Femtosecond laser plasma assisted multi-ion doping for photonic material engineering

Rare-earth (RE) doped optical materials, compatible with CMOS processing, are essential for the development of planar optical loss-less circuits and amplifiers to facilitate the progress of next generation optical interconnects[1]. However, the lack of a suitable optical material with high (~1022 atoms/cm3) RE solubility and long fluorescent lifetime(milliseconds) is hindering the realization of dielectric based integrated planar amplifiers at present[2]. We report a novel technique, ultrafast laser plasma implantation (ULPI)[3], that enables the simultaneous implantation of multiple, atomically dissimilar ions into a silica optical platform, enabling silica to contain a record high Er3+-ion concentration of 1.4 at.% and the highest lifetime-density product 8.94×1019 s.cm-3. This was achieved through the integration of chemically incompatible materials, RE doped tellurite and silica, assisted by ablation of RE (Er/Yb) enriched tellurite target glass using ultrashort pulse(100 fs) laser and subsequent implantation into the silica substrate, maintained at ~973K . The high energy plasma and the process temperature initiate an interfacial reaction with the silica surface, forming a well-defined metastable homogeneous modified layer of silica, characterized by X-Ray Photoelectron Spectroscopy (XPS) and Rutherford back scattering spectrometry. Such a modified glass layer formation is thermodynamically unstable through conventional means, such as melting and unachievable through any known glass processing methods. The subsequent optical and photoluminescence studies indicate the formation of a high refractive index, n=1.6, optically transparent (>95%) layer having typical photoluminescence characteristics of Er3+-ions in silica host. A method to precisely engineer the optical layer thickness and refractive index by tuning the fs-laser energy will also be presented