Two-Lens Infrared Optical System for Gas Detection
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Solution Overview
Problem
Existing infrared optical systems for gas detection in the 3 to 5 μm wavelength band face challenges in achieving high transmittance and optical performance with a minimal number of lens elements, often resulting in light loss and difficulty in aligning the pupil, especially when used in cooled sensors.
Innovation Solution
An infrared optical system comprising a first meniscus-shaped negative lens element and a biconvex second lens element, with a band-pass filter placed between the second lens element and the image surface, both made of silicon or germanium and featuring aspherical surfaces, fulfilling specific conditional formulae to ensure high transmittance and optical performance with only two lens elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If three lens elements are arranged (positive-negative-positive) to correct various aberrations including chromatic aberration, then optical performance is improved, but the number of lens elements increases and light loss on lens surfaces occurs
Solution Approach 1:
The patent extracts and eliminates unnecessary lens elements from the conventional three-element design. By using only two lens elements (both with negative optical power) and strategically positioning an aperture stop, the system removes redundant components while maintaining aberration correction capability through optimized surface curvatures and materials.
Solution Approach 2:
The patent changes key parameters including making both lens elements have negative optical power (unconventional), using aspherical surfaces on both sides of each element, and positioning the aperture stop between the two elements. These parameter changes enable effective aberration correction with fewer elements.
2Reliability
If an aperture stop is arranged between the first and second lens elements to secure satisfactory optical performance with two lens elements, then optical performance is improved, but a cold aperture must be arranged separately on the image surface side to shield unnecessary light, leading to pupil misalignment
Solution Approach 1:
The aperture stop positioned between the two lens elements serves multiple functions simultaneously: it acts as the pupil for the optical system, provides cold shielding for the sensor, and contributes to aberration control. This eliminates the need for a separate cold aperture on the image surface side, ensuring proper pupil alignment while maintaining thermal shielding.
3Reliability
If multiple lens elements are used to correct aberrations, then optical performance is improved, but light loss on lens surfaces increases
Solution Approach 1:
The patent removes unnecessary lens elements from the optical path, reducing the total number of air-glass interfaces where light loss occurs. By achieving aberration correction with only two lens elements through optimized design, the system minimizes reflective and absorptive losses while maintaining image quality.
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 allows for high transmittance and optical performance in cooled sensors, enabling effective gas detection and image input functions in digital appliances like cameras at a lower cost, while minimizing light loss and aberration correction difficulties.
Implementation Method 1
a first lens element which has a negative optical power and which has a meniscus shape convex to the object side; a second lens element which has a biconvex shape
Implementation Method 2
with a band-pass filter arranged between the second lens element and the image surface
Data Source
AI summary
This infrared optical system using the wavelength range of 3 to 5 μm comprises, in the order from an object side, a first lens having a negative power and formed with a convex meniscus toward an object, a second lens that is convex on both sides, and a cold aperture. A bandpass filter is provided between the second lens and the image surface. The first and second lenses are configured with silicon or germanium with each provided with an aspheric surface at least on one side. The infrared optical system satisfies the conditional expressions: 0.1 μm<λ2−λ1<1 μm, 3 μm<λ1<5 μm, and 3 μm<λ2<5 μm. (Where λ1 and λ2 respectively represent a wavelength near the shorter wavelengths and a wavelength near the longer wavelengths in a half width of the transmission wavelength region of the bandpass filter).