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Graphene can be utilized in designing tunable photonic devices due to its unique properties such as high optical transparency and tunable conductivity. In this paper, a tunable triple-band perfect absorber is designed and numerically demonstrated, which is composed of a stacked graphene nanodisk, L-shape graphene layer and a gold ground plane spaced by insulator layers. The results show that there are three higher than 99% absorption peaks in the infrared range with a wide incident angle range up to 50°, and the absorber is insensitive for TE and TM polarized incident light. Moreover, the perfect absorption peak wavelength can be tuned by changing Fermi levels or geometric parameters of graphene layers. The findings above indicate that the designed perfect absorber can be used in the field of photodetectors, thermal emitters and photovoltaics.

This paper proposes a vanadium dioxide metamaterial-based tunable, polarization-independent coherent perfect absorber (CPA) in the terahertz frequency range. The designed CPA demonstrates intelligent reconfigurable switch modulation from an ultra-broadband absorber mode to a dual-band absorber mode via the thermally controlled of VO2. The mode of ultra-broadband absorber is realized when the conductivity of VO2 reaches 11850 S/m via controlling its temperature around T = 328 K. In this mode, the CPA demonstrates more than 90% absorption efficiency within the ultra-wide frequency band that extends from 0.1 THz to 10.8 THz. As the conductivity of VO2 reaches 2×105 S/m (T = 340 K), the CPA switches to a dual-band absorber mode where a relatively high absorption efficiency of 98% and 99.7% is detected at frequencies of 4.5 THz and 9.8 THz, respectively. Additionally, using phase modulation of the incident light, the proposed CPA can regulate the absorption efficiency, which can be intelligently controlled from perfect absorption to high pass-through transmission. Owing to the ability of the proposed CPA to intelligently control the performance of light, this study can contribute towards enhancing the performance of stealth devices, all-optical switches and coherent photodetectors.

A surface plasmon resonance-based biosensor, consisting prism, silver, barium titanate (BaTiO3) and graphene layers, is presented by using angular interrogation. The structure is specially designed to further enhance the sensitivity and to decrease the full width at half maximum (FWHM) thereby improving the sensor performance. Theoretical analysis shows that the highest sensitivity can reach at 257°/RIU where the thickness of Ag layer is 45 nm with 10 nm BaTiO3 and one graphene layer. Compared with existing biosensors, the proposed biosensor exhibits higher sensitivity, lower FWHM and two times better preformation in the quality factor of the sensor, which would make our design have more applications in the field of biosensors.

Graphene as a promising material for terahertz-infrared region plays an important role in nanoplasmonic devices owing to its tunability. We propose a hybrid graphene nanoplasmonic waveguide and analyze its propagation properties by finite element method. The results show that the light in terahertz-infrared region can be confined at low-index material and the fundamental mode can be tuned flexibly by changing Fermi energy level of graphene. Then an application of the designed waveguide, an electrically controllable directional coupler is designed and its performance is numerically verified. This approach can be extended to novel designs of nanoscale integrated photonic devices.

In this paper, we design a polarization-independent and angle-insensitive broadband THz graphene metamaterial absorber based on the surface plasmon-polaritons resonance. Full-wave simulation is conducted, and the results show that the designed metamaterial absorber has an absorption above 99% in the frequency range from 1.23 THz to 1.68 THz, which refers to a very high standard. Furthermore, the absorber has the properties of tunability, and the absorption can be nearly adjusted from 1% to 99% by varying the Fermi energy level of the graphene from 0 eV to 0.7 eV. In the simulation, when the incident angles of TE and TM waves change from 0° to 60°, the average absorption keeps greater than 80%. The proposed absorber shows promising performance, which has potential applications in developing graphene-based terahertz energy harvesting and thermal emission.

In this paper, a metal-dielectric metamaterial absorber is proposed to achieve ultrabroadband absorption at frequencies from ultraviolet to near-infrared. Based on finite element method solutions, the average absorption of the absorber is 97.75% from 382 nm to 1100 nm, with a maximum of 99.92%, resulting from multiple resonance coupling. The influences of geometric parameters and incident conditions on absorption are investigated. Broadband and narrowband absorption changes are realized by changing incident light polarization. Polarization-independent properties can be realized by changing the dielectric structure to centrosymmetric. The average absorption of the polarization-independent structure is 97.11% from 250 nm to 1115 nm, with a maximum of 99.98%. The proposed absorber structure has wide optical applications including solar energy harvesting and light-emitting devices.

One-dimensional metal-oxides (1D-MO) nanostructure has been regarded as one of the most promising candidates for high-performance photodetectors due to their outstanding electronic properties, low-cost and environmental stability. However, the current bottlenecks are high energy consumption and relatively low sensitivity. Here, Schottky junctions between nanotubes (NTs) and FTO were fabricated by electrospinning SnO

In this paper, tunable dual plasmon-induced transparency (PIT) is achieved by using a monolayer graphene metamaterial in the terahertz region, which consists of two graphene strips of different sizes and a graphene ring. As the dual PIT effect is induced by the destructive interference between the two quasi-dark modes and the bright mode, we propose a four-level plasmonic system based on the linearly coupled Lorentzian oscillators to explain the mechanism behind the dual PIT. It is proved that the theoretical results agree well with the simulation results. Most importantly, the sensing properties of the designed device have been investigated in detail and we found that it can exhibit high sensitivities and figure of merit (FOM). Furthermore, the dual PIT windows can be effectively modulated by changing the Fermi energy of the graphene layer and the angle of incidence. Thus, the proposed graphene-based metamaterial can hold wide applications for switches, modulators, and multi-band refractive index sensors in the terahertz region.

Focusing by the designed negative Luneburg lens which is based on graded annular photonic crystals (GAPCs) are studied in this paper. The GAPCs are composed of ring-shaped silicon pillars in a hexagonal lattice. The gradient of refractive index is achieved by modifying the radii of inner holes. The effective negative refractive index is analyzed based on the photonic band structures and verified by the simulation of negative refraction in APCs flat lens. Numerical simulation results show that a 0.6λ focusing spot can be realized by our designed Luneburg lens and it has the potential to be utilized in photonic integrated circuits.

Fano resonances have been studied intensely in the last decade, since it is an important way to decrease the resonance line width and enhance local electric field. However, achieving a Fano line-shape with both narrow line width and high spectral contrast ratio is still a challenge. In this paper, we theoretically predict the Fano resonance induced by the extinction of normal plane wave in a ring-shaped hexamer cluster at near-infrared wavelength. In order to obtain the narrow Fano line width and high spectral contrast ratio, the relationships between the Fano line-shape and the parameters of the nanostructure are analyzed in detail. The nanostructure is simulated by using commercial software based on finite element method. The simulation results show that when the structural parameters are optimized, the Fano line width can be narrowed down 0.028 eV with a contrast ratio of 86%, and the local electric field enhancement factor at the Fano resonance wavelength can reach to 36. Furthermore, the effective mode volume of the structure is 3.9 × 10 − 23 m 3 which is lower than the available literature. These results indicate many potential applications of the Fano resonance in multiwavelength surface-enhanced Raman scattering and biosensing.

We propose an all-dielectric metamaterial composed of bi-layered silicon structures orthogonally arranged on the sandwiched silica substrate, which exhibits giant dual-band asymmetric transmission of linearly polarized wave in the near-infrared regime, with one band working for the x-polarization and the other one for y-polarization. The dual-band AT phenomenon is explained by the distributions of electric field. In addition, the affection of the geometric parameters and incident angles to the AT parameters has been analyzed. Such an AT metamaterial has potential applications in polarization converters, switches and integrated photonic circuits.

We theoretically predict and numerically simulate the discrete plasmonic Talbot effect in dielectric graphene plasmonic waveguide (DGPW) arrays at THz wavelengths. The super-modes in DGPW arrays are analyzed by using super-mode theory and the field intensity distributions in the designed DGPW arrays are explained by the superposition of different super-modes and simulated by using commercial software (COMSOL) based on finite element method (FEM). The discrete plasmonic Talbot effect is realized by superposition of different super-modes. The Talbot distance can be actively tuned by varying the Fermi energy of graphene and it decreases monotonically with increasing Fermi energy. In addition, it is found that the Talbot distance increases with the period of the DGPW arrays. Simulation results show a good agreement with the theoretical analysis.

We theoretically predict self-imaging induced by multi-mode interference in multi-walled carbon nanotube arrays at visible wavelengths. To obtain propagation constants of guided modes and positions of self-imaging, the dispersion relation based on a dielectric function of frequency of the designed multi-walled carbon nanotube arrays is analyzed. The field distribution of self-imaging is performed by utilizing finite element modeling of wave propagation. The results show that single image and two-fold image are reproduced alternatively in constant intervals along the propagation direction. And the constant intervals or Talbot distances increase with the radius of carbon nanotube. Numerical simulation results agree well with theoretical expectations. The self-imaging effect in multi-walled carbon nanotube arrays may have potential applications at visible wavelengths in the integrated circuits or multi-walled carbon nanotube based imaging.

In this paper, we propose a tunable dual-band metamaterial absorber with wide-angle characteristics. The absorber is composed of a cross-shaped graphene layer and a layer of gold separated by a dielectric spacer. The simulated results show that there are two near-perfect absorption peaks in infrared band. Also, the peak wavelengths of absorber can be adjusted by changing the Fermi energy of the graphene and geometric parameters. In addition, the absorber can maintain a high absorption at a wide range of incident angles for both TE and TM waves. Such a device could be used as tunable sensors, filters, detector or other graphene-based photonic devices.

In this paper, a composite grating with nanogaps was designed to realize local field enhancement. The composite grating consists of a short and a long rod each period, which is seperated by a nanogap with two alternating metal width. And a small rectangle is dug in the middle of long rods. The simulation result shows that the local field can be greatly enhanced. This is because that the plasmonics resonance couple between each metal section occurs. And this nanostructure can be used in improving local field enhancement.

Recently, metal-transparent-metallic-oxides (MTMO) grayscale photomasks fabricated by laser direct writing technology have been widely considered for its advantages, such as a low cost system, simple preparation techniques, high resolution, and good photo-thermal stability. Compared with In-MTMO, Sn-MTMO grayscale photomasks are more stable and cheaper, but its oxide components are more complex. In this paper, we proposed a simple Sn/SnO x multilayer oxidation model to simulate the laser-induced oxidation processes of fabricating Sn-MTMO grayscale photomasks based on the laser-induced Cabrera-Mott oxidation theory. Simulation results are consistent with the experimental results. This work will pave the way to study the fabrication improvements of Sn-MTMO grayscale photomasks on resolution and efficiency.

Laser direct writing titanium dioxide (TiO2) nanostructured materials have been widely studied in recent years. Analysis of the kinetics of laser-induced titanium oxidation and an exploration of the key factors for improving resolution are meaningful. In this paper, we propose a simulation model of TiO2/Ti film to study the kinetics of the laser-induced titanium oxidation process. We compared the time-varying oxide thickness with temperature, and analyzed the oxidation degrees, maximum temperature, and the laser-induced Mott potential distribution along the radial direction for laser power changes from 2.8 mW to 3.4 mW. We found that the laser-induced Mott potential is the more crucial factor in the determination of the final oxidation degrees. An effective way to improve the laser machining resolution is to apply the threshold power and short-duration pulse laser irradiates on the film repetitively.

In this paper, composite nanoantenna arrays are simulative designed for energy harvesting in visible range. The composite nanoantenna on SiO2 substrate consists of staircase bowtie and rectangular nanoaperture. Due to the interaction among rectangular nanoaperture, staircase bowtie and different layers of the staircase bowtie, the designed nanoantenna exhibits an ultrahigh localized intensity enhancement. Results show that the maximum intensity enhancement reaches higher than 9 × 104 ( E e 2 ∕ E 0 2 ), and the composite nanoantenna can confine electric field distribution uniformly around the bowtie in z direction. When the incident wavelength varies from 660 nm to 760 nm, the intensity enhancement reaches more than 2 × 104 ( E e 2 ∕ E 0 2 ). The excellent dual-resonance enhancement performance of the composite nanoantenna makes it especially suitable for surface enhanced Raman scattering (SERS), the maximum enhancement factor of SERS can reach 2.2 × 109.

Based on the combination of generalized cylindrical vector beams and radial polarized beams, the designed three-zone pure phase filter, and interferences effect, we present a theoretical approach to generate optical bubble. Simulation results show that two small optical bubbles can be obtained with the designed optical system when objective lens with NA = 0.8. The optical bubble size defined by full width half maximum of the intensity is calculated to be λ . It can be used in microscopy techniques such as stimulated emission depletion microscopy.

A kind of polarization beam splitter with triangular lattice of multi-walled carbon nanotube arrays is designed and simulated. In the employed structure transverse-electric (TE) light is confined in the line defect with photonic band gap effect, while transverse-magnetic (TM) light is guided through it with extremely low diffraction. The performance of the designed polarization beam splitter is evaluated by utilizing optical properties of multi-walled carbon nanotubes, finite element modeling of wave propagation and transmission through periodic arrays. Simulation results indicate that the designed polarization beam splitter has low loss and less cross talk, and thereby may have practical applications in the integrated optical field.

A plasmonic metasurface structure consisting of periodically arranged bimolecular units is proposed to realize PIT effect in a way that differ from traditional ways. A high transmission window can be realized by utilizing phase coupling between sub-resonances of the designed bimolecular system. Phase coupling which is benefit from the intense and stable sub-resonances plays an important role in the generation of PIT effect. In the designed metasurface structure, influence of some components on transmission can be eliminated by destructive interference of the phase. The designed metasurfaces can be used in manufacture of optical devices at near infrared region, and general principle has potential applications in terahertz and microwave bands.

Plasmonic-induced transparency (PIT) in the metal-insulator-metal plasmonic waveguide with two side-coupled rectangular ring disk structures is numerically investigated. The PIT resonance occurs as a consequence of the destructive interference between the two structures. It is found that the transmittance can be easily adjusted by changing the parameters of the structure and coupling distance between the structure and waveguide. By optimizing the parameters, the transmittance of the structure can up to 75% in our discussion. These results may have important applications for designing integrated devices such as narrow-frequency optical filters, novel sensors and high-speed switches.

In this paper, we theoretically demonstrate a dual-band independently tunable absorber consisting of a stacked graphene nanodisk and graphene layer with nanohole structure, and a metal reflector spaced by insulator layers. This structure exhibits a dipole resonance mode in graphene nanodisks and a quadrupole resonance mode in the graphene layer with nanoholes, which results in the enhancement of absorption over a wide range of incident angles for both TE and TM polarizations. The peak absorption wavelength is analyzed in detail for different geometrical parameters and the Fermi energy levels of graphene. The results show that both peaks of the absorber can be tuned dynamically and simultaneously by varying the Fermi energy level of graphene nanodisks and graphene layer with nanoholes structure. In addition, one can also independently tune each resonant frequency by only changing the Fermi energy level of one graphene layer. Such a device could be used as a chemical sensor, detector or multi-band absorber.

In this paper, a novel metallic nanostructure consisting of two rings with different diameter is proposed to generate intense plasmonic Fano Resonances (FRs). In this nanostructure, the FRs is explained by the interference between spectrally overlapping narrow subradiant (dark) and broad superradiant (bright) plasmonic modes and is simulated by COMSOL Multiphysics based on Finite Element Method. The simulation shows that dipolar resonance only occurs in the small-diameter ring as a bright plasmon mode, other than the large-diameter ring. It can be found that the Fano resonance can be generated in a metallic nanostructure consisting of two rings with different diameter. Such structure will have many potential applications in the field of chemical and biological sensors in the future.

In this paper, we theoretically demonstrate a polarizing filter consisted of graphene ribbon arrays with varying width placed on the top surface of dielectric and a metal reflector rested at the bottom of the structure. It is found that proper ribbon width, which corresponds to resonant frequency of graphene plasmons, is a crucial factor that can significantly influence the absorption effect. The results of fullwave numerical simulations indicate that total absorption of more than 90% for TE polarization and approaching to 1% for TM polarization can be achieved at normal incidence in the infrared range. Therefore, this characteristic can be applied into polarizing filter by adjusting the coupling effect between the graphene ribbon arrays. Such structure will be beneficial to the manufacture of infrared nano-photonic devices for optical filtering and selective absorption.

In this paper, we proposed a perfect absorber composed of a periodic double-layer graphene ribbon arrays placed on a metallic reflector separated by a dielectric layer for infrared sensing. The anti-symmetric dipole-dipole coupling mode is excited as the impedance matchingCnar-rowband absorption spectrum. Numerical simulations show that the absorption and reflection properties of the absorber are sensitive to the refractive index of the surrounding medium. Furthermore, the plasmon resonance wavelength can be tuned by varying the Fermi energy level of graphene. Such a plas-monic absorber with high sensitivity can be beneficial for chemical and biosensor applications.

In this paper, a heterogeneous Au-Ag nanostructure consisting of a rod and concentric square ring-disk is pro-posed to generate intense plasmonic Fano resonances. And the Fano resonance in plasmonic nanostructures is produced by the coupling between broad bright mode and narrow dark mode, causing a Fano dip in the scattering spectrum. One of the main characteristic of the Fano dip is the line width which can be reduced to 0.0135 eV in this nanostructure, and the local electric field enhancement factor can reach 64, which enables its promising applications in biosensing, detecting and surface-enhanced Raman scattering.

With operating frequency f = 1thz, two-dimensional (2D) graded eye-shape scatterers were firstly applied into photonic crystal waveguide (PCW) for slow light effect in two ways: (1) selecting group index n g from 31.4 to 95.0, low-dispersion bandwidth ( n g varies within a 10% range) was got from 0.736 μm to 2.334 μm, and ultralow-dispersion bandwidth ( n g varies within a 1% range) was got from 0.438 μm to 0.945 μm by grading the eye-shape scatterers along the longitudinal direction; (2) selecting group index n g from 32.1 to 98.3, low-dispersion bandwidth was got from 0.559 μm to 1.765 μm, and ultralow-dispersion bandwidth was got from 0.296 μm to 0.661 μm by grading the eye-shape scatterers along the transverse direction. The 2D graded structures can also used in asymmetrical structures and heterostructures for slow light effect.

A novel and simple multi-wavelength band-pass filter based on metal-insular-metal (MIM) waveguide with different nanodisk cavity is proposed and investigated numerically by Finite-Element-Method (FEM) simulations. According to resonant theory of nanodisk, multi-wavelength band-pass filter can be achieved for different wavelength. It also shows that the transmission characteristics of the filter and the resonant wavelength can be easily manipulated by changing the gap between nanodisk and straight waveguide or changing the radius of the nanodisk. This kind of plasmonic waveguide filter may become important promising application in highly plasmonic integrated circuits.

An axisymmetric model of 50 nm titanium thin film on glass substrate is proposed to study the mechanism of pulsed-laser-induced oxidation of titanium. The oxidation rate is determined by the oxygen ions migration rate, which is significantly influenced by the laser-induced Mott potential and temperature. The oxidation processes are calculated by finite-difference time-domain method. The simulation results are in good agreement with experiment results, which verify that the laser-induced Cabrera-Mott oxidation theory is the mechanism of laser-induced oxidation of titanium. This work is beneficial to study the improvements for fabricating TiO 2 nanostructured materials on the resolution and efficiency.

In this study, a surface plasmon resonance (SPR) biosensor based on graphene–barium titanate nanocomposites is optimized by using an Ag–Au bimetallic configuration to achieve sensitivity enhancement. The angular interrogation method is used for the analysis of the reflectance from the sensor. By optimizing parameters, a sensitivity and figure of merit as high as 294°/RIU and 42.13 1/RIU can be obtained with Ag–Au bimetallic film at a wavelength of 633 nm. Compared with conventional SPR biosensors with a single metal film, the sensitivity of the proposed biosensor with Ag–Au bimetallic film can be greatly enhanced. Also, Au thin film can be used as a protective layer to prevent oxidation of the Ag layer.

A new reflecting polarizing beam splitter (RPBS), based on a metal–multilayer dielectric grating (MMDG), was designed using rigorous coupled wave analysis method and a genetic algorithm. The RPBS reflects the TE wave in the −1st order and TM wave in the 0th order for 800 nm. The optimized RPBS has an extinction ratio of over 20 dB, from 765 nm to 823 nm, and a large angle, from 43.8° to 60°. At 800 nm, the extinction ratios of the 0th and −1st orders reach a maximum of 41.0 dB and 53.2 dB, respectively. Furthermore, analysis suggests that the designed RPBS allows sufficient manufacture tolerance. These results show the potential of MMDGs in fabrication of a RPBS, which can be widely used in optical systems.

An optical system is proposed for the controlled focus shaping of generalized cylindrical vector beams by a high-numerical-aperture lens. A segmented electro-optical filter with four concentric belts is introduced and works with a double-λ/2-plate. By controlling the rotational angle of the plate and the voltage applied to the filter with proper azimuth angle, a three-dimensional engineered focusing field, such as an electrically controlled axial-shifted focus, extended depth of focus, and a diffraction-limited optical tube, can be achieved. The main advantage of this focusing system is that the focused field can be adjusted and formed by the applied voltage and the rotational angle of the half-wave plates. It can provide a new focus shaping technique with free adjustability and flexibility.

Eye-shaped scatterers are adopted into a photonic crystal waveguide (PCW) in two ways: (1) slow light with wide bands and group index ng from 14.1 to 32.8 can be generated by simply replacing the first and second rows of air holes adjacent to the linear defect with eye-shaped scatterer and (2) slow light with wide bands of ng from 36.5 to 287.5 are achieved by substituting all air holes with eye-shaped scatterers. More simulation results show that the latter method can achieve slow light with low dispersion at large ng, and near zero dispersion structures by adjusting the lattice parameter a and parameter e (e is inversely related to the ratio of the radius of the minor axis c to that of the major axis b).

A broadband and high efficiency metal–multilayer dielectric grating (MMDG), which was used to compress and stretch an ultra-short laser pulse in a chirped-pulse amplification (CPA) system, was designed. The diffraction characteristics of the MMDG were analyzed using the method of rigorous coupled wave analysis. The reflective mirror used for the broadband and high diffraction grating is made up of non-quarter wave metal–multi-layer dielectric coatings. Taking the diffraction efficiency of the −1 order as merit function, the parameters such as groove depth, residual thickness and reflective mirror were optimized to obtain broadband and high diffraction efficiency. The optimized MMDG shows an ultra-broadband working spectrum with an average efficiency exceeding 97% over 120 nm wavelength centered at 800 nm and TE polarization. The optimized MMDG should have potential application in CPA systems.

Reported in this paper is a new design of the quasi-achromatic phase-only superresolving pupil filters (QAPSFs) relatively independent of wavelength based on the zero order Bessel function of the first kind. The effect of design parameters of the new filters on the superresolving performance parameters such as the normalized spot size ( G ) and the Strehl ratio ( S ) is discussed and analyzed in detail. As an example, the performance parameters of QAPSFs made of optical quartz glass are simulated and compared with phase only pupil filters, which indicate that this kind of filters is less independent of wavelength in the range from 300 nm to 589 nm for superresolution, and a high Strehl ratio is also obtained. The equivalent performance parameters are derived to characterize the superresolution performance of the quasi-achromatic filter.

In this paper, super-resolution imaging and negative refraction by a two-dimensional (2D) triangular lattices graded photonic crystal (GPC) were studied. The graded photonic crystal (GPC) was obtained by varying the radius in each row so that its efiective refractive index changes along the transverse direction. By using Plane Wave Expansion (PWE) method and Finite-Difierence Time-Domain (FDTD) method, we show that negative refraction and superlensing can be realized in the designed graded photonic crystal. Numerical simulations show that the photonic crystal structures and frequency have an impact on the resolution.