Athermal Doublet Lens Using Opposing Thermo-Optic Coefficients
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Solution Overview
Problem
Plastic lenses are unsuitable for cameras that need to operate across a wide temperature range due to significant variations in optical properties with temperature, while glass lenses are more stable but costly and less flexible in design.
Innovation Solution
An athermal lens system is created using a converging lens element with a negative thermo-optic coefficient and a diverging lens element with an even more negative thermo-optic coefficient, coupled together to form a converging athermal doublet lens, allowing for temperature compensation and reduced cost through the use of plastic materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If plastic lenses are used, then manufacturing cost and design flexibility are reduced, but optical performance stability across temperature range deteriorates
Solution Approach 1:
The patent combines two different plastic materials with contrasting thermo-optic properties (one with positive dn/dT and one with negative dn/dT) into a compound lens system. This composite approach allows the lens to maintain both the manufacturing advantages of plastic and the thermal stability previously only achievable with glass, directly resolving the contradiction between ease of manufacture and reliability.
Solution Approach 2:
The invention changes the material parameters by selecting plastics with opposite signs of thermo-optic coefficients. By carefully choosing materials where one expands optically with temperature while the other contracts, the system achieves temperature compensation, maintaining optical performance stability while using cost-effective plastic materials.
2Reliability
If glass lenses are used, then optical performance stability across temperature range is improved, but manufacturing cost and design flexibility worsen
Solution Approach 1:
The patent replaces expensive glass lenses with cheaper plastic alternatives that achieve comparable thermal stability through the compound design. This substitution maintains reliability while dramatically reducing manufacturing cost, effectively using economical materials to replace premium ones without sacrificing performance.
Solution Approach 2:
Instead of using traditional glass, the invention creates a composite plastic lens system that replicates the thermal stability of glass through the combination of materials with opposing thermo-optic coefficients, thereby achieving glass-level reliability at plastic-level cost.
3Device complexity
If single plastic lens elements are used, then device complexity is reduced, but temperature compensation capability deteriorates
Solution Approach 1:
The patent divides a single plastic lens into two separate lens elements made from different materials with opposite thermo-optic coefficients. This segmentation allows each element to contribute differently to temperature compensation, achieving thermal stability that would be impossible in a single homogeneous lens, while keeping the overall structure relatively simple.
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 athermal doublet lens maintains performance across a wide temperature range from -45°C to 105°C with minimal temperature-induced changes, offering a cost-effective solution for temperature-stable imaging applications.
Implementation Method 1
The dependence of the index of refraction, n, on temperature, T, is characterized by the thermo-optic coefficient dn/dT. For most optical plastics, the thermo-optic coefficient is on the order of −100 ppm/K.
Data Source
AI summary
An athermal lens system includes a converging lens element having a negative first thermo-optic coefficient, and a diverging lens element having a second thermo-optic coefficient more negative than the first thermo-optic coefficient, wherein the diverging lens element is coupled with the converging lens element to form a converging athermal doublet lens.