Graphene is used as an ideal platform for plasmonic optical devices due to its unique electrical and optical characteristics. We proposed a unique effective index method to evaluate a graphene-based half Maxwell fish-eye (HMFE) plasmonic lens on a single flake of graphene, which can focus a surface plasmon polariton plane wave and transform into a spherical wave. Similar to traditional optics, the proposed method can be used to investigate the focusing performance of an HMFE lens versus different parameters, including the incident frequencies, the discrete semiring numbers, the chemical potentials, and the size of the proposed lens. In addition, we use two proposed lenses to build an optical-coupling element, which can transform the beam of a plane wave into a different beam width. The proposed effective index method can be used as a reference in designing plasmonic optical devices with a variable effective index profile on a flake of graphene. The finite element method is employed to realize the numerical simulation, which demonstrates results almost consistent with our design methodology.
We study the contribution of Surface-plasmons coupling with a single dipole to enhance the emitter emission. When the
Ag film is inserted into GaN, the emission efficiency of single dipole in GaN can be enhanced greatly. With 3D-FDTD
method, the numerical simulation results demonstrate that the SPs play a key role in enhancement light emitter efficiency.
Furthermore, SPs is sensitive not only to the thickness and refractive index of dielectric, but also to the geometry and
dispersion model of Ag film. By changing the parameters of GaN and Ag film, the location of the enhancement peak of
the emission efficiency in the visible region can be controlled. According to the simply optimal parameters, about 9
times enhancement at 470nm occurs. Our results are of very importance for improving the light-emitting devices of GaN.
We study the characteristics of nano-optical antenna made of two gold nano-particles by three dimensional numerical
calculations at visible and near infrared band. To carry the computational burden and guarantee the precision and speed
of a 3D FDTD calculation, adaptive mesh refinement technology is used. We first highlight the concrete way of
controlling over the emitter position to fulfill the requirements of larger spontaneous emission enhancement. By exciting
the resonance of surface plasmon polaritons (SPPs), we find that the far field directivity is strongly influenced and obtain
around 5000-fold spontaneous emission enhancement. Choosing the incident wavelength of 600nm, we compute the
decay rates and radiant efficiency as a function of antenna geometry limitations, showing the particle with an aspect ratio
of L/R=4 is best for enhancing spontaneous emission. Furthermore, we proceed a spectrum analysis and find an exact
relationship between the particle length and resonant wavelength.
A four channel photonic crystals filter is designed using 2-D photonic crystals. First, General conditions for obtaining
100% drop efficiency are derived in a three-port channel drop filter. Based on this modeling, a photonic crystal-based
four-channel drop filter is design. The performance of filter is simulation using 2D FDTD (finite difference time domain)
method. The coupling efficiency of every channel is higher than 90% from seeing the simulation results. The frequency
of the four-channel is from 1530nm to 1580nm when the lattice constant is 550nm, and the interval of every channel is
less than 20nm. The interference of every channel is very small. The design method giving a good theory for design and
made multi-channel photonic crystals filter.
In this paper, the transmission characteristic in nano-size metallic photonic crystals (MPCs) is studied with the finite
difference time domain (FDTD) method. It's show that the size and the layout of the metal decide the transfer
characteristic of the metallic photonic crystals.
Using plane wave expansion (PWE) method and finite-difference time-domain (FDTD) method, we study the photonic band gap (PBG) and transmission properties of two-dimensional photonic crystals (PCs). A holographic fabrication design is used to construct the two-dimensional PCs in our work. To produce the lattice holographically, we use an equation to demonstrate a light intensity distribution. In this equation, there are several variant to control the lattice constant, the shape of dielectric columns, etc. The PBG calculation results using PWE method and FDTD method agree with each other very well.
Band structures of two-dimensional photonic crystal composed of metallic cylinders are numerically studied with FDTD
method. Four kinds of metal: Cu, Ag, Au and Al are considered. Bandgaps varing with lattice constant (a) and filling
factor (f) are drawn and analyzed.
Zero-n photonic gap in a periodic structure of positive and negative refractive index materials is studied with a transfer matrix method. A zero-n gap is found in the photonic spectra of this periodic structure. It is demonstrated that the zero-n gap is less sensitive to the incident angle and the scale in contrast to the Bragg gap.
This paper presents a new parallel finite-difference time-domain (FDTD) numerical method in a low-cost network environment to stimulate optical waveguide characteristics. The PC motherboard based cluster is used, as it is relatively low-cost, reliable and has high computing performance. Four clusters are networked by fast Ethernet technology. Due to the simplicity nature of FDTD algorithm, a native Ethernet packet communication mechanism is used to reduce the overhead of the communication between the adjacent clusters. To validate the method, a microcavity ring resonator based on semiconductor waveguides is chosen as an instance of FDTD parallel computation. Speed-up rate under different division density is calculated. From the result we can conclude that when the decomposing size reaches a certain point, a good parallel computing speed up will be maintained. This simulation shows that through the overlapping of computation and communication method and controlling the decomposing size, the overhead of the communication of the shared data will be conquered. The result indicates that the implementation can achieve significant speed up for the FDTD algorithm. This will enable us to tackle the larger real electromagnetic problem by the low-cost PC clusters.
A multiresolution time-domain (MRTD) method based on Daubechies scaling functions is proposed for the time-domain analysis of planar optical waveguide devices. The anisotropic perfectly matched layer absorbing boundary condition is implemented for the MRTD method. The proposed scheme is used to model the parallel-slab directional coupler, and the simulation results are in good accord with the analytical solutions. Compared with the standard finite-difference time-domain method, this scheme can save considerably computer resources without loss of accuracy.
In a polarization-division multiplexing soliton system, the multiple soliton interactions are studied numerically, the effects of soliton interactions on timing jitter are analyzed, and a countermeasure using nonlinear gain to suppress the soliton interactions is developed with the help of computer modeling. It is found that the mutual interactions between neighboring solitons cause soliton transmission instability and lead to timing jitter. The interactions of more than two solitons are stronger than that of two solitons. Therefore, the maximum transmission distance limited by the soliton interactions should be inferred from the collision distance of multiple soliton interactions, not the mutual interactions of two solitons. Nonlinear gain combined with a filter is suggested to effectively suppress the soliton interactions and stabilize soliton propagation.
Under the influence of self-frequency shift, the interactions between in-phase and out-phase neighboring fundamental and second-order optical solitons are investigated numerically, and the impacts of soliton interactions to timing jitter are analyzed. It is found that under the influence of self-frequency shift, the periodic collision of neighboring fundamental in-phase soliton pair is broken. They are apart from each other rapidly after one collision and the self-frequency shift phenomenon is much more obvious after the collision. While for neighboring out-phase fundamental soliton pair, two solitons both shift to the dropping edge and the impacts of self-frequency shift are weaker than that of in-phase soliton pair. For second-order solitons, either in-phase or out-phase soliton pair will be split. Two split stronger solitons will collide with each other during the propagation in the optical fiber and the difference between in-phase soliton pair and out-phase soliton pair exists that the interactions of out-phase pair is weaker than that of in-phase soliton pair and the collision distance of out-phase pair is much longer than that of in-phase soliton pair. A nonlinear gain can be used to effectively suppress soliton interactions as well as effects of soliton self-frequency shift, and stabilize the soliton propagation.
Using a conventional optical receiver model, we analyzed the penalties on the optical signal performance due to low-frequency subcarriers with a new approach, regarding the subcarrier as a sinusoidal distributed random variable of which the standard deviation is applied in the formula derivation. Then, the Q factor is derived as a simple analytic function of modulation index, OSNR, and the number of subcarriers. By using numerical analysis, our method agrees well with the proved theory and is more efficient and convenient for calculation.
An adaptive step-size method for the coupled equations of multi-pumped broadband Raman amplifiers is proposed based on Runge-Kutta-Fehlberg methods. This algorithm adjusts the step-size appropriately according to the presupposed precision and the local truncation error of each step. Simulation results indicate that our adaptive step-size method improves the accuracy and the simulating speed efficiently compared with other traditional algorithms and suits the numerical simulation for fiber Raman amplifier.
Power propagation equations of multi-pumped fiber Raman amplifier (FRA) is reasonably simplified, multistep average power method is applied to compute composite Raman gain of multi-signals in dense wavelength division multiplexed system (DWDM) amplified by multi-pumped FRA. Based on such a simple and effective model, the influence of the number, input power and wavelength distribution of multi-pumps on Raman gain is researched, the rules to decide their values are reached and the ultra broad and flat Raman gain bandwidth is implemented. All the simulation and analyses supply helpful references for the application of multi-pumped FRA in DWDM system.
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