Laser Diode Mode-Splitting Layer for Beam Divergence

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Solution Overview

Problem

Existing laser diodes often compromise between small vertical far-field beam divergence and large vertical optical confinement factor, with most achieving one at the expense of the other.

Innovation Solution

Incorporating a mode-splitting layer with a low refractive index between waveguide layers in the laser diode's layer stack to increase vertical near-field beam width while maintaining a high optical confinement factor, achieved by an asymmetric refractive-index and thickness profile that enhances the overlap of the optical mode with the active layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Shape

If the thickness of the waveguide layer is increased to increase vertical near-field beam width, then vertical far-field beam divergence is reduced, but vertical optical confinement factor decreases

Engineering Contradiction:

Improvevertical near-field beam widthVSAvoidvertical optical confinement factor

Core Design Contradiction:

ShapeVSReliability

Solution Approach 1:

The waveguide structure is segmented into multiple layers: a first waveguide layer, a mode-splitting layer, and a second waveguide layer. This segmentation allows the optical mode to be distributed across multiple regions, increasing the vertical near-field beam width while maintaining strong confinement through the combined effect of all layers. The mode-splitting layer specifically divides the optical mode into two lobes, achieving broader beam width without sacrificing confinement factor.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The mode-splitting layer acts as an intermediary between the first and second waveguide layers. With a refractive index lower than the waveguide layers, it mediates the optical mode distribution, creating a dual-lobe intensity profile that extends vertically while maintaining effective confinement. This intermediary layer enables the decoupling of beam width from confinement factor.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Shape

If a mode-splitting layer with low refractive index is inserted between waveguide layers, then vertical near-field beam width increases, but device complexity increases

Engineering Contradiction:

Improvevertical near-field beam widthVSAvoidlayer stack complexity

Core Design Contradiction:

ShapeVSDevice complexity

Solution Approach 1:

The mode-splitting layer is designed with specific parameter ranges: thickness between 0.05-0.5 μm and refractive index 0.01-0.1 lower than adjacent waveguide layers. By optimizing these parameters, the layer achieves effective mode splitting with minimal impact on overall device complexity. The relatively thin thickness keeps the additional complexity manageable while achieving the desired optical effect.

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If asymmetric refractive-index profile is used to skew optical mode toward n-type region, then free-hole absorption is reduced, but manufacturing precision requirements increase

Engineering Contradiction:

Improvefree-hole absorption lossVSAvoidrefractive-index profile precision

Core Design Contradiction:

Loss of energyVSManufacturing precision

Solution Approach 1:

The laser diode employs an asymmetric refractive-index profile where the first cladding layer has higher refractive index than the second cladding layer, and the waveguide layers are positioned asymmetrically relative to the active layer. This asymmetry skews the optical mode toward the n-type region, reducing overlap with holes and minimizing free-hole absorption losses. The asymmetric design is implemented through precise control of layer thicknesses and refractive indices during fabrication.

Inventive Principle:

Principle #4Asymmetry

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 allows for a significant reduction in vertical far-field beam divergence while maintaining a high vertical optical confinement factor, outperforming prior-art laser diodes in terms of beam quality and confinement efficiency.

Implementation Method 1

Incorporating a mode-splitting layer with a low refractive index between waveguide layers in the laser diode's layer stack to increase vertical near-field beam width

Methodology Applied

Scientific EffectOptical mode splitting: Refraction

Implementation Method 2

a first waveguide layer, for propagating the optical mode... a second waveguide layer, for propagating the optical mode... a third waveguide layer, for propagating the optical mode

Methodology Applied

Scientific EffectOptical waveguide propagation: Waveguide (optics)

Implementation Method 3

a first cladding layer, for confining an optical mode... a second cladding layer, for confining the optical mode

Methodology Applied

Scientific EffectOptical confinement: Total Internal Reflection

Implementation Method 4

an active layer, for generating the optical mode

Methodology Applied

Scientific EffectLight generation: Laser

Data Source

PatentUS7830938B2Laser diode

Publication Date: 2010.11.09 WELLS FARGO BANK NA

AI summary

The present invention provides a laser diode having both a small vertical far-field beam divergence and a large vertical optical confinement factor, as well as a method of fabricating the laser diode. The laser diode comprises a layer stack of semiconductor material, which includes a mode-splitting layer having a low refractive index inserted between waveguide layers. In addition to increasing the vertical near-field beam width of the laser diode, the mode-splitting layer also produces a shoulder in an optical mode generated in an active layer of the layer stack, increasing vertical overlap of the optical mode with the active layer.