Coupling Light in Ion-Exchanged Waveguides by Silver Nanoparticle-Based Nanogratings: Manipulating the Refractive Index of Waveguides

We report the fabrication and properties of ion-exchanged optical waveguides based on low-cost soda-lime glasses embedded with silver ions and nanoparticles. Using the thermal ion-exchange process, we embed silver ions into soda-lime glasses by covering the glasses with different ratios of AgNO3:NaNO3 molten salt (2:98, 4:96, and 6:94) at 350 °C. The ion-exchanged glasses containing silver nanoparticles were characterized by using X-ray fluorescence spectroscopy, UV–visible spectroscopy, the X-ray diffraction technique, X-ray photoelectron spectroscopy, and atomic force microscopy of the surface. It is shown that the ion-exchanged glasses make low-loss optical waveguides. Furthermore, we evaluate the refractive index of ion-exchanged waveguides by laser coupling into the waveguide. For this purpose, the ion-exchanged glasses were coated with a silver chloride thin film loaded with silver nanoparticles (Ag-AgCl). When the Ag-AgCl layer is irradiated by a polarized coherent light beam, silver nanograting is formed on the surface of the ion-exchanged glass, and the light beam is simultaneously coupled into the glass. The line-space of nanograting determines the effective refractive index of the ion-exchanged glass. Although we expected the sample with the highest ratio of AgNO3:NaNO3 salt (6:94) to have the largest refractive index, our results demonstrate that the ion-exchanged sample with 4% AgNO3 has the largest effective refractive index, which is due to the penetration of more silver ions and nanoparticles in the glass matrix. Therefore, it is further demonstrated that using a Ag-AgCl layer on an ion-exchanged waveguide is an effective method for coupling light into the waveguides and measuring its refractive index. The mentioned coupling technique in combination with easily fabricated ion-exchanged waveguide has served as an excellent platform for applications in integrated optical circuits.