Realization of Ag+/Na+ ion-exchanged surface and buried waveguides on germanate glasses

Ion-exchange technology on glass has been successfully used for more than twenty years to manufacture dependable and low cost integrated optics active and passive devices on silicate or phosphate glasses substrates in the telecommunication wavelengths operation range (from λ = 0.8 to 1.7 μm). However, the recent developments of integrated optics instruments for astronomical interferometers or biological sensors have lead to an increase of the devices operation range towards the mid-infrared. For these reasons, we present in this paper the realization of both surface and buried waveguides by means of ion-exchange on a glass which is transparent until λ = 5 μm. In this study, the choice of germanate glass BGA-G115 from Kigre Inc. has been made because of both its similarity with silicate glass, its content of Na + ions and its excellent transparency in the considered operation range. A complete study of the silver ion diffusion on this new glass matrix has been performed allowing the determination of silver and sodium ion-diffusion coefficients at working temperature and silver concentration. Using theses data, simulations have shown that an ion-exchange of 90 min in a 0.03AgNO 3- 0.97NaNO 3 molten salt at a temperature of 330°C can lead to the realization of surface single mode channel waveguides at either λ = 1.55 μm or λ = 3.39 μm depending on the diffusion window width. To demonstrate channel waveguides on BGA-G115, a specific technological process based on the deposition of a polycrystalline silicon masking layer has been implemented. Single-mode channel waveguides, with a 2.5 μm diffusion window width, have thus been realized and characterized at the wavelength of 1.55 m. Modal size has been measured to be 10 μm ± 1 μm x 7 μm ± 1 μm for propagation losses of 1.2 dB/cm ± 0.5 dB/cm for a 2 cm ± 0.1 cm long device. As for buried waveguides, their feasibility has been demonstrated on multimode ones where a burying depth of 25 μm ± 2 μm has been measured.