Rare-earth-activated glass–ceramic waveguides S. Berneschi a , S. Soria a , G.C. Righini a , G. Alombert-Goget b , A. Chiappini b , A. Chiasera b , Y. Jestin b , M. Ferrari b, * , S. Guddala b,c,g , E. Moser c , S.N.B. Bhaktha b,d , B. Boulard e , C. Duverger Arfuso e , S. Turrell f a CNR – Nello Carrara Institute of Applied Physics, MDF Lab (Photonic Materials and Devices), via Madonna del Piano 10, 50019 Sesto Fiorentino, Firenze, Italy b CNR-IFN, CSMFO Lab., via alla Cascata 56/C, Povo, 38123 Trento, Italy c Dipartimento di Fisica, Università di Trento, via Sommarive 14, Povo, 38123 Trento, Italy d LPMC, CNRS-UMR 6622, Université de Nice-Sophia Antipolis, Parc Valrose, 06108 Nice Cedex 02, France e Lab. LdOF, UMR CNRS 6010, Université du Maine, Av. O. Messiaen, 72085 Le Mans, France f LASIR (CNRS, UMR 8516), Université des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq, France g School of Physics, University of Hyderabad, Hyderabad 500046, India article info Article history: Received 20 January 2010 Accepted 19 April 2010 Available online 21 May 2010 Keywords: Glass–ceramics Waveguides Sol–gels Erbium Europium abstract This work presents a short review of the activity performed in developing sol–gel-derived SiO 2 –HfO 2 and SiO 2 –SnO 2 glass–ceramic waveguides activated by Er 3+ and Eu 3+ ions, respectively. Fabrication by top- down and bottom-up techniques is reported and optical and spectroscopic assessment of glass ceramic waveguides is discussed. Luminescence enhancement is demonstrated. Refractive index modulation upon UV exposure is measured in SiO 2 –SnO 2 film. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Silica-based glasses take up a consolidated place as materials for photonic [1]. This outcome has been driven mainly by the suc- cessful application in telecommunication of Wavelength Division Multiplexing (WDM) components and Erbium-Doped Fiber Ampli- fiers (EDFAs). Silica-based glasses offer solubility for rare-earth ions of about 6 Â 10 20 cm À3 , are transparent from the visible to near-infrared region, and are easily compatible with integrated op- tics technology [2]. The fruitful exploitation of silicate glasses is not restricted only to the area of Information and Communication Technology. Many other photonic devices, with a large spectrum of applications covering Health and Biology, Structural Engineer- ing, and Environment Monitoring Systems, have been developed during the last years. Even if several of these devices are actually available on the market, at the state of the art the strength of the research on silica-based glasses is focused on optimising chemical composition and developing innovative fabrication processes, in order to reduce the costs and increase the performances of the de- vices so obtained. In this context a significant role is played by glass ceramics (GCs) in planar format. Rare-earth-activated glass– ceramics, where a glass host is loaded with a crystalline phase con- taining the active ions, are emerging material in photonics because they combine the advantages of optical glasses with crystal-like spectroscopic characteristics. This kind of nanocomposite material combines the mechanical and optical properties of the glass with a crystal-like environment for the rare-earth ions, so that their high- er cross-sections can be exploited in order to fabricate more com- pact devices [3]. Moreover, ceramic glasses materials may be a valid alternative method to control chemical parameters of the rare-earth, and thus may avoid undesirable effect like clustering as proposed by Auzel and Goldner [4]. Thanks to the low phonon environment favourable to enhance the radiative rate and quan- tum efficiency, significant results have been achieved using oxyflu- oride and fluoride transparent glass–ceramics activated by rare- earth ions incorporated in fluoride nano-crystalline phases [5,6]. The aim of this paper is to give a short review of the use of SiO 2 – HfO 2 and SiO 2 –SnO 2 systems for fabrication of rare-earth-activated GCs planar waveguides. 2. SiO 2 –HfO 2 glass–ceramic waveguides During the last years our group has carried out the research in this field in particular on sol–gel-derived Er 3+ -activated HfO 2 - based glass–ceramics. Jestin et al. have shown that SiO 2 –HfO 2 :Er 3+ glass–ceramic planar waveguides prepared by sol–gel route pres- ent valuable optical, spectroscopic and structural features for suc- 0925-3467/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2010.04.035 * Corresponding author. Tel.: +39 (0)461 881684; fax: +39 (0)461 881696. E-mail address: mferrari@science.unitn.it (M. Ferrari). Optical Materials 32 (2010) 1644–1647 Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat