Abstract
Six niobium rich glasses presenting different sodium contents were synthetized. On the basis of complementary infrared and Raman analysis, the influence of the sodium content and its role on the structure of the glasses prior to and following poling was examined. Correlative second harmonic generation (SHG)/Raman microscopy on the poled glasses cross section has shown a co-localization of the SHG signal and the structural variations. It also evidenced similar structural rearrangements whether sodium is removed through poling (230–300 °C) or through the alkali content defined by the starting glass compositions (melted at 1300–1500 °C). The effect of the sodium content on the optical properties, prior to and after thermal poling, is also discussed. It was found that refractive index variations induced by poling (ranging between 10−3 and 3 × 10−2) are mainly the result of a density decrease in the poled region rather than compositional and structural changes. The electro-optic origin of the poling-induced second order nonlinear response is confirmed by the Maker Fringe SHG analysis, and the evolution of χ(2) (2–2.5 pm/V) with the sodium content is discussed based on a selection of parameters influencing either the third order susceptibility [χ(3)] or the internal electric field strength of the poled layer.
Highlights
The development of technologies such as photonic integrated circuits (PICs) requires the use of a combination of materials presenting and/or mixing different functionalities
This means that the glass matrix is flexible enough so that, whether the sodium content is decreased in the glass composition or by thermal poling, the resulting structural rearrangements are equivalent
We have shown that if, regarding the structure and composition, this layer presents the attributes of a glass with low sodium content, it is not the case of its optical properties
Summary
The development of technologies such as photonic integrated circuits (PICs) requires the use of a combination of materials presenting and/or mixing different functionalities Such optical functionality can include emission as light sources, guiding elements, diffractive elements, and materials with a desired nonlinear response. Thermal poling involves the application of a DC field to a heated glass sample providing sufficient mobility to ionic charge carriers, and cooling the sample back to room temperature before switching the voltage off. This process enables control of several properties of the glass. It has to be noted that among the different phenomena described after poling, a majority of studies are dedicated to second order nonlinear (SONL)
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