Mid-infrared ChG-on-MgF2 waveguide gas sensor based on wavelength modulation spectroscopy

A novel, to the best of our knowledge, mid-infrared chalcogenide (ChG) on magnesium fluoride (MgF2) waveguide gas sensor was fabricated by using the lift-off method. MgF2 was used as a lower cladding layer to increase the external confinement factor for enhancing light–gas interaction. Wavelength modulation spectroscopy (WMS) was used in carbon dioxide (CO2) detection at the wavelength of 4319 nm (2315.2cm−1). The limit of detection for the 1-cm-long sensing waveguide based on WMS is ∼0.3%, which is >8 times lower than the same sensor using direct absorption spectroscopy (DAS). The combination of WMS with the waveguide gas sensor provides a new measurement scheme for the performance improvement of on-chip gas detection.