Abstract
Slot waveguide has emerged as a potential candidate for the design of evanescent field absorption based photonic gas sensors, etc. In this paper, three different slot waveguide structures, i.e., conventional slot, partial-strip-loaded slot, and full-strip-loaded slot waveguides have been explored, to analyze their sensing performance for methane gas. In anticipation of improvement in evanescent field ratio in slot region, and hence, the sensing capabilities of the gas sensor, the slot waveguide structures have been designed by depositing the germanium layer over the calcium fluoride in different manners. Several waveguide parameters, such as evanescent field ratio, propagation loss, and sensitivity have been considered for the analysis and comparison of the presented slot waveguide structures, by varying the arm-width and thickness of germanium layer. Simulation results have demonstrated that the full-strip-loaded slot waveguide has the superior performance, in terms of higher evanescent field (28%), and higher sensitivity (73.76 L/Mol), which is closely followed by the partial-strip-loaded slot waveguide, for a target value of propagation loss (3 dB/cm). However, the conventional slot waveguide provides slightly larger optimum waveguide length (0.86 cm), as compared to other presented slot waveguides.
Highlights
The photonic waveguide based sensor applications are very popular due to its low cost, ultra-compact size, high sensitivity, easy to fabricate, and CMOS compatibility (Bogaerts et al 2005), which can be used in various applications, such as bio-medical, chemical detection, gas detection, etc
The authors in (Butt et al 2017; Huang et al 2014) have demonstrated that the slot waveguide has the highest Evanescent field ratio (EFR) (Evanescent Field Ratio) in the slot region than the other photonic waveguide structures, which comes at the cost of higher propagation loss (Ding et al 2010; Almeida et al 2004; Debnath et at. 2016; Rifat et al 2019)
It is apparent that the amplitude of the normalized electric field in the slot region is significantly larger than that recognized with conventional slot waveguide structure
Summary
The photonic waveguide based sensor applications are very popular due to its low cost, ultra-compact size, high sensitivity, easy to fabricate, and CMOS compatibility (Bogaerts et al 2005), which can be used in various applications, such as bio-medical, chemical detection, gas detection, etc. The sensitivity of the photonic sensor is mainly dependent on the percentage of evanescent field/light in the upper cladding region; it can be anticipated that slot waveguide can offer significantly higher sensitivity than the other photonic waveguide structures. The current work explores the possibilities of different slot waveguide structures, designed with germanium (Ge) and calcium fluoride (CaF2) materials, for gas sensor applications. In this analysis, two important waveguide parameters, evanescent field and propagation loss have been investigated in order to determine the sensitivity of the gas sensor. As the peak absorption of methane gas is in the mid-infrared region, near around 3.31 μm; for the current analysis the operating wavelength has been considered as 3.31 μm
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