Freeform Folded Optical System for Compact Telephoto Imaging
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Solution Overview
Problem
Conventional small form factor cameras in mobile devices struggle to capture high-resolution, high-quality images due to limitations in optical system design, requiring compact imaging lens systems that maintain image quality and fit within the device's physical constraints.
Innovation Solution
A freeform folded optical system using two freeform prisms with optical power, without a lens stack between them, which folds the optical axis three or four times, allowing for long focal lengths and reduced Z-axis height, utilizing optical plastic or glass materials to correct aberrations and improve image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional lens systems are used in small form factor cameras, then the device can be compact, but image resolution and quality deteriorate
Solution Approach 1:
The patent folds the optical axis multiple times (three or four times) using freeform prisms, transforming a linear optical path into a multi-dimensional folded structure. This allows long focal lengths to be achieved within a compact Z-axis height by utilizing spatial folding rather than linear extension.
Solution Approach 2:
The optical system is divided into distinct freeform prism elements with specific optical powers, eliminating the need for a traditional lens stack between prisms. Each prism segment performs specific optical functions (folding, focusing, aberration correction) that were previously distributed across multiple lens elements.
2Length of moving object
If additional lens elements are added to achieve long focal lengths, then focal length increases, but Z-axis height increases
Solution Approach 1:
The optical axis is folded three or four times using freeform prisms, transforming a long linear optical path into a compact multi-dimensional structure. This achieves long focal lengths (9-31mm effective focal length) while maintaining reduced Z-axis height suitable for mobile devices.
Solution Approach 2:
Multiple optical functions (folding, focusing, aberration correction) are merged into integrated freeform prism elements with optical power, eliminating the need for separate lens stacks and reducing the overall Z-axis footprint while maintaining long focal length capability.
3Quantity of substance
If pixel size is reduced to increase pixel count, then more pixels fit in small sensor, but individual pixel quality and light gathering deteriorate
Solution Approach 1:
The system achieves low F-numbers (2.0-4.0) by optimizing the optical path through freeform prisms with specific optical powers and configurations. This improves light gathering efficiency across all pixels while maintaining high pixel counts, as the improved optical efficiency compensates for smaller individual pixel sizes.
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 enables high-resolution image capture with reduced Z-axis height, achieving long focal lengths and low F-numbers without additional lens elements, while maintaining compactness and improving optical performance.
Implementation Method 1
a first surface that is a transmitting and total internal reflection (TIR) surface that transmits light received from an object field and reflects light received from a second surface of the first freeform prism by TIR to a third surface of the first freeform prism
Implementation Method 2
The second surface of the first freeform prism is a reflecting surface coated with a mirror coating that reflects light received through the first surface of the first freeform prism back to the first surface of the first freeform prism
Implementation Method 3
The third surface of the first freeform prism is a transmitting surface that transmits light received from the first surface of the first freeform prism
Implementation Method 4
a first surface that is a transmitting surface that transmits light received from the first freeform prism to a second surface of the second freeform prism
Implementation Method 5
The second surface of the second freeform prism is a transmitting and TIR surface that reflects light received through the first surface of the second freeform prism by TIR to the third surface of the second freeform prism
Implementation Method 6
The third surface of the second freeform prism is a reflecting surface coated with a mirror coating that reflects light received from the second surface of the second freeform prism back to the second surface of the second freeform prism
Data Source
AI summary
A freeform folded optical system that include two freeform prisms with optical power. At least one of the freeform prisms is configured to fold the optical axis twice. Thus, embodiments of the freeform folded optical system fold the optical axis three or four times. Folding the optical axis three or four times in the freeform prisms allows for long focal lengths required for telephoto lens applications without requiring additional lens elements between the prisms. In addition, the configuration of the freeform folded optical system provides reduced Z-axis height when compared to conventional folded lens systems with similar optical characteristics.