Broad-band EDFA gain flattening by using an embedded long-period fiber grating filter

An erbium-doped fiber amplifier (EDFA) gain flattening technique using an embedded long period grating (ELPG) is proposed. By bending the ELPG, due to different coupling strengths yielded from different bending curvatures, it can be used for both the static and dynamic gain flattening despite of the different pump currents of the EDFA. The experimental results demonstrate that the flattened gain region of 34 nm can be achieved within 1 dB ripple.     

Optimizing the EDFA gain for WDM lightwave system with temperature dependency

The gain-flattened erbium-doped fiber amplifier (EDFA) is a key device for wavelength division multiplexing (WDM) modern optical network systems. A flat spectral gain EDFA has been achieved by controlling the doped fiber length and the pump power. The purpose of this paper is to study the variation of gain flattening over the temperature range from ?20 to +60 °C. The results obtained here indicate that gain flatness increases as temperature increases.     

Designing optimal long-period fiber gratings with the overlapped Gaussian-apodization method for flattening EDFA gain spectra

A new and effective optimization approach to the inverse design problems of complex long-period fiber grating (LPG) filters was developed in the present study. The proposed synthesis method was based on the overlapped Gaussian-apodization method and the evolutionary optimization algorithm which can efficiently search for optimal solutions and simultaneously take into account various experimental requirements for the fabrication of the designed filters. To verify the effectiveness of the proposed method, a LPG filter for flattening EDFA gain spectra was designed. Compared to the existing results from discrete layer-peeling (DLP) inverse scattering algorithms, an LPG filter with adaptive grating lengths and much simpler, smoother, and less complicated coupling coefficient profiles for taking the practical fabrication conditions for gain flattening into account, was used in the proposed method. Simulation results confirm that optimal solutions of an LPG filter design are suitable for practical fabrication.     

Adjustable EDFA gain equalization filter for DWDM channels based on a single LPG excited by flexural acoustic waves

A fast adjustable gain equalization filter for dense wavelength division multiplexing (DWDM) system is reported. The method is based on a single long period fiber grating (LPG) which is excited by means of flexural acoustic waves. The equalization of a typical erbium doped fiber amplifier (EDFA) gain spectrum with a gain flatness of <0.3 dB over a 32 nm bandwidth is demonstrated. The filter adjustment is obtained by choosing different acoustic loads applied to the acousto-optic modulator, which presents a switching time of ～17 μs. A maximum power penalty of 0.84 dB, relatively to the back-to-back signal, was achieved.     

Enhanced optical gain clamping for upstream packet based traffic on hybrid WDM/TDM-PON using fiber Bragg grating

In this paper, we propose a method to mitigate the temporal power transients arising from Erbium doped fiber amplifiers (EDFAs) on packeted/bursty scenario. The technique, applicable on hybrid WDM/TDM-PON for extended reach, is based on a low power clamping provided by a distributed feedback (DFB) laser and a fiber Bragg grating (FBG). An improvement in the data signal Q factor was achieved keeping the clamping control signal with a low power, accompanied by a maximum reduction in the gain excursion of 1.12 dB.     

Limitation in the intrinsic method of EDFA gain optimization for 32 × 40 Gbit/s WDM systems

The gain flattening of the erbium doped fiber amplifier (EDFA) is one of the most important aspects in the EDFA which the gain is wavelength dependent. For the first time the limitation of EDFA gain optimizing for a 32-channel wavelength division multiplexing (WDM) systems is investigated and reported in this paper. In a 32-channel WDM system the most favorable flatness gain achieved was 23.16 ± 1.51 dB with an average noise figure of 5.70 dB. This outcome proposes that the method does not achieve a uniform spectral gain in a 32-channel WDM system that incorporates a bandwidth of around 25 nm. Based on the simulation results the intrinsic optimization of EDFA causes the poor SNR and peak signal power with great variation over a transmission distance of 480 km single mode fiber.     

开放边界条件下改进的Nagel-Schreckenberg交通流模型的研究

在开放边界条件下,采用改进的NagelSchreckenberg交通流模型,数值模拟了在不同参数下的交通流基本图,结果表明,改进的NagelSchreckenberg模型的交通流量较原来的模型有明显提高,并分析和讨论了从自由运动相转化为最大流量相或从阻塞相转化为自由运动相的特性及其临界点变化规律 关键词： 元胞自动机 交通流 开放边界条件 相变     

一种改进Nagel-Schreckenberg模型在开放边界条件下交通流的研究

研究了一种改进的Nagel-Schreckenberg模型在开放边界条件下交通流的性质，分析了边界条件，安全距离，刹车概率对交通流的影响. 关键词： 元胞自动机 交通流 安全距离 延迟起动     

Polarization-invariant grating based on a photoaligned liquid crystal in an oppositely twisted binary configuration

We demonstrate a polarization-invariant liquid-crystal (LC) grating in an oppositely twisted and mutually orthogonal configuration. The polarization-invariant LC grating with high diffraction efficiency is fabricated using a single-masking process with two-step exposure of a linearly polarized ultraviolet light. It is found that the zeroth- and the first-order diffracted beams are linearly polarized and perpendicular to each other irrespective of the incident polarization for the phase retardation of m pi (m=integer).     

Transient two-wave mixing in a linear configuration of an adaptive interferometer based on Er-doped fiber with saturable absorption

We report results of transient two-wave mixing (TWM) in Er-doped fibers with saturable absorption in a linear configuration of an adaptive interferometric vibrometer with essentially different powers of recording waves. The TWM signal modulation depth detected in the weak (reflected) wave was shown to be twice as strong as in the symmetric configuration with equal recording powers. In accordance with theoretical predictions, the experimentally observed TWM signal amplitude grew continuously with the fiber optical density in the whole investigated range of alpha(0)L approximately 0.2-4. At the recording wavelength 1492 nm it proved to be quite close to the theoretical limit of approximately alpha(0)L/2 for weakly absorbing fibers, and in 1-m-long fiber of high optical density reached maximal value of approximately 0.8. The TWM response time went down with the recording light power and for P(0) approximately 10 mW was in the submillisecond region.     

A prediction method for road traffic noise generated from arbitrary non-poisson type traffic flow based on an approach equivalent to that for a standard poisson type traffic flow

In order to establish a prediction method for road traffic noise generated from actual traffic flow of an arbitrary non-Poisson type, a new approach equivalent to that for an idealized Poisson type traffic flow is proposed for practical use. This prediction method is able to treat any kind of road traffic noise fluctuation generated from actual non-Poisson type traffic flow, once information has been obtained on the wave form of the level time pattern observed when one vehicle passes directly in front of an observation point. The validity of the proposed prediction method has been experimentally confirmed by applying it to actually observed road traffic noise data.     

High-speed all-optical differentiator based on a semiconductor optical amplifier and an optical filter

We demonstrate a novel all-optical differentiator that carries out the first-order temporal derivation of optical intensity variation at high speed. It consists of a semiconductor optical amplifier (SOA) and an optical filter (OF) serving as an optical phase modulator and a frequency discriminator, respectively. A polarity-reversed derivative pair with a certain bias can be obtained by locating the probe wavelength at the positive or negative slope of the OF. Differentiations of super-Gaussian and Gaussian signals are obtained at various data rates. Defined as the mean absolute deviation of the measured result from the ideal result, total average errors of less than 0.12 are observed in all cases. Input power dynamics as well as control wavelength dependence are investigated and show that the cross-gain modulation in the SOA is detrimental to the differentiation performance.     

基于元胞自动机模型的高速公路可变速度限制交通流特性分析

在STNS模型的基础上,建立了可利用智能交通系统实时信息的高速公路可变速度限制区段元胞自动机模型,对动态速度控制区段的交通流特性进行模拟,分析了不同有效限速值、区段长度与交通状况下的限速对交通流和道路通行能力的影响,以及限速有效性条件．模拟结果表明可变速度限制作为交通管理控制的辅助手段,具有一定的使用条件,针对不同交通状况采用不同的最优限速值和区段长度的动态速度控制方法,可在保证交通安全的前提下达到抑制交通拥堵、减少车辆总通行时间从而提高道路实际通行能力的目的．     

A quantitative analysis of an athermal design for a long period grating based tunable filter

In this paper, a quantitative analysis of an athermal design for a unique all-fiber tunable filter based on the combination of a single resonant band long period grating (LPG) with an electro-optic polymer second cladding layer is presented. The single resonant band LPG is used to select the resonant wavelength, which can be tuned by changing the refractive index of an electro-optic polymer second cladding layer via external electric field. Although the basic operational principle and implementation of this unique tunable filter have been previously reported, this paper is focused on the quantitative analysis of the athermal design, which may significantly enhance the practicability of the proposed tunable filter.     

A splitting method for incompressible flows with variable density based on a pressure Poisson equation

A new fractional time-stepping technique for solving incompressible flows with variable density is proposed. The main feature of this method is that, as opposed to other known algorithms, the pressure is determined by just solving one Poisson equation per time step, which greatly reduces the computational cost. The stability of the method is proved and the performance of the method is numerically illustrated.     

New design for a variable optical attenuator based on a bent channel waveguide

We present a new method for bend loss control in a curved channel optical waveguide and employ it in a novel design of a thermo-optic variable optical attenuator. We show that the introduced asymmetric refractive index profile of the waveguide structure, combined with the optimal placement of the heating electrodes, leads to a significant increase of the dynamic range of the attenuator. PACS 42.82.Et; 42.70.Jk; 42.79.Ta     

Noise squeezing in a semiconductor laser with an inhomogeneously broadened gain line

This paper is a theoretical analysis of the noise produced by a single-mode semiconductor laser. We allow for spectral hole-burning in the gain line and for the nonlinear dependence of the carrier spontaneous recombination rate on the number of carriers in the active area. We show that these processes do not inhibit the squeezing of the outgoing photon flux noise below the shot noise level at high pump currents but that the degree of squeezing decreases considerably. Finally, we establish that these processes also considerably narrow the squeezing bandwidth. Zh. éksp. Teor. Fiz. 112, 429–440 (August 1997)     

A gain-clamped-semiconductor-optical-amplifier combined with a distributed Raman-fiber-amplifier: a good candidate as an inline amplifier for WDM networks

A gain-clamped semiconductor optical amplifier (SOA) is used as an inline amplifier in combination with a distributed Raman fiber amplifier. The combined amplifier has 20 dB gain and a noise figure below 2.7 dB. The optical signal to noise ratios after five spans of 20 dB loss, equivalent to 5 × 80 km, are over 25.2 dB for eight-channel transmissions. In addition, the potentially compact amplifier shows negligible transients under dynamic add-drops.     

Algebraic conditions for a function on an abelian group

We characterize functions on an Abelian group which satisfy certain algebraic conditions. We then apply this result to obtain generalizations of the Jordan-von Neumann theorem on quadratic forms. These last results are then used to prove a theorem on observable systems in axiomatic quantum mechanics.