Planar Waveguide Gas Sensor Evanescent Field Miniaturization
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Solution Overview
Problem
Existing gas sensors face limitations in miniaturization while maintaining sensitivity due to optical losses in mirrors and large device sizes, which restrict response speed in low gas flows and volumes.
Innovation Solution
A sensor device with a waveguide having an evanescent field outside the core, supported by a structure with a high width-to-height ratio, allowing for miniaturization and reduced optical losses through planar microfabrication, featuring a free-hanging waveguide design and a thermal or semiconductor-based detecting element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high quality mirrors are used to achieve long optical path-length, then sensitivity is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the mirrors from the optical path by using a waveguide-based evanescent field sensing configuration. The waveguide allows the electromagnetic wave to interact with the gas sample without requiring mirrors to extend the optical path, thereby removing the complexity and cost associated with high-quality mirror fabrication while maintaining sensitivity through the evanescent field interaction.
Solution Approach 2:
The patent replaces the mechanical mirror-based optical path extension system with a waveguide structure that uses electromagnetic field confinement and evanescent wave propagation. This substitution eliminates the need for physical mirrors and their associated alignment and fabrication complexities, while achieving the same goal of extended interaction length through the waveguide's evanescent field.
2Measurement precision
If physical path length is increased to achieve long optical path-length, then sensitivity is improved, but device size increases
Solution Approach 1:
The patent transitions from extending the optical path in one dimension (physical length) to achieving extended interaction through the evanescent field in the transverse dimension. The waveguide confines the electromagnetic wave, creating an evanescent field that extends beyond the waveguide core, allowing sensitive gas detection in a compact footprint by utilizing the field's spatial extension rather than increasing the physical device length.
Solution Approach 2:
The patent embeds the sensing function within the waveguide structure itself, where the evanescent field interacts with the gas sample in the region surrounding the waveguide core. This nesting of the sensing interaction within the waveguide's electromagnetic field allows for compact device design, as the sensing volume is effectively nested within the waveguide's near-field region rather than requiring a separate extended optical path.
3Measurement precision
If large volume gas chamber is used to maintain sufficient gas sample, then sensitivity is maintained, but response speed decreases
Solution Approach 1:
The patent uses a thin waveguide structure with a high width-to-height ratio, where the evanescent field extends into the surrounding gas. This thin-film-like waveguide configuration allows for efficient gas interaction in a minimal volume, enabling fast response speeds while maintaining sensitivity through the evanescent field's interaction with the gas molecules in the immediate vicinity of the waveguide surface.
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 solution enables a compact, sensitive gas sensor capable of detecting components in low gas volumes with reduced optical losses and improved response speed, utilizing a waveguide with a high width-to-height ratio and a thermal or semiconductor-based detecting element.
Implementation Method 1
The features of the waveguide provide for guiding an electromagnetic wave, having an evanescent field outside the waveguide core
Implementation Method 2
Optical sensing using the absorption bands of various gases in the visible or infrared (IR) wavelength range is an established method
Data Source
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AI summary
The invention relates to a sensor device (1) comprising a planar substrate (3) defining a substrate plane (4) and a waveguide (2) for guiding an electromagnetic wave. The waveguide (2) extends in a length direction in a waveguide plane (4´) parallel to the substrate plane (4) and has a width (W, w) and a height (h) wherein the width (W, w) to height (h) ratio is more than 5. The height (h) of the waveguide (2) is less than the wavelength of the electromagnetic wave. The waveguide (2) is supported on the substrate (3) by a support structure (5) extending from the substrate (3) to the waveguide (2), along the length direction of the waveguide (2), having a width (Ws) which is smaller than the width (W, w) of the waveguide (2). The invention further relates to a method of detecting a component in gas and a method of fabricating a sensor device (1).