Deposition of coatings on long-period fiber gratings: tunnel effect analogy
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- Villar, I.D., Matias, I.R. & Arregui, F.J. Opt Quant Electron (2006) 38: 655. doi:10.1007/s11082-006-9002-3
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The sensitivity of Long-period fiber gratings (LPFGs), coated with high-refractive-index thin film overlays, to the refractive index and the thickness of the overlay, and to the ambient refractive index, can be enhanced with a design based on a two-overlay coating of an LPFG. The first overlay of lower refractive index than the cladding affects the guidance of a cladding mode in the second overlay of higher refractive index than the cladding. This causes a more abrupt cladding modal redistribution than with the deposition of a unique high-refractive-index overlay. The phenomenon is analyzed with a method based on a vectorial analysis of modes and the application of coupled mode theory.