Switchable and tuneable multi-wavelength Er-doped fibre ring laser using Sagnac filters

We demonstrate experimentally a simple configuration to perform wavelength-tuning and multi-wavelength operation in a fibre ring laser that is composed of an Erbium-doped fibre and includes a fibre-optic Sagnac interferometer as a spectral filter. We consider three different Sagnac filters including a 3 dB coupler, two wave retarders (WRs) and respectively 7 cm, 1 and 7 m of high birefringence fibre. The transmission spectrum of each filter is sinusoidal with a 70, 6, and 0.85 nm period, and its maxima can be shifted over one period by adjusting the angle of the retarders in the loop. By adjusting the WRs included in the filter and in the laser ring, tuneable single wavelength and several two- or three-wavelength lasing regimes were observed. In particular, fine adjustments of the WRs allow observing two- and three- wavelength operation with wavelength separations well below the homogeneous bandwidth of the gain medium. The stability of these modes of operation however strongly depends on environmental conditions at room temperature.     

Noise robustness of the nonlocality of entangled quantum states

We study the nonlocal properties of states resulting from the mixture of an arbitrary entangled state rho of two d-dimensional systems and completely depolarized noise, with respective weights p and 1-p. We first construct a local model for the case in which rho is maximally entangled and p at or below a certain bound. We then extend the model to arbitrary rho. Our results provide bounds on the resistance to noise of the nonlocal correlations of entangled states. For projective measurements, the critical value of the noise parameter p for which the state becomes local is at least asymptotically log(d) larger than the critical value for separability.     

远红外窄带滤光片厚度的鲁棒性分析

鉴于在制备过程中存在介质层厚度的随机扰动,计算了远红外窄带滤光片厚度的鲁棒性。结果表明:当随机度小于0.05时,窄带滤光片全向带隙和带隙率变化不大,但缺陷层的透射率只有原来的1/3左右;当随机度大于0.1时,随着厚度的随机扰动逐渐增大,窄带滤光片的全向带隙和带隙率都逐渐减小;当随机度达到0.2时,窄带滤光片的第一个全向带隙消失,第二个全向带隙向短波方向偏移明显,缺陷层的透射率也只有原来的1/3左右;当随机度达到0.5时,窄带滤光片的两个全向带隙全部消失。制备了一种远红外窄带滤光片,其结果较好地验证了厚度的随机扰动对滤光片的影响。     

远红外窄带滤光片厚度的鲁棒性分析

鉴于在制备过程中存在介质层厚度的随机扰动,计算了远红外窄带滤光片厚度的鲁棒性。结果表明:当随机度小于0.05时,窄带滤光片全向带隙和带隙率变化不大,但缺陷层的透射率只有原来的1/3左右;当随机度大于0.1时,随着厚度的随机扰动逐渐增大,窄带滤光片的全向带隙和带隙率都逐渐减小;当随机度达到0.2时,窄带滤光片的第一个全向带隙消失,第二个全向带隙向短波方向偏移明显,缺陷层的透射率也只有原来的1/3左右;当随机度达到0.5时,窄带滤光片的两个全向带隙全部消失。制备了一种远红外窄带滤光片,其结果较好地验证了厚度的随机扰动对滤光片的影响。     

Photo-acoustic and photo-refractive detection of small absorptions in liquids

The sensitivities of pulsed photo-acoustic and photo-refractive (e.g., thermal lensing) techniques for the measurement of small absorptions in liquids have been evaluated both theoretically and experimentally. Electrostriction limits the sensitivity of both techniques, this limitation is less severe for the photo-refractive technique. The minimum absorption constants observed experimentally, for a 200-μm laser spot size in liquid N₂, are 4 × 10^-5 cm^-1 for the photo-acoustic measurement and 6 × 10^-7 cm^-1 for the photo-refractive measurement. The calculated electrostrictive limits are 2 × 10^-5 cm^-1 and 7 × 10^-11 cm^-1, respectively.     

Development of a tuneable channel cut crystal

We have developed the first tuneable channel cut crystal for ultra small angle neutron scattering and neutron optical experiments. The Darwin range of a perfect crystal can be reduced down to a fraction of its natural width. This “Darwin reduction” was realised without any change of the beam geometry which yields an intensity gain relative to conventional asymmetric Bragg diffraction. With such tuneable channel cut crystal peaks nearly δ-peaks can experimentally be realised.     

Raman scattering from tuneable hot phonons and polaritons

We report the observation of Stokes and anti-Stokes Raman scattering from angular tuneable hot phonons and polaritons which have been pumped in uniaxial RbClO₃ crystals by a Q-switched CO₂ laser and probed with a c.w. argon ion laser.     

A tuneable 600 GHz bandpass-filter with large free-spectral-range

Considering recent ozon problems in the upper atmosphere the measuring technique in the spectral range of about some hundred GHz gains in importance increasingly. Ozon concentration is measured by high sensitive radiometers consisting of several quasioptical components. A tunable bandpass filter represents a versatile component in such a test assembly. The bandpass filter is realized as interferometer and can be adapted to its respective application by individual tuning of its coupling links. Metallic meshes of different aperture size are used for injection and feedback of the electromagnetic wave. A stepper motor control serves for the integration in an automatic measurement setup. The construction principles of the interferometer are summarized. An analysis of the component by means of plane wave theory is extended to a theory of diffraction. Finally the theoretical approach is verified on an application as single-sideband filter comparing the measured results with the computed values of the simulation.     

Cavity QED based tuneable,delayed-choice quantum eraser

We propose an experimentally feasible idea for the delayed-choice quantum eraser, having adjustable path distinguishability/fringe visibility. The schematics are based on resonant, dispersive and Ramsey interactions of atoms under cavity QED scenario. The option for tuneability of the fringes in a delayed-choice setup stringently marks the conception of the time in the quantum theory, operational meanings of the state vector reduction and raises questions about Ψ$\Psi$-ontic models while helping to shed out the controversies surrounding the quantum eraser theme. The proposal can be efficiently executed experimentally within the prevailing cavity QED experimental research scenario with good overall success probability and fidelity.     

可调谐二极管激光吸收光谱二次谐波检测方法的研究

可调谐二极管激光吸收光谱技术(TDLAS)是利用二极管激光器的波长扫描和电流调谐特性来实现痕量气体吸收曲线二次谐波检测的一种新技术,具有高灵敏、高选择性、高精度等特点。理论分析和实验结果表明:利用二次谐波检测到的信号特征除了与被测气体的吸收特征有关外,还与波长扫描参数和电流调制参数有密切的关系。通过研究不同波长的扫描参数和在功率调制参数下的二次谐波曲线,分析了它们的波形特征和稳定性,以便寻求最佳的波长扫描参数和功率调制参数,从而使二次谐波曲线的稳定性和形状达到最佳。     

Multi-component chemical analysis of gas mixtures using a continuously tuneable lidar system

Differential absorption lidar (DIAL) measurements are usually made on single compounds by alternately switching the wavelength between on and off a resonance line. The selection of more than two wavelengths is a mathematical necessity for simultaneous measurement of multiple species or for resolving interference effects between a compound of interest and a background gas such as water vapour or carbon dioxide. This is especially true in the mid-IR region, where many hydrocarbon compounds have important spectral features. We present a method for remote measurement of gas mixtures in the mid-IR region based on a newly developed fast-switching, frequency-agile optical parametric oscillator lidar transmitter. A multivariate statistical procedure has also been applied for this system, which combines a genetic algorithm for wavelength selection with a partial least squares method for identifying individual compounds from their combined absorption spectrum. A calibration transfer is performed for compounds of interest using reference spectra from an absorption spectra database. Both indoor absorption cell measurements and outdoor remote range resolved measurements of hydrocarbon mixtures were performed to explore the performance of the method. PACS 42.62 Fi; 42.79 Qx; 02.50 Sk     

Theory of filters

We consider the following statistical problem: suppose we have a light beam and a collection of semi-transparent windows which can be placed in the way of the beam. Assume that we are colour blind and we do not possess any colour sensitive detector. The question is, whether by only measurements of the decrease in the beam intensity in various sequences of windows we can recognize which among our windows are light beam filters absorbing photons according to certain definite rules? To answer this question a definition of physical systems is formulated independent of “quantum logic” and lattice theory, and a new idea of quantization is proposed. An operational definition of filters is given: in the framework of this definition certain nonorthodox classes of filters are admissible with a geometry incompatible to that assumed in orthodox quantum mechanics. This leads to an extension of the existing quantum mechanical structure generalizing the schemes proposed by Ludwig [10] and the present author [13]. In the resulting theory, the quantum world of orthodox quantum mechanics is not the only possible but is a special member of a vast family of “quantum worlds” mathematically admissible. An approximate classification of these worlds is given, and their possible relation to the quantization of non-linear fields is discussed. It turns out to be obvious that the convex set theory has a similar significance for quantum physics as the Riemannian geometry for space-time physics.     

Interference filters

An account is given of the application of thin-film interference to the production of both anti-reflection and high-reflection coatings on glass, and the more recent developments of multiple-film, Fabry-Perot, and frustrated total internal reflection filters. Applications include the 'cold mirror' which reflects visible light and transmits infra-red, and the 'dichroic mirror' used for colour separation in the colour television camera which is described briefly.     

Analysis of robustness of urban bus network

In this paper,the invulnerability and cascade failures are discussed for the urban bus network.Firstly,three static models(bus stop network,bus transfer network,and bus line network) are used to analyse the structure and invulnerability of urban bus network in order to understand the features of bus network comprehensively.Secondly,a new way is proposed to study the invulnerability of urban bus network by modelling two layered networks,i.e.,the bus stop-line network and the bus line-transfer network and then the interactions between different models are analysed.Finally,by modelling a new layered network which can reflect the dynamic passenger flows,the cascade failures are discussed.Then a new load redistribution method is proposed to study the robustness of dynamic traffic.In this paper,the bus network of Shenyang City which is one of the biggest cities in China,is taken as a simulation example.In addition,some suggestions are given to improve the urban bus network and provide emergency strategies when traffic congestion occurs according to the numerical simulation results.