Direct-Laser-Written Polymer Nanowire Waveguides for Broadband Single Photon Collection from Epitaxial Quantum Dots into a Gaussian-like Mode

Abstract

Single epitaxial quantum dots (QDs) embedded in nanophotonic geometries are a leading technology for quantum light generation. However, efficiently coupling their emission into a single mode fiber or Gaussian beam often remains challenging. Here, direct laser writing (DLW) is used to address this challenge by fabricating 1 mu m diameter polymer nanowires (PNWs) in-contact-with and perpendicular-to a QD-containing GaAs layer. QD emission is coupled to the PNW's HE11$HE_{11}$ waveguide mode, enhancing collection efficiency into a single-mode fiber. PNW fabrication does not alter the QD device layer, making PNWs well-suited for augmenting pre-existing in-plane geometries. Standalone PNWs and PNWs in conjunction with metallic nanoring devices that have been previously established for increasing extraction of QD emission are studied. Methods that mitigate standing wave reflections and heat, caused by GaAs's absorption/reflection of the lithography beam, and which otherwise prevent PNW fabrication, are also reported. A maximum improvement of (3.0 +/- 0.7)x$3.0\nobreakspace \pm \nobreakspace 0.7)\times$ in a nanoring system with a PNW compared to the same system without a PNW is observed, in line with numerical results, and highlighting the PNW's ability to waveguide QD emission and increase collection efficiency simultaneously. These results demonstrate new DLW functionality in service of quantum emitter photonics that maintains compatibility with existing top-down fabrication approaches. Polymer nanowires (PNWs) are high index-contrast cylindrical waveguides that can directly couple a quantum dot's (QD's) emission into the HE11$HE_{11}$ optical mode, which improves collection efficiency into a single mode fiber. PNWs can be used as standalone devices or in conjunction with top-down fabricated QD devices. Strategies for successful PNW fabrication are presented, and enhancement from a PNW is demonstrated.image