Near-eye display diffractive optical element for bidirectional pupil expansion
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Solution Overview
Problem
Current near-eye display systems for augmented reality face challenges in achieving a larger field of view (FOV), expanding the eye box, improving brightness and uniformity, while reducing power consumption and system volume, with existing pupil expansion methods being complex, costly, and limited to unidirectional expansion.
Innovation Solution
A near-eye display system utilizing a diffractive optical element, comprising a laser light source, diffusion sheet, MEMS scanning mirror, collimating lens module, mirror, and reflective diffraction structure, which divides light into multiple beams for bidirectional pupil expansion, allowing for simpler manufacturing and reduced processing difficulty and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple splitting films are embedded in a waveguide sheet to achieve pupil expansion, then the eye box is expanded in the transverse direction, but the processing difficulty increases and mass production yield decreases due to precise control requirements of reflection and transmittance rates
Solution Approach 1:
The patent combines multiple splitting film functions into a single diffractive optical element with multiple grating regions. Instead of embedding multiple separate splitting films in the waveguide, the invention uses one integrated component with different grating areas (first grating area for transverse expansion, second grating area for longitudinal expansion) that performs multiple pupil expansion functions simultaneously, thereby simplifying the manufacturing process and improving mass production yield.
Solution Approach 2:
The diffractive optical element serves multiple functions: it expands the eye box in both transverse and longitudinal directions, couples light into the waveguide, and directs light to the exit pupil. This multi-functional design replaces the need for multiple specialized components (multiple splitting films, coupling-in gratings, turning gratings, and coupling-out gratings), reducing manufacturing complexity while achieving comprehensive pupil expansion.
2Area of stationary object
If three grating regions are distributed on the waveguide sheet to achieve bidirectional pupil expansion, then both transverse and longitudinal eye box expansion are achieved, but the processing difficulty and cost become extremely high due to precise regulation requirements of grating area positions and heights
Solution Approach 1:
The patent merges the functions of multiple grating regions into a single diffractive optical element. The element contains a first grating area for transverse pupil expansion and a second grating area for longitudinal pupil expansion, all integrated in one component. This eliminates the need for precise positioning and height regulation of multiple separate grating regions on the waveguide, significantly reducing manufacturing precision requirements and costs.
Solution Approach 2:
The diffractive optical element uses diffraction patterns to create multiple virtual images of the light source, effectively copying the light path multiple times through different grating areas. This allows bidirectional pupil expansion without requiring physical adjustment of multiple grating heights, as the diffraction pattern inherently provides the necessary light distribution across different angles and positions.
3Area of stationary object
If the area of the micro display screen is increased to achieve a greater field of view, then the field of view is expanded, but the volume and weight of the system increase
Solution Approach 1:
The patent changes the optical parameters of the system by introducing a diffractive optical element that manipulates light through diffraction rather than requiring larger physical components. By using diffraction to create multiple exit pupil images and expand the field of view optically, the system achieves greater FOV without increasing the physical size of the micro display screen or other system components, thereby maintaining compact volume and weight.
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 system achieves enhanced FOV, eye box, brightness, and contrast with reduced power consumption and system volume, enabling bidirectional pupil expansion and facilitating mass production with improved manufacturing efficiency.
Implementation Method 1
a diffractive optical element, arranged on an emergent light path of the MEMS scanning mirror, and configured to divide the scanning light beam into a plurality of beams of scanning light
Implementation Method 2
a reflective diffraction structure, arranged on a reflection light path of the mirror, and configured to diffract a plurality of beams of reflected light to a human eye
Data Source
Figure 1~2(b)
Figure 3~5
AI summary
A near-eye display system for pupil expansion based on a diffractive optical element includes: a laser light source or an LED light source; a diffusion sheet, arranged on an emergent light path of the laser light source or the LED light source; a micro-electro-mechanical system (MEMS) scanning mirror, arranged on an emergent light path of the diffusion sheet; a diffractive optical element, arranged on an emergent light path of the MEMS scanning mirror; a collimating lens module, arranged on an emergent light path of the diffractive optical element; a mirror, arranged on an emergent light path of the collimating lens module; and a reflective diffraction structure, arranged on a reflection light path of the mirror such that a human eye sees a superimposed image of a real world and a virtual world.