COST Action
MP1401

Prof. Stefano Taccheo

Future perspectives on Fibre Lasers: from Materials to Applications
opening ceremony lecture

An overview of the European Action COST MP1401 "Advanced fibre laser and coherent source as tools for society, manufacturing and lifescience" scope and activities will be presented by the chairman of the Action in this special opening ceremony lecture.

Prof. Alicia Durán

Transparent oxyfluoride glass-ceramics: bulk, fibres and thin films by different processing routes

The growing field of photonics demands the design of new optical materials for diverse technological applications, such as lasers, wavelength down-converters, lighting, etc. Rare Earth (RE) doped oxyfluoride glass-ceramics are promising candidates for this role thanks to their good processing and optical properties. They combine the good chemical and mechanical stability of oxide glass matrixes with the good optical properties of low phonon energy fluoride nano-crystals. Particularly, transparent glass-ceramics containing LaF₃ nano-crystals are very relevant due to the incorporation of the RE ions in the crystalline structure.
LnF₃ and LnRF₄ containing nano glass-ceramics (nGCs) have been prepared by melting-quenching (MQ) and by sol-gel (SG) to study the effect of processing on their properties and the new opportunities opened with alternative methods.
Crystallisation mechanisms depend on the processing route that also permits to obtain different types of materials, from bulk to fibres prepared from the glass precursors, up to coatings prepared by sol-gel. The properties of the different materials are discussed correlating the processing method with the structure and optical properties of the final glass-ceramic materials.

Prof. Angela Seddon

Spectroscopy of rare earth doped chalcogenide glass fibres

We will start by introducing the spectroscopy of rare earth ions, covering 4f energy levels, free rare earth ions, rare earth ions in a crystal field, rare earth ions in glasses and optical spectra. We will cover Judd-Ofelt theory, fundamental properties of transition cross-sections, Einstein theory and the Ladenburg-Fuchtbauer Relation, McCumber theory of emission cross-sections, fluorescent lifetimes, linewidths and broadening, ion trapping/diffusion. Population dynamics, including multiphonon decay and phonon-assisted transitions, will be considered. We will apply our thinking to the rare earth ion Er³⁺, doped into various glass hosts discussing gain and excited state absorption. We will touch on rate equation analysis of the population dynamics. Applying all of this to the very low phonon energy environment of rare earth ions doped within chalcogenide glasses, we will see that the rare earth ion electronic transitions now overlap in energy with fundamental vibrational transitions of water based impurities in the glass network, offering an additional barrier to photoluminescence and lasing. We will finish with a ‘state of the nation’ summing up of how close we are to making mid-infrared fibre lasers for above 4 microns’ wavelength operation.

Borut Lenardič, MSc.

MCVD preform technology for special optical fibers

While MCVD technology has lost its importance for fabrication of standard telecom fibers, it is still one of the most important and most often used techniques for manufacturing of special optical fibers. MCVD permits creation of a variety of weaveguide structures and glass compositions by using a wide range of dopants and precursors. The equipment and principles of this widely spread technology are examined and state-of-art deposition techniques are presented through practical examples of special optical fiber preforms. The importance and suitability of MCVD technology for fabrication of laser and sensor optical fibers is evaluated.

Prof. Dominik Dorosz

RE- doped non-silica materials and spectroscopy

Development of new photonic devices based on optical fibres is possible thanks to constant searching for advanced materials adapted to specific applications of optical waveguide structures and also due to the development of technological processes used for their production or further processing.
In the presentation the properties of RE non - silica materials and optical fibres for emission in VIS, 1µm and 2µm spectral region will be shown. In particular up-conversion processes in co-doped (i.a. Yb³⁺/Ho³⁺, Yb³⁺/Tm³⁺) antimony and tellurite glasses and optical fibres will be discussed. The analysis of mechanisms influencing the differences in luminescent properties of the glasses and optical fibres suggests that the concentration and molar ratio of lanthanide ions are crucial for emission. Luminescent properties of optical fibres indicate that non-silica glasses are promising material for fibre ASE sources in VIS-NIR region.

Prof. Johann Troles

IR- transparent materials and fibers for lasers

The infrared limit of silica fibers is around 2.5 - 3µm. For the realization of new generation fiber lasers emitting longer wavelength, other materials have to be considered and investigated. In this lecture, the different infrared windows will be defined, and the interest of Mid-infrared (mid-IR) fibers and mid-IR fiber lasers will be presented. And, an overview about different materials and glasses that can be used for the realization of Mid-IR fibers and Mid-IR fibers lasers will be discussed (Heavy oxides, fluorides, silver halides, chalcogenides...)

Dr. Kay Schuster

From advanced methods of preform fabrication to specialty coated fibers – REPUSIL and Fiber Drawing Technology

The lecture will focus on the recently developed “Reactive Sintering of Powdered Silica – REPUSIL” as an alternative to standard MCVD technologies in particular for laser applications. However, even the technologies are new; they face old problems (e.g. glass defects and their absorptions) and follow similar rules (e.g. incremental influence of glass dopants on the refractive index). A summary on potentials and limits of the described fabrication technique for active as well as passive glass preforms and fibers will be given.
The drawing of fibers is well understood for standard telecommunication fibers. However, specialty fibers require well adapted drawing conditions with regard to different materials, preform volumes, fiber diameters, fiber cross sections etc. The lecture will give a summary on the principles of fiber drawing and on the specifics of specialty fiber fabrication. The performance of an optical fiber is strongly characterized by its outer layer which is usually an optical coating. The optical function mainly characterized by its refractive index and the protection against mechanical and environmental impacts are the main issues. For the great variety of polymers there are a couple of techniques for the application of standard and specialty coatings on the fiber. Beside polymer coatings for advanced sensor applications (Fiber Bragg Grating sensors based on Draw Tower Gratings®) and high power lasers new materials like metals became of great interest due to the increased resistance to temperature and humidity and the improved coolability.

PhD. Laeticia Petit

Optical fiber preform preparation

In this lecture, we will review the different conventional techniques to prepare RE-doped silica preforms which cannot be obtained using standard melt-quench technique. We will also discuss about the development of new approaches such as nanoparticle dispersions solution-doping to process preforms with better homogeneity of dopants concentration distribution. Finally we will review the different tools used to analyze the preforms such as for example refractive index profiler and EPMA.

Dr. Martin Becker

Fiber Bragg Gratings for Fiber Lasers

Fiber Bragg gratings (FBGs) are key components for fiber lasers. Fiber Bragg grating pairs replace dielectric mirrors and allow the construction of monolithic high power fiber lasers. Volume Bragg gratings stabilize pump lasers, and large grating arrays pave the way to wavelength tuning. Additionally, wavelength scaling allows to expand the accessible laser wavelength range from the visible to the infrared. Three main aspects make FBG inscription for fiber lasers challenging. To reduce the amount of splice connections, FBGs have to be written in rare-earth doped fibers that do not provide classical photosensitivity. Additionally, the target wavelength range turns out to be larger than in telecom and sensing. Finally, the increase of the size of the fiber core to increase the amount of guided light induces new challenges that prevent good filtering properties of the gratings. Therefore, the realization of fiber Bragg gratings for fiber lasers usually requires a careful choice of the laser system for inscription and FBG inscription technology.
Keywords: fiber Bragg gratings, optical fibers, two-beam interferometry, femtosecond laser, photosensitivity

Dr. Sébastien Février

Ultrafast Fiber Lasers

Thanks to key advantages such as diffraction limited beam, compactness, stability, high power, and turn-key operation, ultrafast fiber lasers are gaining popularity in several industrial and scientific applications such as precision material processing, nonlinear microscopy, precision metrology and high-field physics, to name a few. Expanding the application area of ultrafast fiber lasers will require intense research efforts on key components such as waveguides and fibers (e.g. for the near to mid-infrared spectral region) as well as on laser architectures. In this hot context, the first section of this lesson will cover the fundamentals of ultrafast fiber laser technology. Then, we will discuss how specialty fibers can allow us to transpose the potential held by modern laser architectures (e.g. chirped pulse oscillator) to unexplored long wavelengths. Finally we will describe how ultrafast fiber lasers could unleash the potential held by new bio-imaging modalities.

Dr. Virginie Nazabal

Sensor based on fluorescence of RE doped chalcogenide waveguides

The 3-15 µm range is a key region for a large number of applications in diverse areas such as biology and medicine, molecular spectroscopy, environmental monitoring... Infrared (IR) spectroscopy is a simple, reliable, fast, cost-efficient, non-destructive method for the detection and monitoring of molecules. As a part of this presentation, we will discuss our concerns in the field of material sciences; i.e. chalcogenide glasses as materials of choice for IR sensor devices. With high refractive index and an appropriate rare earth (RE) solubility, chalcogenide glasses exhibit high spontaneous emission probabilities. The low phonon energy of these materials limits the non-radiative multiphonon relaxation rates. All these properties result in interesting quantum efficiencies for RE ion transitions. Moreover, these glasses can be produced into the form of fibers or rib/ridge waveguides allowing the light to be guided improving the brightness of the source. Consequently, these mid-IR fluorescent waveguides can be introduced into optical sensor. Aknowledgement: V. Nazabal is thankful to Brittany region, Intercarnot IFREMER/BRGM, ANR SEED CGSµLAB, ANR LOUISE, ADEME for financial support.

Dr. Wilfried Blanc

Luminescence properties of rare-earth ions doped nanoparticles embedded in glassy matrix

Rare-earth ions are unique chemical elements covering a wide range of applications. In particular, they allowed many innovative applications in the field of optical fibers. In order to develop new features, a growing interest is the use of nanoparticles doped with rare-earth ions, such as nanoparticles used for medical imaging or nanoparticles contained in glass-ceramics. This lecture will provide a review on the spectroscopic properties of rare-earth ions in these materials. In particular, I will discuss changes induced by the insertion of rare-earth ions in nanoparticles and the influence of the glassy matrix. Understanding these different phenomena opens new perspectives for photonics and optical fibers.