Compact Head-Mounted Display Using Moth-Eye Air Gap Film

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Solution Overview

Problem

Conventional compact optical modules for head-mounted displays become bulky and impractical as the desired field-of-view increases, suffering from limited eye-motion-box and manufacturability issues, and require complex solutions that are not sufficiently compact or robust for practical applications.

Innovation Solution

A compact tight-guide optical element (LOE) utilizing a moth-eye structure air gap film as an angular sensitive reflective mechanism, which preserves total internal reflection and allows attachment of optical elements while maintaining light transmission and reflection efficiency, even at oblique angles.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If conventional free-space optical modules are used to increase field-of-view, then the field-of-view increases, but the system becomes larger, heavier and bulkier

Engineering Contradiction:

Improvefield-of-viewVSAvoidsystem size

Core Design Contradiction:

Illumination intensityVSVolume of moving object

Solution Approach 1:

The patent merges multiple optical functions (collimating lens, combiner, imaging lens) into a single substrate-guided optical element. The light guide substrate integrates the collimating function through its geometry and the combiner function through the reflecting surface, eliminating the need for separate free-space optical components and reducing overall system volume while maintaining wide field-of-view capability

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent transitions from conventional free-space optical paths to substrate-guided light propagation, utilizing the third dimension (depth within the substrate) to guide light. This dimensional change allows compact integration of optical functions within the substrate thickness, enabling wide field-of-view without increasing lateral system dimensions

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Volume of moving object

If compact optical solutions are implemented to reduce system size, then the system becomes more compact, but the eye-motion-box becomes very small (less than 8 mm)

Engineering Contradiction:

Improvesystem compactnessVSAvoideye-motion-box

Core Design Contradiction:

Volume of moving objectVSEase of operation

Solution Approach 1:

The patent applies local quality by creating a specifically optimized exit pupil region on the substrate surface. The reflecting surface geometry is locally tailored to expand the eye-motion-box area at the exit location, providing sufficient pupil motion space (greater than 8 mm) while maintaining overall system compactness through the substrate-guided light path

Inventive Principle:

Principle #3Local quality

3Adaptability or versatility

If optical elements are attached to external surfaces of the light guide, then additional optical functions are added, but total internal reflection is degraded

Engineering Contradiction:

Improveoptical element attachmentVSAvoidtotal internal reflection

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent introduces an intermediary layer (such as a low refractive index coating or air gap) between the attached optical element and the light guide substrate external surface. This intermediary maintains the refractive index contrast necessary for total internal reflection while allowing mechanical attachment and integration of additional optical elements, thus preserving reflection efficiency while enabling system versatility

Inventive Principle:

Principle #24Intermediary (Mediator)

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 LOE provides a wide field-of-view with large eye-motion-box, achieving high-quality images and accommodating large eye movements, while being significantly more compact and manufacturable than state-of-the-art solutions, suitable for various imaging applications including portable devices.

Implementation Method 1

The main physical principle of the LOE's operation is that light waves are trapped inside the substrate by total internal reflections from the external surfaces of the LOE

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 2

it is required to add at the external surfaces an angular sensitive reflective mechanism that will substantially reflect the entire light waves which are coupled inside the LOE and impinge on the surfaces at oblique angles, and substantially transmit the light waves which impinge on the surfaces close to a normal incidence

Methodology Applied

Scientific EffectAngular sensitive reflection: Reflection

Data Source

PatentUS11543661B2Compact head-mounted display system protected by a hyperfine structure

Publication Date: 2023.01.03 LUMUS LTD

AI summary

There is provided an optical system, including a light-transmitting substrate (20) having at least two external major surfaces and edges, an optical element for coupling light waves into the substrate (20) by internal reflection, at least one partially reflecting surface located in the substrate (20), for coupling light waves out of the substrate (20), at least one transparent air gap film (110) including a base (112) and a hyperfine structure (111) defining a relief formation, constructed on the base, wherein the air gap film is attached to one of the major surfaces of the substrate (20), with the relief formation facing the substrate (20) defining an interface plane (58), so that the light waves coupled inside the substrate (20) are substantially totally reflected from the interface plane (58).