Optical Materials 101 (2020) 109767 Available online 5 March 2020 0925-3467/© 2020 Elsevier B.V. All rights reserved. Waveguides written in silver-doped tellurite glasses Jonathas M. Oliveira a , Alcenisio J. Jesus-Silva b , Anielle C.A. Silva c , Noelio O. Dantas c , Eduardo J.S. Fonseca b, * a Instituto Federal de Alagoas, Coruripe, Alagoas, 57230-000, Brazil b Instituto de Física, Universidade Federal de Alagoas, Macei� o, Alagoas, 57061-970, Brazil c Laborat� orio de Novos Materiais Nanoestruturados e Funcionais, Instituto de Física, Universidade Federal de Alagoas, Macei� o, Alagoas, 57061-970, Brazil A R T I C L E INFO Keywords: Femtosecond laser writing Waveguides Tellurite glass Silver nanoparticles ABSTRACT We have studied the optical properties of channel waveguides written using a femtosecond laser in tellurite-zinc glasses doped with metallic silver (%TeO 2 %ZnO:Ag). Our fndings showed that the tellurium dioxide glasses could be signifcantly affected by the silver presence, even with low silver concentration. By properly choosing the parameters and glassy matrix the written waveguides presented lower optical insertion losses and greater refractive index change. 1. Introduction It is well known since 90’s decade that the interaction between ul- trashort pulse lasers and transparent materials can permanently alter the structure of the material [1]. When a femtosecond laser is focused inside of a dielectric, the radiation is absorbed through nonlinear processes such as multiphoton absorption, tunneling and avalanche ionization. These processes are responsible to permanently modify the small focal volume after energy relaxation [2,3]. Three types of structural changes can be observed: a smooth refractive index change, birefringent refractive index modifcation, and microexplosions leading to empty voids [4]. The ultrashort laser direct inscription has established itself as a powerful tool for the fabrication of photonic devices [5–7]. In particular, the construction of waveguides in glasses has attracted much interest due to low propagation losses, easy matching to optical fbers, high yield, cheap and reliable fabrication. Additionally, a uniform modif- cation of the refractive index is preferred because it reduces the prop- agation losses and enables the construction of photonic circuits. The study of glasses doped with nanostructures has opened new perspectives for applications, for instance, sensing purposes [8,9]. From this perspective, a variety of glasses have been investigated as host to buried waveguides including silicates, chalcogenides, fuorides and crystals. Particularly, tellurite glasses have attracted interest due to low phonon energy (~750 cm 1 ), thermo-mechanical stability, high linear refractive index (>2.0), corrosion resistance, high concentration solubility, and wide transmission range (0.4 μm–5 μm) [10–14]. In fact, several works have been developed using tellurium oxide glassy matrices with different synthesis methods, concentrations, components and dopants applied to construct photonic devices via direct laser writing [11,15–18]. Besides, the incorporation of silver nanoparticles in glassy matrix has attracted interest due to a wide range of properties like coloring, charge transfer mechanisms, feld enhancement and sensi- tizing effects, making the silver-doped glasses a versatile class of mate- rials, mainly to optical waveguides technology [19–21]. There is still room to understand how the writing parameters can be adjusted, according to each glass, to reduce the propagation losses, in- crease the refractive index change and reduce the modifed volume. In the present work, we wrote channel waveguides into the binary tellurite-zinc glasses doped with metallic silver and related their optical properties with the glass components. Our fndings showed that the tellurium dioxide glasses can be affected by the silver presence, even in low concentration, enabling a higher or lower change of the refractive index, depending on the matrix, and waveguides with low propagation losses. 2. Materials and methods 2.1. Preparation of TeZn glass samples The glassy matrices with a nominal composition of 60TeO 2 ⋅40ZnO (mol%) and 80TeO 2 ⋅20ZnO (mol%) were synthesized by the fusion * Corresponding author. E-mail address: eduardo@fs.ufal.br (E.J.S. Fonseca). Contents lists available at ScienceDirect Optical Materials journal homepage: http://www.elsevier.com/locate/optmat https://doi.org/10.1016/j.optmat.2020.109767 Received 9 December 2019; Received in revised form 3 February 2020; Accepted 17 February 2020