Transforming polarisation to wavelength via two-colour quantum dot plasmonic enhancement

Optical nano-antennas have become a hot topic in photonics research recently due to their ability to manipulate electromagnetic radiation on the subwavelength scale. Of particular interest is the application of optical nano-antennas to enhancement of quantum sources such as semiconductor Quantum Dots (QD) and Nitrogen Vacancy (NV) centers in nano-diamond. Much like their Radio Frequency (RF) cousins, optical nano-antennas are able to enhance and direct radiation from a localized source in the near-field of the antenna to the far-field. The work reported here exploits RF antenna designs by applying them to the development of optical nano-antennas for enhancement of multiple semiconductor QDs. In particular, the Vee antenna design, commonly used in improvised military RF applications, is utilized in this work as an optical nano-antenna to enable the selective excitation of two different color QDs via polarization control. The Vee antenna has two bright resonant modes in the visible spectrum, typically spectrally separated by approximately 50 nm, which are excited by orthogonal polarizations of the excitation field. Using these two resonant modes of the Vee antenna, two different color QDs can be selectively enhanced. The Vee antennas are fabricated with E-beam Lithography using aluminum as the antenna material on a multilayer SiO2/Al/glass substrate. The Vee antenna design consists of two dipole antennas, orientated at 90° to each other, where the gap between the antennas and the thickness of the SiO2 spacer layer is used to tune the spectral separation of the orthogonal resonances.