Optical Package Lens and Index Matching Fluid for DFB-LD to Si PIC Coupling

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Solution Overview

Problem

The coupling efficiency between distributed feedback laser diodes (DFB-LD) and silicon photonic integrated-circuit (Si PIC) edge couplers is limited by mismatched mode sizes, leading to high coupling loss and compatibility issues with QSFP form factors, particularly in data center applications.

Innovation Solution

An optical package is designed with a DFB-LD, Si PIC, single mode fiber or fiber array, a lens, and a spacer or isolator, where the lens minimizes the mismatch between the output spot size of the DFB-LD and the input edge coupler of the Si PIC, and the spacer or isolator is bonded with an index matching fluid to reduce return loss.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a lens is used to couple DFB-LD to Si PIC edge coupler, then coupling efficiency is improved, but return loss increases

Engineering Contradiction:

Improvecoupling efficiencyVSAvoidreturn loss

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent introduces an index matching fluid as an intermediary substance between the lens and the Si PIC edge coupler. This fluid has a refractive index that matches both the lens and the silicon waveguide, creating a gradual transition that reduces reflection and return loss while maintaining the coupling efficiency provided by the lens.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the refractive index parameter by introducing an index matching fluid with a specific refractive index value that bridges the gap between the lens material and the silicon waveguide. This parameter adjustment optimizes the optical interface to minimize reflections and maximize power transfer.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If DFB-LD is directly coupled to Si PIC edge coupler, then device complexity is reduced, but coupling loss increases due to mode size mismatch

Engineering Contradiction:

Improvecoupling structure complexityVSAvoidcoupling loss

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The patent introduces a lens as an intermediary optical component between the DFB-LD and the Si PIC edge coupler. This lens acts as a mode adapter that transforms the Gaussian beam from the laser diode into a mode that better matches the edge coupler's optical mode, thereby reducing coupling loss despite adding a component to the system.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If grating coupler is used in Si PIC, then coupling efficiency with single mode fiber is improved, but spectral bandwidth is limited

Engineering Contradiction:

Improvecoupling efficiencyVSAvoidspectral bandwidth

Core Design Contradiction:

ProductivityVSAdaptability or versatility

Solution Approach 1:

Instead of using a grating coupler that couples light vertically from the fiber to the chip, the patent inverts the approach by using an edge coupler with a lens system that couples light horizontally in the plane of the chip. This inverted coupling geometry naturally provides broader spectral bandwidth while maintaining efficient coupling through proper mode matching.

Inventive Principle:

Principle #13The other way round (Inversion)

4Adaptability or versatility

If edge coupler is used in Si PIC, then compatibility with QSFP form factors is improved, but coupling loss with DFB-LD increases due to mode size mismatch

Engineering Contradiction:

ImproveQSFP form factor compatibilityVSAvoidcoupling loss

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The patent introduces a specifically designed lens as an intermediary component that performs mode transformation. The lens converts the Gaussian beam from the DFB-LD into a mode that matches the edge coupler's optical mode profile, enabling efficient coupling while maintaining compatibility with QSFP form factors through the in-plane edge coupler geometry.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

The optical package achieves high-efficient coupling with suppressed return loss, optimizing the link budget and enabling compatibility with QSFP form factors, thereby enhancing the performance of Si PICs in data center applications.

Implementation Method 1

The spacer or isolator is bonded with an index matching fluid to reduce return loss

Methodology Applied

Scientific EffectIndex matching: Refraction

Data Source

PatentUS9787054B2Optical package providing efficient coupling between DFB-LD and silicon PIC edge couplers with low return loss

Publication Date: 2017.10.10 SIFOTONICS TECH CO LTD

AI summary

An optical package for providing efficient coupling between a distributed feedback laser diode (DFB-LD) and a silicon photonic integrated-circuit chip (Si PIC) edge couplers with low return loss, as well as variations thereof, is described. The optical package may include a DFB-LD, a Si PIC, a single mode fiber or fiber array assembly, a lens and a spacer. The Si PIC may include an input edge coupler and an output edge coupler. The single mode fiber or fiber array assembly may be aligned to the output edge coupler. The lens may be disposed between the DFB-LD and the input edge coupler, and may be configured to minimize a mismatch between an output spot size of the DFB-LD and a spot size of the input edge coupler of the Si PIC. The spacer may be bonded to a facet of the input edge coupler with an index matching fluid.