Silicon-erbium ytterbium silicate nanowire waveguides with optimized optical gain

Single-crystal erbium silicate nanowires have attracted considerable attention because of their high optical gain. In this work, we report the controlled synthesis of silicon-erbium ytterbium silicate core- shell nanowires and fine-tuning the erbium mole fraction in the shell from x = 0.3 to x = 1.0, which corresponds to changing the erbium concentration from 4.8 ×10^21 to 1.6 ×10^22 cm^-3. By controlling and properly optimizing the composition of erbium and ytterbium in the nanowires, we can effectively suppress upeonversion photoluminescence while simultaneously enhancing near-infrared emission. The composition-optimized nanowires have very long photoluminescence lifetimes and large emission cross- sections, which contribute to the high optical gain that we observed. We suspended these concentration- optimized nanowires in the air to measure and analyze their propagation loss and optical gain in the near-infrared communication band. Through systematic measurements using wires with different core sizes, we obtained a maximum net gain of 20 ± 8 dB·mm^-1, which occurs at a wavelength of 1534 nm, for a nanowire with a diameter of 600 nm and a silicon core diameter of 300 nm.