Dual-Field IR Imaging Diffractive Lens Achromatization
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Solution Overview
Problem
Existing compact PC (small field) GC (large field) infrared systems suffer from significant chromatic aberrations in the IR2 spectral band, limiting their use with a single detector across both IR2 and IR3 bands.
Innovation Solution
A dual-field imaging system with a diffractive element and lenses made from specific materials like Germanium (Ge) and Zinc Sulfide (ZnS) or Zinc Selenide (ZnSe) is used, featuring a convergent diffractive lens and a relay group with Germanium lenses, optimized for diffraction orders in both bands to reduce lens power and number while maintaining optical quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional optical combination is used for IR3 band, then the system is compact and optimized for thermal infrared, but significant chromatic aberrations occur in IR2 band
Solution Approach 1:
The patent applies parameter changes by modifying the optical combination to include a diffractive element with specific diffraction orders optimized for both IR2 and IR3 bands. The diffractive profile is designed with different diffraction orders (order 1 for IR3, order 2 for IR2) to correct chromatic aberrations across both spectral bands, enabling the system to maintain optical quality while covering multiple bands.
Solution Approach 2:
The patent uses composite materials by combining Ge (germanium) and ZnS (zinc sulfide) or Ge and ZnSe (zinc selenide) in a doublet configuration for all lenses. This material combination allows the optical system to achieve achromatization in both IR2 and IR3 bands while maintaining compactness and reducing the number of lenses required.
2Reliability
If multiple lenses are used to correct chromatic aberrations, then optical quality improves, but system compactness and lens power increase
Solution Approach 1:
The patent extracts the chromatic correction function from multiple conventional lenses and concentrates it into a single diffractive element within the head group. This diffractive element, combined with the Ge/ZnS or Ge/ZnSe doublet, provides the necessary chromatic aberration correction for both IR2 and IR3 bands while reducing the total number of lenses and maintaining system compactness.
3Use of energy by moving object
If the system is optimized for IR3 band with cold screen aperture, then photometric behavior is optimized, but chromatic aberrations compromise IR2 band performance
Solution Approach 1:
The patent applies universality by designing the diffractive element and material doublet to simultaneously correct chromatic aberrations in both IR2 and IR3 bands. The cold screen aperture at the head lens maintains photometric optimization for IR3 while the diffractive correction enables reliable IR2 performance, making the system universally applicable to both spectral bands without requiring separate optimization.
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 configuration results in a compact dual-field IR2-IR3 imaging system with reduced chromatic aberrations, allowing for effective use across both spectral bands without vignetting and improved resolution.
Implementation Method 1
the head group G1 comprises a diffractive convergent L1A lens made of Ge
Implementation Method 2
a converging head diopter group G1 of focal length F
Implementation Method 3
the lenses of the optical combination are composed of materials chosen from 2 materials. Preferably, the materials are Ge and ZnS or Ge and ZnSe
Data Source
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AI summary
The invention relates to a dual-field (SF and LF) imaging system including an optronic detector (1) and an optical combination of small field focalisation (Fpc) comprising on an optical axis: a head lens; a small-field inlet pupil in the vicinity of the head lens; a real large-field inlet pupil, i.e. provided upstream the head lens; an intermediate focal plane (IFP); the optical combination further comprising on the optical axis the following dioptric groups: a convergent head group G1 having a focal F, with F<Fpc/2, said G1 group including the head lens; a field changing divergent group G2 capable of displacement along the optical axis, said group being located upstream the IFP in a SF configuration and downstream the IFP in a LF configuration; a relay group G3 imaging the IFP on the focal plane of the detector. It comprises a cooled IR2 and IR3 detector and an optical combination including 6 lenses, including at least one diffractive lens, in the head group G1, and the lenses of the optical combination are made of materials selected among 2 materials.