Tapered Waveguide Coupling for Misalignment Tolerance

Solution Overview

Problem

Current fiber-to-waveguide coupling technologies, such as grating couplers and butt coupling, require active alignment to minimize loss due to misalignment, posing challenges for the mass production and commercialization of silicon photonic devices.

Innovation Solution

A passive alignment technique using a D-shape optical fiber and a tapered high index contrast rectangular waveguide, allowing for evanescent coupling with high tolerance to z-axis and x-axis misalignment, and a polymer bridge with a ramped portion for efficient light transfer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If grating couplers or butt coupling are used for fiber-to-waveguide coupling, then light coupling can be achieved, but active alignment is required to minimize loss due to misalignment

Engineering Contradiction:

Improvecoupling lossVSAvoidalignment complexity

Core Design Contradiction:

Loss of energyVSEase of operation

Solution Approach 1:

The waveguide is pre-tapered during fabrication to create a gradual width transition. This preliminary structural preparation enables the waveguide to automatically adapt to fiber positioning variations, eliminating the need for active alignment during packaging while maintaining low coupling loss through the adiabatic mode transformation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The waveguide width is gradually changed along the propagation direction, transforming the effective refractive index from lower than the fiber's effective index to higher than it. This parameter change enables adiabatic coupling that is tolerant to misalignment while maintaining efficient energy transfer from fiber to waveguide.

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If active alignment is used to optimize light coupling, then coupling efficiency is improved, but packaging complexity and production difficulty increase

Engineering Contradiction:

Improvecoupling efficiencyVSAvoidpackaging complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The tapered waveguide structure serves itself by automatically compensating for misalignment through its gradual width variation. The adiabatic coupling mechanism inherently tolerates positioning variations, allowing simple pick-and-place packaging without complex alignment systems or feedback loops, thus reducing packaging complexity while maintaining high coupling efficiency.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The waveguide is pre-tapered during fabrication to create a gradual width transition. This preliminary structural preparation enables the waveguide to automatically adapt to fiber positioning variations, eliminating the need for active alignment during packaging while maintaining low coupling loss through the adiabatic mode transformation.

Inventive Principle:

Principle #10Preliminary action

3Ease of manufacture

If direct physical abutment of fiber with waveguide is used, then coupling is achieved, but mode mismatch results between integrated waveguide and optical fiber

Engineering Contradiction:

Improvecoupling implementationVSAvoidmode mismatch loss

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The waveguide width is gradually changed along the propagation direction, transforming the effective refractive index from lower than the fiber's effective index to higher than it. This parameter change enables adiabatic coupling that is tolerant to misalignment while maintaining efficient energy transfer from fiber to waveguide.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The waveguide structure is made dynamic through its gradual width variation, allowing the mode field to continuously adapt during propagation. This dynamic transformation enables smooth mode matching between the fiber and waveguide, reducing mode mismatch loss while maintaining ease of manufacture through a single fabrication process.

Inventive Principle:

Principle #15Dynamics

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

Enables robust packaging and high-efficiency light coupling with reduced need for feedback loops, allowing for simple pick and place approaches and high tolerance to misalignment, making it suitable for mass production of photonic integrated circuits.

Implementation Method 1

a D-shape optical fiber can be placed directly on top of a high index contrast rectangular waveguide and they can be evanescently coupled with each other

Methodology Applied

Scientific EffectEvanescent coupling: Total Internal Reflection

Implementation Method 2

The disclosed techniques provide for a slow adiabatic transition of the super-mode formed by the coupled waveguide and fiber which can results in the energy transfer from the fiber to the waveguide

Methodology Applied

Scientific EffectAdiabatic transition: Adiabatic Heating

Data Source

PatentUS10746935B2Fiber-to-waveguide coupling with high alignment tolerance

Publication Date: 2020.08.18 THE TRUSTEES OF COLUMBIA UNIV IN THE CITY OF NEW YORK

AI summary

An optical coupling apparatus comprising a substrate having a trench formed therein, the trench having a width measured between two opposing walls that define a portion of the trench; and a waveguide disposed on or in the substrate, the waveguide having a width that tapers along an axis of light propagation.