Enhancing on/off ratio of a dielectric-loaded plasmonic logic gate with an amplitude modulator.

Plasmonic waveguides allow focusing, guiding, and manipulating light at the nanoscale and promise the miniaturization of functional optical nanocircuits. Dielectric-loaded plasmonic (DLP) waveguides and logic gates have drawn attention because of their relatively low loss, easy fabrication, and good compatibility with gain and active tunable materials. However, the rather low on/off ratio of DLP logic gates remains the main challenge. Here, we introduce an amplitude modulator and theoretically demonstrate an enhanced on/off ratio of a DLP logic gate for XNOR operation. Multimode interference (MMI) in DLP waveguide is precisely calculated for the design of the logic gate. Multiplexing and power splitting at arbitrary multimode numbers have been theoretically analyzed with respect to the size of the amplitude modulator. An enhanced on/off ratio of 11.26 dB has been achieved. The proposed amplitude modulator can also be used to optimize the performance of other logic gates or MMI-based plasmonic functional devices.

Efficient modulation of subwavelength focusing via meta-aperture-based plasmonic lens for multifunction applications.

Subwavelength focusing is crucial for many applications in photonics including super-resolution micro/nanoscopy, nanolithography, and optical trapping. However, most nanostructures exhibit poor ability to modulate focusing spot, which makes them hard to achieve ultra-small resolution. Here, we propose three kinds of plasmonic lens (PL) by utilizing different meta-aperture designs for efficient subwavelength focusing modulation. The shape of nanoaperture strongly influences the diffraction properties. Spatial modulation of focusing spot by employing a circular array of proposed nanoapertures is explored. The best focusing performance among these PLs is the design of T-shape nanoaperture, which has great resolution achieving ultra-small focusing spot of 0.14 λ2 and 0.20 λ2 (λ = 633 nm) for simulation and experiment respectively, better than lots of focusing devices especially by using linear polarization. Multiple-object trapping can be realized by using T-shape nanoaperture-based PL. Our designed PLs with different nanoapertures demonstrate the capability to broaden and integrate different functionalities for on-chip nanotechnologies development.

Engineering surface lattice resonance of elliptical gold nanodisk array for enhanced strain sensing.

We demonstrate an elliptical gold nanodisk array (GNA) for engineering the spectral profile of surface lattice resonance (SLR). The nanodisk's shape has a great impact on SLR. Small linewidth of 20 nm at an aspect ratio of 1.17, as well as large wavelength tuning of 64 nm within 4% strain via different orientations and polarizations, are achieved experimentally. The enhanced wavelength response of 6.93 nm per 1% strain variation for elliptical GNA is 2.4 times better than that for general circular GNA. Furthermore, the strain sensing for elliptical GNA approaches is 5.7 times greater than that for circular GNA.

The aspect ratio effect on plasmonic properties and biosensing of bonding mode in gold elliptical nanoring arrays.

We investigate both numerically and experimentally the optical properties and biosensing of gold elliptical nanoring (ENR) arrays with various aspect ratios. The gold ENR exhibits a strong localized surface plasmon bonding mode in near-infrared region, whose peak wavelength is red-shifted as increasing the aspect ratio under longitudinal and transverse polarizations. Furthermore, the disk- and hole-like optical properties for longitudinal and transverse modes are observed, which cause different behaviors in field intensity enhancement. For biomolecule sensing, we find that both modes show increased surface sensitivities when enlarging the aspect ratio of gold ENR.