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Two-dimensional materials have emerged as new type of smart materials that may impact advanced photonic devices. Here, to increase the light absorption, a black phosphorus-based nanostructure is proposed. The presented nanostructure has a grating-shaped structure based on monolayer/multilayer black phosphorus and silica. To access reasonable absorption, the structure is numerically simulated by the finite difference time domain (FDTD) method. To benchmark this nanostructure, the black phosphorus permittivity in the wavelength range of 5 to 15 μm was calculated, to achieve the transfer spectrum based on the lateral length changes of black phosphorus (i.e., L = 100, 150, 170 nm) and the silica substrate which is extracted from Palick experimental results; the proposed nanostructure is simulated using the FDTD method. Also, changes in the refractive index of the surroundings have been used to compute significant parameters in the nanosensors, such as sensitivity, FWHM, and FOM. The proposed nanostructure can be used in tunable absorbers in the range of infrared wavelengths.

We report a simple route to design highly sensitive triangular silver nanoplates (TSNPs)-based SERS substrate for the trace-level detection of explosive molecules. The size-dependent localized surface plasmon resonance (LSPR) tunability for the synthesis of TSNPs is achieved by controlling reaction kinetics and seed volume in a modified seed-mediated approach. The computed extinction spectra of TSNP, using the finite-difference time-domain (FDTD) method, are in excellent agreement with the experimental results, therefore assisting further in the investigation of the plasmonic properties of TSNP. The higher electric field enhancement offered by TSNP is systematically investigated by performing the FDTD simulations for various sizes and corner rounding of TSNP. The FDTD results show that the dipolar plasmon resonance wavelength, size, and corner rounding of TSNP are the principal contributing factors for designing the high-performance SERS substrate. Herein, we have used a portable Raman system for the SERS-based detection of three important explosive molecules: picric acid (PA), ammonium nitrate (AN), and 2, 4-dinitrotoluene (DNT). The TSNP-based SERS substrates display excellent intensity enhancement factors of ~ 107 for rhodamine 6G (R6G) and PA and ~ 105 for AN. The high sensitivity of SERS substrate with limit-of-detection (LOD) of value 2.3 × 10−11 M for PA and 3.1 × 10−8 M for AN and effective batch-to-batch reproducibility for DNT, thus offering its potentials for field detection of explosive molecules at trace-level.

This paper discusses modeling and optimizing the performance of hybrid plasmonic bidirectional coupler which is used as a basic building block in modeling high transmission efficiency of opto-electronic devices such as filter, wavelength division multiplexer, logic gates, and switching matrix with the help of an active material (indium tin oxide) that has an electrically adjustable permittivity. All the proposed devices satisfied high transmission efficiencies at the desired output ports over a suitable wavelength range. The realized structures are characterized and simulated by 3D finite-difference time-domain (FDTD). The components would be useful in the optical interconnection networks, photonic integrated circuits, and signal processing system.

The steering of guided light in surface plasmon resonance (SPR) sensing platforms introduced more than eight decades ago from the first proposed optical sensor in 1983. However, sensing the environmental variation considering transverse modes is still require the attention from the scientist. Here, for the first time, by considering steering of guided light a high-performance SPR sensor base on Otto structure is proposed. By incorporating the graphene and white graphene in to a prism-waveguide configuration, we calculated the excitation of both TE(TM) modes as refractive index is changed from 1 to 1.04. to analysis of the structure finite-difference time-domain (FDTD) is applied. To benchmark of the structure performance parameters including sensitivity, figure of merit, polarization extinction ratio (PER), and insertion loss (IL) are calculated. Numerical results show that maximum sensitivity and figure of merit are obtained for TM modes of 1226 and 27 respectively. In such a case, graphene monolayer is applied. By considering coupling condition, at the μc = 0.4 eV, the maximum value of PER is 75 dB, and IL is 0.022 dB. Moreover, it is obtained that in all these conditions PER is higher than 8 dB, and IL is less than 0.04 dB.

In this paper, a plasmonic perfect absorber based on metal-insulator-graphene-metal structure is proposed as a tunable sensor. The absorption spectrum of this absorber is calculated using the 3D finite difference time domain (FDTD) numerical method for perpendicular incidence of a plane wave light within the 25–65-µm wavelength range. According to the simulation results, a resonance peak is observed in the output absorption spectrum of the device, which is significantly blue-shifted by applying a gate bias voltage to the graphene nano-strips in the structure and increasing the chemical potential of graphene from 150 to 300 meV with 50-meV steps. In another step, in order to investigate the sensing capability, analytes with different refractive indices are poured on the upper surface of the structure, in which the resonance peak is red-shifted with increasing refractive index of the analyte. The sensitivity of this resonance peak is obtained from the relation of S = Δλ/Δn equal to 10,400 nm/RIU, which indicates the excellent ability of the device to detect analytes with a low refractive index difference.

We propose a robust equivalent circuit model for the accurate prediction of magnetic polariton (MP) resonances in SiC grooves. By considering the boundary effects and introducing a parasitic capacitance, the analytical results of the structural-dependent MP resonances are in good agreements with the numerical results calculated by finite difference time domain (FDTD) method. With the model, we further propose a MP absorber with a broad bandwidth successfully. We believe this robust circuit model offers us opportunities in the design of novel applications based on MPs such as filters, detectors, and coherent sources in the infrared fields.

The temperature sensors are remarkably required for highly sensitive temperature monitoring in advanced applications including nanobiosensing, healthcare, disease diagnosis, and so on. Therefore, this paper presents a fiber Bragg gating (FBG)–based sensor designed for demanding novel applications, such as temperature measurements in biotechnology. We propose a highly sensitive temperature sensor in the near-infrared range made from germanium-doped silica core optical fiber, which provides high-performance properties. To evaluate the structure, several practical parameters are considered including environmental temperature variations. The structure first is numerically simulated by the finite difference time domain method. Then, by using the PSO algorithm, appropriated results are obtained. Finally, a fabricated structure is presented. It is demonstrated that the sensitivity of the transmitted light can be tuned through temperature variations of FBG. Moreover, the effects of alteration of FBG period on the sensitivity have been analyzed. Results show that the sensitivity of the proposed temperature sensor can be controlled by tuning the temperature. In the optimum design of the proposed FBG-based temperature sensor, the maximum value of sensitivity is achieved as high as S = 717 1/°C as temperature change from 0 to 140 °C. This work may have significant prospects in tunable, highly sensitive temperature sensors in optical biotechnology.

Digital encoders are one of the key devices required in optical communication and digital signal processing systems. In this paper, a new photonic crystal structure is used to design all optical 4x2 encoder constructed from GaAs rods with square lattice in the pentane bachground based on plasmonic effect. Gold rods have also been used at the interface of dielectric rods and lines defect, which create plasmonic properties into the photonic crystal structure. The designed optical device is composed of four input waveguides and two output waveguides with two ring resonators at the resonant wavelength of 1.4mm with TM polarization. The presented encoder platform has the small size of 19 mm ×33 mm, that makes it to integration into all optical communication systems. The encoder operation is simulated and analyzed with numerical Finite Difference Time Domain (FDTD) method hand Plane Wave Expansion (PWE) method. In the proposed structure, we have shown that by selecting the appropriate radius size for the resonant cavities, the desirable wavelength can be obtained. The maximum values of transmission efficiency for the first and second outputs are 82% and 96%, respectively. Resonant cavities are also located in the crystal lattice in such a way that by activating third input, 50% and 48% of the input signal will be obtained in each output ports indicating (1,1) logic state. So the new plasmonic photonic crystal encoder could be future applicable in the field of optical computing.

In this paper, a structure based on metal-graphene-insulator–metal (MGIM) is designed as a tunable plasmonic perfect absorber (PPA) in the FIR-band range. Simulation results performed with the 3D finite difference time domain (FDTD) method show that in the perpendicular incidence of a plane wave light in the range of 35 to 105 µm, the absorption spectrum of the proposed device has a resonance peak with absorption above 95%, which can show excellent tunability by applying a gate bias voltage to the graphene nanolayers in the structure. In our proposed structure unit cell, there is a C1 graphene nanolayer in the center and a C2 graphene nanolayer around it that bias voltage is applied only to C2, then changing the chemical potential of the two graphene nanolayers relative to each other, the absorption spectrum of the device shifts in the desired wavelength range.

Noble metals, especially Ag and Au nanostructures, have unique and adjustable optical attributes in terms of surface plasmon resonance. In this research, the effect of Ag and Au nanoparticles with spherical and rod shapes on the light extraction efficiency and the FWHM of OLED structures was investigated using the finite difference time domain (FDTD) method. The simulation results displayed that by changing the shape and size of Ag and Au nanostructures, the emission wavelength can be adjusted, and the FWHM can be reduced. The presence of Ag and Au nanoparticles in the OLEDs showed a blue and red shift of the emission wavelength, respectively. Also, the Ag and Au nanorods caused a significant reduction in the FWHM and a shift to the longer wavelengths in the structures. The structures containing Ag nanorods showed the narrowest FWHM and longer emission wavelength than the other structures.

A multifunction plasmonic metasurface made of metal-dielectric-metal (MDM) layers is designed, and its chiral, absorption, and refractive index sensing properties are studied numerically using finite difference time domain (FDTD) computation. Top layer of the proposed novel metasurface consists of four L-shape gold strips arranged in a specific orientational sequence into a square unit cell whose period (along X direction and Y direction) is varied from 800 to 1400 nm in a step of 200 nm. The proposed super-structure shows highly chiral behaviour with multi bands circular dichroism (CD) between ~ 600 and 1200 nm with highest CD value of about 0.4. The CD spectral response is seen to be tunable with the structural parameters such as periods and appropriate L-strip length. True chiral nature of the proposed structure is cross-checked by computing its enantiomer that shows a mirror reflection of CD response of the original structure. Multi-work functionalities are investigated by studying perfect absorption and refractive index sensing properties of the metasurface. The study shows polarization independent multi-resonance spectral absorption that reaches to ~ 100% in some cases. On the other hand, refractive index sensing study shows high sensitivity (S) of 700–750 nm/RIU (per refractive index unit) with figure of merit (FOM) of 5–10. Owing to its exotic optical properties, the novel metasurface may be considered for chip level integration for multi-purpose work functionalities.

In the few past years, the economic and eco-friendly Cu2ZnSnS4 (CZTS) solar cells have caught lots of attentions. However, due to rather poor efficiency, identifying deficiencies and making improvements is necessary. In the present study, the performance improvement of ultrathin CZTS solar cells was achieved through (1) incorporation of anti-reflective coating (ARC) on the surface of cell and (2) embedding Al plasmonic nanostructures with different radius, periods, and vertical positions in the absorber layer. Various thicknesses of CZTS absorber layer were simulated optically and electrically using FDTD and DEVICE solver of Lumerical software. The reference solar cell consists of a 1.5-nm-thick CZTS absorber and exhibit an efficiency of up to 5.67%, short-circuit current density (Jsc) of 18.48 mA cm−2 and open circuit voltage of 0.58 V. Result showed a remarkable performance enhancement of the solar cell in spite of a very thin absorber layer. For a 500-μm-thick CZTS solar cell with the assistance of ARC and embedding Al plasmonic nanostructures, the efficiency is increased to 7.45% due to an increase in Jsc to 22.62 mA cm−2 with an open circuit voltage of 0.62 V.

Surface-enhanced Raman scattering (SERS) is a very promising detection/diagnostic technique at trace levels as the molecules exhibit a significant increase in their Raman signals when they are attached or are in proximity to plasmonic structures. In this study, a numerical design of SERS substrate as a probe has been demonstrated for detection and diagnosis of blood, water and urea samples. The proposed nanospiral design is polarization independent, and it offers the enhancement of the electric field strength ~ 109. The substrate design is based on 3D finite difference time domain simulations and is robust, versatile and sensitive even at low concentrations of the analyte. It works equally well when used in the reflection mode. In this study, the cavity quantum electrodynamics (CQED) Purcell factor has also been transposed to plasmonics. The Purcell factor in corroboration with CQED has been used to achieve efficient light–matter interaction at nanoscale by providing a more realistic result. It takes into account the randomness of incident wave polarizations and arbitrary orientations of interacting molecules. This gives a deeper insight into electromagnetic Raman gain in SERS and can be used to design novel SERS substrates.

In this manuscript, a plasmonic refractive index sensor with two sequential ring resonators is presented. Due to the dual-band unidirectional reflectionless light propagation phenomena, both the sensitivity and figure of merit are improved. The finite-difference time-domain (FDTD) method is used to simulate the structure numerically. Moreover, the device is investigated analytically, using the coupled-mode theory (CMT). A good agreement between the analytical and numerical results is observed. The proposed device indicates a high sensitivity of ∼1000 nm/RIU, a significant figure of merit of 133 RIU−1, and a large quality factor of 132.8 for sensing different materials with the refractive indices of n = 1, 1.2, 1.3, 1.4, 1.5, and 1.6. Also, the presented structure is investigated as a temperature sensor in which the sensitivity to the temperature changes is obtained as 0.41 nm/°C.

Tunable local surface plasmon resonance (LSPR) enhancement properties of cavity-nanoparticle scaffold-based clusters were investigated via finite-difference time-domain (FDTD) simulations. Hollow Au-cylinder-based and hollow Au-sphere-based nanocomposites models were presented with calculated optical spectra, near-field distribution, and average enhancement. Focusing on surface curvature, concave and convex Au-surface/Au-nanoparticles were built for further understanding on the local shape dependency in complicate scaffold-based clusters. Tunable near-field enhancement contributions and scaffold-dependency were discussed for potential in plasmonic applications such as surface-enhanced Raman spectroscopy (SERS), LSPR sensor, and nanoantenna.

Titanium nitride (TiN) metadevices as perfect absorbers are studied using finite-difference time-domain (FDTD) simulations. In this paper, we demonstrate a metastructure including a top silica (SiO2) layer, two layers of TiN nano-ribbon arrays, a SiO2 dielectric layer, and a TiN film to realize efficient solar energy harvesting. We theoretically optimize the geometrical parameters of each active layer to achieve high absorption rates with an average value of up to 95% within an ultra-wide band from 0.4 to 1.8 microns, covering over 93% of total energy in the solar spectrum. Our detailed analysis of the electric field enhancement indicates that such ultra-broadband high absorption in the visible/near-infrared ranges can be attributed to surface plasmon resonances, Fabry-Perot resonances, and strong plasmon hybridization between adjacent TiN nano-ribbons. Together with refractory properties of TiN and SiO2, the designed metadevice may exhibit great potential in efficient solar energy harvesting applications, particularly in harsh environments.

The photoconductivity antenna is a promising technology to generate THz wave. However, the technology is problematic in THz low antenna gain. The improvement of efficiency and directive is very important to the photoconductivity antenna. Here, a super directivity THz photoconductivity antenna (PCA) is proposed. The antenna uses the dielectric resonator to enhance the directivity which yields the super directivity in radiation. The eigen mode analysis is performed to the super directivity antenna, which is used to help design the antenna and understand the mechanism for the super directivity. The spherical cap is used as the dielectric resonate antenna (DRA), and the relationship between the radius of sphere and the height of cap and super directivity is surveyed. The dielectric cap height and sphere radius are found both playing an important role in enhancing the directivity of the antenna. To validate the proposed design, a THz photoconductivity antenna is designed. The simulations are performed using FDTD and FEM method. Both results show that the designed THz antenna has the super directivity value above 9.0 at 2.0 THz.

Resonances in micrometer metal cavity structures are very important for the interactions between materials and light. Three similar cavities connected with waveguides are investigated through the finite difference time domain (FDTD) method and the coupled mode theory. Two fundamental surface resonance modes are demonstrated in the two simple cavities separately. Then two simple cavities are combined to form the third cavity. The fundamental resonant modes couple positively or oppositely to form coupled-mode resonances in the combined cavity. When the combined cavity structures are symmetric, the coupled-mode resonances lead to two transmission peaks. While the symmetry is broken with tens of nanometers displacements, the transmission peaks convert to dips. It is believed the Q value variation of coupled-mode resonances plays a key role in the conversion. When the structure is symmetric, the coupled-mode resonances in the upper and lower parts of the cavity have the same Q value and are degenerate. The superposition of them leads transmission peaks. While the symmetry is broken, the Q values of resonances in the upper and lower part of the cavity are different, leading to the degenerate coupled mode division. The superposition of the different Q-factor modes leads to the dips. The sensitive variation to the symmetry of structures can be used to control light-material interactions, optical switch, and improve the sensitivity of sensor devices.

Plasmon-induced transparency (PIT) is a spotlight technique for environmental monitoring. In this regard, a highly sensitive and tunable multilayer sensor including Ag–SiO2–Ag is presented in near-infrared range for both transverse mode (TE) and transverse mode (TM) modes at different incident waves. Actually, the proposed multilayer plasmonic sensor is presented to study the optical and sensing properties at near-infrared frequencies based on 3D finite-difference time-domain (FDTD). Sensitivity and tunability of all optical sensors are important parameters in their design, which are calculated based on propagation properties including absorption and reflection spectra, numerically and analytically. Results of absorption and reflection show that the proposed sensor has max sensitivity of 693.8 nm/RIU by Δn = 0.05 changing of middle refractive index and figure of merit (FoM) equal to 9.8. Also, the proposed nano-scale sensor can operate as a light propagation controlling with slow and fast light and multispectral sensor. By using silver metal in the sensor structure, the fast and slow light coefficient is obtained at 220 and 70, respectively. In addition, by increasing the incident angle of light, multiabsorption peaks are created which can be used as multiwindow sensor and PIT. The analytical results are in good agreement with the obtained results of coupled mode theory (CMT) method.

The wedge angle-dependent propagation characteristics of two coupled semi-infinite Au rib nanoplasmonic waveguides are investigated using the three-dimensional finite-difference time-domain (3D FDTD) method with the fast Fourier transform and curve fitting techniques. The simulation results show that the propagation loss and modal index of the fundamental mode are closely related to the field distribution of the supermode which can be manipulated by varying the wedge angle from 75° to 100°. Understanding of the nanostructure-induced enhancement of the propagation characteristics of nanoplasmonic waveguides helps us find the best way to optimize the metallic waveguiding structures.

Plasmonic pressure sensors play a major role in advanced applications due to their unique properties including their small footprint and high sensitivity. The design of sensors with a wide pressure range and high sensitivity, especially at low pressure (0–5 KPa), is in high demand. To this end, here, a tunable, ultra-sensitive and wide-range plasmonic pressure sensor based on nanostructure gratings is proposed. We present a numerical method for designing a pressure sensor based on surface plasmon resonance (SPR) that can adjust the coupling state by varying the surface of the metal grating. The design is based on grating coupling changes according to the pressure applied. We used grating coupling for phase matching between light and surface plasmon polaritons (SPP). The light reflection output from the grating surface is proportional to the input pressure, where we illustrate that the SPR pairing state can be controlled by varying the grating pitch by changes in pressure applied to the diaphragm. In our numerical simulation, we consider solid deformation and transmission or reflection of light using the finite-difference time-domain (FDTD) and finite element method (FEM) to simulate the optical and mechanical properties, respectively. The many advantages of the proposed sensor include nanoscale, integrability, tunability, low power, low cost and wide pressure range. This sensor is capable of detecting pressure in the range of 0–1 kPa.

In this paper, a novel nanoscale refractive index sensor topology, which incorporates a ring resonator containing circular tapered defects coupled to a metal-insulator-metal (MIM) plasmonic waveguide with tapered defects, is proposed. For the proposed design, the effect of introduction of defects on transmittance value, shape of magnetic field, and sensor parameters such as sensitivity (S) and figure of merit (FOM) are investigated numerically and simulated using finite-difference time-domain (FDTD) method. By optimizing the ring radius and selecting the appropriate waveguide width, we have achieved a maximum sensitivity of 1295 nm per refractive index unit (RIU) and a fairly high FOM equal to 159.6 RIU−1. The structure can be used as a high accuracy refractive index sensor for refractive indices ranging from 1 to 1.65. Due to the small size, wide detection range, and the high detection resolution of the proposed sensor, it is a good choice for integrated bio-sensing applications.

Highly lossy nature of metals has severely limited the scope of practical applications of plasmonics. The conventional approach to circumvent this limitation has been to search for new materials with more favorable dielectric properties (e.g., reduced loss), or to incorporate gain media to overcome the inherent loss. In this study, however, we turn our attention to the source and show that the wealth of new SPP modes with simultaneous complex frequencies and complex wave vectors that are otherwise unreachable can be excited by imposing temporal decay on the excitation. Therefore, to understand the possible implications of these new modes and how to be able to tune them for specific applications, we propose a framework of pseudo-monochromatic modes that are generated by introducing exponential decays into otherwise monochromatic sources. Within this framework, the dispersion relation of complex SPPs is re-evaluated and cast to be a surface rather than a curve, depicting all possible ω − k pairs (both complex in general) that are supported by the given geometry. To demonstrate the potentials of the complex modes and the use of the framework to study them selectively, we have chosen two important, and somewhat limiting, features of SPPs to investigate; resolution in plasmonic lenses and propagation length in SPP waveguides. While the former is mainly used to validate the proposed method and the framework on the recent improvement of resolution in plasmonic superlenses, the latter provides a novel approach to extend the propagation length of the SPP modes in planar waveguides significantly. Since the improvement in propagation length due to the introduction of temporal decay to the excitation is rather counter-intuitive, the dispersion-based theoretical predictions (the proposed approach) have been validated via the FDTD simulations of Maxwell’s equations in the same geometry without any a priori assumptions on the frequency or the wave vector.

This paper produces a more compact and efficient design for hybrid plasmonic 2 × 2 electro-optic routing switch, with aid of an active material that has an electrically tunable permittivity, and discusses its ability for realizing more advanced structures. The proposed 2 × 2 electro-optic switch, with foot print of 11.6 μm2 and switching time of 0.949 pS, satisfies transmission values (coupling efficiency) less than 7% at OFF state and greater than 75% at ON state at the telecommunication wavelength. This design is used as a base unit to realize two advanced structures: (a) the 3 × 3 switching matrix, with a foot print of 47–49 μm2, which satisfies transmission greater than 60% at ON states and transmission less than 10% at OFF states, and (b) the 4 × 4 switching matrix, with a foot print of 88 μm2, which satisfies transmission greater than 70% at ON states and transmission less than 5% at OFF states. The obtained results have a validation with older researches. A 3D finite-difference time-domain (FDTD) solver is employed to simulate and characterize the realized structures. The components would be useful in the optical interconnect networks, photonic integrated circuits, and signal processing system.

In this paper, for improving the refractive index sensitivity, we propose different sensor devices by optical metamaterial nanoabsorbers. The presented absorbers are designed by different configurations such as basic model, nanorods, and nanotube array. With three-dimensional finite difference time domain (FDTD) method, their absorption, transmission, and reflection spectra, and sensitivity and figure of merit (FOM) values are numerically investigated. The simulation results show that the resonances at longer wavelengths have higher values of sensitivity and FOM. For presenting the applicability, we examine the sensor for detecting cancerous cells. The proposed absorbers have been coated with an outer material with a thickness of 100 nm and refractive indices of 1 ⁓ 1.2. The maximum sensitivity is obtained at 1055 nm/RIU for the absorber with nanotube array, while its FOM is 19.5 RIU−1. Due to its spectral characteristics, the proposed structures can be used to detect other materials such as human blood group, ethanol, and hemoglobin concentrations of some materials.

Surface plasmon polariton (SPP) Airy beams are very attractive in theory and applications. We propose a new method to design dielectric relief holographical structures for controlling the SPP wave propagations and generating SPP Airy beams on metal surface. In the dielectric relief holography (DRH) method, both phase and amplitude are considered. The thickness of designed dielelctric films is proportional to the intensity of SPPs interference in holography. The films designed by the DRH method are coated on metal surface and can control SPPs propagation effectively. The complicated Airy beams can also be generated through the films designed by the method. The finite difference time domain (FDTD) method is used to test the functionalities of the designed structures and find the optimal parameters. The structures designed by the DRH method can be manufactured with traditional die or corroding methods. The investigation on the method extends SPP device manufacture methods, and therefore may open up the possibility for mass industrial manufacture of plasmonic devices.

In this paper, a wavelength demultiplexing structure based on multi-teeth-shaped metal-insulator-metal (MIM) plasmonic waveguide is designed and numerically studied using the finite-difference time-domain (FDTD) method. Investigating the characteristics of a multi-teeth-shaped plasmonic waveguide structure reveals that with the design of the structure, it was possible to create a mode inside the bandgap of the filter. Based on the created mode inside the bandgap of the filter, the demultiplexer structure has been proposed and investigated. By changing the geometric parameters of the structure, the transmission wavelength of the demultiplexer channel can be adjusted. The proposed demultiplexer can be used in integrated optical circuits.

In this paper, a novel technique for realization of all-optical plasmonic switches is presented. The proposed structure is based on an asymmetric metal-insulator-metal plasmonic directional coupler. A Bragg grating is used on one of the directional coupler’s adjacent waveguides while the other remains intact. Such a modification results in dissimilar input-output transmission spectrums for each of the two input ports. The Bragg grating creates a bandgap region in one of the signal paths while the other path has no bandgap. The directional coupler is filled with a dielectric with high Kerr-type nonlinearity. One of the input ports is used for the data signal and the other port for the control (pump) signal. When the pump signal is present, a small modification in the refractive index of the Kerr material occurs which slightly changes the bandgap region. The input signal’s wavelength is chosen at the bandgap edge so that it can only pass through the structure when the control signal is present. The structure proposed in this paper is numerically simulated using finite difference time domain method. Silver and Ag/BaO composite are used as the metal and dielectric materials. Since the proposed topology incorporates two different input ports for the control and data signals, it has the potential to be used in complex-integrated optical circuits.

In this paper, a novel surface plasmon polariton (SPP) based all-optical 1× 2 demultiplexer, which is based on a modified Y-branch structure and a controllable switching module, is presented. In the modified Y-branch structure, which acts as an ideal wide-band splitter, the width of the branches are chosen as one half the input waveguide. The switching module is constructed using two nano-plasmonic racetrack-shaped disk resonators which are side coupled to the branches of the Y-branch structure. It has been shown that using a pump light power, the transmissions of the input signal into the output ports can be controlled. The simulation results are based on the two dimensional finite-difference time-domain (2D FDTD) method. In the proposed device, the “on” state transmission coefficients and the extinction ratios (measured at the output ports), for the pump light source with the wavelength of 660 nm and the intensity of 1.75 MW/cm2, are about 0.74 and 28.75 dB, respectively. Furthermore, in this case, the switching times of the proposed device, measured at the port 1 and port 2, are about 100 fs and 180 fs, respectively. It is expected that the proposed device can find applications in all-optical signal processing.

Tunable triple-peaks with the transmission intensity of more than 90% plasmonically induced transparency metamaterial resonator based on nested double π-shaped metallic structure is proposed at the terahertz frequency region, which is consisted of three sets of gold nanorods with different sizes placed on a dielectric substrate of SiO2. The coupling effect of localized electric field between different parts of the proposed structure can be used to explain the physical mechanism of three transparent windows. The finite-difference time-domain (FDTD) is used to study the spectral properties of the proposed structure, and the influence of the size of the nanorods and the relative distance between them on the spectral characteristics are also discussed. It can be seen that some obvious shift phenomena occur in the spectra with the change of these nanorods. These results indicate that the proposed structure opens up new avenues in many related applications, especially for multi-channel filters, optical switches, and sensors.

In this paper, we propose an ultra-broadband multi-slot cross bowtie (MSCB) nanoantenna for light absorption, whose elements compose of dual rectangles and cross bowtie and rectangular slots. The optical characteristics are analysis numerically by the three-dimensional finite-difference time-domain (FDTD) method. The results show that the average absorptivity of the nanostructure is over 90% in 400–1800-nm waveband, which covered the visible and near-infrared region. We attribute the better absorption property of the nanoantenna to the combining of plasmon coupling effects between slots, high-order modes, and surface plasmon resonance. Our work provides a promising method for the future developments of more advanced absorber for energy harvesting, thermoelectrics, and imaging.

Recently, many researches are reported on using germanium in silicon-based lasers but acquiring this potential for a plasmonic nanolaser may also be important for development of silicon-compatible plasmon sources. In this paper, a custom-shaped nanocavity plasmon source based on highly doped tensile-strained germanium/silicon-germanium multiple quantum well gain medium is introduced and theoretically investigated. We have used a semi-classical macroscopic rate equation model for calculation of the output performance characteristics. Also, modal analysis has been done based on FDTD method. The proposed nanolaser has a tiny footprint of 0.1225 μm2, possible room temperature performance, and fabrication process based on a silicon substrate. The output performance of the nanolaser structure as estimated is noticeable and the calculated results, using some previously reported experimental data and redundant software double checking, show acceptable compatibility. In 1550-nm output wavelength, it provides 15.6 mW output power in the 21-mA threshold current and 600 μW in 1-mA pump current, while maintaining its performance in a wide spectral bandwidth about 2 THz. It also can be electrically modulated by the pump current up to 3 GHz. This remarkable performance is achieved, thanks to the high Purcell factor of the parabolically notched nanocavity of about 700 and its high quality factor of about 58.

In this paper, we present a computational method to investigate optical properties of materials using a combination of density functional theory (DFT) calculations and finite-difference time-domain (FDTD) method. We show our method in the framework of an example for analyzing the effect of Au doping on optical transmission behavior of TiN compounds with a given geometry. First, DFT is employed based on generalized gradient approximation (GGA) exchange-correlation potential to investigate the electronic properties as well as dielectric function of TiN with respect to different percentages of doped Au. Our results reveal a growth in the imaginary part of dielectric function for energies below 4 eV by increasing Au doping level due to compression of Ti1−xAuxN DOS into the Fermi energy. In order to clarify the impact of Au doping on the optical behavior of Ti1−xAuxN with a given geometry, the optical dielectric function calculated from DFT was used as an input data for FDTD method to simulate a perforated surface plasmon system originated from Ti1−xAuxN-dielectric configuration via Optiwave package. It is observed that an increase in the Au level decreases the transmission intensity of excited modes of the perforated surface plasmon system, which is in agreement with the observed behavior for the imaginary part of dielectric function from DFT calculations. This implies that an enhanced imaginary part of dielectric function leads to more energy dissipation and finally less transmitted wave. The proposed method enables us to simulate optical properties of a wide range of compounds with arbitrary geometries and material-specific properties.

The improvement of excitation efficiency from free space to the longitudinal propagating plasmonic-guided wave attracts growing researchers’ interests recently. In this work, a coupling structure composed of counterpart coaxial split ring resonators and a plasmonic stripe waveguide was proposed to investigate the characteristics of the plasmonic waveguide mode excitation by using finite-difference time-domain (FDTD) method. Results showed that an extremely wide spectrum bandwidth about 930 nm which covered the communication region from 1070 nm to 2 μm was achieved and the excitation efficiencies at resonant wavelengths of 1235 nm and 1636 nm reached 36.1% and 24.5%, respectively. And the coupling wavelength can be modulated by rotating the outer split ring. Our research provides potential applications for next-generation plasmonic integrated chips and functional devices.

We theoretically present the nanofocusing of the metal-coated fiber tip under internal excitation of the radial vector beam within visible band based on the finite difference time domain (FDTD) analysis. The electric field intensity enhancement factor of the localized surface plasmons (LSP) mode at the tip apex is quantitatively shown in relation with incident wavelength, coating material, conical angle of tip, and coating film thickness/length. Specially, the evolution of fiber radial vector mode to surface mode with respect to the radius of metal-coated fiber tip is calculated under typical excitation wavelengths of 633 nm and 785 nm. Furthermore, the reason of the tip eliminating far-field background signal is explained, and the transverse electric field distributions of LSP mode and the tip-substrate coupling are also given at the optimal excitation wavelength. These calculation results will be a good reference for the fabrication of metal-coated fiber tips and for the experimental design of the tip-enhanced spectroscopy (TES) system.

In this paper, a high-resolution refractive index sensor is proposed based on a novel metal–insulator–metal plasmonic topology. The structure is based on a Si nano-ring located inside a circular cavity. It acts as an optical notch filter with a quality factor equal to 269. The proposed filter topology is numerically simulated using the finite difference time domain method. It is shown that the proposed filter can also act as a refractive index sensor with a sensitivity of 636 nm/RIU and a fairly high figure of merit (FoM) equal to 211.3 RIU−1. It is shown that the sensor can easily detect a refractive index change of ± 0.001 for dielectrics whose refractive index is between 1 and 1.2. For the refractive index range of 1.33 to 1.52, the maximum FoM of the sensor is 191 RIU−1. The simplicity of the design and its high resolution are the two main features of the proposed sensor which make it a good candidate for biomedical applications.

In this paper, the farfield under small scattering angle was investigated in the rectangular Ag–Si–SiO2 cavity by FDTD. The simulation results showed that Re(E) of the farfield was related to the monitoring wavelength and was a function of monitoring wavelengths. Moreover, in the rectangular Ag–Si–SiO2 cavity, the amplitude of Re(E) changed as the silicon height d varied, and maximum amplitude A of Re(E) could be approximated as the functions of transverse length l and thickness t of silver film under small scattering angle. Re(E) was independent of the transverse length w2 and the longitudinal length d of the cavity in RCM and was also irrelevant with the dielectric constant of silver films. The amplitude A of Re(E) increased as l and t of silver film increased.