Evanescent multimode longitudinal pumping scheme for Si-nanocluster sensitized Er3+ doped waveguide amplifiers

We present a multimode longitudinal pumping scheme for integrated rare-earth doped waveguide amplifiers which allows an efficient use of low cost multimode pump sources. The scheme is based on evanescent pump light coupling from a multimode low loss waveguide, which is gradually transferred to a single mode Si-nc sensitized Er 3+ doped active core. Population inversion is ensured along the whole amplifier length, thus overcoming the main limitation of conventional single mode pump butt-coupling in case of strongly absorbing active materials. Great flexibility in controlling the pump power intensity values within the active core is also provided. We propose this pumping scheme at 477 nm for Si-nanocluster sensitized Erbium doped waveguide amplifiers, in which top pumping by LED arrays is limited by the low pump intensity values achievable within the active region. The coupling between the multimode waveguide and the active core has been numerically studied for slab waveguide structures using a 2D split-step finite element method. Numerical simulation results, based on propagation and population-rate equations for the coupled Er 3+ /Si-nanoclusters system, show that high pump intensities are indeed achieved in the active core, ensuring good uniformity of the population inversion along the waveguide amplifier. Although longitudinal multimode pumping by high power LEDs in the visible can potentially lead to low-cost integrated amplifiers, further material optimization is required. In particular, we show that when dealing with high pump intensities, confined carrier absorption seriously affects the amplifier performance, and an optimization of both Si-nc and Er 3+ concentrations is necessary.