ZnS Infrared Objective Lens with Diffractive Curved Focal Surface

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Solution Overview

Problem

Current infrared objective lens designs for wide-field, fast-F# applications face challenges with field curvature aberrations, which limit the use of lower-cost materials like Zinc Sulphide (ZnS) without increasing the number of lens components.

Innovation Solution

A novel objective lens design using only ZnS optical material, featuring two lenses with aspheric curvatures and negative-power diffractive surfaces, optimized for a curved focal plane to mitigate field curvature considerations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If lower-cost materials like ZnS are used instead of Germanium, then material cost is reduced, but field curvature aberration worsens and requires additional lens components

Engineering Contradiction:

Improvematerial costVSAvoidnumber of lens components

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

The patent applies aspheric surfaces to the lens elements to correct field curvature aberration. By using curved surfaces with specific aspheric coefficients, the lens system achieves proper field flatness without requiring additional lens components, thus maintaining the cost advantage of using ZnS material while eliminating the complexity penalty

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The patent modifies optical parameters by introducing diffractive optical elements with specific groove depths and patterns. These diffractive structures change the phase of light waves to correct chromatic and field curvature aberrations, enabling the use of single-material ZnS lenses without increasing component count

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If the number of lens components is reduced to lower cost, then device complexity is reduced, but aberration correction capability worsens

Engineering Contradiction:

Improvenumber of lens componentsVSAvoidaberration correction

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent combines refractive optics (aspheric lens surfaces) with diffractive optics (microstructured surfaces) within single lens elements made of ZnS. This composite approach integrates multiple correction functions into unified components, achieving superior aberration correction with reduced component count while maintaining system reliability

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent merges multiple optical functions (focusing, field curvature correction, chromatic aberration correction) into single integrated lens elements. By combining aspheric shaping and diffractive patterning in the same component, the design achieves comprehensive aberration correction without requiring separate correction lenses

Inventive Principle:

Principle #5Merging (Combining)

3Reliability

If aspheric surfaces and diffractive elements are added to correct aberrations, then optical performance is improved, but manufacturing complexity increases

Engineering Contradiction:

Improveoptical performanceVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent replaces complex multi-element mechanical lens assemblies with single-element lenses featuring integrated diffractive optical elements. The diffractive patterns are fabricated using direct laser writing or lithography methods, substituting traditional multi-step mechanical polishing and assembly processes with more efficient direct-write manufacturing approaches

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 design achieves a wide field of view of ±20.0° with corrected chromatic aberrations over the 8-11 micron infrared wavelength band, operating at a fast F#/1.0, while reducing the burden on lens design and potentially lowering costs by using a single material.

Implementation Method 1

Each lens has a negative-power diffractive surface on its 2nd surface to provide correction of chromatic aberrations

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

Each lens having aspheric curvatures on both faces, resulting in a low positive power (≈5 diopter) from the first lens and stronger positive power (≈35 diopter) from the second lens

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS20250147289A1Infrared Objective Lens with Curved Focal Surface

Publication Date: 2025.05.08 UNITED STATES OF AMERICA THE AS REPRESENTED BY THE SEC OF THE ARMY

AI summary

A low-cost objective lens design uses only ZnS optical material, suitable for use with an uncooled infrared bolometer having a curved focal plane. Its objective lens field of view is at least ±20.0° over a 1280×720 pixel array with 0.0012 mm pitch. Lens chromatic aberrations are corrected over at least the 8-11 micron infrared wavelength band. The objective lens operates at a relatively fast F #/1.0 which is common in the art for bolometer applications.