Double helical plasmonic antennas
Plasmonic double helical antennas are a means to funnel circularly polarized light down to the nanoscale. Here, an existing design tool for single helices is extended to the case of double helices and used to design antennas that combine large chiroptical interaction strength with highly directional light emission. Full-field numerical modeling underpins the design and provides additional insight into surface charge distributions and resonance widths. The helical antennas are fabricated by direct writing with a focused electron beam, a technique that is unrivaled in terms of spatial resolution and 3D shape fidelity. After the printing process, the structures are purified using ozone plasma at room temperature, resulting in the smallest continuous double helix antennas ever realized in gold. Fabricated antennas are studied regarding their polarization-dependent transmission behavior, which shows a large and broadband dissymmetry factor in the visible range. Since the polarization of light is an important tool for implementing logic functionality in photonic and quantum photonic devices, these helices are potential building blocks for future nanophotonic circuits, but also for chiral metamaterials or phase plates.