We present the preparation and characterization of holmium-doped silica-based optical fibers for fiber lasers operating around two micrometers. The fibers were prepared by a modified chemical vapor deposition process and co-doped with aluminum oxide. Alumina was doped with the use of two different methods – solution doping and nanoparticle doping. Prepared optical preforms and fibers were characterized according to their optical, spectral and laser properties. It was observed that the doping by alumina nanoparticles improve a fluorescence lifetime and laser characteristics such as laser threshold and slope efficiency. The comparison of both doping methods is presented and results are discussed.
We review the results of investigation of a special mode of self-pulsing, longitudinal-mode-instability regime, so-called self-induced laser line sweeping. This description reflects the fact that the self-pulsing (in the form of self-sustained relaxation oscillations) coexists with a spectacular laser line drift with time. It is accompanied by creation of dynamic refractive index gratings along the active fiber in the laser cavity. Such gratings have pitch of less than a micrometer, defined by half of the wavelength of the laser mode responsible for the grating build-up. Although longitudinal mode instabilities in fiber lasers are known for a long time, the associated refractive index gratings were studied just recently. An estimation of reflectivity of the dynamics gratings in self-swept fiber lasers is given using numerical model.
We present preparation and characterization of thulium-doped silica-based optical fibers for fiber lasers. The fibers were
prepared by modified chemical vapor deposition process and doped with alumina and thulium ions. Alumina co-doping
was achieved through two different methods – solution doping and nanoparticle doping method. Prepared preforms were
characterized in terms of refractive index profiles and dopants distribution. For the drawn fibers, their spectral
attenuation, fluorescence lifetime and laser performance were measured. In the case of nanoparticle doping, better laser
characteristics were observed. Discussion and explanation of the trends for laser efficiency improvement is given.
In this work we report on the determination of the cross-relaxation energy-transfer coefficients from the measurements of
the fluorescence lifetimes of the <sup>3</sup>F<sub>4</sub> and <sup>3</sup>H<sub>4</sub> energy levels of Tm<sup>3+</sup> ions in the experimentally prepared optical fibers.
Optical fiber preforms were prepared by solution-doping of Tm<sup>3+</sup> ions with either Al<sup>3+</sup> ions or dispersed alumina
nanoparticles. Optical fibers were characterized by means of Tm, Al and Ge concentrations, refractive index profiles,
optical spectral attenuations, luminescence spectra and fluorescence lifetimes. Highly aluminium-codoped optical fibers
exhibited fluorescence lifetimes of up to 756 μs.
Silica optical fibers doped with rare-earth elements are key components of high-power fiber lasers operating in near-infrared region up to 2.1 μm. In this contribution we deal with preparation and optical characterization of silica-based optical preforms and fibers doped with thulium for fiber lasers operating around 2 μm. A set of fibers with thulium concentration ranges 1000-5000 ppm was prepared by the MCVD solution doping method and characterized. A decrease of fluorescence lifetime of thulium from 487 μs to 378 μs was observed with increasing rare-earth concentration in fiber core. This phenomenon can be explained by energy transfer between ions and ion clustering. Fabricated fibers were suitable for use in fiber lasers.
In this paper we present experimental results of characterization of the experimentally prepared thulium-doped optical fibers in double-clad hexagonal fiber geometry for cladding optical pumping at a wavelength of 793 nanometers. The fiber was fabricated by the modified chemical vapor deposition and solution doping method and coated with polymer with lower refractive index than silica. The fiber was characterized in views of its refractive index profiles, thulium ions concentration, spectral absorptions, fluorescence lifetime, and performance in fiber laser.
The paper deals with the preparation and characterization of the silica optical fibers doped with nanocrystalline holmium-yttrium titanates (Ho<sub>x</sub>Y<sub>1-x</sub>)<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub> with optimized luminescence properties. The sol-gel approach was employed to prepare colloidal solution of (Ho<sub>x</sub>Y<sub>1-x</sub>)<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub> precursors. The concentration of Ho<sup>3+</sup> ions in the compounds was varied up to x=0.4. Prepared sols were calcined at 1000 °C forming xerogels which were characterized by X-ray diffraction to confirm their structure. The xerogels were analyzed by the mean of steady-state luminescence technique to optimize the concentration of Ho3+ ions in the compound. The most intensive emission at 2050 nm was observed for the compound (Ho<sub>5</sub>Y<sub>95</sub>)<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub>. Sol of the corresponding composition was soaked into the porous silica frit deposed inside the silica substrate tube which was collapsed into preform and drawn into optical fiber. Single mode optical fiber with the core diameter 12 μm and outer diameter 125 μm was prepared. Numerical aperture of prepared fiber was 0.16. The concentration of Ho<sup>3+</sup> ions in the fiber core was 0.03 at %. Background attenuation of prepared fiber at 850 nm was smaller than 0.5 dB⋅m<sup>-1</sup>.
In this work we report on the fluorescence lifetime characterization of the experimentally prepared Tm-doped silica
optical fibers with increased quantum conversion efficiency (QE). Optical fibers were drawn from preforms prepared by
conventional solution-doping of thulium and aluminium chlorides and by deposition of dispersed alumina nanoparticles
with thulium chloride. Prepared preforms and optical fibers were characterized by means of thulium and aluminium
concentrations, refractive index profiles, optical spectral attenuations (absorptions) and fluorescence lifetimes. Highly
aluminium-codoped optical fiber prepared from alumina nanoparticles exhibited fluorescence lifetime of about 690 μs,
which is about 40% higher compared to the conventionally prepared Tm-doped silica fiber.
Optical fibers with non-circular cross-sections can be effectively used for pumping of fiber lasers and amplifiers. Noncircular
fiber-optic structures can be also employed for a control of propagating light polarization. Details of preparation
of three types of optical fibers with non-circular cross-sections are presented. A polarization-maintaining (PM-) fiber
with elliptical core was drawn from non-circular preform to study the effect of drawing temperature onto the fiber
geometry. A stabilization of fiber rotation during the drawing was successfully tested during preparation of double-clad
(DC-) optical fibers with hexagonal and special tailored cross-sections. The conservation of original geometry during the
drawing was examined.
Thulium-doped fiber lasers are attractive light sources in the infrared region at around 2 micrometers. Their slope efficiency may reach 70 % and thus they are challenging the well-established ytterbium-doped fiber lasers operating at around 1 micrometer. Two-micrometer radiation sources have many advantages over the one-micrometer sources, e.g., better eye-safety, relaxed non-linear limits and more efficient material processing for some types of materials. Particularly important applications of lasers at 2 micrometers are in nonlinear frequency conversion to mid-infrared wavelength. In this paper we review our recent progress in research of thulium-doped fibers and fused fiber components.
In this contribution we demonstrate the effect of the nanostructured optical fiber core matrix, doped with erbium and Al<sub>2</sub>O<sub>3</sub>, on the resulting optical properties. Several optical fibers with nanostructured cores were drawn from preforms prepared by different techniques, i.e., by conventional doping from solution of erbium and aluminium chlorides, by deposition of the dispersed alumina nanoparticles with either Er<sup>3+</sup> ions or Er<sub>2</sub>O<sub>3</sub>. Reference bulk samples were prepared by the solid-state approach and thermally treated by similar way as optical fibers. Prepared optical fibers and bulk samples were investigated by the absorption spectroscopy. Reference samples were analyzed by the X-ray diffraction for the determination of the crystalline properties of formed nanostructures. It was found that nanocrystals inside the optical fiber core matrix improves the homogeneity and decreases the basic optical attenuation. Nanostructured alumina inside the fiber core matrix enhances the absorption properties of Er<sup>3+</sup> ions.