Gérard Monnom

Erbium-doped silica fibers for intrinsic fiber-optic temperature sensors

The variation in the green intensity ratio ((2)H(11/2) and (4)S(3/2) energy levels to the ground state) of Er ions in silica fibers has been studied as a function of temperature. The different processes that are used to determine the population of these levels are investigated, in particular 800-nm excited-state absorption in Er-doped fibers and 980-nm energy transfer, in Yb-Er-codoped fibers. The invariance of the intensity ratio at a fixed temperature with respect to power, wavelength, and doped fiber length has been investigated and shown to permit the realization of a high-dynamic-range (greater than 600 °C), autocalibrated fiber-optic temperature sensor.

Thermalization effects between upper levels of green fluorescence in Er-doped silica fibers

We present a spectroscopic study of the green fluorescence resulting from pump excited-state absorption in Er-doped silica fibers excited in the 800-nm range. The absorption and emission bands are selectively attributed to the (4)S(3/2) and (2)H(11/2) levels. The fluorescence response at two excitation wavelengths, the temperature behavior, and lifetime measurements demonstrate a fast thermalization between the (4)S(3/2) and (2)H(11/2) levels. This explains an important part of the (2)H(11/2) emission and the increase of the fluorescence intensity at high temperature.

Self-referenced point temperature sensor based on a fluorescence intensity ratio in Yb 3+ -doped silica fiber

An optical fiber temperature sensor, based on the fluorescence intensity ratio from the (2)F (5/2)(a) and (2)F(5/2)(b) Stark sublevels in ytterbium-doped silica fiber, has been investigated. Results of a sensor prototype demonstrate an accuracy near 1 degrees C in a 600 degrees C temperature range. Changes in the fluorescence intensity ratio because of variation in pump power, pump wavelength, and induced fiber bending loss are demonstrated to be small, supporting development of a practical sensor based on the technique described.

Clustering effects on double energy transfer in heavily ytterbium–erbium-codoped silica fibers

We study clustering effects in heavily ytterbium–erbium-codoped silica fibers. We demonstrate that the fraction of both ions found in clusters can exceed 50% in such fibers. A clustering effect is at the origin of an efficient double energy transfer process that generates a green fluorescence. An original method, based on a dynamic analysis of the ytterbium–erbium system, permits determination of the intracluster transfer rates involved, which are found to be high enough to compensate for the weak metastability of the erbium intermediate level.

Clustering-induced nonsaturable absorption phenomenon in heavily erbium-doped silica fibers.

Nonsaturable absorption experiments in heavily erbium-doped fibers demonstrate that the behavior of the absorption with pump power cannot be interpreted with an ion-pair model but requires that the presence of larger clusters be taken into account. Numerical modeling permits the determination of the percentage of ions organized in clusters, as much as 52% of the dopants in the tested fiber, and the intracluster transfer rate, up to 2 × 106 s−1.

1.2-μm transitions in erbium-doped fibers: the possibility of quasi-distributed temperature sensors

We propose the principle of a high-dynamic, quasi-distributed temperature sensor based on the behavior of the 1.13- and the 1.24-µm emission lines in erbium-doped silica fibers. The ratio of fluorescent intensity of these lines presents a temperature dynamic of more than 11 dB between room temperature and 600 °C. As the lower level of these transitions is not the fundamental, the emission lines are absorption free, and no dependence of the intensity ratio of the two lines has been observed, with power and wavelength pump variations permitting the realization of self-calibrated quasi-distributed sensors.

Indirect measurement of the magnitude of ion clustering at high doping densities in Er:ZBLAN fibers

We report precise quantification of the percentage of ion clusters in Er:ZBLAN fibers by measurement of nonsaturable optical absorption and fitting of these data to a simple theoretical model that includes the role of clustering. In particular, using this indirect measurement technique, we demonstrate that 51% of the ions are present in clusters in Er:ZBLAN fibers with an average doping density of 10,000 parts per million, whereas similar fibers with an average doping density of 1,000 parts per million show negligible effects of clustering. Application of this technique to the more precise design of 2.7-µm Er:ZBLAN fiber lasers, to the characterization of the fiber-drawing process, and to more precise determination of cross-relaxation parameters in Er:ZBLAN fibers are discussed.

Estimation of energy transfer parameters in thulium- and ytterbium-doped silica fibers

Silica-based thulium-doped fibers sensitized by ytterbium are being developed for applications in fiber amplifiers and lasers at various wavelengths (around 800 nm, 1470 nm and 2 µm). Several studies have been performed to design and optimize thulium- and ytterbium-doped fiber (TYDF) amplifiers and lasers at the above mentioned wavelengths. Although some papers dealing with modeling of such a system exist, the parameters used in the simulations, like energy transfer coefficients, have not been experimentally determined to date. In this paper we present an estimation of the energy transfer coefficients by comparison of the measured emission of three TYDF samples with numerical simulations of the respective emission using a spectrally and spatially resolved model of TYDF. We found that the energy transfer coefficients are higher than those reported in Tm/Yb-doped fluoride based crystals. This fact together with the possibility of increasing the energy transfer efficiency, by improvement of excited level lifetime of thulium by high alumina codoping, makes thulium/ytterbium co-doped silica fibers promising for applications in fiber lasers and amplifiers.

Thermal variation of absorption in Yb3+-doped silica fiber for high-temperature sensor applications

Rare-earth materials doped into low-loss silica fibers are of interest for temperature sensing applications since the absorption properties of such are temperature dependant. Such absorption properties have been studied in ytterbium doped silica fiber using relative absorption and cut-back techniques at temperatures between 77 and 1163 K in the wavelength range 800 to 1150 nm. The wavelength dependant thermal sensitivity varies from -0.012 to 0.033 dB/K for a standardized one meter long 1000 ppm-doped fiber. These significant changes in absorption with temperature have been attributed to homogeneous line broadening. The fibers investigated show excellent potential for use as the sensing element in intrinsic fiber-optic high-temperture sensors.

Luminescent Ions in Silica-Based Optical Fibers

Abstract We present some of our research activities dedicated to doped silica-based optical fibers, aiming at understanding the spectral properties of luminescent ions, such as rare-earth and transition metal elements. The influence of the local environment on dopants is extensively studied: energy transfer mechanisms between rare-earth ions, control of the valence state of chromium ions, effect of the local phonon energy on thulium ions emission efficiency, and broadening of erbium ions emission induced by oxide nanoparticles. Knowledge of these effects is essential for photonics applications.