Parallel Substrate Optical Device for Stripe-Free Exit Pupil Enlargement
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Solution Overview
Problem
Existing virtual image display systems face challenges in enlarging the exit pupil without causing undesirable stripes, particularly due to the complexity of existing configurations and limitations in manufacturing large-size displays with high image quality.
Innovation Solution
An optical device with a first reflective face and a partially transmissive reflective face, spaced apart in parallel, where the refractive index of the second substrate is higher than the section between the reflective faces, allowing light to be repeatedly reflected and transmitted without total reflection, thereby enlarging the exit pupil without using a diffraction grating and preventing stripe formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a diffraction grating with multiple inclined reflective faces is used to extract light from a combiner, then the exit pupil can be enlarged, but the structure becomes complex and manufacturing difficulty increases
Solution Approach 1:
The optical device is divided into two separate substrates: a first substrate with a reflective face and a second substrate with a partially transmissive reflective face. This segmentation allows each component to perform its function independently, simplifying the overall structure while achieving pupil enlargement through the coordinated interaction of these simplified elements rather than requiring a complex integrated diffraction grating
Solution Approach 2:
A gas-filled space acts as an intermediary medium between the two substrates. This gas layer with lower refractive index enables total internal reflection at the interfaces while allowing light transmission, providing a simple mechanical and optical coupling mechanism that replaces the need for complex diffraction grating structures
2Adaptability or versatility
If a diffraction grating is used to extract light from a combiner, then the exit pupil can be enlarged, but manufacturing large-size displays becomes difficult
Solution Approach 1:
By segmenting the optical system into two separate substrates with distinct functions, each component can be manufactured independently using standard fabrication techniques. The first substrate with reflective face and the second substrate with partially transmissive face can be produced separately and then assembled, making large-size display manufacturing feasible compared to monolithic diffraction grating structures
Solution Approach 2:
The invention changes the optical parameters by using a gas-filled space with lower refractive index between the substrates. This parameter change enables total internal reflection and light extraction without requiring complex diffraction grating patterns, allowing for easier scaling to large display sizes using conventional manufacturing processes
3Adaptability or versatility
If a diffraction grating is used to extract light from a combiner, then the exit pupil can be enlarged, but image quality deteriorates due to stripe artifacts
Solution Approach 1:
The harmful diffraction grating structure that causes stripe artifacts is completely removed from the system. Instead, the invention extracts and utilizes the beneficial optical phenomena of total internal reflection and refraction at the gas-substrate interfaces, achieving pupil enlargement without the detrimental stripe effects that characterize diffraction grating-based systems
Solution Approach 2:
By changing the refractive index parameter through the introduction of a gas-filled space, the system achieves total internal reflection at the interfaces. This parameter change fundamentally alters the light extraction mechanism from diffraction-based to reflection/refraction-based, eliminating stripe artifacts while maintaining pupil enlargement capability and preserving image quality
4Reliability
If the refractive index of the section between reflective faces is made lower than the second substrate, then light can be transmitted without total reflection, but the structure becomes more complex
Solution Approach 1:
A gas-filled space serves as an intermediary medium with lower refractive index between the two substrates. This intermediary enables controlled total internal reflection at the interfaces while allowing light transmission when incident at appropriate angles, achieving reliable light extraction without requiring complex additional optical components or structures
Solution Approach 2:
The refractive index parameter of the medium between substrates is changed from solid (higher index) to gas (lower index). This parameter change creates the conditions for total internal reflection while maintaining a simple two-substrate structure, achieving reliable light transmission and extraction without increasing structural complexity
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 solution effectively enlarges the exit pupil of the viewer system while maintaining image quality and simplifying the structure, allowing for easier manufacturing and reducing the size of virtual image display apparatuses without introducing stripes.
Implementation Method 1
light incident into the section between the first reflective face and the partially transmissive reflective face which are spaced apart is repeatedly reflected between the first reflective face and the partially transmissive reflective face
Implementation Method 2
a refractive index of the second substrate is higher than a refractive index of a section between the first reflective face and the partially transmissive reflective face which are spaced apart, and in which light incident into the section between the first reflective face and the partially transmissive reflective face which are spaced apart is repeatedly reflected
Data Source
AI summary
A partially transmissive reflective film is provided on a second transparent substrate, and a reflector is provided on a first transparent substrate. The partially transmissive reflective film and the reflector are held parallel to each other with a predetermined spacing therebetween. Thereby, light is incident from a protrusion portion on which the reflector of the first transparent substrate is formed, the light is reflected by the partially transmissive reflective film and the reflector, and the incident light is guided by an air layer between the partially transmissive reflective film and the reflector. A refractive index of the air layer is lower than that of the second transparent substrate. A part of the guided light is extracted from the partially transmissive reflective film, and is emitted from the second transparent substrate on a side opposite to a surface on which the partially transmissive reflective film is provided.