Preparation of Yb3+ and Er3+ codoped phosphate glasses for active waveguides

Fibers and fiber lasers are widely used in photonics as well as in medical applications. Hence, research on fiber lasers utilizing glasses activated with rare-earth (RE) ions has been of great interest. One of the most studied fiber laser glass is Erbium-doped silicate glasses. However, low solubility of Er3+ ions in silicate glasses results in Er−Er cluster formation for higher concentrations. Phosphate glasses are able to accommodate a larger amount of rare earth dopants compared to silicate glasses because of their two dimensional structure, which makes these glasses prospective candidates for different applications ranging from telecommunication systems, upconverters, fibers, optical amplifiers and solid-state lasers. In this thesis, we explored the possibility of using RE-doped phosphate-based glasses for planar waveguides and fiber lasers. Er3+ and Yb3+ codoped phosphate glasses were prepared using melt quenching method with different concentration of ZnO and Y2O3 and these glasses were optimized for thin film deposition and fiber drawing. From the thermal properties of the glasses, all the investigated glasses are expected to have a good thermal stability against crystallization which is a crucial property when depositing the glass into films and also when drawing it into fiber. The changes in the structural properties induced by the changes in the glass composition were studied with infrared and Raman spectroscopies. Based on the optical and luminescence properties of the glasses, the RE sites are not expected to be strongly affected by the change in the glass composition. The glass with composition (49P2O5-39.2SrO-9.8Na2O-0.5Er2O3-1.5Yb2O3) (in mol%) was selected for film deposition and preform casting. Thin film was deposited using e-beam evaporation. However, films contained no heavier RE atoms and they suffered serious spallation and delamination upon aging. Nevertheless, single core fiber with a 115 µm diameter was successfully drawn from a 10 cm long preform with 1 cm diameter. Losses were estimated using cutback method and found to be 0.1–0.4 dB·cm-1 at 700 nm. Emission spectra from fiber showed a broadband centered at 1.5 µm and the bandwidth measured greater than 70 nm. The broad luminescence source is highly demanded in several applications such as LIDAR or optical coherence tomography. The spectral hole-burning effect was observed in the phosphate fiber with the length exceeding 3 cm, which could be interesting for ultra-high density optical data storage