Impedance matching and emission properties of optical antennas in a nanophotonic circuit

An experimentally realizable prototype nanophotonic circuit consisting of a receiving and an emitting nano antenna connected by a two-wire optical transmission line is studied using finite-difference time- and frequency-domain simulations. To optimize the coupling between nanophotonic circuit elements we apply impedance matching concepts in analogy to radio frequency technology. We show that the degree of impedance matching, and in particular the impedance of the transmitting nano antenna, can be inferred from the experimentally accessible standing wave pattern on the transmission line. We demonstrate the possibility of matching the nano antenna impedance to the transmission line characteristic impedance by variations of the antenna length and width realizable by modern microfabrication techniques. The radiation efficiency of the transmitting antenna also depends on its geometry but is independent of the degree of impedance matching. Our systems approach to nanophotonics provides the basis for realizing general nanophotonic circuits and a large variety of derived novel devices

Ultrafast spatiotemporal chiroptical response of dielectric and plasmonic nanospheres

We theoretically examine the spatiotemporal evolution of enhanced near-field optical chirality (OC) in both plasmonic and dielectric nanospheres when excited by ultrashort optical pulses. We demonstrate distinct spatiotemporal variations in near-field OC arising from the differing natures of plasmonic and dielectric resonators. The electric dipole resonant plasmonic nanosphere generates instantaneous near-field OC that relies on the interference between incident and scattered (induced) fields. Conversely, a resonant dielectric nanosphere sustains long-lasting OC even after the incident field diminishes due to the scattered field from resonant electric and magnetic dipole modes. We further demonstrate the control over the near-field OC using vector beams. Our work opens up opportunities for spatiotemporal control of nanostructure-enhanced chiral-light matter interactions

Emission Manipulation by DNA Origami‐Assisted Plasmonic Nanoantennas

Plasmonic nanoantennas mediate far and near optical fields and confine the light to subwavelength dimensions. The spatial organization of nanoantenna elements is critical as it affects the interelement coupling and determines the resultant antenna mode. To couple quantum emitters to optical antennas, high precision on the order of a few nm with respect to the antenna is necessary. As an emerging nanofabrication technique, DNA origami has proven itself to be a robust nanobreadboard to obtain sub-5 nm positioning precision for a diverse range of materials. Eliminating the need for expensive state-of-the-art top-down fabrication facilities, DNA origami enables cost-efficient implementation of nanoscale architectures, including novel nanoantennas. The ability of DNA origami to deterministically position single quantum emitters into nanoscale hotspots further boosts the efficiency of light–matter interaction controlled via optical antennas. This review recapitulates the recent progress in plasmonic nanoantennas assisted by DNA origami and focuses on their various configurations. How those nanoantennas act on the emission and absorption properties of quantum emitters positioned in the hotspots is explicitly discussed. In the end, open challenges are outlined and future possibilities lying ahead are pointed out for this powerful triad of biotechnology, nanooptics, and photophysics. © 2021 The Authors. Advanced Optical Materials published by Wiley-VCH Gmb

Signal and noise analysis for chiral structured illumination microscopy

Recently, chiral structured illumination microscopy has been proposed to image fluorescent chiral domains at sub-wavelength resolution. Chiral structured illumination microscopy is based on the combination of structured illumination microscopy, fluorescence-detected circular dichroism, and optical chirality engineering. Since circular dichroism of natural chiral molecules is typically weak, the differential fluorescence is also weak and can be easily buried by the noise, hampering the fidelity of the reconstructed images. In this work, we systematically study the impact of the noise on the quality and resolution of chiral domain images obtained by chiral SIM. We analytically describe the signal-to-noise ratio of the reconstructed chiral SIM image in the Fourier domain and verify our theoretical calculations with numerical demonstrations. Accordingly, we discuss the feasibility of chiral SIM in different experimental scenarios and propose possible strategies to enhance the signal-to-noise ratio for samples with weak circular dichroism

Signal and Noise Analysis for Chiral Structured Illumination Microscopy

Recently, chiral structured illumination microscopy has been proposed to image fluorescent chiral domains at sub-wavelength resolution. Chiral structured illumination microscopy is based on the combination of structured illumination microscopy, fluorescence-detected circular dichroism, and optical chirality engineering. Since circular dichroism of natural chiral molecules is typically weak, the differential fluorescence is also weak and can be easily buried by the noise, hampering the fidelity of the reconstructed images. In this work, we systematically study the impact of the noise on the quality and resolution of chiral domain images obtained by chiral SIM. We analytically describe the signal-to-noise ratio of the reconstructed chiral SIM image in the Fourier domain and verify our theoretical calculations with numerical demonstrations. Accordingly, we discuss the feasibility of chiral SIM in different experimental scenarios and propose possible strategies to enhance the signal-to-noise ratio for samples with weak circular dichroism.Comment: 18 page

Driving plasmonic nanoantennas at perfect impedance matching using generalized coherent perfect absorption

Coherent perfect absorption (CPA) describes the absence of all outgoing modes from a lossy resonator, driven by lossless incoming modes. Here, we show that for nanoresonators that also exhibit radiative losses, e.g. plasmonic nanoantennas, a generalized version of CPA (gCPA) can be applied. In gCPA outgoing modes are suppressed only for a subset of (guided plasmonic) modes while other (radiative) modes are treated as additional loss channels - a situation typically referred to as perfect impedance matching. Here we make use of gCPA to show how to achieve perfect impedance matching between a single nanowire plasmonic waveguide and a plasmonic nanoantenna. Antennas with both radiant and subradiant characteristics are considered. We further demonstrate potential applications in back-ground-free sensing

Correction: Design and characterization of a plasmonic Doppler grating for azimuthal angle-resolved surface plasmon resonances

The authors regret that Fig. 1e of the original paper contained an error in the curves displayed for the silver, aluminium and palladium gratings. Specifically, a different value of the ‘index of the environment’ (1.65) was used in the calculation of these curves compared to that used for calculating the optical response of the gold grating (1.33). The correct Fig. 1 below, displays the curves calculated with the same value of the index of the environment (1.33). No amendments are made to the caption of Fig. 1 or the other sub-figures presented in the figure. This error does not affect any of the results or conclusions reported in the paper; only the display of the figure. (Figure Presented) The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers

Generation of Optical Chirality Patterns with Plane Waves, Evanescent Waves and Surface Plasmon Waves

We systematically investigate the generation of optical chirality patterns by applying the superposition of two waves in three scenarios, namely plane waves in free space, evanescent waves of totally reflected light at dielectric interface and propagating surface plasmon waves on a metallic surface. In each scenario, the general analytical solution of the optical chirality pattern is derived for different polarization states and propagating directions of the two waves. The analytical solutions are verified by numerical simulations. Spatially structured optical chirality patterns can be generated in all scenarios if the incident polarization states and propagation directions are correctly chosen. Optical chirality enhancement can be obtained from the constructive interference of free-space circularly polarized light or enhanced evanescent waves of totally reflected light. Surface plasmon waves do not provide enhanced optical chirality unless the near-field intensity enhancement is sufficiently high. The structured optical chirality patterns may find applications in chirality sorting, chiral imaging and circular dichroism spectroscopy