An integrated optical instrumentation for measuring NO2 gas using one dimensional photonic crystal

Air pollution is one of main problems in human health, especially in big cities. There are five pollutants material which is indicated as a source of air pollution, one of them is nitrogen oxide (NO₂). The proper environmental monitoring system for air pollution management has demanding requirements. We have designed an integrated optical sensor to measure NO₂ gas concentration using 1-D photonic crystal. The phenomenon of photonic pass band (PPB) has been used as a frequency filter in liquid concentration measurement. Photonic crystal, LED, and photodiode were designed to operate in NO₂ absorption spectra that are in the range between 557.23 and 558.01 nm. The NO₂ gas concentration is inversely proportional to intensity of peak PPB spectra. We built electronic signal conditioning circuit which is consisting of: current to voltage converter, voltage follower, active low pass filter, and instrumentation amplifier, to get an appropriate signal. The experimental results show that our optical integrated instrumentation is able to measure NO₂ gas concentration, while requiring a filtering circuit addition because of the presence of internal noise.