The increasing demand for small-footprint and cost-effective devices in fiber optical communications links has prompted significant research activity into developing efficient silicon-based lasers. The operating wavelengths of interest are in and neighboring the C-band lines (1530-1565 nm). Some effort has been focused on combining the function of two lasers into one by achieving dual-wavelength emission from separate dopant ions. Dual-band lasers using the emissions of erbium (Er) and other neighboring ions such as Tm, Nd, Yb and Ho in glasses have been reported. However, there are few reports on the co-doping of Er and Tm into crystalline hosts for realization of broadband optical waveguide amplifiers and dual-wavelength light emitters on silicon in the telecommunications bands.

We succeeded in observing sharp light emissions from Tm³⁺ ions in the wavelength regions of 1300 and 1470 nm and from Er³⁺ ions at 1530 nm from a mixture of polycrystalline Er_2xTm_2-2xSiO₅ and Er_2xTm_2-2xSi₂O₇ formed on Si [1]. We demonstrated that Er³⁺ ions in the mixed compounds act as not only 1530 nm wavelength light emitters but also as effective sensitizers to the 1300 nm wavelength light emissions from Tm³⁺ ions (Fig.1). The resonant energy transfers between higher energy levels of Er³⁺ and Tm³⁺ ions play an important role in the simultaneous sharp light emissions in O and S+C bands when excited with λ_exc = 532 nm (Fig. 2). Additionally, we demonstrated the dual-wavelength sharp light emissions in the S and C bands at λ_exc = 785 nm.

A future objective of this work will be the deeper understanding and optimization of the mixture formation on silicon and the lifetime measurements of the light emissions, which is important for obtaining high-quantum-efficiency dual-wavelength light emitters in the telecommunications bands.