Neodymium-Doped Tantalum Pentoxide Waveguide
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Neodymium-Doped Tantalum Pentoxide Waveguide Lasers B. Unal, M.C. Netti, M.A. Hassan, P.J. Ayliffe, M.D.B. Charlton, F. Lahoz, N.M.B. Perney, D.P.Shepherd, C.Y.Tai, J.S. Wilkinson & G.J. Parker The fabrication, spectroscopic properties, and laser 3+ performance of Nd -doped Ta2O5 channel waveguide lasers are described. Lasing is obtained at both 1.066µm and 1.375µm with threshold pump powers as low as 2.7mW. The rib waveguides are reactive-ion-etched into Nd:Ta2O5 layers formed by reactive magnetron sputtering. These high-index, low-loss, rare-earthdoped waveguides are fabricated on silicon substrates and offer the potential for integration with photonic crystal structures for compact optical circuits.
Index Terms—Integrated Optics, Lasers, Waveguides.
L
I. INTRODUCTION
IGHT propagation in thin high-index dielectric films is of increasing importance due to the advent of new photonic crystal waveguide technologies [1] and evanescent optical sensors with high surface sensitivity [2]. The production of passive devices such as integrated optical waveguides, splitters and multiplexers in conventional glasses and lowindex films is well established [3] and a present goal in photonic device research is to increase integration and device packing density, to increase functionality, and to reduce cost. Ta2O5 is a promising candidate material for functional photonic crystal waveguide devices as it allows a large index contrast (having a refractive index of over 2), it offers low loss over a broad wavelength region and high radiative efficiency due to relatively low maximum phonon energy [4], Manuscript received August 1st 2005. This work was supported in part by the U.K. Engineering & Physical Sciences Research Council under Grant GR/N37261/01. Bayram Unal ([email protected]) was with the School of Electronics & Computer Science, University of Southampton, SO17 1BJ, UK, and is now with the Department of Physics, Queen Mary University of London, Mile End Road, London, E1 4NS. Greg Parker ([email protected]) and Martin Charlton ([email protected]) are with the School of Electronics & Computer Science, University of Southampton, SO17 1BJ, UK. Caterina Netti ([email protected]) and Peter Ayliffe ([email protected]) are with Mesophotonics Limited, Chilworth Business Incubator, 2 Venture Road, Chilworth Science Park, Southampton, SO16 7NP, UK. Chao-Yi Tai ([email protected]), David Shepherd ([email protected]. uk), Majid Hassan ([email protected]), and James Wilkinson (corresponding author; phone: +44 23 8059 2792; fax: +44 23 8059 3149; email: [email protected]) are with the Optoelectronics Research Centre, University of Southampton, SO17 1BJ, UK. Fernando Lahoz ([email protected]) is with the Department Fisica Fundamental y Experimental, University of La Laguna, 38206 La Laguna, Tenerife, Spain. Nicolas Perney ([email protected]) is with the School of Physics and Astronomy, University of Southampton, SO17 1BJ, UK.
it has a large third-order non-linearity [5], and significant photosensitivity [6]. In addition to promising optical properties, Ta2O5 films also have very good thermal and mechanical properties and excellent compatibility with Si and SiO2 technology, being widely used for high-k gate dielectrics [7]. This compatibility with silicon processing renders Ta2O5 waveguides an appropriate choice for mass-manufacturable low-cost integrated optical devices in future systems. Rare-earth-doped Ta2O5 waveguide films have the potential to provide compact sources and amplifiers for a wide range of applications in telecommunications and elsewhere. Towards this goal, Er-doped Ta2O5 layers have previously been realised by deposition on SiO2 substrates followed by Er ionimplantation, and their losses (between 2 and 10dB/cm at 488nm) and luminescence properties have been studied [8]. In our laboratory we have recently demonstrated the first laser action in rare-earth-doped Ta2O5 waveguides [9]. This initial demonstration was based on Nd-doping and the waveguides were found to have propagation losses of ~2dB/cm at 1.06µm. To date there have been no other reports on Nd-doped Ta2O5, although the growth and absorption and fluorescence spectra of NdTa7O19 crystals has been reported with a view to realising solid-state lasers [10]. In this work we provide details of the optimised growth conditions of neodymium-doped tantalum pentoxide films and their optical properties, including their absorption and fluorescence spectra and fluorescence decay measurements. A detailed analysis of oscillator strengths, spontaneous emission probabilities and decay dynamics has been carried out to provide estimates of the radiative quantum efficiencies. Through optimisation of the growth conditions, and the subsequent channel fabrication via reactive ion etching, we demonstrate an order of magnitude improvement in propagation losses (
Neodymium-Doped Tantalum Pentoxide Waveguide Lasers B. Unal, M.C. Netti, M.A. Hassan, P.J. Ayliffe, M.D.B. Charlton, F. Lahoz, N.M.B. Perney, D.P.Shepherd, C.Y.Tai, J.S. Wilkinson & G.J. Parker The fabrication, spectroscopic properties, and laser 3+ performance of Nd -doped Ta2O5 channel waveguide lasers are described. Lasing is obtained at both 1.066µm and 1.375µm with threshold pump powers as low as 2.7mW. The rib waveguides are reactive-ion-etched into Nd:Ta2O5 layers formed by reactive magnetron sputtering. These high-index, low-loss, rare-earthdoped waveguides are fabricated on silicon substrates and offer the potential for integration with photonic crystal structures for compact optical circuits.
Index Terms—Integrated Optics, Lasers, Waveguides.
L
I. INTRODUCTION
IGHT propagation in thin high-index dielectric films is of increasing importance due to the advent of new photonic crystal waveguide technologies [1] and evanescent optical sensors with high surface sensitivity [2]. The production of passive devices such as integrated optical waveguides, splitters and multiplexers in conventional glasses and lowindex films is well established [3] and a present goal in photonic device research is to increase integration and device packing density, to increase functionality, and to reduce cost. Ta2O5 is a promising candidate material for functional photonic crystal waveguide devices as it allows a large index contrast (having a refractive index of over 2), it offers low loss over a broad wavelength region and high radiative efficiency due to relatively low maximum phonon energy [4], Manuscript received August 1st 2005. This work was supported in part by the U.K. Engineering & Physical Sciences Research Council under Grant GR/N37261/01. Bayram Unal ([email protected]) was with the School of Electronics & Computer Science, University of Southampton, SO17 1BJ, UK, and is now with the Department of Physics, Queen Mary University of London, Mile End Road, London, E1 4NS. Greg Parker ([email protected]) and Martin Charlton ([email protected]) are with the School of Electronics & Computer Science, University of Southampton, SO17 1BJ, UK. Caterina Netti ([email protected]) and Peter Ayliffe ([email protected]) are with Mesophotonics Limited, Chilworth Business Incubator, 2 Venture Road, Chilworth Science Park, Southampton, SO16 7NP, UK. Chao-Yi Tai ([email protected]), David Shepherd ([email protected]. uk), Majid Hassan ([email protected]), and James Wilkinson (corresponding author; phone: +44 23 8059 2792; fax: +44 23 8059 3149; email: [email protected]) are with the Optoelectronics Research Centre, University of Southampton, SO17 1BJ, UK. Fernando Lahoz ([email protected]) is with the Department Fisica Fundamental y Experimental, University of La Laguna, 38206 La Laguna, Tenerife, Spain. Nicolas Perney ([email protected]) is with the School of Physics and Astronomy, University of Southampton, SO17 1BJ, UK.
it has a large third-order non-linearity [5], and significant photosensitivity [6]. In addition to promising optical properties, Ta2O5 films also have very good thermal and mechanical properties and excellent compatibility with Si and SiO2 technology, being widely used for high-k gate dielectrics [7]. This compatibility with silicon processing renders Ta2O5 waveguides an appropriate choice for mass-manufacturable low-cost integrated optical devices in future systems. Rare-earth-doped Ta2O5 waveguide films have the potential to provide compact sources and amplifiers for a wide range of applications in telecommunications and elsewhere. Towards this goal, Er-doped Ta2O5 layers have previously been realised by deposition on SiO2 substrates followed by Er ionimplantation, and their losses (between 2 and 10dB/cm at 488nm) and luminescence properties have been studied [8]. In our laboratory we have recently demonstrated the first laser action in rare-earth-doped Ta2O5 waveguides [9]. This initial demonstration was based on Nd-doping and the waveguides were found to have propagation losses of ~2dB/cm at 1.06µm. To date there have been no other reports on Nd-doped Ta2O5, although the growth and absorption and fluorescence spectra of NdTa7O19 crystals has been reported with a view to realising solid-state lasers [10]. In this work we provide details of the optimised growth conditions of neodymium-doped tantalum pentoxide films and their optical properties, including their absorption and fluorescence spectra and fluorescence decay measurements. A detailed analysis of oscillator strengths, spontaneous emission probabilities and decay dynamics has been carried out to provide estimates of the radiative quantum efficiencies. Through optimisation of the growth conditions, and the subsequent channel fabrication via reactive ion etching, we demonstrate an order of magnitude improvement in propagation losses (
