Volume Holographic Optical Waveguide Switching for Uniform AR Displays
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Solution Overview
Problem
Existing AR display apparatuses based on volume holographic grating waveguides suffer from poor display uniformity, particularly in brightness and color uniformity, due to non-uniform optical field distribution and low diffraction efficiency, which affects image clarity and visual effect.
Innovation Solution
Implement a switchable grating structure with directionally selectable and continuously switchable coupling regions, utilizing a control system to modulate the grating structure, ensuring maximum diffraction efficiency and uniformity by concentrating light beams in specific regions and rapidly switching them across the grating array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a diffraction optical waveguide with volume holographic grating is used to transport virtual images, then the exit pupil and field angle are reproduced, but brightness uniformity deteriorates due to non-uniform optical field distribution and energy loss during multiple diffractions
Solution Approach 1:
The patent introduces a switchable grating structure that can dynamically change its diffraction efficiency in different regions. By controlling the switching state of the grating in each region, the system can adapt the optical field distribution to achieve uniform brightness across the exit pupil, resolving the contradiction between maintaining exit pupil reproduction and improving brightness uniformity.
Solution Approach 2:
The patent modifies the diffraction efficiency parameter of the holographic grating by introducing a switchable mechanism. By changing the diffraction efficiency from a fixed value to a controllable parameter that varies across different regions, the system can balance the optical energy distribution and eliminate brightness non-uniformity while preserving the exit pupil characteristics.
2Area of moving object
If the beam is propagated and diffracted multiple times through fold grating and coupling-out grating to expand the eye box, then the field angle is increased, but brightness deteriorates due to energy loss at each diffraction
Solution Approach 1:
The switchable grating structure allows dynamic control of diffraction efficiency at each grating location. By optimizing the switching state of the grating during the beam propagation path, the system can maintain high diffraction efficiency to minimize energy loss while still achieving the required eye box expansion through controlled beam deflection.
Solution Approach 2:
The patent ensures continuous and efficient beam propagation by maintaining high diffraction efficiency throughout the entire optical path. The switchable grating structure prevents energy loss at each diffraction interface, allowing the beam to traverse multiple gratings without significant intensity degradation, thus achieving both eye box expansion and brightness maintenance.
3Illumination intensity
If variable diffraction efficiency is introduced in the coupling-out grating to balance optical field distribution, then brightness uniformity is improved, but device complexity increases due to special processing technology and complex processing processes
Solution Approach 1:
Instead of using complex static processing to create variable diffraction efficiency, the patent employs a dynamic switching mechanism that can be controlled electronically. This approach achieves brightness uniformity through real-time control of the grating's diffraction efficiency in different regions, eliminating the need for complex manufacturing processes while maintaining processing simplicity.
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
Improves brightness and uniformity of the displayed images by ensuring consistent diffraction efficiency and balanced optical field distribution, enhancing the overall display quality and visual experience without introducing additional stray light or complexity.
Implementation Method 1
The beam projected by a projection optical machine is subjected to beam expansion and collimation and is coupled into the waveguide from the coupling-in grating region, and then diffracted by the coupling grating to produce a beam performing total reflection in the waveguide
Implementation Method 2
the coupling grating to produce a beam performing total reflection in the waveguide, the total reflection beam obtained can be propagated along the waveguide direction in the waveguide
Data Source
AI summary
The present disclosure provides a method and apparatus for improving display uniformity of a volume holographic optical waveguide. Specifically, the volume holographic optical waveguide includes a switchable grating structure, a partial region on the switchable grating structure is directionally selected as a coupling region thereof, such that a light source can only be coupled out of the coupling region at the maximum diffraction efficiency thereof. The coupling region on the switchable grating structure is continuously switched, and the time in which the coupling region covers all the regions is made not more than the visual retention time of human eyes.