Optical Integrated Element Splicing Loss Reduction

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Solution Overview

Problem

The integration of semiconductor optical amplifiers and phase modulators on the same substrate leads to increased splicing loss due to mismatched waveguide layer thicknesses, causing reflection and adverse effects on optical integrated element characteristics, and complicates the fabrication process.

Innovation Solution

An optical integrated element is designed with a substrate having a first waveguide region and an active region, where the waveguide layers are optimized to minimize splicing loss by ensuring the second core layer and quantum well layer are close within the mode field range, and the first core layer is butt-jointed to them, allowing for adjusted spot sizes and reduced optical loss.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If waveguide layer thicknesses are optimized for each element's characteristics, then element performance is improved, but splicing loss increases at connection portions

Engineering Contradiction:

Improveelement performanceVSAvoidsplicing loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

A spot size conversion region is introduced as an intermediary between waveguide regions with different thicknesses. This conversion region gradually transforms the mode field diameter from one size to another, enabling efficient optical coupling between elements with different waveguide thicknesses while maintaining optimal performance characteristics for each element

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The waveguide layer thickness is varied continuously in the spot size conversion region to transform the mode field diameter. By changing the geometric parameter (thickness) gradually rather than abruptly, the patent achieves adiabatic mode field transformation that minimizes splicing loss while allowing different elements to have their own optimized thicknesses

Inventive Principle:

Principle #35Parameter changes

2Reliability

If waveguide layer thicknesses are optimized for each element, then element characteristics are improved, but reflection increases at connection parts

Engineering Contradiction:

Improveelement characteristicsVSAvoidreflection

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The spot size conversion region acts as a transition intermediary that gradually changes the refractive index profile and mode field characteristics. This gradual transition prevents abrupt refractive index discontinuities at connections, thereby reducing reflection while allowing each element to maintain its optimized waveguide thickness for optimal characteristics

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent addresses the one-dimensional thickness mismatch problem by introducing a spatial transition region where the mode field diameter evolves gradually in the propagation direction. This adds a dimensional aspect to the transition, allowing smooth impedance matching between waveguides of different thicknesses and reducing reflection

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Loss of energy

If spot size conversion region is disposed between waveguide layers of different thicknesses, then splicing loss is reduced, but fabrication process becomes difficult

Engineering Contradiction:

Improvesplicing lossVSAvoidfabrication process

Core Design Contradiction:

Loss of energyVSEase of manufacture

Solution Approach 1:

The spot size conversion region is merged with the existing waveguide structure by using the same layer stacking sequence (lower cladding layer, core layer, upper cladding layer) throughout. This integration allows the conversion region to be fabricated using the same epitaxial growth process as the rest of the waveguide, simplifying manufacturing while still achieving the desired mode field transformation

Inventive Principle:

Principle #5Merging (Combining)

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 configuration effectively reduces splicing loss and optical loss due to inter-valence-band absorption, enabling efficient integration of elements with different waveguide layer thicknesses while maintaining optimal performance for both phase modulators and semiconductor optical amplifiers.

Implementation Method 1

a quantum well layer that amplifies light when a current is injected

Methodology Applied

Scientific EffectStimulated emission:

Implementation Method 2

a lower cladding layer, a first core layer having a refractive index higher than the refractive index of the lower cladding layer, and an upper cladding layer having the refractive index lower than the refractive index of the first core layer are sequentially laminated

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Data Source

PatentUS11281029B2Optical integrated element and optical module

Publication Date: 2022.03.22 FURUKAWA ELECTRIC CO LTD

AI summary

An optical integrated element includes: a substrate; a first waveguide region in which a lower cladding layer, a first core layer, and an upper cladding layer are sequentially laminated in this order on the substrate; and an active region in which the lower cladding layer, a second core layer, a quantum well layer that amplifies light when a current is injected, and the upper cladding layer are sequentially laminated on the substrate. Further, the second core layer and the quantum well layer are close to each other within a range of a mode field of light guided in the second core layer, and the first core layer is butt-jointed to the second core layer and the quantum well layer.