Exploring the Compositional Limits of Y2O3-Al2O3-SiO2 Optical Fibers

Of the widely varying compositions fabricated into optical fibers using the molten core method (MCM), the most studied by far as been those in the Y2O3-Al2O3-SiO2 (YAS) system. Such fibers have been shown to be of interest for fiber amplifiers and lasers since they exhibit a good balance between reasonable loss, intrinsically low optical nonlinearities, and efficient gain. The majority of the fibers studied globally to-date have primarily focused on YAG-derived fibers, i.e., YAG (Y3Al5O12) single crystals drawn in a pure SiO2 cladding glass) as well as a limited few that deviated from the YAG-SiO2 pseudo-binary. This research considerably expands the range of studied compositions within the YAS ternary system relative to the extent literature and the practical limitations of the molten core method within the YAS system were established. It was determined that the range of precursors that can be utilized span from 100Al2O3 to 66.4Y2O3-33.4Al2O3 (mol%), and compositions with a Y2O3 content greater than 78 mol% have too high a melting temperature to be utilized with the MCM. Furthermore, the dissolution / diffusion “boundaries” were identified for the first time. For YAS fibers drawn in a 3x30 mm silica preform to a target diameter of 125 μm, the lower diffusion boundary of SiO2 is ~74 mol% at 2000°C and 81 mol% at 2100°C. Once the practical limitations were established, how those limits impacted the optical properties of the fibers was studied. It was determined that of the three compositional constituents of the YAS system (i.e., Y2O3, Al2O3, SiO2), Y2O3 had the greatest impact on attenuation as it possessed the greatest change in attenuation over the shortest compositional range. In addition, the Brillouin frequency shift of YAS fibers had iii a strong dependency on SiO2 concentration and depended primarily on SiO2 vs. non-SiO2 content rather than Al2O3, Y2O3, or their ratio independently. Finally, for YAS fibers drawn in a 3x30 mm silica preform to a target diameter of 125 μm, the maximum achievable Brillouin gain coefficient relative to SiO2 was approximately -12 dB for fibers drawn at 2000°C and -10 dB for fibers drawn at 2100°C.