T. Georges

Modeling of pair-induced quenching in erbium-doped silicate fibers

It is shown that in low-concentration erbium-doped silicate fibers (below 1000 p.p.m.), a residual absorption at 980 nm cannot be saturated. Usual models for upconversion of Er/sup 3+/ cannot match this behavior nor explain a fluorescence lifetime independent of pump power and erbium concentration. A phenomenon, the pair induced quenching (PIQ), that is compatible with the previous experimental results is exhibited. The influence of erbium and aluminum concentration on the ion pair proportion is shown. >

Experimental evidence of two types of photorefractive effects occuring during photoinscriptions of Bragg gratings within germanosilicate fibres

Abstract Photoinscriptions of Bragg gratings have been carried out within six germanosilicate fibres. Real time measurements of the spectral transmission, of the fwhm bandwidth and of the resonance wavelength of the Bragg gratings permit to estimate the refractive index change photoinduced in the core of the fibre. It has been observed that the refractive index changes were strongly nonlinear as a function of the number of ultraviolet (UV) laser pulses used for writing the gratings. Experimental results show that, at least, two photorefractive effects should be responsible for the complicated dynamical evolution of the grating growth observed within some fibres.

Reduction of the dispersive wave in periodically amplified links with initially chirped solitons

It is shown that a prechirping of the input solitons can reduce the dispersive wave created by the focal mismatch between linear and nonlinear effects on a link with large amplifier spacing (Z/sub A//spl ges/50 km) and a small dispersion length (Z/sub c/<Z/sub A/). This technique is shown to be compatible with the chirped (bandwidth limited) amplification and to increase its domain of application.

Second order diffraction efficiency of Bragg gratings written within germanosilicate fibres

Abstract Second order diffraction has been observed from Bragg gratings written within germanosilicate glass fibres. Experimental results are reported on the evolution of the first and the second order Bragg grating reflectivities as function of the uv laser shot number used for the inscription. Second order diffraction can be detected once the first order grating reflectivity has begun to saturate. Possible explanations of the second order grating formation are discussed. Our experimental results are consistent with a saturation in the photo-induced change in refractive index.

Behavior of Bragg gratings, written in germanosilicate fibers, against /spl gamma/-ray exposure at low dose rate

Bragg gratings have been written within four germanosilicate fibers either by a pulsed or by a continuous-wave exposure of each fiber to a coherent UV two-beam interference pattern. These gratings have been exposed under steady state conditions to /spl gamma/-ray doses as high as 10/sup 4/ Grays. The dose rates ranged between 10 Gy/h and 1.3/spl times/10/sup 2/ Gy/h. The transmission spectra of the fibers have been recorded during and after the /sup 60/Co irradiation, near the grating Bragg wavelengths. Whereas the induced loss reached 600 dB/km near 1.3 /spl mu/m, no significant change in the spectral characteristics of the gratings could be detected within the experimental accuracy, enabling their future use in a nuclear environment.<<ETX>>

Behaviour of spectral transmissions of Bragg gratings written in germania-doped fibres: writing and erasing experiments using pulsed or cw uv exposure

Abstract Photoinscriptions of Bragg gratings have been carried out within several germanosilicate fibres via uv side writing near 244 nm. The gratings have been written with a pulsed or a continuous-wave (cw) laser. It has been observed that the refractive index changes were strongly non linear as a function of the exposure time whatever the nature of the source may be. Uv pulsed or cw photobleaching experiments have been performed using gratings written under various conditions in fibres for which complex evolutions of spectra could be observed. Uv fringeless illumination of a grating firstly can erase the first order transmission spectrum and then build a new spectrum. Results of thermal annealing of gratings written using pulsed exposure or using cw light are analysed. We render a phenomenological account of the experimental results by assuming that, at least, two photorefractive effects are responsible for the grating formation or erasure.

Narrow band 1.02 Tbit/s (51/spl times/20 Gbit/s) soliton DWDM transmission over 1000 km of standard fiber with 100 km amplifier spans

1.02 Tbit/s (51-wavelength each at 20 Gbit/s) dense WDM (0.4 nm channel-spacing) soliton transmission over 1000 km of standard step-index fiber with 100 lan (21 dB loss) amplifier spans was successfully achieved for the first time.

TEM characterization of structural changes in glass associated to Bragg grating inscription in a germanosilicate optical fibre preform

Abstract Bragg gratings were written in a slice of an optical fibre preform using two interfering uv pulsed laser beams at 243 nm. Microstructural changes within the germanosilicate glass were studied by transmission electron microscopy (TEM) and infrared spectroscopy. TEM investigation shows that the glass is densified at the grating grooves. Infrared absorption spectra have been recorded on a germanosilicate glass sample before and after in irradiation by a fringeless uv pulsed beam. Our conclusion is that uv irradiation-induced bond breaking allows structural relaxation of the non-equilibrium glass network which tends to densify without any noticeable change in coordination.

Experimental evidence of pseudoperiodical soliton propagation in dispersion-managed links

A new technique for measuring chirp evolution of Gaussian-like pulses transmitted on single-mode fiber is presented. It is used in a recirculation loop experiment to characterize propagation in anomalous-dispersion regime over megametrical distances. In-quadrature periodical variations of the two characteristic parameters of pulses (i.e., spectral width and chirp) are measured versus distance for different values of prechirp and in-line power. This constitutes the first experimental evidence of pseudoperiodical soliton propagation in dispersion-managed links. It also demonstrates that the prechirp is a key element for the control of nonlinearity as predicted by the theory.

Birefringence effect of optical fiber laser with intracore fiber Bragg grating

The spectra of Nd/sup 3+/- and Pr/sup 3+/-doped fibre lasers utilizing an intracore Bragg grating reflector written at 1.08- mu m Bragg wavelength and a dichroic mirror for cavity feedback have been investigated under 0.6-GHz resolution. Two oscillating frequencies corresponding to two orthogonal linear polarization states of laser emission were observed. The frequencies and orientations of the two linearly polarized emissions could be changed by varying the fiber birefringence with an inline polarization controller. A phenomenological model is proposed to explain the experimental results.<<ETX>>