Broad Area Quantum Cascade Lasers Sidewall Lossy Material Mode Control

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Solution Overview

Problem

Broad area quantum cascade lasers (BA-QCLs) face challenges in maintaining fundamental transverse mode operation as they scale in power, often resulting in high-order transverse modes that lead to multi-lobed emission and reduced brightness due to modal instability and beam steering.

Innovation Solution

Incorporating an optically lossy material on the sidewalls of the optical cavity, strategically positioned to induce losses to high-order transverse modes, thereby promoting the fundamental transverse mode operation, which can be achieved through a modification of the standard fabrication process to allow direct contact of the lossy material with the sidewalls or positioning it at a predetermined distance to provide sufficient losses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the cavity width of the QCL is increased to generate additional power, then the power output is improved, but high-order transverse modes emerge causing mode competition and beam steering

Engineering Contradiction:

Improvepower outputVSAvoidtransverse mode stability

Core Design Contradiction:

PowerVSStability of the object's composition

Solution Approach 1:

The patent applies local quality by positioning optically lossy material specifically at the sidewalls of the optical cavity. This creates a non-uniform loss distribution where the edges experience higher losses than the center, selectively suppressing high-order transverse modes that concentrate their intensity near the sidewalls, while allowing the fundamental mode to dominate

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the optical loss parameter by introducing optically lossy material at the sidewalls. This modifies the effective refractive index and loss characteristics of the cavity, creating a potential well that favors fundamental mode operation. The loss parameter is tuned by adjusting the position and material properties of the lossy layer

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If the cavity width is kept narrow to maintain fundamental transverse mode operation, then the transverse mode stability is improved, but the power generation capability is limited

Engineering Contradiction:

Improvetransverse mode stabilityVSAvoidpower generation capability

Core Design Contradiction:

Stability of the object's compositionVSPower

Solution Approach 1:

The patent introduces a new dimensional approach by adding the vertical dimension (z-direction) through optically lossy material layers at the sidewalls. This allows the cavity to maintain a narrow effective optical confinement in the transverse direction while physically accommodating a broader structure, enabling power scaling without sacrificing mode stability

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Power

If high-order transverse modes are allowed to operate in broad area QCLs, then the power output is increased, but the beam quality deteriorates with multi-lobed emission and reduced brightness

Engineering Contradiction:

Improvepower outputVSAvoidbeam brightness

Core Design Contradiction:

PowerVSIllumination intensity

Solution Approach 1:

The patent converts the harmful effect of sidewall proximity on high-order modes into a beneficial selective loss mechanism. By placing optically lossy material at the sidewalls, the natural tendency of high-order modes to concentrate intensity near edges is transformed into a mechanism that selectively attenuates these modes, while the fundamental mode remains unaffected and produces high-quality single-lobed emission

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 effectively suppresses high-order transverse modes, restoring single-lobed emission along the optical axis, enhancing the brightness and operational simplicity of BA-QCLs, making them more suitable for various applications by maintaining fundamental transverse mode operation even at larger cavity widths.

Implementation Method 1

an optically lossy material disposed on at least a first portion of one or more of the two sidewalls... such that the optically lossy material induces losses to at least one high order transverse optical mode

Methodology Applied

Scientific EffectOptical absorption: Absorption (EM radiation)

Data Source

PatentUS11031753B1Extracting the fundamental mode in broad area quantum cascade lasers

Publication Date: 2021.06.08 THE GOVERNMENT OF THE UNITED STATES AS REPRESENTED BY THE SECRETARY OF THE AIR FORCE

AI summary

A broad area quantum cascade laser includes an optical cavity disposed between two sidewalls, the optical cavity including an active region for producing photons when a current is applied thereto, where the optical cavity is subject to a presence of at least one high order transverse optical mode due to its broad area geometry. The broad area quantum cascade laser may also include an optically lossy material disposed on at least a first portion of one or more of the two sidewalls.