Refractive Index Reconstruction Using Partial Coherent Illumination

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Solution Overview

Problem

Current refractive index distribution estimation systems face challenges in accurately reconstructing the refractive index distribution of samples, particularly for thick samples, due to limitations in measurement techniques and computational methods, which result in low accuracy and inefficiency.

Innovation Solution

A refractive index distribution estimating system that employs partial coherent illumination, an imaging optical system, and a processor to calculate and optimize the refractive index distribution by summing intensity distributions from multiple light sources and updating the estimation sample through repeated calculations and optimizations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If linear computation (first-order Born approximation) is used for image computation, then calculation time is short, but calculation accuracy is low because multiple scattering is ignored

Engineering Contradiction:

Improvecalculation speedVSAvoidcalculation accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent transitions from linear computation (first-order Born approximation) to nonlinear computation (Rytov approximation), changing the computational parameter to account for multiple scattering effects. This allows the system to maintain reasonable calculation speed while significantly improving accuracy for thick samples by incorporating higher-order scattering terms in the wave propagation model.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If incoherent illumination is used with a large light source, then the sample can be illuminated from various directions, but the spatial coherence of illumination light is low

Engineering Contradiction:

Improveillumination coverageVSAvoidspatial coherence

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent implements partial coherent illumination by positioning a condenser lens to create a focused illumination region on the sample. This allows different regions of the sample to receive illumination with appropriate coherence levels - the central region receives more coherent light for high-resolution imaging, while peripheral regions receive divergent light for broader coverage, optimizing both spatial coherence and illumination versatility.

Inventive Principle:

Principle #3Local quality

3Measurement precision

If the size of the light source is made extremely small to be considered as a point light source, then coherent illumination is achieved, but the illumination coverage is limited

Engineering Contradiction:

Improvecoherence qualityVSAvoidillumination coverage

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The patent uses a dynamically adjustable illumination system where the condenser lens can be positioned at different heights relative to the sample. By adjusting the lens position, the system can dynamically change the illumination characteristics between more coherent (lens closer to sample) and more divergent (lens farther from sample), allowing adaptation to different sample thicknesses and imaging requirements.

Inventive Principle:

Principle #15Dynamics

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 system achieves improved accuracy in reconstructing the refractive index distribution of both thin and thick samples by utilizing partial coherent illumination and advanced computational methods, leading to more precise and efficient refractive index estimation.

Implementation Method 1

an illumination optical system configured to illuminate a sample

Methodology Applied

Scientific EffectLight propagation: Light

Implementation Method 2

illumination using an incoherent light source is classified into incoherent illumination, coherent illumination, and partial coherent illumination

Methodology Applied

Scientific EffectCoherent illumination: Coherent Light

Implementation Method 3

an imaging optical system configured to form an optical image of the sample

Methodology Applied

Scientific EffectOptical focusing: Focusing

Data Source

PatentUS11867624B2System for reconstructing and outputting a structure of an estimation sample using refractive index distribution of updated estimation sample

Publication Date: 2024.01.09 EVIDENT CORP

AI summary

A refractive index distribution estimating system includes an illumination optical system configured to illuminate a sample, an imaging optical system configured to form an optical sample image, an image sensor configured to capture optical images of the sample, and a processor configured to reconstruct a refractive index distribution of the sample from images. The processor performs processing including the steps of: estimating the sample; calculating the estimated sample image from a plurality of first wavefronts emanating from a plurality of modeled light sources; optimizing a refractive index distribution of the estimated sample from a plurality of second wavefronts after the first wavefronts pass through the estimated sample, the captured image, and the image of the estimated sample; updating the estimation sample by repeating calculation of the estimated sample image and optimization of the refractive index distribution of the estimated sample; and reconstructing and outputting a structure of the estimated sample.