PVA THIN FILM BASED OPTICAL WAVEGUIDE SENSOR AND ITS APPLICATION IN XYLENE DETECTION

Abstract

The optical waveguide(OWG) sensor used consists of a substrate,waveguide layer(K + ion exchanged layer or tin-diffused OWG) and thin top layer(sensing layer).The semiconductor laser beam(630 ～ 680 nm) was introduced into the OWG using a prism coupler(glass prism,n = 1.78;and a matching liquid,diiodomethane,n = 1.74),and it emerged from another prism coupler.The intensity of the output light was monitored by using a photomultiplier detector,and the output light intensity was recorded by a computer.Pure air that functioned as a carrier and dilution gas flowed through the cell at a constant rate of 40 mL /min in order to transfer the xylene gas to the sensor.All measurements were made at room temperature.Pure PVA and Vc embedded PVA were chosen as sensitive materialst,he PVA film /tin-diffused glass OWG and VC-PVA thin film /tin-diffused glass OWG were fabricated by spin-coating methods.We used this two OWG sensors to detect xylene gas,and the experimental result shows that the PVA film /tin-diffused glass OWG exhibited a good response to xylene gasi,ts detection range was 10-4 ～ 10-7.While the Vc-PVA thin film /tin-diffused glass OWG exhibited higher sensitivity and larger response range(this OWG sensor has a considerable response to 10-8 of xylene gas).These sensors were also characterized by high sensitivitys,imple structure and were easily fabricated.