评价研究光纤中调制不稳定性的扰动表达形式

对描述光纤中与强背景波一起传播的扰动场的各种数学表达方式及其得出的结果进行了分析和对比。研究表明 ,正确表达方式应该引出丰富得多的扰动演化特征 ,而由文献中常见的表达方式引出的只是扰动演化的渐进行为。讨论了前人表达方式的缺欠 ,分析了缺欠式依然能得到具有一定正确性的结论的原因     

Modal spot size of axially nonsymmetrical fibres

The modal spot size of the fundamental modes in axially nonsymmetrical fibres with axially nonsymmetrical cross-section is theoretically investigated. As the definition of modal spot size, two methods are proposed based on the quadratic moment of light power and the Gaussian fitting of the field. Simulated results using the finite-element method are presented for typical stress-applied polarisation-main taming fibres. It is shown that the spot shape depends mark edly both on the position of stress-applying parts and on normalised frequency.     

Reciprocal but nonsymmetrical transmission characteristics of tapered irises

Both the input impedance and the transmission coefficient of an H plane tapered iris are found to be reciprocal but asymmetrical. The H plane tapered iris behaves similarly to a transformer of nonunity turn ratio.     

Optical broadband phase devices using axially nonsymmetrical W-typeoptical fibers

This paper describes a numerical analysis of axially nonsymmetrical W-type optical fibers as optical-fiber-type broadband phase devices. Using these devices, phase difference between two orthogonal linear polarizations can be kept constant in a broad wavelength range. The propagation characteristics along a circular core with an elliptical cladding structure and an elliptical core with a circular cladding structure are numerically analyzed by the boundary-integral method. Using the numerical results, the performances of various broadband phase devices are theoretically compared     

Synthesis of transfer functions by nonsymmetrical lattice networks using lossy coils

A method for realising a v.t.f.by a nonsymmetrical lattice in which all coils can be made lossy is given.     

Electrical current instability at gate breakdown in GaAs MESFET

The gate burnout (irreversible breakdown) of GaAs MESFET has been studied using two-dimensional (2-D) numerical simulation and experimental measurements of 10 ns pulsed gate-drain I-V characteristics, it is shown, that at some critical level of gate avalanche current the gate current instability appears. The instability results in formation of the negative differential conductivity (NDC) region on the S-shape gate-drain I-V characteristic, spatial instability of avalanche current and formation of high density current filaments. At some critical length of n⁺-contact regions a spatial instability results in spontaneous formation of multiple spatial-periodic filaments     

室温HgCdTe双光子光学双稳性及不稳定性

1.HgCdTe的带隙可以通过改变组分和工作温度来改变,因此在半导体光学双稳性的研究中它是一种具有吸引力的材料.A.Miller等人曾报道了分别用30ns脉宽和1.75μs脉宽的CO_2激光脉冲在组分配比参数为x=0.23的HgCdTe中实现的光学双稳现象.由于HgCdTe的载流子复合寿命约为90ns,用30ns的窄脉冲较难实现双稳性;而用1.75μs的脉冲,在10.6μm的红外光作用下有可能引起较大的温度变化,从而导致带隙的较大改变.我们采用脉宽介于两者之间时100ns CO_2激光脉冲射入HgCdTe标准具,实现了室温双光子光学双稳性.在x=0.223和x=0.234两种样品中观察到明显的开关转换.开启时间约为10ns,开启功率密度为400kW/cm~2.当入射功率密度达到500kW/cm~2时,两种样品都观察到了输出光强的不稳定现象.     

Threshold voltage instability at low temperatures in partiallydepleted thin-film SOI MOSFETs

A threshold voltage instability phenomenon at low temperatures in partially depleted thin-film silicon-on-insulator (SOI) SIMOX (separation by implantation of oxygen) MOSFETs is reported. This phenomenon was investigated under normal MOSFET operating conditions for temperatures ranging from 300 K down to 10 K, with both the magnitude and duration of the instability observed to be strongly dependent on temperature. Threshold voltage shifts as small as 0 V at room temperature and as large as 0.29 V at 10 K are reported. The duration of the instability ranged in the tens of minutes and was observed to increase as the temperature was decreased     

保偏光纤中任意偏振方向矢量调制不稳定性

利用光脉冲在非线性双折射光纤中传播时所遵守的相干耦合非线性薛定谔方程,研究了保偏光纤中偏振方向与双折射轴成任意角度时,在反常色散区和正常色散区所产生的调制不稳定性。结果表明:在反常色散区对于任意的偏振角和任意输入功率的光脉冲都产生调制不稳定性;正常色散区的存在不稳定区域和稳定区域,对应不同的不稳定区域输入临界功率不同,脉冲有不同的增益谱。并且,给出了调制不稳定性增益谱随固有双折射和偏振角的变化关系。     

A new class of nonuniform, broadband, nonsymmetrical rectangular coaxial-to-microstrip directional couplers for high power applications

An innovative class of coaxial-to-microstrip broad-band high power directional couplers is studied. The new devices overcome the drawbacks of both stripline and coaxial couplers and allow simple and low cost mechanical construction. In this letter, we present the design, realization and characterization of a set of broad-band (900 MHz to 5.5 GHz) low coupling (-30 dB, -40 dB) directional couplers with directivity of more than 10 dB over the whole band, demonstrating good agreement between predicted and obtained performances.     

Negative bias temperature instability modeling for high-voltage oxides at different stress temperatures

The temperature bias instability of high-voltage oxides is analyzed. For the investigation of negative bias temperature instability (NBTI) we present an enhanced reaction–diffusion model including trap-controlled transport, the amphoteric nature of the P_b centers at the Si/SiO₂ interface, Fermi-level dependent interface charges, and fully self-consistent coupling to the semiconductor device equations. Comparison to measurement data for a stress/relaxation cycle and a wide range of temperatures shows excellent agreement.     

Threshold voltage instability of nanoscale charge trapping non-volatile memory at steady phase

Post program/erase (P/E) cycled threshold voltage (Vt) instability is one of the major reliability concerns for nanoscale charge trapping (CT) non-volatile memory (NVM) devices. In this study, anomalous program state Vt instability of fully annealed nanoscale nitride based CT NVM device at steady phase is carefully examined. To the best knowledge of the authors, for the first time, the relationship between the derived apparent activation energy (Eaa) of this anomalous program state Vt instability at steady phase and the P/E cycle count is established. They are found to adhere to the power law decay relationship. Anomalous program state Vt instability at steady phase was found to favor lateral redistribution of trapped charge model instead of vertical charge transport model. Physical interpretations of its underlying physical mechanisms and reliability implications to reliability performance of nanoscale nitride based CT NVM were presented. Plausible technical solutions to mitigate the reliability degradation induced by this anomalous program state Vt instability on nanoscale nitride based CT NVM were proposed.     

Measurement of axially nonsymmetrical refractive-index distribution of-a single-mode fiber by a multidirectional scattering-pattern method

A high spatial resolution, typically0.2 sim 0.3 mum, has previously been achieved by the "scattering-pattern method" proposed by one of the authors for measuring refractive-index profiles of optical fibers. This method, therefore, is especially suitable for measuring the index profiles of single-mode fibers. Described in this paper is the modification of this technique for measuring nonsymmetrical index distributions in single-mode fibers. In the modified method, a two-dimensional index distribution in an axially nonsymmetrical fiber is computed from a set of its forward scattering patterns for different directions of incident light. The distribution to be measured is somewhat restricted, i.e., it must have point symmetry. However, the point symmetry includes double symmetry which holds in most of polarization-maintaining fibers. The spatial resolution is as high as the scattering-pattern method for the axially symmetrical case; in the present experiment the resolution limit is 0.28 μm. Results of computer simulation and measurement are shown.     

Damage-induced spectral perturbations in multilongitudinal-modesemiconductor lasers

Mechanical stressing was applied to commercial Fabry-Perot semiconductor lasers to create damage at controlled locations along the optic axis. This damage induces spectral perturbations sinusoidal in wavelength space whose periods are inversely proportional to the distance from the damage to the nearest facet. Experimental and theoretical evidence is presented for a new spectrum-based analytical technique which can provide quantitative information on the location and relative absorption strength of damage sites within the active region. Applications and limitations of this new technique are discussed     

Electron transient response and impact-ionized plasma instability in GaAs at very high electric fields

Dynamic behavior of electrons in GaAs under impact ionization conditions is studied by the Monte Carlo technique. The relaxation time of impact ionization generation rate is estimated. The linear stage of instability caused by the generation rate lagging the electric field is investigated. The nonlinear regime of this instability is numerically simulated. The electric field and plasma density oscillations with a frequency of the order of 50–1000 GHz are obtained.     

Two-stream electrostatic instability

The variations of the maximum growth rate and the associated frequency of oscillation and the drift velocity with the change in the number density of the streaming electrons relative to that of the stationary electrons are discussed for the instability of the longitudinal plasma wave having its wave vector in the direction of the electron stream. It is found that the maximum growth rate has the largest value when the number densities of the stationary and the streaming electrons are equal.     

Far-infrared laser gain resulting from rotational perturbations

A simplified model is used to calculate the unsaturated gains of far-infrared rotational and vibrational-rotational laser transitions that are caused by rotational perturbations. Inversions are derived from the perturbation of an initial Boltzmann distribution of rotational populations, permitting the calculation of laser gains in terms of the perturbation parameters and the vibrational populations. The gain equations are applied to the three perturbations of H2O¹⁶that result in the largest number of laser lines. Numerical gain values in good qualitative agreement with experimental results are obtained.     

Internet routing instability

This paper examines the network interdomain routing information exchanged between backbone service providers at the major US public Internet exchange points. Internet routing instability, or the rapid fluctuation of network reachability information, is an important problem currently facing the Internet engineering community. High levels of network instability can lead to packet loss, increased network latency and time to convergence. At the extreme, high levels of routing instability have led to the loss of internal connectivity in wide-area, national networks. We describe several unexpected trends in routing instability, and examine a number of anomalies and pathologies observed in the exchange of inter-domain routing information. The analysis in this paper is based on data collected from border gateway protocol (BGP) routing messages generated by border routers at five of the Internet core's public exchange points during a nine month period. We show that the volume of these routing updates is several orders of magnitude more than expected and that the majority of this routing information is redundant, or pathological. Furthermore, our analysis reveals several unexpected trends and ill-behaved systematic properties in Internet routing. We finally posit a number of explanations for these anomalies and evaluate their potential impact on the Internet infrastructure     

Sensitivity of phase-conjugate resonators to intracavity phase perturbations

The sensitivity of phase-conjugate resonators to phase perturbations is analyzed numerically. It is shown that as long as the phase-conjugate mirror (PCM) intercepts most of the light traveling towards it, this type of resonator provides much improvement over conventional optical cavities.