Prism Optical System for Head-Mounted Displays
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Solution Overview
Problem
Existing head-mounted image display apparatuses with virtual-image optical systems face challenges in conforming to the user's face shape, achieving reduced thickness along the field of view, and maximizing light utilization efficiency due to limitations in optical arrangement and light reflection efficiency.
Innovation Solution
The design incorporates a prism with a first and second planar or curved optical surface, an incident optical surface with an angle between 30 degrees and 90 degrees relative to the normal, and a reflective transmitting surface, along with a phase difference optical component and a reflective optical component, allowing for total internal reflection and improved polarization state change, enabling a coaxial or offset optical system that conforms to the user's face and enhances light utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional virtual-image optical system with a prism is used, then the optical system can guide image light, but the image display device and optical pupil must be arranged on the same side of the prism, making it difficult to achieve an optical arrangement along the viewer's face
Solution Approach 1:
The patent introduces a new dimensional arrangement by placing the image display device on the opposite side of the prism from the optical pupil, utilizing the third dimension (depth/thickness of the prism) to resolve the spatial constraint. This allows the optical system to conform to the viewer's face by arranging components along the optical path rather than being constrained to a single plane.
2Loss of energy
If a first reflecting surface in the prism is used to change the proceeding direction of image light by 90 degrees, then the light path can be redirected, but 100% reflection cannot be achieved, significantly lowering light utilization efficiency
Solution Approach 1:
The patent changes the reflection mechanism from partial reflection (using a reflecting surface) to total internal reflection by utilizing the critical angle of incidence. By designing the light path to enter the prism at an angle that satisfies the critical angle condition, the system achieves 100% reflection efficiency without energy loss.
3Length of stationary object
If the image light is bent 90 degrees by the first reflecting surface, then the light path can be changed, but an angle of 45 degrees is needed as the tilt of the second reflecting/transmitting surface, resulting in increased prism thickness along the field of view
Solution Approach 1:
The patent changes the tilt angle parameter of the second reflecting/transmitting surface from the conventional 45 degrees to a smaller angle. By optimizing this angle parameter, the prism thickness along the field of view is reduced while still achieving the necessary light path redirection, thereby making the apparatus more compact and comfortable for wear.
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 allows for a more comfortable fit by conforming to the user's face shape, reduces the apparatus thickness along the field of view, and increases light utilization efficiency compared to systems using reflective mirrors, while maintaining an enlarged virtual image display.
Implementation Method 1
The prism guides the image light incident on and proceeding into the prism from the incident optical surface up to the reflective transmitting surface as the image light undergoes internal total reflection on the first planar optical surface and on the second planar optical surface
Implementation Method 2
a phase difference optical component arranged on a light path of the first planar optical surface of the prism and the reflective optical component, sandwiching an air layer between the phase difference optical component and the first planar optical surface or the reflective optical component, the phase difference optical component changing the state of polarization of the image light
Data Source
AI summary
An image display apparatus for a viewer to view a two-dimensional image demonstrated on an image display device as an enlarged virtual image by a virtual-image optical system. The image display apparatus includes a prism and a reflective transmitting surface for reflecting or transmitting image light incident from an incident optical surface. The image display apparatus also includes a reflective optical component for reflecting image light reflected from the reflective transmitting surface and radiated from a first planar optical surface towards the reflective transmitting surface as a collimated light beam and a phase difference optical component arranged on a light path between the first planar optical surface and the reflective optical component to the state of polarization of the image light.