Optical Waveguide Transition With Mode Removal for Low TM Loss

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Solution Overview

Problem

Conventional inter-waveguide transition structures in optical devices experience significant optical loss and mode conversion due to discontinuous cross-sectional portions, particularly in the TM mode, leading to increased scattering and interaction between different waveguides with mismatched refractive indices.

Innovation Solution

The optical device employs a transition unit where the second waveguide acts as a single mode waveguide at the input and multi-mode waveguide at the output, with a specific refractive index inversion, and a removing unit to eliminate higher-order modes, using overlapping waveguides with controlled refractive index differences to minimize scattering and loss.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional inter-waveguide transition structure with discontinuous cross-sectional portions is used, then waveguide width can be gradually changed for adiabatic transition, but optical loss increases due to light scattering at discontinuous portions

Engineering Contradiction:

Improvetransition efficiencyVSAvoidoptical loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The transition structure is divided into multiple sections: a first waveguide section, a second waveguide section with different material, and a third waveguide section. This segmentation allows gradual material transition while maintaining continuous waveguide geometry, reducing scattering loss at discontinuous portions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces an intermediate waveguide structure that bridges between the first and third waveguide sections. This intermediate structure acts as a mediator that enables gradual refractive index transition, allowing adiabatic mode transformation without abrupt discontinuities that cause scattering.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If waveguides with different materials are used for different optical components, then characteristic improvement is achieved, but refractive index mismatch causes increased scattering and optical loss

Engineering Contradiction:

Improveoptical component performanceVSAvoidscattering and optical loss

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent gradually changes the refractive index parameter along the waveguide transition path by using different material compositions in sequential sections. This parameter change enables smooth transition between waveguides with different material properties, minimizing scattering caused by abrupt refractive index differences.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The transition structure employs composite material sections where different waveguide materials are combined in a controlled sequence. This composite approach allows optimization of light confinement in each section while managing the overall refractive index profile to reduce scattering at material interfaces.

Inventive Principle:

Principle #40Composite materials

3Adaptability or versatility

If TM mode light is transmitted through indirect transition between different waveguides, then polarization transmission capability is achieved, but optical loss is increased due to weaker light confinement

Engineering Contradiction:

Improvepolarization transmission capabilityVSAvoidoptical loss in TM mode

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The patent applies different waveguide structures and material compositions to different spatial sections of the transition path. The local waveguide geometry and material properties are optimized for each section to provide adequate light confinement for TM mode, compensating for the inherently weaker confinement in vertical polarization.

Inventive Principle:

Principle #3Local quality

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 approach effectively reduces optical loss and mode conversion by minimizing light scattering and interaction between waveguides, maintaining signal integrity and reducing interference.

Implementation Method 1

light propagates by indirect transition between different waveguides

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 2

transitioning light scatters caused by the discontinuous cross-sectional portions

Methodology Applied

Scientific EffectScattering: Scattering

Data Source

PatentUS12487400B2Optical device, substrate type optical waveguide element, optical communication apparatus, and inter-waveguide transition method

Publication Date: 2025.12.02 FUJITSU OPTICAL COMPONENTS LTD

AI summary

An optical device includes a transition unit in which a first waveguide and a second waveguide are disposed in an overlapped manner such that a magnitude relationship of an effective refractive index between the vertical modes propagating the first waveguide and the vertical modes propagating the second waveguide is inverted at the positions of input and output. The transition unit allows, at the input, the second waveguide to be a single mode waveguide and allows, at the output, the second waveguide to be a multi-mode waveguide through which TM0 light in the maximum vertical mode and light in a higher-order mode propagate. The optical device includes a removing unit that allows the second waveguide to be a single mode waveguide through which the TM0 light propagates by removing the light in the higher-order mode from the light received from the transition unit.