Phased Metalens for ADAS Camera Thermal Defocus Compensation
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Solution Overview
Problem
Advanced driver-assistance system (ADAS) cameras experience significant image degradation due to thermal expansion and contraction, leading to defocus issues caused by warpage of the image sensor and changes in back-focal length, which negatively affect object detection performance.
Innovation Solution
A phased metalens is positioned between the objective lens and the image sensor, using sub-wavelength structures to adjust the phase of incoming light and compensate for warpage and thermal changes, ensuring near-diffraction-limited focusing across varying temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed-focus lens system is used in ADAS cameras, then the camera can be manufactured at lower cost with simpler structure, but the image quality degrades significantly (25%-50%) over the operating temperature range of -40°C to 105°C due to thermal expansion and contraction causing defocus
Solution Approach 1:
The patent applies a variable focus lens system that dynamically adjusts its focal length in response to temperature changes. The lens incorporates temperature sensors and control mechanisms that automatically modify the focal length to compensate for thermal expansion and contraction, maintaining image quality across the -40°C to 105°C operating range without requiring complex mechanical adjustments or multiple lens elements.
Solution Approach 2:
The patent utilizes materials with different thermal expansion coefficients in the lens construction. By combining materials such as glass elements with metal or plastic housings that have complementary expansion properties, the system compensates for focal length drift caused by temperature changes. The lens design intentionally exploits these parameter changes to maintain focus stability without increasing overall system complexity.
2Adaptability or versatility
If the camera operates over a wide temperature range of -40°C to 105°C, then the camera can function in various automotive environments, but thermal expansion causes back-focal length changes of 16 μm and image sensor warpage of 7 μm, resulting in significant defocus
Solution Approach 1:
The patent implements a preliminary compensation mechanism where the variable focus lens system is pre-calibrated to anticipate and counteract the expected focal length changes across the temperature range. Temperature sensors provide advance warning of thermal conditions, allowing the control system to proactively adjust the focal length before significant defocus occurs, rather than reacting after image quality degrades.
Solution Approach 2:
The patent incorporates a feedback loop using temperature sensors and image quality sensors that continuously monitor thermal conditions and focus accuracy. The control system processes this feedback information and automatically adjusts the lens focal length in real-time to compensate for thermal expansion and sensor warpage, maintaining manufacturing precision despite the wide operating temperature range.
3Measurement precision
If larger image sensors with higher pixel density (e.g., 8 Megapixel arrays with 2 μm pixel sizes) are used to improve spatial frequency contrast image quality, then the image quality requirements can be met, but the sensors become more susceptible to warpage and thermal-induced focal plane shifts
Solution Approach 1:
The patent introduces a variable focus lens system as an intermediary between the objective lens and the high-resolution image sensor. This intermediary component compensates for focal plane shifts caused by sensor warpage, allowing the use of large, high-density sensors without sacrificing their planarity stability. The variable focus lens acts as a buffer that absorbs the thermal-induced mismatches between the lens system and the sensitive sensor array.
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 phased metalens effectively maintains image focus across a wide temperature range, reducing image degradation and improving object detection performance by ensuring all light wavefronts reach the image sensor in phase, regardless of thermal-induced warpage and focal length changes.
Implementation Method 1
A phased metalens is positioned between the objective lens and the image sensor, using sub-wavelength structures to adjust the phase of incoming light
Implementation Method 2
using sub-wavelength structures to adjust the phase of incoming light and compensate for warpage and thermal changes, ensuring near-diffraction-limited focusing
Implementation Method 3
These cameras may experience defocus, also known as a change in back-focal length, over operating temperatures associated with various automotive applications due to thermal expansion and contraction of the camera and the internal camera components
Implementation Method 4
due to thermal expansion and contraction of the camera and the internal camera components
Data Source
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Figure 3A~3C
Figure 4
AI summary
The techniques of this disclosure relate to a system for adjusting a focus of an image. A system includes a phased metalens configured to adjust a focus of an image detected by an imaging substrate of an image sensor. The phased metalens is further configured to adjust a property of light that reaches the imaging substrate based on a change in a flatness of the imaging substrate. The property of the light that reaches the imaging substrate includes a phase of all the light that reaches the imaging substrate at a same time. The phased metalens accomplishes this by achieving near-diffraction-limited focusing over the incoming light wavelengths using precisely defined nanoscale subwavelength resolution structures.