Tuning Multiple Fano Resonances for On-Chip Sensors in a Plasmonic System

Excitation of multiple Fano resonances on all-dielectric nanoparticle arrays

In this paper, an all-dielectric metasurface consisting of a unit cell containing a nanocube array and organized periodically on a silicon dioxide substrate is designed and analyzed. By introducing asymmetric parameters that can excite the quasi-bound states in the continuum, three Fano resonances with high Q-factor and high modulation depth may be produced in the near-infrared range. Three Fano resonance peaks are excited by magnetic dipole and toroidal dipole, respectively, in conjunction with the distributive features of electromagnetism. The simulation results indicate that the discussed structure can be utilized as a refractive index sensor with a sensitivity of around 434 nm/RIU, a maximum Q factor of 3327, and a modulation depth equal to 100%. The proposed structure has been designed and experimentally investigated, and its maximum sensitivity is 227 nm/RIU. At the same time, the modulation depth of the resonance peak at λ = 1185.81 nm is nearly 100% when the polarization angle of the incident light is 0 °. Therefore, the suggested metasurface has applications in optical switches, nonlinear optics, and biological sensors.

Design and simulation of a plasmonic density nanosensor for polarizable gases

In this paper, an optical method of measuring the mass density of polarizable gases is proposed using a plasmonic refractive index nano-sensor. Plasmonic sensors can detect very small changes in the refracting index of arbitrary dielectric materials. However, attributing them to a specific application needs more elaboration of the material's refractive index unit's (RIU) relation with the introduced application. In a gaseous medium, the optical properties of molecules are related to their dipole moment polarizability. Hence, the theoretical index-density relation of Lorentz-Lorenz is applied in the proposed sensing mechanism to interpret changes in the gas' refractive index and to changes in its density. The proposed plasmonic mass density sensor shows a sensitivity of 348.8nm/(gr/cm³) for methane gas in the visible light region. This sensor can be integrated with photonic circuits for gas sensing purposes.

Multi frequency multi bit amplitude modulation of spoof surface plasmon polaritons by schottky diode bridged interdigital SRRs

Multi-frequency multi-bit programmable amplitude modulation (AM) of spoof surface plasmon polaritons (SPPs) is realized at millimeter wave frequencies with interdigital split-ring resonators (SRRs) and In-Ga-Zn-O (IGZO) Schottky diodes. Periodic SRRs on a metal line guide both SRR mode and spoof SPP mode, the former of which rejects the spoof SPP propagation at the SRR resonant frequencies. To actively modulate the amplitude of spoof SPPs, IGZO Schottky diodes are fabricated in the SRR gaps, which continuously re-configure SRRs to metallic loops by applying bias. Interdigital gaps are designed in SRRs to increase the capacitance, thus red shifting the resonant frequencies, which significantly broadens the operation bandwidth of multi-frequency AM. Thus, cascading different kinds of interdigital SRRs with Schottky diodes enables multi-frequency multi-bit AM programmable. As a demonstration, a dual-frequency device was fabricated and characterized, which achieved significant multi-bit AM from −12.5 to −6.2 dB at 34.7 GHz and from −26 to −8.5 dB at 50 GHz independently and showed programmable capability.

High Sensitivity Plasmonic Sensor Based on Fano Resonance with Inverted U-Shaped Resonator

Herein, we propose a tunable plasmonic sensor with Fano resonators in an inverted U-shaped resonator. By manipulating the sharp asymmetric Fano resonance peaks, a high-sensitivity refractive index sensor can be realized. Using the multimode interference coupled-mode theory and the finite element method, we numerically simulate the influences of geometrical parameters on the plasmonic sensor. Optimizing the structure parameters, we can achieve a high plasmonic sensor with the maximum sensitivity for 840 nm/RIUand figure of merit for 3.9 × 105. The research results provide a reliable theoretical basis for designing high sensitivity to the next generation plasmonic nanosensor.

Independently tunable Fano resonances in a metal-insulator-metal coupled cavities system

Herein, multiple Fano resonances with excellent ability to be tuned independently are produced in a sub-wavelength metal-insulator-metal system. The input and output waveguides are separated by a metal gap, and a stub and an end-coupled cavity are placed below and to the right side of the input waveguide, respectively, as discrete states. Owing to the mode interferences, double ultra-sharp and asymmetric Fano resonant peaks are observed in the transmission spectrum. Successfully, the basic structure is extended by two extra rectangular cavities, giving rise to four Fano resonances with high refractive index sensitivity and figure of merit. Due to the discrete modes of Fano resonances from different coupling cavities, their resonant wavelengths can be controlled independently, which can provide greater flexibility for tuning Fano resonances. The performances of the proposed structure are investigated by both the finite-difference time-domain method and the multimode interference coupled-mode theory. It is believed that the research can provide important guidance in designing Fano resonance structures, and the proposed structure has a wide application in sensors, switches, and nano-photonic integrated circuit devices.