ACTA

Temperature Cross-Sensitivity for Highly Refractive Index Sensitive Nanocoated Long-Period Gratings

J. Grochowski^a, M. Myśliwiec^a, P. Mikulic^b, W.J. Bock^b and M. Śmietana^a
^aInstitute of Microelectronics and Optoelectronics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland
^bCentre de Recherche en Photonique, Université du Québec en Outaouais, 101 Rue St Jean Bosco, Pavillon Lucien Brault, Gatineau, Québec, J8X 3X7, Canada

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There is a demand for highly refractive index sensitive devices simultaneously insensitive to temperature (T) changes. We investigate both T and refractive index sensitivity of long-period gratings coated with 100 nm thin high refractive index (n ≈ 1.9 at λ = 1550 nm) silicon nitride (SiN_x) film. The long-period gratings with period of 500 μm were induced in standard Corning SMF28 fibre using electric arc and nanocoated with SiN_x by radio frequency plasma enhanced chemical vapour deposition method. As a sensorial effect we investigated resonance shift with temperature variations (from 30 to 70°C) for measurement in deionized water (n_D = 1.33) and glycerine (n_D = 1.46). In case of measurements in water for resonance observed at λ = 1510 nm, refractive index sensitivity of - 85 nm/RIU and temperature sensitivity of 0.09 nm/°C (H₂O) were obtained which gives refractive index-T sensitivity ratio (RI/T) of - 944°C/RIU. Refractive index and T sensitivity of sensor covered with SiN_x film increased to - 618 nm/RIU and 0.22 nm/°C, respectively. Thanks to nanocoating deposition, refractive index-T sensitivity ratio was improved by factor of 3. In case of measurements in glycerine significant influence of glycerine's thermo-optic coefficient on obtained results was observed. It is worth noticing that SiN_x coating stabilizes sensing behaviour of the sensor.

DOI: 10.12693/APhysPolA.124.421
PACS numbers: 42.70.Ce, 42.79.Gn, 07.07.Df, 81.20.Fw