Colloidal quantum dots decorated micro-ring resonators for efficient integrated waveguides excitation

Micro-ring resonators made of titanium dioxide were decorated with local light sources comprising CdSe/CdS colloidal quantum dot aggregates. The active micro-resonators are operated to achieve efficient evanescent excitation of nearby co-planar integrated waveguides. Coupled-mode analysis and numerical simulations are used to capture the dynamic of the optical interaction between locally activated resonators and integrated waveguides. In this context, we exemplify the key role of resonator intrinsic loss. Next, we show that locally activated or bus-waveguide excited resonators are in optimum waveguide interaction for the same so-called critical coupling condition, although the physical origin of this property is different for each configuration. More importantly, we found that a locally activated resonator is a fabrication imperfection tolerant configuration for the coupling light of local sources into waveguides. This remarkable property originates from the opposite change of the power cycling into the resonator and the waveguide coupling efficiency as a function of the resonator-waveguide separation gap. By operating an 8-μm-radius ring resonator with loaded quality factors around Q = 2100, we experimentally demonstrate a 5.5-dB enhancement of the power coupled into the output waveguide compared to a direct local source waveguide excitation.