Femtosecond laser plasma assisted rare-earth doping in silica for integrated optics

Abstract

Highly rare-earth doped silicates have the potential to enact far-reaching changes in photonic device integration by providing loss-compensated optical platforms for next generation system in packages (SiP). However, the limited solubility of rare-earths in silica hinders this endeavour. A novel technique based on femtosecond (fs) laser ablation of erbium-doped tellurite glass to enhance the Er3+ ion concentration in silica is presented in this thesis. The engineered material subsequently displays superior spectroscopic properties of Er3+ ions in the silicate matrix at high concentrations. The analysis reveals the formation of a homogeneous glass layer with a high refractive index of ~1.6 at 1550 nm, which has a sharp boundary to the pristine silica. An extensive study of the process dynamics involving fs laser energy, process time, substrate temperature and gas pressure are undertaken to understand the process. The modified silica layer thickness, refractive index, and photoluminescence properties are evaluated using a range of target glasses with varying erbium concentrations. A record high erbium concentration, 1.6 at.%, in silica with a luminescent lifetime of 10.5 ms is accomplished. A new approach for co-doping erbium and ytterbium is also sought through a sequential doping process using individual erbium/ytterbium doped tellurite glasses. A unique interlayer mixing is observed, regardless of the two disparate targets used. This method has the potential to eliminate the process issues related to a highly dense single target. The co-doping demonstrated 2.8 at.% of erbium and ytterbium in silica. The in-situ high-temperature X-ray diffraction, transmission electron microscopy cross-sectional imaging, and selected area diffraction pattern give a direct observation of the crystalline transformations of erbium-doped silica at temperatures above 600 °C and validate the suitability of such layers for optical waveguide fabrication in industry. Microstructure patterning, using a real-time masking of silica with shadow masking and photolithographically defined mask, demonstrates the in-situ masking approach for waveguide fabrication. This shows this technology’s viability for engineering structures, such as amplifiers, splitters, to form a photonic integrated circuit