Search results for "Optical Fibers"
showing 10 items of 107 documents
Assessing sensory versus optogenetic network activation by combining (o)fMRI with optical Ca2+ recordings
2016
Encoding of sensory inputs in the cortex is characterized by sparse neuronal network activation. Optogenetic stimulation has previously been combined with fMRI (ofMRI) to probe functional networks. However, for a quantitative optogenetic probing of sensory-driven sparse network activation, the level of similarity between sensory and optogenetic network activation needs to be explored. Here, we complement ofMRI with optic fiber-based population Ca2+ recordings for a region-specific readout of neuronal spiking activity in rat brain. Comparing Ca2+ responses to the blood oxygenation level-dependent signal upon sensory stimulation with increasing frequencies showed adaptation of Ca2+ transient…
Nonlinear femtosecond pulse propagation in an all-solid photonic bandgap fiber
2009
Nonlinear femtosecond pulse propagation in an all-solid photonic bandgap fiber is experimentally and numerically investigated. Guiding light in such fiber occurs via two mechanisms: photonic bandgap in the central silica core or total internal reflection in the germanium doped inclusions. By properly combining spectral filtering, dispersion tailoring and pump coupling into the fiber modes, we experimentally demonstrate efficient supercontinuum generation with controllable spectral bandwidth.
Vector FWM in optical fibers: tuning techniques and applications
2022
Recientemente, el efecto no lineal de mezcla de cuatro ondas (FWM) en fibras ópticas ha atraído un gran interés para el desarrollo de nuevas fuentes de luz de fibra óptica debido a la emisión de luz múltiple producida por este efecto no lineal. En los últimos años, estas fuentes de luz basadas en FWM han demostrado una gran utilidad en áreas como la óptica cuántica y la microscopía avanzada basada en efecto Raman. Además, según el estado de polarización de la luz de bombeo responsable del efecto FWM y la birrefringencia de la fibra, la luz producida por FWM puede presentar diferentes propiedades de polarización dada la naturaleza vectorial de FWM. Esto posibilita el diseño y desarrollo de f…
In-situ observation of beta-ray induced UV optical absorption in a-SiO2: radiation darkening and room temperature recovery
2006
International audience; We studied the optical absorption in the 3.0-6.2 eV range induced in bulk amorphous SiO2 by beta-ray irradiation up to similar to 1 MGy at room temperature. The induced absorption was measured in situ both during irradiation and in the post irradiation time. Our data evidence E', center as the main defect induced by irradiation and the partial decay of their absorption band at about 5.8 eV after irradiation. A quantitative analysis of the time evolution of the induced absorption shows that the transmission recovery observed after irradiation is compatible with the reaction of radiation-induced defects with H-related (H-2, H2O) species diffusing in the amorphous matrix
Neutron-induced defects in F-doped fibers
2014
We present a study on 0.8 MeV neutron-induced defects up to fluences of 1017 n/cm² in fluorine doped fibers by using electron paramagnetic resonance, optical absorption and confocal micro-luminescence techniques. Our results allow to address the microscopic mechanisms leading to the generation of some Silica-related point-defects such as E’, H(I), POR and NBOH Centers.
Waveguiding properties of a photonic crystal fiber with a solid core surrounded by four large air holes
2009
The polarization-dependent guiding properties of a hexagonal-lattice photonic crystal fiber with a solid-core surrounded by four large air holes are investigated. The appearance of a polarization dependent cutoff frequency, together with several parameters as the birefringence, the modal effective area, the group velocity dispersion and the polarization dependent loss are analyzed. A collection of fibers with different structural parameters were fabricated and characterized. An effective anti-guide structure from at least 450 nm to 1750 nm, a polarizing fiber with a polarization dependent loss of 16 dB/m at 1550 nm, and an endlessly singlemode polarization-maintaining fiber with group biref…
Multioctave midinfrared supercontinuum generation in suspended-core chalcogenide fibers
2014
An As2S3 fiber-based supercontinuum source that covers 3500 nm, extending from near visible to the midinfrared, is successfully reported by using a 200-fs-pulsed pump with nJ-level energy at 2.5 μm. The main features of our fiber-based source are two-fold. On the one hand, a low-loss As2S3 microstructured optical fiber has been fabricated, with typical attenuation below 2 dB/m in the 1-4 μm wavelength range. On the other hand, a 20-mm-long microstructured fiber sample is sufficient to enable a spectral broadening, spreading from 0.6 to 4.1 μm in a 40 dB dynamic range.
Mid-infrared supercontinuum generation in chalcogenide and telluride fibers for sensor devices
2019
This thesis reports on the progress made during my PhD concerning supercontinuum generation and its application in two types of materials: chalcogenide and tellurite glasses. Concerning the chalcogenide axis, two new arsenic-free compositions are developed: Ge20Se60Te20 and Ge20Se70Te10. Thermal and optical properties of these two glasses are studied and two types of fibers are manufactured: a step-index fiber and a suspended core fiber. The generation of supercontinuum in these two fibres, pumped by an optical parametric amplifier, gives competitive results compared to the current state of the art of supercontinuum generation in chalcogenide fibres. Supercontinuums widening between 2 and 1…
Bleaching of optical activity induced by UV Laser exposure in natural silica
2004
We report experimental data on two types of natural silica, differing for their OH content, irradiated with UV photons (4.66 eV) from a pulsed Nd:YAG laser. Irradiation induces a reduction of the absorption band at 5.12eV and of the associated emissions at 3.14eV and 4.28eV, ascribed to twofold coordinated Ge (=Ge'') centers pre-existing in our samples. The bleaching is mainly due to the post-irradiation conversion of =Ge'' into the paramagnetic H(II) center via trapping of a H atom. Comparison with literature data points out the peculiarities of silica with a low Ge concentration as regards UV induced transformations.
UV-Photoinduced Defects In Ge-Doped Optical Fibers
2005
We investigated the effect of continuous-wave (cw) UV laser radiation on single-mode Ge-doped H2- loaded optical fibers. An innovative technique was developed to measure the optical absorption (OA) induced in the samples by irradiation, and to study its dependence from laser fluence. The combined use of the electron spin resonance (ESR) technique allowed the structural identification of several radiation-induced point defects, among which the Ge(1) (GeO4 -) is found to be responsible of induced OA in the investigated spectral region.