and the fiber Bragg gratings inscription. The excitation of high order odd-modes in the core of the fiber has been identified as the main loss mechanism; it can be prevented by means of symmetric illumination of the fibers. We also demonstrate the excitation of high order cladding modes (cladding-air modes) along the taper transitions; these modes can be removed without a significant increment of the insertion loss.
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L. A. Herrera-Piad, M. Delgado-Pinar, J. L. Cruz, A. Carrascosa, A. Díez, R. Rojas-Laguna, M. V. Andrés, "Single-mode Bragg Gratings in Tapered Few-Modes and Multimode Fibers", Optics Letters, Vol. 44, pp. 4024-4027, (2019)