Search

Tunning localized surface plasmon resonance (LSPR) in transparent conducting oxides (TCO) has a great impact on various LSPR-based technologies. In addition to the commonly reported mechanisms used for tunning LSPR in TCOs (e.g., size, shape, carrier density modifications via intrinsic and extrinsic doping), integrating them in core-shell structures provides an additional degree of freedom to expand its tunability, enhance its functionality, and widen its versatility through application-oriented core-shell geometrical optimization. In this work, we explore the tuneability and functionality of two TCO nanostructures; indium doped tin oxide (ITO) and gallium doped zinc oxide (GZO) encapsulated with silver shell within the extended theoretical Mie theory formalism. The effect of core and shell sizes on LSPR peak position and line width as well as absorption and scattering coefficients is numerically investigated. Simulations showed that LSPRs of ITO-Ag and GZO-Ag core-shell nanostructures have great tunning capabilities, spanning from VIS to IR spectral range including therapeutic window of human tissue and essential solar energy spectrum. Potential functionality as refractive index sensor (RIS) and solar energy absorber (SEA) are examined using appropriate figure of merits (FoM). Simulations indicate that a geometrically optimized core-shell architecture with exceptional FoMs for RIS and SEA can be realized. Contrary to carrier density manipulation, integrating TCO cores to metallic shells proves to be an effective approach to enhance tunability and optimize functionality for high performance TCO-based plasmonic devices, with minimum impact on the inherited physical and chemical properties of the used TCO-core materials. • Integrating plasmonic TCOs with noble metals in nanoshells enables broader tunability and enhanced plasmonic functionality. • Unlike single Ag, ITO, and GZO nanospheres of limited tunability, ITO-Ag and GZO-Ag nanoshells can be tuned from VIS to NIR. • Small-size TCO-Ag nanoshells suit absorption applications, while larger sizes are ideal for scattering-based applications. • Geometrically optimized TCO-Ag nanoshells exhibited high FoM for refractive index sensing and solar energy absorption. [ABSTRACT FROM AUTHOR]

• A novel hafnium dioxide (HfO 2) and gold (Au) based PCF sensor optimized for refractive index measurement in the 1.3 µm to 1.6 µm spectrum. • Geometrically optimized D-shaped fiber geometry to facilitate efficient light-matter interaction and surface plasmon coupling. • Performance metrics including confinement loss (<10–6 dB/m), propagation constant (β) ∼6 × 106, V-Parameter <2.3, and a peak relative sensitivity of 99.05 %. • Precise discrimination in refractive indices ranging from 1.32 to 1.40. • Addressed the practical aspects of fabricating the proposed HfAu-PCF sensor design. In this study, we introduce a novel hafnium dioxide (HfO 2) and thin gold layer based photonic crystal fiber (HfAu-PCF) sensor for refractive index measurement and optimize in the spectrum of 1.3 µm to 1.6 µm. The proposed sensor incorporates a D-shaped geometry for enhanced light-matter interaction, and the core of the fiber is surrounded by periodic air holes to facilitate efficient coupling of the guided mode with surface plasmons. The proposed HfAu-PCF sensor is geometrically optimized using finite element method (FEM) by fine-tuning air hole diameter, core size, layer thickness dimensions of the fiber to achieve performance stability. Leveraging the unique optical properties of HfO 2 and Au, the sensor demonstrates superior performance metrics, achieving confinement loss (<10−6 dB/m), propagation constant (β) ∼ 6 × 106, V-Parameter < 2.3, a peak relative sensitivity of 99.05 % across the tested wavelength of 1.3 µm to 1.6 µm. Our findings reveal that choosing suitable parameters could lead to further enhancements in sensitivity, making the sensor for applications in bio-sensing, environmental monitoring, and chemical analysis, etc. [ABSTRACT FROM AUTHOR]

Utilizing the asymmetry of the micro-nano structure to excite Fano resonance in dielectric metasurfaces presents low loss and high field enhancement factors, and has a broad range of applications in optical sensing. Nevertheless, the asymmetry of the structure often leads to polarization-sensitive characteristics, significantly reducing the quality factor and sensitivity of the metasurface, thereby hindering its further application. In this study, the metasurface composed of dielectric materials is designed to be completely insensitive to x and y polarization. The metasurface is composed of semicircular disks, which are asymmetrically and periodically placed on a quartz substrate. By controlling the radius of the two semicircular disks, the symmetry is broken, and the bound states in the continuum (BIC) transition to quasi-bound states in the continuum (q-BIC), resulting in an ultra-narrow Fano resonance peak. Simulation results show that the magnetic dipole (MD) dominates the resonance. The designed metasurface structure was fabricated and then integrated into a microfluidic system for spectral refractive index sensing experiments. In the near-infrared band, our tests demonstrate refractive index sensing performance of 405 nm/RIU and a Q factor of up to 319, with significant symmetry of the polarization angle, which agrees well with theoretical simulations. Furthermore, the spectral response of the designed structure can be flexibly controlled by adjusting the polarization angle of the incident light. We believe that this study provides a novel integrated platform for applications such as biosensing and environmental detection, and also has certain reference value for the design of polarization optical switches and metasurface absorbers for encrypted communication. • The q-BIC metasurface is excited in the near-infrared by asymmetric nano disks. • The transmission intensity can be controlled by the polarization characteristics. • In the experiment we obtained a sensitivity of 405 nm/RIU and a Q factor of 319. [ABSTRACT FROM AUTHOR]

[Display omitted] • An innovative refractive index sensor with MIM nanohole array integrated with ring-shaped AgNPs is proposed. • The hybrid plasmonic structures are fabricated using an ultrahigh-throughput and cost-effective NSL and site-selective photocatalytic reaction. • The sensitivities can achieve 835 nm/RIU within the refractive index range of 1 to 1.5. The field of plasmonic sensing has witnessed rapid advancements in recent years. This work proposes an innovative methodology that employs metal–insulator-metal (MIM) nanohole arrays integrated with ring-shaped silver nanoparticles (AgNPs) to serve as an effective plasmonic refractive index sensor. The hybrid substrates are prepared using a combination of nanosphere lithography (NSL), reactive ion etching, and an enhanced plasmonic site-selective photocatalytic reaction, ensuring large-area fabrication, high throughput, and cost-effectiveness. The resonance peaks observed in the visible-NIR spectra are attributed to the coupling of surface plasmon resonance modes between MIM structures and AgNPs. The resonance wavelength exhibits sensitively to changes in the surrounding medium within the refractive index range of 1 to 1.5, with a remarkable sensitivity of 835 nm/RIU. Our findings reveal the significant potential of this technology for advancing optical sensing applications. [ABSTRACT FROM AUTHOR]

• Multifunctional integrated metasurface is a potential development direction. • A multifunctional high Q -factor metasurface-based platform is realized. • Metasurface realizes polarization selective absorption, sensing and chiral response. • High-performance refractive index sensing is realized. • Chiral bound states in the continuum is realized. As application scenarios grow in complexity, multifunctional integrated metasurfaces have been proposed as a potential development direction. We propose a multifunctional high Q -factor metasurface-based platform composed by size-scaled metasurface polarization selective absorbers (MPSAs) capable of polarization selective absorption, refractive index sensing and chiral response. By designing a gold step-shaped unit structure that can break the in-plane and out-of-plane symmetry, bound states in the continuums (BICs) with chiral response and a surface lattice resonance (SLR) are realized. The overall absorption amplitude of the quasi-BIC can reach a maximum value of 0.87 and a Q -factor of 153 while the SLR possesses a high Q -factor exceeding 1274 and a maximum absorption amplitude of 0.93. High extinction ratio up to 13 dB between the transverse magnetic and transverse electric polarization can be achieved. For refractive index (RI) sensing, the bulk RI sensitivities of the proposed MPSA for quasi-BIC and SLR are S BIC = 4000 nm/RIU and S SLR = 3740 nm/RIU, which leads to a high figure of merit (FOM) of FOM BIC = 161 /RIU and FOM SLR = 1247 /RIU, respectively. For chiral response, the maximum circular dichroism (CD) for the proposed MPSA is 0.88 by oblique incidence still maintaining a Q -factor exceeding 120, which indicates that it has potential application for chiral sensing. The proposed multifunctional metasurfaces-based platform possesses the potential to promising future applications for polarization manipulation, chiral biosensing, chiral drug analysis and quantum optics. [ABSTRACT FROM AUTHOR]

Photonic crystal waveguide, to be used as a highly sensitive platform for refractive index based sensing applications, has been analyzed in this paper. The sensing performance is estimated by using dispersion diagram through using plane wave expansion simulations. The dispersion diagram is used to obtain transmittance and cut-off wavelengths for analyzing the sensor characteristics. It has been proposed that the photonic crystal waveguide with ring-type line defect provides a better perspective for sensing applications as compared to the conventional photonic crystal waveguide. An optimized ring-type photonic crystal waveguide structure with a defect filling factor of 50% shows a refractive index sensitivity of 450 nm/RIU having almost double the output signal strength compared to hole-type line defect waveguide with the same filling factor. [ABSTRACT FROM AUTHOR]

A bi-controllable all dielectric metasurface structure is designed at terahertz, which consists of an InAs micro-cylindrical array on the gold ground plane. The maximum absorptance frequency is tunable with the help of an external magnetic field and also by geometrical rotation of the metasurface as InAs is a gyrotropic material whose property depends on the magnitude and direction of an external magnetic field. Simulation results indicate that the proposed metasurface can achieve an absorptance of more than 99 % at 9.756 THz as well as it can provide a high tunability rate of around 2.55 THz T−1 in lower band and 3.33 THz T−1 in the upper band frequency spectrum with the application of the magnetic field. Additionally, the metasurface also acts as polarization insensitive when no external magnetic field is applied. Furthermore, the maximum absorptance frequency shows sensitivity towards the change in the refractive index value of the surrounding medium, thus the metasurface can be used for chemical and biosensing applications. It shows high chemical sensitivity of around 2727 GHz/RIU for the detection of different chemicals and bio sensitivity of 787 GHz/RIU for the detection of various viruses. • A bi-controllable all dielectric metasurface structure is designed at terahertz, which consists of an InAs micro-cylindrical array on the gold ground plane. • The maximum absorptance frequency is tunable with the help of an external magnetic field and also by geometrical rotation of the metasurface as InAs is a gyrotropic material whose property depends on the magnitude and direction of an external magnetic field. • Furthermore, the maximum absorptance frequency shows sensitivity towards the change in the refractive index value of the surrounding medium, thus the metasurface can be used for chemical and biosensing applications. • It shows high chemical sensitivity of around 2727 GHz/RIU for the detection of different chemicals and bio sensitivity of 787 GHz/RIU for the detection of various viruses. [ABSTRACT FROM AUTHOR]

• This novel sensor can simultaneously detect gas–liquid analytes in the external and internal environment of organisms. • The proposed MOF-SPR sensor can be operated in the infrared range to detect the analyte RIs of ultra-wide scope from 1.00 to 1.38. • Maximum wavelength sensitivity is 20,000 nm/RIU boasting a resolution of 5.00 × 10−6 RIU. • Compared to the single-open-loop model, this dual-open-loop design is capable of bidirectional and simultaneous excitation of SPR to further promote sensing properties. To achieve simultaneous detection of analytes with different states in internal and external environments, A microstructured optical fibers (MOFs) biochemical sensor based on surface plasmon resonance (SPR) is proposed. The micro-polished dual-open-loop structure with anti-corrosive gold as the sensing layer is designed, which greatly improves the phase matching between fundamental mode and plasmonic mode to further stimulate SPR effect. Numerical simulation by the full-vector finite element method (FEM) reveals that the even mode for y-polarized state has better sensing properties due to the more eminent electric field distribution and shift of the confinement loss peak. In order to better evaluate and analyze the output characteristics of this sensor, the wavelength modulation and amplitude interrogation methods are adopted. The results manifest that the maximum wavelength sensitivity (WS) of 20,000 nm/RIU and amplitude sensitivity (AS) of 208.21 RIU−1 with resolution (R) of 10−6 order can be acquired in operable infrared region (900–2,750 nm). Furthermore, this sensor has realized a broad range of detection for gas and liquid analytes with RIs from 1.00 to 1.38. On account of its simple structure, low cost, and industrial compatibility, this sensor has large potential in environmental and biological applications such as atmospheric monitoring, sewage treatment, food safety, humoral regulation, and medical diagnosis. [ABSTRACT FROM AUTHOR]

We propose and numerically demonstrate the existence of bound state in the continuum (BIC) in silicon-based one-dimensional photonic crystal nanobeam (1D-PCN). The 1D-PCN is formed by introducing rectangular air nanoholes in a simple 1D nanobeam waveguide. By engineering the structure parameters, an ideal BIC with infinite quality (Q) factor is demonstrated in 1D-PCN. On this basis, we further investigate the refractive index sensing performance with quasi-BIC by introducing defects into the aforementioned 1D-PCN structure, and an ultrahigh Q factor of ∼ 4.1 × 107 is obtained. Compared to the conventional sensing mechanism based on the shift of forbidden bands modes, the 1D-PCN sensor based on quasi-BIC has a comparable figure of merit (FOM) higher than 106. It is worth mentioning that the quasi-BIC can be directly excited by external light sources without the special coupling mechanism, which provides a new method for ultrasensitive refractive index sensing. [ABSTRACT FROM AUTHOR]

The advent of nanostructures with localized surface plasmon resonance extending into the near infrared region has opened avenues for optical absorbance based sensors operating in this region. Sensing using the near infrared band has been known to confer many advantages, particularly for biosensing. Here we explore the basic refractive index sensing capabilities of such a sensor, made by coating gold nanoshells on a ‘U’ shaped optical fiber, as a prelude for its later application in biosensing. [ABSTRACT FROM AUTHOR]

The paper presents an effect of fiber bending on sensitivity of long-period gratings (LPGs) to temperature and to surrounding refractive index (RI). The LPGs were manufactured by UV-exposure of hydrogen-loaded Corning SMF28 fibers and their annealing was followed by wet etching in hydrofluoric acid up to dispersion turning point (DTP) where the LPG shows the highest sensitivity. The LPGs were subjected to curvatures in range 0.8 to 4.8 m -1 when their temperature (T=20-100 °C) and refractive index (RI) responses (n D =1 to 1.47) were measured. Bending sensitivity reaching 54 nm/m -1 has been obtained. It has been found that as a result of bending, coupling to asymmetrical cladding modes takes place. It results in the resonances increasing their depth and shifting towards longer wavelengths with bending. The bending effect also allows for post-fabrication tuning of the LPGs working at DTP. The LPGs with bending-modified temperature sensitivity up to 0.54 nm/°C have been shown. The method can also be applied for tuning of RI sensitivity of the LPGs. [ABSTRACT FROM AUTHOR]

Abstract: Fabrication procedure and refractive index (RI) sensitivity of a diamond-like carbon (DLC) nano-coated optical fiber sensing structure is presented. The overlays were deposited by Radio Frequency Plasma Assisted Chemical Vapor Deposition (RF PACVD) method on both cores of a polymer-clad silica (PCS) multimode optical fibers and oxidized silicon wafers. It is shown that thin (120 to 330nm in thickness measured on the silicon wafers) and high refractive index (∼2.14 at λ=620nm) overlays can effectively modify optical response of the structures to variation of the external RI. By deposition of the overlay we achieved 5-times increase in the RI sensitivity of the investigated samples. [Copyright &y& Elsevier]

Abstract: We fabricated a type II fiber Bragg grating in a ∼7.6μm diameter microfiber, using a KrF excimer laser at a high fluence level of ∼ 1.1J/cm2 through a phase mask. The proposed microfiber Bragg grating (MFBG) is used to sense the refractive index (RI) of the surrounding medium. [Copyright &y& Elsevier]

• A polarization-insensitive metasurface is designed by combining asymmetric metasurfaces that excite quasi-BICs. • We obtain a dual-band response with high-quality factors due to the excitation of two quasi-BICs. • The sensitivities are 2756.67 nm/RIU and 2319.93 nm/RIU, corresponding FOM values of 820.44 RIU−1 and 532.09 RIU−1. The introduction of distortions into the metasurfaces with in-plane symmetry offers a possibility to achieve resonances with high quality (Q) factors, but such distortions make the metasurfaces sensitive to the polarization state of the incident light. Here, we propose and numerically demonstrate a polarization-insensitive dual-band refractive index (RI) sensor. In this work, the proposed metasurface is imparted with fourfold symmetry by combining two pairs of asymmetric silicon elliptical nanodisks, allowing it to acquire polarization-insensitive properties to the incident light. Two narrow-band reflection peaks with full width at half maximum (FWHM) of 3.36 nm and 4.53 nm are excited and tailored for RI sensing. Their sensitivities are 2756.67 nm/RIU and 2319.93 nm/RIU, with figure of merit (FOM) values of 820.44 RIU−1 and 532.09 RIU−1. This work provides a new approach to realize polarization-independent and high-performance RI sensor devices. [ABSTRACT FROM AUTHOR]

Resonant plasmonic nanostructures have attracted much attention due to their exotic optical properties. In this work, we numerically investigate single- and dual-gap ring structures, respectively, and they can be used for refractive index sensing by exciting the gap plasmon mode with sharp resonance spectra. The dual-gap ring plasmonic sensor shows the dual-channel properties and the corresponding sensitivities are 513 nm/RIU and 809 nm/RIU with the refractive indices range of 1.32–1.37, respectively. Furthermore, the gap ring structures are highly symmetrical, and have advantages in fabrication and pave the way for advanced optical devices to detect bio-molecules. [ABSTRACT FROM AUTHOR]

• A graphene based metamaterial four band near unity absorber with dynamical tunability is designed. • The proposed absorber is simple in design, easy to be fabricated, and excellent in performance. • By adjusting the chemical potential, dynamic controllable absorption characteristics can be realized. • It can well detect the change of the refractive index of the surrounding analyte. • It has potential application prospects in multispectral sensing, filtering, stealth, and so on. In this paper, a classic three-layer metamaterial absorber (MA) is designed to achieve quad-band perfect absorption. The unit cell of the top graphene pattern layer is made up of a periodically arranged graphene split-ring nested with a cross-like graphene structure formed by four L-shaped strips. The middle dielectric spacer layer is SiO 2 and the ground layer is gold. Simulation results show that four absorption bands with near unity peak absorption rate will occur in the interested frequency range of 3–11 THz. The absorption mechanism and the parameter dependency are discussed at first, which will provide guiding significances for the actual fabrication. Meanwhile, when the Fermi level of graphene is increased, the four absorption bands will have different degrees of blue-shift, and when the relaxation time of graphene is increased, the four absorption peaks will increase first and then decreases. As a result, dynamical tunability of the absorption properties can be achieved by changing the Fermi level or the relaxation time of the graphene without changing the geometry of the proposed MA. Further investigation indicates that the proposed absorber is independent of the polarization of the input electromagnetic (EM) wave and can maintain well absorption properties when the incident angle is changed within a broader range. Considering the potential sensing applications, it is shown that the proposed MA can be operated as a type of refractive index sensor with highest sensitivity of 2.97THz/RIU, and the maximum figure of merit (FOM) is 47.5. In terms of these unique performances, the proposed MA has broad application prospects in multispectral optical stealth, optical filtering, integrated photo detecting, sensing and so on. [ABSTRACT FROM AUTHOR]

The design, optimization, and analysis of two-dimensional metal-assisted guided mode resonance (MAGMR) based sensing structures have been presented focusing on the visible range of operation. The study has been conducted for square and hexagonal lattice geometries and the sensing properties and performance of the MAMGR structures have been compared with the traditional guided-mode resonance (GMR) structures sharing identical design parameters. The effect of various design parameters on the individual resonant polarization modes has also been investigated and the superior bulk sensitivities of the MAGMR structures have been highlighted in comparison with the GMR structures. • Analysis of two-dimensional metal-assisted guided mode resonance based sensors. • Analysis for different resonant polarization modes. • Investigation of the role of design parameters on the sensing performance. • Study of the working principle and sensing mechanism of the hexagonal and square periodic structures. • Comparison with the traditional guided-mode resonance based sensors. [ABSTRACT FROM AUTHOR]

• A graphene based metamaterial dual band near unity absorber with dynamical tunability is designed. • The proposed absorber is a typical three-layer structure, which is simple in design, easy to be fabricated, and is excellent in performance. • By adjusting the geometrical parameters, the absorber with different working frequency can be well designed. By changing the chemical potential of the graphene, dynamic controllable absorption characteristics can be realized. • When been used as a sensor, it can well detect the change of the refractive index of the covering analyte with thinner thickness. In this paper, we propose a metamaterial perfect absorber (MPA), which is a three-layer structure composed of a periodically placed "ǂ" type graphene array on top of a gold layer separated by a SiO 2 dielectric spacer, to achieve dual band perfect absorption. The absorption mechanism is analyzed, and the simulation results show that at the frequencies of 5.16 THz and 10.30 THz, the absorption rates are as high as 99.7% and 99.6%, respectively. In addition, the absorber is insensitive to the polarization of the incident wave and has a good tolerance to the incident angle. Moreover, the position and peak absorption of the absorber can be adjusted flexibly by changing the structure parameters and the Fermi level μ c of graphene. In addition, the position of absorption frequency is sensitive to the surrounding medium, so the proposed MPA has potential applications in the field of refractive sensor. This paper provides a new idea for the design of tunable dual-band ideal terahertz absorber. Because of its good performance, the proposed absorber has a wide range of application prospects in terahertz and mid-infrared optical filter, optical sensor, and radiation thermal imaging, stealth and communication fields. [ABSTRACT FROM AUTHOR]