Diffractive Microlens for Chromatic Aberration in OCT Endoscopes

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Solution Overview

Problem

Miniature OCT endoscopes face challenges in achieving ultrahigh-resolution imaging due to chromatic aberration, which degrades both axial and lateral resolution, and existing solutions like multi-element achromatic lenses are costly and impractical for miniature probes.

Innovation Solution

Incorporating a diffractive lens at the distal end of the OCT imaging probe to mitigate wavelength-dependent aberration, using a diffraction element with high diffraction efficiency over a broad spectral range to correct chromatic aberration and improve focal accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If multi-element achromatic lenses are used to correct chromatic aberration, then chromatic aberration is reduced, but device complexity and manufacturing cost increase significantly

Engineering Contradiction:

Improvechromatic aberration correctionVSAvoidlens element quantity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent changes the optical parameters by introducing a diffractive optical element with specific diffraction characteristics. This element introduces wavelength-dependent phase shifts that counteract the chromatic aberration produced by the GRIN lens, achieving correction without adding multiple refractive lens elements. The diffractive element's zone plate structure with varying focal lengths for different wavelengths enables this parameter-based correction approach.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical/optical system of multiple refractive lens elements with a diffractive optical element that uses diffraction physics. Instead of relying on the mechanical stacking of multiple achromatic lens elements, the invention uses a single diffractive zone plate that optically corrects chromatic aberration through wavelength-dependent diffraction patterns, simplifying the overall optical system.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If broadband light sources at 800 nm are used for ultrahigh-resolution OCT imaging, then axial resolution improves, but chromatic aberration increases

Engineering Contradiction:

Improveaxial resolutionVSAvoidchromatic aberration

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a diffractive optical element as an intermediary component between the broadband light source and the GRIN lens. This intermediate element modifies the wavefront of different wavelengths differently, compensating for the chromatic aberration that would otherwise be introduced by the GRIN lens when using broadband 800 nm light sources. The diffractive element acts as a mediator that enables the use of broadband sources without suffering from their chromatic effects.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Volume of moving object

If GRIN lenses are used in miniature OCT probes, then miniaturization is achieved, but chromatic aberration degrades image quality

Engineering Contradiction:

Improveprobe sizeVSAvoidimage quality

Core Design Contradiction:

Volume of moving objectVSManufacturing precision

Solution Approach 1:

The patent merges the focusing function of the GRIN lens with the chromatic correction function of the diffractive optical element into a single integrated probe tip. The diffractive zone plate is positioned at or near the distal end of the GRIN lens, combining miniaturization with chromatic aberration correction in one compact configuration. This merged design achieves both small probe size and high image quality without requiring separate correction components.

Inventive Principle:

Principle #5Merging (Combining)

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 solution significantly reduces chromatic aberration, enhancing axial and lateral resolution, enabling high-quality, cost-effective ultrahigh-resolution OCT imaging in miniature endoscopes for internal luminal organs, as demonstrated by improved imaging of human esophagus and rat trachea tissues.

Implementation Method 1

a diffractive lens positioned at a distal end of a compound lens within the OCT imaging probe... a diffraction element configured to mitigate wavelength dependent aberration

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentUS10646105B2Device and methods for color corrected OCT imaging endoscope/catheter to achieve high-resolution

Publication Date: 2020.05.12 JOHNS HOPKINS UNIVERSITY

AI summary

The present invention is directed to an achromatic endoscope which employs a diffractive microlens. Along with a broadband rotary joint and a custom 800 nm SD-OCT system, ultrahigh-resolution 3D volumetric imaging over a large area becomes possible. The diffractive microlens can be used directly with a GRIN lens, making the endoscope design simpler and cost effective. Preliminary ex vivo 3D intraluminal imaging was performed with the endoscope in conjunction with a home-built broadband rotary joint and a spectral-domain OCT system, demonstrating the performance of the diffractive endoscope. Considering the miniature OCT imaging probe is the required component for using the OCT technology in internal organs, the proposed approach will have a broad impact on endoscopic OCT imaging by improving OCT resolution in any applications that involve a miniature OCT probe, as intravascular OCT imaging, gastrointestinal (GI) tract imaging, airway imaging etc.