Gas sensor design using a Fabry-Perot interferometer and a pyroelectric detector

A gas sensor design based on cross correlation spectroscopy using a FPI With long cavity length (>500 mu m) as a modulator and with a pyroelectric detector is presented. This technique can be suitable to detect molecules with very well defined ro-vibrational lines such as CO, CO2 and CH4. To induce modulation one mirror of the FPI is scan over lambda/2, this will shift the spectral FPI transmission fringe pattern producing the cross correlation principle. In this design the FPI is illuminated with a converging beam and it is placed just in front of the pyroelectric; detector, this configuration can be useful if the FPI and the detector are integrated within a MEMS. Furthermore here the FPI scan is driven using a triangular waveform. Therefore in this work we will analyze the effects of illuminate the FPI with a converging beam and their consequences in the overall sensor response. Moreover we will review some possible effects in the sensor response for driving the FPI mirror scan with a triangular waveform. This issue can be very important since it can change the harmonic composition of the modulated signal and consequently the overall sensor response since the pyroelectric detector responsivity is frequency dependant. Finally, simulation results and experimental measurements are provided.