Temperature Tunable Narrow-Band Terahertz Metasurface Absorber Based on InSb Micro-Cylinder Arrays for Enhanced Sensing Application

Ultra-broadband tunable terahertz metasurface absorber with multi-mode regulation based on artificial neural network

Terahertz perfect absorber based on InSb metasurface for both temperature and refractive index sensing

Terahertz narrowband perfect metasurface absorber based on micro-ring-shaped GaAs array for enhanced refractive index sensing

Although the design of graphene-based tunable broadband terahertz (THz) absorbers has attracted much attention, improving the functionality of the absorbers to adapt to different scenarios is still worth studying. This paper presents an innovative design of a quad-functional metasurface absorber (QMA) in the THz region, which can switch the absorption frequency/band by means of dual voltage/thermal manipulation. By electrically manipulating the chemical potential of graphene, the QMA can switch freely between the narrowband absorption mode ("NAM") and the broadband absorption mode ("BAM"), while thermally manipulating the phase transition of VO2 allows switching between the low-frequency absorption mode ("LAM") and the high-frequency absorption mode ("HAM"). Detailed mechanistic analysis shows that the "NAM" and "BAM" are due to the switching of the fundamental and second order graphene surface plasmon polariton (SPP) resonances, respectively, and the switching between "LAM" and "HAM" is due to the phase transformation of VO2. Furthermore, the QMA is polarization insensitive in all absorption modes and maintains excellent absorption performance at large angular incidence of TE- and TM-polarized waves. All the results indicate that the proposed QMA has great potential for stealth, sensing, switching, and filtering applications.

Dual-band tunable terahertz perfect absorber based on all-dielectric InSb resonator structure for sensing application

Tunable multiple band THz perfect absorber with InSb metamaterial for enhanced sensing application

Nonlinear metamaterials hold a promising platform for generating terahertz (THz) waves. In this paper, we present an all-dielectric metamaterial with multiple surface plasmon polariton (SPP) resonances for enhanced THz frequency mixing. The metamaterial is composed of graphene ribbons, a dielectric layer, and a one-dimensional photonic crystal, displaying the multiple absorptions with simultaneous excitation of three SPP resonances. Taking advantage of SPP resonances with high Q factor and strong localized field at the input frequency, the third-order nonlinear processes are remarkably enhanced, including third-harmonic generation and four-wave mixing, producing a variety of frequencies in the THz range. The proposed efficient nonlinear metamaterials offer promising applications for THz frequency synthesis.

In order to enhance the working performance of existing temperature sensor and refractive index sensor of sub-wavelength waveguide, the design of ring regular octagon surface plasmon resonance sensor with sharp transmission peak, high sensitivity and high integration was proposed in this paper based on surface plasmon polaritons. The feasibility of using ethanol as a thermosensitive filler to establish a linear conversion relationship between temperature and effective refractive index was analyzed theoretically. The reason why the real part of effective refractive index changes abruptly with the change of waveguide width is also explained. The multimode interference coupled mode theory (MICMT) was used to fit and analyze the transmission peak of the sensor, and then the finite element methods (FEM) is used for simulation analysis. Results obtained by the theory of the MICMT are consistent very well with those from simulation. In order to obtain the optimal parameter setting of the ring regular octagon surface plasmon resonance sensor, various parameters of the sensor are simulated by FEM. It is found that increasing <i>L</i> and decreasing <i>H</i> will improve the sensitivity of the sensor, while decreasing parameter <i>w</i> can not only improve the amplitude of transmission peak, but also keep the sensitivity unchanged. This characteristic of parameter <i>w</i> greatly improves the robustness of the sensor. All kinds of physical phenomena in this paper are analyzed in detail. Firstly, the phenomenon of transmission peak displacement caused by parameter changes is explained through the analysis of magnetic field distribution, and then the phenomenon of inconsistent sensitivity of different transmission peaks is explained through photon energy formula. Compared with the previous structural design, the dual-purpose sensor has many advantages such as wide operating wavelength range, narrow full width at half maximum and easy to integrate. As a temperature sensor and refractive index sensor, its sensitivity was as high as 0.9 nm/℃ and 2400 nm/RIU. The study of this structure broke through the limitations of some traditional cavities, in order to provide a high- performance cavity selection for the micro-nano photon temperature and refractive index dual-purpose sensor based on the design of surface plasmon polaritons in the future.

Dual-band terahertz perfect metasurface absorber based on bi-layered all-dielectric resonator structure

A reflective fiber-optic refractive index sensor based on multimode interference in a coreless silica fiber

A self-referenced terahertz (THz) refractive index sensor is proposed. The structure consists of two opposite-facing, graphene-covered distributed Bragg reflectors (DBRs), with a cavity formed in between. The cavity is filled with the ambient medium, and its resonance frequency is sensitive to the changes of the ambient refractive index. On the other hand, Tamm-plasmonic modes, which are excited at the DBR-graphene boundaries, are insensitive to the ambient refractive index and thus provide a frequency reference. The proposed structure is studied using a semi-analytical transfer matrix method (TMM). The sensor, studied for gas sensing, achieves a sensitivity of 0.982 THz per refractive index unit (THz/RIU), and a figure of merit (FoM) of 142RIU-1 at the cavity resonance frequency of 1.1 THz. The effects of different parameters on the sensor's performance are also investigated. Compared to the previous high-performance THz refractive index sensing approaches, the proposed structure is simpler because it requires no phase- or polarization-matching devices, such as polarizers, prisms, and gratings. Moreover, it provides a self-referenced operation, which was rarely achievable using previous methods.

SummaryLogic gates are important components in integrated photonic circuitry. Here, a series of logic gates to achieve fundamental logic operations based on linear interference in spoof surface plasmon polariton waveguides are demonstrated at terahertz frequencies. A metasurface-based plasmonic source is adopted to couple free-space terahertz radiation into surface waves, followed by a funnel-shaped metasurface to efficiently couple the surface waves to the waveguides built on a domino structure. A single Mach-Zehnder waveguide interferometer can work as logic gates for four logic functions: AND, NOT, OR, and XOR. By cascading two such interferometers, NAND and NOR operations can also be achieved. Experimental investigations are supported by numerical simulations, and good agreement is obtained. The logic gates have compact sizes and high intensity contrasts for the output “1” and “0” states. More complicated functions can be envisioned and will be of great value for future terahertz integrated computing.

Temperature and refractive index sensor based on perfect absorber in InSb double rectangular ring resonator metamaterials

In this study, we present experimentally measured transmission enhancement of microwaves through periodic slit arrays in metallic films. Enhanced transmission peaks and sharp transmission dips are clearly observed around the theoretically expected surface plasmon polariton(SPP) resonance frequencies. Dependence of the transmittance spectra on the geometrical properties of slits is also demonstrated by varying the slit width, slit periodicity and the thickness of metallic films. Transmission peaks and dips are originated from the coupling between the incident light and SPPs which are caused by the slit array that acts like a grating coupler. The obtained results are theoretically explained by solving the Maxwell's equations and by the diffraction theory with appropriate boundary conditions, and they are in good agreement with those calculated by the finite-difference time-domain method.

Tunable dual-band composite metasurface absorber in the mid-infrared region based on LSPs-SPPs interaction