Dispersion compensation in optical transmission systems using high negative dispersion chalcogenide/silica hybrid microstructured optical fiber

In this paper, a new hybrid microstructured optical fiber (H-MOF) based upon photonic bandgap (PBG) light guiding mechanism which can be used for dispersion compensation in optical transmission systems is designed and simulated. The H-MOF core is made up of silica glass and the holes in the cladding network are filled with As₂Se₃ chalcogenide glass. By selecting an appropriate geometrical parameters for the structure, the dispersion and confinement losses of the proposed H-MOF at 1.55 µm are calculated to be ?6700 ps/nm/km and 6?×?10^?4 dB/m, respectively. Relative dispersion slope (RDS) of the H-MOF at 1.55 µm is about 0.00347 nm^?1. The proposed H-MOF is suitable for use in wavelength division multiplexing and dispersion compensating systems in optical fiber transmission networks.     

压缩六角点阵椭圆孔光子晶体光纤的低色散高双折射效应

设计了一种新型结构低色散高双折射光子晶体光纤,该光纤纤芯缺失一根空气柱,包层沿光纤长度方向排布压缩六角点阵椭圆空气孔.采用全矢量平面波法,对其色散和双折射特性进行了数值模拟.研究发现,通过改变光纤结构参数,即改变六角点阵压缩比ξ、相对孔间隔f和空气孔椭圆率η,可以调节该光纤低色散高双折射工作波长.若调整光纤结构参数ξ=048, f=035, η=055, x方向孔间隔Λ_x=12　μm时,该光纤呈现低色散高双折射效应,在1360—167 关键词： 导波与光纤光学 全矢量平面波法 低色散高双折射 六角点阵压缩比     

近椭圆内包层高双折射偏振稳定光子晶体光纤设计及特性分析

设计了一种新型近椭圆内包层(NEIC)结构的高双折射偏振保持光子晶体光纤(PCF),并利用带有各向异性完全匹配层吸收边界条件的全矢量有限元法(FEM)对这种光纤的特性参数进行了数值分析.结果表明这种结构的光子晶体光纤在1.55μm的双折射系数高达2.0×10^-3,在长轴和短轴方向上的模场直径分别为9.2μm和2.4μm.同时当短轴方向最内层空气孔的孔径在1.30—1.18μm范围内变化时(孔径变化范围～10%),其双折射系数的劣化小于1.2×10^-5,表明这种结 关键词： 光子晶体光纤 双折射 近椭圆内包层 偏振稳定性     

Effective nonlinear GaSe crystal. Optical properties and applications

We present an overview of the current state of the literature and research performed by the authors of the present paper on the experimental and theoretical results on the structural-, optical-, nonlinear optical (NLO)-properties (including two-photon absorption (TPA) and the terahertz (THz) range of spectra) and practical applications of a highly anisotropic Gallium Selenide (GaSe) semiconductor with emphasis on the ?-GaSe. Physical properties of ?-GaSe are important to researchers and designers developing different devices by using this material. This crystal possesses an outstanding NLO properties: high optical birefringence Δn ～ 0.3 at 700 nm; high transparency range (0.7?18.0 μm) with low absorption coefficient (α ≤ 0.3 cm^?1); very high nonlinear susceptibility χ⁽²⁾ (d ₂₂ ≈ 86 ± 17 pm/V, corresponding to (2.0 ± 0.4) × 10^?7 esu) that is used for phase matched second harmonic generation (SHG) in a wide transparency range; high power threshold for optical damage; possibility to perform optical frequency conversion under phase-matching conditions in the near- to mid-IR and THz range of spectra, etc. The domain structure of crystal in connection with the NLO properties is discussed as studied by confocal Raman microscopy experiments. Perspectives for future research of GaSe are considered in the present article, which does not pretend to be one reflecting all existing papers on GaSe crystal and discussed subjects.     

新型矩形点阵光子晶体光纤的高双折射负色散效应

设计了一种新型矩形点阵光子晶体光纤,该光纤纤芯缺失一根空气柱,包层沿光纤长度方向在普通矩形点阵光子晶体光纤中每两列之间隔一行插入一列空气孔而形成正方形网孔结构.采用全矢量有限元法并结合各向异性完美匹配边界条件,对该光纤的色散、双折射和约束损耗进行了数值模拟.结果发现,该光纤具有高双折射负色散效应和较强的模约束能力,约束损耗小于10-2dB·m-1,通过改变光纤结构参数(即空气孔间隔Λ和相对孔间隔d/Λ),可以调节该光纤高双折射负色散工作波长.若调整光纤结构参数Λ=2.0μm,d/Λ=0.4,该光纤在C波段(1.53—1.565μm)呈现负色散并具有负色散斜率,双折射高达10-2,非线性系数接近55km-1W-1.该光纤将在保偏光通信、色散补偿以及基于四波混频的波长转换器设计等方面具有重要的应用.     

V形高双折射光子晶体光纤特性研究

本文基于全矢量有限元法,设计了一种V形结构高双折射光子晶体光纤,数值分析结果表明:当光纤的包层孔间距Λ为1.0 μm,包层大空气孔D和小空气孔d分别为0.95 μm,0.7 μm时,在波长为1.55 μm处,该光纤的双折射度B达到1.225×10^-2,比传统光纤高约两个数量级. 另外,分别在可见光和近红外波段出现了两个零色散波长,使钛宝石飞秒激光器工作波段(700—980 nm) 处于光纤的反常色散区,为新颖的光子晶体 关键词： 光子晶体光纤 高双折射 有限元法 V形结构     

Full-scale atomistic simulations of dislocations in Ni crystal by embedded-atom method

Full-scale atomistic simulations by the nudged elastic band method are performed to determine the energetics and core structures of dislocations in a Ni lattice using an embedded-atom method potential. We find that for an edge dislocation, the potential yields very weak coupling between the partials which move almost individually. For a screw dislocation, the coupling between the partials is somewhat stronger and the partials move with some dependence. As expected, the results indicate that stacking fault energy has a controlling influence on the coupling behaviour of the partials. The effective Peierls energies and stresses are 1.30?×?10^?6?eV/Å and 2.79?×?10^?6?μ for the edge dislocation, and 1.62?×?10^?4?eV/Å and 2.02?×?10^?4?μ for the screw dislocation.     

High-birefringence hollow-core anti-resonant THz fiber

A novel high-birefringence hollow-core anti-resonant THz fiber is proposed in this paper. This fiber has a simple structure which consists of only ten Topas tubes. High birefringence is achieved by introducing two large tubes. The first two resonant frequencies are 1.44 and 2.88 THz by fixing tube thickness at 0.09 mm, which makes two low-loss transmission windows exist in the frequency range from 0.8 to 3.0 THz. The lowest loss is 2.10 dB/m occurring at 1.2 THz in the first transmission window and 1.68 dB/m at 2.34 THz in the second transmission window. By optimizing the structure parameters, high birefringence above 7 × 10^?4 in the frequency range from 1.0 to 1.24 THz are obtained. The highest birefringence is up to 8.7 × 10^?4 at 1.04 THz. Birefringence can be further increased to the order of 10^?3 by adjusting the structure parameters at the cost of loss increasing and the bandwidth decreasing. In addition, bent performance of this fiber is also discussed. In addition, this fiber can keep good performance when it is bent for x-direction. At the bend radius of 15 cm, the loss and birefringence has a more slightly change in the first transmission window than the second transmission window. The first transmission window own much better bent-insensitive characteristics.     

Mid-infrared high birefringence bow-tie-type Ge20Sb15Se65 based PCF with large nonlinearity by using hexagonal elliptical air hole

A high birefringence Ge₂₀Sb₁₅Se₆₅ based photonic crystal fiber (PCF) is proposed. It consists of a central defect core surrounded by two kinds of elliptical air holes with different size. The Finite Difference Time Domain method (FDTD) is used to simulate the guided modes of the designed PCF. The properties of this PCF are investigated including the birefringence, nonlinearity, and polarization mode dispersion in the mid-infrared range. The results show that for the optimized structure parameters, the highest birefringence of 0.1176 is obtained. The maximum nonlinearity coefficients of 38390 w^?1km^?1 and 49760 w^?1km^?1 for x- and y-polarization modes are achieved.     

Highly birefringent soft glass rectangular photonic crystal fibers with elliptical holes

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.     

A study of the α ↔ γ transformation in pure iron: rate variations revealed by means of thermal analysis

The α???γ transformation in nominally high purity Fe is shown to occur with a stepped peak in differential thermal analysis on both heating and cooling at rates between 0.5?K?min^?1 and 10?K?min^?1. The composite peaks mark changes in the transformation rate. To endorse the findings, the instrumental output has been thoroughly analyzed providing evaluations of time lags, suggestions for calibration and for the use of the derivative of the peak. The change in rate occurred in all samples irrespective of their grain size (average values from 91?µm to 1100?µm). The rate of movement of the interface in the α???γ transformation is estimated between 4?×?10^?5?m?s^?1 and 3?×?10^?6?m?s^?1. The present results extend previous dilatometric work in which the rate variation was detected only for large grain size and low undercooling. Possible reasons for the variation in rate are outlined: local development of strain in the austenite due to lattice misfit with respect of the growing ferrite, formation of a ragged microstructure and pinning of the boundaries by impurity.     

Extremely large birefringence and shifting of zero dispersion wavelength of photonic crystal fibers

Three different types of photonic crystal fibers have been investigated which promise very large birefringence. The first type fiber is band gap guiding, the second index guiding, while the third type is index guiding with high refractive index circular and elliptical regions in the innermost ring. The birefringence, group velocity dispersion, modal effective index and mode field area of these fibers have been numerically estimated by employing finite difference time domain method. When elliptical regions are introduced in the first and second rings with the combination of small circular regions, each of these proposed fibers exhibits large birefringence with shifted zero dispersion point. Among these three different types of fibers, the band gap guiding photonic crystal fiber promises the largest birefringence (～5.45×10^?2) reported so far. The value of the birefringence and group velocity dispersion of these fibers can be controlled by controlling the hole pitch. Largest birefringence is achieved with a specific value of hole pitch.     

A new design of low-loss and ultra-flat zero dispersion photonic crystal fiber using hollow ring defect

New hollow ring defect structure is introduced in photonic crystal fiber design for ultra- flat zero dispersion with very low waveguide losses. The hollow ring defect consisted of a central hole surrounded by a doped silica ring provides highly flexible defect engineering capabilities in photonic crystal fibers to achieve precise control of dispersion value and dispersion slope while independently maintaining low waveguide losses, which was not attainable in previous designs. A nearly flat zero dispersion of D=0±0.51 ps/nm km was obtained in the wavelength range of 1.44–1.61 μm with the maximum slope of ?2.7×10^?2 ps/nm² km. The confinement loss was less than 5.75×10^?8 dB/m along with the bending loss of 2.8×10^?6 dB/m for the radius of 10 mm, and splice loss of less than 1.57 dB to conventional single mode fiber at 1.55 μm.     

Detective quantum efficiency,modulation transfer function and energy resolution comparison between CdTe and silicon sensors bump‐bonded to XPAD3S

XPAD3S is a single‐photon‐counting chip developed in collaboration by SOLEIL Synchrotron, the Institut Louis Néel and the Centre de Physique de Particules de Marseille. The circuit, designed in the 0.25 µm IBM technology, contains 9600 square pixels with 130 µm side giving a total size of 1 cm × 1.5 cm. The main features of each pixel are: single threshold adjustable from 4.5 keV up to 35 keV, 2 ms frame rate, 10⁷ photons s^?1 mm^?2 maximum local count rate, and a 12‐bit internal counter with overflow allowing a full 27‐bit dynamic range to be reached. The XPAD3S was hybridized using the flip‐chip technology with both a 500 µm silicon sensor and a 700 µm CdTe sensor with Schottky contacts. Imaging performances of both detectors were evaluated using X‐rays from 6 keV up to 35 keV. The detective quantum efficiency at zero line‐pairs mm^?1 for a silicon sensor follows the absorption law whereas for CdTe a strong deficit at low photon energy, produced by an inefficient entrance layer, is measured. The modulation transfer function was evaluated and it was shown that both detectors present an ideal modulation transfer function at 26 keV, limited only by the pixel size. The influence of the Cd and Te K‐edges of the CdTe sensor was measured and simulated, establishing that fluorescence photons reduce the contrast transfer at the Nyquist frequency from 60% to 40% which remains acceptable. The energy resolution was evaluated at 6% with silicon using 16 keV X‐rays, and 8% with CdTe using 35 keV X‐rays. A 7 cm × 12 cm XPAD3 imager, built with eight silicon modules (seven circuits per module) tiled together, was successfully used for X‐ray diffraction experiments. A first result recently obtained with a new 2 cm × 3 cm CdTe imager is also presented.     

Formation of two-dimensional photonic-crystal structures in silicon for near-infrared region using fine focused ion beams

One of the two variants of producing two-dimensional photonic crystals in silicon is the formation of ordered macropore structures in a silicon substrate. The characteristic pore dimensions (the diameter and the wall thickness between pores) determine the wavelength range in which such a pore structure exhibits the properties of a photonic crystal. For the near-infrared region, these dimensions approach 1 μm or fall in a submicron region. An ordered structure of macropores with such dimensions is formed in this work using fine focused ion beams to provide the stimulating effect of implanted ions on pore nucleation in given sites on the silicon substrate surface. Pores are shown to nucleate at sites subjected to ion irradiation even at a low implantation dose (2×10¹³ ion/cm²). A model describing the orienting effect of ion irradiation on pore nucleation is proposed. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 1, 2004, pp. 35–38. Original Russian Text Copyright ? 2004 by Vyatkin, Gavrilin, Gorbatov, Starkov, Sirotkin.     

Optimization of highly nonlinear dispersion-flattened photonic crystal fiber for supercontinuum generation

A simple type of photonic crystal fiber (PCF) for supercontinuum generation is proposed for the first time. The proposed PCF is composed of a solid silica core and a cladding with square lattice uniform elliptical air holes, which offers not only a large nonlinear coefficient but also a high birefringence and low leakage losses. The PCF with nonlinear coefficient as large as 46 W 1 · km-1 at the wavelength of 1.55 μm and a total dispersion as low as ±2.5 ps · nm-1 · km-1 over an ultra-broad waveband range of the S-C-L band (wavelength from 1.46 μm to 1.625 μm) is optimized by adjusting its structure parameter, such as the lattice constant Λ , the air-filling fraction f , and the air-hole ellipticity η. The novel PCF with ultra-flattened dispersion, highly nonlinear coefficient, and nearly zero negative dispersion slope will offer a possibility of efficient super-continuum generation in telecommunication windows using a few ps pulses.     

Investigation of third-order optical nonlinearity in KBe2BO3F2 crystal by Z-scan

The third-order optical nonlinearity of deep-ultraviolet (DUV) nonlinear optical (NLO) crystal KBe₂BO₃F₂ (KBBF) was investigated using single-beam Z-scan technique for the first time. The Z-scans were performed on a c-cut KBBF crystal and a KBBF prism-coupling device (PCD) with picosecond pulses at 355?nm. No two-photon absorption was observed in the experiment. The measured nonlinear refraction index n ₂ showed positive signs, indicating self-focusing Kerr effects. The n ₂ values were estimated to be (1.75±0.35)×10^?15?cm²/W with the c-cut sample and (1.85±0.37)×10^?15?cm²/W with the PCD, corresponding to the third-order nonlinear optical susceptibilities $\chi_{\mathrm{eff}}^{(3)}$ of (0.99±0.20)×10^?13?esu and (0.94±0.19)×10^?13?esu, respectively. The results are expected to promote the investigation of frequency conversion processes with ultra-short laser in KBBF crystal.     

Synthesis and Analytical Application of a Novel Fluorescent Hg2+ Probe 3′, 6′-Bis(Diethylamino)-2-((2,4-Dimethoxybenzylidene)Amino)Spiro[Isoindoline-1,9′-Xanthene]-3-Thione

A novel probe, 3′,6′ - bis(diethylamino) -2- ((2,4-dimethoxybenzylidene)amino) spiro [isoindoline-1,9′-xanthene]-3-thione (RBS), was designed and synthesized. Its structure was characterized with elemental analysis, IR spectra and ¹H NMR. The probe displayed highly selective and sensitive recognition of Hg²⁺. Reacting with mercury ions in aqueous solution, its fluorescence intensity was enhanced significantly, while its color was changed from colorless to pink. So, a new fluorescence method of detection of Hg²⁺ was proposed. Its dynamic response concentration range and detection limit for Hg²⁺ were 5.00?×?10^?9 M to 1.00?×?10^?6 M detected and 1.83?×?10^?9 M, respectively. Satisfying results were obtained when the probe was applied to detect spiked Hg²⁺ in samples.     

Magnetostriction measurements of CoS2 single crystal

The magnetorestriction constants of CoS₂ single crystal were measured by a capacitance method in a temperature range from liquid N₂ to the Curie temperatures.The constants γ₁₀₀ and γ₁₁₁ are ?1.9 × 10^?6 and 5.7 × 10^?6 at liquid N₂ temperature respectively, and the absolute values of the constants decrease monotonically with the increase of the temperature. The volume magnetorestriction constant δω/δH at 110 K in the ferromagnetic state is 6 × 10^?10 Oe^?1.     

Effects of silicon negative ion implantation in semi-insulating gallium arsenide

ABSTRACT

In the present work, effects of silicon negative ion implantation into semi-insulating gallium arsenide (GaAs) samples with fluences varying between 1?×?10¹⁵ and 4?×?10¹⁷?ions?cm^?2 at 100?keV have been described. Atomic force microscopic images obtained from samples implanted with fluence up to 1?×?10¹⁷?ion?cm^?2 showed the formation of GaAs clusters on the surface of the sample. The shape, size and density of these clusters were found to depend on ion fluence. Whereas sample implanted at higher fluence of 4?×?10¹⁷?ions?cm^?2 showed bump of arbitrary shapes due to cumulative effect of multiple silicon ion impact with GaAs on the same place. GXRD study revealed formation of silicon crystallites in the gallium arsenide sample after implantation. The silicon crystallite size estimated from the full width at half maxima of silicon (111) XRD peak using Debye-Scherrer formula was found to vary between 1.72 and 1.87?nm with respect to ion fluence. Hall measurement revealed the formation of n-type layer in gallium arsenide samples. The current–voltage measurement of the sample implanted with different fluences exhibited the diode like behavior.