Design of aluminium oxide (Al2O3) fiber optic gas sensor based on detection of refracted light in evanescent mode from the side-polished modified clad region

Abstract

There is a significant demand for improved design and performance of gas sensors today. A fiber optic gas sensor based on light detection from a side-polished clad modified optical fiber (Evanescent mode) coated with nanocystalline aluminium oxide (Al2O3) is proposed for detecting VOCs such as acetone, methanol, ammonia, and ethanol gases. It is observed that there is an increase in the output light intensity for evanescent mode with an increase in the gas concentration, whereas a decrease in the transmission mode (light received from the end of fibre). The sensor exhibits excellent gas sensitivity and selectivity towards acetone gas in the evanescent mode. The normalized gas sensitivity for acetone was 603 × 10−3 /kPa in the evanescent mode and 29 × 10−3 /kPa in transmission mode, which is about 20 times better at sensitivity in evanescent mode compared to transmission mode. The dynamic characteristics of the sensor were also studied. A theoretical model for light dynamics in the optical fiber during gas sensing and its correspondence with sensing mechanism has been discussed.