Jakub Cajzl

All-fiber Ho-doped mode-locked oscillator based on a graphene saturable absorber

In this Letter, we demonstrate a graphene mode-locked, all-fiber Ho-doped fiber laser generating 1.3 nJ energy pulses directly from the oscillator. The graphene used as a saturable absorber was obtained via chemical vapor deposition on copper substrate and immersed in a poly(methyl methacrylate) support. The laser generated ultrashort soliton pulses at 2080 nm with bandwidth up to 6.1 nm. The influence of the output coupling ratio and the SA modulation depth on the mode-locking performance was also investigated.

The influence of nanostructured optical fiber core matrix on the optical properties of EDFA

In this contribution we demonstrate the effect of the nanostructured optical fiber core matrix, doped with erbium and Al2O3, 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 Er3+ ions or Er2O3. 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 Er3+ ions.

Thulium-doped fibre broadband source for spectral region near 2 micrometers

Abstract We demonstrated two methods of increasing the bandwidth of a broadband light source based on amplified spontaneous emission in thulium-doped fibres. Firstly, we have shown by means of a comprehensive numerical model that the full-width at half maximum of the thulium-doped fibre based broadband source can be more than doubled by using specially tailored spectral filter placed in front of the mirror in a double-pass configuration of the amplified spontaneous emission source. The broadening can be achieved with only a small expense of the output power. Secondly, we report results of the experimental thulium-doped fibre broadband source, including fibre characteristics and performance of the thulium-doped fibre in a ring laser setup. The spectrum broadening was achieved by balancing the backward amplified spontaneous emission with back-reflected forward emission.

Special optical fibers doped with nanocrystalline holmium-yttrium titanates (HoxY1-x)2Ti2O7 for fiber-lasers

The paper deals with the preparation and characterization of the silica optical fibers doped with nanocrystalline holmium-yttrium titanates (HoxY1-x)2Ti2O7 with optimized luminescence properties. The sol-gel approach was employed to prepare colloidal solution of (HoxY1-x)2Ti2O7 precursors. The concentration of Ho3+ 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 (Ho5Y95)2Ti2O7. 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 Ho3+ ions in the fiber core was 0.03 at %. Background attenuation of prepared fiber at 850 nm was smaller than 0.5 dB⋅m-1.

Erbium luminescence in various photonic crystalline and glass materials - a review

Er3+ ion is being utilised in photonics because of its strong emission in the third communication window around 1550 nm. It is a region of the very low absorption of silicate glasses, i.e. the materials that have been widely used for the fabrication of optical fibres and erbium-doped fibre lasers. This article reviews our experiments where the effect of the crystal field in various matrices has been investigated. It provides a comparison of the luminescence properties of amorphous silicate glasses and various crystals (LiNbO3, α-Al2O3, ZnO (wurtzite), diamond). In the amorphous glass matrix, the presence of non-bonding oxide has a positive effect on the luminescence properties. In various crystals, it follows that for high luminescence, erbium inevitably occupies substitutional and, preferably, octahedral positions in in highly ordered structure.

Evaluation of energy transfer coefficients in Tm-doped fibers for fiber lasers

In this work we report on the determination of the cross-relaxation energy-transfer coefficients from the measurements of the fluorescence lifetimes of the 3F4 and 3H4 energy levels of Tm3+ ions in the experimentally prepared optical fibers. Optical fiber preforms were prepared by solution-doping of Tm3+ ions with either Al3+ 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.

Preparation of optical fibers with non-circular cross-section for fiber lasers and amplifiers

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.

Characterization of fluorescence lifetime of Tm-doped fibers with increased quantum conversion efficiency

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.

Thulium-doped optical fibers and components for fiber lasers in 2 µm spectral range

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.

Erbium Luminescence Centres in Single- and Nano-Crystalline Diamond—Effects of Ion Implantation Fluence and Thermal Annealing

We present a fundamental study of the erbium luminescence centres in single- and nano-crystalline (NCD) diamonds. Both diamond forms were doped with Er using ion implantation with the energy of 190 keV at fluences up to 5 × 1015 ions·cm−2, followed by annealing at controllable temperature in Ar atmosphere or vacuum to enhance the near infrared photoluminescence. The Rutherford Backscattering Spectrometry showed that Er concentration maximum determined for NCD films is slightly shifted to the depth with respect to the Stopping and Range of Ions in Matter simulation. The number of the displaced atoms per depth slightly increased with the fluence, but in fact the maximum reached the fully disordered target even in the lowest ion fluence used. The post-implantation annealing at 800 °C in vacuum had a further beneficial effect on erbium luminescence intensity at around 1.5 μm, especially for the Er-doped NCD films, which contain a higher amount of grain boundaries than single-crystalline diamond.