Phosphate glasses for GRIN structures by ion exchange Dmitry K. Tagantsev a, * , Andrey A. Lipovskii b , Peter C. Schultz c , Boris V. Tatarintsev a a S.I. Vavilov State Optical Institute, Babushkina 36-1, St.-Petersburg, Russia b St.-Petersburg State Polytechnic University, Polytechnicheskaia 29, St.-Petersburg 195251, Russia c Schultz Technologies LLC, P.O. Box 87, Essex NY 12936, USA Available online 26 November 2007 Abstract Phosphate glasses were treated as a material for GRIN-lens production by silver-alkaline ion exchange. Glass durability (in salt melts) known to be a general obstacle for using these glasses in ion exchange technologies was found to profoundly increase in the sequence of meta ) piro ) orthophosphate. It is supposed to be due to the structure of phosphate glasses, which transforms in this sequence from 1D to 3D space arrangement of the glass-forming network. Ion exchange properties of these glasses were studied as well, and the maximal index variation in sodium–silver ion exchange was found to be 0.17. Ó 2007 Elsevier B.V. All rights reserved. PACS: 42.70.C; 82.65.F; 66.30; 42.79.R Keywords: Chemical durability; Ion exchange; Diffusion and transport; Glasses; Phosphates 1. Introduction Today GRIN (graded-index) structures, like lenses, optical waveguides, diffractive gratings etc., are widely used in many fields of optics and optoelectronics [1,2]. Most of such structures are based on alkaline-containing glasses and produced by an ion exchange technique. It is because these glasses, being immersed in alkaline or silver salt melts, are capable of exchanging host univalent ions for ones in the salt melt, and this exchange results in increasing or decreasing glass refractivity in the ion exchanged layer. The magnitude of the refractive index variation (Dn max ), which can be achieved in ion exchange process, is that glass characteristic, which conditions limits of optical parame- ters of GRIN structures, which could be produced using a given glass. The bigger Dn max , the wider these limits. In particular, numerical aperture (NA) of a GRIN lens is a linear function of Dn 1/2 , where Dn is the index variation between optical axis of the lens and its lateral surface, with the Dn being limited by Dn max . The value and sign of available Dn max , in its turn, is strongly dependent on glass composition and types of ions participating in ion exchange. Nowadays glasses and salt melts used for commercial production of converging GRIN lenses with a high NA (>0.5) contain thallium (highly toxic chemical element), and the process ensuring necessary value and sign of index variation is a direct ion exchange of host thallium ions for potassium ones (or other alkaline ions) contained in a salt melt. In particular, this process is used by the main GRIN lens producer – Nippon Sheet Glass Co., Ltd, who pro- duces GRIN lenses with NA up to 0.58 that corresponds to Dn  0.1. The only other non-toxic technology used in the production of converging GRIN lenses having NA > 0.5 (this corresponds to Dn > 0.085) is based on a double ion exchange [3] that makes the technology time consumable. This technology is used by GRINTECH GmbH. In a double ion exchange, the first ion exchange, which is the full ion exchange replacement of the host sodium ions with silver ones (this step is called the stuffing), 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.11.030 * Corresponding author. Tel.: +7 812 5601878; fax: +7 812 5609574. E-mail address: tagan@dt1386.spb.edu (D.K. Tagantsev). www.elsevier.com/locate/jnoncrysol Available online at www.sciencedirect.com Journal of Non-Crystalline Solids 354 (2008) 1142–1145