Detection of organic aromatic compounds in paraffin by a long-period fibergrating optical sensor with optimized sensitivity

A long-period grating (LPG) sensor is used to detect small variations in th e concentration of an organic aromatic compound (xylene) in a paraffin (hep tane) solution. A new design procedure is adopted and demonstrated to maxim ize the sensitivity of LPG (wavelength shift for a change in the surroundin g refractive index, (d lambda /dn(3))) for a given application. The detecti on method adopted is comparable to the standard technique used in industry (high performance liquid chromatograph and UV spectroscopy) which has a rel ative accuracy between similar to +/-0.5% and 5%. The minimum detectable ch ange in volumetric concentration is 0.04% in a binary fluid with the detect ion system presented. This change of concentration relates to a change in r efractive index of Deltan similar to 6 x 10(-5). (C) 2001 Elsevier Science B.V. All rights reserved.