Chromatic Aberration OCT Sample Arm for Extended Depth of Focus
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Solution Overview
Problem
High-resolution optical coherence tomography (OCT) systems face a trade-off between lateral resolution and depth of focus (DOF), with high NA lenses reducing DOF and systems like Bessel beams compromising signal-to-noise ratio (SNR) and introducing artifacts.
Innovation Solution
An OCT system utilizing a wide wavelength band of light to induce chromatic focal shift in the sample arm, combined with a dispersive lens pair and image reconstruction algorithms like the chromatic gating (ChG) algorithm to maintain high SNR and expand DOF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high NA lenses are used to increase lateral resolution, then lateral resolution is improved, but depth of focus is reduced
Solution Approach 1:
The patent introduces chromatic dispersion as a new parameter to control the focal properties of light. By using a dispersive lens that creates wavelength-dependent focal shifts, the system can extend the depth of focus while maintaining high lateral resolution. Different wavelengths are focused at different axial positions, creating an extended focal region that resolves the traditional trade-off between resolution and depth of focus.
Solution Approach 2:
The patent adds the chromatic dimension to the traditional focus control. Instead of only controlling focus in the axial direction with conventional lenses, the dispersive lens introduces wavelength-dependent focusing, effectively adding a spectral dimension to the focus control. This allows the system to achieve extended depth of focus by utilizing the chromatic dispersion of the lens.
2Length of stationary object
If Bessel beam optical systems are used to increase depth of focus, then depth of focus is improved, but system signal-to-noise ratio decreases
Solution Approach 1:
The patent applies local quality by creating wavelength-specific focal regions. Instead of using a uniform Bessel beam that extends focus uniformly, the dispersive lens creates localized focal points for different wavelengths at different axial positions. This allows the system to maintain high signal quality at each local focal plane while achieving extended overall depth of focus through the combination of these localized focal regions.
Solution Approach 2:
The patent segments the focal region into wavelength-dependent sub-regions. By dividing the spectrum into different wavelength components and focusing each at a different axial position, the system creates multiple localized focal regions that collectively provide extended depth of focus. This segmentation approach allows the system to maintain high SNR in each region while achieving the desired extended focus range.
3Length of stationary object
If Bessel beam optical systems are used to increase depth of focus, then depth of focus is improved, but image artifacts are introduced
Solution Approach 1:
The patent extracts and eliminates the harmful side lobes associated with Bessel beams by using a dispersive lens approach. Instead of relying on the characteristic side lobes of Bessel beams that cause artifacts, the system uses wavelength-dependent focusing to create a clean, artifact-free focal region. The dispersive lens separates different wavelengths spatially, allowing the system to focus only the desired central light at the target position without the harmful side lobes.
4Length of stationary object
If software-based techniques like ISAM are used to expand depth of focus, then depth of focus is improved, but phase stability requirements become excessively high
Solution Approach 1:
The patent replaces complex software-based phase correction methods with a simpler optical approach using a dispersive lens. Instead of requiring high phase stability and complex signal processing to achieve extended depth of focus, the system uses the physical property of chromatic dispersion in a lens to create wavelength-dependent focal shifts. This optical method achieves the same goal with much lower phase stability requirements and simpler system requirements.
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
Achieves high-resolution and high-sensitivity tomographic images with expanded DOF and improved SNR by focusing measurement light of different wavelengths at different points axially, minimizing artifacts and noise.
Implementation Method 1
a dispersive lens pair that induces chromatic focal shift of the measurement light by allowing the measurement light to have multiple different divergence angles depending on the wavelength
Implementation Method 2
combines the reflected measurement light and the reflected reference light provided from the sample arm and the reference arm, respectively, to output combined light including an interference signal between the measurement light and the reference light
Data Source
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AI summary
An optical coherence tomography (OCT) system includes a light source assembly that generates original light, a sample arm that provides measurement light to a sample and provides measurement light reflected from the sample to an optical coupler, a reference arm of an optical structure that reflects a reference light, the optical coupler divides the original light into the measurement light and the reference light and provides them to the sample arm and the reference arm, respectively, and combines the reflected measurement light and the reflected reference light provided from the sample arm and the reference arm, respectively, to output combined light including an interference signal between the measurement light and the reference light, and an optical detector that analyzes the interference signal of the combined light provided from the optical coupler to generate an optical coherence tomographic image, wherein the sample arm includes a dispersive lens pair that induces chromatic focal shift of the measurement light by allowing the measurement light to have multiple different divergence angles depending on the wavelength.