High Er concentration phosphate glasses for planar waveguide amplifiers

Cooperative upconversion processes and Yb-Er energy transfer efficiencies in high Er concentration phosphate glasses were studied. The cooperative upconversion coefficients were deduced from the pump intensity dependence of luminescence decay curves. Cooperative upconversion coefficients of 4(13/2)(I) level, for Er3+ concentrations higher than 1 x 10(20) cm(-3), are one order of magnitude smaller than the ones reported for silica glass. The increase in the cooperative upconversion coefficient with the increase in Er3+ concentration was found to be small and Er3+ concentrations as high as 3.7 x 10(20) cm(-3) in this glass are feasible. Yb-Er energy transfer efficiency in Yb/Er codoped phosphate glasses, with Er concentrations as high as 1.9 x 10(20) cm(-3) and 2.4 x 10(20) cm(-3), were measured with a pump and probe technique and also estimated from lifetime measurements. The energy transfer efficiencies exceed 95%, although the ratio of the concentrations, Yb/Er, is only about 1.2 and 2 in the samples studied. This confirms that efficient pumping of high Er3+ concentration phosphate glass, required in waveguide amplifiers, can be achieved utilizing Yb/Er codoping.