Gradient-Index Rod Lens Array for Larger Depth of Field
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Solution Overview
Problem
Existing gradient-index rod lenses have large aperture angles, which are not advantageous for achieving a large depth of field, leading to issues in image clarity and defect detection in inspection systems.
Innovation Solution
A rod lens array comprising gradient-index rod lenses with a refractive-index distribution n(r)=n0·{1−(A/2)·r2} and an aperture angle of 3 to 6°, along with a base glass composition of 40%≤SiO2≤65%; 0%≤TiO2≤10%; 0.1%≤MgO≤22%; 0.15%≤ZnO≤15%; 0.5%≤Li2O<4%; 2%≤Na2O≤20%; 0%≤B2O3≤20%; 0%≤Al2O3≤10%; 0%≤K2O≤3%; 0%≤Cs2O≤3%; 0%≤Y2O3≤5%; 0%≤ZrO2≤2%; 0%≤Nb2O5≤5%; 0%≤In2O3≤5%; 0%≤La2O3≤5%; 0%≤Ta2O5≤5%, and at least two of CaO, SrO, BaO, with specific ratios, to achieve a depth of field of 1.5 to 3.0 mm and a modulation transfer function of 30% or more at 6 lp/mm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If gradient-index rod lenses with large aperture angles are used, then light collection capability is improved, but depth of field deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the aperture angle parameter to be within 3° to 6° and the refractive index difference Δn to be within 0.002 to 0.008. This optimization resolves the contradiction by finding the optimal parameter range that simultaneously provides sufficient light collection capability while achieving adequate depth of field, rather than using excessively large aperture angles that would compromise depth of field
2Reliability
If gradient-index rod lenses with small aperture angles are used, then depth of field is improved, but light collection capability deteriorates
Solution Approach 1:
The patent resolves this contradiction by optimizing the aperture angle parameter to a specific range of 3° to 6°, which is larger than conventional small aperture angles but controlled to maintain depth of field. Additionally, by optimizing the refractive index difference Δn within 0.002 to 0.008, the lens achieves enhanced light collection capability while maintaining the desired depth of field
3Manufacturing precision
If refractive index difference Δn is increased, then focusing performance is improved, but manufacturing difficulty increases
Solution Approach 1:
The patent applies parameter changes by setting the refractive index difference Δn within the optimized range of 0.002 to 0.008. This resolution of the contradiction is achieved by avoiding excessively large Δn values that would make manufacturing difficult while still providing sufficient focusing performance. The specific range balances optical performance with manufacturing feasibility
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 solution provides a rod lens array with a large depth of field, enhancing image clarity and defect detection accuracy in inspection systems, while maintaining a compact size and reducing manufacturing and maintenance costs.
Implementation Method 1
A gradient-index rod lens is a rod-like (bar-like) lens that has a refractive-index distribution in which the refractive index continuously decreases from the center toward the outer periphery
Data Source
AI summary
A rod lens array 10a includes a plurality of gradient-index rod lenses 1b arrayed to have optical axes parallel to each other, and forms an erecting equal-magnification image. The gradient-index rod lenses 1b each have a refractive-index distribution in a radial direction thereof. The refractive-index distribution n(r) is approximated by n(r)=n0·{1−(A/2)·r2}, where a refractive index at a center of the gradient-index rod lens 1b is represented by n0, a refractive-index distribution constant of the gradient-index rod lens 1b is represented by √A, and a distance from the center of the gradient-index rod lens 1b is represented by r. The gradient-index rod lens 1b has an aperture angle θ of 3 to 6°, the aperture angle θ represented by θ=sin−1(n0√A·r0), where a radius of the gradient-index rod lens is represented by r0. The rod lens array 10a has an imaging distance of 45 to 75 mm and a depth of field of 1.5 to 3.0 mm with value of modulation transfer function (MTF) of 30% or more at a spatial frequency of 6 lp/mm.