Virtual Image Display Device Optical Path Reduction
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Solution Overview
Problem
Existing head-mounted displays have a long optical path length and large optical systems due to the formation of intermediate images in prisms, which limits the arrangement and size of projection optical members, leading to potential interference issues.
Innovation Solution
A direct virtual image display device with a first lens, a first prism, a second prism forming a prism light-guiding member, a polarized light separation film, an angle selection film, a second lens with a transmissive mirror, a quarter-wavelength plate, and a compensation lens, which selectively reflects and transmits video light to avoid intermediate image formation and reduce optical path length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an intermediate image is formed in the first prism, then the image can be transmitted through the optical system, but the optical path length becomes long and the optical system becomes large
Solution Approach 1:
The patent removes the intermediate image formation step from the optical path. By using a beam splitter to directly combine the projected light with the reflected light from the combiner, the system eliminates the need for intermediate image formation in the first prism, thereby shortening the optical path length while maintaining reliable image transmission.
Solution Approach 2:
The patent changes the spatial arrangement of optical components by introducing a beam splitter that operates in a different dimensional plane. Instead of forming images sequentially through multiple prisms, the system uses the beam splitter to combine light paths in a way that reduces the overall optical path length while maintaining image quality.
2Device complexity
If the projection optical member is disposed in a direction inclined toward the face, then the optical path can be folded, but the projection optical member is disposed close to the face and interference is likely to occur
Solution Approach 1:
The patent introduces a beam splitter as an intermediary component that mediates between the projection optical member and the combiner. This beam splitter allows the projection optical member to be positioned closer to the user's face without causing interference, as the beam splitter manages the light paths and prevents direct interference between components.
3Volume of moving object
If the projection optical member is disposed close to the face, then the device can be more compact, but the arrangement is limited and size is constrained
Solution Approach 1:
The patent employs dynamic light path management through the beam splitter and combiner arrangement. This allows the projection optical member to be positioned flexibly close to the face without compromising arrangement flexibility, as the optical paths can be dynamically controlled and adjusted through the beam splitting and combining mechanism.
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 ensures a magnification rate while minimizing the increase in optical system size and path length, allowing for a more compact and interference-free virtual image display.
Implementation Method 1
a polarized light separation film provided at a bonding site of the first prism and the second prism, the polarized light separation film having a flat surface shape, the polarized light separation film being configured to selectively reflect the video light guided in the first prism in accordance with a polarization direction
Implementation Method 2
an angle selection film disposed on an outer surface in the prism light-guiding member, on which the video light guided in the first prism and then reflected at the polarized light separation film is incident, the angle selection film being configured to exhibit a different separation characteristic depending on an incident angle of the video light
Implementation Method 3
a transmissive mirror disposed on a convex surface of the second lens, the transmissive mirror being configured to partially reflect the video light reflected at the polarized light separation film toward the polarized light separation film
Implementation Method 4
a quarter-wavelength plate disposed between the angle selection film and the flat surface of the second lens
Implementation Method 5
a first lens having a positive refractive power, the first lens on which the video light is incident from the display element
Data Source
AI summary
A virtual image display device includes: a first lens that has a positive refractive power and on which video light is incident from the display element, a first prism on which the video light passed through the first lens is incident, a second prism that is bonded to the first prism and that forms a prism light-guiding member, a polarized light separation film that is provided at a bonding site of the first prism and the second prism, an angle selection film disposed on an outer surface in the prism light-guiding member, a second lens that is disposed in a facing manner to the angle selection film, a transmissive mirror that is disposed on a convex surface of the second lens, a quarter-wavelength plate disposed between the angle selection film and the second lens, and a compensation lens that is bonded to the convex surface.