Stepped Free-Form Prism for Thinned HMD Optical System
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Solution Overview
Problem
The existing head-mounted display devices with correction prisms of the same shape as free-form surface prisms face challenges in miniaturization due to increased thickness, making it difficult to reduce the size of the display optical system.
Innovation Solution
The proposed optical element includes a first prism with an incident, semi-reflecting, and emitting surface, and a second prism with a free-form surface divided by stepped surfaces for external light, allowing for internal reflection and emission, which reduces the thickness of the display optical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a correction prism with the same shape as the free-form surface prism is used, then external light transmission is achieved, but the thickness of the display optical system increases
Solution Approach 1:
The optical system is divided into two separate prisms: a free-form surface prism for guiding display light and a correction prism for transmitting external light. This segmentation allows each prism to be optimized for its specific function, enabling the correction prism to have a thinner profile while maintaining external light transmission capability.
Solution Approach 2:
The correction prism is designed with non-uniform thickness, being thinner in regions where external light transmission is required and thicker only where structurally necessary. This local quality variation allows the prism to transmit external light effectively while minimizing the overall thickness of the display optical system.
2Volume of moving object
If the display optical system is miniaturized, then device compactness is improved, but image quality may deteriorate
Solution Approach 1:
By segmenting the optical system into specialized prisms, each component can be miniaturized independently while maintaining its optical function. The free-form surface prism handles display light guidance and the correction prism handles external light transmission, allowing compact design without compromising image quality.
Solution Approach 2:
The prisms utilize free-form surfaces with specifically optimized curvature radii and surface shapes. By carefully controlling these geometric parameters, the optical system achieves miniaturization while maintaining proper light guidance and image quality through precise optical path control.
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 thinner display optical system, improving miniaturization and maintaining image quality by aligning external light phases and reducing internal reflections, thus enhancing the image display device's compactness and clarity.
Implementation Method 1
a first prism that includes an incident surface, a semi-reflecting surface, and an emitting surface each configured of a free-form surface, and in which light of a display element is incident from the incident surface, is internally reflected between the emitting surface and the semi-reflecting surface
Data Source
AI summary
The optical element is thinned. The optical element includes a first prism and a second prism. The first prism includes an incident surface, a semi-reflecting surface, and an emitting surface each configured of a free-form surface, and in which the light of a display element is incident from the incident surface, internally reflected between the emitting surface and the semi-reflecting surface, and emitted from the emitting surface to an observation portion of the light. The second prism includes an external light incident surface configured in a shape in which a free-form surface is divided by at least one stepped surface and on which external light is incident, and an external light emitting surface from which the incident external light is emitted to the semi-reflecting surface.