Active Autofocus Optics with Varifocal Fourier-Pattern Detection
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Solution Overview
Problem
Passive autofocus systems in imaging devices fail to reliably determine the focusing plane under poor or non-uniform lighting conditions, leading to errors in image focus.
Innovation Solution
An autofocus system utilizing a varifocal lens and a focus tunable lens, combined with a processor, adjusts the focal length and control parameters to achieve accurate focus by analyzing the spatial frequencies of a predefined pattern generated through a Fourier transform of a semi-transparent pattern, ensuring correct focus even in challenging lighting conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive autofocus systems use image features to optimize focus, then the system can focus correctly by analyzing captured images, but the system fails under poor or non-uniform lighting conditions
Solution Approach 1:
The system projects a known test pattern onto the scene before capturing the image, allowing the autofocus algorithm to analyze predetermined frequency components rather than relying on unpredictable image features from poor lighting conditions
Solution Approach 2:
The system transforms the focus detection problem from spatial domain (image contrast) to frequency domain (spatial frequencies of projected pattern), making the measurement insensitive to lighting variations
2Measurement precision
If the system uses a varifocal lens with adjustable focal length, then the system can achieve accurate focus by analyzing spatial frequencies, but the device complexity increases
Solution Approach 1:
The varifocal lens acts as an intermediary optical element that enables Fourier transform of the projected pattern, allowing frequency analysis without requiring complex sensor modifications or multiple optical paths
3Measurement precision
If the system uses focus tunable lens with control parameters, then the system can fine-tune focus accuracy, but the device complexity and control mechanism complexity increase
Solution Approach 1:
The focus tunable lens replaces mechanical lens movement with electrical or optical control mechanisms, allowing precise focus adjustment through control parameters without complex mechanical assemblies
Solution Approach 2:
The system uses feedback from the analyzed spatial frequencies to iteratively adjust the control parameters of the focus tunable lens, converging to the optimal focus setting through measured frequency distortion
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 system effectively avoids focus oscillation and achieves more accurate focus than traditional contrast detection techniques by using a Fourier-optics projection and fine-tuning lens parameters, ensuring reliable focus under varying lighting conditions.
Implementation Method 1
a varifocal lens or zoom lens, as further described herein, arranged in front of the light source. The varifocal lens may be configured to receive the light wave after the light wave has passed through a semi-transparent pattern (e.g., a pattern that causes a portion of the light wave to pass therethrough) on a rear focal plane of the varifocal lens, and generate a Fourier transform of the semi-transparent pattern therefrom
Implementation Method 2
The imaging system may also include a focus tunable lens positioned in front of the image sensor, and through which the reflected light wave passes. The processor may adjust a control parameter of the focus tunable lens until one or more spatial frequencies of the predefined pattern detected at the image sensor match one or more predefined spatial frequencies
Implementation Method 3
The optical path splitter may include a semi-transparent mirror
Data Source
AI summary
Systems and methods for autofocus may include a light source for generating a light wave and a varifocal lens arranged in front of the light source. The varifocal lens may receive the light wave and generate a Fourier transform of a known semi-transparent pattern positioned on the rear focal plane (or input plane) of the varifocal lens therefrom. An image sensor may receive the Fourier transform carried by the light wave after being reflected from an object. A focus tunable lens may be arranged in front of the image sensor and through which the reflected light wave passes. A processor may adjust a focal length of the varifocal lens to cause the Fourier transform carried by the light wave to form a predefined (expected) pattern detected by the image sensor, and adjust a control parameter of the focus tunable lens until one or more spatial frequencies of the predefined pattern detected at the image sensor match one or more predefined spatial frequencies.