Ultra-low-threshold Er:Yb sol-gel microlaser on silicon.

Ultra-low threshold lasers which operate in the telecommunications band and which can be integrated with other CMOS compatible elements have numerous applications in satellite communications, biochemical detection and optical computing. To achieve sub-mW lasing thresholds, it is necessary to optimize both the gain medium and the pump method. One of the most promising methods is to use rare-earth ions in a co- or tri-dopant configuration, where the lasing of the primary dopant is enhanced by the secondary one, thus improving the efficiency of the overall system. Here, we demonstrate an Erbium:Ytterbium co-doped microcavity-based laser which is lithographically fabricated on a silicon substrate. The quality factor and pump threshold are experimentally determined for a series of erbium and ytterbium doping concentrations, verifying the inter-dependent relationship between the two dopants. The lasing threshold of the optimized device is 4.2 microW.