Heike Ebendorff-Heidepriem

Bismuth glass holey fibers with high nonlinearity.

We report on the progress of bismuth oxide glass holey fibers for nonlinear device applications. The use of micron-scale core diameters has resulted in a very high nonlinearity of 1100 W-1 km-1 at 1550 nm. The nonlinear performance of the fibers is evaluated in terms of a newly introduced figure-of-merit for nonlinear device applications. Anomalous dispersion at 1550 nm has been predicted and experimentally confirmed by soliton self-frequency shifting. In addition, we demonstrate the fusion-splicing of a bismuth holey fiber to silica fibers, which has resulted in reduced coupling loss and robust single mode guiding at 1550 nm.

Mid-IR Supercontinuum Generation From Nonsilica Microstructured Optical Fibers

In this paper, the properties of nonsilica glasses and the related technology for microstructured fiber fabrication are reviewed. Numerical simulation results are shown using the properties of nonsilica microstructured fibers for mid-infrared (mid-IR) supercontinuum generation when seeding with near-IR, 200-fs pump pulses. In particular, bismuth glass small-core fibers that have two zero-dispersion wavelengths (ZDWs) are investigated, and efficient mid-IR generation is enabled by phase-matching of a 2.0-mum seed across the upper ZDW into the 3-4.5 mum wavelength range. Fiber lengths considered were 40 mm. Simulation results for a range of nonsilica large-mode fibers are also shown for comparison.

Highly nonlinear and anomalously dispersive lead silicate glass holey fibers

In this paper we present significant progress on the fabrication of small-core lead-silicate holey fibers. The glass used in this work is SF57, a commercially available, highly nonlinear Schott glass. We report the fabrication of small core SF57 fibers with a loss as low as 2.6 dB/m at 1550 nm, and the fabrication of fibers with a nonlinear coefficient as high as 640 W-1km-1. We demonstrate the generation of Raman solitons at ~1550 nm in a short length of such a fiber which highlights the fact that the group velocity dispersion can be anomalous at these wavelengths despite the large normal material dispersion of the glass around 1550nm.

Formation and UV absorption of cerium, europium and terbium ions in different valencies in glasses

Cerium, europium and terbium ions can exist in diAerent valencies in glasses. The formation and ultraviolet (UV) absorption features of the ions were studied in a fluoride phosphate (FP) and two phosphate glasses. Various melting conditions and X-ray irradiation were applied to change the redox states of the ions. Band separation of the UV absorption spectra was carried out to reveal the components and to determine their spectroscopic properties. The UV absorption spectra of the lower valent Eu 2a ,T b 3a and Ce 3a ions are due to 4f‐5d transitions, which are split in several bands by the local field around the rare-earth (RE) ions. The crystal field splitting of the trivalent ions diAers from the one of the divalent ion. The UV absorption spectra of the higher valent Eu 3a ,T b 4a and Ce 4a ions are caused by charge transfer (CT) transitions from oxygen and fluorine to the RE ions. The positions and oscillator strengths of the 4f‐5d and CT transitions are studied in dependence on the RE and glass type. Furthermore, the ligand field strength of Eu 2a ions is investigated. Redox tendency, site symmetry and charge of the RE ions are important factors considering the influence of the RE type. DiAerent polarizability and electron donor power of the ligands as well as diAerent RE site symmetry in the glasses cause the compositional dependence of the transition properties. ” 2000 Elsevier Science B.V. All rights reserved.

Extrusion of complex preforms for microstructured optical fibers

We report a significant advance in preform extrusion and die design, which has allowed for the first time the fabrication of complex structured preforms using soft glass and polymer billets. Structural preform distortions are minimized by adjustment of the material flow within the die. The low propagation loss of an extruded complex bismuth glass fiber demonstrates the potential of this advanced extrusion technique for the fabrication of novel soft glass and polymer microstructured fiber designs.

High-nonlinearity dispersion-shifted lead-silicate holey fibers for efficient 1-/spl mu/m pumped supercontinuum generation

This paper reports on the recent progress in the design and fabrication of high-nonlinearity lead-silicate holey fibers (HFs). First, the fabrication of a fiber designed to offer close to the maximum possible nonlinearity per unit length in this glass type is described. A value of /spl gamma/=1860 W/sup -1//spl middot/km/sup -1/ at a wavelength of 1.55 /spl mu/m is achieved, which is believed to be a record for any fiber at this wavelength. Second, the design and fabrication of a fiber with a slightly reduced nonlinearity but with dispersion-shifted characteristics tailored to enhance broadband supercontinuum (SC) generation when pumped at a wavelength of 1.06 /spl mu/m-a wavelength readily generated using Yb-doped fiber lasers-are described. SC generation spanning more than 1000 nm is observed for modest pulse energies of /spl sim/ 100 pJ using a short length of this fiber. Finally, the results of numerical simulations of the SC process in the proposed fibers are presented, which are in good agreement with the experimental observations and highlight the importance of accurate control of the zero-dispersion wavelength (ZDW) when optimizing such fibers for SC performance.

Spectroscopic properties of Eu3+ and Tb3+ ions for local structure investigations of fluoride phosphate and phosphate glasses

Abstract The relationships between glass structure and spectroscopic properties of the doped ions Eu3+ and Tb3+ are of interest. Eu3+ and Tb3+ ions are used as structure-sensitive ions. The Ω t - parameters of Eu3+ were determined from absorption and emission spectra. The lifetime of the 5D0 state of Eu3+ was calculated from Ω t and compared with the experimentally determined lifetime. The electron-phonon coupling strength and phonon energy were obtained from phonon sideband spectroscopy. The f → d absorption transition of Tb3+ was used for determination of the nephelauxetic parameter. With increasing phosphate content the covalency between rare earth ions and surrounding ligands increases due to substitution of fluoride ions by oxygen ions having higher electron polarizability. This effect leads to increasing nephelauxetic shift, Ω 2 - parameter and electron-phonon coupling strength. In fluoride phosphate glasses, the diphosphate groups dominate the spectroscopic properties of the rare earth ions.

Suspended nanowires: Fabrication, design and characterization of fibers with nanoscale cores

We report a new approach for the fabrication of nanowires: the direct drawing of optical fibers with air suspended nanoscale cores. The fibers were made from lead silicate glass using the extrusion technique for preform and jacket tube fabrication. Fibers with core diameters in the range of 420-720 nm and practical outer diameters of 110-200 microm were produced, the smallest core sizes produced to date within optical fibers without tapering. We explored the impact of the core size on the effective mode area and propagation loss of these suspended nanowires relative to circular nanowires reported to date. As for circular nanowires, the propagation loss of these suspended nanowires is dominated by surface roughness induced scattering.

Fifty percent internal slope efficiency femtosecond direct-written Tm³⁺:ZBLAN waveguide laser.

We report a 790 nm pumped, Tm³⁺ doped ZBLAN glass buried waveguide laser that produces 47 mW at 1880 nm, with a 50% internal slope efficiency and an M² of 1.7. The waveguide cladding is defined by two overlapping rings created by femtosecond direct-writing of the glass, which results in the formation of a tubular depressed-index-cladding structure, and the laser resonator is defined by external dielectric mirrors. This is, to the best of our knowledge, the most efficient laser created in a glass host via femtosecond waveguide writing.

THz porous fibers: design, fabrication and experimental characterization

Porous fibers have been identified as a means of achieving low losses, low dispersion and high birefringence among THz polymer fibers. By exploiting optical fiber fabrication techniques, two types of THz polymer porous fibers--spider-web and rectangular porous fibers--with 57% and 65% porosity have been fabricated. The effective refractive index measured by terahertz time domain spectroscopy shows a good agreement between the theoretical and experimental results indicating a lower dispersion for THz porous fiber compared to THz microwires. A birefringence of 0.012 at 0.65 THz is also reported for rectangular porous fiber.