Varied-Width Waveguide for Semiconductor Laser Coupling

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Solution Overview

Problem

Conventional semiconductor lasers with tapered waveguides face challenges in efficiently coupling laser light to coupling targets due to elliptical far field patterns, leading to reduced coupling efficiency and usable optical power, despite increased optical intensity.

Innovation Solution

A semiconductor laser with a waveguide structure featuring a first narrow portion, a wide portion, a second narrow portion, and tapered portions connecting them, designed to maintain uniform widths and specific length and width ratios to achieve single-mode operation and high coupling efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the width of the waveguide is increased to reduce electrical resistance and increase saturated optical power, then the optical intensity increases, but the lateral mode turns into multimode and the far field pattern becomes elliptical, reducing coupling efficiency

Engineering Contradiction:

Improvesaturated optical powerVSAvoidcoupling efficiency

Core Design Contradiction:

PowerVSEase of operation

Solution Approach 1:

The waveguide is segmented into multiple sections with different widths: a first narrow portion (3 μm) for single-mode operation, a wide portion (6 μm) for reduced electrical resistance and high optical intensity, and a second narrow portion (3 μm) for circular far field pattern. This segmentation allows each section to fulfill different functional requirements simultaneously.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different sections of the waveguide are assigned different local qualities (widths) optimized for specific functions: the first narrow portion ensures single-mode operation, the wide portion provides low electrical resistance for high power, and the second narrow portion creates a circular far field pattern for efficient coupling. This local optimization resolves the contradiction between power and coupling efficiency.

Inventive Principle:

Principle #3Local quality

2Power

If the width of the waveguide is increased only at the output facet side while keeping the rear facet side narrow to maintain single mode, then high-intensity laser light in single mode is achieved, but the far field pattern becomes elliptical, reducing coupling efficiency to circular targets

Engineering Contradiction:

Improveoptical intensityVSAvoidfar field pattern shape

Core Design Contradiction:

PowerVSShape

Solution Approach 1:

Instead of narrowing the waveguide only at the output facet (conventional approach), this invention narrows the waveguide at both the input and output facets while maintaining a wide central portion. This inverted structure allows the wide portion to provide high optical intensity while the narrow facets restore the circular far field pattern for efficient coupling.

Inventive Principle:

Principle #13The other way round (Inversion)

3Stability of the object's composition

If a tapered waveguide structure is used to connect portions with different widths, then single-mode operation is maintained, but the far field pattern becomes elliptical and coupling efficiency to circular targets is reduced

Engineering Contradiction:

Improvesingle-mode operationVSAvoidcoupling efficiency

Core Design Contradiction:

Stability of the object's compositionVSEase of operation

Solution Approach 1:

The waveguide is divided into distinct segments (first narrow portion, wide portion, second narrow portion) connected by tapered portions. This segmentation allows the main sections to maintain single-mode operation while the final narrow portion shapes the far field pattern into a circle, resolving the contradiction between mode stability and coupling efficiency.

Inventive Principle:

Principle #1Segmentation

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 proposed waveguide structure enhances coupling efficiency and increases saturated optical power by shaping the far field pattern into a circular shape, allowing for higher-intensity laser light output via a lens system.

Implementation Method 1

confining the light inside an active layer with an index waveguide structure

Methodology Applied

Scientific EffectOptical waveguide confinement: Waveguide (optics)

Implementation Method 2

the output light usually is provided for use after being collimated and optically-coupled to a coupling target, such as an optical fiber and a recording surface of an optical disk, by a lens system

Methodology Applied

Scientific EffectOptical lens focusing: Lens

Data Source

PatentUS8811447B2Semiconductor laser with varied-width waveguide and semiconductor laser module including the same

Publication Date: 2014.08.19 FURUKAWA ELECTRIC CO LTD

AI summary

A semiconductor laser outputs a laser light from an output facet of a waveguide having an index waveguide structure, via a lens system. The waveguide includes, in order from a rear facet opposite to the output facet, a first narrow portion, a wide portion that is wider than the first narrow portion, a second narrow portion narrower than the wide portion, a first tapered portion formed between the first narrow portion and the wide portion, which expands toward the wide portion, and a second tapered portion formed between the wide portion and the second narrow portion, which narrows toward the second narrow portion. Each of the first narrow portion, the wide portion, and the second narrow potion has a uniform width.