Bernard Dussardier

Three-hole microstructured optical fiber for efficient fiber Bragg grating refractometer

We present a photosensitive three-hole microstructured optical fiber specifically designed to improve the refractive index sensitivity of a standard fiber Bragg grating (FBG) sensor photowritten in the suspended Ge-doped silica core. We describe the specific photowriting procedure used to realize gratings in such a fiber. We then determine their spectral sensitivity to the refractive index changes of material filling the holes surrounding the core. The sensitivity is compared with that of standard FBGs photowritten in a six-hole fiber with a larger core diameter. We demonstrate an improvement in the sensitivity by two orders of magnitude and reach a resolution of 3 x 10(-5) and 6 x 10(-6) around mean refractive index values of 1.33 and 1.40, respectively.

Visible and Near Infra-red Up-conversion in Tm3+/Yb3+ Co-doped Silica Fibres Under 980 nm Excitation

The spectroscopic properties of Tm(3+)/Yb(3+) co-doped silica fibers under excitation at 980 nm are reported. Three distinct up-conversion fluorescence bands were observed in the visible to near infra-red regions. The blue and red fluorescence bands at 475 and 650 nm, respectively, were found to originate from the (1)G(4) level of Tm(3+). A three step up-conversion process was established as the populating mechanism for these fluorescence bands. The fluorescence band at 800 nm was found to originate from two possible transitions in Tm(3+); one being the transition from the (3)H(4) to (3)H(6) manifold which was found to dominate at low pump powers; the other being the transition from the (1)G(4) to (3)H(6) level which dominates at higher pump powers. The fluorescence lifetime of the (3)H(4) and (3)F(4) levels of Tm(3+) and (2)F(5/2) level of Yb(3+) were studied as a function of Yb(3+) concentration, with no significant energy back transfer from Tm(3+) to Yb(3+) observed.

Fibre Bragg grating photowriting in microstructured optical fibres for refractive index measurement

We report results relating to fibre Bragg grating photowriting in two kinds of Ge-doped core microstructured optical fibre devoted to sensing applications. A cross-comparison between theoretical and experimental modal field patterns is carried out. We present the first values of the spectral sensitivity of a Bragg grating in relation to the refractive index of calibrated oils inserted into the holes.

Theoretical modeling of fiber laser at 810 nm based on thulium-doped silica fibers with enhanced 3H4 level lifetime.

A compact upconversion fiber laser operating around 810 nm is proposed using thulium-doped silica-based fiber with locally modified thulium environment by high alumina codoping. Using a comprehensive numerical model of thulium doped fiber we investigate performance of the proposed laser. Comparison with two other thulium hosts, fluoride glass and standard silica, is presented. Efficient lasing can be expected even for silica based fiber for specific ranges of the fiber and laser cavity parameters, especially when 3H4 lifetime is enhanced. With moderate pump power of 5 W at wavelength of 1064 nm, the predicted output power of the upconversion laser is about 2 W at 810 nm.

Tilted Fiber Bragg Grating photowritten in microstructured optical fiber for improved refractive index measurement

We report what we believe to be the first Tilted short-period Fiber Bragg Grating photowritten in a microstructured optical fiber for refractive index measurement. We investigate the spectral sensitivity of Tilted Fiber Bragg Grating to refractive index liquid inserted into the holes of a multimode microstructured fiber. We measure the wavelength shift of the first four modes experimentally observed when calibrated oils are inserted into the fiber holes, and thus we determine the refractive index resolution for each of these modes. Moreover, a cross comparison between experimental and simulation results of a modal analysis is performed. Two simulation tools are used, respectively based on the localized functions method and on a finite element method. All results are in very good agreement.

Long-period fiber grating as wavelength selective element in double-clad Yb-doped fiber-ring lasers

Cladding-pumped ytterbium-doped fiber lasers belong presently among the most attractive high-power laser sources for wavelengths around 1060 nm. While the most typical configuration of the fiber laser cavity is linear Fabry-Perot arrangement with fiber Bragg gratings (FBGs), for some applications the ring cavity is preferable as it offers higher stability when unidirectional operation is enforced with fiber optic isolator [1]. Indeed, Yb doped fiber lasers are prone to the so-called sustained self pulsing that in the case of highly Yb-doped fiber (YDF) may lead to relatively stable self-Q-switched operation [2]. Occurrence of this phenomenon complicates investigation of laser configurations that use other Q-switching mechanism possibly allowing for more stable operation, other repetition rate and peak power, etc

Chromium-doped silica optical fibres: influence of the core composition on the Cr oxidation states and crystal field

Abstract We have made chromium-doped, silica-based preforms and optical fibres by modified chemical vapour deposition (MCVD) and have studied the influence of the chemical composition of the doped region on the Cr-oxidation states and the spectroscopic properties of the samples. Chromium, introduced initially as Cr3+, is partially or totally oxidized during the fabrication process, and is stabilized in the core of the preforms and fibres as Cr3+ in octahedral coordination, and/or as Cr4+ in distorded tetrahedral coordination (Cs). Small concentrations (∼1–2 mol%) of codopants in silica, such as germanium or aluminium, suffice to promote a particular oxidation state. Particularly, 1 mol% of aluminium stabilizes all the present chromium into Cr4+. The ligand field parameters, Dq, B and Dq/B, for Cr3+ and Cr4+ are derived. It is shown that the chromium ions in our samples are in low-to-intermediate ligand field and that Dq and Dq/B decrease when the aluminium content increases. The absorption cross-sections of Cr3+ are similar to those reported in glasses and crystals, whereas Cr4+ has lower values than the reference laser materials.

Erbium emission properties in nanostructured fibers

A new route was recently proposed to modify some spectroscopic properties of rare-earth ions in silica-based fibers. We had shown the incorporation of erbium ions in amorphous dielectric nanoparticles, grown in fiber preforms. Here we present the achieved stabilization of nanometric erbium-doped dielectric nanoparticles within the core of silica fibers. We present the nanoparticle dimensional characterization in fiber samples. We also show the spectroscopic characterization of erbium in preform samples with similar nanoparticle size and composition. This new route could have important potentials in improving rare-earth-doped fiber amplifiers and laser sources.

Large-mode-area leaky optical fiber fabricated by MCVD

A large-mode-area single-mode optical fiber based on leaky-mode filtering was prepared by a modified chemical vapor deposition (MCVD) technique. The fiber has a leaky cladding that discriminates the fundamental mode from higher-order modes. A preliminary version has a 25 μm core diameter and 0.11 numerical aperture. A Gaussian-like mode with 22 μm mode field diameter was observed after 3 m propagation, in agreement with modeling.

Coherent combining in an Yb-doped double-core fiber laser

We have experimentally demonstrated coherent combining in an Yb doped double core fiber laser. More than 85% of the total output power is combined on the fundamental mode of one of the two cores. This efficient power combining is confirmed by the expected modulated spectrum of the emitted radiation. Finally, this combining method can be scaled with a good efficiency to a larger number of cores with a good efficiency leading to a high power single mode emission.