BUSCADOR RECOLECTA

A fiber optic liquid-level sensor based on a long period grating (LPG) is proposed and experimentally validated. The principle of operation is based on a technique used to analyze microwave photonics filters. A 4-cm-long LPG cascaded with a high-reflectivity fiber Bragg grating is employed to achieve a continuous liquid-level sensor. The measurements have been performed using a modulator and a photo-detector with a modest bandwidth of less than 500 MHz, showing a sensitivity of −12.71 dB/cm and a standard deviation of 0.52 dB. One of the significant advantages of such sensing structure is that it is based on low-bandwidth radio frequency and off-the-shelf photonic components. In addition, the simple proposed scheme presents good repeatable performance and proves to be intrinsically robust against environmental changes, stable, and easy to reconfigure., This work was supported in part by the Accion Financiada por el Ministerio de Educacion, Cultura y Deporte through the framework of the Programa de Campus de Excelencia Internacional VLC/Campus, in part by the Spanish MINECO under Project TEC2014-60378-C2-1-R, in part by the Grant of the SANTIAGO GRISOLIA Program, in part by the Research Excellency Award Program GVA PROMETEO 2013/012, in part by the Project TEC2013-43679-R, and in part by an UPNA Predoctoral Grant. The associate editor coordinating the review of this paper and approving it for publication was Dr. Anna G. Mignani.

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.