L-band EDFA 性能与增益光纤长度关系的分析

分析和模拟L_band EDFA的增益特性对其优化设计和实验有着重要的意义。基于Giles模型,数值模拟了L_band EDFA中的信号光、泵浦光和放大自发辐射(ASE)在一定泵浦功率下与铒光纤长度的关系;分析了L_band EDFA本征增益平坦的产生机理;数值模拟了小信号增益平坦特性。结果表明,在一定的泵浦功率下,如果在所选择的L_bandEDFA中铒光纤长度合适,则不需要任何平坦化处理就可以得到比较平坦的增益谱线。     

Design and implementation of fuzzy logic based automatic gain controller for EDFAs

In this study, the design and implementation of a fuzzy logic (FL) based automatic gain controller card (AGC) is performed in order to control the pump laser current with respect to signal power and signal wavelength. The FL-AGC card consists of an amplifier, an analogue to digital converter (ADC), a digital to analogue converter (DAC), and a FL based software that is embedded to a microcontroller. With this configuration, gain flattening at the output of the erbium doped fibre amplifier (EDFA) along C band is achieved. In this way, ergonomically designed FL-AGC card can be easily matched with EDFAs and can be applicable to optical system applications.     

低噪声、高增益的L -band EDFA的实验研究

针对传统的L-band EDFA的工作效率低,提出了一种基于单根光纤光栅、泵浦分配、两段级联的EDFA的新结构,其中的光纤光栅用来反射无用的后向C-band ASE.系统地研究了泵浦比例和光纤光栅波长对增益噪声指数的影响关系.最后经实验验证,得到了低噪声、高增益的L-band的EDFA.其在输入信号光（1570 nm）功率为-30 dBm及泵浦功率为70 mW时,增益为22.26 dB,增益噪声指数为4.96 dB.     

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.     

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.     

Gain optimization of an erbium-doped fiber amplifier and two-stage gain-flattened EDFA with 45 nm flat bandwidth in the L-band

An erbium-doped fiber amplifier (EDFA) is simulated. The variation of gain with different parameters is obtained and the values of these parameters are optimized to achieve a maximum value of gain. A two-stage gain-flattened EDFA consisting of two EDFAs in series is also simulated. In the operating range of 1565-1610 nm, the flat gain of 46 dB is obtained.     

A Novel Approach for the Temperature Dependence of the Saturated Signal Power in EDFAs

The temperature dependence of the saturated signal power for the ⁴I_13/2 → ⁴I_15/2 transition in erbium-doped fiber amplifiers (EDFAs) pumped at 980 nm and 1480 nm pumping wavelengths within a temperature range from −20 to 60°C are investigated by a novel approach. This approach is based on the temperature dependence of the saturated signal power. The influence of pump excited-state absorption (ESA) is inserted into the rate equations so as to investigate a generally situation. For 1480 nm pumping regime, it is seen that the saturated signal power increases more quickly than that of 980 nm pumping regime, with the increasing temperature. The variation in the saturated signal power with temperature is nearly constant at 980 nm pumping regime. In addition, the population inversion with respect to the increasing normalized signal power is examined and it is seen that it is independent temperature for 980 nm but it strongly depends on temperature for 1480 nm especially at lower normalized signal powers.     

Temperature dependent direct-bandgap light emission and optical gain of Ge

Band structure, electron distribution, direct-bandgap light emission, and optical gain of tensile strained, n-doped Ge at different temperatures were calculated. We found that the heating effects not only increase the electron occupancy rate in the Γ valley of Ge by thermal excitation, but also reduce the energy difference between its Γ valley and L valley. However,the light emission enhancement of Ge induced by the heating effects is weakened with increasing tensile strain and n-doping concentration. This phenomenon could be explained by that Ge is more similar to a direct bandgap material under tensile strain and n-doping. The heating effects also increase the optical gain of tensile strained, n-doped Ge at low temperature, but decrease it at high temperature. At high temperature, the hole and electron distributions become more flat, which prevent obtaining higher optical gain. Meanwhile, the heating effects also increase the free-carrier absorption. Therefore, to obtain a higher net maximum gain, the tensile strained, n-doped Ge films on Si should balance the gain increased by the heating effects and the optical loss induced by the free-carrier absorption.     

The L-band EDFA of high clamped gain and low noise figure implemented using fiber Bragg grating and double-pass method

The L-band erbium-doped fiber amplifier (EDFA) of low noise figure and high clamped-gain using gain-clamped and double-pass configuration is presented in this paper. A total of five different configurations of EDFAs by reflection scheme with single forward pumping schemes are examined and compared here. Among these configurations, we first find the configuration of 1480-nm pumped L-band EDFA with optimum gain and noise figure value. To further minimize the gain variation, a fiber Bragg grating (FBG) with 1615-nm center wavelength and 1-nm bandwidth is determined and added in double-pass L-band EDFA. The gain variation and maximum noise figure of EDFA while channel dropping is investigated. As the number of channel dropping from 32 to 4, the L-band type-A EDFA keep the variation of gain within 2.9 dB and the maximum noise figure below 5 dB with each channel’s input power of −23 dBm.     

热管平板集热器设计优化

简单介绍了热管平板集热器的特点及应用前景,在分析传热的基础上,讨论各因素对传热效率的影响,从而进行优化设计。     

低温下单壁碳纳米管拉曼光谱温度效应研究

在单壁碳纳米管的低温拉曼光谱测量过程中,发现径向呼吸模(RBM)和正切拉伸模(GM)的拉曼频移在低温下的温度效应和在高温时的温度效应存在着很大的区别,在低温下拉曼光谱的频移和温度并不呈线性关系。而且,在温度为210K时,单壁碳纳米管内部的振动结构可能发生了变化。在低温下单壁碳纳米管拉曼峰的强度的变化是不可逆的。     

Field plate structural optimization for enhancing the power gain of GaN-based HEMTs

A novel source-connected field plate structure, featuring the same photolithography mask as the gate electrode, is proposed as an improvement over the conventional field plate (FP) techniques to enhance the frequency performance in GaN-based HEMTs. The influences of the field plate on frequency and breakdown performance are investigated simultaneously by using a two-dimensional physics-based simulation. Compared with the conventional T-gate structures with a field plate length of 1.2 μm, this field plate structure can induce the small signal power gain at 10 GHz to increase by 5-9.5 dB, which depends on the distance between source FP and dramatically shortened gate FP. This technique minimizes the parasitic capacitances, especially the gate-to-drain capacitance, showing a substantial potential for millimeter-wave, high power applications.     

光聚合物中全息光栅的温度依赖性研究

在Polyacrylic Acid(PPA)光聚合物中用双光束相干的方法成功地写入了全息光栅,用He-Ne 激光器作为探测光对光栅的写入过程进行了实时监测.分两种情况重点研究了温度对光栅成栅过程的影响,一是在不同的温度下写入光栅;二是在室温下写入光栅,待光栅强度达到最高时再改变温度来研究温度对光栅的影响.实验中温度的变化范围为25 ℃~100℃.     

Investigation of the optical gain and noise figure for multi-channel amplification in EDFA under optimized pump condition

We present the results of an investigation of optical gain and noise figure for simultaneous multi-channel amplification of an erbium doped fibre amplifier (EDFA) under optimized pump condition. Different pump configurations with varying input signal levels show interesting features on gain flatness. In the experiment, population inversion along the fibre length which determines the gain-spectra and noise characteristics of the amplifier is adjusted through optimized fibre length and injected pump power in order to minimize the gain-tilt at C-band. It is observed that bi-directional pumping manifests the best combination of low noise and high gain of EDFA which are useful as in-line repeaters in WDM network. We obtain 30 ± 1.5 dB intrinsically flat small signal gain from 1538 nm to 1558 nm band of wavelength with noise figure <4 dB for 16-channel simultaneous amplification in a single stage EDFA without gain flattening filter.     

加偏压光伏光折变晶体中低振幅屏蔽光伏明孤子的温度特性

在忽略扩散效应的条件下,讨论了加偏压光伏光折变晶体中低振幅屏蔽光伏明孤子的温度特性.当温度一定时,晶体中可形成稳态屏蔽光伏明孤子,当温度改变时,孤子由一稳态变为另一稳态.通过适当调节温度,可以控制孤子的空间形态.     

Temperature dependence of transport ac losses in Bi-2223/Ag multifilamentary tapes

Temperature dependence of transport ac losses in two Bi-2223/Ag multifilamentary tapes with different dc current–voltage characteristics was measured using a lock-in technique at power frequencies. At each temperature, different criteria for critical current determination were used. Comparisons of normalised ac losses with predictions of theoretical models for a tape with elliptical cross-section and a thin strip were made. It was found that the form of the current–voltage characteristic and the critical current criterion play an important role in comparison with theoretical data. A new normalisation procedure of ac loss data is proposed.     

Temperature dependence of photoluminescence from CdSe nanocrystals embedded in silica matrix

In this work, CdSe nanocrystals (NCs) embedded in SiO₂ matrix were grown by radio frequency (RF)-sputtering technique. X-ray technique was used to characterise the structural properties of the system. The NC's size was estimated to be around 4±1 nm in diameter. The temperature dependence of the photoluminescence from the CdSe/SiO₂ system showed carriers thermal exchange between the NCs and deep defects in the matrix. The evolution of the excitonic energy emission with temperature is about 10 meV in the temperature range 15-295 K. This weak shift was explained by thermal mismatch between the matrix and the NCs.     

Temperature dependence of GMR and effect of annealing on electrodeposited Co-Ag granular films

The magnetoresistance of Co-Ag granular films composed of superparamagnetic and ferromagnetic particles was studied at different temperatures. The increase in the GMR values while decreasing temperature down to 20 K was quantified. The non-saturating behaviour of the MR(H) curves was retained even at the lowest measurement temperature, which was mainly attributed to the dipolar interaction among the superparamagnetic particles. The influence of the annealing conditions on the magnetoresistance was also studied. In all conditions, a decrease in the GMR values was measured being attributed to an increase in the particle size.     

水的衰减系数及有效增益长度对受激布里渊散射输出能量的影响

本文从理论和实验上分析了水的衰减系数及有效增益长度对受激布里渊散射(SBS)输出能量的影响。实验结果表明,衰减系数越小,SBS输出能量越高。由于脉宽压缩效应,当入射光能量足够高并且有效增益长度相对较长时,SBS易获得高能量而形成极高的峰值功率。一旦这种峰值功率超过受激拉曼散射(SRS)或者二阶SBS阈值,SBS就会作为一个新的激发源去激发SRS或者二阶SBS,从而消耗掉部分SBS的能量,所以会出现后向有效增益长度越长,SBS的输出能量越低的现象。 关键词： 受激布里渊散射 衰减系数 有效增益长度 脉宽压缩     

Temperature dependence of luminescence emission from cerium and europium doped MgO under x-ray excitation

Temperature dependence of luminescence emission from cerium- and europiumdoped MgO is reported. The emission intensity changes with increase in the phosphor temperature. The phosphor showed peaks in the brightness-temperature curves. The intensities at static temperatures were always lower, indicating that temperature quenching occurs in almost all cases. The same is also evident from spectral distribution curves obtained at different temperatures.