Diffractive Optical Element Needle-Shaped Beam for OCT Depth of Focus
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Solution Overview
Problem
Current optical coherence tomography (OCT) systems face limitations in extending the depth of focus, which affects the imaging quality and resolution, especially in applications requiring deeper penetration into biological specimens.
Innovation Solution
The use of a diffractive optical element with a predetermined phase profile to generate a needle-shaped beam with multiple foci along the axial direction, providing a large depth of focus and narrow beam diameter, is employed. This beam is created by a diffractive optical element with a substrate of unit cells, each containing multiple phase elements with incremental phase values, allowing for optimized axial positions and additional phase factors to adjust beam parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a conventional OCT system uses a standard illumination beam, then the system structure is simple, but the depth of focus is limited and imaging quality deteriorates at greater depths
Solution Approach 1:
The illumination beam is segmented into multiple foci distributed along the axial direction using a diffractive optical element with unit cells containing phase elements. This segmentation creates multiple focal points that collectively extend the depth of focus while maintaining imaging quality at each focal plane
Solution Approach 2:
The patent transitions from a single focal point in the transverse plane to multiple foci distributed in the axial dimension. By introducing the axial dimension for focus distribution, the system achieves extended depth of focus while maintaining lateral resolution through the needle-shaped beam profile
2Manufacturing precision
If the beam diameter is reduced to improve lateral resolution, then lateral resolution is improved, but the depth of focus is shortened
Solution Approach 1:
The beam is segmented into multiple axial foci, allowing each focus to maintain a narrow diameter for lateral resolution while the collection of multiple foci extends the overall depth of focus. The unit cell structure enables independent control of lateral and axial beam properties
Solution Approach 2:
The patent decouples the relationship between beam diameter and depth of focus by distributing foci along the axial dimension. The needle-shaped beam maintains narrow diameter in the transverse plane for lateral resolution while extending along the axial direction through multiple foci to achieve extended depth of focus
3Length of stationary object
If a diffractive optical element with multiple phase elements is used to generate needle-shaped beam, then depth of focus is extended, but the device complexity increases
Solution Approach 1:
The diffractive optical element is segmented into repeating unit cells, each containing a small number of phase elements. This modular segmentation allows the complex phase profile to be constructed from simple repeating units, making the design systematic and manufacturable
Solution Approach 2:
The patent uses a finite number of discrete phase elements within each unit cell (M phase elements with N phase values) to approximate the ideal continuous phase profile. This partial action approach achieves the needle-shaped beam generation with practical, manufacturable discrete structures rather than requiring perfect continuous phase modulation
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 enhances the depth of focus in OCT systems while maintaining lateral resolution, enabling clearer imaging of specimens at greater depths with improved axial uniformity and reduced side lobes, as demonstrated by improved imaging of polystyrene beads and biological samples.
Implementation Method 1
a diffractive optical element with a predetermined phase profile is utilized to generate a beam with multiple foci distributed along the axial direction of propagation
Data Source
AI summary
A diffractive optical element includes a substrate including a plurality of unit cells arrayed across the substrate. Each of the unit cells includes M phase elements and each of the M phase elements is characterized by one of a set of N phase values. Each of the set of N phase values is equal to an incremental phase value times an index m, wherein M>1 and m=1 . . . N.