L. Di Labio, W. Lüthy, V. Romano, T. Feurer Transitions and mechanisms Multiply RE-doped single core broadband fibre   L. Di Labio, W. Lüthy, V. Romano, T. Feurer Institute of Applied Physics, University of Bern, Sidlerstr. 5, 3012 Bern  F. Sandoz Silitec Fibers SA, Route de la Gare 70, 2017 Boudry <loredana.dilabio@iap.unibe.ch> Abstract A single core fibre doped with five different rare earths, Nd3+, Ho3+, Er3+, Tm3+, and Yb3+, is manufactured with the technique of dry granulated oxides. Under excitation of 804 nm wavelength, fluorescence of the five dopant ions occurs. Excited state absorption and / or energy transfer up-conversion lead to an extremely broad spectrum ranging from 363 nm up to 2300 nm. With an output power of 34 mW and a NA of 0.1, a radiance exceeding 3 kW·sr-1·cm-2 is reached. Preform Fabricated with granulated oxides Mixture 0.1 at. % Nd3+ 0.3 at. % Ho3+ 0.1 at. % Er3+ 0.3 at. % Tm3+ 0.2 at. % Yb3+ 7 at. % Al3+ Fibre drawing Preheating at ~1300 °C for 1 h Evacuation and preheating for an additional hour Drawing at approx. 1850 °C Fibre Øcladd = 180 mm, Øcore = 6.5 mm Attenuation: 1.87 dB/m and 1.09 dB/m Radiance: 3.27 kW·sr-1·cm-2 Excitation is performed with an Ar-ion laser pumped Ti:sapphire laser around 800 nm RE2O3 SiO2 Al2O3 Spectrum Fluorescence spectrum upon 804 nm excitation. The line with “*” is assigned to a second order peak of the 977 nm Yb3+ emission Transitions and mechanisms GSA: ground state absorption; ESA: excited state absorption; ET: energy transfer (donor); ETU: energy transfer up-conversion (donor) Wavelength [nm] RE Assigned transition Abs. length [cm] Excitation mechanism 363 Tm3+ 1D2 → 4H6 4.46 ESA 458 1D2 → 3F4   475 Er3+ Ho3+ 1G4 → 3H6 4F7/2 → 4I15/2 5F3 → 5I8 4.44 ETU (Nd3+, Yb3+) ETU (Yb3+) 522 2H11/2 → 4I15/2 3.81 ESA, ETU (Yb3+) 546 4S3/2 → 4I15/2 (5F4, 5S2) → 5I8 5.01 650 1G4 → 3F4 5F5 → 5I8 4F9/2 → 4I15/2 4.97 ETU (Nd3+) ESA, ET (Tm3+), ETU (Yb3+) 792 4I9/2 → 4I15/2 4.16 ETU (Yb3+) (?) 890 Nd3+ 4F3/2 → 4I15/2 GSA 977 Yb3+ 2F7/2 → 2F5/2 8.90 1064 4F3/2 → 4I11/2 8.11 1333 4F3/2 → 4I13/2 7.33 1531 4I13/2 → 4I15/2 7.78 1667 5I5 → 5I7 1803 3F4 → 3H6 7.46 1954 2nd order of 977 nm transition 2120 5I7 → 5I8 7.50 Publications L. Di Labio, W. Lüthy, V. Romano, F. Sandoz, T. Feurer: ”Broadband emission from a multicore fiber fabricated with granulated oxides”, Applied Optics 47 (10), 1581-1584 (2008) L. Di Labio, W. Lüthy, V. Romano, F. Sandoz, T. Feurer: ”Superbroadband fluorescence fiber fabricated with granulated oxides”, Optics Letters 33 (10), 1050-1052 (2008) Acknowledgements We thank D. Weber for technical assistance. M. Mühlheim, M. Neff, R. Scheidegger and S. Scheidegger we are grateful for their help with fibre drawing. This work was supported in part by the Swiss Commission for the Encouragement of Scientific Research CTI under project 7864.2 NMPP-NM.