Freeform-Prism Eyepiece With Reflective Image Array

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Solution Overview

Problem

Current head-mounted display (HMD) devices face significant radiant-energy losses in transmissive LCD arrays and inadequate luminance in OLED arrays, particularly when used in augmented-reality (AR) mode, which affects battery life and image brightness.

Innovation Solution

The implementation of a reflective image-forming array combined with a compact light source featuring a waveguide and freeform-prism eyepiece, where the light source includes a grating to confine and release light efficiently, and the reflective array forms and reflects images through the waveguide to the eyepiece for enhanced brightness and energy efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If transmissive LCD arrays are used, then device complexity is reduced, but radiant-energy losses increase significantly

Engineering Contradiction:

Improvedisplay structure complexityVSAvoidradiant-energy losses

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The patent inverts the conventional transmissive display approach by using a reflective image-forming array instead. Light enters through the waveguide, reflects off the image-forming array (LCOS or DMD), and returns through the waveguide to the eyepiece. This reflective architecture eliminates the need for a backlight and reduces radiant-energy losses while maintaining manageable device complexity.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent replaces the mechanical backlight illumination system of transmissive LCDs with an optical waveguide-based reflective system. The waveguide confines and guides light optically through total internal reflection, eliminating the need for complex backlight units, diffusers, and polarizers, thereby reducing both energy losses and mechanical complexity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Loss of energy

If OLED arrays are used, then energy efficiency is improved, but output luminance is insufficient for AR mode

Engineering Contradiction:

Improveenergy efficiencyVSAvoidoutput luminance

Core Design Contradiction:

Loss of energyVSIllumination intensity

Solution Approach 1:

The patent introduces an intermediary image-forming array (LCOS or DMD) between the light source and the eyepiece. This array reflects and modulates light to form the display image, enabling high luminance output suitable for AR mode while maintaining the energy efficiency of reflective architectures. The intermediary array acts as a light modulator that preserves energy while enhancing output brightness.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Loss of energy

If reflective image-forming array is used, then energy efficiency and luminance are improved, but device complexity increases

Engineering Contradiction:

Improveenergy efficiencyVSAvoiddisplay structure complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent merges the light guiding function and the image formation function into a single integrated optical path. The waveguide both confines the light from the emitter and serves as the medium through which the reflected image from the image-forming array is transmitted to the eyepiece. This merging reduces the number of separate optical components and simplifies the overall device structure while maintaining energy efficiency and luminance performance.

Inventive Principle:

Principle #5Merging (Combining)

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 configuration provides a brighter and more energy-efficient display image, especially in AR mode, by utilizing reflective image-forming arrays like LCOS or DMD, which are more efficient than OLEDs, while maintaining an unobstructed field of view and supporting both virtual and real imagery integration.

Implementation Method 1

The waveguide is configured to confine the light from the light emitter

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 2

The waveguide includes a grating and is configured to release the light through the grating

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 3

The reflective image-forming array is configured to form a display image using light from the light source and to reflect the display image back through the waveguide

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 4

The freeform-prism eyepiece is configured to receive the display image and to present the display image for viewing, together with an external image transmitted through the eyepiece

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS9164351B2Freeform-prism eyepiece with illumination waveguide

Publication Date: 2015.10.20 MICROSOFT TECHNOLOGY LICENSING LLC

AI summary

An imaging panel includes a light source, a reflective image-forming array, and a freeform-prism eyepiece. The light source includes a light emitter and a waveguide having a grating. The waveguide is configured to confine the light from the light emitter and to release the light through the grating. The reflective image-forming array is configured to form a display image using light from the light source and to reflect the display image back through the waveguide. The freeform-prism eyepiece configured to receive the display image and to present the display image for viewing, together with an external image transmitted through the eyepiece.