共查询到20条相似文献,搜索用时 15 毫秒
1.
H. Y. Zhang Y. P. Zhang T. Y. Shang Y. Zheng G. J. Ren P. Wang J. Q. Yao 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(1):37-40
The band structures of symmetrical Fibonacci sequences
(SFS) composed of positive and negative refractive index materials are
studied with a transfer matrix method. A new type of omnidirectional
zero-
gaps is found in the SFS. In contrast to the Bragg gaps, such
an omnidirectional zero-
gap is insensitive to the incident angles
and polarization, and is invariant upon the change of the ratio of the
thicknesses of two media. It is found that omnidirectional zero-
gap exists in all the SFS, and it is rather stable and independence of the
structure sequence. 相似文献
2.
T. Feng L. Fan Y. H. Li C. L. Zhang Z. Feng 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(3):315-319
In this paper, the tunneling phenomenon occurring in the photonic
heterostructure consisting of single-negative (SNG) metamaterials is
experimentally studied. First, the SNG metamaterials are fabricated using
coplanar waveguide with lumped-element series capacitors and shunt inductors
loading. Then, the tunneling phenomenon occurring in the photonic
heterostructure containing SNG media is experimentally demonstrated.
Moreover, the insensitivity of the tunneling frequency to the
breakdown of periodicity of phonotic crystals was also illustrated. 相似文献
3.
C. P. Yin T.-B. Wang J.-W. Dong Y. H. Chen H. Z. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(3):357-361
By means of transfer matrix method, we investigate the transmittance and
reflectance of Thue-Morse (T-M) structure composed of negative-permittivity
and negative-permeability materials. It is shown that the width and location
of an omnidirectional reflectance band remain invariant with the change of
generation order, and that the omnidirectional reflectance band is
determined by both TE and TM polarization, which different completely from
that in dielectric T-M structure. Moreover, a flat-top total transmission
band occurs around the same frequency in which the general zero average
permittivity and permeability are both satisfied in T-M structure. The basis
for these phenomena are presented and discussed. 相似文献
4.
S. L. Qiu P. M. Marcus 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(1):1-6
A procedure for finding the many stable phases of an element under hydrostatic pressure p is discussed and applied to zinc. Five new phases are found with several different Bravais symmetries under the constraint of one atom per cell and their stabilities as functions of p calculated. The procedure seems generalizable to find all the phases in all Bravais symmetries in a given range of pressure. In particular fcc Zn, which is unstable at p = 0, is shown to be very stable above 320 kbar to at least 1000 kbar. In agreement with Müller et al. [Phys. Rev. B 60, 16448 (1999)], a rhombohedral (rh) phase is found to be stable at p = 0, and several more rh phases are found at pressures up to 320 kbar. The Gibbs free energies of all phases are evaluated as functions of p, and the pressures of thermodynamically favored phase transitions are found. The behavior of Zn is compared to similar behavior of vanadium, which also shows stable rh phases and cubic phase instability in a range of pressure; the bcc phase instability is also healed by additional pressure. 相似文献
5.
W. Y. Liang J. W. Dong G. Q. Liang H. Z. Wang 《Applied physics. B, Lasers and optics》2009,96(4):781-785
We study the collimated emission characteristics from a dipole source inside a negative-effective-refractive-index photonic
crystal with a quasi-cavity constructed by a concave photonic crystal reflector. The emissions along the ±X and −Y directions are forbidden by the quasi-cavity, so that most emissions propagate along the +Y direction. Simulation results show that a narrow collimated beam is achieved due to the near-zero negative effective refractive
index. Moreover, the half-power beam width of such a collimated beam can be reduced to 3.48° by optimizing the size of the
source area. Such a compact structure would have potential applications in micro-optical devices. 相似文献
6.
S. Li H.-W. Zhang Q.-Y. Wen Y.-Q. Song W.-W. Ling Y.-X. Li 《Applied physics. B, Lasers and optics》2009,95(4):745-749
Based on the plane-wave expansion method, we calculate TE/TM gaps of 2-D photonic crystals (PCs) with typical square lattices
composed of the silicon rods in air. Using the finite-difference time-domain method, we simulate the electromagnetic field
distribution of THz waves in photonic crystals T-splitters. By the improved T-splitter with a rod in the junction, we achieved
the amplitude–frequency characteristics of a pass band of 84% from 1.12 to 1.22 THz and surpassed by 76% the amplitude consistency
of common T-splitters. And using the finite-difference time-domain method, we demonstrated that the improved T-splitter excels
a common T-splitter in the degree of separation between the two output ports. These results provide a useful guide and a theoretical
basis for the developments of THz functional components. 相似文献
7.
H. Xiao D. Z. Yao C. X. Wang S. Chen 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):219-229
The absolute photonic band gap (PBG) in two-dimensional (2D) photonic crystal with excentric core-shell rods is studied in
this paper. The core rod shifts away from the core-shell rod center, and its position is decided by two new introduced parameters
— the shift angle θ and the offset ρ. We use the FDTD algorithm to calculate the photonic bands of the photonic crystal, and analyze how the offset and shift
angle affect the photonic bang gap of excentric core-shell photonic crystal for different core rod size. It has been shown
that the variation of the photonic band gap is quite peculiar. 相似文献
8.
Omnidirectional and independently tunable defect modes in fractal photonic crystals containing single-negative materials 总被引:1,自引:0,他引:1
Y. H. Chen 《Applied physics. B, Lasers and optics》2009,95(4):757-761
The properties and applications of omnidirectional and independently tunable defect modes in fractal photonic crystals containing
single-negative materials are demonstrated. The proposed fractal structures can produce as many defect modes as desired by
adjusting its structural parameters. The interaction effect between the defect states of such fractal structures is avoided,
so the frequency of each defect mode can be tuned independently. Furthermore, these defect modes inside the zero effective-phase
gap are insensitive to the incident angle. With perfect transmission, mode controllability and omnidirectional compatibility,
these structures open a promising way for designing omnidirectional multichannel filters with specific channels. 相似文献
9.
H. Y. Zhang Y. P. Zhang W. H. Liu Y. Q. Wang J. G. Yang 《Applied physics. B, Lasers and optics》2009,96(1):67-70
We show theoretically that the frequency range of the zero-averaged refractive-index gap can be substantially extended in
a photonic heterostructure containing negative-index materials. This photonic heterostructure consists of different one-dimensional
(1D) photonic crystals. The constituent 1D photonic crystals have to be properly chosen in such a way that their zero-averaged
refractive-index gap of the adjacent photonic crystals overlap each other. 相似文献
10.
A new application of one-dimensional photonic crystals containing negative-index materials is proposed as low-pass spatial
filters. Through optimizing the parameters of defect layer, a series of polarization-independent defect modes in the zero-average-index
gap of the photonic crystals are obtained with the increase of the incident angle. Based on these defect modes, polarization-independent
low-pass spatial filters are designed. The spatial-frequency bandwidth of the spatial filters can be adjusted by changing
the period number of the defective photonic crystal structures. In addition, the effect of the losses of negative-index materials
on the spatial filters is considered. 相似文献
11.
In recent years the application of 2-Dimensional (2D) metallic Photonic-Crystal (PC) structures to high-power microwave devices,
such as particle accelerators and gyrotrons, has gained increased interest. In this paper we focus on the effect disorder
has on the resonant frequency and peak electric field in the defect site of a 2D PC structure. For disorders up to a maximum
of 15% variation in position and radius, we found that disorder applied to the innermost rods surrounding the defect site
dominates in determining the peak field and resonant frequency of the structure. We also show that small disorder (∼1%) can
lead to an increase in peak field in certain cases due to structure optimization. We find that increasing levels of disorder
lead to a decreasing average peak field for all structures. Whereas the mean resonant frequency remains constant for increasing
disorder while the standard deviation increases. We then develop an understanding for this behaviour in terms of frequency
detuning and mode confinement. 相似文献
12.
H. Kurt 《Applied physics. B, Lasers and optics》2009,95(2):341-344
To obtain highly directional light output from photonic crystal waveguides (PCWs), the emission characteristics of the narrow-width
waveguide structures are investigated by tailoring the geometry of the exit sides. The local structural deformations in the
form of air hole removal from the triangular-lattice photonic crystal (PC) show the effectiveness of the previously proposed
approach that was implemented by us for another type of PC. The spatial broadening of the beam is greatly suppressed. With
the modified waveguide exits, highly directional emissions with small side lobes are achieved. The frequency dependency of
the directional emissions is evaluated. We show that the divergence angles of the beams depend linearly on the wavelength
for a regular type of PCW but the modified PCW exits have local minima with respect to wavelength in terms of the divergence
angle. The present work may prove to be helpful in the design of couplers and edge-emitting lasers and in the implementation
of free-space optical communications. 相似文献
13.
Christian Imhof Remigius Zengerle 《Applied Physics A: Materials Science & Processing》2009,94(1):45-49
We report on microwave experiments with a metamaterial composed of pairs of metallic crosses. The transmission properties
of the structure show a left-handed transmission band at frequencies around 10.2 GHz. The validity of the negative effective
index of refraction is verified by a Snell’s law refraction experiment performed on a wedge-shaped sample of the metamaterial.
A second measurement of a similar wedge made from blank FR4 boards is done for reference. The results of the measurements
show positive refraction over the whole measured frequency band for the FR4 wedge as well as the refraction of the incident
radiation to negative angles within the designated left-handed frequency band for the metamaterial sample. 相似文献
14.
E. Xifré-Pérez L. F. Marsal J. Ferré-Borrull J. Pallarès 《Applied physics. B, Lasers and optics》2009,95(1):169-172
We report on the fabrication and characterization of a porous silicon omnidirectional reflector formed by periodic substructures
stacked together. For these substructures, a low refractive index contrast has been used, resulting in substructures without
omnidirectional reflectivity band. The use of a low refractive index contrast involves the reduction of the requirements to
obtain omnidirectional reflectors. We demonstrate the existence of an omnidirectional reflectivity range with a high gap-to-midgap
ratio by means of reflectivity spectra measurements for a range of incidence angles. The results are in good agreement with
a theoretical model of the reflector. The fabricated structure is the first reported porous silicon reflector suitable for
1.55 μm applications. 相似文献
15.
N. D. Lu Y. Q. Zhou T. G. Shen P. L. Ji J. Sun B. G. Yuan F. C. Yu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(3):707-710
The paper investigated a composite photonic crystal patch antenna by using the method of finite difference time domain (FDTD).
The results show that there exists a wave resonance state at 2.635 GHz, where the real part of the permittivity and permeability
are all negative; its refraction index is –1. The effect has largely enhanced the electromagnetic wave’s resonance intensity,
and has improved the localized extent of electromagnetic energy obviously in such photonic crystal structure (PBG), resulting
in a higher antenna gain, a lower return loss, and a better improvement of the antenna’s characteristics. Due to such the
advantages, the use of patch antennas can be extended to such fields as mobile communication, satellite communication, aviation,
etc. 相似文献
16.
We report on the experimental observation of the beaming effect in photonic crystals using experimentally mapped spatial field
distributions of energy emitted from a subwavelength photonic crystal waveguide into free-space, rendering with crisp clarity
the diffractionless beaming of energy. Our experimental data agree well with our numerical studies of the beaming enhancement
in photonic crystals with modulated surfaces. Without loss of generality, we study the beaming effect in a photonic crystal
scaled to microwave frequencies and demonstrate the technological capacity to deliver long-range wavelength-scaled beaming
of energy. 相似文献
17.
E. V. Ponizovskaya A. M. Bratkovsky 《Applied Physics A: Materials Science & Processing》2009,95(4):1137-1142
Negative index materials (NIM) enable subwavelength resolution and are promising for applications in integrated optical systems,
since the mode volume is small. Most promising NIM systems essentially use noble metals (Ag, Au) with material losses much
lower than in other metals, but still rather hefty, like in metal–dielectric–metal “fishnets”. Therefore, we perform extensive
finite-difference time-domain modeling of NIM “fishnets” in combination with gain medium, InGaAsP multiple quantum wells in
the present work. The signal recovery is weak, which is related to weak overlap between the radiation field and the gain medium.
The signal modulation speed may be very large, in a picosecond range. 相似文献
18.
D. J. Liu Z. X. Zhou 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(1):95-101
The propagation of partially polarized and partially coherent beams in
uniaxial crystals orthogonal to the optical axis is investigated. The
analytical formulae for the elements of the cross-spectral density matrix of
partially polarized and partially coherent beams propagating through
uniaxial crystals orthogonal to the optical are derived. The numerical
results show that the degree of polarization decreases with the increase of
the ratio of extraordinary to ordinary refractive indices at a certain
propagation distance, and the influence of uniaxial crystals on the degree
of coherent is not so evident. And the beams spread more rapidly in the
direction parallel to the optical axis than orthogonal to the optical axis
in positive crystal with the propagation distance increasing. 相似文献
19.
Collective surface plasmon resonance (SPR) excitations in an ordered array of silver nanoshells have been theoretically studied
using generalized Mie theory. Near- and far-field radiative coupling between the nanoshells in the array result in a non-monotonic
shift of the collective SPR band. When the distance between the shells in the array approaches that of the collective SPR
wavelength, we observe narrowing of the collective SPR band due to constructive interference between the scattered electric
field from the particles in the array. Further increase of the distance between the nanoshells in the array leads to destructive
interference and broadening of the collective SPR band. 相似文献
20.
We investigate the resonance tunneling modes of photonic double quantum well made of two photonic crystals with two different single-negative materials. It is found that these resonance modes split pairs, due to a coupling between two photonic wells. It is observed that when two photonic quantum wells are far away from each other, resonance modes appear as a single peak. And the quality factors of the transmittance resonance peaks can be greatly improved by increasing the period number of the outer barrier. The effects of the losses coming from ENG and MNG materials on the resonance modes are also specifically explored. 相似文献