Recent evolution in nanoscience and nanotechnologies has brought novel possibilities in the development of optical fibers. Dual-wavelength fiber lasers have attracted scientific attention due to their prospective applications in fields including next-generation optical fiber communication, ranging systems, and spectroscopy. Nanostructurization has shown itself as a suitable method for preparing fiber lasers operating simultaneously at dual wavelengths. We report on the design of nanostructured or “pixelated” core fabricated by assembling erbium- and ytterbium elements, as well as on the optimization of the average concentration of rare earth elements using numerical modeling. Preliminary experimental results of erbium- and ytterbium-doped nanostructured-core fiber will be presented.
For applications in fiber lasers and amplifiers, silica glass remains a perspective host for rare-earth ions thanks to favorable material properties. However, the luminescence of RE ions is hindered by the high phonon energy of silica lattice and low solubility of RE ions, which cause luminescence quenching. Pure silica thus needs to be co-doped with suitable additives such as Al2O3, which form a beneficial low-phonon environment and increase the solubility of RE ions. Luminescence lifetime is one of the most important parameters to determine the suitability of RE-doped silica fibers for laser operation. Optical fibers with higher luminescence lifetime typically exhibit higher values of slope efficiency and lower laser threshold. It was previously shown that the environment of Tm3+, Ho3+ or Yb3+ ions and luminescence lifetime may be significantly affected by fabrication processing at high temperatures, probably due to the chemical changes occurring in the matrix. However, the effect of fabrication processing on the spectroscopic properties of another important RE ion, Er3+, is different to the other ions and remains unclear. In this contribution, we present a study on the fluorescence lifetime of a highly-doped optical fiber prepared by the MCVD method combined with nanoparticle-doping. The fluorescence lifetime of Er3+ was studied in several stages of fabrication processing. The influence of fabrication processing on the fluorescence lifetime of Er3+ ions was analyzed and discussed.
In recent years the novel active glass materials for optical fibers with broadband emission are of great interest due to potential application in spectroscopy, environmental monitoring or medicine. Development of that kind materials is based on elaborating the glass matrix co-doped with different rare earth ions, e.g. Er, Yb, Ho, Tm. Glasses doped with multiple rare earths characterize with a high number of spectroscopic parameters, due to the presence of energy transfer phenomena between those different rare earth ions. Nonlinear nature of that phenomena varying with the dopants concentration levels, makes the design and development of optical fibers made of glass doped with several active ions not trivial. In this work, we present the nanostructured material composed of several separated glass areas with subwavelength size with individually designed parameters. As a proof-of-concept, we propose the active phosphate fiber with the core consisted of two types of glasses doped with Yb3+ and Er 3+ ions, which exhibit independent performance. The presented phosphate fiber laser operates simultaneously at dual wavelengths at 1.04 μm and 1.535 μm with very good beam quality of M2=1.14 and slope efficiency of 23.0% and 9.8%, respectively. To our knowledge, this kind of fiber has not been demonstrated previously
Holmium-doped aluminosilicate fibers are frequently used in holmium-doped fiber lasers (HDFL) thanks to their strong emission at 2 μm. Fluorescence lifetime is one of the most important parameters to determine the suitability of holmium doped optical fibers for use in fiber lasers. One of the potential mechanisms for the shortening of fluorescence lifetime is the diffusion of RE ions and Al2O3 at high temperatures during the fiber preparation process. We have prepared a Ho-doped aluminosilicate optical fiber preform using MCVD combined with nanoparticle doping. The prepared preform was subjected to various fabrication processes such as preform elongation, fiber drawing or additional heat treatment, the fluorescence lifetime was measured in all stages of the experiment and its dependency on the fabrication process was discussed. The original preform exhibited a long fluorescence lifetime of 1.433 ms. Gradual application of fiber fabrication processes such as preform elongation or fiber drawing resulted in a decline of fluorescence lifetime down to 1.174 ms in the case of overcladded optical fiber. The decrease of fluorescence lifetime was ascribed to the diffusion of dopants and the changes in the Ho3+ ion environment, which increased the rate of multiphonon relaxation, as well as clustering of holmium ions, which increased concentration quenching.
In this paper, we investigate the influence of various nanostructured-core fiber fabrication processes, such as preform elongation or fiber drawing, on the fluorescence lifetime of Yb3+ ions. The optical fiber preform was prepared using Modified Chemical Vapor Deposition (MCVD) method combined with Al2O3 nanoparticle doping. The optical fiber preform was subjected to various processing treatments involving heat and mechanical stresses, i.e. preform elongation and fiber drawing, and the fluorescence lifetime was measured in all stages of fiber fabrication, i.e. original preform, elongated preform (cane), fiber and overcladded fiber. It was found that the time-resolved photoluminescence properties of Yb3+ ions in silica glass are strongly dependent on the processing of the material. The fluorescence lifetime of the 2F5/2 level of Yb3+ ions decreased with the heat and mechanical treatment, which was explained by the break-up of Al2O3 nanoparticles, diffusion of dopants and changes in the Yb3+ phonon environment as well as clustering of the Yb3+ ions. The fiber drawing exhibited a stronger effect compared to preform elongation which was ascribed to the high rate of cooling and mechanical stresses during the drawing process. In general, the heat and mechanical processing of Yb-doped optical fiber preforms leads to a deterioration of time-resolved photoluminescence properties.
We report for the first time successful inscription of high reflectivity Bragg grating in nanostructured core active fiber. Nanostructurization of the fiber core allows to separate the active and photosensitive areas and to distribute them all over the core. As a result unfavorable clustering between germanium and ytterbium particles is avoided. The distribution of discrete glass areas with feature size smaller than λ/5 results in effectively continuous refractive index profile of the fiber core. We present a single-mode fiber with built-in Bragg grating for laser application with the core composed of ytterbium and germanium doped silica rods. The core structure is arranged as a regular lattice of 1320 doped with ytterbium and 439 doped with germanium silica glass rods. The average germanium doping level within the core of only 1.1% mol allowed efficient inscription of Bragg grating. The nanostructured core was 8.6 μm and the internal cladding was 112 μm in diameter coated with low index polymer to achieve the double-clad structure. In the first proof-of-concept in the laser setup we achieved 35 % of slope efficiency in relation to launched power for the fiber length of 18 m. The output was single-mode with spectrum width below 1 nm. The maximum output power limited by pumping diode was 2.3 W. The nanostructurization opens new opportunities for development of fibers with a core composed of two or more types of glasses. It allows to control simultaneously the refractive index distribution, the active dopants distribution and photosensitivity distribution in the fiber core.
We demonstrate the 3%mol ytterbium doped phosphate glass air-clad photonic crystal fibre (PCF) laser of 43 cm length
in single-mode operation. The fabrication and testing of the fibre laser is introduced. The laser generates from the 12 μm
core of photonic microstructure at wavelength of 1030 nm. Near 4-W output power and 14.6% slope efficiency against
the launched pump power is demonstrated in preliminary characterization.
Double-clad photonic crystal fibre structure for laser applications is demonstrated. The double-clad structure of the fibre has the air-cladding with glass bridges of waists less than 500nm. The fibre was produced with phosphate glass and the core region was doped with ytterbium. The fibre was investigated and we found it to be monomode for generation wavelength of 1008nm. Whole fibre producing process including doped and undoped glass manufacturing and fibre drawing was held in Institute of Electronic Materials Technology.
We present experimental realization of elliptical-hole rectangular lattice photonic crystal fibres fabricated from multi-component glass. The photonic cladding has a lattice constant 2.17 μ and 3.72 μ for main axis, respectively and elliptical holes with ellipticity 2.14. The rectangular lattice is chosen to obtain two-fold geometry and to increase the global asymmetry of photonic structure, which enhance birefringence of fibre. Rectangular lattice allows also a better control of elliptical air holes uniformity during fabricating process. Fabricated fibres have a cladding with a rectangular cross-section. It allows for easy identification of the fibre's principal axes and orientation of the fibre with respect to directional measured perturbation like axial stress, bending force in sensor applications. Using a full vector plane-wave expansion method an influence of structure parameters such as ellipticity of air holes and aspect ratio of rectangular lattice on birefringence and modal properties of the fibres are studied. Potential applications of the fibres are discussed.
A range of integrated fiber optic structures - lightguides, image guides, multicapillary arrays, microstructured (photonic) fibers - manufactured in the Institute of Electronic Materials Technology (ITME) is described. All these structures are made of multicomponent glasses (a part of them melted in ITME). They can be manufactured in similar multistep process that involves drawing glass or lightguide rods and tubes preparing glass performs, stacking a bundle with rods and (or) tubes, drawing multifiber or multicapillary performs. Structure formation, technological process, characterization and applications of different integrated structures are presented.
KEYWORDS: Optical fibers, Polarization, Birefringence, Photonic crystal fibers, Solids, Silica, Capillaries, Near field, Near field optics, Refractive index
A square lattice photonic crystal fiber is described. The square lattice structures were fabricated, characterized and their polarization properties were investigated. The polarization properties of the fibers were not as strong as those reported previously in highly birefringent PCF, but these structures have considerable potential for high birefringence.
The use of piezoelectric transducer and acoustooptically induced waves were proposed for mode field excitation on a single-mode microbend fiber taper structure. As the result the in-line fiber attenuator was proposed tuned easily by the transducer low power drive voltage which was fully telecommunication compatible. The tuning range was up to 13 dB and the excess losses not exceeded 0.3 dB typically.
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