VCSEL Gain Switching for High-Energy Picosecond Pulses

Solution Overview

Problem

Existing edge-emitting semiconductor lasers face limitations in beam quality and spectral linewidth, making them unsuitable for applications requiring short, high-energy laser pulses and narrow spectral linewidth, particularly in biotechnology and biological measurements.

Innovation Solution

A vertical cavity surface emitting laser (VCSEL) operating in a gain switching regime with quantum wells positioned to achieve a standing wave factor between zero and one, optimized with distributed Bragg reflectors and detuned from antinodes, enhancing beam quality and lasing efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If edge-emitting semiconductor laser is used to achieve high pulse energy, then pulse energy is improved, but beam quality deteriorates

Engineering Contradiction:

Improvepulse energyVSAvoidbeam quality

Core Design Contradiction:

Use of energy by moving objectVSShape

Solution Approach 1:

The patent inverts the conventional edge-emitting laser architecture by using a vertical-cavity surface-emitting laser (VCSEL) structure instead. This fundamental geometric inversion allows the laser to achieve high pulse energy through gain switching while simultaneously providing superior beam quality due to the vertical emission geometry and circular beam profile inherent to VCSELs.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes key structural parameters by positioning quantum wells at specific locations within the cavity where the standing wave factor ξ is between 0 and 1, rather than at the conventional antinodes (ξ=1). This parameter change optimizes the overlap between the optical field and gain medium, enabling efficient energy extraction while maintaining excellent beam quality.

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If edge-emitting semiconductor laser is used to achieve high pulse energy, then pulse energy is improved, but spectral linewidth deteriorates

Engineering Contradiction:

Improvepulse energyVSAvoidspectral linewidth

Core Design Contradiction:

Use of energy by moving objectVSMeasurement precision

Solution Approach 1:

The patent inverts the conventional edge-emitting laser architecture by using a vertical-cavity surface-emitting laser (VCSEL) structure instead. This fundamental geometric inversion allows the laser to achieve high pulse energy through gain switching while simultaneously providing superior beam quality due to the vertical emission geometry and circular beam profile inherent to VCSELs.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes key structural parameters by positioning quantum wells at specific locations within the cavity where the standing wave factor ξ is between 0 and 1, rather than at the conventional antinodes (ξ=1). This parameter change optimizes the overlap between the optical field and gain medium, enabling efficient energy extraction while maintaining excellent beam quality.

Inventive Principle:

Principle #35Parameter changes

3Power

If quantum wells are positioned at standing wave antinodes, then lasing efficiency is improved, but pulse duration deteriorates

Engineering Contradiction:

Improvelasing efficiencyVSAvoidpulse duration

Core Design Contradiction:

PowerVSDuration of action of moving object

Solution Approach 1:

The patent changes the positioning parameter of quantum wells from antinodes (ξ=1) to positions where the standing wave factor ξ is between 0 and 1. This parameter change creates an optimal balance: sufficient overlap for efficient lasing while avoiding the excessive energy extraction that would otherwise extend pulse duration beyond the desired picosecond range.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs gain switching dynamics with carefully controlled injection current pulses (modest amplitude, more than nanosecond long) that interact with the detuned quantum well positions to produce temporally short (picosecond) high-energy pulses. The dynamic interplay between the injection profile and the detuned quantum well positioning achieves the desired pulse characteristics.

Inventive Principle:

Principle #15Dynamics

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 VCSEL achieves excellent beam quality and narrowband lasing, generating high-energy picosecond pulses efficiently with improved pulse energy distribution and reduced quasi-stationary trails, suitable for applications like 3D imaging and spectroscopy.

Implementation Method 1

The cavity is terminated by reflectors at both ends for enabling a standing wave of optical radiation therebetween

Methodology Applied

Scientific EffectBragg reflection: Bragg Diffraction

Implementation Method 2

enabling a standing wave of optical radiation therebetween

Methodology Applied

Scientific EffectStanding wave: Resonance

Implementation Method 3

gain switched vertical cavity surface emitting laser (VCSEL)

Methodology Applied

Scientific EffectStimulated emission: Laser

Implementation Method 4

The cavity comprises at least one quantum well

Methodology Applied

Scientific EffectQuantum well:

Data Source

PatentUS8934514B2Laser

Publication Date: 2015.01.13 UNIV OF OULU

AI summary

A vertical cavity surface emitting laser (VCSEL) configured to operate in a gain switching regime includes a cavity that is terminated by reflectors at both ends for enabling a standing wave of optical radiation therebetween. The cavity comprises at least one quantum well, each of the quantum wells located at a position where a value of a standing wave factor for each quantum well is between zero and one, 0<ξ<1.