Optical 2D Spot-Size Conversion via Mode Rotation

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Solution Overview

Problem

There is a lack of an effective solution for coupling light between arrays of thin and thick waveguides, which requires wide transmission spectrum, polarization-independent operation, low insertion loss, small size, and low manufacturing and assembly costs.

Innovation Solution

The optical assembly achieves horizontal and vertical spot-size conversion by combining two horizontal spot-size conversions and rotating the mode between the waveguides, using up-reflecting waveguide mirrors or rotating the waveguide chips.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a horizontal spot-size converter is used to couple light between waveguides of different widths, then the coupling efficiency is improved, but the device complexity increases due to the need for additional conversion structures

Engineering Contradiction:

Improvecoupling efficiencyVSAvoidconverter structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent combines two horizontal spot-size converters with a mode rotation element into a single integrated 2D spot-size converter structure. This merging approach achieves both horizontal and vertical spot-size conversion simultaneously, improving coupling efficiency while avoiding the complexity of separate converter structures.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent introduces mode rotation as a dimensional transformation technique, rotating the optical mode by 90 degrees between the two horizontal converters. This allows the first converter to address width mismatch and the second converter to address thickness mismatch, achieving 2D spot-size conversion through dimensional manipulation.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Manufacturing precision

If separate vertical and horizontal spot-size converters are used, then the spot-size conversion accuracy is improved, but the manufacturing cost increases due to multiple processing steps

Engineering Contradiction:

Improvespot-size conversion accuracyVSAvoidmanufacturing cost

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent merges separate vertical and horizontal spot-size conversion functions into a single integrated converter structure fabricated in one waveguide layer. This eliminates the need for multiple processing steps and separate converter chips, reducing manufacturing cost while maintaining spot-size conversion accuracy through the combined action of two horizontal converters and mode rotation.

Inventive Principle:

Principle #5Merging (Combining)

3Reliability

If a thick waveguide layer is used to achieve vertical spot-size conversion, then the coupling between waveguides is improved, but the device complexity increases due to the need for wafer-level processing

Engineering Contradiction:

Improvewaveguide couplingVSAvoidprocessing technique complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Instead of using vertical tapering or thick waveguide layers to achieve vertical spot-size conversion, the patent inverts the approach by using two horizontal spot-size converters with mode rotation. This unconventional method achieves the same coupling improvement without requiring complex wafer-level processing or thick waveguide fabrication.

Inventive Principle:

Principle #13The other way round (Inversion)

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 solution enables efficient coupling of light between thin and thick waveguides with low loss and polarization independence, while maintaining a compact size and reducing manufacturing costs.

Implementation Method 1

up-reflecting waveguide mirrors

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Data Source

PatentEP4078256B1Optical 2d spot-size conversion

Publication Date: 2025.03.05 TEKNOLOGIAN TUTKIMUSKESKUS VTT OY

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AI summary

An optical assembly for realizing horizontal and vertical spot-size conversion to couple light from a thin waveguide to a thick waveguide is disclosed. The assembly comprises at least one first thin waveguide with a first section having a first optical mode field and a horizontal spot-size expansion section providing spot-size conversion for a first horizontal dimension of said first optical mode field of a light beam propagating in said first waveguide, and at least one second thick waveguide with a second section having a second optical mode field and a horizontal spot-size reduction section providing spot-size conversion for a second horizontal dimension of said second optical mode field of a light beam propagating in said second waveguide. The expanded end of said first waveguide is aligned and rotated to interface with the reduced end of said second waveguide, so that the mode fields in said first and second waveguides are rotated 90 degrees with respect to each other, whereby the spot size of a light beam so coupled between the first and second waveguides is expanded or shrunk in both transverse dimensions, depending on the direction of the light beam.