Athermal Compact Lens Design for Thermal Stability

Solution Overview

Problem

There is a need for optical lenses with high performance, compact size, and excellent thermal stability to capture high-resolution images across a wide field of view, particularly in harsh environments with varying temperatures, and low lighting conditions, as required for automotive driver assistance and surveillance systems.

Innovation Solution

The design consists of three lens groups: a first group with negative or positive power, a second group with positive power including an aperture stop and athermal optical material, and a third group with 1 to 3 elements, where one or more elements can be aspherical, optimized to maintain image quality and compactness across a wide temperature range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Weight of stationary object

If the lens is designed to be compact and light for portable devices, then portability is improved, but maintaining high performance characteristics becomes more difficult

Engineering Contradiction:

Improvelens weightVSAvoidoptical performance

Core Design Contradiction:

Weight of stationary objectVSReliability

Solution Approach 1:

The lens is divided into three distinct groups (Group 1 with negative or positive power, Group 2 with positive power containing the aperture stop and athermal material, and Group 3 with 1-3 elements). This segmentation allows each group to be optimized for specific functions while maintaining overall compactness and performance.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs composite material strategies by combining different glass types (positive and negative do/dT materials) within the lens groups. Specifically, Group 2 contains at least one element made from athermal optical material with negative do/dT, combined with other optical materials to create a composite lens structure that achieves both compactness and thermal stability.

Inventive Principle:

Principle #40Composite materials

2Adaptability or versatility

If the lens is designed for wide field of view (20 to 145 degrees), then field coverage is improved, but thermal stability becomes more challenging to maintain

Engineering Contradiction:

Improvefield of view coverageVSAvoidthermal stability

Core Design Contradiction:

Adaptability or versatilityVSStability of the object's composition

Solution Approach 1:

Different regions of the lens are assigned different material properties: Group 2 contains athermal optical material with negative do/dT specifically positioned to counteract thermal expansion, while other groups use materials optimized for their specific optical functions. This local differentiation of material properties enables wide field coverage while maintaining thermal stability.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the thermal parameters of the lens system by incorporating materials with negative do/dT (athermal materials) that have opposite thermal expansion characteristics to conventional optical materials. This parameter change in material selection enables the lens to maintain focus and optical performance across wide temperature excursions while covering 20 to 145 degrees field of view.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If the lens operates in harsh environments with wide temperature excursions, then environmental adaptability is improved, but maintaining fixed focus and back focal length becomes more difficult

Engineering Contradiction:

Improveenvironmental adaptabilityVSAvoidback focal length stability

Core Design Contradiction:

Adaptability or versatilityVSStability of the object's composition

Solution Approach 1:

The patent changes the thermal parameters of the lens system by incorporating materials with negative do/dT (athermal materials) that have opposite thermal expansion characteristics to conventional optical materials. This parameter change in material selection enables the lens to maintain focus and optical performance across wide temperature excursions while covering 20 to 145 degrees field of view.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful effect of thermal expansion into a beneficial effect by using athermal optical materials with negative do/dT. These materials expand in the opposite direction to conventional materials when heated, and when properly positioned in Group 2, they counteract the thermal expansion of other lens elements, thereby maintaining back focal length stability in harsh environments.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

4Illumination intensity

If the lens is designed for low F-number (F/1.6 to F/1.8), then low lighting performance is improved, but lens complexity increases

Engineering Contradiction:

Improvelow lighting performanceVSAvoidlens complexity

Core Design Contradiction:

Illumination intensityVSDevice complexity

Solution Approach 1:

The lens is divided into three distinct groups (Group 1 with negative or positive power, Group 2 with positive power containing the aperture stop and athermal material, and Group 3 with 1-3 elements). This segmentation allows each group to be optimized for specific functions while maintaining overall compactness and performance.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Group 2 serves multiple functions simultaneously: it contains the aperture stop for controlling light intensity, incorporates athermal optical material for thermal stability, and provides positive power for focusing. This multi-functionality reduces overall lens complexity while achieving low F-number performance.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 system achieves high-resolution imaging across a wide field of view from 20 to 145 degrees with excellent thermal stability and compact size, suitable for applications in automotive and surveillance systems, maintaining performance in harsh environments.

Implementation Method 1

At least one of the positive powered elements in this group is made from a material having a negative do/dT over the operating temperature range, where n is the index of refraction of the material at d-line (587.56 nm) and T is the temperature of the environment. Such material is known as 'athermal optical material'.

Methodology Applied

Scientific EffectAthermal compensation:

Implementation Method 2

One or more elements in Group 1 and 3 may be an aspherical element. An aspheric element is a lens element such that at least one of its two surfaces is described by a general aspheric equation... Aspheric elements can be made from a suitable glass or plastic material.

Methodology Applied

Scientific EffectAspherical refraction:

Implementation Method 3

This group comprises at least one cemented doublet.

Methodology Applied

Scientific EffectChromatic aberration correction: Refraction

Data Source

PatentUS10935761B1Large aperture compact lenses

Publication Date: 2021.03.02 NING ALEX

AI summary

Large aperture compact lens and a camera design using the lens are described. The lens comprises from object to image, three lens groups with a first lens group having a negative or positive power and comprising 3-4 lens elements, a second lens group having positive power and 3-4 elements including an aperture stop, at least one cemented doublet and one positive power lens made from athermic optical material, and a third lens group comprising 1-3 elements.