In this paper, a high sensitivity optical fiber pH sensor based on lossy mode resonance (LMR) generated with transversal electric (TE) and transversal magnetic (TM) polarized light is presented. Poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) polymeric thin-films fabricated onto side-polished Dshaped optical fibers are used as pH-sensitive as well as LMR supporting coatings. The adequate selection of the pH-sensitive coating fabrication parameters enables to obtain devices working at different pH regions. Two devices have been obtained in order to measure pH from 4.0 to 5.0 and from 7.0 to 8.0 respectively. Obtained optical fiber pH sensors based on TE and TM LMRs showed a maximum sensitivity of 69 nm/pH, which means a resolution of ∼0.0008 pH units by using a conventional communications Optical Spectrum Analyzer (OSA) with 0.06 nm resolution.

This work was supported by the Spanish Economy and Competitiveness Ministry-Feder TEC2013-43679-R and Fundación CAN2015-70221 Research Grants