A tip-enhanced quantum emitter with integrated TiO2 slot waveguides in the optical regime

We study the coupling between a nanoscopic dielectric slot waveguide and a metallic-tip-enhanced dipole quantum emitter and search for optimal emission and guiding of photons along a titanium dioxide photonic waveguide. Finite element calculations are used to characterize the mode properties of the waveguide over a range of parameters and predict the efficiency of emission guidance along the waveguide. We show how the effective quantum yield is dependent on the waveguide parameters as well as the dipole position and orientation and show that the integrated system can reach a maximum quantum yield of more than 30% along each direction of the waveguide. By placing the dipole emitter near the apex of a silver nanotip situated above or inside the slot waveguide to increase the overall emission rate, we also enable the capability of controlling the emitter-waveguide coupling in situ. We numerically compute the excitation and radiation fields and find that despite a reduction in the quantum yield, a 35-fold increase in the overall emission rate can be obtained due to very large field enhancement factors of up to 4000 at the location of the dipole. By using alternative materials for the tip, this tip-enhanced-waveguide approach has the potential of further increasing the guided photon emission rate. With the possibility of controlling emitter-waveguide coupling in situ, this tip-enhanced emitter configuration provides an alternative approach for the realization of an efficient single-photon source.