Asymmetric Microlens PDAF Detector Autofocus Accuracy
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Solution Overview
Problem
Compact and cost-effective digital cameras face challenges in achieving accurate and fast autofocus due to limitations in phase-detection autofocus systems, which are typically found in more advanced cameras, making it difficult to maintain high PDAF accuracy.
Innovation Solution
The implementation of an asymmetric-microlens PDAF detector with a plurality of pixels forming a sub-array and a rotationally asymmetric microlens above each pixel, which improves angular sensitivity and reduces the crossing angle, thereby enhancing PDAF accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a symmetric microlens is used in the PDAF detector, then the device complexity is reduced and manufacturing is easier, but the PDAF accuracy and angular sensitivity deteriorate due to larger crossing angles
Solution Approach 1:
The patent applies asymmetry by designing a microlens with rotationally asymmetric refractive index distribution. The refractive index varies differently in the first radial direction compared to the second radial direction, creating an asymmetric optical path that reduces the crossing angle between light rays from different object points. This asymmetric design improves PDAF accuracy while maintaining manufacturing feasibility through a single-lens structure.
2Reliability
If a dedicated phase-detection sensor is included in addition to the image sensor, then the PDAF speed and reliability are improved, but the device complexity and cost increase
Solution Approach 1:
The patent merges the phase-detection function with the image sensor by integrating a PDAF detector directly into the image sensor structure. The PDAF detector shares the same substrate and pixel array with the image sensor, eliminating the need for a separate dedicated phase-detection sensor. This integration reduces device complexity and cost while maintaining reliable autofocus functionality through the asymmetric microlens design.
3Measurement precision
If the microlens is made rotationally asymmetric with different refractive index variations in different radial directions, then the angular sensitivity is improved and crossing angle is reduced, but the manufacturing precision requirements increase
Solution Approach 1:
The patent implements parameter changes by varying the refractive index distribution within the microlens in an asymmetric manner. The refractive index is modified differently along the first radial direction compared to the second radial direction, creating the desired asymmetric optical characteristics. This approach achieves improved angular sensitivity and reduced crossing angles through material property modification rather than complex geometric shaping, thereby managing manufacturing precision requirements.
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 asymmetric-microlens PDAF detector enhances PDAF accuracy by minimizing the crossing angle, leading to improved autofocus performance and image quality in compact digital cameras, such as camera phones and compact digital cameras.
Implementation Method 1
a microlens that is rotationally asymmetric about an axis perpendicular to the sub-array... The asymmetric microlens PDAF detector minimizes a crossing angle between a first set of light rays from a first object point and a second set of light rays from a second object point
Data Source
AI summary
A PDAF imaging system includes an image sensor and an image data processing unit. The image sensor has an asymmetric-microlens PDAF detector that includes: (a) a plurality of pixels forming a sub-array having at least two rows and two columns, and (b) a microlens located above each of the plurality of pixels and being rotationally asymmetric about an axis perpendicular to the sub-array. The axis intersects a local extremum of a top surface of the microlens. The image data processing unit is capable of receiving electrical signals from each of the plurality of pixels and generating a PDAF signal from the received electrical signals. A method for forming a gull-wing microlens includes forming, on a substrate, a plate having a hole therein. The method also includes reflowing the plate.