Curved Infrared Cut-off Filter for Image Sensor Modules
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Solution Overview
Problem
Infrared cut-off filters in image sensor modules cause a central area on the light receiving surface to appear redder than the peripheral area due to their sensitivity to incident angle, leading to increased noise when attempting to regulate white balance by adjusting gain values.
Innovation Solution
An image sensor module with a concave-shaped infrared cut-off filter that reduces the maximum incidence angle and suppresses the cut-off wavelength shift phenomenon, allowing for uniform color representation across the image surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat infrared cut-off filter is used, then the filter is simple in structure and easy to manufacture, but the cut-off wavelength shifts to shorter wavelengths as incident angle increases, causing the central area to appear redder than the peripheral area
Solution Approach 1:
The patent applies curvature to the infrared cut-off filter by forming a concave surface on the image sensor side. This curved surface compensates for the incident angle dependence of the cut-off wavelength, preventing the wavelength shift that occurs with flat filters. The concave shape ensures that light rays entering at different angles experience consistent optical path lengths, maintaining stable cut-off characteristics across the entire image sensor area.
2Measurement precision
If gain value of peripheral area is increased to regulate white balance, then color representation improves, but noise increases
Solution Approach 1:
The curved infrared cut-off filter eliminates the need for differential gain adjustment across different areas of the image sensor. By maintaining uniform cut-off wavelength characteristics, the filter allows a single white balance setting to work effectively across the entire sensor area, avoiding the noise amplification that would result from increasing peripheral gain values.
3Device complexity
If flat infrared cut-off filter is used, then manufacturing is simple, but transmittance characteristic is sensitive to incident angle causing non-uniform color representation
Solution Approach 1:
The concave surface formed on the image sensor side of the infrared cut-off filter compensates for angle-dependent optical path differences. This curvature ensures that light rays at different incident angles traverse comparable effective paths through the filter, maintaining uniform transmittance characteristics and consistent color representation across the entire image sensor area without requiring complex multi-layer structures.
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 curved infrared cut-off filter minimizes noise and enables a single white balance adjustment to accurately represent colors from various light sources, reducing the difference in red color between the central and peripheral areas.
Implementation Method 1
The infrared cut-off filter 140 is implemented by laminating a multi-layered infrared cut-off layer on one side or each side of a glass substrate with opposite flat sides. The infrared cut-off filter 140 is designed in such a manner that infrared lights reflected from the layers of the infrared cut-off layer are destructively interfered with each other to disappear.
Implementation Method 2
Each of the first to third lenses 110, 120 and 130 refracts an incident light, and to form an image of a subject on the image surface 150.
Data Source
AI summary
An image sensor module includes: an image sensor having an image surface; a plurality of lenses arranged sequentially from an object side to the image surface side, each of the lenses refracting an incident light; and at least one infrared cut-off filter configured to cut off an infrared component from the incident light. At least one surface of the infrared cut-off filter has a concave shape in relation to the object side.