High-Speed Plasmonic Electro-Optic Beam Deflectors

Near-Field Observation of the Photonic Spin Hall Effect

The photonic spin Hall effect, referring to the spatial separation of photons with opposite spins due to spin-orbit interactions, has enabled potential for various spin-sensitive applications and devices. Here, using scattering-type near-field scanning optical microscopy, we observe spin-orbit interactions introduced by a subwavelength semiring antenna integrated in a plasmonic circuit. Clear evidence of unidirectional excitation of surface plasmon polaritons is obtained by direct comparison of the amplitude- and phase-resolved near-field maps of the plasmonic nanocircuit under excitation with photons of opposite spin states coupled to a plasmonic nanoantenna. We present details of the antenna design and experimental methods to investigate the spatial variation of complex electromagnetic fields in a spin-sensitive plasmonic circuit. The reported findings offer valuable insights into the generation, characterization, and application of the photonic spin Hall effect in photonic integrated circuits for future and emerging spin-selective nanophotonic systems.

Surface plasmons in anisotropic 3D gapped topological insulators

Topological insulators (TIs) are materials having conductive surfaces but insulating bulk, which are ideal platforms for plasmonic applications. The most commonly known TIs, such as Bi₂Se₃and Bi₂Te₃, are in fact highly anisotropic. The dielectric constants are largely different parallel and perpendicular to the surface. Here, we have extended the electromagnetic calculations of the surface plasmons in TIs to the anisotropic case. Magnetic field perpendicular to the surface is allowed, which opens a gap among the surface states. We model anisotropic TIs as bulk dielectric materials with different in-plane and out-of-plane permittivities; the surface states caused by the band inversion lead to a two-dimensional conductivity which supports surface plasmons. We have found two rather than one surface modes. Due to such anisotropy, quasi transverse electric (TE) polarized mode may occur near the interband transition threshold. Far below the transition frequency, another mode with both TE and transverse magnetic polarized components dominates, the dispersion relation of which is seriously modified by the Hall conductivity. By taking Bi₂Te₃as an example, we have derived the conductivity tensor with the consideration of the hexagonal warping effect, and solved the above mentioned two surface plasmon modes. In the end, finite element method has been used to calculate the electric field distributions. Our extension of the electromagnetic calculations of surface plasmons including a specific kind of anisotropy might be useful in other surface conductive materials with similar symmetry as well.

Plasmonic Lithium Niobate Mach-Zehnder Modulators

Lithium niobate Mach-Zehnder modulators (MZMs) are present in a wide range of technologies and though fulfilling the performance and reliability requirements of present applications, they are becoming progressively too bulky, power inefficient, and slow in switching to keep pace with future technological demands. Here, we utilize plasmonics to demonstrate the most efficient (V_πL = 0.23 Vcm) lithium niobate MZM to date, consisting of gold nanostripes on lithium niobate that guide both plasmonic modes and electrical signals that control their relative optical phase delay, thereby enabling efficient electro-optic modulation. For high linearity (modulation depth of >2 dB), the proposed MZM inherently operates near its quadrature point by shifting the relative phase of the signal in the interferometric arms. The demonstrated lithium niobate MZM manifests the benefits of employing plasmonics for applications that demand compact (<1 mm²) and fast (>10 GHz) photonic components operating reliably at ambient temperatures.

Efficient multi-step coupling between Si3N4 waveguides and CMOS plasmonic ferroelectric phase shifters in the O-band

In this paper we present a thorough simulation-based analysis for the design of multi-step couplers bridging seamlessly plasmonic barium titanate oxide (BTO) ferroelectric phase shifters and thick silicon nitride (Si₃N₄) waveguides for the O-band. The targeted plasmonic waveguides are a hybrid plasmonic waveguide (HPW) providing low propagation losses and a plasmonic metal-insulator-metal (MIM) slot waveguide offering a high confinement factor for high modulation efficiency. The proposed plasmonic platforms are formed by Copper (Cu) providing CMOS compatibility. The analysis is based on 2D-FD eigenvalue and 3D-FDTD numerical simulations targeting to identify the optimum geometries ensuring the lowest coupling losses, calculated as 1.75dB for the HPW geometry and 1.29dB for the MIM configuration. The corresponding confinement factors are 31.39% and 56.2% for the HPW and MIM waveguides, respectively.