Femtosecond laser-written long period fibre gratings coated with titanium dioxide for improved sensitivity

Duarte Viveiros; José M. M. M. de Almeida; Luís Coelho; Helena Vasconcelos; Vítor A. Amorim; João M. Maia; Pedro A. S. Jorge; Paulo V. S. Marques

doi:10.1117/12.2555686

1 April 2020 Femtosecond laser-written long period fibre gratings coated with titanium dioxide for improved sensitivity

Duarte Viveiros, José M. M. M. de Almeida, Luís Coelho, Helena Vasconcelos, Vítor A. Amorim, João M. Maia, Pedro A. S. Jorge, Paulo V. S. Marques

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Proceedings Volume 11354, Optical Sensing and Detection VI; 113540C (2020) https://doi.org/10.1117/12.2555686
Event: SPIE Photonics Europe, 2020, Online Only

Abstract

Long Period Fibre Gratings (LPFGs) were fabricated by femtosecond (fs) laser direct writing in a standard single-mode fibre (SMF-28e) to measure variations in the surrounding refractive index (SRI). The sensing sensitivity of these structures was optimized with the deposition of homogeneous thin layers of titanium dioxide (TiO₂) by physical vapour deposition (PVD) process. A set of LPFGs were coated with different thickness layers of TiO₂, and the spectral features were monitored for different SRI solutions. The wavelength shift and the optical power variation of the LPFG minimum attenuation band were measured achieving sensitivities of ~570 nm/RIU at using SRI near to 1.3600 in the case of the LPFG coated with 60 nm of TiO₂, a 10-fold increase over the corresponding for a bare LPFG. For SRI values higher than the cladding refractive index, a sensitivity over ~3000 nm/RIU was determined for 30 nm of TiO₂ thick film, a region where the bare LPFGs are useless. For 30 nm of TiO₂, the optical power variation follows a quasi-linear function of the SRI, with a range of ~10 dB. Moreover, values as high as 50 and 120 dB/RIU at 1.3200 and 1.4200, respectively, can be obtained by choosing the proper film thickness. Preliminary studies revealed that coating fs-laser direct writing LPFGs with titanium dioxide improves their performance.

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Duarte Viveiros, José M. M. M. de Almeida, Luís Coelho, Helena Vasconcelos, Vítor A. Amorim, João M. Maia, Pedro A. S. Jorge, and Paulo V. S. Marques "Femtosecond laser-written long period fibre gratings coated with titanium dioxide for improved sensitivity", Proc. SPIE 11354, Optical Sensing and Detection VI, 113540C (1 April 2020); https://doi.org/10.1117/12.2555686

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