Prism-Coupling Systems for Large Depth-of-Layer Waveguide Characterization
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Solution Overview
Problem
Conventional prism-coupling systems struggle to precisely measure the refractive index profiles of dual ion-exchanged (DIOX) glasses with large depth-of-layer (DOL) due to under-sampling of high-order modes, leading to inadequate resolution of spectral lines, especially when using conventional coupling prisms with a 60° output-side angle.
Innovation Solution
A prism-coupling system with a coupling angle between 0.81αmax and 0.99αmax is used, where αmax is the maximum coupling angle for total internal reflection, adjusting the mode spectrum to better separate higher-order mode lines and allowing for efficient use of detector space, followed by post-processing to correct mode-line spacings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional coupling prism with a 60° output-side angle is used, then the system is simple and cost-effective, but the high-order modes are under-sampled and spectral lines cannot be adequately resolved
Solution Approach 1:
The patent changes the critical parameter of the prism angle from the conventional 60° to a specific range (45°-55° or 70°-80° depending on the embodiment). This parameter change optimizes the angular separation of mode lines, allowing high-order modes to be properly resolved by the photodetector array without requiring more complex or expensive equipment.
2Measurement precision
If a larger photodetector with more pixels is used to improve measurement resolution, then the mode spacing resolution improves, but the system cost and complexity increase substantially
Solution Approach 1:
Instead of increasing photodetector size or pixel count, the patent changes the prism angle parameter to optimize the angular distribution of mode lines. This causes high-order modes to spread out more in the angular domain, allowing standard photodetector arrays to adequately sample and resolve the modes, thereby avoiding the need for larger, more expensive detectors.
3Length of stationary object
If the depth-of-layer of the waveguide is increased to accommodate deeper segments, then the measurement depth increases, but the high-order modes become increasingly under-sampled and impossible to resolve
Solution Approach 1:
The patent addresses the sampling problem by changing the prism angle parameter. This modification optimizes the angular sensitivity and mode line spacing, ensuring that even high-order modes from deep waveguide segments are adequately separated and sampled by the photodetector array, enabling precise measurement of large depth-of-layer waveguides.
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 configuration enables proper sampling of high-order modes and efficient use of detector space, improving measurement resolution and accuracy of the DIOX profile without the need for larger, more expensive photodetectors or optical systems.
Implementation Method 1
a coupling prism having a coupling angle α with a maximum coupling angle αmax at which total internal reflection occurs
Implementation Method 2
reflected light exits the output surface of the coupling prism... whose adjusted mode-line spacing allows for proper sampling of the otherwise tightly spaced mode lines
Data Source
AI summary
Prism-coupling systems and methods for characterizing large depth-of-layer waveguides are disclosed. The systems and methods utilize a coupling prism having a coupling angle α having a maximum coupling angle αmax at which total internal reflection occurs. The prism angle α is in the range 0.81αmax≦α≦0.99αmax. This configuration causes the more spaced-apart lower-order mode lines to move closer together and the more tightly spaced higher-order mode lines to separate. The adjusted mode-line spacing allows for proper sampling at the detector of the otherwise tightly spaced mode lines. The mode-line spacings of the detected mode spectra are then corrected via post-processing. The corrected mode spectra are then processed to obtain at least one characteristic of the waveguide.