A terahertz plastic wire based evanescent field sensor for high sensitivity liquid detection

Abstract

A highly sensitive detection method based on the evanescent wave of a terahertz subwavelength plastic wire was demonstrated for liquid sensing. Terahertz power spreading outside the wire core makes the waveguide dispersion sensitive to the cladding index variation, resulting in a considerable deviation of waveguide dispersion. Two liquids with transparent appearances, water and alcohol, are easily distinguished based on the waveguide dispersion, which is consistent with theoretical predictions. A melamine alcohol solution with various concentrations is identified successfully, and the detection limit is up to 20ppm, i.e. equivalent to the index variation on the order of 0.01. (C) 2009 Optical Society of America