Four-Lens ToF Assembly Shortening Length and Boosting Resolution
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Solution Overview
Problem
Current lens assemblies for Time of Flight (ToF) applications face challenges in achieving miniaturization, large field of view, small F-number, and high resolution simultaneously while maintaining good optical performance.
Innovation Solution
A lens assembly comprising a first lens with negative refractive power, a second lens with positive refractive power, a third lens with refractive power, and a fourth lens, arranged along an optical axis, which satisfies specific conditions such as 3≤f3/f≤5.5 and 0.2≤f/AAG≤0.3 to achieve shortened total lens length, increased resolution, and corrected aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the lens assembly is miniaturized to reduce total lens length, then the size is reduced, but the field of view and resolution deteriorate
Solution Approach 1:
The lens assembly is divided into four distinct lens elements with different refractive powers arranged in sequence. The first lens has negative refractive power, the second has positive refractive power, and the third and fourth lenses have positive refractive power with specific focal length ratios. This segmentation allows each lens to contribute differently to the overall optical performance, enabling miniaturization while maintaining resolution through optimized individual lens functions.
Solution Approach 2:
The patent applies specific parameter constraints to resolve the contradiction: the ratio of the effective focal length of the third lens to the effective focal length of the lens assembly is controlled within 3≤f3/f≤5.5, the ratio of the effective focal length to the sum of air intervals is 0.2≤f/AAG≤0.3, and the ratio of effective focal length to back focal length is 0.72≤f/BFL≤1.04. These parameter optimizations enable compact design while preserving high resolution imaging capability.
2Area of stationary object
If the lens assembly is designed for large field of view, then the coverage area is increased, but the F-number increases and resolution decreases
Solution Approach 1:
The four-lens segmented structure with specific refractive power distribution enables the system to capture a wide field of view while maintaining resolution. The negative power first lens expands the field of view, while the subsequent positive power lenses correct aberrations and maintain image quality across the expanded field.
Solution Approach 2:
The parameter constraint 0.2≤f/AAG≤0.3 optimizes the relationship between effective focal length and air intervals, enabling large field of view while controlling F-number. The back focal length ratio 0.72≤f/BFL≤1.04 further ensures that resolution is maintained across the expanded field of view by properly positioning the image plane.
3Illumination intensity
If the F-number is reduced to improve light gathering, then the aperture is increased, but the lens length and complexity increase
Solution Approach 1:
The parameter optimization 0.72≤f/BFL≤1.04 controls the back focal length to maintain a small F-number for improved light gathering, while the overall lens length is constrained through the 0.2≤f/AAG≤0.3 ratio. This parameter balancing allows reduced F-number without proportionally increasing lens length.
Solution Approach 2:
The segmented four-lens structure with optimized air intervals between elements enables compact packaging that achieves small F-number. The distribution of refractive powers across four elements allows light gathering improvement without requiring a single large aperture that would increase overall length.
4Measurement precision
If multiple lens elements are added to improve resolution, then the resolution is increased, but the total lens length and device complexity increase
Solution Approach 1:
The lens assembly uses exactly four lens elements with specific refractive power assignments (negative, positive, positive, positive) to achieve high resolution. This segmented structure corrects various aberrations through the interaction of different power elements, enabling resolution improvement without excessive lengthening.
Solution Approach 2:
The parameter constraint 0.2≤f/AAG≤0.3 optimizes the density of optical elements by controlling the sum of air intervals relative to focal length. This ensures that four lens elements are packed efficiently to achieve high resolution while minimizing the total length occupied by the lens assembly.
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 assembly effectively shortens the total lens length, increases resolution, and corrects aberrations, while maintaining good optical performance by adjusting the focal lengths and air intervals to meet the requirements of miniaturization and high resolution.
Implementation Method 1
The first lens has negative refractive power, the second lens has positive refractive power, the third lens has refractive power, and the fourth lens has refractive power
Data Source
AI summary
A lens assembly includes a first lens, a second lens, a third lens, and a fourth lens. The first lens is with negative refractive power. The second lens is with positive refractive power. The third lens is with refractive power. The fourth lens is with refractive power. The first lens, the second lens, the third lens, and the fourth lens are arranged in order from an object side to an image side along an optical axis. The lens assembly satisfies at least one of the following conditions: 3≤f3/f≤5.5; 0.2≤f/AAG≤0.3; 0.72≤f/BFL≤1.04.