Semiconductor Waveguide Sensor for Compact Trace-Gas Detection
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Solution Overview
Problem
Existing optical absorption methods for trace gas detection, such as cavity ring-down spectroscopy, are large, expensive, and require expert handling, limiting their practicality and accessibility for atmospheric trace-gas determinations.
Innovation Solution
A compact optical absorption sensor using a curved and elongate semiconductor waveguide integrated with in-coupling and out-coupling windows, supported by a dielectric layer, which achieves long path lengths for analyte detection through total internal reflection and evanescent wave interaction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cavity ring-down spectroscopy is used to achieve long path lengths for trace gas detection, then sensitivity of analyte detection is improved, but device size, cost, and operational complexity increase
Solution Approach 1:
The patent transforms the path length achievement from a spatial dimension (meters apart mirrors) to a temporal dimension (light bouncing back and forth thousands of times). By confining light within a compact cavity and utilizing multiple reflections, the effective path length extends to several meters while maintaining a small physical footprint, thus resolving the contradiction between long path length and compact device size
Solution Approach 2:
The patent embeds the light propagation path within a compact cavity structure, nesting multiple reflection events within a small physical space. The light traverses the cavity repeatedly, effectively packing a long optical path into a small volume, which resolves the contradiction between long path length and small device size
2Measurement precision
If cavity ring-down spectroscopy is used to achieve long path lengths, then sensitivity of analyte detection is improved, but manufacturing cost increases
Solution Approach 1:
The patent employs inexpensive dielectric mirrors and standard optical components to construct the cavity, replacing expensive specialized equipment. The use of commercially available materials and simplified optical design reduces manufacturing costs while maintaining the long effective path length necessary for sensitive detection
Solution Approach 2:
The patent replaces complex mechanical alignment systems with a stable optical cavity design that maintains precise mirror alignment through its structure. This eliminates the need for expensive active alignment mechanisms and expert handling, reducing both manufacturing cost and operational 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 sensor provides high sensitivity and compact form factor for trace-gas determination, reducing costs and complexity by integrating semiconductor materials like silicon or silicon nitride, allowing for sensitive analyte detection without active temperature control.
Implementation Method 1
the probe light bounces back and forth between mirrors that can be spaced meters apart, resulting in a very great path length
Implementation Method 2
Optical absorption sensing can be used as an analytical tool to quantify trace gases in the atmosphere
Data Source
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AI summary
A method for fabricating a sensor comprises: (a) providing a wafer comprising a substrate, a dielectric layer on the substrate, and a semiconductor adlayer on the dielectric layer; (b) enacting microlithographic processing on the semiconductor adlayer to define: (i) a curved and elongate semiconductor waveguide confined to the dielectric layer, (ii) an in-coupling window arranged at a first end of the waveguide and configured to couple optically to an optical source, and (iii) an out-coupling window arranged at a second end of the waveguide and configured to couple optically to an optical detector; and (c) selectively etching the dielectric layer to define: (iv) a first dielectric region that supports and encloses the first end of the waveguide; (v) a second dielectric region that supports and encloses the second end of the waveguide; and (vi) a third dielectric region that supports but does not enclose a middle segment of the waveguide.