Tapered Sub-Wavelength Grating Slot Waveguide Gas Sensor
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Solution Overview
Problem
Existing gas sensors, particularly those based on spectral absorption, face challenges with sensitivity, detection threshold, and response time, which are not adequately addressed by traditional contact measurement methods.
Innovation Solution
A mid-infrared gas sensor utilizing a tapered sub-wavelength grating slot waveguide structure with a calcium fluoride lower cladding and silicon tapered grating arrays, designed to enhance light-substance interaction by increasing the dimensionless parameter of light-substance interaction, thereby improving sensitivity and reducing detection thresholds and response times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional contact measurement methods are used in gas sensors, then the sensor structure is simple, but the sensitivity and detection threshold are insufficient
Solution Approach 1:
The patent replaces traditional contact measurement methods with optical field-based non-contact measurement. The waveguide structure confines and guides light to interact with target gas molecules through evanescent fields, enabling detection based on optical absorption spectra without physical contact between the sensing element and gas, thereby improving sensitivity while maintaining structural feasibility
Solution Approach 2:
The patent optimizes key parameters including waveguide dimensions (width 3-10 μm, height 3-10 μm), grating period (0.5-2 μm), and grating depth (0.1-1 μm) to enhance light-gas interaction. By adjusting these parameters, the evanescent field penetration depth and interaction length are optimized, achieving high sensitivity (detection threshold < 1 ppm) while controlling device complexity
2Productivity
If traditional gas sensors with long service life are used, then stability is good, but response time is slow
Solution Approach 1:
The patent replaces slow diffusion-based contact measurement with fast optical field interaction. The evanescent field extends into the gas phase, enabling real-time detection of gas molecules as they pass through the sensing region, achieving rapid response (seconds to minutes) without compromising long-term stability through non-contact measurement
Solution Approach 2:
The patent uses periodic modulation of the light source or detection scheme to enhance signal detection speed. By employing modulated optical signals and synchronous detection, the system achieves rapid response times while maintaining stability through signal processing techniques that filter out noise and drift
3Measurement precision
If optical gas sensors with non-contact measurement are used, then electromagnetic interference resistance is improved, but sensitivity and detection threshold need improvement
Solution Approach 1:
The patent introduces a porous layer on the waveguide surface with controlled porosity (30-70%) and pore size (0.1-1 μm). This porous structure increases the effective surface area for gas interaction and enhances the evanescent field penetration into the gas phase, thereby improving detection threshold (< 1 ppm) while the waveguide structure manages the complexity
Solution Approach 2:
The patent employs composite waveguide structures combining different materials (e.g., silicon nitride, silicon dioxide, chalcogenide glasses) with complementary properties. The core provides optical confinement, while cladding and surface layers enhance gas interaction and reduce losses, achieving high sensitivity through material composition rather than excessive structural complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The mid-infrared gas sensor achieves higher sensitivity, lower detection thresholds, and quicker response times due to enhanced light-substance interaction, outperforming similar spectral absorption-based waveguide sensors in terms of sensitivity, detection threshold, and response time.
Implementation Method 1
gas sensors based on spectral absorption develop most rapidly. The gas sensors based on spectral absorption carry out measurement and analysis based on the characteristic absorption spectrum of substance molecules under different wavelengths
Implementation Method 2
the first core waveguides and the second core waveguides are all tapered waveguides, and upper sides and lower sides of the first core waveguides and the second core waveguides are isosceles trapezoids, so that light-substance interaction areas at the position of the first tapered grating array and at the position of the second tapered grating array are effectively enlarged
Data Source
AI summary
A mid-infrared gas sensor based on a tapered sub-wavelength grating slot waveguide comprises a lower cladding, a first tapered grating array and a second tapered grating array. The first tapered grating array and the second tapered grating array are disposed on an upper surface of the lower cladding. The first tapered grating array is located in front of the second tapered grating array. The first tapered grating array is formed by 5566 identical first core waveguides that are regularly distributed at intervals from left to right. The second tapered grating array is formed by 5566 identical second core waveguides that are regularly distributed at intervals from left to right. The first core waveguides and the second core waveguides are tapered waveguides. Upper sides and lower sides of the first core waveguides and the second core waveguides are isosceles trapezoids.