Dispersion Managed Fiber Stretcher for Femtosecond Laser

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Solution Overview

Problem

Current fiber laser systems face challenges in achieving high energy levels, particularly with 1 mJ femtosecond lasers, due to nonlinear effects like self-phase modulation and stimulated Raman scattering, and third-order dispersion, which limit pulse quality and scalability.

Innovation Solution

Implementing a pulse stretcher with a special dispersion management fiber having a flat or negative dispersion slope, specifically using fibers with depressed cladding structures, to manage and compensate for dispersion effects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If higher doping concentrations are used in Yb-fibers to increase power output, then power extraction efficiency is improved, but nonlinear effects such as self-phase modulation and stimulated Raman scattering worsen

Engineering Contradiction:

Improvepower extraction efficiencyVSAvoidnonlinear effects

Core Design Contradiction:

Use of energy by moving objectVSObject-generated harmful factors

Solution Approach 1:

The patent changes the dispersion parameter by introducing a depressed cladding structure with specific refractive index profile. This modifies the fiber's dispersion characteristics to achieve flattened dispersion across the spectral range, allowing high doping concentrations to be used without excessive nonlinear effects

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite fiber structure combining core, cladding, and depressed cladding layers with different refractive indices. This composite structure enables simultaneous achievement of high power extraction and controlled nonlinear effects through careful material selection and structural design

Inventive Principle:

Principle #40Composite materials

2Power

If higher stretching ratio is used in chirped pulse amplification to increase pulse energy, then output energy is improved, but third order dispersion effects worsen and limit pulse compression

Engineering Contradiction:

Improveoutput energyVSAvoidpulse quality

Core Design Contradiction:

PowerVSManufacturing precision

Solution Approach 1:

The patent changes the dispersion slope parameter by designing a fiber with depressed cladding that provides negative dispersion slope. This compensates for the positive third-order dispersion accumulated during high stretching ratio amplification, enabling efficient pulse compression even at high output energies

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies preliminary dispersion compensation by incorporating the depressed cladding fiber in the stretcher section before amplification. This pre-compensates for the third-order dispersion that will be accumulated during subsequent high-power amplification, preventing pulse quality degradation

Inventive Principle:

Principle #9Preliminary anti-action

3Device complexity

If conventional fiber designs are used to achieve high energy output, then system simplicity is maintained, but dispersion management capability deteriorates

Engineering Contradiction:

Improvesystem simplicityVSAvoiddispersion management

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The depressed cladding fiber structure serves multiple functions simultaneously: it provides flattened dispersion across the spectral range, enables negative dispersion slope for TOD compensation, and maintains high power extraction efficiency. This multi-functionality eliminates the need for separate dispersion compensation components

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent modifies the fundamental fiber structure by introducing a depressed cladding layer with lower refractive index than the inner cladding. This structural parameter change fundamentally alters the dispersion characteristics, providing both flattened dispersion and negative dispersion slope in a single fiber design

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

This approach enables efficient pulse stretching and compression, improving pulse quality and scalability of fiber laser systems, as demonstrated by a 40% pulse width reduction in experiments with a 10 micro-Joule high-energy fs fiber laser.

Implementation Method 1

a pulse stretcher with a special dispersion management fiber having a flat or negative dispersion slope

Methodology Applied

Scientific EffectDispersion: Dispersion (of waves)

Implementation Method 2

nonlinear effects like self-phase modulation and stimulated Raman scattering

Methodology Applied

Scientific EffectSelf-phase modulation:

Implementation Method 3

nonlinear effects like self-phase modulation and stimulated Raman scattering

Methodology Applied

Scientific EffectStimulated Raman scattering:

Data Source

PatentUS7430226B2Dispersion managed fiber stretcher for high-energy short pulse femotosecond fiber laser system

Publication Date: 2008.09.30 POLARONYX

AI summary

A fiber Chirped Pulse Amplification (CPA) laser system that includes a fiber mode-locking oscillator for generating a seed laser for projecting to a stretcher for generated a pulse-stretched laser for projecting to a multiple stage amplifier. The multiple stage amplifier further amplifying said laser for projecting to a compressor for compressing said laser to generate an output laser of an original pulse width. In this invention, pulse stretcher is implemented with a special dispersion management fiber that has a flat dispersion or a negative TOD (dispersion slope, or a slope of dispersion versus wavelength).