Catoptric Optical System With Posterior Aperture Stop
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Solution Overview
Problem
Current optical systems for scanning surveillance and infrared imaging applications lack a wide field of view, long back focal length, and an external posterior aperture stop, making them unsuitable as foreoptics for dewar-enclosed detectors and double-pass spectrometers.
Innovation Solution
An all-reflective imaging optical system with a set of mirrors, where only the last mirror has positive optical power and all others have negative power, providing a full-angle field of view of at least 30 degrees and a back focal length equal to or greater than the effective focal length, with an external posterior aperture stop between the last mirror and the image plane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional optical systems are used, then the system structure is simple, but the field of view is narrow and the back focal length is insufficient
Solution Approach 1:
The optical system is divided into multiple mirror elements (at least three mirrors) with different optical powers. The first mirror has negative optical power, the second mirror has negative optical power, and the third mirror has positive optical power. This segmentation allows each mirror to contribute differently to the overall optical performance, enabling a wide field of view while maintaining a manageable system structure.
Solution Approach 2:
The patent employs a complex three-dimensional arrangement of mirrors in the optical path, utilizing spatial dimensionality to achieve wide field of view. The mirrors are positioned and oriented in specific three-dimensional configurations that allow light rays from different angles to be properly directed to the image plane, effectively using spatial dimensionality to expand the field of view without simply increasing system size linearly.
2Length of stationary object
If the back focal length is increased to position back-end components outside the dewar, then the foreoptics can be positioned outside the container, but the system complexity increases
Solution Approach 1:
The optical path is segmented into multiple reflection stages using at least three mirrors. This segmentation allows the back focal length to be extended by distributing the optical power across multiple elements rather than relying on a single long focal length element, thereby achieving the required back focal length while controlling system complexity.
Solution Approach 2:
The patent introduces an external posterior aperture stop as an intermediary element positioned in the optical path between the last mirror and the image plane. This aperture stop serves as a mediator that controls the angular acceptance of the system and helps define the field of view, allowing the back focal length to be extended while maintaining proper optical control and minimizing system complexity.
3Object-affected harmful factors
If an external posterior aperture stop is positioned within the dewar, then thermal noise is minimized, but the optical path configuration becomes more complex
Solution Approach 1:
The external posterior aperture stop acts as an intermediary element that is strategically positioned within the dewar environment. This aperture stop mediates between the optical path requirements and the thermal environment, allowing thermal noise to be minimized by placing the stop in the cold environment of the dewar while still maintaining proper optical control through its specific positioning and sizing in the optical path.
Solution Approach 2:
The patent applies local quality by positioning the aperture stop with specific properties (size, shape, position) that are optimized for its location within the dewar. The aperture stop has local optical control functions that are tailored to its specific position in the optical path and thermal environment, allowing it to minimize thermal noise while maintaining proper optical performance without requiring complex system-wide modifications.
4Area of stationary object
If all mirrors have negative optical power except the last one, then a wide field of view is achieved with long back focal length, but the manufacturing precision requirements increase
Solution Approach 1:
The optical power is segmented across multiple mirror elements rather than concentrated in a single element. The first mirror has negative optical power, the second mirror has negative optical power, and the third mirror has positive optical power. This segmentation distributes the optical power requirements, allowing each mirror to be manufactured with more relaxed precision tolerances while achieving the overall wide field of view and long back focal length performance.
Solution Approach 2:
The patent utilizes parameter changes by varying the optical power signs and magnitudes across different mirror elements. The first mirror has negative optical power, the second mirror has negative optical power, and the third mirror has positive optical power. This parameter variation allows the system to achieve wide field of view and long back focal length while distributing manufacturing precision requirements across multiple elements with different optical characteristics.
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 configuration enables the optical system to effectively serve as foreoptics for dewar-enclosed detectors and double-pass spectrometers, offering a wide field of view and minimizing thermal noise by positioning the external posterior aperture stop within the dewar, while maintaining a long back focal length for optimal performance.
Implementation Method 1
an all-reflective imaging optical form... a set of mirrors including at least three mirrors on the beam path
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A catoptric, wide-angle optical system includes at least three mirrors. Only the last mirror on the beam path (22) has a positive optical power and all other mirrors have negative optical power. The sum of the optical powers of the mirrors is zero. An external posterior aperture stop (35) is located on the beam path (22) between the last mirror and the image plane (24). The back focal length of the optical system (20) is equal to or greater than an effective focal length of the optical system (20). The field of view is large, and typically at least 30-40 degrees in one plane.