Optical Element Mode Converter for Polarization

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Solution Overview

Problem

Existing optical waveguide elements do not effectively convert the polarization mode of visible light from TM0 mode to TE0 mode.

Innovation Solution

An optical element comprising a substrate with a core layer made of material with electro-optic effect, featuring a mode converter with a first waveguide having a taper section and a first line section, and a second waveguide with a second line section, forming an asymmetrical directional coupler to convert visible light from TM0 to TE0 mode.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional optical waveguide element is used, then the structure is simple, but the polarization mode conversion from TM0 to TE0 for visible light is not achieved

Engineering Contradiction:

Improvepolarization mode conversion capabilityVSAvoidwaveguide structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The mode converter is divided into distinct functional sections: a taper section for initial mode transformation and an asymmetrical directional coupler section for polarization conversion. This segmentation allows each section to perform its specific function optimally, achieving TM0 to TE0 conversion while maintaining manageable structural complexity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The asymmetrical directional coupler employs asymmetric waveguide structures with different effective refractive indices for TE0 and TE1 modes. This asymmetry is crucial for achieving efficient polarization mode conversion from TM0 to TE0, as it creates the necessary phase differences and coupling conditions for the transformation

Inventive Principle:

Principle #4Asymmetry

2Productivity

If the waveguide structure is made more complex to achieve TM0 to TE0 conversion, then the conversion efficiency improves, but the manufacturing precision requirements increase

Engineering Contradiction:

Improveconversion efficiencyVSAvoiddimensional control precision

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The design utilizes changes in effective refractive index parameters along the waveguide structure. By carefully controlling the dimensional parameters of the taper section and asymmetrical directional coupler, the effective refractive indices are engineered to achieve the necessary conditions for efficient TM0 to TE0 conversion, balancing performance with manufacturability

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If existing optical waveguide elements are used, then the manufacturing process is simple, but they do not effectively convert visible light polarization mode

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidpolarization conversion effectiveness

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The mode converter structure is designed to handle visible light specifically, with the taper section and asymmetrical directional coupler configured for the wavelength range of visible light. This universal design approach allows the same structure to effectively convert polarization modes for various visible light applications while maintaining ease of manufacture

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

Achieves efficient conversion of visible light polarization from TM0 mode to TE0 mode, improving the performance of optical elements in devices such as laser modules, retinal projection devices, and near-eye wearable devices.

Implementation Method 1

a core layer provided on the main surface and made of a material having an electro-optic effect

Methodology Applied

Scientific EffectElectro-optic effect: Electro-Optic Effects

Implementation Method 2

a taper section including a first incident end on which the visible light is incident and a first emission end from which the visible light is emitted, the taper section having a length in a second direction along the main surface and intersecting the first direction that increases from a first length at the first incident end to a second length toward the first emission end

Methodology Applied

Scientific EffectWaveguide mode conversion: Waveguide (optics)

Implementation Method 3

The first line section and the second line section constitute an asymmetrical directional coupler

Methodology Applied

Scientific EffectOptical coupling: Waveguide (optics)

Data Source

PatentUS20250189832A1Optical element, laser module, retinal projection device, and near-eye wearable device

Publication Date: 2025.06.12 TDK CORP

AI summary

A mode converter of an optical element includes a taper section having a length in a second direction increases from a first length, at which a first effective refractive index of a TM0 mode is higher than a second effective refractive index of a TE1 mode, to a second length, at which the first effective refractive index is lower than the second effective refractive index. Lengths of a first line section and a second line section in the second direction are set such that a magnitude relationship between the second effective refractive index in the first line section and a third effective refractive index of the TE0 mode in the second line section at a position is inverted to a magnitude relationship between the second effective refractive index in the first line section and the third effective refractive index in the second line section at a second incident end.