Compact Imaging Optical System with High Incidence Angle Control
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Solution Overview
Problem
Conventional imaging devices in mobile information terminals face challenges in reducing thickness while maintaining optical performance, due to limitations in the incidence angle of principal rays on the image-forming plane, which affects the sensitivity and resolution of the image sensor, especially in front side illumination CMOS sensors.
Innovation Solution
The imaging device incorporates an image-forming optical system with a maximum incidence angle exceeding 33°, utilizing a solid state image sensor with an organic photoelectric conversion layer or back side illumination type, and a configuration of two or more lenses to achieve a reduced thickness of less than 3.6 mm, allowing for improved optical performance and increased incidence angle without significant aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the image-forming optical system is shortened to reduce device thickness, then the device thickness is reduced, but the incidence angle of principal rays increases causing deterioration of photoelectric conversion efficiency
Solution Approach 1:
The patent changes the structural parameters of the optical system by introducing a negative lens component and optimizing the focal length ratio (f/fL between -0.3 and -1.5), which allows the system to achieve both short thickness and controlled incidence angles. This parameter optimization enables the optical system to maintain photoelectric conversion efficiency while achieving device thickness of 3.6mm or less
Solution Approach 2:
The patent employs a composite optical system combining multiple lens materials with different refractive indices and optical properties. By using a combination of positive and negative lenses with specific material characteristics, the system achieves aberration correction and incidence angle control in a compact form factor, resolving the contradiction between thickness reduction and efficiency maintenance
2Length of moving object
If the incidence angle is increased to further shorten the optical system, then the optical system length is reduced, but aberrations increase causing image quality deterioration
Solution Approach 1:
The patent divides the optical system into multiple discrete lens components (positive lens G1, negative lens G2, positive lens G3, and negative lens G4) with specific focal lengths and positions. This segmentation allows each component to be optimized for specific functions: G1 and G3 for focusing, G2 and G4 for aberration correction. The segmented structure enables the system to achieve high image quality with reduced length by distributing optical functions across multiple elements
Solution Approach 2:
The patent utilizes aspheric surfaces on lens components to correct spherical aberration and other optical imperfections. The aspheric shapes allow for more precise control of light paths at high incidence angles, enabling the compact optical system to maintain image quality despite the increased angles resulting from shortened optical path length
3Use of energy by moving object
If a front side illumination CMOS sensor is used to improve aperture efficiency, then normal incident light conversion is improved, but obliquely incident light is blocked causing peripheral darkening
Solution Approach 1:
The patent applies preliminary anti-action by designing the optical system to pre-correct for the known problem of oblique light incidence. Through careful optimization of lens positions, focal lengths, and the negative lens configuration, the system proactively reduces incidence angles before light reaches the sensor, preventing peripheral darkening before it occurs. This anticipatory design allows the use of cost-effective front-side illumination sensors without suffering from their oblique light sensitivity limitations
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
This configuration enables a miniaturized imaging device with enhanced image-forming performance, eliminating the need for an IR cut filter and reducing manufacturing costs, while maintaining high sensitivity and resolution, even at increased incidence angles.
Implementation Method 1
The solid state image sensor photoelectrically converts a subject image formed by the image-forming optical system
Data Source
AI summary
An imaging device with a short length and small aberration is provided. A total length D of an image-forming optical system is less than 3.6 mm. A maximum incidence angle of a principle ray on an image forming plane exceeds 33°. Conditions f/fL<−1.50 or f/fL<−0.9, and D/f<1.10 are satisfied where f denotes a focal length of the entire image-forming optical system and fL denotes a focal length of a last lens.