Near-Infrared Spectroscopic Gas Detection Using a Surface Plasmon Resonance Photodetector with 20 nm Resolution

This paper reports on gas sensing based on near-infrared (NIR) reconstructive spectroscopy using a surface plasmon resonance (SPR) photodetector. The reconstructive spectrometer consists of an Au grating structure on an n-type silicon substrate. When the Au grating is irradiated with transverse magnetic polarized light, SPR emerges at different incident angles for each wavelength, producing an electric current via the Schottky barrier at the Au/n-type Si interface. The irradiated light spectrum can be derived by analyzing the relationship between the incident angle and the current. The proposed reconstructive spectrometer presented a 20 nm wavelength resolution in the NIR region. NIR light absorption appeared at approximately 1392 nm in the 1.5% ethanol gas spectrum by the SPR photodetector, which is coherent with Fourier transform infrared spectroscopy, indicating that the proposed reconstructive spectrometer is applicable to gas measurements.