Simultaneous measurement of humidity and temperature based on a partially coated optical fiber long period grating

A humidity and temperature optical fiber sensor based on a long-period grating (LPG), which can provide simultaneous response to both magnitudes, is proposed and demonstrated via experiments. Previously, the LPG was fully coated with humidity sensitive nanostructured polymeric thin films by the Layer-by-Layer (LbL) nano assembly technique. Hence the surrounding refractive index was changed, so provoking wavelength shifts of the attenuation bands of the transmission spectrum. This fully coated LPG was exposed to relative humidity (RH) and temperature tests, varying from 20% to 80% RH and from 25 to 85ºC, respectively. Then, half of the LPG coating was chemically removed and this results in the splitting of the main attenuation band into two different contributions. When this semi-coated LPG was also exposed to RH and temperature tests, the new two attenuation bands presented different behaviors for humidity and temperature. This novel dual-wavelength based sensing method enables the simultaneous measurement of RH and temperature using only one LPG.This work was supported in part by the Spanish Ministry of Economy and Competitiveness - through the projects CICYT-FEDER TEC2013-43679-R and TEC2014-60378-C2-1-R. It was also supported by a UPNA pre-doctoral research grant, by the Program of International Excellence Campus VLC/Campus, by the grant of program SANTIAGO GRISOLIA, and by the Research Excellency Award Program GVA PROMETEO 2013/012.Urrutia, A.; Goicoechea, J.; Ricchiuti, AL.; Barrera Vilar, D.; Sales Maicas, S.; Arregui, FJ. (2016). Simultaneous measurement of humidity and temperature based on a partially coated optical fiber long period grating. Sensors and Actuators B: Chemical. 227(5):135-141. doi:10.1016/j.snb.2015.12.031S135141227