Narrow Results

We proposed a novel two-dimensional (2D) photonic crystal (PC) flat lens based on the surface-edge engineering of a PC slab, operating as an n = -1 superlens at λ = 1.55 μm. The cross-section at the truncated edge of the flat lens is similar to an "anti-reflection grating", which is employed to reduce the reflectivity of propagative waves. The PC flat lens with a low reflectance of 1% was realized by the proposed truncated surface-edge for an InP/InGaAsP/InP 2D PC slab. The simulation results obtained with finite-difference time-domain (FDTD) method show that a PC flat super lens with a far-field resolution of 0.41 λ and a high transmittance of 81.9% can be achieved by the engineering of the truncated surface-edge at hetero-interface.

We present a theoretical mechanism for electric field enhancement with SERS of InAs particles of subwavelength apertures under THz excitation. The distribution of electric field confirms that there is a strong enhancement in the InAs particles at THz frequencies. The InAs with a Drude-like behavior in THz range, which is similar to metals at optical frequencies, leads to different SERS when the parameters of these two particles change. The SERS enhancement factor can reach $10^{11}$ under the certain conditions.

When space (time) translation symmetry is spontaneously broken, the space crystal (time crystal) forms; when permittivity and permeability periodically vary with space (time), the photonic space crystal (photonic time crystal) forms. We rewrote Maxwell’s equations in photonic time crystal, and discretized Maxwell’s equations with finite difference time domain (FDTD) method, deduced the discretized electric and magnetic field, and simulated electromagnetic wave propagation in two-dimensional (2D) photonic space-time crystal and photonic space crystal (or photonic crystal), and discussed the effect of parameters on the band gap.

The underwater photoelectric detection equipment mainly uses 532 nm laser as the light source, but the corresponding photocathodes like Na₂KSbCs, GaAs and GaAsP have a wide spectral response region and are easily affected by other signals. Thereby, GaAlAs are materials worth developing because of their adjustable band gap, which usually is used as a window layer of GaAs-based photocathode. In this paper, the finite difference time domain (FDTD) method is used to carry out nanostructure design simulations. The results show that GaAlAs with Al component of 0.63 can obtain the cutoff wavelength near 532 nm, which is an excellent photocathode material to meet the requirement of narrow-band spectral response of 532 nm laser. Furthermore, the light absorptance can be improved effectively by the quadrangular prism or cylinder nanostructured array prepared on the Ga${}_{0.37}$Al${}_{0.63}$As emission layer surface, and the maximum light absorptance can reach 96.2% at 532 nm for the cylinder nanostructure array with a height of 900 nm and a base width of 100 nm. Nevertheless, the reflection-mode Ga${}_{0.37}$Al${}_{0.63}$As photocathode with the quadrangular prism nanostructured array can be slightly influenced with incident angle of light.

Research on the improvement of the photoelectric conversion efficiency of solar cells is always the focus. In this paper, an efficient anti-reflection micro/nanostructure is proposed to improve the conversion efficiency of the solar cell. Graded effective refractive index theory is used to achieve the anti-reflection effect while the simulation model is established by FDTD. A specific periodic nanostructure is obtained, which can achieve a good anti-reflection effect. According to the simulation model, the reflectivity of the solar cell is reduced by 0.85% and the transmittance is increased by 0.85% in the band range of 200 nm to 1000 nm. Specifically, high anti-reflection phenomena are obtained in the band range of ultraviolet and blue light, in which the reflectivity is reduced by 1.56% and the transmittance is increased by 1.55%. Based on the simulation results, the array nanostructure is produced by etching the self-assembled polystyrene (PS) microspheres. Finally, the required structure is formed on the silicon wafer by nanoimprinting and etching technology. The reflectivity of 2.8% is obtained on silicon, which can potentially increase the opto-electrical performance of the solar cell.

GaInAsSb has an important application value in the field of infrared photoelectricity. In this paper, the optical properties of Ga${}_{0.84}$In${}_{0.16}$As${}_{0.14}$Sb${}_{0.86}$ nanopillar arrays with different shapes are studied by using the finite-difference time-domain (FDTD) method. The simulation results show that the peaks of all structures occur at 950nm to 1100 nm bands and peak up to 97%. Among them, the period and height of the nanopillars and the inclination angle of the incident light will significantly affect the size of the absorption peak of the nanopillars, but not the peak position. However, with the increase of the diameter, the absorption peak of the nanoparticles showed a trend of increasing first and then decreasing, and the peak position of the absorption peak showed a significant redshift. In addition, for the triangular prism structure, its absorption rate in the array structure with high duty cycle is higher than 90%, which provides an important reference for the preparation of high-density integrated infrared optical detector.

In this paper, three structures (cylinder, square column, and hexagonal prism) of InGaAsP nanowire arrays are designed based on the excellent light trapping effect of nanostructures. The effects of nanowire aperture, array period, and nanowire height on the light absorption properties are simulated and analyzed using the finite-domain time-difference (FDTD) method. The photoelectron emission capacity of the nanowire arrays was also calculated using MATLAB. The results show that the cylindrical nanowire array has phenomenon of resonance enhancement (absorption peak) in the near-infrared band of 820–1000nm, and the shift of absorption peaks can be achieved by adjusting the geometric parameters. Meanwhile, the quantum efficiency is taken to 9.98%. These simulation results provide some reference for the photocathode design of InGaAsP in the near-infrared band.

In this paper, three kinds of controllable nonlinear left-handed materials (DNLHMs) are proposed and analyzed, which are designed by introducing inductors and capacitors into the traditional nonlinear left-handed materials (NLHMs) as inhomogeneous doped elements. Due to such changes, several new transmission properties have been presented through finite-difference time-domain (FDTD) simulations. These have brought new features to our DNLHMs. On one hand, the original passband in the traditional nonlinear left-handed material is narrowed after introducing inductors. In addition, a new passband, which does not exist in doped linear LHMs, is generated. On the other hand, through introducing capacitors, the original passband of the nonlinear left-handed material can be shifted, resonance frequency can be changed, and a new passband can be generated. When capacitors and inductors are introduced simultaneously, the material properties, such as the number of passbands, the characteristic resonance frequency, and the bandwidth, can also be changed. Noting these characteristics, the values of the introduced inductors and capacitors are varied to investigate the spectrum changes of DNLHMs. Then, a series of controllable properties of the DNLHMs can be retrieved. And more importantly, the designed DNLHMs give the adjustability of suppressing high harmonics, which is not possible in the past materials.

In this paper, we propose and simulate the surface plasmon polariton nanofocusing process by using Finite-difference Time-domain (FDTD) method. The maximum enhancement factor at the taper end area is optimized with different wavelength of the excitation laser. With the advantage of SNOM, the SPP nanofocusing is experimentally observed by illuminating the tapered CdS nanoribbon deposited on the Ag film. The SPP dispersion is used to predict the optimal taper angles of the structure. As the emission of the focused SPP at the taper end, the proposed plasmonic structure can be severed as a light nanosource emitter in the future optical integrated circuits.

Two-photon absorption and optical limiting of two fluorenyl-based derivatives, 9,9-dimethyl-2,7-bis((E)-4-nitrostyryl)-9H-fluorene and 9,9-dimethyl-2,7-bis((E)-4-((E)-4-nitrostyryl)styryl)-9H-fluorene, in gas phase and solvent with nanosecond laser pulse have been theoretically investigated by solving the coupled rate equations and the field intensity equation employing an iterative predictor–corrector finite-difference time-domain (FDTD) method. The results show that both optical limiting properties and two-photon absorption cross-section strongly depend on the length of these molecules and the solvent. Moreover, the dynamical two-photon absorption behavior is affected by the thickness of samples and the pulse duration. These discoveries demonstrate that these fluorenyl-based derivatives possess highly promising characteristics and have potential applications for optical limiting devices.

In this study, we report photonic band structures and optical transmissions of some SiC polytypes, such as 3C, 2H, 4H, and 6H, and their multilayers, which have the form of a hexagonal photonic crystal at two-dimensional (2D) scale. Through the finite-difference time-domain computational simulations, we found that spatial electric-field variations of electromagnetic waves depend on the radius of dielectric rods of the multilayer crystal structure, and the central structural geometry of 4H- and 6H-SiC hexagonal polytypes was found to cause a remarkable increase of the wave vector $k$ in $x$ and $y$ directions. We also found a correlation between the local central structures of the optical modes in the 2D hexagonal crystal of 4H- and 6H-SiC polytypes. The wave-guiding in 4H- and 6H-SiC polytypes in the central core of the model geometry enabled the integration of defects to achieve a wide spectrum of technological functionalities, such as devices with striking features for miniaturized sensors and quantum information processing.