Preform fabrication and drawing of KNbO 3 modified tellurite glass fibers N. Syam Prasad a , J. Wang a , R.K. Pattnaik a,b , H. Jain a,c , J. Toulouse a,b, * a Center for Optical Technologies, Lehigh University, Bethlehem, PA 18015, United States b Department of Physics, Lehigh University, Lewis Building, 16 Memorial Drive East, Bethlehem, PA 18015, United States c Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015, United States Available online 13 March 2006 Abstract For fiberization of tellurite glasses the 70TeO 2 –25ZnO–5Na 2 O composition is selected based on its good thermal stability and refrac- tive index compatibility with most of the ferroelectric oxides. A modified built-in casting method is used to fabricate preforms. The fiber drawn by the rod-in-tube technique consists of two layers of cladding glass and a core with 5 mol% ferroelectric KNbO 3 . In this study we also address the low mechanical strength problem with tellurite glass fibers, by subjecting the preforms to polishing and wet chemical etching. Apart from the fabrication methods, we also report here a selective core heat-treatment and ferroelectric phase crystallization in a low dimensional system. Ó 2006 Elsevier B.V. All rights reserved. PACS: 81.05.Pj; 77.90.+k; 42.81.Bm; 78.20.Jq; 42.65.Ky Keywords: Crystallization; Optical fibers; Tellurites 1. Introduction Non-linear optical processes have received considerable attention for applications in a variety of optoelectronic and photonic devices. Fibers that are capable of second har- monic generation (SHG) and electro-optic (EO) modula- tion are potential candidates for optical switching devices in fiber networks. Because of their isotropic structure, glass fibers do not exhibit second order optical non-linearity or the linear electro-optic effect, which are required for wave- length conversion and the modulation of light signal for photonic information technology. Although glasses exhibit third harmonic activity and a quadratic electro-optic effect, they are unsuitable for the above-mentioned applications because of the low value of the corresponding coefficients [1]. For this reason, existing fibers are used only as passive components in optical transmission networks. Many researchers around the globe have tried modifying the glass structure at atomic level to introduce SHG and EO effects. Thermal [2] and UV poling [3] are the most common methods to induce second order optical non-line- arity in SiO 2 glass fibers. These methods have two serious setbacks: one is that the dielectric polarization degrades with time and the other is that the induced non-linearity is weak in many glasses. These reasons prompted us to con- sider dispersing ferroelectric nanocrystallites in the core, and induce second order non-linearity and electro-optic activity for active device applications. A number of glass nanocomposites comprising well-known ferroelectric crys- talline phases (BaTiO 3 , PbTiO 3 , LiNbO 3 , LiTaO 3 , etc.) in silica, borate and tellurite glass matrices have been fabri- cated and investigated for their SHG and EO properties [4–7]. Because of low loss and refractive index matching requirements, tellurite glasses with small concentrations of ferroelectric oxides are promising systems for second 0022-3093/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2005.11.069 * Corresponding author. Address: Department of Physics, Lehigh University, Lewis Building, 16 Memorial Drive East, Bethlehem, PA 18015, United States. Tel.: +1 610 758 4233; fax: +1 610 758 3526. E-mail address: jt02@lehigh.edu (J. Toulouse). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 352 (2006) 519–523