Erbium-Ytterbium ions codoped phosphate glass planar optical waveguide amplifier

Abstract

Erbium-doped Fiber Amplifiers (EDFA) have been successful in the low loss telecommunications window. The successes of EDFA stimulate the development of planar optical waveguide amplifier, which can be integrated with other optoelectronic components. Moreover, the high optical gain is achieved in short length device. Rare earth doped phosphate glasses are the suitable candidates for such development due to their superior spectroscopic properties even at high rare earth concentration. In this project, the Er³+:Yb³+ codoped phosphate glasses (designated as QP) were fabricated and used to compare with other type Er³+:Yb³+ codoped phosphate glasses (designated as MM2). Yb³+ was recognized as efficient sensitizer to Er³+, which increases the pumping efficiency at 980 nm. Some basic glass properties were characterized using energy dispersive X-ray analysis EDXA, prism coupling method and differential thermal analysis. The glass transition temperatures of QP and MM2 phosphate glasses are 511°C and 543°C respectively, which indicates that MM2 glass is more suitable for the waveguide fabrication using the thermal ion exchange method. Spectroscopic properties of both QP and MM2 phosphate glasses were also characterized. Fluorescence spectra were measured and the fluorescence bandwidths were found to be about 40 nm, which can enable the broadband communication. Phonon energies were measured to be approximately 1200 cm-¹, which is high enough to accelerate the multiphonon relaxation rate from 4I1½ to 4I¹⅔ levels under 980 nm pumping and hence gives very strong 1.5 µm emission. Based on the measured absorption spectra, the Judd-Ofelt intensity parameters were determined and used to calculate some important radiative properties and lifetimes of Er³+. Comparing the fluorescence lifetimes and radiative lifetimes of Er³+:4I¹⅔ level, the radiative quantum efficiencies were calculated to be near 60 % and 100 % for QP and MM2 glasses respectively. The 100 % radiative quantum efficiency of MM2 glasses in the transition 4I¹⅔  4I15/2 reveals that no significant concentration quenching of Er³+ ions and non-radiative de-excitation are caused by hydroxyl group in the glasses. In phosphate glasses, the hydroxyl group is a serious quencher that influences the Er³+: 1.5 µm emission. MM2 glass, which is under the special dehydration process, demonstrates lower hydroxyl group concentration than QP glass. Fluorescence lifetime of 8 ms and near 100 % radiative quantum efficiency indicate that MM2 glass is a suitable material for planar waveguide amplifier. Infrared transmission spectra also confirm that hydroxyl group concentration is low in MM2 glasses. Planar waveguide amplifier of lithium based phosphate glasses (MM2) were successfully fabricated using Ag+-Li+ ion exchange process. For the 6 µmwide channel, only one transverse mode is supported by the waveguide. With 140 mW pump power, the net gains were measured to be 1.87, 3.52,4.76 and 6.02 dB for waveguide lengths of 0.5, 1, 1.5 and 2 cm, respectively. The normalized average gain was ~ 3.4 dB/cm with an input signal wavelength of 1.535 µm at a power of - 40 dBm.

Date of Award	3 Oct 2001
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Yue Bun Edwin PUN (Supervisor)