Mid-infrared ChG-on-MgF 2 waveguide gas sensor based on wavelength modulation spectroscopy

A novel, to the best of our knowledge, mid-infrared chalcogenide (ChG) on magnesium fluoride ( M g F 2 ) waveguide gas sensor was fabricated by using the lift-off method. M g F 2 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 ( C O 2 ) detection at the wavelength of 4319 nm ( 2315.2 c m − 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.