Ultrahigh Figure Research Articles

Quasi-analytical solutions of hybrid platform and the optimization of highly sensitive thin-film sensors for terahertz radiation

We present quasi-analytical solutions (QANS) of hybrid platform (HP) comprising metallic grating (MG) and stacked-dielectric layers for terahertz (THz) radiation. The QANS are validated by finite difference time domain simulation. It is found that the Wood anomalies induce the high-order spoof surface plasmon resonances in the HP. The QANS are applied to optimize new perfect absorber for THz sensing of large-area thin film with ultrahigh figure of merit reaching fifth order of magnitude for the film thickness 0.0001p (p: MG period). The first-order Wood's anomaly of the insulator layer and the Fabry-Perot in the slit's cavity account for the resonance of the perfect absorber. The QANS and the new perfect absorber may lead to highly sensitive and practical nano-film refractive index sensor for THz radiation.

Theoretical analysis of ultrahigh figure of merit sensing in plasmonic waveguides with a multimode stub.

We propose an expanded coupled mode theory to analyze sensing performance in a plasmonic slot waveguide side-coupled with a multimode stub resonator. It is confirmed by the finite-difference time-domain simulations. Through adjusting the parameters, we can realize figure of merit (FOM) of ∼59,010, and the sensitivity S can reach to 75.7. Compared with the plasmonic waveguide systems in recent Letters, our proposed structure has the advantages of easy fabrication, compactness, sensitivity, and high FOM. The proposed theory model and findings provide guidance for fundamental research of the integrated plasmonic nanosensor applications.

Infrared Perfect Ultra-narrow Band Absorber as Plasmonic Sensor.

We propose and numerically investigate a novel perfect ultra-narrow band absorber based on a metal-dielectric-metal-dielectric-metal periodic structure working at near-infrared region, which consists of a dielectric layer sandwiched by a metallic nanobar array and a thin gold film over a dielectric layer supported by a metallic film. The absorption efficiency and ultra-narrow band of the absorber are about 98 % and 0.5 nm, respectively. The high absorption is contributed to localized surface plasmon resonance, which can be influenced by the structure parameters and the refractive index of dielectric layer. Importantly, the ultra-narrow band absorber shows an excellent sensing performance with a high sensitivity of 2400 nm/RIU and an ultra-high figure of merit of 4800. The FOM of refractive index sensor is significantly improved, compared with any previously reported plasmonic sensor. The influences of structure parameters on the sensing performance are also investigated, which will have a great guiding role to design high-performance refractive index sensors. The designed structure has huge potential in sensing application.

Tunable double transparency windows induced by single subradiant element in coupled graphene plasmonic nanostructure

We present the coupling-induced transparency (CIT) effect by employing the localized surface plasmon mode supported by a periodic array of graphene nanoribbons destructively interfering with the quasiguided mode supported by a single-layer graphene sheet. It is found that the resonance strength and linewidth are strongly dependent on the coupling distance. It is also shown that the degeneracy between the symmetric and antisymmetric quasiguided modes is lifted owing to the oblique incidence, resulting in the double CIT effect with an ultrahigh figure of merit (FOM) (as high as 271), which may provide potential applications in dynamic optical switching and biochemical sensing.

Ultrasensitive THz – Plasmonics gaseous sensor using doped graphene

We propose a surface plasmon resonance (SPR) based gas sensor in terahertz frequency with Otto configuration based on attenuated total reflection (ATR) technique using free standing doped graphene monolayer. Angular interrogation method has been used to study the performance of the sensor in terms of sensitivity and detection accuracy. Different chemical potential of graphene monolayer has been investigated to study its effect on these performance parameters. The results show that the optimization of the gap distance between the prism base and the graphene monolayer has significant effect on the reflectivity of SPR sensing. This SPR based gas sensor shows ultrahigh sensitivity of 34.11deg/RIU along with an ultrahigh Figure of Merit (FOM) of more than 1150RIU−1.

Foldable Electrochromics Enabled by Nanopaper Transfer Method

An innovative nanopaper‐transfer method enabled by the high surface free energy of nanocellulose is reported. Utilizing this technique, Ag nanowire percolating network based transparent conductive electrodes with ultrahigh figure of merit are realized. With the exceptional surface properties of this novel nanopaper electrode, a foldable electrochromic nanopaper device with a stable performance is demonstrated for the first time. This nanopaper‐transfer technique holds great promise for the next generation deformable electronics.

An ultrahigh-contrast and broadband on-chip refractive index sensor based on a surface-plasmon-polariton interferometer.

Using a double-slit structure fabricated on a gold film or a subwavelength (300 nm) plasmonic waveguide, high-contrast and broadband plasmonic sensors based on the interference of surface plasmon polaritons (SPPs) are experimentally demonstrated on chips. By adjusting the focused spot position of the p-polarized incident light on the double-slit structure to compensate for the propagation loss of the SPPs, the interfering SPPs from the two slits have nearly equal intensities. As a result, nearly completely destructive interference can be experimentally achieved in a broad bandwidth (>200 nm), revealing the robust design and fabrication of the double-slit structure. More importantly, a high sensing figure of merit (FOM*) of >1 × 10(4) RIU(-1) (refractive index unit), which is much greater than the previous experimental results, is obtained at the destructive wavelength because of a high contrast ratio (C = 0.96). The high-contrast and broadband on-chip sensor fabricated on the subwavelength plasmonic waveguide may find important applications in the real-time sensing of particles and molecules.

Sharp Fano Resonance within Bi-periodic Silver Particle Array and Its Application as Plasmonic Sensor with Ultra-high Figure of Merit

In this research paper, a new type of Fano resonance originating from the far-field interference of lattice collective resonances of two sets of interlacing silver particle arrays with different radii is investigated numerically. The anti-phased collective resonance of the two arrays acts as “dark state”, while the phased one serves as “bright state”. The structure has the advantage to achieve both high modulation depth and sharp linewidth simultaneously, which is very attractive for plasmonic sensor, and the sensitivity and figure of merit can reach as high as 633 nm/RIU and 2000, respectively. Also, the structure has the merit of high Q factor up to 320.

Coupled-Resonator-Induced Fano Resonances for Plasmonic Sensing with Ultra-High Figure of Merits

Fano resonances are numerically predicted in an ultracompact plasmonic structure, comprising a metal-isolator-metal (MIM) waveguide side-coupled with two identical stub resonators. This phenomenon can be well explained by the analytic model and the relative phase analysis based on the scattering matrix theory. In sensing applications, the sensitivity of the proposed structure is about 1.1 × 103 nm/RIU and its figure of merit is as high as 2 × 105 at λ = 980 nm, which is due to the sharp asymmetric Fano line-shape with an ultra-low transmittance at this wavelength. This plasmonic structure with such high figure of merits and footprints of only about 0.2 μm2 may find important applications in the on-chip nano-sensors.

Design of dispersion-compensating Bragg fiber with an ultrahigh figure of merit

We report a novel idea for achieving highly efficient dispersion-compensating Bragg fiber by exploiting a modified quarter-wave stack condition. Our Bragg fiber yielded an average dispersion of approximately -1800 ps/(nm km) across the C band for the fundamental TE mode and an ultrahigh figure of merit of approximately 180,000 ps/(nm dB), which is at least 2 orders of magnitude higher than that of conventional dispersion-compensating fibers. The proposed methodology could be adopted for the design of a dispersion compensator across any desired wavelength range.