All-optical switching and nonlinear optical properties of HBT in ethanol solution

This paper demonstrates an all-optical switching model system comprising a single pulsed pump beam at 355 nm and a CW He--Ne signal beam at 632.8 nm with 2-(2^\prime -hydroxyphenyl)benzothiazole (HBT) in ethanol solution. The origins of the optical switching effect were discussed. By the study of nonlinear optical properties for HBT in ethanol solvent, this paper verified that the excited-state intramolecular proton transfer (ESIPT) effect of HBT and the thermal effect of solvent worked on quite different time scales and together induced the change of the refractive index of HBT solution, leading to the signal beam deflection. The results indicated that the HBT molecule could be an excellent candidate for high-speed and high-sensitive optical switching devices.     

基于可调谐Fano干涉的超快全光开关

简要介绍了量子相干和干涉效应的研究动态和一项最新理论研究进展.设计了一个存在Fano类型隧穿感应量子干涉的GaAs/A lxGa1-xAs非对称量子阱结构.在该量子阱中,可通过一束控制光抑制量子干涉,进而调制信号光的传播特性.这一现象可用来实现一个宽带超快全光开关.     

基于可调谐Fano干涉的超快全光开关

简要介绍了量子相干和干涉效应的研究动态和一项最新理论研究进展.设计了一个存在Fano类型隧穿感应量子干涉的GaAs/AlxGa1-xAs非对称量子阱结构.在该量子阱中,可通过一束控制光抑制量子干涉,进而调制信号光的传播特性.这一现象可用来实现一个宽带超快全光开关.     

Ultrafast all optical switching via tunable Fano interference

Tunneling induced quantum interference experienced by an incident probe in asymmetric double quantum wells can easily be modulated by means of an external control light beam. This phenomenon, which is here examined within the dressed-state picture, can be exploited to devise a novel all-optical ultrafast switch. For a suitably designed semiconductor heterostructure, the switch is found to exhibit frequency bandwidths of the order of 0.1 THz and response and recovery times of about 1 ps.     

Optical properties of amyloid stained by Congo red: History and mechanisms

Amyloid stained by Congo red has striking optical properties that generally have been poorly described and inadequately explained, although they can be understood from principles of physical optics. Molecules of Congo red are orientated on amyloid fibrils, and so the dye becomes dichroic and birefringent. The birefringence varies with wavelength in accordance with a fundamental property of all light-transmitting materials called anomalous dispersion of the refractive index around an absorption peak. The combination of this and absorption of light, with modification by any additional birefringence in the optical system, explains the various colours that can be seen in Congo red-stained amyloid between crossed polariser and analyser, and also when the polariser and analyser are progressively uncrossed. These are called anomalous colours.     

Phase-controlled absorption-gain properties and optical switching in nanodiamond nitrogen-vacancy center

We study phase-controlled absorption-gain and dynamic switching behaviors in a nanodiamond nitrogen-vacancy (NV) center. The NV center is driven coherently by a weak probe laser field, a control laser field and a microwave field. To describe the transient behavior of the system, we go beyond the steady-state approximation and simultaneously solve the coupled Bloch–Maxwell equations for the NV center and the probe field on numerical grids as functions of space and time. The results show that the continuous-wave input weak probe field can be switched on and off when the relative phase of the applied field is externally varied periodically in time. The proposed scheme may have applications in the design of optical switching and optical gain devices.     

Non-linear optical properties of silver nanoparticles prepared by hydrogen reduction method

Silver nanoparticles have been prepared using hydrogen gas as the reducing agent for silver nitrate and poly(vinyl pyrrolidone) as the capping agent; the reaction was carried out at 70 °C for 3 h. The size of the nanoparticles was found to be about 20 nm as analyzed using transmission electron micrographs. The X-ray diffraction pattern revealed the face-centered cubic (fcc) structure of silver nanoparticles. The linear absorption of Ag nanoparticles, α, is obtained about 3.71 cm⁻¹. The non-linear refractive indices of silver nanoparticles were defined by the z-scan technique using CW He-Ne laser (λ = 632.8 nm) at different incident intensities. The magnitude of non-linear refractive index (n₂) was measured to be in the order of 10⁻⁷ (cm²/W) with a negative sign. Therefore self-defocusing phenomena is taking placed for Ag nanoparticles.     

Low temperature reflectivity and optical properties of red mercury iodide

The reflectivity of red HgI₂ in the spectral range of 2–10 eV at 100 K with E⊥c is studied and the optical constants are deduced by means of the Kramers and Kronig relations. It is evidenced that the valence band is split in two subbands. Furthermore reflectivity spectra on good natural surfaces at 15 K in the two polarizations have been measured, and a high energy excitonic series, characterized by a large value of the Rydberg, is found.     

Linear and nonlinear optical properties of Ag-As-Se chalcogenide glasses for all-optical switching

We prepared Ag(x)(As0.4Se0.6)(100-x) chalcogenide glasses by a melt-quenching method and measured their linear and nonlinear optical properties to evaluate their potential applications to all-optical ultrafast switching devices. Their nonlinear refraction and absorption were measured by the Z-scan method at 1.05 microm. The addition of Ag to As2Se3 glass led to an increase in the nonlinear refractive index without introducing an increase in the nonlinear absorption coefficient. The glass with a Ag content of x = 20 at. % revealed high nonlinearity ranging from 2000 to 27,000 times that of fused silica, depending on the incident optical intensity.     

Third-order nonlinear optical properties of gold nanoshells in aqueous solution

The third-order nonlinear optical properties of gold nanoshells in aqueous solution have been investigated by using open- and closed-aperture Z-scan methods. The real and imaginary third-order nonlinear susceptibilities are obtained to be about -1.1422×10^-13 and -2.4302×10^-14 esu, respectively. We further have investigated the electric field enhancement for gold nanoshells in aqueous solution by means of a finite-element method and ascribed the small third-order nonlinear susceptibility to the smaller volume fraction and local field factor. PACS  42.65.Re; 78.67.Bf; 73.22.Lp     

Non-linear applications of microstructured optical fibres

The enhancement of different non-linear processes in microstructured optical fibres can be achieved through manipulation of the dispersion characteristics of the fibre. This is demonstrated by extending the region of short wavelength operation of high power supercontinuum generation through four wave mixing in a cascaded fibre geometry where the dispersion of each fibre decreased on propagation. The technique is further refined in a demonstration utilizing long lengths of dispersion decreasing tapered microstructured fibres, where the supercontinuum extends to around 300 nm with spectral power densities in excess of 2 mW/nm in the uv. These long length tapers can also be utilized for adiabatic soliton pulse compression in new spectral regions, allowing the compression of 655 fs pulses to 45 fs.     

Sonocatalytic rapid degradation of Congo red dye from aqueous solution using magnetic Fe0/polyaniline nanofibers

Nano-sized magnetic Fe⁰/polyaniline (Fe⁰/PANI) nanofibers were used as an effective material for sonocatalytic degradation of organic anionic Congo red (CR) dye. Fe⁰/PANI_, was synthesized via reductive deposition of nano-Fe⁰ onto the PANI nanofibers at room temperature. Prepared catalyst was characterized using HR-TEM, FE-SEM, XRD, FTIR instruments. The efficacy of catalyst in removing CR was assessed colorimetrically using UV–visible spectroscopy under different experimental conditions such as % of Fe⁰ loading into the composite material, solution pH, initial concentration of dye, catalyst dosage, temperature and ultrasonic power. The optimum conditions for sonocatalytic degradation of CR were obtained at catalyst concentrations = 500 mg.L⁻¹, concentration of CR = 200 ppm, solution pH = neutral (7.0), temperature = 30 °C, % of Fe⁰ loading = 30% and 500 W ultrasonic power. The experimental results showed that ultrasonic process could remove 98% of Congo red within 30 min with higher Q_max value (Q_max = 446.4 at 25 °C). The rate of degradation of CR dye was much faster in this ultrasonic technique rather than conventional adsorption process. The degradation efficiency declined with the addition of common inorganic salts (NaCl, Na₂CO₃, Na₂SO₄ and Na₃PO₄). The rate of degradation suppressed more with increasing salt concentration. Kinetic and isotherm studies indicated that the degradation of CR provides pseudo-second order rate kinetic and Langmuir isotherm model compared to all other models tested. The excellent high degradation capacity of Fe⁰/PANI under ultrasonic irradiation can be explained on the basis of the formation of active hydroxyl radicals (OH) and subsequently a series of free radical reactions.     

Electronic structure and optical properties of the red and yellow mercuric iodides

With the help of the ab initio full-potential linearized augmented plane wave (FPLAPW) method, calculations of the electronic structure and linear optical properties are carried out for red HgI₂ and yellow HgI₂. It is found that the red HgI₂ has a direct gap of 1.22834 eV and the yellow HgI₂ has an indirect gap of 2.11222 eV. For the red HgI₂, the calculated optical spectra are qualitatively in agreement with the experimental data. Furthermore, the origins of the different peaks of ε ₂ (ω ) are discussed. Our calculated anisotropic dielectric function of the red HgI₂ is a nice match with the experimental results. Our calculated results are able to reproduce the overall trend of the experimental reflectivity spectra. Although no comparable experimental and theoretical results are available, clearly, the above proves the reliability of our calculations, suggesting that our calculations should be convincing for the yellow HgI₂. Finally, the different optical properties are discussed.     

Synthesis of Mn-doped ZnS architectures in ternary solution and their optical properties

Mn-doped ZnS sea urchin-like architectures were fabricated by a one-pot solvothermal route in a ternary solution made of ethylenediamine, ethanolamine and distilled water. The as-prepared products were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and photoluminescence spectra (PL). It was demonstrated that the as-prepared sea urchin-like architectures with diameter of 0.5-1.5 μm were composed of nanorods, possessing a wurtzite structures. The preferred growth orientation of nanorods was found to be the [0 0 2] direction. The PL spectra of the Mn-doped ZnS sea urchin-like architectures show a strong orange emission at 587 nm, indicating the successful doping of Mn²⁺ ions into ZnS host. Ethanolamine played the role of oriented-assembly agent in the formation of sea urchin-like architectures. A possible growth mechanism was proposed to explain the formation of sea urchin-like architectures.     

Non-linear ramsey resonance in the optical region

The interaction of gas particles with three separated light fields has been considered. It has been shown that a resonance with the width equal to the reciprocal transit time appears in such a system. The resonance is due to coherence conservation and change of distribution of a number of particles by nonlinear interaction with the fields. Its properties are close to the Ramsey resonance in the microwave range. This new type of resonance may have a relative width of 10⁻¹¹ to 10⁻¹².     

Separation and insertion of optical bit-serial label in optical packet switching

The bipolar phase-shift-keying (BPSK) optical orthogonal codes (OOCs) are inserted into the optical packet format of bit-serial label. The ultra-fast separation of the label and payload is performed through the auto-correlation pulses indicating the time position at which the optical switch changes the state.The insertion of the new label can also be realized by detecting the auto-correlation pulse at the line rate. Especially, the scheme can be adapted to the asynchronous separation and insertion and realize the variable-length packet switching. The results of simulation verify the feasibility of the scheme.     

Gain-assisted optical switching in plasmonic nanocavities

A plasmonic cavity filled with active material is proposed to explain optical switching. Optical properties, including transmission, response time, and field distribution of on/off state, are numerically investigated. We demonstrate that such a gain-assisted plasmonic structure can achieve optical switching in the nan- odomain and shorten the switching time to the subpicosecond level. Our results indicate the potential application of the proposed structure in optical communication and photonic integrated circuits.     

光突发交换中交换矩阵配置时间的影响研究

光突发交换是近几年出现的一种很有前途的交换技术。在光突发交换网络的核心节点中,光交换矩阵是一个关键部件,其配置时间影响到光突发交换网络的性能。这种影响表现在对数据信道可用时间施加了限制。在考虑光交换矩阵配置时间的基础上给出了修正后的LAUC算法,并通过计算机仿真研究了这种配置时间对光突发交换性能的影响。结果表明,光交换矩阵配置时间的增大会导致输出数据信道利用率的降低,进而增大了数据丢失率。     

Nonlinear optical properties of silver colloidal solution by in situ synthesis technique

The silver colloidal solutions were prepared by in situ synthesis technique in the presence of the Polymethyl Methacrylate, which was polymerized by reversible addition-fragmentation transfer. The UV–VIS spectra and transmission electron microscopy had shown the formation of sphere silver nanoparticles with average size of 10 nm. Nonlinear optical properties as a function of silver concentration were studied using Z-scan technique with 13 ns pulse duration at 532 nm. The optical nonlinearity enhancement was observed by increasing the concentration. The third-order nonlinear susceptibility χ⁽³⁾ was measured to 1.045 × 10⁻¹¹ esu when the concentration was 2.13 mg/ml. Besides, the sample was founded to exhibit a shift from saturable absorption to reverse saturable absorption at higher incident laser energy. The reverse saturable absorption was observed to be responsible for the optical limiting characteristics in our experiments.