Passively Athermalized Infrared Lens Design
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Solution Overview
Problem
Conventional longwave infrared (LWIR) lenses are expensive to manufacture and often require complex athermalization mechanisms, such as moving parts or nested barrels, due to the temperature sensitivity of materials used, which increases production costs and complicates the alignment process.
Innovation Solution
A passively athermalized infrared imaging system is developed using an object side meniscus lens with one aspheric surface and an image side meniscus lens with two aspheric surfaces, made from materials like chalcogenide glass, germanium, or gallium arsenide, where the thermal glass constants are selected to maintain focus over a temperature range of 0 to +40 degrees Celsius, eliminating the need for active alignment and costly athermalization components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional LWIR lenses use standard materials and simple lens structures, then manufacturing is simpler, but temperature sensitivity causes focus drift and degraded imaging performance
Solution Approach 1:
The patent uses composite lens structures combining materials with different thermal glass constants (Tg). Specifically, it employs a meniscus lens with one aspheric surface made from a first material and another meniscus lens with two aspheric surfaces made from a second material, where Tg2 ≥ 1.6×Tg1. This composite approach allows passive athermalization where temperature-induced focus drift in one material is compensated by the other, achieving stable imaging performance across 0 to +40°C without active correction mechanisms.
Solution Approach 2:
The patent changes the thermal parameters of the lens system by selecting materials with specific thermal glass constants and designing lenses with particular aspheric surface parameters. The object side meniscus lens has an optical power that is at least 1.6 times the optical power of the image side meniscus lens. By carefully controlling these parameters, the system achieves athermalization where the effective focus position remains stable over the temperature range.
2Reliability
If LWIR lenses incorporate athermalization mechanisms like nested barrels or moving parts, then temperature compensation is achieved, but manufacturing cost and device complexity increase
Solution Approach 1:
The patent extracts and eliminates the need for complex active athermalization mechanisms (nested barrels, moving parts) by incorporating passive athermalization directly into the lens materials and structures themselves. The athermalization function is built into the lens design through material selection and geometric configuration rather than requiring separate compensation mechanisms, thereby reducing manufacturing cost and simplifying production.
Solution Approach 2:
The lens system performs self-athermalization through its inherent material properties and optical design. The combination of materials with different thermal glass constants and the specific aspheric surface configurations cause the lens system to automatically compensate for temperature-induced focus drift without requiring external active control mechanisms, reducing both cost and complexity.
3Device complexity
If LWIR lenses use passive athermalization through material selection and optical design, then active alignment mechanisms are eliminated, but precise control of thermal glass constants is required
Solution Approach 1:
The patent specifies precise parameter requirements for the lens materials, particularly that the thermal glass constant Tg2 of the second material must be at least 1.6 times Tg1 of the first material. The optical powers are also precisely controlled with the object side meniscus lens having optical power at least 1.6 times that of the image side lens. These controlled parameters enable passive athermalization while eliminating the need for complex active alignment mechanisms.
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 solution reduces manufacturing costs and simplifies the alignment process by achieving athermalization without active focus correction or nested barrels, resulting in a more compact and efficient LWIR imaging system with improved image quality across varying temperatures.
Implementation Method 1
an object side meniscus lens that forms at least one aspheric surface, and an image side meniscus lens that forms two aspheric surfaces
Implementation Method 2
an optical power of the image side meniscus lens is at least 1.6 times an optical power of the object side meniscus lens such that an effective focus position of the imaging system is athermalized over a range of 0 to +40 degrees Celsius
Data Source
AI summary
An infrared imaging system is formed by passively aligning two or more lens wafers including a plurality of lenses. The lens wafers may be pre-fabricated lens wafers in which the plurality of lenses are aligned utilizing an alignment jig having a plurality of conduits for distributing bonding material. Alternatively, the lens wafers may be formed of a base material molded around the plurality of optical lenses. The lens wafers may have a variety of alignment features, alignment inserts and/or alignment elements.