Doping silica beyond limits with laser plasma for active photonic materials

Abstract

Abstract:The limited solubility of rare-earths in silica hampers the development of loss-compensated photonic integrated circuits. We report a novel method using femtosecond laser plasma assisted hybrid material integration of rare-earth-doped tellurite with silica, achieving high doping concentration of Er 3+

Tm3+ Tellurite-Modified-Silica Glass Thin Films Fabricated Using Ultrafast Laser Plasma Doping

“…The refractive index of the tellurite-modified-silica layer has previously been shown to increase with increasing rare earth ion concentration [1], and this was determined to be due to an increase in density of the modified layer due to the incorporation of heavy rare earth and tellurium ions in the silica glass network which is therefore more closely packed [2]. In tellurite glass however, increasing rare earth concentration (or decreasing TeO 2 ) concentration results in decreasing refractive index as can be seen in Fig.…”

“…U LTRAFAST laser plasma doping (ULPD) has recently been shown to be a viable method for the production of thin glass films with interesting properties. Notable features of the thin films fabricated using this method include the ability to produce a SiO 2 glass network which is modified with TeO 2 based glass without phase separation or crystallization [1], which is not normally possible through traditional glass fabrication techniques; and importantly doping of the telluritemodified-silica glass layer with larger concentrations of Er 3+ than is possible in pure silica without crystallization, clustering and the associated detrimental effects on Er 3+ spectroscopy, resulting in a record high lifetime-density product of Er 3+ ions in silica [1], [2]. The same benefits were found when applying the technique using a substrate of silica-on-silicon which is an important material for a range of photonic devices [3], and the tellurite-modified-silica material is compatible with CMOS manufacturing processes thanks to its stability up to temperatures of around 600°C [4].…”

“…The same benefits were found when applying the technique using a substrate of silica-on-silicon which is an important material for a range of photonic devices [3], and the tellurite-modified-silica material is compatible with CMOS manufacturing processes thanks to its stability up to temperatures of around 600°C [4]. RBS, TEM and EDX analysis of thin films fabricated using ULPD revealed that the doped layer is amorphous, homogeneous and that a very well-defined boundary exists between the modified layer and the pristine silica substrate which is necessary for the production of stepindex waveguides [1], [2]. Codoping of the modified layers can be achieved either by codoping the target glass, or by sequential ablation of separate singly-doped target glasses, providing additional flexibility of fabrication and the ability to produce bespoke doping profiles within the modified layers [2].…”

“…RBS, TEM and EDX analysis of thin films fabricated using ULPD revealed that the doped layer is amorphous, homogeneous and that a very well-defined boundary exists between the modified layer and the pristine silica substrate which is necessary for the production of stepindex waveguides [1], [2]. Codoping of the modified layers can be achieved either by codoping the target glass, or by sequential ablation of separate singly-doped target glasses, providing additional flexibility of fabrication and the ability to produce bespoke doping profiles within the modified layers [2]. The benefits of using tellurite glass as a target material include its ability to dissolve higher concentrations of rare-earth ions than silica glass, resulting in potentially higher optical gains [1] and more compact devices due to the larger absorption and emission cross-sections of rare earth ions in tellurite compared to silicate, fluoride and germanate glasses [5].…”

Ultrafast laser plasma assisted rare-earth doping for silicon photonics

“…In this unique process, the rare-earth elements (erbium (Er)/ytterbium (Yb)) were initially dissolved in tellurite base material (TZNE: (80-x)TeO2-10ZnO-10Na2O-xEr2O3) to prepare the target glass and subsequently ablated using a 100 femtosecond (fs) pulsed laser operating at 800 nm wavelength [6,7]. The complex interfacial reactions between the laser plasma and the hot substrate (silica/silica-on-silicon) produce a tellurite modified dense silica-rich layer with a homogeneous distribution of target glass components as indicated in Fig.1(a) and Fig.…”