Rib Optical Waveguide Reverse Taper for Low-Loss Fiber Coupling

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Solution Overview

Problem

Existing optical waveguide elements face challenges in miniaturization and high insertion loss when coupled with optical fibers due to limitations in mode field diameter (MFD) and bending radius, particularly with materials like LiNbO3, which are difficult to thin and integrate with optical fibers effectively.

Innovation Solution

An optical waveguide element with a rib structure and reinforcing substrate, featuring a reverse tapered design, a high refractive index structure covering the tapered portion, and a low refractive index coating layer, which facilitates MFD adjustment and reduces multimode propagation, enabling efficient coupling with optical fibers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If the optical waveguide is thinned to reduce MFD for miniaturization, then the bending radius can be reduced and device size can be miniaturized, but the mechanical strength and structural stability deteriorate

Engineering Contradiction:

Improvedevice sizeVSAvoidmechanical strength

Core Design Contradiction:

Volume of moving objectVSStrength

Solution Approach 1:

The patent embeds the thinned optical waveguide (rib structure) within a supporting substrate, creating a nested configuration where the weak thinned waveguide is protected by the stronger substrate structure, allowing miniaturization while maintaining mechanical strength

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The patent uses composite structures combining the optical waveguide material with the supporting substrate, creating a composite system that provides both the optical functionality of the thinned waveguide and the mechanical strength of the substrate

Inventive Principle:

Principle #40Composite materials

2Volume of moving object

If the optical waveguide MFD is reduced to below 3 μm for miniaturization, then the device can be miniaturized, but the coupling loss with optical fiber increases

Engineering Contradiction:

Improvedevice sizeVSAvoidcoupling loss

Core Design Contradiction:

Volume of moving objectVSLoss of energy

Solution Approach 1:

The patent employs a tapered waveguide structure where the width dynamically changes along the propagation direction, transitioning from a narrow section (for miniaturization) to a wider section (for better coupling), allowing the system to adapt its effective MFD at different positions

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the geometric parameters of the waveguide, specifically the width, along its length to create a tapered profile that transforms the mode field diameter from a small value at the narrow end to a larger value at the wide end, optimizing both miniaturization and coupling

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If the optical waveguide width is increased to reduce coupling loss, then the coupling efficiency improves, but multimode propagation occurs and single-mode operation is lost

Engineering Contradiction:

Improvecoupling lossVSAvoidsingle-mode propagation

Core Design Contradiction:

Loss of energyVSStability of the object's composition

Solution Approach 1:

The patent divides the waveguide into multiple sections with different width characteristics - a narrow section for maintaining single-mode operation and a wider tapered section for reducing coupling loss, allowing each section to perform its specific function optimally

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a spatial dimension variation along the waveguide length, using a tapered profile that changes the width in the propagation direction, thereby solving the contradiction between narrow width (for single-mode) and wide width (for coupling)

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 minimizes insertion loss and supports miniaturization by maintaining single-mode propagation while expanding the MFD, enhancing mechanical strength, and facilitating alignment with optical fibers.

Implementation Method 1

a structure made of a material having a higher refractive index than a material constituting the reinforcing substrate is provided so as to cover the tapered portion

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 2

a rib optical waveguide that is made of a material having an electro-optic effect

Methodology Applied

Scientific EffectElectro-optic effect: Electro-Optic Effects

Data Source

PatentUS12422628B2Optical waveguide element, and optical modulation device and optical transmission apparatus using same

Publication Date: 2025.09.23 SUMITOMO OSAKA CEMENT CO LTD

AI summary

An optical waveguide element that suppresses insertion loss related to coupling to an optical fiber or the like while miniaturizing the optical waveguide element is provided. There is provided an optical waveguide element including: a rib optical waveguide (10) that is made of a material (1) having an electro-optic effect; and the reinforcing substrate (2) that supports the optical waveguide, in which one end of the optical waveguide forms a tapered portion (11) of which a width narrows toward an end surface of the reinforcing substrate, a structure (3) made of a material having a higher refractive index than a material constituting the reinforcing substrate is provided so as to cover the tapered portion, and a coating layer (4) made of a material having a lower refractive index than the material constituting the structure is disposed so as to cover the structure.