Planar antenna designs for efficient coupling between a single emitter and an optical fiber.

Fluorescence detection is a well-established readout method for sensing, especially for in-vitro diagnostics (IVD). A practical way to guide the emitted signal to a detector is by means of an optical fiber. However, coupling fluorescence into a fiber is challenging and commonly lacks single-molecule sensitivity. In this work, we investigate specific fiber geometries, materials and coatings that in combination with a planar Yagi-Uda antenna reach efficient excitation and collection. The simulation of a practical setting determines more than 70% coupling efficiency for a horizontally oriented dipole, with respect to the planar antenna, emitting at 700 nm and embedded in polyvinyl alcohol (PVA). Moreover, the coupling efficiency would only scale by a factor of 2/3 for emitters with random orientation, as a result of the antenna geometry. These findings are relevant for single-molecule detection with fiber optics and have implications for other applications involving the coupling of light with nano-scale sources and detectors. Scanning the surface of a sample with such fibers could also be advantageous for imaging techniques to provide a low background noise and a high resolution.