GRIN Waveguide Lateral Coupler for Low-Loss Fiber Alignment

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Solution Overview

Problem

Efficient coupling between photonics integrated circuits (PICs) waveguides and external optical fibers is challenging due to modal mismatch, particularly when the optical fiber is not perpendicular to the waveguide, leading to significant beam power loss in current grating coupling methods.

Innovation Solution

A gradient-index (GRIN) waveguide lateral coupler with a non-constant refractive index profile and a dielectric or metallic mirror is used to refract the beam perpendicular to the waveguide's direction of propagation, allowing for lateral coupling via a surface parallel to the propagation direction, manufactured using gray-scale lithography or sub-wavelength gratings.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If grating couplings are used to couple out-of-plane optical fibers to PIC waveguides, then coupling is achieved, but significant beam power loss occurs and design/manufacturing becomes difficult

Engineering Contradiction:

Improveease of manufactureVSAvoidbeam power loss

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The patent changes the refractive index parameter by introducing a gradient-index (GRIN) profile in the lateral coupling region. This continuous variation of the refractive index enables smooth mode transformation between the waveguide mode and the free-space mode, significantly reducing beam power loss while simplifying the coupling design compared to traditional grating couplings

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The GRIN lateral coupler acts as an intermediary structure between the PIC waveguide and the external optical fiber. It provides a transition region with a graded refractive index profile that mediates the mode matching between the guided mode in the waveguide and the radiative mode in the fiber, achieving efficient coupling without the complex grating structures

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If grating couplings are used to couple out-of-plane optical fibers to PIC waveguides, then coupling is achieved, but design and manufacturing become difficult

Engineering Contradiction:

Improvecoupling capabilityVSAvoiddesign complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

By changing the refractive index parameter through a gradient profile rather than using periodic grating structures, the patent achieves coupling capability with much simpler design and manufacturing requirements. The GRIN profile can be realized through standard semiconductor fabrication processes like ion implantation or diffusion, avoiding the complex multi-step lithography and etching required for grating couplings

Inventive Principle:

Principle #35Parameter changes

3Productivity

If a non-constant refractive index profile is used in the active region, then lateral coupling efficiency is improved, but manufacturing precision requirements increase

Engineering Contradiction:

Improvecoupling efficiencyVSAvoidrefractive index profile precision

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent uses parameter changes (refractive index gradient) to improve coupling efficiency while relying on established semiconductor fabrication techniques such as ion implantation, thermal diffusion, or selective epitaxy to create the GRIN profile. These standard processes provide sufficient manufacturing precision without requiring exotic or ultra-precise fabrication methods

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The non-constant refractive index profile is applied locally only in the lateral coupling region of the waveguide, while the rest of the waveguide maintains a constant refractive index. This localized approach minimizes the impact on overall manufacturing precision requirements while achieving the desired coupling efficiency improvement in the specific region where it is needed

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 reduces beam power loss and enables efficient coupling of PIC waveguides to external optical fibers, maintaining low aberration and distortion while allowing the beam to exit the waveguide via a surface parallel to its propagation direction, thus improving coupling efficiency.

Implementation Method 1

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 2

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS10473857B2Gradient-index waveguide lateral coupler having an active region with an index of refraction that is non-constant laterally

Publication Date: 2019.11.12 MELLANOX TECHNOLOGIES LTD(IL)

AI summary

A waveguide having a gradient-index (GRIN) waveguide lateral coupler is provided. In an example embodiment, the waveguide comprises an active region. The refractive index profile of the active region is non-constant.