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 materials

the 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 gas

its 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 sensitivity

simple structure and were easily fabricated.