Ceramics-Silikáty 49 (1) 53-57 (2005)

Planar optical waveguides in newly developed Er:silicate glasses: A comparative study of K⁺ and Ag⁺ ion exchange

L. Salavcová, B. Švecová, S. Janáková, O. Kolek, M. Míka, J. Špirková, A. Langrová

Materials containing laser-active ions (e.g. erbium and other rare earths) in combination with planar optical waveguides technology are being recently investigated in order to obtain optical amplifying or lasing structures for photonics applications. This contribution reports about fabrication of optical waveguides in newly designed silicate glass substrates by ion exchanges (IE) K⁺ « Na⁺ and Ag⁺ « Na⁺. The content of erbium and sodium in these glasses was kept constant while the ratio of glass intermediates, MgO, CaO and ZnO differed. The optical properties´ characterisation of the fabricated layers (i.e. number of modes and refractive index profile) was performed by dark mode spectroscopy at 671 nm. Another important information on depth of the optical layers was obtained by polarising optical microscope. Concentration depth profiles of the exchanged ions were analysed by scanning electron microscopy. Special attention was paid to possibility of Er ions migration during the fabri-cation process. The Ag⁺ exchange proceeds with much higher velocity than the K⁺ one and provides optical layers with more or less step-like refractive index profiles. On the other hand the K⁺ waveguides have graded shape of these profiles with much smaller refractive index increment (approx. 0.009) compared with Ag⁺ ones (approx. 0.09) and relatively high TE-TM birefringence. Neither difference in Er ions distribution nor micro-cluster formation was observed (being under the detection limit). The results are discussed from the point of view of the glass matrix permeability for the exchanged ions and potential applications of both types of the waveguides.

Keywords: Silicate glass, Erbium, Optical waveguides, Ion exchange