Freeform Waveguide Prism and Compensation Lens for Ergonomic HMDs
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Solution Overview
Problem
Current head-mounted display (HMD) designs are hindered by a cumbersome, helmet-like form factor, leading to fatigue and discomfort, and lack the ability to provide a wide, minimally blocked or degraded see-through field of view, which is essential for daily tasks and demanding applications.
Innovation Solution
The development of ergonomically designed freeform optical systems for optical see-through HMDs with an eyeglass-form appearance, utilizing a freeform waveguide prism and a see-through compensation lens, which includes multiple refractive and reflective surfaces to provide a clear, magnified image of virtual content and an unobstructed view of the real world across a wide field of view, while minimizing weight and maintaining superior optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional HMD optical systems are used, then virtual image display function is achieved, but the device has a cumbersome helmet-like form factor causing fatigue and discomfort
Solution Approach 1:
The optical system is divided into separate functional components: a waveguide prism for virtual image guidance and a compensation lens for see-through view correction. This segmentation allows each component to be optimized independently, resulting in a lighter, more compact overall structure that eliminates the need for a bulky helmet form factor.
Solution Approach 2:
The compensation lens is positioned outwardly of and integrated with the waveguide prism, creating a nested configuration where the lens works in conjunction with the prism. This nested arrangement consolidates multiple optical functions into a compact unit that fits comfortably around the human head in an eyeglass-like form factor.
2Area of stationary object
If traditional HMD optical systems are used, then virtual image display is achieved, but the see-through field of view is blocked or degraded
Solution Approach 1:
The waveguide prism is designed with selectively coated surfaces: some surfaces have high-reflectivity coatings to guide virtual images, while other surfaces remain transparent to allow see-through views. This local differentiation of surface properties enables simultaneous achievement of wide see-through FOV and effective virtual image display without compromising either function.
3Weight of moving object
If freeform surfaces are introduced to reduce system weight, then lightweight HMD design is achieved, but optical performance may be compromised
Solution Approach 1:
Freeform curved surfaces are employed in both the waveguide prism and compensation lens to achieve compact, lightweight design. These curved surfaces enable efficient light guidance and see-through view correction while reducing material requirements and overall system weight, without compromising 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 solution enables a lightweight, compact, and ergonomic HMD design that fits comfortably around the human head, offering a wide see-through field of view and superior optical performance, allowing users to view virtual content overlaid on the real world without fatigue or discomfort.
Implementation Method 1
The injected rays propagate through the waveguide prism via multiple reflections (typically 3 or more)
Implementation Method 2
The display viewing optics includes a light guiding device (referred to hereafter as a freeform waveguide prism) containing multiple freeform refractive and reflective surfaces
Data Source
AI summary
Optical systems such as image display systems include a freeform optical waveguide prism and a freeform compensation lens spaced therefrom by a gap of air or index cement. The compensation lens corrects for aberrations which the optical waveguide prism will introduce in light or images from an ambient real-world environment. The optical waveguide prism receives actively projected images at an entry location, and emits the projected images at an exit location after internally reflecting the images along an optical path therein. The image display system may include an image source and coupling optics. The approach permits design of an optical viewing device, for example in optical see-through HMDs, achieving an eyeglass-form appearance and a wide see-through field of view (FOV).