Plasmonic chirality shows great potential in analytical chemistry, biomedicine, and life science due to the strong chiroptical response generated from metallic nanostructures. However, significant chiral effects are mainly realized in three-dimensional structures because of their high structural asymmetry and large plasmon mode volume. This paper describes planar plasmonic “τ”-shaped structure arrays that can obtain significantly enhanced chiroptical responses for single-molecule detection. The “τ”-shaped structure arrays based on a chiral–achiral coupling scheme are constructed to generate a large superchiral field and enhanced circular dichroism (CD). Numerical simulations show that the chiroptical responses can be efficiently manipulated by the near-field coupling strength of plasmons determined by the parameters of the arrays and the structural chirality of the unit cells. The planar “τ”-shaped structure arrays with a large CD signal and enhanced superchiral field enable ultrasensitive detection of single-molecule bovine serum albumin (BSA) protein.
This paper describes a quasi-planar chiral metamaterial of metal–insulator–metal (MIM) tetramer arrays that support multiplasmon modes from a hybridization scheme to achieve significant chiroptical responses with the largest circular dichroism (CD) value of 42%. The chiroptical responses can be actively switched on and off by tuning the field coupling regime from near field to far field through the insulator (or spacer) thickness. Numerical calculations demonstrate that near-field coupling of the hybridized plasmons on the stacked metallic tetramers governs the chiroptical responses at small insulator thickness (t SiO2 < 160 nm). In contrast, far-field coupling of the plasmon radiations dominates at large spacing (t SiO2 > 160 nm) as phase retardation plays a crucial role. The quasi-planar chiral metamaterial with tunable plasmonic chirality enables efficient light modulation for polarization conversion: from circular to elliptical/linear polarization.
Waveguide–plasmon polaritons sustained in metallic photonic crystal slabs show fascinating properties, such as narrow bandwidth and ultrafast dynamics crucial for biosensing, light emitting, and ultrafast switching. However, the patterning of metallic photonic crystals using electron beam lithography is challenging in terms of high efficiency, large area coverage, and cost control. This paper describes a controllable patterning technique for the fabrication of an Ag grating structure on an indium–tin oxide (ITO) slab that enables strong photon–plasmon interaction to obtain waveguide–plasmon polaritons. The Ag grating consisting of self-assembled silver nanoparticles (NPs) exhibits polarization-independent properties for the excitation of the hybrid waveguide–plasmon mode. The Ag NP grating can also be annealed at high temperature to form a continuous nanoline grating that supports the hybrid waveguide–plasmon mode only under transverse magnetic (TM) polarization. We tuned the morphology and the periodicity of the Ag grating through the concentration of silver salt and the photoresist template, respectively, to manipulate the strong coupling between the plasmon and the waveguide modes of different orders.
Strong light−matter interaction enables significant modification of fundamental properties of coupled matter, such as chemical reaction rate, conductivity, and energy transfer, which is crucial for designing efficient light-emitting devices and lowthreshold lasing. Strong photon−plasmon coupling in metallic photonic crystal slabs has been extensively exploited for band gap engineering, third-harmonic generation, and enhanced Faraday rotation. However, current research focuses on coupling the waveguide mode to the dipolar plasmon that is inherently lossy and has a small quality factor. This paper reports a metallic photonic crystal slab constructed by placing split nanoring dimer arrays onto an indium−tin−oxide (ITO) waveguide to excite dipolar and highorder waveguide−plasmon polaritons with large Rabi splitting. The dimer unit comprises two identical split nanorings and supports dipolar and high-order hybrid plasmons derived from structural symmetry breaking and plasmon hybridization. Arrangement of the dimer into arrays on the ITO slab creates a strong coupling channel for the hybrid plasmons and the waveguide mode to generate dipolar and high-order waveguide−plasmon polaritons with distinct anticrossing dispersions. The strong coupling effect remarkably modifies the plasmon oscillations by altering the directions and strength of their dipole moment. We used the strongly coupled plasmons with narrow spectral line shapes as a refractive index sensor and obtained the largest sensitivity of 250 nm•RIU −1 and a figure of merit of 11.62 RIU −1 .
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