Abstract
A new gas absorption module, the substrate-embedded hollow waveguide (eHWG) model, is proposed. It consists of a substrate with a curved channel and a hollow waveguide. The hollow waveguide is curved into the channel and works as a gas absorption cell as well as a transmission medium for mid-infrared light. Owing to the low loss property of the hollow waveguide, the signal-to-noise ratio (SNR) was improved for the sensing system. A polycarbonate (PC) base tube was used to obtain flexibility in the fabrication of the hollow waveguide. A silver (Ag) layer and a silver iodide (AgI) layer were inner-coated to ensure a low loss property at the fingerprint wavelength of methane gas. A sensing system was established using a Fourier transform infrared spectrometer (FTIR), an external detector, and an eHWG. Experimental investigations were carried on the sensing performance of eHWGs with various channel shapes. Comparison studies were made on eHWGs embedded with Ag-coated or Ag- and AgI-coated hollow waveguides. The Ag- and AgI-coated hollow waveguides with inner diameters of 0.7, 1.4, and 2.0 mm were used in the eHWGs. The large bore waveguide had low loss but high bending additional loss. The large bore waveguide had a low detection limit due to high coupling efficiency with the light source. A limit of detection (LOD) as low as 2.7 ppm was attained for the system using the eHWG with the long and large bore waveguide.
Highlights
Spectroscopic gas sensing in the mid-infrared (MIR) regions is an attractive gas detection method due to its intrinsic molecular selectivity, high sensitivity, fast response, and non-toxic characteristics [1,2]
Eight groups of data were measured using four embedded hollow waveguide (eHWG) with Ag or AgI/Ag waveguides with an an ID of 1.4 mm
We note that the eHWG with an Ag waveguide had a slightly higher sensitivity waveguide length
Summary
Spectroscopic gas sensing in the mid-infrared (MIR) regions is an attractive gas detection method due to its intrinsic molecular selectivity, high sensitivity, fast response, and non-toxic characteristics [1,2]. Dielectric-coated metallic hollow waveguides [7,8] have a low loss property in the MIR regions, in which many hazardous gases have strong absorptions. The loss is normally 0.1–1 dB/m for various mid-infrared lasers in the wavelength of 1.0–11 μm, compared to the loss of more than 3 dB/m for a metallic waveguide Flexibility makes it possible to coil a long waveguide into a small space to realize a miniaturized gas absorption cell. The substrate-integrated hollow waveguide (iHWG) is a recently proposed gas absorption cell [9]. High SNR and low LOD were expected compared to the iHWG due to the low loss property of the waveguide in the mid-IR region
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
