Er3+-Yb3+ codoped phosphate glasses used for an efficient 1.5 μm broadband gain medium

In order to develop efficient optical amplifiers with broad and flat gain profiles in the near-infrared range an active phosphate matrix codoped with Er3+ and Yb3+ rare earth optically active ions has been studied by carrying out steady-state and time-resolved luminescence spectroscopies. Taking advantage of the high absorption transition probability of the Yb3+ ions, these ions are excited with cw 980 nm radiation from a commercial laser diode and subsequently de-excited by efficiently transferring energy to the Er3+ ions, producing an intense emission at around 1.5 μm at which wavelength-division-multiplexing devices work. From the experimental data, the emission cross-section σem(λ) of the 4I13/2 → 4I15/2 transition at 1.5 μm has been calculated using the Füchtbauer-Landerburg method. The result of this calculation, together with the absorption cross-section σabs(λ), allows the gain cross-section G to be estimated. Other important spectroscopic parameters associated with this transition, such as full width at half maximum FWHM, effective bandwidth Δeff and lifetime of the 4I13/2 level τexp, have been measured and analysed as a function of the Er3+ concentration. As figures of merit, FWHM × σem(λ), Δeff × σem(λ) and σem(λ) × τexp calculations have been carried out. Comparing the obtained values to those reported in other Er3+-doped materials, the phosphate glasses doped with 1 mol% of Yb2O3 ions and 1-2 mol% of Er2O3 can be considered excellent candidates for developing broadband optical amplifiers, providing a large gain cross-section that covers the C (1530-1565 nm) and the L (1565-1625 nm) bands in the optical telecommunication window.