Opaque Light-Blocking Element for Prism Coupling Contrast
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Solution Overview
Problem
Nondestructive stress measurements in chemically strengthened cover glasses with steep refractive index profiles are challenging due to broadening of coupling resonances, leading to increased standard deviation of compressive stress measurements, which is problematic for quality control in manufacturing of portable electronic devices.
Innovation Solution
The introduction of an opaque light-blocking element in the prism-sample coupling interface, with variable transmission, helps improve the contrast of coupling resonances and reduces distortion, allowing for more precise measurements by controlling the light interaction and preventing excessive light from reaching the detector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a low-index layer is used to control coupling strength, then the spectral lines become sharp with high contrast, but the measurement precision deteriorates due to increased sensitivity to background illumination variations and stricter cleanliness requirements
Solution Approach 1:
The patent introduces a diffuser as an intermediary element between the light source and the prism-sample interface. This diffuser flattens the angular distribution of illumination, reducing the sensitivity of resonance detection to background illumination variations. The diffuser acts as a mediator that transforms the light field to achieve both good contrast and reduced measurement uncertainty
Solution Approach 2:
The patent modifies the illumination parameters by introducing a diffuser that changes the angular distribution of light. This parameter change flattens the illumination profile, which reduces the sensitivity to background variations and improves measurement precision while maintaining spectral line contrast
2Illumination intensity
If the prism-sample interface is kept clean with sub-micron oil layer thickness, then coupling resonance contrast is improved, but the device complexity and operation difficulty increase due to stricter cleanliness requirements
Solution Approach 1:
The diffuser serves as an intermediary that decouples the strict cleanliness requirements from the measurement process. By flattening the angular distribution of illumination, the diffuser makes the system more robust to interface imperfections, allowing operation with less stringent cleanliness control while maintaining good measurement quality
3Use of energy by moving object
If the illuminated length at the prism-sample interface is extended, then more light is collected for detection, but the contrast of coupling resonances decreases due to excessive coupling between prism light and waveguide light
Solution Approach 1:
The patent applies local quality by using a diffuser that creates a localized flattening of the angular distribution of illumination at the prism-sample interface. This local modification of the light field properties allows extended illumination length to be used without proportionally increasing the harmful coupling effects, as the diffused light interacts differently with the interface regions
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
This approach significantly reduces the standard deviation of compressive stress measurements from over 50 MPa to below 10 MPa, enhancing the precision and accuracy of stress measurements in chemically strengthened glasses with steep refractive index profiles.
Implementation Method 1
An opaque light-blocking element is placed in the portion of the light beam closest to the plane of contact between prism and measured sample
Implementation Method 2
prism coupling technique of industry-standard FSM-6000
Implementation Method 3
excessive coupling between the light propagating in the prism and light propagating in the waveguide region
Data Source
AI summary
A method and apparatus for improving contrast in prism coupling measurements of waveguide mode spectra, wherein the measured waveguide sample has a surface region of rapidly decreasing index, characterized with normalized slopeλnⅆnⅆz>0.0004.An opaque light-blocking element is placed in the portion of the light beam closest to the plane of the contact between prism and measured sample, on the input side, output side or both sides of the prism. The light blocking element prevents light from the light source to reach a portion of the length of the prism-sample coupling interface along the optical path, prevents light reflected from a portion of the aforementioned length to reach the detector, or both when input and output light-blocking elements are used.