In-line Holographic Imaging Phase Diversity Illumination
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Solution Overview
Problem
In-line holographic imaging faces the twin-image problem due to the loss of phase information, resulting in degraded image quality with two overlaid images, one in focus and one out of focus, during the reconstruction process.
Innovation Solution
The use of two light sources arranged at different angles relative to the object provides phase diversity in the interference patterns, allowing for accurate reconstruction of the optical image by processing these patterns using an iterative phase retrieval algorithm, which accounts for the fixed optical setup and initial calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If in-line holography is used for imaging transparent objects, then the imaging method becomes simple and cost-effective, but the twin-image problem occurs leading to degraded image quality
Solution Approach 1:
The patent introduces a new dimension by using multiple illumination angles to capture interference patterns. Instead of relying on a single in-line configuration, the system captures holograms from different angular perspectives, adding spatial dimensionality to the data acquisition process. This enables phase retrieval algorithms to distinguish between the object and its twin image, resolving the image quality degradation while preserving the simplicity of the optical setup.
2Device complexity
If a single interference pattern is acquired, then the set-up remains simple, but phase information is lost resulting in two indistinguishable solutions
Solution Approach 1:
The patent applies preliminary action by capturing multiple interference patterns at different illumination angles before performing the reconstruction process. This pre-acquisition of diverse angular data provides the necessary phase information upfront, enabling the subsequent iterative phase retrieval algorithm to resolve the twin-image ambiguity without requiring complex post-processing or additional optical elements.
3Measurement precision
If iterative phase retrieval is performed using multiple holograms, then phase information can be retrieved, but the method and set-up become more complex
Solution Approach 1:
The patent changes the parameter of illumination angle to acquire multiple interference patterns. By varying this single parameter (angular position) rather than introducing multiple complex optical paths or sophisticated hardware configurations, the system obtains the necessary diverse data for phase retrieval. This approach maintains relative simplicity while enabling accurate phase information extraction through computational processing.
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 method effectively alleviates the twin-image problem by enhancing image quality through phase information retrieval, providing a robust and stable holographic imaging system with improved accuracy and reliability.
Implementation Method 1
The interference pattern is formed by diffracted light, being scattered by the object, and undiffracted light of the light beam
Implementation Method 2
creating an interference pattern based on object light, being scattered by the object, and reference light of the light beam passing unaffected through the object
Data Source
Figure 1a~1b
Figure 2~3
Figure 4
AI summary
An apparatus for in-line holographic imaging is provided. The apparatus (100) comprises at least a first light source (102) and a second light source (104) arranged for illuminating an object (108) arranged in the apparatus (100) with a light beam; an image sensor (110) being arranged to detect at least a first and a second interference pattern, wherein the first interference pattern is formed when the object (108) is illuminated by the first light source (102) and the second interference pattern is formed when the object (108) is illuminated by the second light source (104), wherein the first and second interference patterns are formed by diffracted light, being scattered by the object (108), and undiffracted light of the light beam; wherein the at least first and second light sources (102, 104) are arranged at different angles in relation to the object (108), and possibly illuminate the object (108) using different wavelengths.