Imaging Optical Filter Layout for Ghost Image Suppression
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Solution Overview
Problem
The challenge in designing high-quality and compact imaging optical systems for portable electronic devices is the formation of ghost images due to glare and limitations in filter dimensions, which affect back focus and hinder compact design.
Innovation Solution
Incorporating an infrared light absorbing element, an infrared light reducing film, and a plate element with a taper structure coating or anti-reflecting multilayer film along a paraxial path, optimized by specific distance and reflectivity conditions, to minimize ghost images and enhance design freedom.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a filter is disposed between the imaging lens assembly and the image sensor to filter infrared and ultraviolet light, then the image sensor is protected from dust and unwanted light, but ghost images are easily formed under glare conditions and the filter dimension is limited affecting back focus
Solution Approach 1:
The filter function is divided into two separate components: an infrared light absorbing element and an infrared light reducing film. This segmentation allows each component to be optimized independently - the absorbing element can be positioned to refract light and reduce ghost images, while the reducing film provides the primary filtering function, thereby resolving the contradiction between protection and ghost image formation
Solution Approach 2:
The infrared light absorbing element acts as an intermediary between the imaging lens assembly and the infrared light reducing film. It refracts incoming light before it reaches the reducing film, reducing the formation of ghost images while still allowing the reducing film to effectively filter infrared light and protect the image sensor
2Reliability
If the filter dimension is limited due to assembling and filtering requirements, then the filtering function is maintained, but the back focus of the imaging optical system is influenced making high quality and compact design difficult
Solution Approach 1:
The invention changes the optical parameters of the system by introducing the infrared light absorbing element with specific refractive properties. This element can be positioned at different distances from the imaging lens assembly (controlled by parameter L1/f ≤ 0.21), allowing optimization of both the filtering function and the back focus distance to achieve compact high-quality design
3Volume of moving object
If the translucent portion is positioned closer to the image sensor, then the optical path is shortened for compact design, but the distance constraints for effective infrared light reduction are not met
Solution Approach 1:
The invention establishes specific parameter ranges for the distances: L1/f (distance between infrared absorbing element and reducing film) ≤ 0.21 and L2/f (distance between infrared reducing film and image sensor) ≥ 0.21. These parameter constraints allow the system to achieve both compact size and effective infrared light reduction by optimizing the positions of the filter components relative to the focal length
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 solution effectively reduces reflectivity and ghost images, allowing for improved imaging quality and compact size in camera modules by optimizing the arrangement and materials of optical components.
Implementation Method 1
The infrared light absorbing element has refractive power, and the infrared light absorbing element is configured to refract a light
Implementation Method 2
The infrared light reducing film is closer to an image surface of the imaging optical system than an incident surface of the infrared light absorbing element
Implementation Method 3
the plate element further includes a taper structure coating disposed on at least one of an incident surface and an exit surface of the translucent portion, the taper structure coating is gradually sparse towards an air direction, and an average reflectivity of a light at a wavelength range between 420 nm and 680 nm is less than 0.98% via the taper structure coating
Implementation Method 4
a plurality of pores are formed on at least one of the incident surface and an exit surface of the translucent portion
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
An imaging optical system includes an infrared light absorbing element, an infrared light reducing film and a plate element in order along a paraxial path. The infrared light absorbing element is made of an infrared light absorbing plastic material, and the infrared light absorbing element is configured to refract a light. The infrared light reducing film is closer to an image surface of the imaging optical system than an incident surface of the infrared light absorbing element to the image surface of the imaging optical system. The plate element is disposed between the infrared light reducing film and the image surface, the plate element includes a translucent portion, a holder portion and a taper structure coating. The taper structure coating is disposed on at least one of an incident surface and an exit surface of the translucent portion.