Improvement in the measurement of index modulation along an optical fiber grating by movement of the probe spot perpendicularly to the fiber axis.

We demonstrate a large improvement in the efficiency of the method proposed by Krug et al. [Opt. Lett.

Refractive-Index Changes of Standard Telecommunication Fiber through Exposure to Femtosecond Laser Pulses at 810 cm.

We report on permanent refractive-index changes as great as 6 x 10(-3) in standard fibers on irradiation with tightly focused femtosecond (120-fs) near-IR (lambda = 800-nm) pulses. The refractive-index increase was measured through changes in the transmission spectrum of an UV photowritten Bragg-grating-based Fabry-Perot interferometer. We depict the dependence of the index variation on exposure time.

Temperature-induced reversible changes in the spectral characteristics of fiber Bragg gratings.

It is reported that reversible changes in the reflectivity of Bragg gratings can be induced by a change in the temperature of the grating (77 K < T < K). The changes have proved to be greater in highly doped Ge fibers than in standard fibers, whereas they could hardly be detected in hydrogenated fibers. The sign of the change for type I gratings was opposite that for type IIA gratings.

Comparison of isochronal and isothermal decays of bragg gratings written through continuous-wave exposure of an unloaded germanosilicate fiber.

We compare the results of thermally induced isochronal and isothermal decays of fiber Bragg gratings written through cw exposure of an unloaded germanosilicate fiber. We show that isochronal step decays can be used to predict isothermal decays, provided that some corrections are carried out to take into account a reversible change in grating reflectivity induced by the increase of the fiber temperature. The isochronal accelerated-aging method enables one to sample most of the initial distribution of trapped site energies in a fairly short time.

Photoinscription of Bragg gratings within a germanosilicate fiber subjected to a high static electric field.

The kinetics of Bragg grating growth in germanosilicate fibers subjected to a high static electric field are compared with those obtained without any electric field. The gratings were written by exposure of the fiber core to laser light at 244 or 193 nm. These experiments gave some clues about the mechanisms responsible for both the photosensitivity in germanosilicate fibers and the nonlinear second-order UV-induced susceptibility in silica glasses.

Efficient Bragg gratings in phosphosilicate and germanosilicate photonic crystal fiber.

We present ArF laser-induced dynamics of Bragg grating (BG) growths in phosphosilicate-doped or germanosilicate-doped core photonic crystal fibers (PCFs). To this end, we have adapted the technique of H2 loading, usually used in conventional fiber, to the case of microstructured fiber, allowing both the concentration of hydrogen in the PCFs to be kept nearly constant for the time of the exposure and the BG spectra to be easily recorded. We compared the characteristics of BG growths in the two types of PCF to those in conventional step-index fibers.

Suppression of discrete cladding mode resonances in fibre slanted Bragg gratings for gain equalisation.

In a slanted Bragg grating, coupling between the fundamental guided mode and the counterpropagative cladding modes result in discrete resonances in the transmission spectrum. These resonances are a drawback when Slanted Bragg Gratings are used for gain flattening of fibres amplifiers. A new method based on a chemical etching of the cladding is proposed leading to an overlap of the resonances and a reduction of the amplitude of the modulation.

Self induced gratings in ternary SiO2:SnO2:Na2O bulk glasses by UV light seeding.

The diffraction efficiency of gratings written in ternary SnO2:SiO2:Na2O bulk glasses rises dramatically with time after the occultation of the cw 244nm light used to write the thick hologram. This self-induced behavior lasts for several hours and ultimately leads to refractive index changes as high as 3 10-3.

Isochronal annealing of Bragg gratings written in H2-loaded or in UV-hypersensitized germano-phosphosilicate planar waveguides: a comparison.

Bragg Gratings (BGs) have been written within either H2-loaded or UV-hypersensitized phosphorous-germanium co-doped silica planar waveguides through exposure to light at 248 nm. The stability of these BGs has been investigated by means of isochronal annealing experiments. It appears that the stability of both the modulation and the Bragg wavelength is higher in the hydrogenated waveguides than in the hypersensitized counterparts.

Comparing the properties of various sensitization methods in H2-loaded, UV hypersensitized or OH-flooded standard germanosilicate fibers.

The properties of three sensitization processes: UV hypersensitization, OH-flooding and H2-loading have been investigated through Bragg grating (BG) inscription within standard germanosilicate fibers. More specifically, the stability of the sensitization processes and that of the UV-induced index changes have been investigated through isochronal annealing experiments. Moreover, the level of excess loss induced near 1.

Thermal stability of the 248-nm-induced presensitization process in standard H2-loaded germanosilicate fibers.

Grating growths through exposure of presensitized standard fibers to KrF light were recorded in various experimental condition. It is shown that there exists an optimum sensitization fluence at which the efficiency of the sensitization process is higher. Isochronal thermal annealing of pre-exposed fibers led to a decrease in the sensitization-induced enhancement of photosensitivity.

Analysis of color-center-related contribution to Bragg grating formation in Ge:SiO 2 fiber based on a local Kramers -Kronig transformation of excess loss spectra.

UV-induced excess losses have been measured at various pulse energy densities and exposure times in germanosilicate optical fiber preform cores. The corresponding refractive-index changes have been determined through a Kramers -Kronig analysis. Because of the nonlinear behavior of the excess losses as a function of both exposure time and fluence per pulse, one should be careful when comparing the refractive-index modulation deduced from such measurements with that obtained from Bragg grating reflectivity.

Design of a photowritten cavity neodymium-doped fiber laser tunable around an absorption molecular line.

Experiments have shown that it is possible to realize laser cavities photowritten within rare-earth-doped silicate fibers. Experimental results on a particular application, namely, the detection of gas traces by identification of one of the gas's absorption lines, are presented. Experiments on an absorption line of atmospheric water have been carried out to illustrate this purpose.

Ultraviolet-induced permanent Bragg gratings in cerium-doped ZBLAN glasses or optical fibers.

A holographic method was used to write refractive-index gratings in ZBLAN fluoroziroconate glasses or fibers doped by a Ce concentration of 5000 or 10,000 parts-in-10(6) weight. Direct pumping of the (2)F(5/2)-5d transitions of Ce(3+) ions near 245 nm resulted in a change in the refractive index. The photoinduced change partly recovered on a time scale of several hours at room temperature.

[Proximal tubular recanalization by endoluminal laser. II. Functional results in the female rabbit].

To evaluate the function of the fallopian tube after a recanalization by endoluminal laser probe, 34 mature female New Zealand white rabbits have been separated into two groups. The group 1 (nb = 12) had for aim to validate the procedure of obstruction. In group 2 (nb = 22), we performed the recanalization six weeks after the obstruction.

[Proximal tubal recanalization by endoluminal laser probe. I. Anatomic results in the female rat].

To evaluate the cicatrization of the uterine horn after the recanalization by endoluminal laser probe, 50 white female rats of Wistar's race have been separated into two groups. The group 1 (nb = 10) had for aim to validated the procedure of obstruction. In group 2 (nb = 40), we performed the recanalization six weeks after the obstruction.

[Development and evaluation of a laser catheter with tip fiberoptic for coronary angioplasty].

A fiber-optic tip catheter has been developed for treating coronary and peripheral atherosclerosis percutaneously. The catheter is coupled to an ionised Argon laser emitting at an optical power of 1 to 7 Watts. It is designed to follow a guide wire and to perform tissue ablation by a new concept combining the effects of central vaporisation and peripheral thermal remodelling of the obstructed artery.

XeCl laser in biliary calculus fragmentation: fluence threshold and ablation products.

The in vitro action of a xenon-chlorine (XeCl) excimer laser on biliary calculi is reported: fluence threshold and rate for ablation process are given. An analysis of gaseous products evolved during irradiation of gallstones, performed through an infrared spectrophotometric technique is also reported. Based on the different results, we discuss the mechanism of destruction.