Linear and nonlinear optical periodic microstructures in niobium germanate glasses by thermal poling

Optical microstructures imprinted in niobium germanate glasses by thermal poling were investigated by correlating Raman, phase contrast imaging, Second Harmonic Generation (SHG) and Atomic Force Microscopy (AFM) measurements. Structural characterizations by Raman microscopy have shown the presence of gradient in-plane poling effects. By varying the microscale anode designs, it has been observed that the difference between the size of the in-plane gradient poling effect and the pitch dimension of the electrode patterns can explain the refractive index contrast at the micrometer scale. SHG signals were localized in microregions located at the edges of the micropatterned anode electrode and the electro-optical origin of the second-order optical responses has been confirmed. Finally, the SHG responses of second-order optical diffraction gratings were studied. The observation of well-defined SHG optical diffraction peaks demonstrates the potential of these EFISH structuration in niobium germanate glasses for the development of nonlinear optical (NLO) micro-scale periodical designs. In this perspective, this paper demonstrated the implementation of NLO properties in germanate glasses containing a wide transmission window and promising for NLO photonic applications such as infrared wavelength conversion and electro-optical devices.