Boosting Second Harmonic Generation Efficiency and Nonlinear Susceptibility via Metasurfaces Featuring Split-Ring Resonators and Bowtie Nanoantennas.

This work investigates a metasurface design to achieve remarkable second harmonic generation (SHG) conversion efficiency and enhance effective nonlinear susceptibility using the finite element method. The elements of the designed structure are composed of a rectangular split-ring resonator Ag film, a bowtie-shaped Ag nanoantenna, and a pair of Bi bars that induce nonlinear optical phenomena due to the nonuniform distribution of the electric and magnetic fields within the device surface. The simulation results agree perfectly with the theory and demonstrate outstanding achievements in terms of SHG conversion efficiency (η) and effective nonlinear susceptibility (χeff(2)). Specifically, the metasurface reaches a peak η value of 4.544×10-8 and an effective nonlinear susceptibility of 3.4×104 pm/V. This work presents a novel and versatile design to achieve high η and χeff(2) in an SHG metasurface.

Effects of external light in the magnetic field-modulated photocatalytic reactions in a microfluidic chip reactor.

Photocatalytic reactions and their magnetic-field enhancement present significant potential for practical applications in green chemistry. This work presents the mutual enhancement of plasmonic photocatalytic reaction by externally applied magnetic field and plasmonic enhancement in a micro optofluidic chip reactor. The tiny gold (Au) nanoparticles of only a few atoms fixed on the surface of titanium dioxide (TiO2) nanoparticles lead to mutually boosted enhancement photocatalytic reactions under an external magnetic field and plasmonic effects. The dominant factor of adding green light to the photocatalytic reaction leads to the understanding that it is a plasmonic effect. The positive results of adding ethanol alcohol (EA) in the experiments further present that it is a hot electron dominant path photocatalytic reaction that is positively enhanced by both the external magnetic field and plasmonic effects. This work offers great potential for utilizing magnetic field enhancement in plasmonic photocatalytic reactions.

Biosensing on a Plasmonic Dual-Band Perfect Absorber Using Intersection Nanostructure.

Optical absorbers with multiple absorption channels are required in integrated optical circuits and have always been a challenge in visible and near-infrared (NIR) region. This paper proposes a perfect plasmonic absorber (PPA) that consists of a closed loop and a linked intersection in a unit cell for sensitive biosensing applications. We elucidate the physical nature of finite element method simulations through the absorptance spectrum, electric field intensity, magnetic flux density, and surface charge distribution. The designed PPA achieves triple channels, and the recorded dual-band absorptance reaches 99.64 and 99.00% nm, respectively. Besides, the sensitivity can get 1000.00 and 650 nm/RIU for mode 1 and mode 2, respectively. Our design has a strong electric and magnetic field coupling arising from the mutual inductance and the capacitive coupling in the proposed plasmonic system. Therefore, the designed structure can serve as a promising option for biosensors and other optical devices. Here, we illustrated two examples, i.e., detecting cancerous cells and diabetes cells.

Breaking the Symmetry of a Metal-Insulator-Metal-Based Resonator for Sensing Applications.

This article designed a novel multi-mode plasmonic sensor based on a metal-insulator-metal waveguide side-coupled to a circular-shaped resonator containing an air path in the resonator. The electromagnet field distributions and transmittance spectra are investigated using finite element method-based simulations. Simulation results show that an air path in the resonator's core would impact the transmittance spectrum of SPPs. Besides, the air path is crucial in offering efficient coupling and generating multiple plasmon modes in the sensor system. The proposed structure has the advantage of multi-channel, and its sensitivity, figure of merit, and dipping strength can reach 2800 nm/RIU, 333.3 1/RIU, and 86.97%, respectively. The achieved plasmonic sensor can also apply for lab-on-chip in biochemical analysis for detecting the existence or nonappearance of diabetes through the human glucose concentration in urine.

A multichannel color filter with the functions of optical sensor and switch.

This paper reports a multichannel color filter with the functions of optical sensor and switch. The proposed structure comprises a metal-insulator-metal (MIM) bus waveguide side-couples to six circular cavities with different sizes for filtering ultra-violet and visible lights into individual colors in the wavelength range of 350-700 nm. We used the finite element method to analyze the electromagnetic field distributions and transmittance properties by varying the structural parameters in detail. The designed plasmonic filter takes advantage of filtering out different colors since the light-matter resonance and interference between the surface plasmon polaritons (SPPs) modes within the six cavities. Results show that the designed structure can preferentially select the desired colors and confine the SPPS modes in one of the cavities. This designed structure can filter eleven color channels with a small full width at half maximum (FWHM) ~ 2 nm. Furthermore, the maximum values of sensitivity, figure of merit, quality factor, dipping strength, and extinction ratio can achieve of 700 nm/RIU, 350 1/RIU, 349.0, 65.04%, and 174.50 dB, respectively, revealing the excellent functions of sensor performance and optical switch, and offering a chance for designing a beneficial nanophotonic device.

Significantly enhanced coupling effect and gap plasmon resonance in a MIM-cavity based sensing structure.

Herein, we design a high sensitivity with a multi-mode plasmonic sensor based on the square ring-shaped resonators containing silver nanorods together with a metal-insulator-metal bus waveguide. The finite element method can analyze the structure's transmittance properties and electromagnetic field distributions in detail. Results show that the coupling effect between the bus waveguide and the side-coupled resonator can enhance by generating gap plasmon resonance among the silver nanorods, increasing the cavity plasmon mode in the resonator. The suggested structure obtained a relatively high sensitivity and acceptable figure of merit and quality factor of about 2473 nm/RIU (refractive index unit), 34.18 1/RIU, and 56.35, respectively. Thus, the plasmonic sensor is ideal for lab-on-chip in gas and biochemical analysis and can significantly enhance the sensitivity by 177% compared to the regular one. Furthermore, the designed structure can apply in nanophotonic devices, and the range of the detected refractive index is suitable for gases and fluids (e.g., gas, isopropanol, optical oil, and glucose solution).

Ultrahigh Sensitivity of a Plasmonic Pressure Sensor with a Compact Size.

This study proposes a compact plasmonic metal-insulator-metal pressure sensor comprising a bus waveguide and a resonator, including one horizontal slot and several stubs. We calculate the transmittance spectrum and the electromagnetic field distribution using the finite element method. When the resonator's top layer undergoes pressure, the resonance wavelength redshifts with increasing deformation, and their relation is nearly linear. The designed pressure sensor possesses the merits of ultrahigh sensitivity, multiple modes, and a simple structure. The maximum sensitivity and resonance wavelength shift can achieve 592.44 nm/MPa and 364 nm, respectively, which are the highest values to our knowledge. The obtained sensitivity shows 23.32 times compared to the highest one reported in the literature. The modeled design paves a promising path for applications in the nanophotonic field.

Perfect Dual-Band Absorber Based on Plasmonic Effect with the Cross-Hair/Nanorod Combination.

Plasmonic effect using a cross-hair can convey strongly localized surface plasmon modes among the separated composite nanostructures. Compared to its counterpart without the cross-hair, this characteristic has the remarkable merit of enhancing absorptance at resonance and can make the structure carry out a dual-band plasmonic perfect absorber (PPA). In this paper, we propose and design a novel dual-band PPA with a gathering of four metal-shell nanorods using a cross-hair operating at visible and near-infrared regions. Two absorptance peaks at 1050 nm and 750 nm with maximal absorptance of 99.59% and 99.89% for modes 1 and 2, respectively, are detected. High sensitivity of 1200 nm refractive unit (1/RIU), figure of merit of 26.67 and Q factor of 23.33 are acquired, which are very remarkable compared with the other PPAs. In addition, the absorptance in mode 1 is about nine times compared to its counterpart without the cross-hair. The proposed structure gives a novel inspiration for the design of a tunable dual-band PPA, which can be exploited for plasmonic sensor and other nanophotonic devices.

Reusable TiN Substrate for Surface Plasmon Resonance Heterodyne Phase Interrogation Sensor.

A TiN-based substrate with high reusability presented high-sensitivity refractive index measurements in a home-built surface plasmon resonance (SPR) heterodyne phase interrogation system. TiN layers with and without additional inclined-deposited TiN (i-TiN) layers on glass substrates reached high bulk charge carrier densities of 1.28 × 1022 and 1.91 × 1022 cm-3, respectively. The additional 1.4 nm i-TiN layer of the nanorod array presented a detection limit of 6.1 × 10-7 RIU and was higher than that of the 46 nm TiN layer at 1.2 × 10-6 RIU when measuring the refractive index of a glucose solution. Furthermore, the long-term durability of the TiN-based substrate demonstrated by multiple processing experiments presented a high potential for various practical sensing applications.

Highly Sensitive and Tunable Plasmonic Sensor Based on a Nanoring Resonator with Silver Nanorods.

We numerically and theoretically investigate a highly sensitive and tunable plasmonic refractive index sensor that is composed of a metal-insulator-metal waveguide with a side-coupled nanoring, containing silver nanorods using the finite element method. Results reveal that the presence of silver nanorods in the nanoring has a significant impact on sensitivity and tunability performance. It gives a flexible way to tune the system response in the proposed structure. Our designed sensor has a sensitivity of 2080 nm/RIU (RIU is the refractive index unit) along with a figure of merit and a quality factor of 29.92 and 29.67, respectively. The adequate refractive index sensitivity can increase by adding the silver nanorods in a nanoring, which can induce new surface plasmon polaritons (SPPs) modes that cannot be found by a regular nanoring. For a practical application, a valid introduction of silver nanorods in the nanoring can dramatically reduce the dimension of the proposed structure without sacrificing performance.