International Journal of

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We report an experimental study on optical and magneto-optical properties of Cesubstituted yttrium iron garnet thin films incorporating gold nanoparticles. Au nanoparticles were formed by heating Au thin film on cubic quartz and garnet substrate in vacuum chamber and a Ce:YIG layer was deposited on them by the aid of Pulsed laser deposition method. A large enhancement of the longitudinal Kerr effect was obtained in sample with Au nanoparticles on quartz substrate and the effect of substrate material on improving optical and magneto-optical response of samples were investigated.

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We have proposed a new ultra-compact optical demultiplexer based on metal-insulator-metal plasmonic waveguides aperture-coupled to the ring resonators. Our proposed device has high performance, small footprint, and high potential for integration and development to more channels.

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In this paper, the scattering of a plane monochromatic electromagnetic wave from a nanowire with circular cross-section in the transverse electric (TE) mode is simulated using the well-known Stratton-Chu surface integral equations. For an ordinary dielectric nanowire the refraction phenomenon is nicely simulated. In the case of a plasmonic nanowire no sign of surface plasmon excitation and propagation is seen. Transition from electrostatic regime to the geometrical shadow through diffraction regime by decreasing the light wavelength is also observable.

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Nanostructures of noble metal materials have been used in organic solar cells for enhancement of performance and light trapping. In this study, we have introduced branched silver cauliflower-like nanopatterns as sub-wavelength structured metal grating in organic solar cells. Self-assembled fabrication process of branched nanopatterns was carried out on a bio-template of cicada wing nanonipple arrays using a gas aggregation dc magnetron sputtering nanocluster source without size filtration. The branched nanostructures provide surface gaps with dimensions near the organic exciton diffusion length, which prevents recombination of charge carriers. An increased power conversion efficiency of 14.8% compared to that of the planar device was achieved mainly due to the enhancement in the short-circuit current density. Besides, these branched cauliflower-like nanopatterns had enhanced optical light absorption in the solar cell as a result of enhancing the optical path length of the reflected light in the active layer and plasmonic effects of the noble metal material.

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For a fiber optical surface plasmon resonance (SPR) sensor a short part of its cladding should be removed to coat a thin layer of a metal. Usually this is problematic when an optical fiber with small core diameter is used. In this paper, a new method using µliter droplet of the HF acid for short fiber optical taper fabrication is reported. Using this method in a multi-mode optical fiber with the core/cladding size of 50/125 µm a 2 mm long taper with 40 µm diameter is fabricated. Roughness of its surface is investigated using an atomic force microscopy. The measured mean value of the roughness is about 8 nm. A 60 nm thin layer of pure silver is coated on the taper surface in order to investigate its performance using a fiber optical SPR sensor.  Using this SPR fiber sensor measurement of the lead concentrations in water ranging from 0.1 to 10 part per million (ppm) is reported.

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In this article, the effect of plasmonics properties of metal nanorods and nanoparticles on solar cell performance were investigated and simulated. Due to the classic solar cell disadvantages, it seems that a plasmonic solar cell is one of these methods. In plasmonic solar cells, because of plasmonic effect, a high electric field builds around metal nanoparticles so that high conversion efficiency is available. In this study, it is shown that the near-field electromagnetic wave severely affects the generation rate, which handles the carrier’s generation in the solar cell equations. By manipulating the plasmonic properties of nanoparticles or nanorods in solar cells structure, distribution of the electromagnetic fields are altered. In this work, optical power and generation rate related to the poynting vector is calculated. So, for improving the generation rate as an important parameter in solar cells, the alteration of nanoparticles or nanorods material, shape, inter-distance between them and medium material, are done. Finally, the comparison between classical solar cell and our improved structure is performed.

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In this paper the transmittance of metal-insulator-metal (MIM) waveguides containing semi-circular ring shaped and rectangular ring shaped grooves are investigated. By varying groove parameters their effects on the transmittance of the MIM waveguides are investigated. The results show that the transmittance spectra of the waveguides have maximum and minimum points, and by using appropriate parameters for the grooves it is possible to make the transmittance maximum or minimum at a required frequency. Therefore by using the ring shaped grooves in the MIM waveguides a frequency splitter is designed. In comparison the efficiency of a MIM waveguide containing the ring shaped groove, on blocking the transmission of a required frequency, is higher than the efficiency of a MIM waveguide containing tooth shaped groove.

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To investigate the plasmonic effect in perovskite solar cells, the effect of depositing Au@SiO₂ nanoparticles on the top and the bottom of mesoporous TiO₂ layers was studied. First, Au@SiO₂ nanoparticles were synthesized. The particles were then deposited at the different interfaces of mesoporous TiO₂ layers. Although the two structures show approximately similar optical absorption, only cells with Au@SiO₂ nanoparticles deposited at the bottom of the mesoporous TiO₂ layers demonstrated an improved photocurrent performance compared to the reference cells. This structure shows a short-circuit current density (JSC) of 20.7 mA/cm² and open circuit voltage of 1081 mV. This enhancement may be attributed either to the interface surface engineering or plasmonic resonance of Au@SiO₂ nanoparticles depends to the NPs size and position.  

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In this article, the effect of plasmonic properties of metal nanoparticles with different shapes, and moreover, their plasmonic-photonic interaction, on solar cell performance were investigated and simulated. Because of low conversion efficiency and then high cost of solar cells, it is difficult to commercialize and replace them with conventional energy resources. But in recent years, the plasmonic solar cell has been very popular. In this study, it is shown that the enhancement of near-field electromagnetic waves severely affects the generation rate, which handles the carrier’s generation in the solar cell equations and causes alteration of the photocurrent. This means that by manipulating the plasmonic properties of nanoparticles (shape and density) and their interaction with photons in solar cell structure, distribution of electromagnetic fields will be altered. Hence, the optical power related to the poynting vector is changed. So, with the aim of improving the solar cell some important parameters such as alteration of nanoparticle shape and their inter-distance were investigated. Finally, a comparison between traditional solar cells and our improved structure was undertaken.

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In this paper, we perform a detailed study of the spectral response of the gold U-shaped nano-structures for different geometrical parameters and polarizations in order to obtain significant localization factor in the wavelength 1.55 μm. The obtained near-field distribution of electric fields reveals that resonances in these nano-structures correspond to the even and odd plasmonic modes depending on the geometrical parameters and polarization directions. Considerably large localization factor is obtained for the first odd mode in specific geometrical parameters. Then, this structure is considered to be surrounded by a typical second-order nonlinear dielectric. The effective susceptibility is calculated for the considered structure, using the nonlinear retrieval method, to demonstrate the enhanced second-harmonic generation quantitatively.   In order to represent the applicability of the investigated structure in nano-scale light sources and frequency doublers, its second harmonic generation efficiency is compared with the efficiency of the nonlinear dielectric alone with the same dimensions.

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in this work, some of the lattice plasmon quantum features are examined. Initially, the interaction of the far-field photonic mode and the nanoparticle plasmon mode is investigated. We probe the optical properties of the array plasmon that are dramatically affected by the array geometry. It is notable to mention that the original goal of this work is to examine the quantum feature of the array plasmon. For this reason, we consider a system containing array of the plasmonic nanoparticles and quantum dots. For a complete understanding, we analyze the system with the full quantum theory. Notably, the full quantum analyzing enables us to investigate the quantum fluctuation of the array field. Here, for instance, we study the second-order correlation function and report its modeling results.
 

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Compared to the long history of plasmonic gratings, there are only a few studies regarding the bandgap in the propagation of plasmonic surface waves. Considering the previous studies on interpretation of plasmonic bandgap formation, we discuss this phenomenon using the effect of both surface plasmon polariton (SPP) and localized surface plasmon (LSP) for our fabricated one-dimensional metallic-polymeric grating. This structure is composed of metallic grating on the surface of PDMS with different concentration of embedded gold nanoparticles. By sweeping the incident angles, we have seen that the SPP, LSP and their coupling cause two gaps in reflection regime which are originated from SPP supported by thin film gold film and LSP supported by gold nanoparticles. The first gap is attributed to the patterned metallic film because it vanishes by increasing the nanoparticles which may destroy the pattern while the second gap can be formed by embedded nanoparticles because it becomes more considerable by raising the incubation time. Therefore, the drowning time of patterned samples (e.g. 24h, 48h, and 72h) in HAuCl4 plays the key role in adjustability of plasmonic bandgap. Notably, the interaction between SPP and LSP can be the origin of the shift in gap center from 300 to 550. To best of over knowledge, this study is the first study on the plasmonic band gap as a function of both SPP and LSP.

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In this paper, we study the entanglement of two-level atoms near a spherical silver nanoparticle. By employing the Von Neumann equation and utilizing of the electromagnetic Green’s tensor associated with a dispersive and dissipative dielectric sphere, the decay rates and the Lamb shift of the atomic system are obtained. Then, by using the concurrence measure, we calculate the degree of entanglement of the atomic system. We observe that the decay rates severely increase near the excitation frequency of the localized plasmon-polariton, while the concurrence value is nearly zero.
 
 

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Silver nanowires are the favorable material in many applications based on their plasmonic double resonance in the visible region. In this paper, thin films of Poly-vinyl-pyrrolidone (PVP) doped with Silver nanowires (Ag NWs) in different concentrations have been prepared. The plasmonic imaging system using a high numerical aperture objective lens excite the Surface Plasmon in these structures. The hot spot results from reflected light intensity of surface plasmon resonance (SPR) proved that increasing of concentration of Silver nanowires yields to get better hot spot in plasmonic imaging systems by choosing the appropriate wavelength. These obtained results accompanying with third order nonlinear investigations show the ability of samples usage in thermoplasmonic applications.

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In hollow nanostructures, the inner and outer surface plasmons couple together that provides interesting plasmonic properties resulting in the enhancement of the plasmonic field. In addition, triangular structures are interesting for plasmonic applications due to their sharp corners and low symmetry. In this work, gold triangular nanostructures with triangular (TTN) and circular (CTN) holes in their centers have been simulated using the FDTD method and their plasmonic properties have been compared. The extinction spectra of the structures display that CTN has only one plasmonic peak, whereas TTN has several plasmonic modes due to its lower symmetry. Each peak presents different interactions between the multipoles that understand from the charge density distribution. Also, the figure of merit (FOM) of the peaks has been calculated and a high value of 33 is obtained for one of the TTN modes, which is appropriate for sensing application.

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In this paper, an all optical graphene-based modulation approach is proposed induced by Modulation Instability (MI). The device structure is based on graphene sheets transferred on the both arms of a Mach-Zehnder interferometer to support amplified Surface Plasmon Polaritons (SPPs). Due to the nonlinear nature of MI to interfere in the modulation process, the proposed approach leads to an enhanced performance in comparison to the conventional Mach-Zehnder modulators; using a low power cw driving beam (~20 µW at λ=50 µm), a high speed modulation rate (~2 Tpps) and subsequently, a high depth (89%), wideband modulation (~81 GHz) can be resulted. Since the MI is a pre-state to the chaotic regime, the modulator can be also used for secure optical communication.

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In this paper, we propose a D-shaped plasmonic optical biosensor based on photonic crystal fiber (PCF) to detecting of the different materials such as water, blood plasma, Yd-10B and hemoglobin by using of the refractive index. The gold layer is coated on the polished surface of D-shaped fiber. To achieve the highest sensitivity of the proposed biosensor, we investigated the effects of variation of the gold layer thickness and the other structure parameters such as hole diameter (d) and the distance between two holes or Pitch (L). The results show that the most sensitivity of the proposed biosensor is 2506 nm per refractive index unit (nm/RIU) with the resolution of 1.25×10^-5 RIU, when d=1.4 µm and Λ=1.9 µm with the gold layer thickness of 45nm.

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Two-dimensional nanomaterials have attracted increasing attention for enhancing surface plasmon resonance (SPR) biosensors application. In this work, we use the graphene layer to improve the sensitivity of the SPR biosensors based on the conventional Kretschmann configuration. We employ Tungsten disulfide (WS₂) and Molybdenum disulfide (MoS₂) Two-dimensional materials as an interlayer to enhance the sensitivity of Au/Graphene biosensor in angle interrogation method. The transfer matrix method (TMM) is used to analyze the characteristics of the device. Results show that using WS₂ in Au/Graphene structure increases sensitivity by about 12.64%, which is higher than MoS₂. Combining graphene based SPR and ellipsometry as a highly sensitive, label-free, real-time, and versatile method can be used to measure a very small concentration of biomolecules, which leads to 170-fold enhancement compared to angle interrogation method and improves the detection accuracy and quality factor.

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The absorption cross-section of gold and silver nanoparticles has been demonstrated in confined wavelength spectra based on Mie's theory. For this purpose, the numerical study performed with COMSOL for defined particle size to clarify absorption spectra and final results have been compared with experimental data to express the absorption peak occurs in higher wavelength for large particle size which is in around 530 nanometers for gold and 400 nanometer for silver particles.  These results show that particle size affects directly on absorption spectra of metallic nanoparticles.

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Recently, color production by using plasmonic structures has widely been studied. In this research, a flat and flexible two-dimensional Kapton-copper plasmonic crystal with very low thickness has been fabricated in a new and optimal way. Color production is performed using our proposed plasmonic structure and different colors are achieved by changing the incidence angle of light. Also, the plasmonic resonance response of the fabricated structure has been recorded at the incidence angle of 58 degrees. Advantages of our proposed structure are low cost, easy fabrication, and very small dimensions, and thus this research can be useful due to the increasing needs for the integration and miniaturizing of optical devices in modern nanophotonic systems.