Hybrid Coupling Diffractive Optical Element for HMD Aberration Correction

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Solution Overview

Problem

Current head-mounted display (HMD) systems for virtual and augmented reality applications face challenges in optimizing image forming performance due to the limitations of refractive elements in projector lenses, which can result in bulky designs and reduced imaging quality.

Innovation Solution

The integration of a multi-functional diffractive optical element (DOE) that functions as both an input coupler to redirect light into a waveguide and a lens element to improve the image forming performance of the projector lens, enabling the potential removal or redesign of refractive elements and maintaining or enhancing image quality.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If refractive elements are used in projector lens, then image forming performance can be maintained, but the projector lens becomes bulky and complex

Engineering Contradiction:

Improveimage forming performanceVSAvoidprojector lens structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent combines multiple functions into a single diffractive optical element: it serves as both an input coupler to redirect light into the waveguide and as a lens element to focus light onto the display. This merging eliminates the need for separate refractive lens elements, reducing structural complexity while maintaining image forming performance through diffraction-based focusing

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The diffractive optical element is designed to perform multiple functions simultaneously: (1) redirecting incident light at specific angles to couple into the waveguide, (2) focusing light onto the display, and (3) correcting optical aberrations. This multi-functionality replaces what would traditionally require multiple separate optical components

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Length of moving object

If refractive elements are removed from projector lens, then the lens length can be shortened, but image forming performance may deteriorate

Engineering Contradiction:

Improveprojector lens lengthVSAvoidimage forming performance

Core Design Contradiction:

Length of moving objectVSReliability

Solution Approach 1:

The patent replaces refractive optics (based on refraction through lens materials) with diffractive optics (based on interference and diffraction from microstructures). The diffractive optical element uses sub-wavelength gratings and phase modulations to achieve focusing and beam shaping without requiring thick refractive materials, enabling compact lens design while maintaining or improving image quality through precise wavefront control

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If a single element performs multiple functions, then device complexity is reduced, but manufacturing precision requirements increase

Engineering Contradiction:

Improvenumber of optical elementsVSAvoidDOE fabrication accuracy

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent employs complex phase profiles with multiple terms (including radial and angular dependencies) to encode multiple optical functions within the diffractive optical element's microstructure. By carefully designing the phase modulation parameters, the single element can achieve multi-functionality while the manufacturing precision requirements are managed through advanced fabrication techniques such as grayscale lithography or two-photon polymerization

Inventive Principle:

Principle #35Parameter changes

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 enhances the image forming performance of HMD systems, allows for the shortening of projector lens length, and improves the overall efficiency of light redirection and aberration correction, leading to more compact and effective virtual and augmented reality displays.

Implementation Method 1

a multi-functional diffractive optical element (DOE) configured to redirect light from the projector into the waveguide

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

configured to receive input light and configured to output the received input light to an eyebox

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Data Source

PatentUS11675192B2Hybrid coupling diffractive optical element

Publication Date: 2023.06.13 META PLATFORMS TECHNOLOGIES LLC

AI summary

A multi-functional diffractive optical element (DOE) for redirecting light into a waveguide and providing higher order aberration correction is described. The multi-functional DOE may be positioned on, connected to, adjacent to, or within a waveguide, and in some examples is positioned at, or near, the exit pupil of the projector lens. In an example, a head-mounted display (HMD) is configured to output artificial reality content, comprising a waveguide configured to receive input light and configured to output the received input light to an eyebox. The HMD further comprises a projector configured to input light into the waveguide, the projector comprising a display, a projection lens, and a multi-functional diffractive optical element (DOE) configured to redirect light from the projector into the waveguide and provide higher order aberration correction of the light from the display.