Narrow-Core QCL Ridge Waveguide for Lower Modal Loss

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Solution Overview

Problem

Conventional quantum cascade lasers (QCLs) suffer from modal losses due to the interaction of the optical mode with the surrounding metal film, particularly in wet-etched ridge waveguides with non-vertical sidewall profiles, and non-uniform current injection across stages, especially in designs with multiple stages.

Innovation Solution

Narrowing the quantum cascade laser core layer relative to the top and bottom cladding layers creates a gap between the QCL core layer and the electrically conductive layer, enhancing refractive index contrast and reducing optical interactions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the QCL core layer width is reduced to improve beam quality and reduce modal losses, then the interaction with electrically conductive layer increases causing efficiency penalties

Engineering Contradiction:

Improvemodal lossesVSAvoidoptical efficiency

Core Design Contradiction:

Loss of energyVSProductivity

Solution Approach 1:

The patent introduces a lateral dimension gap between the QCL core layer and electrically conductive layer, in addition to the vertical separation. This dimensional approach allows the optical mode to be confined vertically while maintaining lateral separation from lossy metal regions, enabling narrow core designs without efficiency penalties

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The patent introduces a dielectric material layer as an intermediary between the QCL core layer and the electrically conductive layer. This dielectric spacer acts as a mediator that electrically isolates the core from the metal while maintaining mechanical support, reducing parasitic interactions and enabling efficient narrow-core operation

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If wet-etched ridge waveguide is used to simplify manufacturing, then non-vertical sidewall profile is created increasing modal losses

Engineering Contradiction:

Improvewaveguide fabricationVSAvoidmodal losses

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The patent changes the critical parameter of sidewall angle from non-vertical (wet-etched) to vertical (dry-etched). This parameter change eliminates the semicircular core profile that causes enhanced metal interaction, achieving low modal losses while maintaining manufacturing feasibility through standard dry etching processes

Inventive Principle:

Principle #35Parameter changes

3Shape

If dry-etched ridge waveguide with reduced ridge width is used to improve beam quality, then sidewall roughness increases causing optical losses

Engineering Contradiction:

Improvebeam qualityVSAvoidoptical losses

Core Design Contradiction:

ShapeVSLoss of energy

Solution Approach 1:

The patent extracts the QCL core layer from direct contact with the electrically conductive layer by introducing a lateral gap. This separation removes the core from the region affected by sidewall roughness scattering, allowing narrow ridge designs for high beam quality without suffering from roughness-induced optical losses

Inventive Principle:

Principle #2Taking out (Extraction)

4Ease of manufacture

If semicircular laser core shape is used in wet-etched QCL, then current injection uniformity across stages deteriorates

Engineering Contradiction:

Improvewaveguide profileVSAvoidcurrent injection uniformity

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent transitions from the symmetric semicircular core profile to an asymmetric rectangular profile with vertical sidewalls and flat top/bottom surfaces. This asymmetric geometry, achieved through dry etching, provides planar current injection surfaces that ensure uniform current distribution across all quantum cascade stages

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 design reduces modal losses and improves current injection uniformity, allowing for narrower QCL core devices without significant efficiency penalties, enhancing beam quality and versatility in applications.

Implementation Method 1

A quantum cascade laser (QCL) is a semiconductor laser that uses intersubband radiative electron transitions between quantized energy levels to generate photons of radiation

Methodology Applied

Scientific EffectIntersubband radiative electron transitions:

Implementation Method 2

increases the refractive index contrast and reduces interactions between the optical mode in QCL core layer and the electrically conductive layer

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS20260058442A1Quantum Cascade Lasers With Narrow Core Ridge Waveguide Design

Publication Date: 2026.02.26 IRGLARE LLC

AI summary

A quantum cascade laser (QCL) includes a ridge waveguide formed on a semiconductor substrate. The ridge waveguide has a ridge with a ridge width and (a) a top cladding layer having a top cladding layer width, (b) a bottom cladding layer having a bottom cladding layer width, and (c) a QCL core layer having a QCL core layer width that is less than the top cladding layer width and the bottom cladding layer width. The QCL core layer is sandwiched between the top cladding layer and bottom cladding layer.