Catadioptric Optical System Corrects Chief Ray Angles
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Solution Overview
Problem
Satellite remote-sensing images suffer from reduced image quality due to diminished luminous flux and brightness contrast caused by micro-lens deformation from radiation and temperature variations, leading to dark stripes in stitched images.
Innovation Solution
A catadioptric optical system with a Ritchey-Chrétien type telescope design, featuring a first mirrors group of hyperbolic mirrors and a second corrector lens group with specific lens elements and refractive powers, corrects chief ray angles, ensuring uniform luminous flux across each pixel area of the image sensing device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If micro-lens elements are added to each pixel to increase luminous flux, then the pixel effective area and image quality are improved, but the micro-lens elements are deformed by radiation and temperature variations in space, leading to deteriorated image quality
Solution Approach 1:
The patent removes the micro-lens elements from the image sensing device, extracting the problematic component that causes deformation under radiation and temperature stress. Instead of using micro-lenses to focus light, the system relies on the catadioptric optical design with corrected chief ray angles to achieve uniform illumination without the reliability issues of space-exposed micro-lenses
Solution Approach 2:
The patent introduces a catadioptric corrector system as an intermediary between the incoming light and the image sensor. This corrector system, consisting of mirrors and lens elements, mediates the light path to correct chief ray angles before light reaches the sensor, thereby achieving uniform illumination without requiring deformation-prone micro-lenses on the sensor surface
2Reliability
If no micro-lens is used on each pixel to avoid deformation, then reliability is improved, but the luminous flux received by the effective pixel area is diminished, decreasing brightness contrast
Solution Approach 1:
The patent replaces the mechanical micro-lens focusing system with an optical correction system. Instead of using physical micro-lenses to concentrate light onto each pixel, the system uses a catadioptric corrector with specific lens elements (positive and negative diopter) to correct the chief ray angles optically, achieving uniform light distribution across the sensor without mechanical micro-lenses
Solution Approach 2:
The patent changes the optical parameters of the light path by introducing a corrector system that modifies chief ray angles. The corrector includes lens elements with specific diopter values (positive and negative) that alter the convergence angle of light rays, transforming the illumination pattern from non-uniform to uniform across the image sensor surface
3Device complexity
If a classical catadioptric Cassegrain telescope is used, then the system structure is simplified, but off-axis aberration is not adequately corrected, affecting image quality
Solution Approach 1:
The patent segments the optical correction function into multiple distinct lens elements with different diopter characteristics (positive and negative). The corrector system is divided into several lens elements, each contributing to the overall correction of off-axis aberrations and chief ray angles, allowing precise control over the optical path without requiring a completely redesigned telescope structure
Solution Approach 2:
The patent employs a composite optical system combining reflective elements (mirrors) and refractive elements (lens groups with positive and negative diopters). This composite catadioptric design integrates the structural simplicity of reflective telescopes with the aberration-correcting capabilities of refractive lens systems, achieving both structural efficiency and high image quality
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 system enhances image quality by maintaining uniform illumination across the image sensing device, reducing dark stripes and improving the overall brightness contrast, making it suitable for satellite remote-sensing applications.
Implementation Method 1
a first mirrors group of Ritchey-Chrétien type hyperbolic mirrors with positive diopter including a concave primary mirror having a central through hole and a convex secondary mirror
Implementation Method 2
a second corrector lens group with negative diopter positioned at an image side of the first mirrors group including a first meniscus lens element having positive refractive power, a second lens element with negative refractive power, a third meniscus lens element having negative refractive power, and a fourth lens element with positive refractive power
Data Source
AI summary
A catadioptric optical system in sequence of ray tracing comprises a first mirrors group of Ritchey-Chrétien type hyperbolic mirrors with positive diopter including a concave primary mirror having a central through hole and a convex secondary mirror, a second corrector lens group with negative diopter positioned at the image-side of the first mirrors group including a first meniscus lens element having positive refractive power and a convex object-side surface, a second lens element having negative refractive power and biconcave surfaces, a third meniscus lens element having negative refractive power and a concave object-side surface, and a fourth lens element having positive refractive power and biconvex surfaces. The infinite conjugate beams of incident light within field of view pass through the catadioptric optical system to become a corrected beam having a small CRA angle.