François Goutaland

Visible emission processes in heavily doped Er/Yb silica optical fibers

Abstract We have studied the spectroscopic behavior of Er 3+ ion in heavily doped silica optical fibers containing different Yb 3+ ions concentrations. A combination of experimental spectra in the visible range obtained under visible (488 nm) and infrared (790–900 nm) excitations allows the upconversion processes to be determined. In this way, evidence is given for blue (410 nm), green (548.7 and 561 nm) and red (660 nm) emissions in the different fibers.

Diamond-like carbon deposited by femtosecond pulsed-laser ablation: evidence of nanocrystalline diamond

Pulsed laser ablation is a well-known technique used for thin film deposition, extending from oxydes to hard and wear resistant Diamond-Line Carbon (DLC) films. Most of the previous studies devoted to DLC thin films elaboration have used pulsed duration in the nanosecond range. The present study concerns femtosecond (10-15 s range) laser ablation of a graphite target for the elaboration of Diamond-Like Carbon. Compared to conventional nanosecond laser ablation, femtosecond laser pulses allow the production of high energy (up to a few keV) ions in the plasma, which may strongly affect the structure and properties of the deposited films. DLC films have been deposited under vacuum onto (100) p-type silicon substrates at room temperature, by ablating graphite targets with femtosecond laser pulses. The nature and properties of the film have been characterized by various techniques, including Raman, XPS and AFM. Discussion will be focused on the comparison between present results obtained using femtosecond laser pulses, with previously published results related to DLC films deposited using nanosecond laser pulses. Especially, Raman spectra of DLC films obtained by nanosecond laser ablation always show the two well-known D and G bands (located respectively at around 1350 cm-1 and 1550 cm-1), whereas some DLC films obtained when using femtosecond laser pulses exhibit an intense peak at 1140 cm-1, which may be attributed to nanocrystalline diamond.

Defect radial repartitions in ultraviolet irradiated germanosilicate optical fibres

We report experimental results about defects induced by ultraviolet light in germanosilicate optical fibres excited with argon laser light (457.9, 488 and 514.5 nm). A spatial filtering technique was developed and it allows us to separate the fibre core defects from those in the fibre cladding. The emission spectra show, unambigously, that some preexisting defects located in the fibre core are not sensitive to the ultraviolet irradiation while several kinds of photo-induced defects (Ge and Si oxygen deficient centres, germanium drawing induced defects and non bridging oxygen hole centres) are created in the fibres.

Defects studies in silica based optical fibers by laser spectroscopy

Abstract We report results of laser induced defect luminescence at 600 nm and 795 nm in silica based optical fibers as a function of the annealing time at 400°C. We also investigated the dependence of these emissions on fibre excited mode (LP 01 or LP 11 ), wavelength excitation (from 459 to 880 nm) and injected pump power density (typically up to 5 MW/cm 2 ). The same study was made for Er 3+ or Yb 3+ doped silica optical fibers. These experiments permit us on the one hand to localize the defects mostly at the core-cladding interface of the fibre, and on the other hand to determine the influence of rare earth ions on the defects present in our fibers.

Temperature, H2 loading and ultra violet irradiation effects in germanosilicate optical fibers: laser spectroscopy measurements

The effects of heat-treatment and ultraviolet (UV) light at 325 nm on virgin and hydrogen loaded germanosilicate optical fibers have been investigated by using laser spectroscopy technique. The luminescence band around 650 nm is sensitive to heat treatment. The hydrogen reloading of the hydrogen loaded fibers subsequent to heat treatment showed a new emission band around 570 nm. The irradiated fibers have an emission band around 383 nm which was not detected in hydrogen loaded fibers.

Luminescence spectroscopy of hydrogen-associated defects in hydrogen-loaded and heated germanosilicate optical fibres

Abstract We report experimental results on the luminescence spectroscopy of hydrogen-loaded-germanosilicate optical fibres annealed in air at various tem-peratures, up to 500°C, excited at 488 nm. Two kinds of Ge-H defect are identified by their emission bands at 650 or 740 nm. Precursors of the former are drawing-induced GeE defects, whereas the latter are due to the reaction of H2 molecules at the Ge-O-Si site. Another band, centred at 390 nm, is also observed in high-temperature-heated fibres and is proposed to be due to germanium-lone-pair-centre luminescence.

High blue power influence on the visible emissions of Er3+-doped germanosilicate optical fibres

Abstract We investigated, using laser spectroscopy, the influence of very strong irradiation at 488 nm on the visible emission spectrum of an Er 3+ -doped germanosilicate optical fibre. The experiments were carried out during three 12-h stages, separated by several hours. A broad emission band centered at 600 nm appeared from the outset of the second stage whereas the green band intensity, due to Er 3+ ion transition, strongly depended on the irradiation time. A model involving the creation/bleaching of Ge(1) centers and the formation of germanium-drawing-induced defects explain these results.

LUMINESCENCE PROPERTIES OF HYDROGEN LOADED GERMANOSILICATE OPTICAL FIBERS

We have used Raman and luminescence spectroscopy in studying the heat treatment effects on hydrogen-loaded germanosilicate optical fibers. The emission bands located at 650 nm and 740 nm were observed and both proposed as Ge-H defects but with different precursors. GeE’ is thought to be precursors for the former which dominant at 200°C, while Ge-O-Si for the latter and dominant at 500 °C. However, the emission band at 740 nm is not stable by rehydrogenation.