Ultrafast laser plasma doping of rare earth ions for optical waveguiding applications

The work presented here is to introduce and investigate a novel material and a fabrication technique for an Er3+ ion doped waveguide amplifier (EDWA) on a silicon platform. EDWA performance strongly depends on the erbium concentration and the nature of the host material. There are two materials studied for this work. For the first material, TeO2-ZnO-Na2O-Er2O3 (Er-TZN) is doped into the silica-on-silicon (SOS) substrate surface, and for the second material, Er-TZN is doped into the surface of Si3N4-on-silicon. For the first material, the mixing of Er-TZN with SiO2 produces a homogeneous layer which has the potential to be used for EDWA applications. The fabrication is carried out using a novel technique which is named ultrafast laser plasma doping (ULPD). In this technique, the Er-TZN target is bombarded using a femtosecond laser and the interfacial reaction between a high energy plasma plume and heated silica-on-silicon substrate results in a highly dense erbium doped silicate that is referred to as erbium-doped tellurite modified silica (EDTS). The success of this EDTS resulted in this work being extended to produce two types of a channel waveguide, i.e. diffused and ridge waveguide. However, for the diffused waveguide, the attempt to fabricate this type of waveguide failed to produce satisfactory results because it is believed that the metal mask moved during the fabrication process. For ridge waveguide, etching results still do not show satisfactory output. Therefore, further optimisation is needed to accomplish a practical optical waveguide. On the other hand, the doping of Er-TZN into Si3N4 which is also prepared using the ULPD technique is less successful compared to SiO2 because the doped layer exhibits inhomogeneous material distribution although various process parameters have been tried. Failure to obtain a layer like EDTS is probably due to the limitation of the current instruments and also the rigid structural network of Si3N4.