查看更多>>摘要：The application of graphene and graphene-like materials in photonics has attracted extensive attention in recent years. However, their nonlinear optical (NLO) properties need to be improved urgently. Herein, we demonstrate a method to improve the NLO properties of reduced graphene oxide (RGO) via the decoration of Ni transition element doped ZnS nanoparticles on RGO sheet. The samples of Ni doped ZnS decorated RGO (Ni-ZnS/RGO) composites with different Ni doping concentrations and ZnS particles sizes were synthesized via a facile solvothermal method. The NLO responses of Ni-ZnS/RGO composites were investigated via the Z-scan technique under a picosecond laser at 1064 nm. The results indicated that Ni-ZnS/RGO composites exhibited saturation absorption and positive nonlinear refraction properties, and they could be adjusted by controlling the doping concentration of Ni and the size of ZnS nanoparticles. The maximum saturation absorption coefficient, nonlinear susceptibility and nonlinear refractive index of Ni-ZnS/RGO among all the samples were obtained to be- 2.5 x 10(-10) mW(-1), 3.2 x 10(-13) cm(2)/W and 14.1 x 10(-14) cm(2)/W, which were 25, 18 and 23 times of those of RGO, and 3.6, 11.7 and 4.2 times of those of ZnS doped with 2.5%Ni, respectively. They were also much greater than those of the direct sum of the two independent units, RGO and Ni-doped ZnS. These highly improved NLO responses of Ni-ZnS/RGO composites were ascribed to the inhibition of the direct electron-hole recombination due to the introduction of Ni doped impurity energy levels within the band gap of ZnS, as well as the charge transfer and synergism between ZnS and RGO. The results of this investigation may promote the development and applications of Ni-ZnS/RGO materials in photonic devices.
查看更多>>摘要：Polarisation is an important characteristic parameter of electromagnetic waves. The controllable adjustment of the polarisation of electromagnetic waves is important for applications in fields such as antenna radiation, satellite communication, and radar stealth. In this study, a reconfigurable metasurface polarisation converter with a square ring structure and an opening was developed based on the reversible metal-insulator phase transition (MIT) of vanadium dioxide (VO2). VO2 is in the insulating high-resistance state (M phase) when its temperature is lower than the MIT temperature (68 degrees C). Finite element simulations showed that the metasurface could convert linearly polarised waves into cross-polarised reflected waves at frequencies of 8-18 GHz, corresponding to the X and Ku bands. The polarisation conversion rate (PCR) was over 90% and the relative bandwidth was up to 79%. VO2 is in the metallic low-resistance state (R phase) when its temperature is higher than the MIT temperature. At frequencies > 9.4 GHz, the PCR of the metasurface was less than 20%. Under these conditions, the polarisation of most of the reflected waves was the same as that of the incident wave. The polarisation converter was designed to work over a wide frequency range, and thus multiple resonances could be produced based on multiple resonance points in the working frequency range. Moreover, the electromagnetic wave component in the v-direction was rotated along 180 degrees; hence, the polarisation of the incident electromagnetic wave rotated along 90 degrees. When the resistance was low, the phases in the u- and v-directions were basically the same and the electromagnetic waves were reflected in the same direction. A smaller VO2 resistance denotes a higher co-polarisation reflection coefficient (R-xx). R-xx > 80% when the resistance of VO2 < 10 51, and R-xx > 90% when the resistance was 1 Omega. The maximum VO2 power loss was achieved when the resistance of VO2 was 188 Omega, i.e., the impedance matched with that of air. The experimental and simulation results were generally consistent. The proposed polarisation converter could have widespread applications in the dynamic control of electromagnetic waves, with uses in antenna radiation and radar cross-section reduction.
Gromyko, D. A.Dyakov, S. A.Zinovyev, V. A.Tikhodeev, S. G....
9页
查看更多>>摘要：The resonant mode approximation of the scattering matrix is considered for calculating the optical properties of multilayered periodic structures within the formalism of the Fourier-modal method for two diffraction thresholds in close proximity of the spectral-angular range of interest. The developed approximation opens up possibilities for the fast calculation of the scattering matrix of these structures when describing the integral characteristics of spectra and dispersion curves containing high-Q resonances, such as bound states in the continuum.
El Barghouti, MohamedHaidar, OumaimaAkjouj, AbdellatifMir, Abdellah...
14页
查看更多>>摘要：We have proposed new localized surface plasmon (LSP) hybrid nanostructures, based on gold nanowires form T (AuNWs-T) deposited on a glass substrate (substrate/AuNWs) or on a graphene-coated Au film (substrate/Au film/graphene/AuNWs). The results have shown that by optimizing the parameters of nanoplasmonic structures and the incidence angle of the excitation wave. This study gives an ultra-detection performance. The detection performance parameters expressed in terms of figure of Merit (FoM) and sensitivity are improved to more than 593% (7 times) for FoM and 284.86% (3.85 times) the sensitivity compared to a traditional AuNWs-based LSPR nanostructure in normal incidence. Due to the improvement of localized surface plasmon resonance (LSPR) which is attributed to the effect of coupling between the AuNWs-T and graphene-coated Au film. This complicated nanoplasmonic resonance LSPR enhancement with the incident angle, especially in the presence of gold nanowires, can be controlled reliably by engineering the dispersion curve. These results are followed by an enhancement of the calculated electric field strength along several cut lines through the hybrid nanostructures. Our results show that the hybrid nanostructures devices hold great promise as biosensors for different types of analytes and for optical nanotechnologies.
查看更多>>摘要：The recently predicted phenomenon of diffraction lensless electromagnetic focusing in small volume of the near zone of a sub-wavelength nanoaperture (Semiconductors, 2020, Vol. 54, p. 1814) is analyzed theoretically. For this, we use the rigorous solution of the problem of plane wave diffraction by a slot in a perfectly conducting screen of arbitrary thickness with a thin dielectric film on a substrate, which plays a part of a radiation receiver (detector) behind the slot. The scalar focusing parameter is introduced for estimation of quality of a diffraction image of a slot in a film from the standpoint of local spectroscopy and optical lithography. It is convenient to use for search of domains of variability of the problem parameters, where the phenomenon of sub-wavelength focusing exists.
查看更多>>摘要：Plasmonic nanostructure-based sensors have a broad range of applications in food assessment, hazardous gas monitoring, medical diagnosis, and vapor sensing. However, it is still challenging to establish a high performance plasmonic sensing platform that simultaneously provides high refractive index sensitivity and high figure of merit values. Based on simulations using the finite element method, we engineered an ultra-sensitive all-metal plasmonic perfect absorber (a-MPPA) for sensing applications. The proposed a-MPPA structure is based on closely spaced silver (Ag) nanocones over an Ag thin film and it exhibits ultra-sharp spectral absorption with robust hot spots of electric and magnetic fields. The high optical absorption and localized giant field enhancement depend on the structural configuration of the platform. We observed that the absorbance of the optimized structure exceeded 99%, with an ultra-narrow plasmonic peak (4.3 nm), thereby suggesting that the proposed nanostructure is a good candidate for sensing applications. The sensing performance of the a-MPPA platform was outstanding, with bulk sensitivity of 1006 nm/RIU, large figure of merit value of 233.9 RIU-1, and high quality factor of 233.4. Theoretical analyses based on Campbell's model indicated that the a-MPPA platform is suitable for molecular detection, with a detection range extending to 50 nm. The proposed narrow-band perfect absorption plasmonic nanostructure has great potential for applications in sensing.
查看更多>>摘要：We report a combined experimental and computational investigation of the multi-wavelength response of a series of focusing non-uniform grating couplers designed on multiple SOI thicknesses interfaced with two different fiber coupling schemes. In particular, we demonstrate either the existence of an asymmetry of the coupling efficiency curve shape, with respect to the tuning wavelength (1550 nm), related to the metastructure features, and how the photonic band structure of such metastructures can be calculated and exploited to evaluate their multiwavelength response, in terms of multi-BW analysis. These results can be a positive stimulus for a further comprehension of the electromagnetic response of non-uniform grating couplers, particularly interesting as a valid option for integrated photonics applications.
Hajian, HodjatRukhlenko, Ivan D.Hanson, George W.Ozbay, Ekmel...
9页
查看更多>>摘要：We propose a black phosphorus-silicon carbide (BP-SiC) metasurface with in-plane structural symmetry that can act as both a nearly perfect anisotropic absorber and tunable polarized source of mid-infrared (MIR) radiation. The metasurface is a periodic array of square SiC patches integrated with a BP flake at the top and separated from a bottom reflector by a BaF2 spacer. We first use analytical calculations and numerical simulations to study the hybridization of the anisotropic plasmons of BP with isotropic phonons of SiC. We also analyze the in-plane characteristics of the resulting hybrid modes of the BP/SiC heterostructure and the BP-SiC metasurface. It is then demonstrated that the proposed metasurface can serve as a nearly perfect anisotropic absorber of MIR radiation with highly selective and omnidirectional features. It is also shown that the metasurface can be used as a polarized MIR source with tunable temperature, which is determined by the thermal equilibrium between the matter and radiation. The suggested design holds promise for artificial coatings that can tune the blackbody thermal signatures, MIR sensing, and highly directional in-plane transportation of the MIR energy.
查看更多>>摘要：The surface lattice resonance (SLR) created by metal nanoparticles in a regular periodic array shows a narrower bandwidth than single nanoparticles, leading to widespread applications in the field of nanolasers and nano sensors. In this work, we studied the plasmonic properties of the Ag trigonal-helix nanostructures (ATHNs). Our results show that an ultra-narrow Fano resonance with linewidths as narrow as-1.5 nm from arrays of ATHNs at lambda 388 nm, which will be especially useful in the UV-applications. Moreover, the resonant wavelength of the Fano peaks shows a strong dependence on the array periodicity, which enables us to adjust Fano resonance at the desired wavelength in all UV-Vis and near-IR regimes. The results of this work may be used to build more advanced sensors based on the Fano plasmon lattice resonance.
查看更多>>摘要：New bound in continuum states and long-lived resonances in one photonic triangular pyramid with two semi infinite leads are reported, together with general theorems giving their existence conditions. The pyramid is composed of connected open loops (of length L). When bound in continuum states exist within state continua, they induce long-lived resonances for specific values of some modified lengths of the 6 open loops constituting the pyramid. This enables to tune these resonances by means of these lengths. The results obtained in this work take due account of the state number conservation between the final system and the reference one constituted by the independent pyramid and semi-infinite leads. The respect of this conservation enables to find all the states of the final system and among them the bound in continuum ones. This is one of the originalities of this work. The other new general results are the different sets of bound in continuum states and long-lived resonances, as well as the theorems giving their existence conditions. These results may have a big impact on general investigations of bound in continuum states, long-lived resonances and communication technology improvements.
NSTL
Elsevier