Materials for optical fiber lasers: A review
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paper_title: High Power Fiber Lasers: A Review

paper_content:

In this paper, we summarize the fundamental properties and review the latest developments in high power fiber lasers. The review is focused primarily on the most common fiber laser configurations and the associated cladding pumping issues. Special attention is placed on pump combination techniques and the parameters that affect the brightness enhancement observed in single-mode and multimode high power fiber lasers. The review includes the major limitations imposed by fiber nonlinearities and other parasitic effects, such as optical damage, transverse modal instabilities and photodarkening. Finally, the paper summarizes the power evolution in continuous-wave and pulsed ytterbium-doped fiber lasers and their impact on industrial applications.
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paper_title: High-power fibre lasers

paper_content:

High-power fibre lasers are in demand for industrial, defence and scientific applications. This review provides an overview of the present state of the art in the field and discusses present challenges and the future outlook.
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paper_title: High brightness fiber coupled modular diode laser platform

paper_content:

High-power and high-brightness fiber coupled diode laser devices are in demand in two main commercial applications. The largest is for solid-state laser pumping, especially the fiber laser market, where the push to higher power fiber lasers is driving the need for bright, high power pump sources. The other market is for direct diode laser material processing, eliminating the use of a “beam quality converter” such as fiber lasers or disc lasers. Without the need for solid state laser beam conversion, a direct diode laser beam is, in principle, more efficient and smaller, but the combined multiple beams from hundreds of individual emitters requires beam shaping and lensing at the expense of efficiency and the module's brightness is confined within the limits of the beam quality of the diode lasers. When the costs for the micro-optical elements and their handling and alignment are considered, the assumption of the economic superiority over solid state laser sources is not so readily apparent.
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paper_title: Rare Earth Magnetism Structures And Excitations

paper_content:

rare earth magnetism structures and excitations is available in our book collection an online access to it is set as public so you can download it instantly. Our digital library hosts in multiple locations, allowing you to get the most less latency time to download any of our books like this one. Merely said, the rare earth magnetism structures and excitations is universally compatible with any devices to read.
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paper_title: Luminescence from lanthanides-doped glasses and applications: A review

paper_content:

In this work, the luminescence behaviors and applications from trivalent lanthanide ions doped glasses have been reviewed. Glasses have advantage is recyclable, good energy storage, high soluble rare earth and can be shaped into any size of interest, including fiber. Glasses are also essential materials and can be utilized in many forms. The trivalent lanthanide ions are also a substance of interest with their optical properties, which allow a variety of technological applications. For examples, the rare earth doped materials have already been developed as sensor devices, energy saving lighting devices, optical displays, optical fibers, amplifiers, and lasers. Visible and Near-infrared luminescence for high power lasers is a current requirement in photonics and modern fiber optic telecommunication network. An emphasis has to be put in recent advances of the emitting materials for amplifiers, fiber lasers, and waveguides. In this review, up and down conversion luminescence properties of the glasses doped with several lanthanide ions, i.e., Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Dy3+, Er3+, Yb3+, Ho3+, Tm3+, and Tb3+. Moreover, the current status of their potential applications are also given.
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paper_title: Operator Techniques in Atomic Spectroscopy

paper_content:

In the 1920s, when quantum mechanics was in its infancy, chemists and solid state physicists had little choice but to manipulate unwieldy equations to determine the properties of even the simplest molecules. When mathematicians turned their attention to the equations of quantum mechanics, they discovered that these could be expressed in terms of group theory, and from group theory it was a short step to operator methods. In this book, first published in 1963, Brian Judd made the operator techniques of mathematicians comprehensible to physicists and chemists. He extended the existing methods so that they could handle heavier, more complex molecules and calculate their energy levels, and from there, it was another short step to the mathematical analysis of spectra. The book provides an introduction to continuous groups for physicists and chemists.
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paper_title: Thermal characteristics of Ytterbium-doped phosphosilicate fiber amplifiers

paper_content:

Rare-earth-doped fiber lasers have played an immense role in pioneering and realizing high optical power regime. Among these rare-earth-doped fiber lasers, Ytterbium-doped (Yb) silicate fibers demonstrate exceptional performance especially in high power regime. Phosphosilicate based Yb-doped fiber offers great advantages such as negligible photo-darkening, relatively longer lifetime than aluminosilicate based fibers and higher damage threshold. In this research, thermal characteristics of Yb-doped phosphosilicate fibers are discussed by presenting experimental results.
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paper_title: High Power Fiber Lasers: A Review

paper_content:

In this paper, we summarize the fundamental properties and review the latest developments in high power fiber lasers. The review is focused primarily on the most common fiber laser configurations and the associated cladding pumping issues. Special attention is placed on pump combination techniques and the parameters that affect the brightness enhancement observed in single-mode and multimode high power fiber lasers. The review includes the major limitations imposed by fiber nonlinearities and other parasitic effects, such as optical damage, transverse modal instabilities and photodarkening. Finally, the paper summarizes the power evolution in continuous-wave and pulsed ytterbium-doped fiber lasers and their impact on industrial applications.
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paper_title: Glass Lasers and Solar Applications

paper_content:

Theoretical predictions of laser cross-sections and population probabilities in rare earth doped glasses are made. These are based on combinations of calculations of radiative and nonradiative transitions of rare earths in a variety of oxide and fluoride glasses and measured values of fluorescence and lifetimes. The theory of Luminescent Solar Concentrators is outlined and the optical efficiencies of the collector plates containing rare earth ions, Mn(II), Cr(III) and organic dyes presented. Energy transfer between ions and molecules in glasses is discussed. The behavior of organic dyes in glasses is described and possible materials for lasers and luminescent solar concentrators presented.
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paper_title: Judd-Ofelt theory: principles and practices

paper_content:

previous ideas and forming a complete picture. So it was in August 1962 when there appeared in the literature, simultaneously and independently, two identical formulations of a theory. One by Brian R. Judd at the University of California at Berkeley and the other by a Ph.D. student, George S. Ofelt, at the Johns Hopkins University in Baltimore. Judd and Ofelt had never met personally, and were not aware of each other’s interest in the intensities of rare earth ions in solids. While there are some differences in the two formulations, the approach and the assumptions used to arrive at the final result are remarkably similar. The titles of the two articles reflect a thought along similar lines. Judd referred to Optical Absorption, while Ofelt referred to Crystal Spectra, and each to Intensities of Rare-Earth Ions. The formulations as originally published by Judd and Ofelt came to be known as the Judd-Ofelt theory of the intensities of rare earth ions. Regarding these publications, the late Professor Brian G. Wybourne has said, “I suggest that the coincidence of discovery was indicative that the time was right for the solution of the problem” [1]. In the light of the advancement in the understanding of complex atomic spectra in the quarter century preceding the 1962 publications of Judd and Ofelt, this suggestion of Wybourne is based on very sound reasoning. The rare earths comprise Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. The last 15 make up the lanthanide series. Most of these elements were discovered over a period of time stretching from the late 18th century to the early 20th century. Promethium (Pm) was the last to be discovered in 1947 at Oak Ridge National Laboratory. So, with the exception of Promethium, all the rare earths were discovered in the span of a little more than a century. Part of the reason why they are called rare earths is two-fold. First, they are very difficult to chemically extract from the earth. Second, they do not exist in nature in high abundance. In the universe, the rare earths are approximately 10 6 times less abundant than the
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paper_title: Judd-Ofelt theory: principles and practices

paper_content:

previous ideas and forming a complete picture. So it was in August 1962 when there appeared in the literature, simultaneously and independently, two identical formulations of a theory. One by Brian R. Judd at the University of California at Berkeley and the other by a Ph.D. student, George S. Ofelt, at the Johns Hopkins University in Baltimore. Judd and Ofelt had never met personally, and were not aware of each other’s interest in the intensities of rare earth ions in solids. While there are some differences in the two formulations, the approach and the assumptions used to arrive at the final result are remarkably similar. The titles of the two articles reflect a thought along similar lines. Judd referred to Optical Absorption, while Ofelt referred to Crystal Spectra, and each to Intensities of Rare-Earth Ions. The formulations as originally published by Judd and Ofelt came to be known as the Judd-Ofelt theory of the intensities of rare earth ions. Regarding these publications, the late Professor Brian G. Wybourne has said, “I suggest that the coincidence of discovery was indicative that the time was right for the solution of the problem” [1]. In the light of the advancement in the understanding of complex atomic spectra in the quarter century preceding the 1962 publications of Judd and Ofelt, this suggestion of Wybourne is based on very sound reasoning. The rare earths comprise Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. The last 15 make up the lanthanide series. Most of these elements were discovered over a period of time stretching from the late 18th century to the early 20th century. Promethium (Pm) was the last to be discovered in 1947 at Oak Ridge National Laboratory. So, with the exception of Promethium, all the rare earths were discovered in the span of a little more than a century. Part of the reason why they are called rare earths is two-fold. First, they are very difficult to chemically extract from the earth. Second, they do not exist in nature in high abundance. In the universe, the rare earths are approximately 10 6 times less abundant than the
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paper_title: DOUBLE CLAD, OFFSET CORE Nd FIBER LASER

paper_content:

The earlier glass lasers in both rod and fiber form were mostly side pumped.1 With the demonstration of single mode CW fiber lasers doped with Nd in low loss glass2 there followed considerable work with end pumped fiber lasers with many of the rare earths that had lased.3-6 In this paper, the behavior of a single mode Nd fiber laser with a double clad configuration is described in which light focused into the first cladding is absorbed by the neodymium core as the pump light proceeds down the fiber. This allows use of multimode pump sources and relatively simple focusing systems for efficient coupling.
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paper_title: High Power Fiber Lasers: A Review

paper_content:

In this paper, we summarize the fundamental properties and review the latest developments in high power fiber lasers. The review is focused primarily on the most common fiber laser configurations and the associated cladding pumping issues. Special attention is placed on pump combination techniques and the parameters that affect the brightness enhancement observed in single-mode and multimode high power fiber lasers. The review includes the major limitations imposed by fiber nonlinearities and other parasitic effects, such as optical damage, transverse modal instabilities and photodarkening. Finally, the paper summarizes the power evolution in continuous-wave and pulsed ytterbium-doped fiber lasers and their impact on industrial applications.
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paper_title: DOUBLE CLAD HIGH BRIGHTNESS Nd FIBER LASER PUMPED BY GaAlAs PHASED ARRAY

paper_content:

We report on the most recent improved version of the double clad configuration for efficient pumping of a single mode fiber laser with a multi-mode pump1 In the earlier report, the first and second claddings were substantially fused slica and the core containing Nd was offset from the center of the fiber axis, as shown in Fig. (1,a).
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paper_title: WideBand OM4 multi-mode fiber for next-generation 400Gbps data communications

paper_content:

We define the bandwidth requirements for OM4 performance within the wavelength window of 850 to 950nm. We have manufactured a MMF meeting these requirements while maintaining full compatibility with legacy OM4. This MMF enables 400Gbps using wavelength division multiplexing.
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paper_title: Recent advances in MMF technology for data networks

paper_content:

Multi-Mode Fibers (MMFs) have been developed since the early age of optical communications till the more recent explosion of the Ethernet traffic. This paper will review state of the art MMF technology for data communications.
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paper_title: Fundamentals of Photonics

paper_content:

Preface to the Second Edition. Preface to the First Edition. 1 Ray Optics. 2 Wave Optics. 3 Beam Optics. 4 Fourier Optics. 5 Electromagnetic Optics. 6 Ploarization Optics. 7 Photonic-Crystal Optics. 8 Guided-Wave Optics. 9 Fiber Optics. 10 Resonator Optics. 11 Statistical Optics. 12 Photon Optics. 13 Photon and Atoms. 14 Laser Amplifiers. 15 Lasers. 16 Semiconductor Optics. 17 Semiconductor Photon Sources. 18 Semiconductor Photon Detectors. 19 Acousto-Optics. 20 Electro-Optics. 21 Nonlinear Optics. 22 Ultrafast Optics. 23 Optical Interconnects and Switches. 24 Optical Fiber Communications. A Fourier Transform. B Linear Systems. C Modes of Linear Systems. Symbols and Units. Authors. Index.
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paper_title: High-power fibre lasers

paper_content:

High-power fibre lasers are in demand for industrial, defence and scientific applications. This review provides an overview of the present state of the art in the field and discusses present challenges and the future outlook.
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paper_title: Robustly Single-mode Polarization Maintaining Er/Yb co-doped LMA Fiber for High Power Applications

paper_content:

We demonstrate a large core diameter PM Er/Yb fiber incorporating a unique raised inner-cladding which facilitates the use of conventional LMA mode selection techniques to achieve robustly single-mode operation, making it ideally suited to high power applications.
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paper_title: Advanced engineering electromagnetics

paper_content:

Time--Varying and Time--Harmonic Electromagnetic Fields. Electrical Properties of Matter. Wave Equation and Its Solutions. Wave Propagation and Polarization. Reflection and Transmission. Auxiliary Vector Potentials, Contruction of Solutions, and Radiation and Scattering Equations. Electromagnetic Theorems and Principles. Rectangular Cross--Section Waveguides and Cavities. Circular Cross--Section Waveguides and Cavities. Spherical Transmission Lines and Cavities. Scattering. Integral Equations and the Moment Method. Geometrical Theory of Diffraction. Greena s Functions. Appendices. Index.
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paper_title: Ytterbium-doped 30/400 LMA fibers with a record-low ∼NA of 0.028

paper_content:

We report ytterbium-doped LMA fibers with ∼30μ and ∼40μ cores and a recordlow NA of 0.028, i.e. ΔN=2.7times;10<sup>−4</sup> critical for overcoming transverse-mode-instability threshold in single-mode fiber lasers and made possible by an innovative fabrication process.
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paper_title: Effectively Single-Mode Chirally-Coupled Core Fiber

paper_content:

We demonstrate Chirally-Coupled-Core (CCC) fiber with 35-µm diameter and 0.07 NA core which is effectively single-mode. This is a new type of fibers whose modal properties are defined both by their longitudinal and transverse structure.
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paper_title: Optical fiber with an acoustic guiding layer for stimulated Brillouin scattering suppression

paper_content:

Experimental results are presented demonstrating significant suppression of stimulated Brillouin scattering (SBS) in a specially designed fiber structure. SBS suppression is achieved using an acoustic guiding layer surrounding an optical core.
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paper_title: Fiber designs for reducing stimulated Brillouin scattering

paper_content:

This paper discusses stimulated Brillouin scattering (SBS) in optical fibers. Theoretical approach for analyzing the SBS in fiber is described. Different fiber design methods for reducing the SBS effect are presented.
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paper_title: Brillouin suppression by fiber design

paper_content:

The design of Brillouin scattering suppressed optical fibers is described, including optimization of the acoustic index profile, designs for acoustic anti-guidance, and materials considerations for both design implementation and further reductions in Brillouin gain.
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paper_title: Suppression of stimulated Raman scattering in a cladding pumped amplifier with an Yb-doped filter fiber

paper_content:

A cladding-pumped, high-power amplifier was built incorporating a star-shaped, Ybdoped filter fiber. Pulsed amplifier measurements demonstrate strong suppression of stimulated Raman scattering accomplished by a special index profile with an up-doped ring.
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paper_title: Laser Diode Modulation and Noise

paper_content:

1 Introduction.- 2 Basic Laser Characteristics.- 2.1 Double heterostructure characteristics.- 2.2 Direct and indirect semiconductors.- 2.2.1 Energy- and momentum conservation.- 2.2.2 Semiconductor materials for direct and indirect semiconductors.- 2.3 Emission and absorption.- 2.3.1 Density of photon oscillation states.- 2.3.2 Principal mechanisms of radiative transitions.- 2.3.3 Carrier lifetime and lifetime of spontaneous emission.- 2.3.4 Gain and stimulated emission.- 2.4 Lasing characteristics of Fabry-Perot-type lasers.- 2.4.1 Lasing conditions.- 2.4.2 Dynamic characteristics of laser operation.- 2.4.3 Light current characteristics, threshold current and quantum efficiency.- 2.4.4 Basic laser structures.- 2.4.5 Modifications for the spontaneous emission term.- 2.5 Dynamic single-mode laser structures.- 2.5.1 DFB laser characteristics.- References.- 3 Longitudinal Mode Spectrum of Lasing Emission.- 3.1 Multimode rate equations.- 3.2 Spectral envelope for Fabry-1 Introduction.- 2 Basic Laser Characteristics.- 2.1 Double heterostructure characteristics.- 2.2 Direct and indirect semiconductors.- 2.2.1 Energy- and momentum conservation.- 2.2.2 Semiconductor materials for direct and indirect semiconductors.- 2.3 Emission and absorption.- 2.3.1 Density of photon oscillation states.- 2.3.2 Principal mechanisms of radiative transitions.- 2.3.3 Carrier lifetime and lifetime of spontaneous emission.- 2.3.4 Gain and stimulated emission.- 2.4 Lasing characteristics of Fabry-Perot-type lasers.- 2.4.1 Lasing conditions.- 2.4.2 Dynamic characteristics of laser operation.- 2.4.3 Light current characteristics, threshold current and quantum efficiency.- 2.4.4 Basic laser structures.- 2.4.5 Modifications for the spontaneous emission term.- 2.5 Dynamic single-mode laser structures.- 2.5.1 DFB laser characteristics.- References.- 3 Longitudinal Mode Spectrum of Lasing Emission.- 3.1 Multimode rate equations.- 3.2 Spectral envelope for Fabry-Perot-type lasers (linear gain).- 3.3 Influence of nonlinear gain on the spectral characteristics.- 3.3.1 Symmetric nonlinear gain.- 3.3.2 Asymmetric nonlinear gain.- 3.3.3 Nonlinear gain, conclusions.- References.- 4 Intensity-Modulation Characteristics of Laser Diodes.- 4.1 Modulation characteristics by studying single-mode rate equations.- 4.1.1 Turn-on delay.- 4.1.2 Rate equations, small signal analysis.- 4.1.3 Relaxation oscillation damping.- 4.1.4 Upper limits for the modulation bandwidth of laser diodes.- 4.2 Influence of lateral carrier diffusion on relaxation oscillation damping.- 4.3 Modulation bandwidth limits due to parasitic elements.- 4.4 Examples for high speed modulation of laser diodes.- 4.5 Modulation and longitudinal mode spectrum.- 4.5.1 Transient spectra of laser diodes.- 4.5.2 Lasing spectra under high speed modulation.- 4.5.3 Dynamic single-mode condition.- 4.6 Modulation with binary signals.- 4.7 Harmonic and intermodulation distortions (without fibre interaction).- 4.7.1 Harmonic and intermodulation distortions for low modulation frequencies.- 4.7.2 Harmonic and intermodulation distortions for high modulation frequencies.- References.- 5 Frequency-Modulation Characteristics of Laser Diodes.- 5.1 Relation between intensity-modulation and frequency modulation.- 5.2 Current/frequency-modulation characteristics.- 5.3 Chirp effects in directly modulated laser diodes.- 5.3.1 Spectral line broadening due to laser chirping.- 5.3.2 Chirp-reduction by proper pulse shaping.- 5.3.3 Time-bandwidth product of chirped pulses.- 5.3.4 Transmission of chirped pulses over single-mode fibres.- 5.4 Possibilities of modifying the chirp parameter ?.- 5.4.1 Dispersion of the chirp parameter ?.- 5.4.2 Chirp of laser diodes, coupled to optical cavities.- References.- 6 Instabilities and Bistability in Laser Diodes.- 6.1 Repetitive self-pulsations due to lateral instabilities.- 6.2 Instability and bistability in laser diodes with segmented contacts.- References.- 7 Noise Characteristics of Solitary Laser Diodes.- 7.1 Relative intensity noise (RIN).- 7.1.1 Basic properties of noise signals.- 7.1.2 Definition and measurement of RIN.- 7.1.3 Requirement of RIN for intensity modulated systems.- 7.2 Introduction of the spontaneous emission noise.- 7.3 Intensity noise of laser diodes.- 7.3.1 Intensity noise of laser diodes by studying single-mode rate equations.- 7.3.2 Mode partition noise.- 7.3.3 Mode partition noise analysis for nearly single-mode lasers.- 7.3.4 Mode-hopping noise.- 7.3.5 1/f-intensity noise.- 7.4 Statistics of intensity noise.- 7.4.1 Statistics of amplified spontaneous emission.- 7.4.2 Probability density distribution for the total laser light output.- 7.4.3 Statistics of mode partition noise.- 7.4.4 Turn-on jitter in laser diodes.- 7.5 Mode partition noise for the transmission of pulse-code modulated (PCM)-signals.- 7.5.1 Multimode lasers.- 7.5.2 The mode partition coefficient k.- 7.5.3 Nearly single-mode lasers.- 7.6 Phase and frequency noise.- 7.6.1 Phase and frequency noise characterization in general.- 7.6.2 Spectral line shape for white frequency noise.- 7.6.3 Spectral line shape for 1/f-frequency noise.- 7.6.4 Frequency noise and spectral linewidth for single-mode laser diodes.- 7.6.5 Power-independent contribution to the linewidth of laser diodes.- 7.6.6 Correlation between FM-noise and AM-noise.- References.- 8 Noise in Interferometers Including Modal Noise and Distortions.- 8.1 Noise in interferometers.- 8.1.1 Complex degree of coherence.- 8.1.2 Interferometric noise analysis for single-mode lasers.- 8.1.3 Interferometric set-ups for measuring the linewidth and the degree of coherence.- 8.1.4 Interferometric noise analysis for multimode lasers.- 8.2 Modal noise.- 8.2.1 Modal noise for monochromatic light sources.- 8.2.2 Modal noise for single-mode lasers with finite spectral linewidth.- 8.2.3 Modal noise for multimode laser diodes.- 8.2.4 Modal distortions.- 8.3 Modal noise and distortions in single-mode fibres.- References.- 9 Semiconductor Lasers with Optical Feedback.- 9.1 Amplitude and phase conditions for laser diodes with external cavities.- 9.1.1 Short external reflectors for longitudinal mode stabilization.- 9.1.2 Emission frequency shifts due to optical feedback.- 9.1.3 Single external cavity mode condition.- 9.1.4 Spectral linewidth for laser diodes with external optical feedback.- 9.2 Dynamics of laser diodes with external reflections.- 9.2.1 Derivation of the time-dependent electric field.- 9.2.2 Modulation characteristics of external-cavity lasers.- 9.3 Laser diodes with distant reflections.- 9.3.1 Classification of feedback regimes.- 9.3.2 Phase and frequency noise of laser diodes with distant reflectors.- 9.3.3 Intensity noise in laser diodes with distant reflectors.- 9.3.4 Coherence collapse.- 9.3.5 Tolerable feedback levels.- References.- 10 Laser Diodes with Negative Electronic Feedback.- 10.1 Modulation characteristics of laser diodes with negative electronic feedback.- 10.2 Linewidth narrowing and phase noise reduction with negative electronic feedback.- References.- 11 Circuitry for Driving the Laser Diode.- 11.1 Schemes for stabilizing the bias current.- 11.2 Laser drivers with optoelectronic integration.- References.
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paper_title: Nonlinear Characterization of a Kilowatt-class Amplifier Based on Laser Gain Competition

paper_content:

The scalability of dual wavelength laser gain competition for the design of beam combinable, high power fiber amplifiers is analyzed by characterizing the nonlinear phase accumulated due to self and cross-phase modulation.
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paper_title: Tailoring the Thermo-Optic Coefficient in Silica Optical Fibers

paper_content:

Compositional design of the thermo-optic coefficient of optical fiber is discussed. The influences of P2O5, B2O3, SrO, and F are presented. Phosphorus borosilicate compositions appear to be the most attractive for reaching negative values.
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paper_title: Self-bleaching phenomenon observed in the Ce/Yb Co-doped silica fiber

paper_content:

We report on a self-bleaching phenomenon observed in the Ce Yb co-doped silica fiber. The excess loss of the Ce/Yb fiber reduces about 1.5 dB/m at 633 nm after the pump laser was turned off for an hour; recovered about 10% of its pristine condition.
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paper_title: Experimental verification of spatial distribution of photodarkening in large mode area ytterbium doped fibers

paper_content:

We experimentally demonstrated that photodarkening is not uniformly distributed in the cross-section of bent LMA fibers. Photodarkening distribution depends on coiling diameter, and affects the use of fibers in applications and their photodarkening propensity measurement.
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paper_title: 488 nm irradiation induced photodarkening study of Yb-doped aluminosilicate and phosphosilicate fibers

paper_content:

Photodarkening in highly Yb-doped aluminosilicate and phosphosilicate fibers, under 488 nm irradiation, is presented. Both irradiation-induced excess loss and post-irradiation temporal loss evaluations reveal that Yb-doped phosphosilicate fiber is highly resistant to photodarkening.
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paper_title: Effect of heat and H2 gas on the photo-darkening of Yb+3 fibers

paper_content:

Heating a photo-darkened ytterbium fiber causes a recovery in spectral transmission to the pre-darkened state. Exposure to H2 at high temperatures causes a permanent change in the visible transmission identical to that caused by photo-darkening.
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Title: Materials for Optical Fiber Lasers: A Review

Section 1: INTRODUCTION
Description 1: This section introduces the topic of fiber lasers, their applications, and the significance of materials in their performance and power scaling.

Section 2: OPTICAL FIBER FABRICATION
Description 2: This section discusses the methods and processes used in the fabrication of optical fibers, focusing on silica-based fibers.

Section 3: Preform formation
Description 3: This subsection explains the chemical vapor deposition methods used to form the glass preforms from which optical fibers are drawn.

Section 4: Compositional limitations in vapor deposition
Description 4: This subsection outlines the limitations in the compositions of glasses that can be formed using vapor deposition methods.

Section 5: Optical fiber formation
Description 5: This subsection describes the process of drawing the preform into optical fiber and the application of polymer coatings.

Section 6: Other characteristics of drawn fiber
Description 6: This subsection reviews additional characteristics of drawn fibers, such as frozen-in stresses and optically active defects.

Section 7: Free ions
Description 7: This subsection introduces the trivalent lanthanide ions used in fiber lasers and discusses their spectroscopic properties.

Section 8: The "big-three"
Description 8: This subsection outlines the basic spectroscopic features of Yb³⁺, Er³⁺, and Tm³⁺, the three most commonly used trivalent lanthanides in fiber lasers.

Section 9: THE ACTIVE ION IN A GLASS HOST
Description 9: This section discusses the behavior of active ions (trivalent lanthanides) when placed into different glass hosts and their spectroscopic properties.

Section 10: Stark splitting, radiative transitions, and Judd-Ofelt theory
Description 10: This subsection covers the splitting of energy levels in the presence of a host material, radiative transitions, and the Judd-Ofelt theory for calculating line-strengths.

Section 11: Magnetic dipole transitions
Description 11: This subsection explains magnetic dipole transitions in trivalent rare earth ions and their contributions.

Section 12: Non-radiative (multiphonon) transitions
Description 12: This subsection discusses non-radiative transitions involving phonons and their impact on the upper state lifetime of active ions.

Section 13: THE OPTICAL FIELD AND LIGHT-MATTER INTERACTIONS
Description 13: This section reviews various light-matter interactions, such as nonlinear optical phenomena, that can limit power scaling in fiber lasers.

Section 14: The optical waveguide
Description 14: This subsection provides an overview of different optical waveguide configurations used in active optical fibers.

Section 15: Nonlinear interactions
Description 15: This subsection describes nonlinear optical interactions, including stimulated Brillouin scattering (SBS) and Raman scattering (SRS).

Section 16: Stimulated Brillouin scattering (SBS)
Description 16: This subsection dives into SBS, its mechanisms, thresholds, and methods for suppression.

Section 17: Stimulated Raman scattering (SRS)
Description 17: This subsection delves into SRS, its gain spectrum, factors influencing it, and suppression techniques.

Section 18: n² related phenomena
Description 18: This subsection examines Kerr nonlinearities, spectral quality impacts, and methods to mitigate self-phase modulation and cross-phase modulation.

Section 19: Transverse mode instability (TMI)
Description 19: This subsection discusses TMI, its adverse impacts on beam quality, and mitigation strategies.

Section 20: First principles to model glass properties
Description 20: This section outlines semi-empirical equations to model properties like refractive index and density in multicomponent glasses.

Section 21: Photodarkening
Description 21: This section reviews the phenomenon of photodarkening in doped fibers, its mechanisms, and approaches to mitigate its effects.

Section 22: CONCLUSION AND FUTURE PERSPECTIVES
Description 22: This concluding section summarizes the review, emphasizes the importance of material engineering in fiber lasers, and suggests future directions for research.

Section 23: Approaches to novel compositions and fiber material microstructures
Description 23: This subsection discusses less conventional methods for achieving novel fiber compositions and microstructures.

Section 24: Sol-gel methods
Description 24: This subsection covers sol-gel methods and their potential for doping silica preforms with a wider range of materials.

Section 25: Nanoparticle "doping"
Description 25: This subsection explains the benefits of heterogeneous systems like nanoparticle doping in modifying the chemical environment of dopants.

Section 26: Compositional comparison of fiber fabrication processes
Description 26: This subsection compares different preform and fiber fabrication processes, including vapor deposition, powder sintering, and the molten core method.