Comparison of Al2O3nano-overlays deposited with magnetron sputtering and atomic layer deposition on optical fibers for sensing purposes

In this work we compare effects of thin (<300 nm) aluminum oxide (Al₂O₃) deposition using advanced physical (Magnetron Sputtering - MS) and chemical (Atomic Layer Deposition – ALD) vapor deposition methods on optical fibers. We investigate an influence of the process parameters on optical properties of the nano-films deposited with MS. In order to investigate the properties of the films directly on the fibers, we induced long-period fiber grating (LPG) in the fiber prior the deposition. Thanks to LPG sensitivity to thickness and optical properties of the overlays deposited on the fiber, we are able to monitor Al₂O₃ nano-overlay properties. Moreover, we investigate an influence of the overlays deposited with both the methods on LPG-based refractive index (RI) sensing. We show and discuss tuning of the RI sensitivity by proper selection of both thickness and optical properties of the Al₂O₃ nano-overlays.