An investigation of novel materials for active optical devices
The potential of a number of doped materials as amplifiers for optical communication has been assessed. This work focuses on transparent glass-ceramics as novel hybrid materials of glasses and crystals. Glass-ceramics comprising of LaF3 crystals in an aluminosilicate glass matrix, doped with Er3+, Pr3+ and Tm3+ have been prepared and characterized. Spectroscopy of these glass-ceramics is focused on the distribution of the dopant ions between the crystals and the residual glass. A novel method to calculate the ion distribution, based on fluorescence lifetime measurements, is developed and applied to both Er3+ and Pr3+ doped glass-ceramics. In the case of Er3+, less than 5% of the ions segregate into the crystals. In contrast to that, up to 50% of the Pr3+ ions are found in the crystals. It is shown that virtually complete segregation of the Pr3+ ions into the crystals is necessary for efficient amplifier operation. Glasses in the yttria-alumina-silica system are prepared and characterized with a view both as a host material for rare earth and transition metal ions, and as a precursor glass for transparent glass-ceramics with YAG nanocrystals. Subsolidus crystallisation studies identify a glass composition promising for YAG glass-ceramics, but also highlight the problem of surface crystallisation. Thulium doped YAS glass is identified as a potential gain medium for a S-band amplifier, because the fluorescence band at 1.47μm has a width of 125nm with an estimated quantum efficiency of 20%. Spectroscopy on Er3+-doped YAS glass shows that the glass can accommodate 26000ppm Er3+ without clustering. The prospect of a Cr4+:YAG glass-ceramic fibre amplifier is discussed.