Lithium Niobate Optical Coupler for Single-Mode RGB Output

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Solution Overview

Problem

Current optical couplers for retinal scanning displays in XR technologies face challenges in coupling RGB light beams efficiently, leading to complex light control and a lack of miniaturization due to the use of glass-based materials and the absence of lithium niobate film configurations, which hinder the output of light in single mode.

Innovation Solution

An optical coupler design incorporating a lithium niobate film with high-order mode removal portions and multimode-interference-type optical coupling portions, allowing for the connection or integration with an optical modulator, and enabling the output of RGB light in single mode by selectively routing each wavelength through appropriate high-order mode removal portions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If glass-based materials are used for optical couplers, then stability is improved, but device size cannot be reduced (miniaturization fails)

Engineering Contradiction:

ImprovestabilityVSAvoiddevice size

Core Design Contradiction:

Stability of the object's compositionVSVolume of moving object

Solution Approach 1:

The patent changes the material parameter from glass-based materials to lithium niobate film, which has different optical properties including higher refractive index. This material substitution enables both miniaturization (reduced device size) and maintains stability, resolving the technical contradiction by finding a material that offers superior characteristics for the intended application.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If optical waveguides are not coupled, then manufacturing is simpler, but light control becomes complicated due to different optical axes for each wavelength

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidlight control complexity

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

The patent merges multiple optical waveguides carrying different wavelengths (RGB) into a single coupled waveguide structure. This coupling aligns the optical axes for all wavelengths, simplifying light control while maintaining manufacturing feasibility through integrated waveguide design.

Inventive Principle:

Principle #5Merging (Combining)

3Productivity

If multimode light is output, then coupling efficiency may be higher, but mode dispersion occurs and propagation loss increases

Engineering Contradiction:

Improvecoupling efficiencyVSAvoidpropagation loss

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent extracts and removes high-order modes from the optical signal, allowing only the fundamental mode to propagate. This is achieved through careful waveguide design and mode filtering, eliminating mode dispersion and reducing propagation loss while maintaining efficient coupling through the fundamental mode.

Inventive Principle:

Principle #2Taking out (Extraction)

4Strength

If lithium niobate substrate with large Δn is used, then coupling strength increases, but coupling length becomes long and miniaturization cannot be performed

Engineering Contradiction:

Improvecoupling strengthVSAvoidcoupling length

Core Design Contradiction:

StrengthVSLength of stationary object

Solution Approach 1:

The patent transitions from bulk lithium niobate substrate to thin-film lithium niobate structure, changing the dimensional configuration. This thin-film approach reduces the coupling length required while maintaining the beneficial large Δn property for strong coupling, enabling miniaturization without sacrificing coupling strength.

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 enables efficient light coupling and miniaturization, reducing light propagation loss and increasing speed by ensuring single-mode output, suitable for glasses-type terminals, and addressing the complexity in light control.

Implementation Method 1

a one- or more-stage optical coupling portion to which a light-input-side optical waveguide and a light-output-side optical waveguide are connected

Methodology Applied

Scientific EffectMultimode interference: Interference

Implementation Method 2

at least one high-order mode removal portion for visible light provided to remove a high mode with respect to each of the plurality of visible light beams

Methodology Applied

Scientific EffectMode filtering: Filter (optical)

Data Source

PatentUS20240329323A1Optical coupler, optical coupling member, visible light source module, and optical engine

Publication Date: 2024.10.03 TDK CORP

AI summary

This optical coupler includes a plurality of light input ports to which a plurality of visible light beams can be input, a light output port capable of coupling all of the plurality of visible light beams and outputting coupled light, an optical coupling portion to which a light-input-side optical waveguide and a light-output-side optical waveguide are connected, and at least one high-order mode removal portion provided to remove a high mode with respect to each of the plurality of visible light beams. The optical coupling portion and each high-order mode removal portion are arranged so that each of the plurality of visible light beams passes through only a high-order mode removal portion for visible light or passes through only the high-order mode removal portion for the visible light and a high-order mode removal portion for visible light having a shorter wavelength than the visible light.