Optical Element Light Recycling VR Head-Mounted Display
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Solution Overview
Problem
Existing optical devices for virtual reality (VR) head-mounted displays suffer from low light utilization efficiency due to the reciprocal reflection of light between the half mirror and the reflective polarizer, resulting in a significant reduction in the optical path length and increased thickness.
Innovation Solution
The proposed optical element comprises a specific configuration of absorptive and reflective polarizing plates, retardation plates, and a partially reflecting mirror, which allows for the efficient recycling of light while maintaining an increased optical path length, thereby improving light utilization efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If light is reciprocated between the half mirror and the reflective polarizer to increase the optical path length, then the optical path length is obtained and the total thickness is reduced, but the light utilization efficiency decreases to about 25%
Solution Approach 1:
The optical element is divided into multiple functional layers including a first reflective linearly polarizing plate, first and second retardation plates, a partially reflecting mirror, and a second reflective linearly polarizing plate. Each layer performs a specific function in the light modulation process, allowing precise control of light polarization states to improve utilization efficiency while maintaining optical path length.
Solution Approach 2:
The patent utilizes changes in light polarization parameters (linear to circular and vice versa) through retardation plates with specific retardation values. By controlling the polarization state transformations, the system achieves higher light utilization efficiency (approximately 50%) compared to the conventional 25% efficiency, while maintaining the folded optical path structure.
2Length of stationary object
If a conventional half mirror and reflective polarizer structure is used, then the device thickness is reduced, but the light utilization efficiency is significantly reduced
Solution Approach 1:
The optical system maintains continuous useful action by ensuring that light is efficiently utilized in both forward and reflected paths. The combination of reflective polarizing plates and retardation plates ensures that light undergoes beneficial polarization transformations continuously, maximizing light utilization efficiency while maintaining the compact folded optical path structure required for reduced device thickness.
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 enhances the light utilization efficiency to approximately 50% of the light emitted from the image display apparatus, achieving a balanced reduction in the size and thickness of the optical device while maintaining an extended optical path length.
Implementation Method 1
a first reflective linearly polarizing plate... a second reflective linearly polarizing plate, in which a turning direction of circularly polarized light that is reflected in a case where light transmits through the first retardation plate and is incident into the first reflective linearly polarizing plate is opposite to a turning direction of circularly polarized light that is reflected in a case where light transmits through the second retardation plate and is incident into the second reflective linearly polarizing plate
Implementation Method 2
a partially reflecting mirror that allows transmission of a part of incident light and reflects a part of the incident light
Implementation Method 3
a first retardation plate... a second retardation plate
Data Source
AI summary
Provide are an optical element that can improve a utilization efficiency of light while increasing an optical path length, an image display unit, and a head-mounted display. The optical element includes, in the following order: a first absorptive linearly polarizing plate; a first reflective linearly polarizing plate; a first retardation plate; a partially reflecting mirror; a second retardation plate; and a second reflective linearly polarizing plate, in which a turning direction of circularly polarized light that is reflected from the first reflective linearly polarizing plate in a case where light transmits through the first retardation plate and is incident into the first reflective linearly polarizing plate is opposite to a turning direction of circularly polarized light that is reflected from the second reflective linearly polarizing plate in a case where light transmits through the second retardation plate and is incident into the second reflective linearly polarizing plate.