UP-CONVERSION IN ER-IMPLANTED AL2O3 WAVE-GUIDES

When pumped with a 1.48 mu m laser diode, Er-implanted Al2O3 ridge wav eguides emit a broad spectrum consisting of several distinct peaks hav ing wavelengths ranging from the midinfrared (1.53 mu m) to the visibl e (520 nm). In order to explain these observations, three different up conversion mechanisms are considered: cooperative upconversion, excite d state absorption, and pair-induced quenching. It is found that for s amples with a high Er concentration (1.4 at. %), cooperative upconvers ion completely dominates the deexcitation of the Er3+ ions. For a much lower concentration (0.12 at. %), the influence of cooperative upconv ersion is strongly reduced, and another upconversion effect becomes ap parent: excited state absorption. These conclusions are based on measu rements of the luminescence emission versus pump intensity, and also o n measured luminescence decay curves. The upconversion coefficient is found to be (4+/-1)x10(-18) cm(3)/s; the excited state absorption cros s section is (0.9+/-0.3)x10(-21) cm(2). It is shown that in spite of t hese upconversion effects, a high fraction of the Er3+ can be excited at low pump powers. For pump powers between 2 and 10 mW the optimum Er concentration is calculated. The results show that for an Er concentr ation of 0.5 at. %, more than 2 dB/cm net optical gain is achievable a t a pump power less than 10 mW. (C) 1996 American Institute of Physics .