Za. Ansari et al., PLANAR OPTICAL WAVE-GUIDE WITH PBCL2 CLADDING - A CHLORINE SENSOR, Journal of materials science. Materials in electronics, 7(4), 1996, pp. 255-259
Single-mode optical waveguides of 1 mm width are fabricated by thermal
indiffusion so that Na+ is replaced by K+ in a simple soda-lime glass
substrate. PbCl2 is selectively vacuum evaporated on to the waveguide
surface as a sensitive layer (cladding). The thickness of the claddin
g is varied from 170 nm to 480 nm, with clad length from 2 mm to 6 mm.
The prism-film coupling method with an He-Ne laser (lambda=632.8 nm)
is used for characterization. The output light intensity of a TM-mode
is detected by a silicon photovoltaic detector. The waveguides are tes
ted for different gases (O-2, H-2, CO2, N-2, Cl-2, H2O), in an airtigh
t glass cham ber. The presence of only Cl-2 in the surrounding air amb
ient reduces the output, even at a few p.p.m.. The Cl-2 gas concentrat
ion is varied from 3 p.p.m. to 1.5%. There are slight changes in sensi
tivity with variation in the cladding thickness and length. A drastic
change in sensitivity for different concentration ranges is observed a
s three distinct regions. The response time over a few p.p.m. to hundr
eds of p.p.m. is around 5 s and beyond 500 p.p.m, is around 2 s.