AlGaInAs Superluminescent Diode Bandwidth Power Trade-off
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Solution Overview
Problem
Existing semiconductor superluminescent diodes (SLDs) in the 1100-1800 nm region face challenges in simultaneously achieving high output power, broad optical bandwidth, and manufacturability, with prior art devices often compromising on either power or bandwidth due to non-uniform charge injection and shallow conduction band potential in the InGaAsP material system.
Innovation Solution
A semiconductor-based superluminescent diode using strained AlGaInAs quantum wells grown on an Indium Phosphide substrate, with a deep conduction to valence band offset ratio of 72:28, enabling uniform charge injection and high output power, and featuring 3 quantum wells with controllable well widths to achieve bandwidth exceeding 100 nm and output power exceeding 50 mW.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If InGaAsP multi-quantum well structures are used to expand bandwidth, then spectral bandwidth is improved, but output power and thermal performance deteriorate due to non-uniform charge injection and shallow conduction band potential
Solution Approach 1:
The patent changes the material system from InGaAsP to AlGaInAs, fundamentally altering the band offset parameters. This material substitution creates a deep conduction band potential (72:28 conduction-valence band offset ratio) that enables uniform charge injection across multiple quantum wells, simultaneously achieving high output power (>50 mW) and broad bandwidth (>100 nm) that were previously mutually exclusive
Solution Approach 2:
The patent employs composite AlGaInAs quantum well structures with specific composition ratios (Al0.2In0.67Ga0.13As) grown on InP substrates. This composite material system combines the advantages of deep conduction band offset for power efficiency with multi-quantum well states for bandwidth expansion, resolving the contradiction between power and bandwidth
2Illumination intensity
If non-uniform well widths or multi-state quantum wells are employed to increase bandwidth, then spectral bandwidth is improved, but charge injection uniformity and thermal performance worsen
Solution Approach 1:
The patent utilizes the deep conduction band offset parameter of AlGaInAs materials to create uniform potential wells across multiple quantum well layers. This parameter change ensures that charge carriers are injected uniformly throughout the active region, maintaining high reliability and thermal performance while still achieving broad bandwidth through the multi-quantum well design
3Illumination intensity
If quantum dots are used as active medium for broad bandwidth, then optical bandwidth is improved, but output power deteriorates due to small fill factor and limited gain
Solution Approach 1:
The patent segments the active medium into multiple AlGaInAs quantum well layers (3-5 wells) instead of using quantum dots. This segmentation provides a larger effective fill factor and higher gain medium volume, enabling simultaneous achievement of broad bandwidth (>100 nm) and high output power (>50 mW) that quantum dot structures cannot achieve
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 AlGaInAs SLD design achieves high output power and broad optical bandwidth, exceeding previous results, with controllable spectral range and improved manufacturability, suitable for applications like Optical Coherence Tomography systems.
Implementation Method 1
Researchers have employed quantum-well active regions exhibiting simultaneous emission from both the first and second quantized state to expand the bandwidth of SLD-based light sources
Implementation Method 2
Semiconductor superluminescent diodes (SLDs) are compact inexpensive light sources for many applications that require large spectral bandwidth
Implementation Method 3
This AlGaInAs quantum well has a deep conduction: valence band offset ratio of approximately 72:28, enabling wide state separation, uniform charge injection, and good thermal and output power performance
Implementation Method 4
A semiconductor-based superluminescent diode using strained AlGaInAs quantum wells grown on an Indium Phosphide substrate
Data Source
AI summary
A superluminescent diode according the present invention employs a uniform AlGaInAs quantum well on an InP substrate, emitting in a range of 1100 to 1800 nm. The favorable conduction band: valence band offset ratio of this material system enables superluminescent diodes which simultaneously provide high power and large optical bandwidth. A recent reduction to practice of the present invention simultaneously demonstrates output power exceeding 100 mW and bandwidth exceeding 100 nm. A preferred embodiment of this invention uses multiple uniform AlGaInAs quantum wells with two confined quantum states and energetic separation in a range of 100-130 nm. An alternate preferred embodiment uses non-uniform wells, with each well having two confined quantum states. The present invention is particularly useful in time domain and spectral domain optical coherence tomography systems, providing increased resolution and tissue penetration for in-vivo imaging.