Spatial Filter Phase Mask Extends Depth of Field
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Solution Overview
Problem
Current optical imaging systems face limitations in extending the depth of field and depth of focus without introducing image distortion or degrading image quality, and existing spatial filters often require post-processing to achieve optimal performance.
Innovation Solution
A method for designing an imaging system with a spatial filter that modifies the phase pupil function to extend the depth of field and focus, using a phase mask with a radial phase profile optimized through a merit function evaluation process, allowing for invariant image quality across the modified depth range without the need for post-processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a spatial filter is used to extend the depth of field, then the depth of field is increased, but image quality and spatial resolution may be degraded
Solution Approach 1:
The patent applies parameter changes by modifying the phase pupil function parameters through optimized phase masks. The phase mask introduces controlled phase shifts that alter the optical transfer function, enabling extension of the depth of field while maintaining image quality. The optimization process adjusts phase parameters to preserve spatial resolution across the extended depth range.
2Length of stationary object
If a spatial filter is used to extend the depth of field, then the depth of field is increased, but post-processing is required to maintain optimal performance
Solution Approach 1:
The patent implements self-service by designing the phase mask to automatically maintain optimal image quality without requiring external post-processing. The optimized phase pupil function inherently compensates for focus variations across the extended depth of field, making the system self-correcting and eliminating the need for additional processing steps.
3Length of stationary object
If the phase pupil function is modified to extend depth of field, then the depth of field is increased, but the optical system complexity increases
Solution Approach 1:
The patent uses an intermediary approach by introducing a phase mask as a mediating element between the optical system and the image plane. This phase mask, positioned in the pupil plane, modifies the phase pupil function to extend depth of field while maintaining a relatively simple optical system architecture. The phase mask acts as a compact intermediary that achieves complex functionality without substantially increasing overall system complexity.
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 method significantly extends the depth of field and focus domain by a factor of at least 10, maintaining image quality and spatial resolution without post-processing, and can be applied to various imaging systems, including those with asymmetrical pupils and complex optical configurations.
Implementation Method 1
A method for designing an imaging system comprising a spatial filter of the phase mask type... initialization of a pupillary phase function of the spatial filter in the pupillary plane of the optical system
Implementation Method 2
The optical system 10 forms an image of this object in the image space 400. More precisely, the optical system 10 optically conjugates the detection plane 40 with an object plane 20
Implementation Method 3
An apodizer filter is generally a spatial transmission filter with an amplitude distribution that allows for the suppression of secondary rings in the diffraction pattern produced by an optical system at an image point
Data Source
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AI summary
The invention relates to a method of designing an imaging system comprising an optical system (10) having a longitudinal optical axis (12), an image detector (30) and a spatial filter (50), the imaging system being configured to form an image of a focus plane (20) on the image detector (30).According to the invention, the optical transfer function (OTF) of the optical system (10) combined with the spatial filter (50) is calculated as a function, on the one hand, of the image spatial frequencies (f), and, on the other hand, of the focus error (Ψ), so as to determine a contrast map and a phase map of the optical system (10) combined with the pupil function of the spatial filter (50), the contrast map and the phase map being functions, on the one hand, of the spatial frequency (f), and, on the other hand, of the focus error (Ψ), and a value of longitudinal extension (|P|) of the depth of focus domain of the imaging system in the useful range of spatial frequencies ([-fc ; fc]) and an average contrast C are determined from these maps. The invention also relates to a spatial filter obtained by this method and to an imaging system comprising such a spatial filter.