Three dimensional Light Bullets (3D-LBs) are the most symmetric solitary waves, being nonlinear optical
wavepackets propagating without diffraction nor dispersion. Since their theoretical prediction, 3D-LB's have
constituted a challenge in nonlinear science, due to the impossibility to avoid catastrophic collapse in conventional
homogeneous nonlinear media. We have recently observed stable 3D-LBs in media with periodically
modulated transverse refractive index profile. We found that higher order linear and nonlinear effects force the
3D-LBs to evolve along their propagation path and eventually decay. The evolution and decay mechanism entails
spatiotemporal effects, which under certain conditions, leads to superluminally propagating wavepackets.
The time-dependence of photodarkening (PD) in Yb-doped fibers is commonly fitted with a stretched exponential
function to determine typical parameters of the process. But, the experimental conditions to obtain consistent results
from the comparison of PD for different pump powers, various concentrations of the dopants, or fibers from different
manufacturers are not adequately regarded up to now. We discuss the requirements concerning the measurement method
as well as the impact of the initial state of the fiber under test.
Further on, the experimental results of PD characteristics are discussed in the framework of a kinetic model of the
observed processes. The discussion of the measurable PD loss is expanded by introducing the concept of the "PD state"
that defines the PD loss as a weighted mean and takes effect on the further evolution of the process. In this way, the basis
of fiber characterization and the understanding of the PD kinetics will be improved.
The doping of silica yields additional degrees of freedom to vary the optical parameters of index guided and band gap
controlled microstructured optical fibers (MOFs). Aside from the widely investigated rare earth doped microstructured
fibers for lasers also the integration of conventionally doped structural elements with passive functions into MOFs allows
to enhance effectively the optical performance of such fibers.
We report on progress in preparation of microstructured fibers with air holes and solid structural elements composed of
germanium and fluorine doped silica materials. The microstructured fibers were prepared by stack-and-draw technology.
The starting materials are preform rods and tubes with graded dopant concentration prepared by MCVD and sintering
technology. They were elongated to millimeter dimensions before packaging to final MOF preforms. We prepared MOFs
with both holey core and holey cladding. The microstructuring of the holey cladding is achieved with fluorine doped
Several applications have been investigated. The high photosensitivity of germanium-silica MOFs makes possible the
inscription of Bragg gratings with high efficiency. In fiber evanescent field sensors, such microstructured fibers improve
the overlap between the propagating light field and the analyte and allow therefore an increased sensitivity e.g. for gas
sensing with optical fibers. Solid MOFs with multiple cores in a highly precise array arrangement can been investigated
as a model system for the study of nonlinear dynamics in discrete optics.
We propose new design parameters for index-guiding holey-fiber (IGHF) that can provide flexibility in defect and lattice design as well as adiabatic mode transformation capability. The new defect consists of the central air hole and germanosilicate-ring surrounding it.
In this paper, utilizing layers of hollow structure as a defect, we introduce a new IGHFstructure and its optical properties are theoretically analyzed and experimentally demonstrated. The annulus mode intensity profile, effective mode area, chromatic dispersion properties and splicing loss for the single-layered and two-layered defect structure are investigated along with their dependence on the proposed defect parameters using plane wave expansion method and 3D full-vectorial Beam Propagation Method (BPM).
Unlike conventional silica defect IGHF, the proposed structure showed an annulus mode profile in the fundamental mode, which can benefit from larger effective area to separate the fiber non-linearity from other unique optical properties of IGHFs. The proposed IGHF also showed low splice loss unlike previous conventional IGHFs with collapsed hole by arc since the newly introduced defect structure, germanosilicate-rings are remained as solid core with high index contrast D. With the new defect parameters we could achieve a large area annulus mode profile, low splice losses to standard fiber, 0.7dB at 1.55 m, and chromatic dispersion with low slope, 0.002ps/km.nm2
A new index-guiding-holey-fiber is proposed for flexible modal birefringence control by introducing a fourlayered defect with central air hole, silica pedestal, germanosilicate ring, and silica clad. Effects of these parameters over birefringence are reported.
We have doped the core of Ytterbium (Yb) laser fibers additionally with Neodymium (Nd) to exploit wavelength-multiplexed high-power pump systems, which are commercially available. By pumping such a Nd:Yb-codoped fiber with the 808/940/978 nm-diode system, we could demonstrate CW output powers of more than 1 kW with high laser slope efficiency. In order to get a better understanding of this laser medium, we studied the fluorescence and the laser behavior of Nd:Yb fibers with different rare earth concentrations in comparison to a fiber doped solely with Nd. A theoretical model for the calculation of the fluorescence decay curve and spectrum as well as the laser characteristic and wavelength was developed, that takes the energy transfer process from Nd to Yb ions into account. Comparing the experimental and theoretical results, the behavior of the Nd:Yb high power fiber laser is understood as a collective emission of both ion types within the same wavelength region. These investigations contribute to the optimization of high power fiber lasers under the viewpoint of thermal load.