Ž . Thin Solid Films 301 1997 82–89 Oxygen sensing properties of V O cladded optical glass waveguide 2 5 Z.A. Ansari a, ) , R.N. Karekar b , R.C. Aiyer a a Center for AdÕanced Studies in Material Science and Solid State Physics, Department of Physics, UniÕersity of Pune, Pune 411 007, India b RCMF Transducer Laboratory, Department of Physics, UniÕersity of Pune, Pune 411 007, India Received 11 September 1996; accepted 16 January 1997 Abstract A new type of oxygen sensor is proposed with an ion-sensitive film of V O on an optical waveguide surface and is characterized 2 5 Ž . using prism-film coupling. Upon exposure to excess oxygen in ambient air, the light l s632.8 nm transmission through the guide alters due to the change in the refractive index of the film, changing the effective index of the guide. The excess O concentration varies from 2 Ž . Ž . Ž . 50 ppm to few per cent 5% . The influence of the cladding thickness 150–490 nm and the length 2–6 mm on the sensor performance are studied. The increase in cladding length enhances the static sensitivity, while the increase in the thickness causes a reduction in the static sensitivity, unaffecting the incremental sensitivity. The performance is identical with static and incremental methods. The response and recovery times are found to be 4–6 and 8 s, respectively. An air ambient sintering of the films gives practically a linear response compared to nonsintered films. The sensors are tested for other gases, namely H and H O, does not show any response except O . 2 2 2 Keywords: Oxygen sensor; Optical guide; V O cladding 2 5 1. Introduction Semiconducting materials are used for sensing oxygen wx and most of these are of the potentiometeric 1 type, which normally work at higher temperatures and at higher Ž . w x oxygen concentration percentage level 1–3 . These types of sensors are used in metallurgical processes, steel plants wx and process controls 2 . In order to have low-temperature w x operating sensors, various solid electrolytes 3–5 are used. Most of these are in the form of galvanic cells with one wx reference electrode 3 of Pt, Pd or Ag supported by an AgCl electrode, etc. The potential difference between the two electrodes is a measure of the oxygen content at the wx ppm level 3 with noticeable sensitivity at room tempera- ture. The electrochemical sensors are also used at rela- tively higher temperature for oxygen detection in combus- tion engines, industrial exhaust and for the indirect detec- wx tion of CO. Schilling and Colbow 5 have reported Pd- doped vanadium pentoxide as a conducting type oxygen Ž sensor for an indirect measure of reducing gases such as ) Corresponding author. . H with lower oxygen concentration of 29 ppm. Aging 2 with the increasing number of operations is a serious w x problem with these sensors 1–5 . The optical sensors with generally known advantages of low-temperature operation, quick response, good repeata- bility, reliability and ease of fabrication and measurements wx with the possibility of integration 6 are being developed rapidly using advanced technologies such as optical fibers Ž . and waveguides. They use a gas absorbing sensitive Ž . coating cladding on the fiber core or on the waveguide wx surface 6 . The absorption of gas by the cladding changes the cladding refractive index, and therefore changes the evanescent field portion within the cladding. This results in a change of the effective refractive index of the guide and hence a change in the absorption and transmission through w x the guide, respectively 6,7 . The present work describes a new method of detecting changes in oxygen concentration in ambient air at room temperature from the ppm to the percentage level using a planar glass waveguide cladded with vacuum-evaporated films of vanadium pentoxide, which is a well-known oxy- wx gen sensitive material 8 . The effects of the film sintering, the cladding length and thickness on the sensor perfor- mance is presented along with a reliability study. 0040-6090r97r$17.00 Copyright q 1997 Elsevier Science B.V. All rights reserved.