Refractive Indexes and Spectroscopic Properties to Design Er 3+ -Doped SiO 2 -Ta 2 O 5 Films as Multifunctional Planar Waveguide Platforms for Optical Sensors and Amplifiers

This paper reports on the news about refractive index measurements and spectroscopic features of thin films, which can be applied as optical planar waveguides, focusing on their manufacturing processes, designs, and possible applications as optical amplifiers and sensors. Er -doped SiO -Ta O planar waveguides, with Si/Ta ratios of 90:10, 80:20, 70:30, 60:40, and 50:50, were prepared by a soft sol-gel process. Multilayer films were deposited by the dip-coating technique onto 10 μm SiO -Si (100) p-type silicon and Si (100) silicon easily and successfully. The mechanisms of the densification process, porosity, and hydroxy group or water molecule occurrence have been accompanied by m-line and vibrational spectroscopy analyses. The thickness and refractive index values were used to understand better the influence of temperature and annealing time on the densification of the bulk films and the reduction of the pore volume as the tantalum oxide concentration increases. The refractive index shows the density of the films, and by the atomic force microscopy (AFM) technique, the films showed low surface roughness, achieving relatively high light confinement within the waveguide structure, and negligible optical loss due to surface scattering. Nanoparticle crystallization of Ta O with size distribution ranging from 2.0 to 15.0 nm embedded in SiO was observed with size depending on annealing time and tantalum concentration. Intense and broadband emission positioned at 1550 nm, which is attributed to the I → I transition of Er ions, was observed for all planar waveguides under excitation at 271, 272, and 278 nm. Depending on the porosity degree, the adsorption of H O molecules occurs, changing the refractive index and contributing to the deactivation of excited states of Er ions, making them an optical platform for use as an optical sensor for different species. Besides, the densified waveguides containing 20 or 30 mol % Ta exhibit high potential for applications as broadband optical amplifiers for wavelength division multiplexing (WDM), optical sensing, or augmented reality.