Gradient Index Microlenses for Optical Crosstalk Reduction
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Solution Overview
Problem
Optical crosstalk in solid state imagers, such as CCD and CMOS devices, occurs when off-axis light strikes a microlens at an obtuse angle, causing light to be directed to adjacent pixels, leading to image quality degradation and color balance issues.
Innovation Solution
The development of gradient index microlenses with a curved profile, formed by layers of transparent lens materials with varying refractive indices, which are designed to minimize optical crosstalk by optimizing the focus and light distribution across the pixel array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional microlenses are used to focus light onto photosensors, then light collection efficiency is improved, but optical crosstalk increases causing image quality degradation
Solution Approach 1:
The patent applies local quality by creating microlenses with spatially varying refractive indices. The gradient index structure allows different regions of the microlens to have different optical properties, enabling precise control over light propagation paths. This resolves the contradiction by maintaining high light collection efficiency while directing off-axis light away from adjacent pixels, thereby reducing optical crosstalk.
Solution Approach 2:
The patent changes the refractive index parameter across the microlens structure to control light behavior. By implementing a gradient index profile where the refractive index varies continuously or in steps from the center to the edge of the microlens, the patent optimizes light focusing while preventing crosstalk. This parameter change allows the microlens to maintain high productivity for light collection while eliminating the harmful optical crosstalk effect.
2Manufacturing precision
If microlenses focus light from large collecting area onto small photosensitive area, then fill factor is improved, but off-axis light strikes adjacent pixels causing color balance issues
Solution Approach 1:
The gradient index structure implements local quality by tailoring the refractive index at different positions within the microlens. This allows the microlens to precisely control where light from different angles lands on the pixel array, maintaining high fill factor while preventing color information loss by directing off-axis light to the correct pixel rather than adjacent pixels.
Solution Approach 2:
The patent introduces a new dimension to microlens design by implementing refractive index variation in the radial direction, in addition to the conventional spherical or aspherical surface profile. This gradient index dimension provides an additional degree of freedom for controlling light paths, enabling simultaneous optimization of fill factor and color accuracy by preventing oblique light from striking adjacent pixels.
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 gradient index microlenses effectively reduce optical crosstalk, improving image quality by ensuring that light is focused accurately onto the intended pixels, thereby enhancing the fill factor and reducing light reading inconsistencies.
Implementation Method 1
gradient index microlenses with a curved profile, formed by layers of transparent lens materials with varying refractive indices, which are designed to minimize optical crosstalk by optimizing the focus and light distribution
Data Source
AI summary
A lens includes a gradient index of refraction and a curved shape. A method of making the lens includes forming a plurality of layers, forming a shaped resist on the plurality of layers, and etching the resist and the plurality of layers to transfer the shape of the resist into the plurality of layers.