A surface-enhanced infrared absorption spectroscopic chalcogenide waveguide sensor based on the silver island film was proposed for the first time to enhance the sensing performance in both liquid and gas phases. The chalcogenide waveguide sensor was fabricated by the lift-off and oblique angle deposition methods. The surface morphology of the silver island film with different thicknesses was characterized. The absorption of ethanol (liquid) at a wavelength of 1654 nm and that of methane (gas) at 3291 nm were measured using the fabricated chalcogenide waveguide sensor. The chalcogenide waveguide sensor integrated with the 1.8 nm-thick silver island film revealed the best sensing performance. With an acceptable increased waveguide loss resulting from the fabrication of the film, the absorbance enhancement factors for ethanol and methane were experimentally obtained to be >1.5 and >2.3, respectively. The 1σ limit of detection of methane for the sensor integrated with the 1.8 nm-thick silver island film was ∼4.11% for an averaging time of 0.2 s. The mathematic relation between the absorbance enhancement factor and the waveguide loss was derived for sensing performance improvement. Also, the proposed rectangular waveguide sensor provides an idea for the design of a sensor-on-a-chip instead of other waveguide sensors with a high requirement of fabrication accuracy, for example, a slot waveguide or a photonic crystal waveguide.
Keywords: chalcogenide waveguide; gas detection; liquid detection; silver island film; surface-enhanced infrared absorption spectroscopy; waveguide sensor.