共查询到20条相似文献,搜索用时 15 毫秒
1.
E. A. Vinogradov V. A. Babintsev V. G. Veselago K. F. Shipilov 《Physics of Wave Phenomena》2007,15(2):126-129
A sound source (3 cm in diameter) image in air, formed in the far wave zone behind a two-dimensional periodic lattice, was
experimentally obtained. The lattice consisted of plane parallel rows of steel cylinders with a diameter of 1.58 cm, forming
an acoustic crystal with hexagonal structure, The crystal lattice constant (a = 2.14 cm) is smaller than the emission wavelength in air (∼ 3.4 cm). The relations between the emission wavelength and lattice
parameters were selected according to model calculation in the second transmission band of the crystal at its negative refractive
index n = −0.7. The lateral size of the focused (over the sound pressure distribution) image of the sound source is close to the
emission wavelength. A distinctive feature of the experiment is the formation of such a sharply focused image under conditions
of an extremely small output aperture (the beam diameter at the acoustic crystal output did not exceed 2.5 acoustic wavelengths
in air). It can be considered that the flat acoustic lens is realized. Possible explanations of the observed effect are discussed. 相似文献
2.
A novel high birefringence polymer photonic crystal fiber (PCF) is proposed in this work. This PCF is composed of a polymer core and a cladding with elliptical air holes and squeezed triangular lattice. The high birefringence is introduced on the combined effect of elliptical air holes and the squeezed lattice. Our numerical results based on the supercell lattice method indicate that the birefringence can reach as high as 0.0018 at 650 nm wavelength with a properly designed cladding structure. We also analyze the dependence of the birefringence on structure parameters. And we design a PCF that has high and flattened birefringence. 相似文献
3.
Maliheh Khatibi Moghaddam Amir Reza Attari Mir Mojtaba Mirsalehi 《Photonics and Nanostructures》2010,8(1):47-53
We investigate a photonic crystal (PC) waveguide coupler which is formed by two closely spaced linear waveguides in a two-dimensional triangular lattice of air holes. Our study shows that shifting one row of the air holes between the waveguides affects the dispersion curves of the guided modes and if the triangular lattice of air holes between the waveguides is replaced by a rectangular lattice, this modification results in an ultra-short coupling structure with coupling length less than 3a, where a is the lattice constant. Also, we investigate the effect of changing the radii of air holes that are adjacent to or between the waveguides on the coupling length and show that increasing the radius of air holes between the waveguides decreases the coupling length. We analyze the output spectrum of an ultra-short channel drop filter designed based on this structure. 相似文献
4.
Galina V. Li Ekaterina V. Astrova Sergey A. Dyakov Anna Baldycheva Tatiana S. Perova Sergey G. Tikhodeev Nikolay A. Gippius 《固体物理学:研究快报》2013,7(7):481-484
The reflection and transmission spectra of a finite thickness 2D photonic crystal slab (PCS) based on macroporous silicon are investigated. Periodic photonic crystal region is separated from air by homogeneous silicon interfacial layers. These interfacial layers at the silicon/air boundary being defects of the photonic crystal lattice, define the properties of surface Tamm states in the photonic stop‐bands (PSBs). It is demonstrated experimentally and theoretically that the reflection spectra of a structure with different thicknesses of the interfacial layers on both sides of the PCS depend on the illuminated side. At the same time, the transmission spectra are identical for both light directions in agreement with the reciprocity principle. Analysis shows that the dependence of the reflection spectrum on the side of light entrance is due to scattering losses in the real structure. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
5.
Maxence Hofman 《Optics Communications》2010,283(6):1169-5813
We propose a III-V semiconductor photonic crystal slab designed to operate as a n = −1 superlens at λ0 = 1.55 μm. The structure consists of air holes arranged in a two-dimensional triangular lattice, of period a, nanopatterned in an InP/InGaAsP/InP slab. Exploiting the second pass-band regime (a/λ0 ∼ 0.31), subwavelength resolutions as low as 0.38λ0 for planar lenses have been obtained by the insertion of hexagonal nanocavities within the crystal. 相似文献
6.
Y. Li C. Wang X. Lü M. Hu Y. Chen B. Liu L. Chai 《Applied physics. B, Lasers and optics》2007,86(2):235-242
Photonic crystal fibers (PCFs) can guide light by the photonic bandgap (PBG) effect created by the periodically arranged air
holes in the cladding. In this paper, the bandgap properties of Kagomé photonic crystal fibers (KPCFs) are investigated in
detail. First, the bandgap properties of PCFs based on the basic Kagomé lattice are analyzed and compared with the PBGs of
PCFs based on honeycomb and triangular lattices. We highlight the similarities between KPCFs and honeycomb PCFs in their PBGs,
both having air-guiding regions only at very large air filling fractions (AIFs), whereas the PBGs of triangular PCFs can have
large air-guiding regions at smaller AIFs due to the difference in the gap structure. In the second half of this paper, we
show how the PBGs of KPCFs can be modified by introducing an extra air hole into the vacant space of the original lattice.
In particular, KPCFs with medium-sized air holes can be designed to guide air by introducing extra air holes of a larger size.
The air-guiding regions of KPCFs with very large air holes can also be greatly extended by the extra air holes. These air-guiding
regions occur at higher normalized frequencies, resulting in larger air hole pitches favorable for fabrication.
PACS 42.70.Qs; 42.25.Bs; 42.81.Qb 相似文献
7.
基于平面波展开法,以介电常数分别为1F/m和12F/m的物质构成三角晶格二维光子晶体,改变空气孔半径r与晶格常数a之间的大小,数值模拟得到了三角晶格二维光子晶体横磁模带隙,当r=.4α时形成三处三角晶格二维光子晶体横磁模的带隙,其中最大三角晶格二维光子晶体横磁模带隙出现在0.6766—0.8000Hz,差值为0.1234Hz。研究结论为光子晶体器件的制作提供参考。 相似文献
8.
We propose a slow-light photonic crystal waveguide, which uses a combination of circular and elliptical air holes arranged in a hexagonal lattice with the background material of silicon nitride (refractive index n = 2.06). Large value of normalized delay bandwidth product (NDBP = 0.3708) is obtained. We have analyzed nonlinear performance of the structure. With our proposed geometry strong SPM is observed at moderate peak power levels. Proposed photonic crystal waveguide has slow light applications such as reduction in length and power consumption of all-optical and electro-optic switches at optical frequency. 相似文献
9.
10.
采用平面波展开法模拟二维光子晶体在E极化和H极化下的能带结构,研究Ge基二维正方晶格光子晶体的填充比以及晶格排列结构对最大禁带宽度的影响。结果表明:在空气背景材料中填充Ge柱的介质柱结构中,可产生TE、TM带隙,且各方向完全带隙出现在r/a=0.19~0.47范围内,最大完全帯隙禁带宽度可以达到0.064(归一化频率);在选取Ge为背景材料的空气孔型结构中,同样可产生TE、TM带隙,且各方向完全带隙出现在r/a=0.46~0.49范围内,最大完全帯隙禁带宽度可以达到0.051(归一化频率)。同时,不论在介质柱型还是空气孔型结构中,带隙宽度都随着r/a的增大呈先增大后减小的趋势。 相似文献
11.
N. M. Galeeva 《Russian Physics Journal》1980,23(3):246-250
The nuclear spin-phonon interaction Hamiltonian for Van Vleck paramagnets is derived in general form with allowance for rotational vibrations of the crystal lattice. The specific form of the Hamiltonian is given for tetragonal crystal symmetry in the cases S=1/2 and S > 1/2. The coefficient of sound absorption at the electron-nuclear levels as well as the electron spin system is calculated. It is verified that the contribution of rotational lattice vibrations can in a number of cases turn out to be an order of magnitude greater than the contribution depending on the shear and compressive strain.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 80–85, March, 1980. 相似文献
12.
Optical properties and photonic bands of GaAs photonic crystal waveguides with tilted square lattice
M. Galli M. Agio L.C. Andreani L. Atzeni D. Bajoni G. Guizzetti L. Businaro E. Di Fabrizio F. Romanato A. Passaseo 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):79-87
Reflectance measurements at variable angle of incidence are performed on GaAs photonic crystal waveguides with unconventional
square lattices. The technique yields the dispersion of photonic bands for the investigated lattices, as first shown by Astratov
et al. [Phys. Rev. B 60, R16225 (1999)]. A sample with a square lattice of air rings and small air fraction yields narrow resonant structures and
a dispersion of photonic modes close to that of free photons. Another sample with a square lattice of dielectric squares and
large air fraction leads to broader structures and to a dispersion of photonic modes which differs strongly for the two polarizations
of light: this sample has a pseudo-gap around 1 micron wavelength. The experimental results are in good agreement with theoretical
calculations of the reflectance and of the photonic mode dispersion in the photonic crystal slabs.
Received 16 January 2002 相似文献
13.
X. Li X. Checoury S. David N. Yam D. Bouchier V. Calvo A. Salomon 《Journal of luminescence》2006,121(2):286-289
Planar two-dimensional photonic crystals can be combined with a one-dimensional Bragg mirror to control the quality factor and out-of-plane coupling of optical Bloch modes. We have investigated the optical properties of such structures fabricated on silicon. The photonic crystals are fabricated in the upper Si layer deposited on top of quarter-wave thick SiO2-polycrystalline Si layers. The optical properties are probed by the room-temperature photoluminescence of Ge/Si self-assembled islands as an internal source. We show that an enhancement of the quality factor can be obtained by controlling the thickness of the silicon upper layer in which the two-dimensional photonic crystal is etched and by controlling the air filling factor of the photonic crystal. Quality factors of 2200 around 1100 nm are obtained by this method for defect-free photonic crystals with a square lattice pattern. The experimental results are supported by three-dimensional finite-difference time-domain (FDTD) calculations of the radiated modes for the investigated structures. 相似文献
14.
Mohd Sharizal Alias Sahbudin Shaari Paul O. Leisher Kent D. Choquette 《Photonics and Nanostructures》2010,8(1):38-46
Single transverse mode control is achieved for multimode GaAs-based VCSEL by utilizing photonic crystal design and etched trench structure. Theoretical analysis is initially performed for photonic crystal design with various lattice constants and air holes diameter. The fabricated photonic crystal VCSEL with etched trench structure exhibits single mode output power of 0.7 mW, threshold current of 3.5 mA, slope efficiency of 0.10 W/A, and continuous single mode output spectrum throughout a wide operating current range. Comparison of typical oxide VCSEL, trench oxide VCSEL, and photonic crystal oxide VCSEL employing trench structure is presented. By combining photonic crystal and trench structure, single transverse mode operation of photonic crystal VCSEL can be much more strictly controlled. 相似文献
15.
A high-concentration in-situ phosphorus-doping technique for silicon low-temperature epitaxial growth with Si2H6 has been developed. Growth temperature has an impact on the crystal quality and on lattice strain of phosphorus-doped silicon layers. Resistivity, micro-Raman spectroscopy, and high-resolution X-ray diffraction indicated that good crystal quality was achieved at a growth temperature of 525 °C. On the other hand, growth pressure has little influence on crystal quality or on lattice strain except for surface morphology. By optimizing epitaxial growth conditions, an extremely high concentration of phosphorous doping was achieved without a high-temperature activation annealing, and the resultant good crystal quality of the phosphorus-doped silicon layer gave a very low resistivity. Accordingly, the high-concentration in-situ phosphorus doping is a powerful technique to fabricate future ultra-high-speed SiGe HBTs. 相似文献
16.
N. A. Poklonskii T. M. Lapchuk V. G. Baev G. A. Gusakov 《Journal of Applied Spectroscopy》2006,73(1):5-9
We have studied the electron spin resonance (ESR) of a 0.59 carat synthetic diamond single crystal at room temperature. The
crystal was grown on a “split-sphere” apparatus in the Fe-Ni-C system by the temperature gradient method. After high-temperature/high-pressure
treatment of the diamond, it was observed that as the microwave power supplied to the sample increased from 70 μW to 70 mW
in an H102 cavity, the ESR signal from the P1 center (a nitrogen atom substituting for carbon at a lattice point of the diamond crystal:
C-form nitrogen) is inverted. In the original diamond (before high-temperature/high-pressure treatment), no inversion of the
ESR signal was observed.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 9–12, January–February, 2006. 相似文献
17.
R. Buczynski I. Kujawa D. Pysz T. Martynkien F. Berghmans H. Thienpont R. Stepien 《Applied physics. B, Lasers and optics》2010,99(1-2):13-17
In this paper we report on the fabrication of highly birefringent photonic crystal fiber with a photonic cladding composed of elliptical holes ordered in a rectangular lattice. The fiber features a group birefringence G of 0.82×10?4 at 725 nm. We discuss the influence of structural parameters including the ellipticity of the air holes and the aspect ratio of the rectangular lattice on the birefringence and on the modal properties of the fiber. 相似文献
18.
T. Minamisono Y. Nojiri K. Matsuta M. Fujinaga T. Iwayama 《Hyperfine Interactions》1987,35(1-4):601-604
Nuclear dipolar broadening in the NMR spectra of β-emitting12N implanted in single crystal V was studied as a function of external magnetic field, orientation of the crystal axes relative
to the field, and temperature of the sample. The implanted12N was located in an interstitial tetrahedral site. The surrounding V atoms nearest to the12N were displaced from the regular lattice position; the lattice expansion of large size Δa/a=0.5 was determined. 相似文献
19.
《Photonics and Nanostructures》2008,6(3-4):219-224
In this paper, a two-dimensional Kagomé lattice photonic crystal (PC) made of GaAs (ɛ = 12.96) dielectric rods in air is considered. This Kagomé lattice PC has an effective refractive index neff = −1 at a low normalized frequency ω = 0.187 × 2πc/a. Imaging quality and the capability of the super-resolution of two point sources are studied for a superlens made of such PC structure. In order to achieve a high quality image and to improve the spatial super-resolution of two sources, a clipping Kagomé lattice PC is designed. Results simulated by finite-difference time-domain method show that imaging quality and super-resolution of two sources can be enhanced greatly as the perfect Kagomé lattice structure are superseded by the clipping Kagomé lattice structure. Coupled-mode theory analysis gives an explanation why the clipping structure is superior to the perfect one for both the imaging quality and the capability of the super-resolution of two sources. This clipping Kagomé lattice PC structure would be widely used in optical devices and integrated circuit. 相似文献
20.
Y. J. Liu H. T. Dai E. S. P. Leong J. H. Teng X. W. Sun 《Applied physics. B, Lasers and optics》2011,104(3):659-663
Electrically switchable two-dimensional photonic crystals were demonstrated using polymer-dispersed liquid crystal materials
based on the Talbot self-imaging effect of a single photomask. With the photomask subjected to a collimated Ar+ laser beam operating at 488 nm, a three-dimensional spatial light intensity pattern was created due to the Talbot self-imaging
effect. The spatial light intensity pattern was then recorded inside a cell filled with the liquid crystal/prepolymer mixture
to create photonic crystal structures. The surface morphology of the photonic crystals was examined by an atomic force microscopy.
It showed square structures with a lattice constant of ∼0.9 μm. The diffraction and electro-optical properties were also presented.
This approach shows a simple and fast fabrication. 相似文献