Near-Infrared Imaging Lens Aspheric Design for Flare Reduction
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Solution Overview
Problem
Current near-infrared (NIR) imaging devices face performance and form factor limitations due to spectral differences between visible and NIR wavelengths, leading to issues like chromatic aberrations and excessive light fall-off, particularly in high-resolution imaging applications.
Innovation Solution
The design of an optical system comprising specific lens elements with tailored refractive indices and aspheric surfaces, optimized to minimize flare from total internal reflection and maintain high image fidelity across the field, includes a first lens with positive refractive power, a second and third meniscus-shaped lenses, and a fourth lens with a lower refractive index material, along with a bandpass filter to block unwanted light, enabling operation at F/2.0 with a diagonal full field of view greater than 80° and reduced optical distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional visible light imaging lens designs are adapted for NIR imaging, then the device can capture visible light, but chromatic aberrations and excessive light fall-off occur at NIR wavelengths
Solution Approach 1:
The patent changes the refractive index parameters by selecting specific optical materials (e.g., LaK7 glass with n=1.537 at 940nm) and designing lens surfaces with specific curvatures and aspheric coefficients optimized for NIR wavelengths, thereby resolving chromatic aberrations and light fall-off issues when adapting visible light lens designs for NIR imaging
Solution Approach 2:
The patent uses composite material structures including multiple lens elements made from different glass types (LaK7, BK7, SF5) with complementary optical properties, where each material contributes specific refractive index and dispersion characteristics to correct chromatic aberrations across the NIR spectrum while maintaining overall image quality
2Measurement precision
If high-resolution imaging is achieved in NIR, then image fidelity improves, but light fall-off at field edges becomes excessive
Solution Approach 1:
The patent employs aspheric surface designs on multiple lens elements with specifically calculated aspheric coefficients (e.g., A4=-0.0219, A6=0.9521 for the fourth lens) that correct spherical aberration and control light ray paths to maintain uniform illumination across the wide field of view while preserving high-resolution imaging capability at F/2.0 aperture
Solution Approach 2:
The patent applies different optical properties to different regions of the lens system, with the fourth lens element featuring aspheric surfaces specifically designed to correct off-axis ray paths and reduce vignetting at field edges, while central regions maintain high-resolution focusing properties
3Area of stationary object
If wide field of view is implemented, then scene coverage increases, but optical distortion and flare increase
Solution Approach 1:
The patent divides the optical system into four distinct lens elements with specific functions: the first element (positive power) for overall focusing, the second and third elements (meniscus shapes) for field curvature and distortion control, and the fourth element (negative power with aspheric surfaces) for flare reduction and off-axis ray correction, thereby achieving wide field of view with minimal distortion and flare
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 high-resolution, compact, and cost-effective NIR imaging lenses with minimal flare and light fall-off, suitable for applications like depth mapping, offering improved image reproduction and immunity to environmental noise.
Implementation Method 1
a bandpass filter, configured to block light other than at the target NIR wavelength, arranged between the fourth lens and the image plane
Implementation Method 2
aspheric coefficients chosen so that rays reaching the rear surface from the object are not totally internally reflected within the fourth lens to impinge on the image plane
Implementation Method 3
a first lens, including a first material having a first index of refraction at the target NIR wavelength and having a positive refractive power
Data Source
AI summary
An optical system for operation at a target near-infrared (NIR) wavelength in imaging an object onto an image plane. The system includes the following optical elements, arranged in order from object side to image side: a first lens, including a first material having a first index of refraction at the target NIR wavelength and having a positive refractive power; a second lens comprising the first material and having a meniscus shape; a third lens comprising the first material and having a meniscus shape; and a fourth lens, including a second material having a second index of refraction at the target NIR wavelength that is lower than the first index of refraction, and having front and rear surfaces of an aspheric form. The aspheric coefficients are chosen so that rays are not totally internally reflected within the fourth lens to impinge on the image plane.