Resonant Plasmonic-Biomolecular Chiral Interactions in the Far-Ultraviolet: Enantiomeric Discrimination of sub-10 nm Amino Acid Films.

Resonant plasmonic-molecular chiral interactions are a promising route to enhanced biosensing. However, biomolecular optical activity primarily exists in the far-ultraviolet regime, posing significant challenges for spectral overlap with current nano-optical platforms. We demonstrate experimentally and computationally the enhanced chiral sensing of a resonant plasmonic-biomolecular system operating in the far-UV. We develop a full-wave model of biomolecular films on Al gammadion arrays using experimentally derived chirality parameters. Our calculations show that detectable enhancements in the chiroptical signals from small amounts of biomolecules are possible only when tight spectral overlap exists between the plasmonic and biomolecular chiral responses. We support this conclusion experimentally by using Al gammadion arrays to enantiomerically discriminate ultrathin (<10 nm thick) films of tyrosine. Notably, the chiroptical signals of the bare films were within instrumental noise. Our results demonstrate the importance of using far-UV active metasurfaces for enhancing natural optical activity.

Method for direct coupling of a semiconductor quantum dot to an optical fiber for single-photon source applications.

We present an effective method for direct fiber coupling of a quantum dot (QD) that is deterministically incorporated into a cylindrical mesa. For precise positioning of the fiber with respect to the QD-mesa, we use a scanning procedure relying on interference of light reflected back from the fiber end-face and the top surface of the mesa, applicable for both single-mode and multi-mode fibers. The central part of the fiber end-face is etched to control the required distance between the top surface of the mesa and the fiber core. Emission around 1260 nm from a fiber-coupled InGaAs/GaAs QD is demonstrated and its stability is proven over multiple cooling cycles. Moreover, a single photon character of emission from such system for a line emitting above 1200 nm is proven experimentally by photon autocorrelation measurements with an obtained value of the second order correlation function at zero time-delay well below 0.5.

Numerical optimization of the extraction efficiency of a quantum-dot based single-photon emitter into a single-mode fiber.

We present a numerical method for the accurate and efficient simulation of strongly localized light sources, such as quantum dots, embedded in dielectric micro-optical structures. We apply the method in order to optimize the photon extraction efficiency of a single-photon emitter consisting of a quantum dot embedded into a multi-layer stack with further lateral structures. Furthermore, we present methods to study the robustness of the extraction efficiency with respect to fabrication errors and defects.

Micro-optically assisted high-index waveguide coupling.

Adapting the concept of solid immersion lenses, we numerically study a micro-optical scheme for conventional high-index and photonic-crystal waveguide coupling by using a combination of different numerical methods such as ray tracing, angular-spectrum propagation, finite-difference time-domain simulations, and finite-element-method simulations. The numerical findings are discussed by means of impedance, group- or energy-velocity, spot-size, and phase-matching criteria. When fabrication constraints for high-index immersion lenses made of silicon are taken into account, a coupling efficiency of -80% can be reached for monomode silicon-on-insulator waveguides with a quadratic cross section of the core and rectangular cross sections of moderate aspect ratio. Similar coupling efficiencies of -80% can be obtained for silicon-on-insulator photonic-crystal waveguides. Tolerances that are due to misalignments and variations of the substrate thickness of the silicon lens are discussed.