Terahertz Localized Surface Plasmon Resonances in Coaxial Microcavities

Abstract

Coaxial microcavities etched into the surface of a doped silicon substrate are shown to support localized surface plasmon resonances at terahertz frequencies. The underlying mechanism involves coupling freely propagating terahertz waves with surface plasmon polaritons (SPPs), which propagate in a coaxial mode along the cavity walls in the axial direction. A Fabry–Pérot resonance is built up when the SPP wavenumber appropriately relates to the cavity depth. Owing to the Ohmic loss of the silicon at terahertz frequencies, the energy of the resonating SPPs is largely dissipated, leading to a modified reflection spectrum. Strong field enhancement is observed inside the cavities at resonance. The theoretical analysis is supported by numerical and experimental results. This study is a promising pathway for development of terahertz devices with applications in the areas of photonic integrated circuits, molecular sensing, and subwavelength imaging.

Plasmonic Resonance toward Terahertz Perfect Absorbers

“…For the coaxial cavity, the fundamental cavity mode needs to satisfy the standing-wave condition 2dβ′ = 0.9π, or β′ = 23562 rad/m. 20 It is noted that the 0.9π rad accounts for a reflection phase change at the bottom of the cavity, observed numerically. From Figure 4, this wavenumber corresponds to the frequency of 1.2 THz, in good agreement with the resonance frequency observed from the experimental and numerical results.…”

“…The design is inspired by our earlier demonstration of complementary plasmonic resonators in the form of annular cavities etched into the surface of a doped silicon wafer. 20 These resonant cavities exhibit relatively strong nonradiative damping, …”

“…The design is inspired by our earlier demonstration of complementary plasmonic resonators in the form of annular cavities etched into the surface of a doped silicon wafer. 20 These resonant cavities exhibit relatively strong nonradiative damping, essential for efficient energy trapping. With dimensions satisfying the critical coupling condition, the cavity array can absorb nearly 100% of incident terahertz energy at resonance.…”

“…The effect can also be explained in terms of equivalent sources on In simulation, the unit cell boundary condition is applied to all transverse boundaries, and the Drude model with measured silicon properties is implemented for the doped silicon. 20 the surface of the central pillar. For the TE polarization, the incident magnetic field component tangential to the surface is not symmetric with respect to the E plane and, hence, leads to an imbalanced distribution of the surface current density J s .…”

A high-performance broadband terahertz absorber based on sawtooth-shape doped-silicon

“…The latter two parameters are determined by the carrier concentration and mobility of the doped silicon, which can be obtained through either Hall Effect analysis 25 or THz reflection spectroscopy. 30 Here we choose ω p = 2π × 5.22 THz and γ = 2π × 1.32 THz in our following structure design since doped silicon with these parameters had already been realized in reference. 25 The structure of our absorber are schematically shown in Fig.…”