Liquid Crystal Waveguide Extraction for Directional Guided Light

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Solution Overview

Problem

Existing active extraction structures for guided modes in integrated waveguides suffer from high losses and lack of directivity due to unnecessary or parasitic diffraction orders, leading to bulky and inefficient micro-displays.

Innovation Solution

A structure comprising a support substrate, a main waveguide, an intermediate waveguide with a liquid crystal core, and electrodes that switch the refractive index to control evanescent coupling, combined with a reflective surface to direct the extracted light efficiently in a single angular direction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If active extraction structures are used to enable controllable light extraction, then the directivity of extracted light can be improved, but losses increase due to parasitic diffraction orders

Engineering Contradiction:

Improvedirectivity of extracted lightVSAvoidlosses due to parasitic diffraction orders

Core Design Contradiction:

Illumination intensityVSLoss of energy

Solution Approach 1:

An intermediate waveguide is introduced between the main waveguide and the output medium. This intermediate waveguide acts as a mediator that receives the guided mode from the main waveguide and couples it to a directional output mode, thereby improving directivity while minimizing parasitic diffraction losses through controlled evanescent coupling.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The extraction structure is divided into distinct functional segments: a main waveguide for guiding the input mode, an intermediate waveguide for mode transformation, and a reflective surface for directional output. This segmentation allows each component to be optimized for its specific function, reducing overall losses while maintaining high directivity.

Inventive Principle:

Principle #1Segmentation

2Device complexity

If conventional diffraction gratings are used for light extraction, then the structure is simple, but the extraction efficiency is fixed and cannot be controlled

Engineering Contradiction:

Improvestructural simplicityVSAvoidcontrollability of extraction efficiency

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The extraction structure incorporates liquid crystal material in the intermediate waveguide that can dynamically change its refractive index in response to applied voltage. This dynamic property enables real-time control of the evanescent coupling between waveguides, allowing the extraction efficiency to be adjusted from fully confined to fully extracted states, thereby achieving adaptability while maintaining reasonable structural simplicity.

Inventive Principle:

Principle #15Dynamics

3Illumination intensity

If the guided mode is fully extracted from the waveguide, then the light intensity is maximized, but the micro-display becomes bulky

Engineering Contradiction:

Improvelight intensityVSAvoidsize of micro-display

Core Design Contradiction:

Illumination intensityVSVolume of moving object

Solution Approach 1:

The intermediate waveguide extends in the vertical dimension above the main waveguide, utilizing the third dimension for mode transformation. This vertical arrangement allows the coupling and extraction processes to occur in a compact footprint, maximizing light intensity extraction while minimizing the horizontal volume of the micro-display device.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 achieves low-loss, high-directivity light extraction, resulting in brighter and more compact micro-displays.

Implementation Method 1

a first electrode and a second electrode, arranged in relation to the core of the intermediate waveguide so as to switch, in a coupling portion of the core of the intermediate waveguide, a refractive index of the liquid crystal... the guided mode, when it is present, is at least partially coupled, by evanescent coupling of the main waveguide to the coupling portion

Methodology Applied

Scientific EffectEvanescent coupling:

Implementation Method 2

switch, in a coupling portion of the core of the intermediate waveguide, a refractive index of the liquid crystal, according to the polarization direction, from a first level to a second level, when a variation of an electrical potential difference is applied

Methodology Applied

Scientific EffectLiquid crystal refractive index switching: Liquid Crystals

Implementation Method 3

a flat surface facing the output face, reflective at the wavelength λ, making a non-zero angle with the upper face of the support substrate

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS20260072210A1Structure for extracting a guided mode

Publication Date: 2026.03.12 COMMISSARIAT A LENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES

AI summary

A structure for extracting a guided mode of wavelength λ, linearly polarized, including: a main waveguide capable of guiding the guided mode; a liquid crystal intermediate waveguide capable of guiding a coupled mode, extending parallel to the upper face of a substrate; a flat reflective surface facing an output face of the intermediate waveguide, making a non-zero angle with the substrate; first and second electrodes arranged in relation to the core of the intermediate waveguide so as to switch a refractive index of the liquid crystal from a first level to a second level, when a variation of an electrical potential difference is applied between the first and second electrodes. The guided mode is coupled by coupled mode evanescent coupling only when the refractive index of the liquid crystal is equal to the second level.