Mode-locked Multi-mode Fiber Laser for High Peak Power

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Solution Overview

Problem

Conventional single-mode fiber amplifiers and lasers are limited by small fiber core size, leading to peak power restrictions due to nonlinearities and modal dispersion, making it difficult to achieve high peak power pulses without pulse distortion and mode-coupling issues.

Innovation Solution

A mode-locked multi-mode fiber laser design with a cavity that includes a saturable absorber, mode-filters, and environmentally stable components, utilizing cladding-pumping and nonlinear polarization evolution to generate high peak power pulses, while minimizing damage and maintaining long-term stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If single-mode fiber amplifiers are used to ensure diffraction-limited output and low noise, then beam quality and noise levels are improved, but peak power is limited due to small fiber core size and nonlinearities

Engineering Contradiction:

Improvebeam qualityVSAvoidpeak power

Core Design Contradiction:

Illumination intensityVSPower

Solution Approach 1:

The system segments the amplification process into two distinct stages: first, a single-mode fiber amplifier provides diffraction-limited beam quality with low noise; second, a multi-mode fiber amplifier boosts the pulse to high peak power. This segmentation allows each amplifier to operate in its optimal regime without compromising the other parameter.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A mode-locked laser serves as an intermediary source that generates initial pulses with good beam quality. These pulses are then sequentially amplified by single-mode and multi-mode fiber amplifiers, transferring the quality characteristics through the system while achieving high peak power in the final output.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Power

If multi-mode fiber amplifiers are used to increase peak power, then peak power is improved, but modal dispersion and pulse broadening occur

Engineering Contradiction:

Improvepeak powerVSAvoidpulse duration

Core Design Contradiction:

PowerVSDuration of action of moving object

Solution Approach 1:

The amplification process is segmented such that the multi-mode fiber amplifier is used only for the final power boosting stage after the pulse has already been formed with appropriate duration characteristics in the single-mode amplifier, minimizing modal dispersion effects on pulse duration.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The single-mode fiber amplifier performs preliminary amplification to establish the pulse characteristics and duration before the signal enters the multi-mode fiber amplifier. This preliminary action ensures that the pulse is already optimized for duration before undergoing power amplification in the multi-mode section.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If single-mode fiber core size is reduced to avoid nonlinearities, then nonlinear distortion is reduced, but peak power capability is limited

Engineering Contradiction:

Improvepulse distortionVSAvoidpeak power

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

The system segments the power amplification task between single-mode and multi-mode fibers. The single-mode section maintains low distortion with its smaller core, while the multi-mode section handles the high peak power amplification, with each segment optimized for its specific function.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system changes the fiber mode parameter from single-mode to multi-mode at the appropriate stage in the amplification process. This parameter change allows the system to transition from a regime optimized for low distortion to one optimized for high peak power capability.

Inventive Principle:

Principle #35Parameter changes

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 design achieves peak powers of approximately 6 kW with 360 fsec pulses, significantly exceeding the limits of conventional single-mode fiber lasers, while maintaining a near-bandwidth-limited output with improved stability and reduced modal dispersion.

Implementation Method 1

A mode-locked multi-mode fiber laser design with a cavity that includes a saturable absorber

Methodology Applied

Scientific EffectSaturable absorption: Absorption (EM radiation)

Implementation Method 2

amplification of high peak-power pulses in a diffraction-limited optical beam in single-mode optical fiber amplifiers

Methodology Applied

Scientific EffectOptical amplification: Laser

Implementation Method 3

utilizing cladding-pumping and nonlinear polarization evolution to generate high peak power pulses

Methodology Applied

Scientific EffectOptical pumping: Absorption (EM radiation)

Implementation Method 4

utilizing cladding-pumping and nonlinear polarization evolution to generate high peak power pulses

Methodology Applied

Scientific EffectKerr effect: Kerr Effect

Data Source

PatentUS8873593B2Mode-locked multi-mode fiber laser pulse source

Publication Date: 2014.10.28 IMRA AMERICA INC

AI summary

A laser utilizes a cavity design which allows the stable generation of high peak power pulses from mode-locked multi-mode fiber lasers, greatly extending the peak power limits of conventional mode-locked single-mode fiber lasers. Mode-locking may be induced by insertion of a saturable absorber into the cavity and by inserting one or more mode-filters to ensure the oscillation of the fundamental mode in the multi-mode fiber. The probability of damage of the absorber may be minimized by the insertion of an additional semiconductor optical power limiter into the cavity.