Virtual Image Display Device Optical Unit Compactness
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Solution Overview
Problem
Existing head-mounted displays (HMDs) face challenges with long optical path lengths, large optical systems, and interference issues due to the placement of projection optical members, which limit their arrangement and size, and struggle to correct color aberration effectively using optical condensing/reflecting plates.
Innovation Solution
A virtual image display device and optical unit that include a first lens, a second lens, a prism light-guiding member with a polarized light separation film, and a quarter-wavelength plate, where the first prism has a higher refractive index than the first and second lenses, and a transmissive mirror, to guide video light and suppress color aberration by optimizing the refractive powers and Abbe numbers of the components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an intermediate image is formed in the first prism, then the optical system can guide light effectively, but the optical path length becomes long and the optical system becomes large as a whole
Solution Approach 1:
The patent removes the intermediate image formation step from the optical path. By using a direct virtual image type configuration where light from the display element passes through lenses and the prism light-guiding member directly to form a virtual image, the optical path is shortened without compromising light guidance effectiveness.
2Volume of stationary object
If the projection optical member is disposed in a direction inclined toward a face, then the optical system can be more compact, but the projection optical member is disposed close to the face and interference is likely to occur, limiting arrangement and size
Solution Approach 1:
The patent positions the display element and optical components in a configuration that extends in the depth direction (optical path direction) rather than only in the lateral direction. This dimensional arrangement allows the optical system to be compact in the lateral direction while maintaining sufficient distance from the face, avoiding interference issues.
3Volume of stationary object
If an optical condensing/reflecting plate is used to achieve a relatively small optical system, then the optical system size is reduced, but it is difficult to correct color aberration
Solution Approach 1:
The patent employs a composite optical system comprising multiple lenses with different refractive powers and Abbe numbers (first lens with positive refractive power and first Abbe number, second lens with positive refractive power and second Abbe number). This composite structure enables effective color aberration correction while maintaining a compact optical system size, overcoming the limitation of simple optical condensing/reflecting plates.
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 compact optical system that directly forms virtual images without intermediate images, reduces optical path length, and effectively suppresses color aberration, allowing for improved magnification and reduced system size while maintaining image quality.
Implementation Method 1
a first lens (30) having a positive refractive power, on which the video light (ML) from the first image forming element (11a) is incident
Implementation Method 2
a second lens (44) having a positive refractive power, on which the video light (ML) passed through the first lens (30) is incident
Implementation Method 3
image light from the projection optical member is incident into a first prism included in the prism member, totally reflected at an outer surface of the prism member
Implementation Method 4
a polarized light separation film (45) provided at a bonding position of the first prism (41) and the second prism (42), the polarized light separation film (45) having a flat surface shape, the polarized light separation film (45) being configured to selectively reflect the video light (ML) guided in the first prism (41) in accordance with a polarization direction
Implementation Method 5
a quarter-wavelength plate (51) disposed between the outer surface (41c) of the first prism (41) and the flat surface (53f) of the third lens (53), the quarter-wavelength plate (51) being for the video light (ML)
Implementation Method 6
a transmissive mirror (56) formed on a convex surface of the third lens, the transmissive mirror (56) being configured to partially reflect the video light reflected at the polarized light separation film toward the polarized light separation film
Data Source
AI summary
A virtual image display device includes: a first lens that has a positive refractive power and on which video light from the display element is incident, a second lens that has a positive refractive power and on which the video light passed through the first lens is incident, a prism light-guiding member that includes a first prism and a second prism, a polarized light separation film that is provided at a bonding position of the first prism and the second prism, a third lens that is disposed facing an outer surface of the first prism and that has a plano-convex shape, a transmissive mirror that is disposed on a convex surface of the third lens and that is configured to partially reflect the video light, and a quarter-wavelength plate disposed between the outer surface and the flat surface of the third lens.