Perfect narrow band absorber for sensing applications

Ultra-broadband near-perfect metamaterial absorber for photovoltaic applications

An ingenious double-grating metamaterial-based ultrathin-broadband absorber consisting of AlGaAs-Ge-GaAs on a titanium film operating in the visible to infrared wavelength was designed in this work. This structure is capable of overcoming the Shockley-Queisser (SQ) limit and the tunneling junction effect of tandem solar cells. Our comprehensive study revealed the structure's absorption mechanism using the finite-difference time-domain (FDTD) technique, which exhibited excellent short-circuit current density and high absorption. Our proposed ultrathin structure of 410 nm thickness provided a high average absorption of 82.2% and 99.7% under unpolarized and TM-polarized light for a wavelength range of 450-2000 nm, respectively. Additionally, we observed high incidence angle tolerability under the plane wave and thermal stability over time for our proposed grating structure. The performance analysis of our proposed structure as an absorber layer of a solar cell revealed its high power conversion efficiency (PCE) of 31.7% with an excellent short-circuit current density of 47.1 mA cm-2 for AM 1.5 G solar irradiance. The double-grating metamaterial absorber structure has enormous potential for diverse applications such as solar harvesting, thermoelectric generation, and photodetection.

High-performance narrowband thermal emitter based on aperiodic Tamm plasmon structures assisted by inverse design

Controlling the bandwidth and directionality of thermal emission is important for a broad range of applications, from imaging and sensing to energy harvesting. Here, we propose a new, to the best of our knowledge, type of long-wavelength infrared narrowband thermal emitter that is basically composed of aperiodic Tamm plasmon polariton structures. Compared to the thermal emitter based on periodic structures, more parameters need to be considered. An inverse design algorithm instead of traditional forward methodologies is employed to do the geometric parameter optimization. Both theoretical and experimental results show that the thermal emitter exhibits a narrowband thermal emission peak at the wavelength of 8.6 µm in the normal direction. The angular response of emission properties of the thermal emitter is dependent on the emission angle. We believe that our proposed thermal emitter provides an alternative for low-cost, high-effective narrowband mid-infrared light sources and would have a great potential in many applications.

A Tunable Terahertz Absorber Based on Double-Layer Patterned Graphene Metamaterials

Graphene is widely used in tunable photonic devices due to its numerous exotic and exceptional properties that are not found in conventional materials, such as high electron mobility, ultra-thin width, ease of integration and good tunability. In this paper, we propose a terahertz metamaterial absorber that is based on patterned graphene, which consists of stacked graphene disk layers, open ring graphene pattern layers and metal bottom layers, all separated by insulating dielectric layers. Simulation results showed that the designed absorber achieved almost perfect broadband absorption at 0.53-1.50 THz and exhibited polarization-insensitive and angle-insensitive characteristics. In addition, the absorption characteristics of the absorber can be adjusted by changing the Fermi energy of graphene and the geometrical parameters of the structure. The above results indicate that the designed absorber can be applied to photodetectors, photosensors and optoelectronic devices.

Near-perfect wide-band absorbers based on one-dimensional photonic crystal structures in 1-20 THz frequencies

This paper investigates the absorption behavior of one-dimensional (1D) photonic crystal (PhC) structures in the 1-20 THz region. The structures are analyzed by the transfer matrix method to achieve accurate results quickly with ordinary simulation facilities. The simulation results indicate a strong dependence of the absorber performance on the thickness and material of the PhC layers, as well as the frequency and angle of incident light. The combination of silica and titanium (Ti) materials as dielectric and metal layers presents a great choice for broadband high-absorption applications so that this structure can absorb, on average, more than 80% of the normal incident radiation in the studied frequency range. Additionally, this absorber has the lowest dependence on incident light with the angle varying from 0° to 80° compared to identical absorbers with silver, aluminum, gold, chromium, nickel, and tungsten metals. The excellent absorption feature of the Ti-based absorber compared to the other absorbers is attributed to the lower permittivity of Ti (in both real and imaginary parts) in comparison with the other metals. In addition to owning simple and fabrication-friendly structures, 1D PhCs can pave the way to achieve various absorption spectra proportional to the needs of photonics, communications, and aerospace applications.

Silicon-based asymmetric dimer-resonator grating for narrowband perfect absorption and sensing

In this work, a method for designing an ultra-narrowband absorber platform is presented with asymmetric silicon-based dimer-resonators grating. Within the infrared range of 3000 ∼ 4000 nm, two narrowband absorption peaks with absorptivity greater than 99% are produced by the absorber. Moreover, during the optical sensing, such an absorber platform shows high-performance sensitivity factors for the absorption wavelengths at λ₁ = 3468 nm (S = 3193 nm/RIU, FOM = 532) and at λ₂= 3562 nm (S = 3120 nm/RIU, FOM = 390). Strong scattering coupling and the magnetic resonances supported in this silicon based grating produce the high absorption. Otherwise, additional methods such as the polarization and incident angles are used to further tune the absorption responses in the intensity and wavelengths, indicating the feasibility for artificial manipulations. The achieved ultra-sharp perfect absorption and the related sensitive response hold the silicon based resonant scheme with wide applications in bio-sensing, spectral filtering and other fields.

Recent Development in Metasurfaces: A Focus on Sensing Applications

One of the fastest-expanding study areas in optics over the past decade has been metasurfaces (MSs). These subwavelength meta-atom-based ultrathin arrays have been developed for a broad range of functions, including lenses, polarization control, holography, coloring, spectroscopy, sensors, and many more. They allow exact control of the many properties of electromagnetic waves. The performance of MSs has dramatically improved because of recent developments in nanofabrication methods, and this concept has developed to the point that it may be used in commercial applications. In this review, a vital topic of sensing has been considered and an up-to-date study has been carried out. Three different kinds of MS absorber sensor formations, all-dielectric, all-metallic, and hybrid configurations, are presented for biochemical sensing applications. We believe that this review paper will provide current knowledge on state-of-the-art sensing devices based on MSs.

Dual-band wide-angle perfect absorber based on the relative displacement of graphene nanoribbons in the mid-infrared range

In this paper, a novel graphene-based dual-band perfect electromagnetic absorber operating in the mid-infrared regime has been proposed. The absorber has a periodic structure which its unit cell consists of a sliver substrate and two graphene nanoribbons (GNRs) of equal width separated with a dielectric spacer. Two distinct absorption peaks at 10 and 11.33 µm with absorption of 99.68% and 99.31%, respectively have been achieved due to a lateral displacement of the GNRs. Since graphene surface conductivity is tunable, the absorption performance can be tuned independently for each resonance by adjusting the chemical potential of GNRs. Also, it has been proved that performance of the proposed absorber is independent of the incident angle and its operation is satisfactory when the incident angle varies from normal to ±75°. To simulate and analyze the spectral behavior of the designed absorber, the semi-analytical method of lines (MoL) has been extended. Also, the finite element method (FEM) has been applied in order to validate and confirm the results.

Polarization-dependent wideband metamaterial absorber for ultraviolet to near-infrared spectral range applications

The need for wideband metamaterial absorbers (WBMA) for applications other than sensing and filtering has demanded modifications to the conventional three-layer metal-insulator-metal (MIM) absorber configuration. This modification often results in complex geometries and an increased number of layers requiring complex lithographic processes for fabrication. Here, we show that a metamaterial absorber with rectangular geometry in the simple MIM configuration can provide wideband absorption covering the ultraviolet and near-infrared spectral range. Due to its asymmetric nature, the WBMA is sensitive to the polarization of the incident light and independent of the angle of incidence up to about 45° depending on the polarization of the incident light. The characteristics of the WBMA presented here may be useful for applications such as detectors for wide spectral band applications.

Designing thermal radiation metamaterials via a hybrid adversarial autoencoder and Bayesian optimization

Designing thermal radiation metamaterials is challenging especially for problems with high degrees of freedom and complex objectives. In this Letter, we develop a hybrid materials informatics approach which combines the adversarial autoencoder and Bayesian optimization to design narrowband thermal emitters at different target wavelengths. With only several hundreds of training data sets, new structures with optimal properties can be quickly determined in a compressed two-dimensional latent space. This enables the optimal design by calculating far less than 0.001% of the total candidate structures, which greatly decreases the design period and cost. The proposed design framework can be easily extended to other thermal radiation metamaterials design with higher dimensional features.

Impedance matching via ultrathin metatronic layer assisted by Smith Chart

Metatronics, as a feasible paradigm of nanocircuits using effective electronic elements (e.g., nanocapacitors, nanoinductors, and nanoresistors), provides the possibility for light manipulation in subwavelength scales assisted by the circuit-related technologies in electronics. As a representative technique in electronics, Smith Chart provides a fast, less-computation and graphical approach to solve the problems related to impedance matching. Here, we transplant the Smith Chart into the paradigm of optical metatronics to develop an analytical approach for impedance matching for light propagation and coined the name of graphical metatronics. In this approach, the impedance characteristics of four basic types of ultrathin metatronic layers are creatively mapped into each rotation trace on the complex Γ mathematical plane (Γ means the reflection coefficient). The impedance matching problems can be graphically solved by searching for feasible rotation traces on the Γ plane without full-wave simulations. Based on this approach, various applications related to impedance matching (e.g., antireflection coating, perfect transmission, absorber, etc.) are developed analytically and validated by numerical results. The proposed approach constructs the bridge among Smith Chart, plasmonics and photonics, providing a fast, visualized and less-computation route and guideline to develop various nanophotonic structures and devices for impedance-matching applications.

Multifunctional analysis and verification of lightning-type electromagnetic metasurfaces

Aiming at the problems that most of the existing electromagnetic metasurfaces have single function and narrow application scope, a highly integrated lightning-type metasurface is proposed in this study. It can realize the functions of circular dichroism (CD), absorption of electromagnetic waves, broadband x-to-y cross polarization conversion (CPC) function, linear-to-circular polarization conversion (LTC-PC) function and asymmetric transmission (AT), and its functions are also analyzed and verified. The designed metasurface consists of the bottom grating structure, the lower SiO₂, the middle lightning-type graphene, the upper SiO₂, the top graphene and photosensitive silicon. Through numerical calculations, the CD of design can reach more than 85% at 4.22 THz. The function of bimodal absorption is achieved at 4.09 and 8.69 THz. At 7.41∼8.21 THz, the polarization conversion ratio (PCR) of the metasurface reaches more than 99%. Simultaneously, the function of LTC-PC can be formed when PCR is 50%. Finally, when the designed metasurface is in the transmissive state, the AT of design is close to 60% at 7.84 THz. This design provides a new design idea and method for biomedical detection, image processing, modulators, smart switches, optical diodes and other fields.

Absorption and scattering in perfect thermal radiation absorber-emitter metasurfaces

Detailed spectral analysis of radiation absorption and scattering behaviors of metasurfaces was carried out via finite-difference time-domain (FDTD) photonic simulations. It revealed that, for typical metal-insulator-metal (MIM) nanodisc metasurfaces, absorbance and scattering cross-sections exhibit a ratio of σ_abs/σ_sca = 1 at the absorption peak spectral position. This relationship was likewise found to limit the attainable photo-thermal conversion efficiency in experimental and application contexts. By increasing the absorption due to optical materials, such as Cr metal nano-films typically used as an adhesion layer, it is possible to control the total absorption efficiency η = σ_abs/σ_sca and to make it the dominant extinction mechanism. This guided the design of MIM metasurfaces tailored for near-perfect-absorption and emission of thermal radiation. We present the fabrication as well as the numerical and experimental spectral characterisation of such optical surfaces.

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.

Theoretical and Numerical Analysis of Active Switching for Narrow-Band Thermal Emission with Graphene Ribbon Metasurface

Components smaller than the wavelength of electromagnetic waves are called meta-atoms. Thermal emission can be controlled by an artificial structure in which these meta-atoms are arranged on the surface. This artificial structure is called a metasurface, and its optical properties are determined by the materials and shapes of the meta-atoms. However, optical devices may require active control of thermal emission. In the present study, we theoretically and numerically analyze a wavelength-selective emitter using a graphene ribbon metasurface. The graphene ribbon metasurface consists of a graphene ribbon array, potassium bromide thin film, and silver substrate. The geometric parameters of the graphene metasurface are determined based on an equivalent circuit model that agrees well with the results of the electromagnetic field analysis (rigorous coupled-wave analysis). The proposed emitter causes impedance matching depending on the conductivity of the graphene ribbon in a very narrow wavelength range. The conductivity of graphene can be actively controlled by the gate voltage. Therefore, the proposed emitters may realize near-perfect emission with a high quality factor and active controllable switching for various wavelengths. In addition, the quality factor can be changed by adjusting the electron mobility of graphene. The proposed emitter can be used for optical devices such as thermophotovoltaic systems and biosensing.

Ultrabroadband and ultrathin absorber based on an encapsulated T-shaped metasurface

Ultrabroadband absorbers are vital for applications such as solar energy harvesting and integrated optoelectronic devices. Herein, we design, fabricate and characterize a novel ultrabroadband and ultrathin absorber based on the encapsulated T-shaped metasurface (ETM). The ETM consists of a 20 nm Cr film and a Cr substrate sandwiched by the T-shaped polymethyl methacrylate (PMMA) arrays. The Cr film provides a robust absorptive surface with improved impedance matching, and ultrabroadband absorption can be achieved via the excitation of the localized surface plasmon (LSP) of this ultrathin film. The average absorption of simulated and experimental results of the ETM in the visible range of 400-800 nm for the TM (TE) polarization are 96.4% (96.3%) and 90.6% (89.4%), respectively. Three-dimensional (3D) power dissipation density distributions of the proposed structure have been investigated, which indicates that the synergistic absorption effect of different parts of the T-shaped ultrathin Cr film contributes to the major absorption enhancement. The absorption of the ETM is very robust to the changes of geometrical parameters and the symmetry of the structure, and it can be maintained almost the same even if T-shaped profiles are changed to L-shaped profiles. Moreover, the absorption performance of the ETM exhibits polarization-insensitive and wide-angle features, which has advantages for many potential applications.

Visible to near-infrared nearly perfect absorption from alternate silica and chromium layers deposited by magnetron sputtering

We present a novel, to the best of our knowledge, broadband and angle-insensitive nearly perfect absorber design composed of alternate silica and chromium layers. We show that by depositing a chromium nanofilm on a chromium substrate with a silica spacer, the absorption will significantly enhance from the visible to near-infrared. Then, another silica film is placed on the top of the layered structure as an antireflection coating, resulting in the broadband near-perfect absorption. We fabricate the proposed absorber by magnetron sputtering. The measured results show that our device has an average absorption over 97% in a wide range of wavelengths ranging from 350 to 1170 nm, and its absorption performance exhibits a good angular tolerance up to 50°. The presented absorber design offers a good prospect for large-scale and low-cost manufacturing of absorption-based optoelectronic devices.

Numerical Investigation of Graphene and STO Based Tunable Terahertz Absorber with Switchable Bifunctionality of Broadband and Narrowband Absorption

A graphene metamaterial and strontium titanate (STO)-based terahertz absorber with tunable and switchable bifunctionality has been numerically investigated in this work. Through electrically tuning the Fermi energy level of the cross-shaped graphene, the bandwidth of the proposed absorber varies continuously from 0.12 THz to 0.38 THz with the absorptance exceeding 90%, which indicates the functionality of broadband absorption. When the Fermi energy level of the cross-shaped graphene is 0 eV, the proposed absorber exhibits the other functionality of narrowband absorption owing to the thermal control of the relative permittivity of STO, and the rate of change of the center frequency is 50% ranging from 0.56 THz to 0.84 THz. The peak intensity of the narrowband absorption approximates to nearly 100% through adjusting the Fermi energy level of the graphene strips. The calculated results indicate that it is not sensitive to the polarization for wide incidence angles. The proposed absorber can realize tunable bifunctionality of broadband absorption with a tunable bandwidth and narrowband absorption with a tunable center frequency, which provides an alternative design opinion of the tunable terahertz devices with high performance for high-density integrated systems.

All-dielectric perfect absorber based on quadrupole modes

In principle, the absorbance of a free-standing ultra-thin film is limited to 50%. To overcome this limitation, an all-dielectric perfect absorber is proposed herein based on the concept of degenerate critical coupling (DCC) of quadrupole modes. We study the absorbance of a dielectric elliptic cylinder and find that perfect absorption can be achieved by spectrally overlapping peaks of electric and magnetic quadrupole modes. This suggests that the DCC method can be extended to the quadrupole modes beyond dipole modes. Such an all-dielectric perfect absorber can be used in photodetectors, optical filters, and optical modulators mediated by the photothermal effect.

Ultranarrow and Wavelength-Scalable Thermal Emitters Driven by High-Order Antiferromagnetic Resonances in Dielectric Nanogratings

Engineering wavelength-selective thermal emission is a promising technology associated with several advanced applications, including thermal imaging, gas sensing, far/near-field thermophotovoltaics, and so on. However, the majority of reported approaches suffer from low Q-factor emission due to intrinsic loss of metallic components or rely on thick structures like multilayers to ensure unitary emissivity, making it challenging to design compatible high-Q narrowband emitters. In this work, we propose a mechanism to tailor thermal emission by taking advantage of optically induced high-order antiferromagnetic (AFM) resonances in a simple subwavelength 2D Si nanobar. Such AFM modes, stemmed from hybrid magnetic dipoles and high-order Fabry-Perot modes, exhibit both pronounced resonant responses and superior light confinement ability. We first reveal its essential roles in ultranarrowband emission control with a sharp (Q ∼ 400) and near-perfect emissivity available. Especially, the measured angle-resolved emission spectra further indicate that the AFM-induced emission peak, being nearly immune to changes of nanogratings' periods and incident angle, is able to be flexibly engineered in a wide waveband by merely tuning the width-to-height ratio of nanobars. Our work provides a promising strategy to design extremely high-Q thermal emitters possessing robust narrowband performance, large spectral tunability and desirable compatibility with advanced planar nanofabrication techniques, which will be more favorable in practice compared with metallic counterparts. Besides, we anticipate that, the revealed mechanism of high-order AFM modes can also stimulate advanced applications in diverse research communities including but not limited to multipolar physics, nonlinear nano-optics, energy harvesting, etc.

Ultra-narrowband near-infrared tunable two-dimensional perfect absorber for refractive index sensing

An ultra-narrow-bandwidth near-infrared perfect plasmonic absorber with a periodic structure composed of metal-insulator-metal configuration is numerically designed and analyzed for a refractive index sensor. A perfect absorptivity of 99.99% and a rather narrow bandwidth of 2 nm are observed in the near-infrared wave band when the light is vertically incident in the structure. The ultra-high absorption and ultra-narrow bandwidth are explained as local surface plasmon resonance stimulated in the structure. The absorber is put into use as a plasmonic refractive index sensor with wavelength sensitivity as high as 1500 nm/RIU and figure of merit as high as 750, which significantly surpass those of many plasmonic sensors proposed in the past few decades. The designed absorber is tunable by changing geometry parameters. Because of the excellent sensing properties mentioned above, the proposed structure can be widely applied in fields such as photodetectors, biosensors, and chemical molecule detection.

Nano-slit assisted high-Q photonic resonant perfect absorbers

We propose and demonstrate a new kind of resonant absorber via introducing the nano-slit into a photonic film. The combination of the nano-slit cavity and the photonic waveguide provides a powerful way to manipulate the light behaviors including the spectral Q factors and the absorption efficiency. Ultra-sharp resonant absorption with the Q factors up to 579.5 is achieved, suggesting an enhancement of ∼6100% in contrast to that of the metal-dielectric flat film structure. Moreover, in comparison with the low absorption of 5.4% for the system without nano-slit, the spectral absorption is up to ∼96.6% for the nano-slit assisted photonic absorber. The high Q resonant absorption can be further manipulated via the structural parameters and the polarization state. The operation wavelengths can be tuned by the lattice constant. As the nano-slit introduced into the dielectric film, strong optical field confinement effects can be achieved by the cavity resonance via the nano-slit itself, and the guided resonant effect in the photonic waveguide cavity formed by the adjacent nano-slits. Otherwise, the photonic-plasmonic hybridization effect is simultaneously excited between the dielectric guided cavity layer and the metal substrate. These findings can be extended to other photonic nano-cavity systems and pave new insights into the high Q nano-optics devices.

Bidirectional band-switchable nano-film absorber from narrowband to broadband

We propose a switchable perfect absorber with broadband and narrowband absorption based on alternating dielectric and metal nano-film structures in this paper. The lithography-free pattern is equipped with polarization insensitivity, good ductility and manufacturability, which has great significance in practical device development and applications. The quasi-complete selective absorption of incident light can be originated from asymmetric Fabry-Perot resonance, which combines the destructive interference in dielectric layers with inherent absorption in metal layers. When the light incidents on the surface covered with ultra-thin metal film of this structure, it acts as a narrowband absorber with over 99.90% absorption at 771 nm wavelength and a full wave at half maximum of 20 nm. When the light incidents on other surfaces covered with anti-reflective dielectric film, it achieves broadband perfect absorption with an average absorption exceeding 96.02% in a 500-1450 nm wavelength range. The absorption spectrum of oblique incidence shows that the broadband absorption behaves big angle range tolerance while the narrowband absorption exhibits angular dependence. The band-switchable performance of this absorber makes it valuable for energy harvesting/re-radiation applications in solar thermal photovoltaic systems.

Broadening Bandwidths of Few-Layer Absorbers by Superimposing Two High-Loss Resonators

Efficient broadband absorption of solar radiation is desired for sea water desalination, icephobicity and other renewable energy applications. We propose an idea of superimposing two high-loss resonances to broaden bandwidths of a few-layer absorber, which is made of dielectric/ metal/dielectric/ metal layers. Both the simulation and experiment show that the structure has an averaged absorption efficiency higher than 97% at wavelengths ranging from 350 to 1200 nm. The bandwidth of the absorption larger than 90% is up to 1000 nm (410-1410 nm), which is greater than that (≤ 750 nm) of previous MIM planar absorbers. Especially, the average absorption from 350 to 1000 nm is kept above 90% at an incidence angle as high as 65°, meanwhile still maintained above 80% even at an incident angle of 75°. The performance of angular insensitivity is much better than that of previous few-layer solar absorbers. The flexible 1D nonoble metasurface absorbers are fabricated in a single evaporation step. Under the illumination of a halogen lamp of P = 1.2 kW/m², the flexible metasurface increases its surface temperature by 25.1 K from room temperature. Further experiments demonstrate that the heat localization rapidly melts the accumulated ice. Our illumination intensity (P = 1.2 kW/m²) is only half of that (P = 2.4 kW/m²) in previous solar anti-ice studies based on gold/TiO₂ particle metasurfaces, indicating that our metasurface is more advantageous topractical applications. Our results illustrate an effective pathway toward the broadband metasurface absorbers with the attractive properties of mechanical flexibility, low cost of the no-noble metals, and large-area fabrications, which have promising prospects in the applications of solar heat utilization.

Perfect Absorption and Refractive-Index Sensing by Metasurfaces Composed of Cross-Shaped Hole Arrays in Metal Substrate

Achieving perfect electromagnetic wave absorption with a sub-nanometer bandwidth is challenging, which, however, is desired for high-performance refractive-index sensing. In this work, we theoretically study metasurfaces for sensing applications based on an ultra-narrow band perfect absorption in the infrared region, whose full width at half maximum (FWHM) is only 1.74 nm. The studied metasurfaces are composed of a periodic array of cross-shaped holes in a silver substrate. The ultra-narrow band perfect absorption is related to a hybrid mode, whose physical mechanism is revealed by using a coupling model of two oscillators. The hybrid mode results from the strong coupling between the magnetic resonances in individual cross-shaped holes and the surface plasmon polaritons on the top surface of the silver substrate. Two conventional parameters, sensitivity (S) and figure of merit (FOM), are used to estimate the sensing performance, which are 1317 nm/RIU and 756, respectively. Such high-performance parameters suggest great potential for the application of label-free biosensing.

Deposited ultra-thin titanium nitride nanorod array as a plasmonic near-perfect light absorber

The transmittance, reflectance, and extinctance that correspond to the localized plasmonic resonance within TiN nanorods were investigated. The obliquely deposited TiN nanorod array shows polarization-independent admittance matching to air. Unlike noble metal nanorods, the near-field localized longitudinal and transverse plasmonic resonance of TiN nanorod arrays present polarization-dependent light extinction in the far field. The longitudinal plasmonic mode presents stronger extinction than transverse plasmonic mode. In order to have high efficient light absorption, an ultra-thin two-layered TiN nanorod array was fabricated with orthogonal deposition planes for upper layer and bottom layer to absorb different polarized light energy. The measured spectrum shows broadband and wide-angle light extinction.

Ultrahigh-figure-of-merit refractive index sensor based on the Rayleigh anomaly resonance

We investigate an all-metal and simple-fabrication grating with an ultranarrow band absorption spectrum in the telecom window range. The influences of structure parameters on the absorption characteristics are investigated. For the best design, the absorption efficiency reaches 94% under normal incidence, with the full width at half-maximum of only 0.17 nm. We demonstrate that this ultranarrow band absorption is the result of the dominant excitation of the Rayleigh anomaly mode. The corresponding figure of merit is calculated to be 8530RIU^-1. The applied procedure has the potential to also be used in designing high-performance reflection-based sensors in other wavelength ranges.

Metal-free plasmonic refractory core-shell nanowires for tunable all-dielectric broadband perfect absorbers

In this work, we numerically demonstrate a new facile strategy for all-dielectric broadband optical perfect absorbers. A monolayer refractory titanium oxide and nitride (TiN/TiO₂) core-shell nanowires array is used to form the grating on the opaque TiN substrate. Multiple resonant absorption bands are observed in the adjacent wavelength range, which therefore leads to the formation of an ultra-broadband absorption window from the visible to the infrared regime. The maximal absorption reaches 95.6% and the average absorption efficiency in the whole range (0.5-1.8 µm) is up to 85.4%. Moreover, the absorption bandwidth can be feasibly adjusted while the absorption efficiency can be still maintained in a high level via tuning the polarization state. Furthermore, the absorption window is observed to be highly adjustable in the wavelength range, showing a nearly linear relationship to the shell's index. These features not only confirm the achievement of the broadband perfect absorption but also introduce feasible ways to artificially manipulate the absorption properties, which will hold wide applications in metal-free plasmonic optoelectronic devices such as the solar harvesting, photo-detection, and thermal generation and its related bio-medical techniques.

A Narrow-Band Multi-Resonant Metamaterial in Near-IR

We theoretically investigate a multi-resonant plasmonic metamaterial perfect absorber operating between 600 and 950 nm wavelengths. The presented device generates 100% absorption at two resonance wavelengths and delivers an ultra-narrow band (sub-20 nm) and high quality factor (Q=44) resonance. The studied perfect absorber is a metal–insulator–metal configuration where a thin MgF2 spacer is sandwiched between an optically thick gold layer and uniformly patterned gold circular nanodisc antennas. The localized and propagating nature of the plasmonic resonances are characterized and confirmed theoretically. The origin of the perfect absorption is investigated using the impedance matching and critical coupling phenomenon. We calculate the effective impedance of the perfect absorber and confirm the matching with the free space impedance. We also investigate the scattering properties of the top antenna layer and confirm the minimized reflection at resonance wavelengths by calculating the absorption and scattering cross sections. The excitation of plasmonic resonances boost the near-field intensity by three orders of magnitude which enhances the interaction between the metamaterial surface and the incident energy. The refractive index sensitivity of the perfect absorber could go as high as S=500 nm/RIU. The presented optical characteristics make the proposed narrow-band multi-resonant perfect absorber a favorable platform for biosensing and contrast agent based bioimaging.

Numerical analysis of an ultra-wideband metamaterial absorber with high absorptivity from visible light to near-infrared

In this study, we designed a novel ultra-wideband (UWB) absorber and numerically analyzed it to demonstrate that its light absorptivity was greater than 90% in the wavelength range of visible light and near-infrared (405-1505 nm). The structure of proposed novel UWB absorber consisted of four layers of films, including silica, titanium, magnesium fluoride, and aluminium, and the upper silica and titanium layers had rectangular cubes in them. For that, the excitations of propagating surface plasmon resonance (PSPR), local surface plasmon resonance (LSPR), and the resonance of Fabry-Perot (FP) cavity were generated at the same time and combined to reach the effect of perfect absorption and ultra-wideband. The proposed absorber had an average absorptivity of 95.14% in the wavelength range of 405 ∼ 1505 nm when the light was under normal incidence. In addition, the UWB absorber was large incident angle insensitive and polarization-independent. The absorber proposed in the paper had great prospects in the fields of thermal electronic equipment, solar power generation, and perfect cloaking.

Photonic Metamaterial Absorbers: Morphology Engineering and Interdisciplinary Applications

Recent advances in nanofabrication technologies have spurred many breakthroughs in the field of photonic metamaterials that provide efficient ways of manipulating light-matter interaction at subwavelength scales. As one of the most important applications, photonic metamaterials can be used to implement novel optical absorbers. First the morphology engineering of various photonic metamaterial absorbers is discussed, which is highly associated with impendence matching conditions and resonance modes of the absorbers, thus directly determines their absorption efficiency, operational bandwidth, incident angle, and polarization dependence. Then, the recent achievements of various interdisciplinary applications based on photonic metamaterial absorbers, including structural color generation, ultrasensitive optical sensing, solar steam generation, and highly responsive photodetection, are reviewed. This report is expected to provide an overview and vision for the future development of photonic metamaterial absorbers and their applications in novel nanophotonic systems.

Triple-Band Perfect Light Absorber Based on Hybrid Metasurface for Sensing Application

A simple design of triple-band perfect light absorber (PLA) based on hybrid metasurface in visible region has been presented in this work, which turns out to be applicable for refractive index (RI) sensing. Distinct from previous designs, the proposed hybrid metasurface for visible PLA is only consisted of periodic silicon cross nanostructure arrays and gold substrate. The periodic silicon cross arrays deposited on the gold substrate contribute to excite the guided modes under the normal incident light illumination. According to the simulation results, it can be found that three perfect absorption peaks of 98.1%, 98.7%, and 99.6% which are located at 402.5 THz, 429.5 THz, and 471.5 THz, respectively, have been clearly observed in PLA. This triple-band perfect absorption effect could be attributed to the intrinsic loss of silicon material originated from the guided mode excitations caused by the standing waves of different orders. It has been confirmed that the perfect absorption properties of the PLA can be easily regulated by changing the geometric parameters of the unit-cell nanostructure. Furthermore, the designed PLA served as a RI sensor can achieve sensitivity of about 25.3, 41.3, and 31.9 THz /refractive index unit (RIU). It can be believed that the proposed design of PLA for RI sensing would provide great potential applications in sensing, detecting, the enhanced visible spectroscopy, etc.

Graphene ultraviolet ultrahigh-Q perfect absorption for nanoscale optical sensing

We propose an ultraviolet perfect ultranarrow band absorber by coating a dielectric grating on the monolayer graphene-dielectric-metal structure. The absorber presents an ultranarrow Fano lineshape with quality (Q) factor of 70 and a nearly perfect absorption of over 99.9% in the ultraviolet region, which is ascribed to the near field coupling of the optical dissipation of graphene and guide mode resonance of the dielectric grating. Structure parameters to the influence of the performance are investigated. The structure exhibits the high optical sensitivity (S = 150 nm/RIU, S* = 48/RIU) and figure of merit (FOM = 50, FOM* = 25374) and can also be used to detect the nanoscale analyte layer of sub-nanometer thickness, suggesting great potential applications in ultra-compact efficient biosensors for a much more sensitive detection of small refractive index changes.

Dual-Axis Metasurface Strain Sensor Based on Polarization-Phase-Deformation Relationship

Herein, we propose an approach for sensitivity improvement of dual-axis strain sensing using the property of a metasurface (MS) that the phase response shifts sharply with the MS deformation. A feasible approach for phase measurement is first demonstrated by calculating multi-polarized reception when the incident electromagnetic (EM) wave has anisotropic phase values. A flexible MS consisting of periodically arranged lantern-shaped elements is designed and fabricated for dual-axis strain sensing and evaluation based on the proposed method. The simulation and measurement results demonstrated a high sensitivity of the proposed MS for strain sensing in the microwave band. The method can be used potentially in both pressure and tensile sensing. Moreover, the operational frequency can be extended to the THz range and even to the optical band.

Numerical Investigation on Multiple Resonant Modes of Double-Layer Plasmonic Grooves for Sensing Application

A high-performance multi-resonance plasmonic sensor with double-layer metallic grooves is theoretically constructed by introducing a polymethyl methacrylate groove with a numerical simulation method. Multiple resonance wavelengths can be generated at the oblique incidence, and the number and feature of resonant mode for sensing detection is different for various incident angles. Specifically, at the incident angle of 30°, the reflection spectrum exhibits two resonant dips, in which the dip at the wavelength of 1066 nm has an extremely narrow line width of ~4.5 nm and high figure of merit of ~111.11. As the incident angle increases, the electric dipole mode gradually weakens, but the surface plasmon resonance and cavity resonance mode are enhanced. Therefore, for an incident angle of 65°, three resonance dips for sensing can be generated in the reflection spectrum to realize three-channel sensing measurement. These double-layer plasmonic grooves have potential in the development of advanced biochemical surface plasmon polariton measurements.

Ultra-High Refractive Index Sensing Structure Based on a Metal-Insulator-Metal Waveguide-Coupled T-Shape Cavity with Metal Nanorod Defects

An ultra-high plasmonic refractive index sensing structure composed of a metal-insulator-metal (MIM) waveguide coupled to a T-shape cavity and several metal nanorod defects is proposed and investigated by using finite element method. The designed plasmonic MIM waveguide can constitute a cavity resonance zone and the metal nanorod defects can effectively trap the light in the T-shape cavity. The results reveal that both the size of defects in wider rectangular cavity and the length of narrower rectangular cavity are primary factors increasing the sensitivity performance. The sensitivity can achieve as high as 8280 nm/RIU (RIU denotes the refractive index unit), which is the highest sensitivity reported in plasmonic MIM waveguide-based sensors to our knowledge. In addition, the proposed structure can also serve as a temperature sensor with temperature sensitivity as high as 3.30 nm/°C. The designed structure with simplicity and ease of fabrication can be applied in sensitivity nanometer scale refractive index sensor and may potentially be used in optical on-chip nanosensor.

Polarization-Independent Perfect Optical Metamaterial Absorber as a Glucose Sensor in Food Industry Applications

Perfect optical metamaterial absorbers (POMMA) utilize intrinsic loss, with the aid of appropriate structural design, to achieve near unity absorption at a certain wavelength. In all the reported absorbers, the absorption occurs only at a single wavelength or dual/multi-band wavelengths where plasmon resonances are ex-cited in the nanostructure. Here we not only show a single-band perfect absorber but also demonstrate that our proposed design has the ability to be multi-band absorber at the same structure. Furthermore, we numerically demonstrate the proposed POMMA can be utilized as a glucose sensor for refractive index sensing which has more than 225 nm/RIU sensitivity at the infrared frequency regime which is good value. Its polarization-independent absorbance is about 100% at normal incidence for both TE and TM polarization modes. The proposed optical glucose sensor offers great potential to maintain the performance of localized surface plasmon (LSP) sensors in nanostructures in food industry applications.

High fabrication-tolerant narrowband perfect graphene absorber based on guided-mode resonance in distributed Bragg reflector

We propose the narrowband perfect absorbers with enormously high fabrication tolerance, which consists of a low-contrast grating and a finite distributed Bragg reflector (DBR) layer with an ultrathin absorbing medium (graphene). It is numerically shown that the proposed perfect absorber outperforms the previously proposed schemes in fabrication tolerance. According to the rigorous coupled wave analysis (RCWA) and coupled mode theory (CMT) fitting, over a considerably wide range of grating width and thickness, the proposed absorber provides a proper ratio of leakage rate to loss rate while preserving resonant condition, so that almost perfect absorption (>99.9%) can be obtained. This result is attributed to the strong electric field confinement in the DBR region rather than the grating layer owing to lower index of grating compared to DBR. In addition, without degrading the fabrication tolerance, the bandwidth of the proposed absorber can be controlled by the DBR thickness (the number of pairs) and a narrow absorbing bandwidth of sub-nanometer is achieved with 8.5 Si/SiO₂ pair stacked DBR.

Ultranarrow-Band Wavelength-Selective Thermal Emission with Aperiodic Multilayered Metamaterials Designed by Bayesian Optimization

We computationally designed an ultranarrow-band wavelength-selective thermal radiator via a materials informatics method alternating between Bayesian optimization and thermal electromagnetic field calculation. For a given target infrared wavelength, the optimal structure was efficiently identified from over 8 billion candidates of multilayers consisting of multiple components (Si, Ge, and SiO₂). The resulting optimized structure is an aperiodic multilayered metamaterial exhibiting high and sharp emissivity with a Q-factor of 273. The designed metamaterials were then fabricated, and reasonable experimental realization of the optimal performance was achieved with a Q-factor of 188, which is significantly higher than those of structures empirically designed and fabricated in the past. This is the first demonstration of the experimental realization of metamaterials designed by Bayesian optimization. The results facilitate the machine-learning-based design of metamaterials and advance our understanding of the narrow-band thermal emission mechanism of aperiodic multilayered metamaterials.

Properties of spoof plasmon in thin structures

Spoof surface plasmon polariton (SSPP) is an exotic electromagnetic state that confines light at a subwavelength scale at a design-specific frequency. It has been known for a while that spoof plasmon mode can exist in planar, thin structures with dispersion properties similar to that of its wide three-dimensional structure counterpart. We, however, have shown that spoof plasmons in thin structures possess some unique properties that remain unexplored. Our analysis reveals that the field interior to SSPP waveguide can achieve an exceptional hyperbolic spatial dependence, which can explain why spoof plasma resonance incurs red-shift with the reduction of the waveguide thickness, whereas common wisdom suggests frequency blue-shift of a resonant structure with its size reduction. In addition, we show that strong confinement can be achieved over a wide band in thin spoof plasmon structure, ranging from the spoof plasma frequency up to a lower frequency considerably away from the resonant point. The nature of lateral confinement in thin SSPP structures may enable interesting applications involving fast modulation rate due to enhanced sensitivity of optical modes without compromising modal confinement.

Plasmonic Metasurface Absorber Based on Electro-Optic Substrate for Energy Harvesting

A highly efficient and broad light absorber capable of wide-angle absorption in the visible and near infrared range is presented and numerically investigated for energy harvesting in a simple geometry. According to the calculated results, the proposed device has a peak absorption level of about 99.95%. The actual absorption efficiency is 76.35%, which is approaching that of complex multilayer absorbers with 88 layers working in the wavelength range of 300 nm to 2000 nm. The electro-optic material has the potential of shifting the absorption peak position, compensating fabrication errors and thus reducing the fabrication technique difficulties. Also, the high electro-optic tunability can be used for filters, infrared detection, and imaging applications. More directly, the proposed absorber can be potentially deployed in solar cells and solar thermals.

Dual narrow-band absorber based on metal-insulator-metal configuration for refractive index sensing

Plasmonic gap mode in metal-insulator-metal (MIM) structure has proven promising for refractive index sensing due to its near unity absorption. However, the sensing performance of gap mode has been limited by the broad resonance band, which is related to high plasmonic loss. In this work, square-patch-based MIM structures are used for simultaneous excitation of both the surface plasmon polariton and Rayleigh anomaly with large absorptions, and demonstrate their excellent sensing performances. For the Rayleigh anomaly, the sensitivity and full width half-maximum are 1470 nm/RIU and 0.23 nm, respectively. The corresponding figure of merit is calculated to be 6400 in wavelength shift form and 58,800 in intensity variation form. It is also observed that the two Wood's anomalies have reverse incident-angle-dependent properties, which can be explained by the opposite propagating direction of surface waves.

Guided Bloch surface wave resonance by near normal and near in-plane illuminations: the hyper azimuthal sensitivity

Refractive index sensors based on the interrogation of guided Bloch surface wave resonance (GBR) in the azimuthal angle domain are studied both theoretically and numerically. The azimuthal sensitivity of the sensors is shown to be inversely proportional to the sines of both the azimuthal angle and the polar angle of the detecting electromagnetic signals. Extremely large azimuthal sensitivity is then achieved when the GBR sensor is designed to work near a small azimuthal angle and the polar angle is also fixed to a small one (For the azimuthal angle domain near φ = 5° and a fixed polar angle of θ = 5°, the azimuthal sensitivity gets larger than 5000 degrees per refractive index unit (Deg/RIU)).

Optically Active Plasmonic Metasurfaces based on the Hybridization of In-Plane Coupling and Out-of-Plane Coupling

Plasmonic metasurfaces have attracted much attention in recent years owing to many promising prospects of applications such as polarization switching, local electric field enhancement (FE), near-perfect absorption, sensing, slow-light devices, and nanoantennas. However, many problems in these applications, like only gigahertz switching speeds of electro-optical switches, low-quality factor (Q) of plasmonic resonances, and relatively low figure of merit (FOM) of sensing, severely limit the further development of plasmonic metasurface. Besides, working as nanoantennas, it is also challenging to realize both local electric FE exceeding 100 and near-perfect absorption above 99%. Here, using finite element method and finite difference time domain methods respectively, we firstly report a novel optically tunable plasmonic metasurface based on the hybridization of in-plane near-field coupling and out-of-plane near-field coupling, which provides a good solution to these serious and urgent problems. A physical phenomenon of electromagnetically induced transparency is obtained by the destructive interference between two plasmon modes. At the same time, ultrasharp perfect absorption peaks with ultra-high Q-factor (221.43) is achieved around 1550 nm, which can lead to an ultra-high FOM (214.29) in sensing application. Particularly, by using indium-doped CdO, this metasurface is also firstly demonstrated to be a femtosecond optical reflective polarizer in near-infrared region, possessing an ultra-high polarization extinction ratio. Meanwhile, operating as nanoantennas, this metasurface achieves simultaneously strong local electric FE(|E_loc|/|E₀| > 100) and a near-perfect absorption above 99.9% for the first time, which will benefit a wide range of applications including photocatalytic water splitting and surface-enhanced infrared absorption.

Ultra-narrow Band Perfect Absorber and Its Application as Plasmonic Sensor in the Visible Region

We propose and numerically investigate a perfect ultra-narrowband absorber with an absorption bandwidth of only 1.82 nm and an absorption efficiency exceeding 95% in the visible region. We demonstrate that the perfect ultra-narrowband absorption is ascribed to the coupling effect induced by localized surface plasmon resonance. The influence of structural dimensions on the optical performance is also investigated, and the optimal structure is obtained with the extremely low reflectivity (0.001) of the resonance dip. The perfect absorber can be operated as a refractive index sensor with a sensitivity of around 425 nm/RIU and the figure of merit (FOM) reaching 233.5, which greatly improves the accuracy of the plasmonic sensors in visible region. Moreover, the corresponding figure of merit (FOM*) for this sensor is also calculated to describe the performance of the intensity change detection at a fixed frequency, which can be up to 1.4 × 10⁵. Due to the high sensing performance, the metamaterial structure has great potential in the biological binding, integrated photodetectors, chemical applications and so on.

Infrared Plasmonic Refractive Index Sensor with Ultra-High Figure of Merit Based on the Optimized All-Metal Grating

A perfect ultra-narrow band infrared metamaterial absorber based on the all-metal-grating structure is proposed. The absorber presents a perfect absorption efficiency of over 98% with an ultra-narrow bandwidth of 0.66 nm at normal incidence. This high efficient absorption is contributed to the surface plasmon resonance. Moreover, the surface plasmon resonance-induced strong surface electric field enhancement is favorable for application in biosensing system. When operated as a plasmonic refractive index sensor, the ultra-narrow band absorber has a wavelength sensitivity 2400 nm/RIU and an ultra-high figure of merit 3640, which are much better than those of most reported similar plasmonic sensors. Besides, we also comprehensively investigate the influences of structural parameters on the sensing properties. Due to the simplicity of its geometry structure and its easiness to be fabricated, the proposed high figure of merit and sensitivity sensor indicates a competitive candidate for applications in sensing or detecting fields.

97 percent light absorption in an ultrabroadband frequency range utilizing an ultrathin metal layer: randomly oriented, densely packed dielectric nanowires as an excellent light trapping scaffold

In this paper, we propose a facile and large scale compatible design to obtain perfect ultrabroadband light absorption using metal-dielectric core-shell nanowires. The design consists of atomic layer deposited (ALD) Pt metal uniformly wrapped around hydrothermally grown titanium dioxide (TiO₂) nanowires. It is found that the randomly oriented dense TiO₂ nanowires can impose excellent light trapping properties where the existence of an ultrathin Pt layer (with a thickness of 10 nm) can absorb the light in an ultrabroadband frequency range with an amount near unity. Throughout this study, we first investigate the formation of resonant modes in the metallic nanowires. Our findings prove that a nanowire structure can support multiple longitudinal localized surface plasmons (LSPs) along its axis together with transverse resonance modes. Our investigations showed that the spectral position of these resonance peaks can be tuned with the length, radius, and orientation of the nanowire. Therefore, TiO₂ random nanowires can contain all of these features simultaneously in which the superposition of responses for these different geometries leads to a flat perfect light absorption. The obtained results demonstrate that taking unique advantages of the ALD method, together with excellent light trapping of chemically synthesized nanowires, a perfect, bifacial, wide angle, and large scale compatible absorber can be made where an excellent performance is achieved while using less materials.

Visible light nearly perfect absorber: an optimum unit cell arrangement for near absolute polarization insensitivity

In this work, we propose an optimum unit cell arrangement to obtain near absolute polarization insensitivity in a metal-insulator-metal (MIM) based ultra-broadband perfect absorber. Our findings prove that upon utilizing this optimum arrangement, the response of the absorber is retained and unchanged over all arbitrary incidence light polarizations, regardless of the shape of the top metal patch. First, the impact of the geometry of the top nanopatch resonators on the absorption bandwidth of the overall structure is explored. Then, the response of the MIM design for different incidence polarizations and angles is scrutinized. Finally, the proposed design is fabricated and characterized.

Ultra-broadband, wide angle absorber utilizing metal insulator multilayers stack with a multi-thickness metal surface texture

In this paper, we propose a facile route to fabricate a metal insulator multilayer stack to obtain ultra-broadband, wide angle behavior from the structure. The absorber, which covers near infrared (NIR) and visible (Vis) ranges, consists of a metal-insulator-metal-insulator (MIMI) multilayer where the middle metal layer has a variant thickness. It is found that this non-uniform thickness of the metal provides us with an absorption that is much broader compared to planar architecture. In the non-uniform case, each thickness is responsible for a specific wavelength range where the overall absorption is the superposition of these resonant responses and consequently a broad, perfect light absorption is attained. We first numerically examine the impact of different geometries on the overall light absorption property of the multilayer design. Afterward, we fabricate the designs and characterize them to experimentally verify our numerical findings. Characterizations show a good agreement with numerical results where the optimum absorption bandwidth for planar design is found to be 620 nm (380 nm-1000 nm) and it is significantly boosted to an amount of 1060 nm (350 nm-1410 nm) for multi-thickness case.

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.

Numerical investigations of a near-infrared plasmonic refractive index sensor with extremely high figure of merit and low loss based on the hybrid plasmonic waveguide-nanocavity system

With vertically slotted hybrid plasmonic waveguides (VSHPWs)-nanocavity system fabricated on the silicon-on-insulator platform, a near-infrared surface plasmon resonances (SPRs)-based refractive index (RI) sensor with extremely high figure of merit FOM = 224.3 and transmission efficiency T = 97.6% is proposed and investigated. Based on the finite element method, effective mode index behaviors together with spectral properties are calculated to analyze and optimize the sensing performance. Within near-infrared region, the wavelength sensitivity (S) and optical resolution (FWHM) can be achieved as S = 1817.5nm/RIU and FWHM = 7.4nm. A mechanism of synergy between propagating SPRs and localized SPRs is also presented for further improving the sensitivity (as high as 2647.5nm/RIU). In addition, the VSHPWs-based RI sensor can be fully realized by CMOS-compatible fabrication technology. In general, the high FOM, S and T achieved by our designed structure may have extensive applications in nanophotonic circuits, environmental monitoring and even pharmaceutical research.