Waveguide Display Diffractive Elements Brightness Uniformity
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Solution Overview
Problem
Conventional optical transmission augmented reality display systems are limited by thickness and size, leading to non-uniform image brightness and reduced system efficiency due to low diffraction efficiency and energy loss during image sequencing, making them unsuitable for wearable applications.
Innovation Solution
A waveguide display device with an input and output diffractive optical element, utilizing total internal reflection and modulated diffraction efficiency to achieve uniform image brightness and improved system efficiency, featuring a waveguide substrate with embedded or adhered diffractive optical elements that optimize diffraction efficiency and maintain constant light flux per unit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If conventional optical components are used to form superposition of virtual and real worlds, then refraction and reflection can be achieved, but the overall optical distance is limited and the system thickness cannot be minimized for wearable applications
Solution Approach 1:
The patent replaces conventional mechanical optical components (lenses, mirrors) with a waveguide-based optical system that uses total internal reflection and diffractive optical elements. This substitution enables the light to be guided through a planar structure, minimizing the overall optical distance and system thickness while maintaining the ability to form the superposition of virtual and real worlds.
Solution Approach 2:
The patent transitions from a conventional three-dimensional optical path to a two-dimensional planar waveguide structure. By confining light propagation within the planar waveguide substrate and using total internal reflection at the waveguide boundaries, the system achieves compact thickness while maintaining sufficient optical path length for image formation.
2Device complexity
If conventional optical display systems are designed, then optical components can be configured, but the size is limited by Lagrangian invariant and cannot perfectly match with user pupils
Solution Approach 1:
The patent employs diffractive optical elements with spatially varying local properties (varying diffraction efficiency, grating periods, and depths across different regions) to control light output. This local quality variation enables precise control of the exit pupil characteristics, allowing the optical display system to perfectly match different user pupil sizes and positions.
3Adaptability or versatility
If light energy is gradually attenuated during image sequencing output in waveguide, then exit pupil expansion is achieved, but diffraction efficiency is low and system energy is significantly lost resulting in non-uniform image brightness
Solution Approach 1:
The patent systematically varies key diffraction grating parameters (grating period, depth, and orientation) across different regions of the output coupler to optimize diffraction efficiency at each stage of the image sequencing process. This parameter optimization ensures uniform light extraction, maintaining consistent image brightness while achieving the required exit pupil expansion.
Solution Approach 2:
The patent incorporates feedback mechanisms where the diffraction efficiency of each output coupler region is calculated based on the remaining light energy in the waveguide, and the grating parameters are adjusted accordingly to extract the optimal amount of light. This feedback-controlled approach prevents over-extraction or under-extraction, ensuring uniform brightness and maximizing system energy efficiency.
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 enhances brightness uniformity and system efficiency, ensuring stable image brightness even with relative displacement and reducing manufacturing costs through optimized diffraction efficiency and energy output, thereby improving user experience and system performance.
Implementation Method 1
The waveguide substrate is arranged for reflecting light from the input diffractive optical element by means of total internal reflection toward the output diffractive optical element
Implementation Method 2
an input diffractive optical element and an output diffractive optical element. The input diffractive optical element is arranged for coupling an output light of a light projector to the waveguide substrate
Data Source
AI summary
An optical waveguide includes an input diffractive optical element arranged for being aligned with an optical projector for diffracting the light beam therefrom, a waveguide substrate arranged for reflecting the light beam diffracted by the input diffractive optical element by means of total internal reflection, and an output diffractive optical element coupled at said waveguide substrate for partially diffracting the light beam as a diffracted light and partially transmitting the light beam as a transmitted light during the total internal reflection of the light beam within the waveguide substrate. The diffracted light is diffracted by the output diffractive optical element and is projected out of the waveguide substrate toward the user eye. The transmitted light is continuously transmitted and reflected within the waveguide substrate by the total internal reflection until the transmitted light is totally diffracted out of the waveguide substrate, so as to complete an exit pupil expansion.