Head Mounted Display Optical Path Folding
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Solution Overview
Problem
The challenge in designing a head-mounted display is to reduce its thickness while maintaining the necessary optical path length for image display, as the lens and display module need to be spaced apart to prevent the black matrix from appearing as a lattice shape, which is exacerbated by the thinness required for user convenience.
Innovation Solution
The solution involves a display module accommodating unit with a quarter wave plate, a semi-transmissive plate, and a reflective polarizing plate, which delays and converts polarized light to maintain the optical path length while allowing for a reduced thickness, by configuring the distances between these components to ensure the light path length remains consistent with the focal distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the lens and display module are spaced apart at a predetermined distance to prevent black matrix lattice appearance, then image quality is improved, but the thickness of the head mounted display increases
Solution Approach 1:
The patent introduces optical path folding using reflective polarizing plates and quarter wave plates to extend the optical path length between the display module and lens in a direction perpendicular to the thickness direction. This allows the optical path length to be increased without increasing the thickness of the head mounted display, effectively resolving the contradiction by changing the dimensional approach to path length extension.
Solution Approach 2:
The patent uses reflective polarizing plates and quarter wave plates as intermediary optical elements to fold and extend the optical path. These intermediaries allow the light to traverse a longer path between the display module and lens while maintaining a compact thickness, thereby achieving both improved image quality and reduced thickness.
2Reliability
If the lens and display module are spaced apart to maintain focal distance, then virtual image distance is improved, but the overall device size increases
Solution Approach 1:
The patent employs optical path folding techniques using reflective polarizing plates to extend the optical path length in a direction that does not increase the overall device volume. By folding the light path within the existing device envelope, the virtual image distance is improved without proportionally increasing the device size.
Solution Approach 2:
The patent nests multiple optical elements (quarter wave plates, reflective polarizing plates) within the compact space between the display module and lens. This nesting allows the optical path to be folded back on itself, effectively packing a longer optical path into a smaller volume, thereby improving virtual image distance without significantly increasing device size.
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 reduction in the thickness of the head-mounted display while maintaining the necessary optical path length, preventing the black matrix from appearing as a lattice shape and enhancing user experience by minimizing thickness without compromising image quality.
Implementation Method 1
a first quarter wave (λ/4) plate arranged between the display module and the lens, delaying a phase of incident light as much as λ/4
Implementation Method 2
a reflective polarizing plate arranged between the second quarter wave plate and the lens, passing through first linear polarized light and reflecting second linear polarized light crossing the first linear polarized light
Implementation Method 3
a semi-transmissive plate arranged between the first quarter wave plate and the second quarter wave plate
Data Source
AI summary
A head mounted display of which thickness may be reduced is disclosed. The head mounted display comprises a lens, and a display module accommodating unit for providing an image to the lens. The display module accommodating unit includes a display module for displaying an image, a first quarter wave (λ/4) plate arranged between the display module and the lens, delaying a phase of incident light as much as λ/4, a second quarter wave plate arranged between the first quarter wave plate and the lens, delaying a phase of incident light as much as λ/4, a reflective polarizing plate arranged between the second quarter wave plate and the lens, passing through first linear polarized light and reflecting second linear polarized light crossing the first linear polarized light, and a semi-transmissive plate arranged between the first quarter wave plate and the second quarter wave plate.