Plastic Reflective Waveguide Molding With Zero-Draft Parallel Mirrors

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Solution Overview

Problem

Conventional reflective optical elements (ROEs) in mixed-reality computing devices, such as HMD devices, are costly and prone to damage due to the use of stacked glass plates, which are heavy and require complex fabrication processes.

Innovation Solution

A plastic reflective waveguide is manufactured using a soft transfer stamp with zero degree draft angle, enabling injection molding of parallel mirrored surfaces through a multi-stage process involving a thermosetting material and optical grade thermoplastic, allowing for cost-effective and durable ROEs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If stacked glass plates are used for reflective optical elements, then optical performance is maintained, but weight increases and damage resistance decreases

Engineering Contradiction:

Improvedamage resistanceVSAvoidweight

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The patent changes the material parameter from glass to plastic (polymer), fundamentally altering the density and mechanical properties. This material substitution reduces weight while maintaining the optical functionality through carefully controlled manufacturing parameters that ensure parallel surface accuracy

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention uses composite construction by embedding mirror elements within a plastic waveguide matrix. This combines the optical reflectivity of mirrored surfaces with the lightweight, damage-resistant properties of plastic, creating a hybrid structure that achieves both optical performance and mechanical durability

Inventive Principle:

Principle #40Composite materials

2Reliability

If stacked glass plates are used for reflective optical elements, then optical performance is maintained, but manufacturing cost increases

Engineering Contradiction:

Improvedamage resistanceVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention replaces expensive, fragile glass components with cheaper plastic alternatives that can be manufactured through injection molding. The plastic material and molding process reduce raw material costs and manufacturing complexity compared to precision glass stacking and alignment

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Manufacturing precision

If zero degree draft angle is used in injection molding, then parallelism of mirrored surfaces is achieved, but mold design complexity increases

Engineering Contradiction:

ImproveparallelismVSAvoidmold design

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent introduces a draft angle compensation mechanism as an intermediary element in the mold design. This compensation feature allows the mold to produce parts with zero draft angle (for parallelism) while the mold itself incorporates the necessary angular elements to enable part release, separating the part geometry requirements from the mold geometry requirements

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention segments the mold design into distinct functional zones: the cavity that defines the zero-draft parallel surfaces, and the ejection mechanism that incorporates draft angles for release. This segmentation allows each zone to optimize for its specific function without compromise

Inventive Principle:

Principle #1Segmentation

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 provides lightweight, damage-resistant, and cost-effective ROEs with maintained parallelism, suitable for various shapes and form factors, enhancing user comfort and reducing manufacturing costs compared to conventional glass-based designs.

Implementation Method 1

Use of a soft transfer stamp supports a zero degree draft angle in injection-molded parts which enables fabrication of parallel partial mirrors

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

The base part is coated with a half-mirror coating

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 3

plastic reflective waveguide apparatus and associated methods of manufacturing that include a cascaded array of parallel partially-mirrored elements embedded in a plastic waveguide

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Data Source

PatentUS12498567B2Plastic reflective waveguide manufacturing

Publication Date: 2025.12.16 MICROSOFT TECHNOLOGY LICENSING LLC

AI summary

A plastic reflective waveguide is manufactured using a soft transfer stamp formed in a first mold using a liquid injection molding process to provide the stamp with parallel wall surfaces having a zero degree draft angle. The soft transfer stamp is placed as an insert in a second mold utilized in a multi-stage thermoplastic injection molding process. A first thermoplastic injection molding stage molds a base part of the plastic reflective waveguide having parallel wall surfaces with a zero degree draft angle. The soft transfer stamp is removed from the second mold and a partially-reflective coating is applied to the base part. A second thermoplastic injection molding stage is utilized to create a secondary part of the plastic reflective waveguide. The raw plastic reflective waveguide is ejected from the second mold and subjected to additional manufacturing processes to realize a finished part meeting design requirements for size and form factor.