MEMS Mirror Angle Doubling via Polarization

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Solution Overview

Problem

Laser projectors used in wearable head-up displays face a trade-off between power conservation and field of view due to the power requirements of scanning mirrors, which are proportional to the square of the maximum angle of articulation, limiting continuous operating time and user experience.

Innovation Solution

Incorporating a polarization beam splitter and quarter-wave plate between the laser light source and scanning MEMS mirror to increase the output angle of reflected laser light by causing it to reflect at least twice, effectively doubling the initial angle of reflection without increasing the maximum angle of mirror articulation, thus reducing power consumption while maintaining a wide field of view.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the maximum angle of mirror articulation is increased to expand the field of view, then the field of view is improved, but the power consumption increases proportionally to the square of the angle

Engineering Contradiction:

Improvefield of viewVSAvoidpower consumption

Core Design Contradiction:

Adaptability or versatilityVSUse of energy by moving object

Solution Approach 1:

A polarization beam splitter is introduced as an intermediary optical element between the laser light source and the scanning MEMS mirror. This beam splitter enables the laser beam to reflect off the mirror at a doubled angle by utilizing polarization state changes, thereby achieving a wider field of view without increasing the mirror's maximum articulation angle and thus maintaining low power consumption.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the polarization state of the laser light using a quarter-wave plate and polarization beam splitter. By converting linearly polarized light to circularly polarized light and back, the system achieves angle doubling through polarization-dependent reflection, effectively changing the optical parameter (output angle) without changing the mechanical parameter (mirror articulation angle).

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If the scanning mirror articulates over a larger angle range to provide wider field of view, then the field of view is improved, but the continuous operating time decreases due to higher power consumption

Engineering Contradiction:

Improvefield of viewVSAvoidcontinuous operating time

Core Design Contradiction:

Adaptability or versatilityVSDuration of action of moving object

Solution Approach 1:

The polarization beam splitter acts as a mediator that enables angle multiplication, allowing the system to achieve a wide field of view with a limited mirror articulation range. This reduces the power consumption of the scanning mirror, thereby extending the continuous operating time of battery-powered wearable devices while maintaining a large field of view.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Use of energy by moving object

If the maximum angle of mirror articulation is reduced to conserve power, then the power consumption is reduced, but the field of view is limited

Engineering Contradiction:

Improvepower consumptionVSAvoidfield of view

Core Design Contradiction:

Use of energy by moving objectVSAdaptability or versatility

Solution Approach 1:

By introducing the polarization beam splitter and quarter-wave plate as intermediary optical elements, the system achieves angle doubling through polarization manipulation. This allows the scanning mirror to operate at a reduced maximum articulation angle (conserving power) while still delivering a wide field of view through the doubled output angle of the laser beam.

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

This configuration reduces the power needed to articulate the scanning mirror by approximately three-quarters, extending the continuous operating time of wearable devices while supporting a large field of view, enhancing user experience.

Implementation Method 1

Methodology Applied

Scientific EffectPolarization: Polarisation

Implementation Method 2

causing it to reflect at least twice, effectively doubling the initial angle of reflection

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS11906738B2Scanning MEMS mirror angle-doubling using polarization

Publication Date: 2024.02.20 GOOGLE LLC

AI summary

Systems and methods for manipulation of the polarization state of light emitted by a laser projector to reduce the angle range of a scanning mirror articulated by a micro-electromechanical system MEMS to reduce power consumption are disclosed. A system includes a light source configured to emit laser light, a scanning mirror, and an angle expander disposed between the light source and the scanning mirror, the angle expander being configured to cause the laser light from the light source to be reflected at least once from the angle expander and at least twice from the scanning mirror.