MWIR Objective Lens Athermalization for Airborne Remote Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
MWIR lenses for airborne remote sensing systems face challenges in achieving high spatial and thermal resolution simultaneously due to the inverse proportionality of these resolutions, and they must maintain focus over a wide environmental temperature range while being compact and efficient, which is difficult with existing athermalization techniques and material limitations.
Innovation Solution
A MidWave InfraRed (MWIR) lens design comprising three optical groups with specific optical powers and materials, including Germanium and Silicon, that corrects for monochromatic and chromatic aberrations over the 3.3 μm to 5.1 μm spectral range, with a focal length of 9 inches and F/# of 2.64, incorporating a scanning mirror and fold mirrors to achieve a large angular field of view and low distortion, and uses a cold filter and Dewar window for efficient thermal management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a compact lens design is used to reduce system size, then system size is reduced, but maintaining focus over wide temperature range becomes difficult
Solution Approach 1:
The patent employs athermalization techniques by selecting materials with complementary thermal properties. The first lens group uses materials with positive thermal expansion, while the second lens group uses materials with negative thermal expansion, creating a compensation effect that maintains focal length stability across temperature ranges
Solution Approach 2:
The lens system uses composite construction with multiple materials including germanium, silicon, and specialized athermalization materials. This composite approach allows the compact design to achieve both size reduction and thermal stability by combining materials whose properties offset each other's thermal effects
2Measurement precision
If multiple materials are used to correct aberrations over wide wavelength range, then optical performance is improved, but device complexity increases
Solution Approach 1:
Different regions of the lens system use different materials optimized for specific functions. The first lens group uses materials optimized for certain wavelength ranges and aberration corrections, while the second and third groups use different materials for complementary corrections. This local optimization achieves comprehensive performance without requiring all materials throughout the entire system
Solution Approach 2:
Each lens group is designed to perform multiple functions simultaneously - correcting spherical aberration, coma, astigmatism, and field curvature while also contributing to athermalization. The negative power second lens group both corrects chromatic aberration and provides thermal compensation, reducing the need for separate correction elements
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 lens achieves high resolution and low distortion across a broad temperature range, maintaining focus and image quality with a compact design, effectively addressing the trade-offs between spatial and thermal resolution and environmental temperature variations.
Implementation Method 1
a first optical group configured to receive MWIR radiation from the remote object and to direct converged light onto the second optical group
Implementation Method 2
uses a cold filter and Dewar window for efficient thermal management
Data Source
AI summary
A Mid-Wave Infrared (MWIR) objective lens having an F # of 2.64 and a 33.6° angular field of view. It is deployed, with a focal plane and scanning system, on an airborne platform for remote sensing applications. Focal length is 9 inches, and the image is formed on a focal plane constituting CCD or CMOS with micro lenses. The lens has, from object to image, three optical element groups with a cold shield/aperture stop. Group 1 has a positive optical power and three optical elements; Group 2 has a positive optical power and four optical elements; Group 3 has a positive optical power and three optical elements. The objective lens is made of two Germanium and Silicon. The lens is both apochromatic and orthoscopic, and corrected for monochromatic and chromatic aberrations over 3.3 to 5.1 micrometers.