Prism Optical Element for Wearable Display Protrusion Reduction
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Solution Overview
Problem
Wearable display devices, such as head-mounted displays (HMDs), face challenges in increasing the field angle without impairing the external design or causing contact between the device and the user's head, particularly when using concave mirrors as the ocular optical system.
Innovation Solution
The use of a prism optical element with a flat refractive surface and a concave mirror, where image light is refracted by the prism surface and reflected by the concave mirror, reduces the mirror protrusion while maintaining a wide field angle, and includes a light guide optical system with lenses and a reflective mirror to correct aberrations and position components away from the head.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the curved surface of the concave mirror is arranged closer to the face of the viewer on the nose side and away from the face on the ear side to increase the field angle, then the field angle is increased, but the amount of forward protrusion of the concave mirror on the ear side increases, impairing the external design of the device
Solution Approach 1:
The patent introduces a prism optical element that changes the optical path direction by 90 degrees, effectively transitioning the problem from a linear protrusion dimension to a multi-dimensional optical path arrangement. This allows the concave mirror to be positioned closer to the nose without increasing ear-side protrusion, as the light path is redirected through the prism rather than requiring linear extension
Solution Approach 2:
The prism optical element acts as an intermediary between the image generation portion and the concave mirror, mediating the optical path to achieve the desired field angle while controlling the physical protrusion. The prism refracts and redirects light, allowing the system to decouple the optical requirements from the physical spatial constraints
2Shape
If the concave mirror is arranged in an inclined posture to reduce the amount of protrusion while maintaining a sufficient field angle, then the external design is improved, but the image light generation portion or light guide system may be brought into contact with the head of the viewer
Solution Approach 1:
The patent uses the prism optical element to change the optical path into a different spatial dimension (90-degree angle), allowing the image generation portion and light guide system to be positioned in a direction perpendicular to the main optical axis. This vertical or lateral arrangement prevents contact with the head while maintaining the inclined posture of the concave mirror for aesthetic purposes
3Shape
If the prism optical element refracts image light to reduce mirror protrusion, then the external design is enhanced, but aberrations may be caused by refraction when light enters the prism optical element
Solution Approach 1:
The patent carefully selects and optimizes the prism's refractive index, apex angle, and material properties to minimize aberrations. By changing the optical parameters of the prism (such as using specific glass types with known refractive indices and designing the prism angle to compensate for chromatic and spherical aberrations), the system achieves both the desired compact protrusion and acceptable optical quality
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 users to recognize large images without compromising the device's external appearance or contacting the head, enhancing the external design and preventing distortion in see-through images.
Implementation Method 1
the image light can be refracted by the first light refractive surface of the prism optical element
Implementation Method 2
is reflected by the concave mirror
Data Source
AI summary
An image display device of the embodiment includes an image generation portion that emits image light, a prism optical element into which the image light enters, and a light guide optical system that guides the image light to the prism optical element. The prism optical element includes a prism member having a light refractive surface formed of a flat surface provided on a light incident side of the image light, and a concave mirror provided opposite the light refractive surface of the prism member and having a shape that is concave away from the light refractive surface.