Fresnel Lens Dynamic Draft for HMD Optical Artifacts
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Solution Overview
Problem
Conventional head-mounted displays are bulky and heavy due to complex optics, limiting their application, and Fresnel lenses, while lighter, suffer from diffractions and optical artifacts, restricting their use in imaging applications.
Innovation Solution
A Fresnel lens with a dynamic draft, featuring a slope facet and a draft facet with a draft angle based on its distance from the lens center, is used in a head-mounted display device to reduce optical artifacts and enhance compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If Fresnel lenses are used to reduce size and weight, then the head-mounted display becomes more compact and lighter, but optical artifacts and diffractions increase
Solution Approach 1:
The patent applies different draft angles to different radial zones of the Fresnel lens. The draft angle is varied as a function of the radial position, with smaller draft angles at the center and larger draft angles at the periphery. This local variation in draft angle optimizes light transmission and reduces optical artifacts in different regions of the lens while maintaining the overall compact size and lightweight design.
Solution Approach 2:
The patent changes the draft angle parameter dynamically across the lens surface based on radial distance. By making the draft angle a function of radial position rather than using a uniform value, the lens achieves optimized optical performance that reduces artifacts while maintaining the Fresnel lens advantages of reduced weight and size.
2Object-generated harmful factors
If conventional lenses are used to achieve good optical performance, then imaging quality is improved, but the device size and weight increase
Solution Approach 1:
The patent uses local quality by varying the draft angle according to radial position in the Fresnel lens. This allows different regions of the lens to be optimized for their specific optical requirements, achieving good imaging quality without needing the bulkier conventional lens design.
Solution Approach 2:
The patent introduces a dynamic draft angle that changes with radial distance, transforming the static uniform draft angle of conventional Fresnel lenses into a dynamic configuration that adapts to local optical requirements, thereby reducing optical artifacts while maintaining the lightweight advantage.
3Ease of manufacture
If uniform draft angle is used in Fresnel lens, then manufacturing is simplified, but optical artifacts increase
Solution Approach 1:
The patent applies local quality by making the draft angle dependent on radial position. While this increases manufacturing complexity slightly compared to uniform draft angle, it significantly reduces optical artifacts. The draft angle is designed to vary smoothly with radial distance, balancing manufacturability with optical performance.
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 Fresnel lens with dynamic draft reduces optical artifacts, making head-mounted displays more compact, lightweight, and efficient, thereby improving user experience in virtual and augmented reality applications.
Implementation Method 1
The draft angle of the respective Fresnel structure is between a first angle and a second angle, the first angle corresponding to a direction of a ray, in the first medium, transmitted from a reference off-axis position through the respective Fresnel structure toward a reference pupil and the second angle corresponding to a direction of the ray, in the optically transparent substrate, transmitted from the reference off-axis position through the respective Fresnel structure toward the reference pupil.
Data Source
AI summary
A lens includes an optically transparent substrate having a first lens surface and a second lens surface opposite to the first lens surface. The first lens surface includes a plurality of Fresnel structures. A respective Fresnel structure of the plurality of Fresnel structures includes a slope facet and a draft facet. The draft facet is characterized by a draft angle which is based on a distance of the respective Fresnel structure from a reference axis of the lens. The draft angle is between a first angle and a second angle, the first angle corresponding to a direction of a ray, in a first medium, transmitted from a reference off-axis position through the respective Fresnel structure toward a reference pupil. The second angle corresponding to a direction of the ray, in the optically transparent substrate, transmitted from the reference off-axis position through the respective Fresnel structure toward the reference pupil.