Enhanced quantum efficiency and Purcell factor of incoherent light-emitting source modulators coupled with nanoantennas: DDA modeling and optimization

Abstract

Gated tunable materials-based devices have proven efficient structures to dynamically control quantum emitters’ (QEs) photonic density of states. The active permittivity control enabled by these materials allows manipulating the coupling and dissipation of evanescent modes radiated by the QE, hence controlling the emission parameters. In this sense, we propose here the design and optimization of a plasmonic device coupled with nanoantennas capable of dynamically manipulating the QEs’ emission at visible wavelengths using a thin gated doped titanium nitrate layer. We explore the use of metallic cubic and bow-tie antennas and study their unique characteristics related to enhancing the QEs’ emission. For the nanoantenna geometrical parameters optimization, we propose a discrete-dipole-approximation (DDA) method to accurately calculate all the radiation parameters of a QE embedded in a layered medium coupled to a nanoantenna. This technique allows calculating the decay behavior of QEs arbitrarily distributed, which is only feasible with knowledge of the Purcell factor and quantum efficiency mapped for all possible positions, easily achieved with the proposed model. We show that by employing the proposed DDA, the time required for optimizing and building those maps to evaluate the device’s response is drastically reduced (98%) compared to conventional numerical techniques. Using the DDA to optimize the antenna allowed the device’s quantum efficiency to be enhanced from 1.8% (no nanoantenna) to 8% and 10.5% using the cubic and bow-tie nanoantenna, respectively. In addition, the nanoantenna helps decrease the QE lifetime by a factor of approximately 2, allowing faster modulation speeds. Finally, our modeling and findings can be used to pave the way for the design of new gated optical modulators coupled with nanoantennas for applications that require amplitude modulation.