Birefringence analysis of multilayer leaky cladding optical fibre

We analyse a multilayer leaky cladding (MLC) fibre using the finite element method and study the effect of the MLC on the bending loss and birefringence of two types of structures: (i) a circular core large-mode-area structure and (ii) an elliptical-small-core structure. In a large-mode-area structure, we verify that the multilayer leaky cladding strongly discriminates against higher order modes to achieve single-mode operation, the fibre shows negligible birefringence, and the bending loss of the fibre is low for bending radii larger than 10 cm. In the elliptical-small-core structure we show that the MLC reduces the birefringence of the fibre. This prevents the structure from becoming birefringent in case of any departures from circular geometry. The study should be useful in the designs of MLC fibres for various applications including high power amplifiers, gain flattening of fibre amplifiers and dispersion compensation.Comment: 18 page

Design and fabrication of an intrinsically gain flattened Erbium doped fiber amplifier

We report design and subsequent fabrication of an intrinsically gain flattened Erbium doped fiber amplifier (EDFA) based on a highly asymmetrical and concentric dual-core fiber, inner core of which was only partially doped. Phase-resonant optical coupling between the two cores was so tailored through optimization of its refractive index profile parameters that the longer wavelengths within the C-band experience relatively higher amplification compared to the shorter wavelengths thereby reducing the difference in the well-known tilt in the gains between the shorter and longer wavelength regions. The fabricated EDFA exhibited a median gain ?28 dB (gain excursion below $\pm$2.2 dB within the C-band) when 16 simultaneous standard signal channels were launched by keeping the I/P level for each at ?20 dBm/ channel. Such EDFAs should be attractive for deployment in metro networks, where economics is a premium, because it would cut down the cost on gain flattening filter head

Electron impact ionization cross sections of phosphorus and arsenic molecules

This paper reports on measurements of electron impact direct ionization and dissociative ionization total cross sections of arsenic As4 and As2 molecules and phosphorus P4 and P2 molecules. Molecular species are produced by thermal effusion. The various ions resulting from electron impact are analysed by mass spectrometry. The electron energy range is 0-200 eV. For each ionization reaction, the threshold value, the behaviour in the vicinity of the threshold, as well as the main features of the curve are given. At the maximum in the ionization efficiency curve, the values of the direct ionization cross sections for P4, As4, P2 and As2 are respectively 17, 23.4, 7.8 and 11.4 πa20. In the same way, for dissociative ionization towards X+n where X = P and As and n = 1, 2 and 3, these values are in the range 1.4-3.8 πa20 with an accuracy of about 16 % on the values of cross sections and of 0.5 eV on those of the energy. Results are discussed against electron energy and against formation processes.Cet article présente des résultats de mesures des sections efficaces totales d'ionisation et d'ionisation dissociative obtenues par bombardement électronique des molécules d'arsenic As4 et As2 et de phosphore P 4 et P2. Les espèces moléculaires sont obtenues par effusion thermique. Les différents ions résultant du bombardement électronique sont analysés par spectrométrie de masse. Le domaine d'énergie des électrons est : 0-200 eV. Pour chaque réaction d'ionisation, la valeur du seuil, le comportement de la section efficace au voisinage du seuil ainsi que l'allure générale de celle-ci sont présentés. Les valeurs maximales des sections efficaces d'ionisation directe pour P4, As4, P2 et As2 sont respectivement 17, 23,4, 7,8 et 11,4 πa20. De même, les sections efficaces d'ionisation dissociative menant aux ions X+n (avec X = P et As et n = 1, 2 et 3), ont des valeurs maximales comprises entre 1,4 et 3,8 πa20. Les erreurs sont estimées à 16 % sur les valeurs des sections efficaces à leur maximum et à 0,5 eV sur l'énergie. L'ensemble des résultats est discuté en fonction de l'énergie des électrons et des processus de formation

OPTICAL PROPERTIES OF POLYCRYSTALLINE THIN FILMS OF GaAs OBTAINED BY MBD

Des couches minces polycristallines d'arséniure de gallium caractérisées par un degré variable de désordre ont été préparées par la méthode des jets moléculaires dans un vide classique. Des substrats de différentes natures ont été utilisés : pyrex, silice fondue, fluorine. Un désordre croissant a pu être observé par l'abaissement de la température du substrat (Ts). Ces couches ont pu être caractérisées à l'aide de la diffraction des rayons X. Dans ce travail, on présente les propriétés les plus marquantes obtenues par des mesures de transmission et de réflexion optiques, notamment dans les régions du proche uv et de l'infrarouge lointain, en liaison avec les conditions de préparation ; la température Ts et le rapport As/Ga de l'intensité des jets étant les paramètres principaux. Les épaisseurs des couches s'échelonnent entre 400 Å et 2.6µm.Gallium arsenide polycrystalline thin films of various degrees of disorder have been prepared by molecular beam deposition in a conventional vacuum system. Different substrates have been used : pyrex, fused silica and fluorine. Increasing degree of disorder is obtained by lowering the substrate temperature (Ts). Characterization was obtained by means of x-ray diffraction. The most striking optical properties obtained by transmission and reflection measurements, mainly in the near-uv and far-infrared range, are presented in relation with the preparation conditions, where the main parameters are Ts and As/Ga beam ratio. Thicknesses range between 400 Å and 2.6µm

Investigations on Excited-State Absorption in Pr3+^{3+} Doped Fluorozirconate Fibers

Excited state absorption (E.S.A.) in Pr$^{3+}$ doped fluorozirconate fibers pumped at 1012 nm is investigated by the pump-probe beam method. Probe wavelengths are successively 830, 780 and 1310 nm, we measure both the attenuation of the probe beam when 1012 nm pumping is applied and the modulation of the visible or 1.3 $\mu$m fluorescence when the probe is lauched into the fiber. Modelisation of these measurements allows us deducing the magnitude of E.S.A. cross-sections at 830, 780 and 1012 nm

Investigations on Excited-State Absorption in Pr3+^{3+} Doped Fluorozirconate Fibers

Excited state absorption (E.S.A.) in Pr$^{3+}$ doped fluorozirconate fibers pumped at 1012 nm is investigated by the pump-probe beam method. Probe wavelengths are successively 830, 780 and 1310 nm, we measure both the attenuation of the probe beam when 1012 nm pumping is applied and the modulation of the visible or 1.3 $\mu$m fluorescence when the probe is lauched into the fiber. Modelisation of these measurements allows us deducing the magnitude of E.S.A. cross-sections at 830, 780 and 1012 nm

Fluorescence de 0,8 à 1,7 μ\mupm de fibres optiques en silice dopées par l'ion Cr4+^{4+}

La luminescence des ions Cr$^{4+}$ dans les fibres optiques en silice est très sensible à la concentration, à la composition du matériau et aux conditions d'excitation. Nous caractérisons ici la luminescence dans le proche infrarouge (IR), de 800 à 1700 nm, résolue dans le temps, de préformes pour fibres optiques réalisées par MCVD. Nous discutons l'intérêt de telles fibres pour le domaine des télécommunications