An efficient conformal locally one-dimensional finite-difference time-domain（LOD-CFDTD） method is presented for solving two-dimensional（2D） electromagnetic（EM） scattering problems. The formulation for the 2D tra...An efficient conformal locally one-dimensional finite-difference time-domain（LOD-CFDTD） method is presented for solving two-dimensional（2D） electromagnetic（EM） scattering problems. The formulation for the 2D transverse-electric（TE） case is presented and its stability property and numerical dispersion relationship are theoretically investigated. It is shown that the introduction of irregular grids will not damage the numerical stability. Instead of the staircasing approximation, the conformal scheme is only employed to model the curve boundaries, whereas the standard Yee grids are used for the remaining regions. As the irregular grids account for a very small percentage of the total space grids, the conformal scheme has little effect on the numerical dispersion. Moreover, the proposed method, which requires fewer arithmetic operations than the alternating-direction-implicit（ADI） CFDTD method, leads to a further reduction of the CPU time. With the total-field/scattered-field（TF/SF） boundary and the perfectly matched layer（PML）, the radar cross section（RCS） of two2 D structures is calculated. The numerical examples verify the accuracy and efficiency of the proposed method.展开更多
The frequency dependent permittivity for dusty plasmas is provided by introducing the charging response factor and charge relaxation rate of airborne particles. The field equations that describe the characteristics of...The frequency dependent permittivity for dusty plasmas is provided by introducing the charging response factor and charge relaxation rate of airborne particles. The field equations that describe the characteristics of Terahertz（THz） waves propagation in a dusty plasma sheath are derived and discretized on the basis of the auxiliary differential equation（ADE） in the finite difference time domain（FDTD） method. Compared with numerical solutions in reference, the accuracy for the ADE FDTD method is validated. The reflection property of the metal Aluminum interlayer of the sheath at THz frequencies is discussed. The effects of the thickness, effective collision frequency, airborne particle density, and charge relaxation rate of airborne particles on the electromagnetic properties of Terahertz waves through a dusty plasma slab are investigated.Finally, some potential applications for Terahertz waves in information and communication are analyzed.展开更多
The piecewise linear recursive convolution （PLRC） finite-different time-domain （FDTD） method improves accuracy over the original recursive convolution （RC） FDTD approach and current density convolution （JEC） b...The piecewise linear recursive convolution （PLRC） finite-different time-domain （FDTD） method improves accuracy over the original recursive convolution （RC） FDTD approach and current density convolution （JEC） but retains their advantages in speed and efficiency. This paper describes a revised piecewise linear recursive convolution PLRC-FDTD formulation for magnetized plasma which incorporates both anisotropy and frequency dispersion at the same time, enabling the transient analysis of magnetized plasma media. The technique is illustrated by numerical simulations of the reflection and transmission coefficients through a magnetized plasma layer. The results show that the revised PLRC-FDTD method has improved the accuracy over the original RC FDTD method and JEC FDTD method.展开更多
In order to eliminate Courant-Friedrich-Levy(CFL) condition restraint and improvecomputational efficiency,a new finite-difference time-domain(FDTD)method based on the alternating-direction implicit(ADI) technique is i...In order to eliminate Courant-Friedrich-Levy(CFL) condition restraint and improvecomputational efficiency,a new finite-difference time-domain(FDTD)method based on the alternating-direction implicit(ADI) technique is introduced recently.In this paper,a theoretical proof of the stabilityof the three-dimensional(3-D)ADI-FDTD method is presented.It is shown that the 3-D ADI-FDTDmethod is unconditionally stable and free from the CFL condition restraint.展开更多
The surface plasmon resonance( SPR) of gold( Au) nanorod can be tuned in a large visible-near infrared( Vis-NIR) region by changing the aspect ratio of nanorod. Compared with the SPR of isolated Au nanorod,assembly of...The surface plasmon resonance( SPR) of gold( Au) nanorod can be tuned in a large visible-near infrared( Vis-NIR) region by changing the aspect ratio of nanorod. Compared with the SPR of isolated Au nanorod,assembly of Au nanorods exhibits strong coupling effect in the nanogap and wealthy changes in the optical spectra. The SPR coupling effects and localized electronic fields for end-to-end( E-E) and side-by-side( S-S) assembled Au nanorods dimers are studied through finite-difference time-domain( FDTD) simulation. With decreasing the gap spacing,the longitudinal SPR( SPRL) red-shifts for the E-E orients Au nanorods dimer and blue-shifts for S-S orientes Au nanorods dimer. The transverse SPR( SPRT) has slight red-shifting for S-S assembly and no shifting for the E-E assembly. Moreover,a new coupling SPR appears for the E-E assembly in a long wavelength in the NIR region,blue-shifting and enhancing with decreasing the gap spacing. Based on the spring oscillator model and the polarization of nanoparticles with incident electric field,the SPR shifting and the appearance of new coupling SPR of assembled Au nanorods are proposed.展开更多
The analysis of electromagnetic propagation in a dispersive medium is complicated in the time-domain because its dielectric constant is frequency-dependent. In this paper, the dielectric constant of the dispersive med...The analysis of electromagnetic propagation in a dispersive medium is complicated in the time-domain because its dielectric constant is frequency-dependent. In this paper, the dielectric constant of the dispersive medium is written as a rational polynomial function, and the relationship between D and E is derived in the time-domain. It is referred to as the shift operator finite-different time-domain （SO-FDTD） method. Compared to an analytical solution and a piecewise linear current density recursive convolution （PLJERC） solution, the high accuracy and efl%iency of this method is verified by calculating the reflectance of the electromagnetic wave through a cold plasma slab. As the electron density in plasma is distributed as the Epstein formula, the effect of distribution grads and electron collision frequency on the reflectance is calculated by using the SO-FDTD method. The result shows that the increase in the distribution grads coefficient affects the reflectance sharply. When it comes to a smaller distribution grads coelBcient, the increase of the collision frequency showed a significant effect on the reflectance, but on the contrary, there is actually less and less effect till it disappears.展开更多
The influence ot oxidation aperture on the output characteristics ot the circularly symmetric vertical-cavity-surtaceemitting laser(VCSEL) structure is investigated.To do so,VCSELs with different oxide aperture sizes ...The influence ot oxidation aperture on the output characteristics ot the circularly symmetric vertical-cavity-surtaceemitting laser(VCSEL) structure is investigated.To do so,VCSELs with different oxide aperture sizes are simulated by the finite-difference time-domain(FDTD) method.The relationships among the field distribution of mode superposition,mode wavelength,output spectra,and far-field divergence with different oxide apertures are obtained.Further,VCSELs respectively with oxide aperture sizes of 2.7 μm,4.4 μm,5.9 μm,7 μm,8 μm,9 μm,and 18.7 μm are fabricated and characterized.The maximum output power increases from 2.4 mW to 5.7 mW with oxide aperture increasing from 5.9 μm to 9 μm.Meanwhile,the wavelength tuning rate decreases from 0.93 nm/mA to 0.375 nm/mA when the oxide aperture increases from 2.7 μm to 9 μm.The thermal resistance decreases from 2.815℃/mW to 1.015℃/mW when the oxide aperture increases from 4.4 μm to 18.7μm.It is demonstrated theoretically and experimentally that the wavelength spacing between adjacent modes increases with the augment of the injection current and the spacing becomes smaller with the oxide aperture increasing.Thus it can be reported that the aperture size can effectively reduce the mode overlaying but at the cost of the power decreasing and the wavelength tuning rate and thermal resistance increasing.展开更多
The full potential of optical absorption property must be further cultivated before silicon（Si） semiconductor nanowire（NW） arrays become available for mainstream applications in optoelectronic devices. In this pap...The full potential of optical absorption property must be further cultivated before silicon（Si） semiconductor nanowire（NW） arrays become available for mainstream applications in optoelectronic devices. In this paper, we demonstrate both experimentally and theoretically that an SiO_2 coating can substantially improve the absorption of light in Si NW arrays.When the transparent SiO_2 shell is coated on the outer layer of Si NW, the incident light penetrates better into the absorbing NW core. We provide the detailed theoretical analysis by a combination of finite-difference time-domain（FDTD） analysis.It is demonstrated that increasing the thickness of the dielectric shell, we achieve 1.72 times stronger absorption in the NWs than in uncoated NWs.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.61331007 and 61471105)
文摘An efficient conformal locally one-dimensional finite-difference time-domain（LOD-CFDTD） method is presented for solving two-dimensional（2D） electromagnetic（EM） scattering problems. The formulation for the 2D transverse-electric（TE） case is presented and its stability property and numerical dispersion relationship are theoretically investigated. It is shown that the introduction of irregular grids will not damage the numerical stability. Instead of the staircasing approximation, the conformal scheme is only employed to model the curve boundaries, whereas the standard Yee grids are used for the remaining regions. As the irregular grids account for a very small percentage of the total space grids, the conformal scheme has little effect on the numerical dispersion. Moreover, the proposed method, which requires fewer arithmetic operations than the alternating-direction-implicit（ADI） CFDTD method, leads to a further reduction of the CPU time. With the total-field/scattered-field（TF/SF） boundary and the perfectly matched layer（PML）, the radar cross section（RCS） of two2 D structures is calculated. The numerical examples verify the accuracy and efficiency of the proposed method.
基金supported by National Natural Science Foundation of China(Nos.41104097,11504252,61201007,41304119)the Fundamental Research Funds for the Central Universities(Nos.ZYGX2015J039,ZYGX2015J041)the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20120185120012)
文摘The frequency dependent permittivity for dusty plasmas is provided by introducing the charging response factor and charge relaxation rate of airborne particles. The field equations that describe the characteristics of Terahertz（THz） waves propagation in a dusty plasma sheath are derived and discretized on the basis of the auxiliary differential equation（ADE） in the finite difference time domain（FDTD） method. Compared with numerical solutions in reference, the accuracy for the ADE FDTD method is validated. The reflection property of the metal Aluminum interlayer of the sheath at THz frequencies is discussed. The effects of the thickness, effective collision frequency, airborne particle density, and charge relaxation rate of airborne particles on the electromagnetic properties of Terahertz waves through a dusty plasma slab are investigated.Finally, some potential applications for Terahertz waves in information and communication are analyzed.
基金National Natural Science Foundation of China (No. 60471002) and the Natural Science Foundation ofJiangxi Province (No. 0412014)
文摘The piecewise linear recursive convolution （PLRC） finite-different time-domain （FDTD） method improves accuracy over the original recursive convolution （RC） FDTD approach and current density convolution （JEC） but retains their advantages in speed and efficiency. This paper describes a revised piecewise linear recursive convolution PLRC-FDTD formulation for magnetized plasma which incorporates both anisotropy and frequency dispersion at the same time, enabling the transient analysis of magnetized plasma media. The technique is illustrated by numerical simulations of the reflection and transmission coefficients through a magnetized plasma layer. The results show that the revised PLRC-FDTD method has improved the accuracy over the original RC FDTD method and JEC FDTD method.
基金Supported by the Specialized Research Fund for the Doctoral Program of Higher Education(No.20010614003)
文摘In order to eliminate Courant-Friedrich-Levy(CFL) condition restraint and improvecomputational efficiency,a new finite-difference time-domain(FDTD)method based on the alternating-direction implicit(ADI) technique is introduced recently.In this paper,a theoretical proof of the stabilityof the three-dimensional(3-D)ADI-FDTD method is presented.It is shown that the 3-D ADI-FDTDmethod is unconditionally stable and free from the CFL condition restraint.
基金Supported by the National Natural Science Foundation of China(11274173,11374159)the Fundamental Research Funds for the Central Universities(NZ2013304,NJ20140005)Qing Lan Project of Jiangsu Province
文摘The surface plasmon resonance( SPR) of gold( Au) nanorod can be tuned in a large visible-near infrared( Vis-NIR) region by changing the aspect ratio of nanorod. Compared with the SPR of isolated Au nanorod,assembly of Au nanorods exhibits strong coupling effect in the nanogap and wealthy changes in the optical spectra. The SPR coupling effects and localized electronic fields for end-to-end( E-E) and side-by-side( S-S) assembled Au nanorods dimers are studied through finite-difference time-domain( FDTD) simulation. With decreasing the gap spacing,the longitudinal SPR( SPRL) red-shifts for the E-E orients Au nanorods dimer and blue-shifts for S-S orientes Au nanorods dimer. The transverse SPR( SPRT) has slight red-shifting for S-S assembly and no shifting for the E-E assembly. Moreover,a new coupling SPR appears for the E-E assembly in a long wavelength in the NIR region,blue-shifting and enhancing with decreasing the gap spacing. Based on the spring oscillator model and the polarization of nanoparticles with incident electric field,the SPR shifting and the appearance of new coupling SPR of assembled Au nanorods are proposed.
基金supported by National Natural Science Foundation of China(Nos.60271005 and 60431010)the National Science Fund for Distinguished Young Scholars of China(No.60325103)
文摘The analysis of electromagnetic propagation in a dispersive medium is complicated in the time-domain because its dielectric constant is frequency-dependent. In this paper, the dielectric constant of the dispersive medium is written as a rational polynomial function, and the relationship between D and E is derived in the time-domain. It is referred to as the shift operator finite-different time-domain （SO-FDTD） method. Compared to an analytical solution and a piecewise linear current density recursive convolution （PLJERC） solution, the high accuracy and efl%iency of this method is verified by calculating the reflectance of the electromagnetic wave through a cold plasma slab. As the electron density in plasma is distributed as the Epstein formula, the effect of distribution grads and electron collision frequency on the reflectance is calculated by using the SO-FDTD method. The result shows that the increase in the distribution grads coefficient affects the reflectance sharply. When it comes to a smaller distribution grads coelBcient, the increase of the collision frequency showed a significant effect on the reflectance, but on the contrary, there is actually less and less effect till it disappears.
文摘The influence ot oxidation aperture on the output characteristics ot the circularly symmetric vertical-cavity-surtaceemitting laser(VCSEL) structure is investigated.To do so,VCSELs with different oxide aperture sizes are simulated by the finite-difference time-domain(FDTD) method.The relationships among the field distribution of mode superposition,mode wavelength,output spectra,and far-field divergence with different oxide apertures are obtained.Further,VCSELs respectively with oxide aperture sizes of 2.7 μm,4.4 μm,5.9 μm,7 μm,8 μm,9 μm,and 18.7 μm are fabricated and characterized.The maximum output power increases from 2.4 mW to 5.7 mW with oxide aperture increasing from 5.9 μm to 9 μm.Meanwhile,the wavelength tuning rate decreases from 0.93 nm/mA to 0.375 nm/mA when the oxide aperture increases from 2.7 μm to 9 μm.The thermal resistance decreases from 2.815℃/mW to 1.015℃/mW when the oxide aperture increases from 4.4 μm to 18.7μm.It is demonstrated theoretically and experimentally that the wavelength spacing between adjacent modes increases with the augment of the injection current and the spacing becomes smaller with the oxide aperture increasing.Thus it can be reported that the aperture size can effectively reduce the mode overlaying but at the cost of the power decreasing and the wavelength tuning rate and thermal resistance increasing.
基金Project supported by the Science and Technology Project of Zhejiang Province,China(Grant No.2017C31120)
文摘The full potential of optical absorption property must be further cultivated before silicon（Si） semiconductor nanowire（NW） arrays become available for mainstream applications in optoelectronic devices. In this paper, we demonstrate both experimentally and theoretically that an SiO_2 coating can substantially improve the absorption of light in Si NW arrays.When the transparent SiO_2 shell is coated on the outer layer of Si NW, the incident light penetrates better into the absorbing NW core. We provide the detailed theoretical analysis by a combination of finite-difference time-domain（FDTD） analysis.It is demonstrated that increasing the thickness of the dielectric shell, we achieve 1.72 times stronger absorption in the NWs than in uncoated NWs.
