Compensation of stray capacitance of the quartz tuning fork for a quantitative force spectroscopy

We have introduced a simple but robust approach to realize stray-capacitance compensation of a quartz tuning fork force gradient sensor by using a tied-prong of the same tuning fork instead of using a variable precision capacitor. The results of quantitative force measurements with the proposed device show excellent agreement with the numerical method of cancellation via the theoretical compensation method with the resonance response curves. Futhermore, the mechanical properties of the condensed nano-water bridges are investigated with the proposed compensator, which provides the potential promise of the intrinsic quartz tuning fork for a quantitative precision force spectroscopy.     

Uplink CFO compensation for FBMC multiple access and OFDMA in a high mobility scenario

We study in this work CFO compensation methods for two multicarrier multiple access techniques in a high mobility scenario. In particular, we consider orthogonal frequency division multiple access (OFDMA) and filter bank multicarrier multiple access (FBMC-MA). The main motivation for this study is not only the different sensitivity these multicarrier techniques have to CFO but also the different methods they use to reduce CFO effect. In a high mobility scenario the CFO is re-estimated to follow its variation. We show that the frequency at which the CFO is re-estimated has a strong influence in the performance and the complexity of the proposed compensation methods. Additionally, we present a low-complexity CFO compensation method for OFDMA that employs a better approximation of the intercarrier interference than previous approaches. Regarding FBMC-MA, we introduce an extension of a CFO-compensation method that allows to consider a multitap channel equalizer. Finally, using simulations, we compare the performance of the compensation methods over several channel and time-varying CFO conditions.     

Optimization of NRZ Data Transmission at 10 Gbit/s over G.652 Without In-Line DFAs

Performance limits of NRZ data transmission at 10 Gbit/s over standard single mode fiber (SSMF, G.652) without the deployment of in-line erbium-doped fiber amplifiers (EDFAs) are evaluated by means of numerical simulation. The fiber system was modeled using the standard split-step Fourier algorithm for the solution of nonlinear Schroedinger equation. The effect of group velocity dispersion (GVD) compensation scheme, degree of GVD compensation of the SSMF, and input optical powers to SSMF and to the dispersion compensating fiber (DCF) have been investigated with the aim to maximize the distance between transmitter and receiver. We have found that a post-compensation scheme performs better than the pre-compensation scheme and that, by careful selection of input powers and degree of GVD compensation, it should be possible to keep the bit-error-ratio (BER) below 10 upper index = 15 for an SSMF length of 270 km.     

Optimization of NRZ Data Transmission at 10 Gbit/s over G.652 Without In-Line DFAs

Performance limits of NRZ data transmission at 10 Gbit/s over standard single mode fiber (SSMF, G.652) without the deployment of in-line erbium-doped fiber amplifiers (EDFAs) are evaluated by means of numerical simulation. The fiber system was modeled using the standard split-step Fourier algorithm for the solution of nonlinear Schroedinger equation. The effect of group velocity dispersion (GVD) compensation scheme, degree of GVD compensation of the SSMF, and input optical powers to SSMF and to the dispersion compensating fiber (DCF) have been investigated with the aim to maximize the distance between transmitter and receiver. We have found that a post-compensation scheme performs better than the pre-compensation scheme and that, by careful selection of input powers and degree of GVD compensation, it should be possible to keep the bit-error-ratio (BER) below 10 upper index = 15 for an SSMF length of 270 km.     

“Aharonov-Bohm antiferromagnetism” and compensation points in the lattice of quantum rings

We investigate the magnetic properties of the lattice of non-interacting quantum rings using the 2D rotator model. The exact analytic expressions for the free energy as well as for the magnetization and magnetic susceptibility are found and analyzed. It is shown that such a system can be considered as a system with antiferromagnetic-like properties. We have shown also that all observable quantities in this case (free energy, entropy, magnetization) are periodic functions of the magnetic flux through the ring's area (as well known, such a behavior is typical for the Aharonov-Bohm effect). For the lattice of quantum rings with two different geometric parameters we investigate the ordinary compensation points (“temperature compensation points”, i.e. points at which the magnetization vanishes at fixed values of the magnetic field strength). It is shown that the positions of compensation points in the temperature scale are very sensitive to small changes in the magnetic field strength.     

Pulse Compression by Filamentation in Argon with an Acoustic Optical Programmable Dispersive Filter for Predispersion Compensation

We have experimentally demonstrated pulses 0.4 mJ in duration smaller than 12 fs with an excellent spatial beam profile by self-guided propagation in argon. The original 52 fs pulses from the chirped pulsed amplification laser system are first precompressed to 32 fs by inserting an acoustic optical programmable dispersive filter instrument into the laser system for spectrum reshaping and dispersion compensation, and the pulse spectrum is subsequently broadened by filamentation in an argon cell. By using chirped mirrors for post-dispersion compensation, the pulses are successfully compressed to smaller than 12 fs.     

Enhancement of noise reduction efficiency based on compensation in the ANC headset using fixed-point DSP

In this paper, we have proposed a new algorithm considering commutation error and feedback effect to enhance the convergence rate and noise reduction efficiency of ANC controller. In order to improve noise reduction performance of the ANC headset with fixed-point DSP, we have proposed a new FxLMS algorithm, FxLMS CF, which considers the commutation error and feedback. Also, using a non-real-time simulation, we have decided the phase and amplitude compensation factors of anti-noise signal considering round-off and quantization error, nonlinear distortion and delay of analog device. We estimated the phase and amplitude compensation factors by simulation without using any special measuring devices or analysis devices, and reduced the broadband noise by 24 dB.     

Versatile 7-fs optical parametric pulse generation and compression by use of adaptive optics

We have compressed the output from a beta-barium borate noncollinear optical parametric amplifier to ~7-fs pulse durations, using a micromachined deformable mirror with an efficient search algorithm. This compression method allows phase compensation of both material and gain dispersion, which produces an optimized wavelength-tunable pulse shape for ultrahigh-resolution time-domain spectroscopy.     

Magnetic properties of a mixed spin-1 and spin-2 Heisenberg ferrimagnetic system: Green’s function study

The magnetic behaviors of a mixed spin-1 and spin-2 Heisenberg ferrimagnetic system on a square lattice are studied by using the double-time temperature-dependent Green’s function technique. In order to decouple the higher order Green’s functions, Anderson and Callen’s decoupling and random phase approximations have been used. The system is described in the presence of an external magnetic field. We illustrate the influences of the nearest- and next-nearest-neighbor interactions and the single-ion anisotropies with an external magnetic field on compensation and critical temperatures. We found that the system that includes only the nearest-neighbor interaction and the single-ion anisotropies does not have a compensation temperature. When the next-nearest-neighbor interactions exceed a certain minimum value, a compensation temperature begins to appear. For some negative values of single-ion anisotropies, there exist first-order phase transitions. The system has first-order phase transition properties when it is under the influence of an external magnetic field.     

A novel scheme to generate dark-RZ pulse and study on its transmission performance

We have proposed and experimentally demonstrated a novel and simple configuration to generate a dark-RZ pulse by a Mach-Zehnder delayed line interferometer. We have also compared the transmission performance between the dark-RZ and bright-RZ pulse in the pre-dispersion compensation and post-dispersion compensation systems. Our experimental results have shown that the dark-RZ is more sensitivity to nonlinear effects than the bright-RZ pulse, and the power penalty will also be larger than that of the bright-RZ at the same BER. The experiment results have also shown that the dark-RZ pulse is not suitable for the signal transmission with pre-dispersion compensation.     

一种基于Optisystem的静态与动态色散补偿相结合方案研究

介绍色散补偿光纤DCF及动态啁啾光纤光栅FBG的补偿技术并比较其优缺点,提出在传统光传输系统末端加入动态FBG的方案,通过Optisystem仿真软件搭建40 Gbit/s的光传输系统,用FBG仿真光传输400 km的Q值为3.745,误码率为7.419 42e-5,用DCF静态混合补偿和静态与动态相结合的补偿方案分别仿真并比较两种方案传输相同距离的Q值和误码率的大小,证明提出的静态加动态的方案提高了光传输性能。     

Compression of Intense Laser Pulse through Filamentation in an Argon-Filled Cell

We demonstrate a pulse compression technique through filamentation in an argon-filled cell. By using a pair of chirped mirrors for dispersion compensation, we have successfully compressed the 53 fs pulse to 15 fs with good spatial qualities and good pulse stability. The total transmitted efficiency is more than 75%. The influence of the experiment parameters to the compressed pulses is also studied experhnentally.     

Efficient reflection grisms for pulse compression and dispersion compensation of femtosecond pulses

Efficient reflection grisms for pulse-compression and material-dispersion compensation have been designed and demonstrated in a 40 fs, 300 microJ, 5 kHz downchirped pulse amplification system for the first time to our knowledge. A grism design for 800 nm femtosecond laser pulse dispersion compensation applications is realized by using standard, commercial diffraction gratings.     

Fiber-based tunable dispersion compensation

Tunable dispersion has been implemented in various technology platforms, including fiber gratings, planar waveguides, thin film etalons, and bulk optic technologies. This paper will focus on fiber grating based tunable dispersion compensation, because fiber gratings are at present one of the best developed TDC technologies available. The paper is divided into three parts. In the first part we describe grating based TDC technologies and discuss their advantages and disadvantages. We focus on thermally tuned linearly chirped fiber gratings, as these have to date been the most successful grating technology for 40 Gbit/s. We also compare grating TDCs to two other prominent tunable dispersion technologies: thin film etalons and planar waveguide ring resonators. In the second section we describe the techniques used to fabricate high performance dispersion compensation gratings as well as the theory of the primary defect of fiber grating dispersion compensation: group delay ripple (GDR). In the third section we describe the telecom system related issues for tunable gratings, including characterization of grating performance, tunability requirements and results from actual system trials using tunable FBGs.     

光阴极微波电子枪中发射度补偿及模拟计算

介绍了上海深紫外自由电子激光用光阴极微波电子枪采用发射度补偿技术的结果 .详细分析了线性空间电荷力的特点及对束流发射度的影响 ,从束流动力学和相空间两方面讨论了发射度补偿原理 .给出了补偿线圈的设计结构及其轴向场分布 .利用PARMELA程序对补偿效果作了模拟计算 .结果表明 ,设计的腔体对单圈 1 .5nC束团 ,在枪出口后 1 .2m处 ,电子能量为 5 .7MeV ,横向归一化发射度εn ,RMS=1 .61 2πmm·mrad. The emittance compensation technology will be used on the photo cathode RF gun for Shanghai SDUV FEL. In this paper, the space charge force and its effect on electron beam transverse emittance in RF gunis is studied, the principle of emittance compensation in phase space is discussed. We have designed a compensation solenoid and calulated its magnetic field distribution. Its performance has been studied by the code PARMELA. A simulation result indicates that the normalized transverse RMS emi...     

强激光大气传输中晕及其补偿

文章给出用4-D程序计算热晕问题的数值结果,用包括信标光在内的4-D程序对相位补偿和场补偿进行了数值模拟,结果表明,单纯的相位补偿是不稳定的(PCI),场补偿是完全有效的。     

Compensation of strong thermal lensing in high-optical-power cavities

In an experiment to simulate the conditions in high optical power advanced gravitational wave detectors, we show for the first time that the time evolution of strong thermal lenses follows the predicted infinite sum of exponentials (approximated by a double exponential), and that such lenses can be compensated using an intracavity compensation plate heated on its cylindrical surface. We show that high finesse approximately 1400 can be achieved in cavities with internal compensation plates, and that mode matching can be maintained. The experiment achieves a wave front distortion similar to that expected for the input test mass substrate in the Advanced Laser Interferometer Gravitational Wave Observatory, and shows that thermal compensation schemes are viable. It is also shown that the measurements allow a direct measurement of substrate optical absorption in the test mass and the compensation plate.     

Nonlinearity management in a dispersion-managed system

We propose using a nonlinear phase-shift interferometric converter (NPSIC), a new device, for lumped compensation for nonlinearity in optical fibers. The NPSIC is a nonlinear analog of the Mach-Zehnder interferometer and provides a way to control the sign of the nonlinear phase shift. We investigate a potential use of the NPSIC for compensation for nonlinearity to develop a dispersion-managed system that is closer to an ideal linear system. More importantly, the NPSIC can be used to essentially improve single-channel capacity in the nonlinear regime.     

兰州重离子加速器腔体反馈电缆漂移的补偿方法

理论分析了兰州重离子加速器腔体的低电平稳定系统中各传输通道对腔体的长期稳定度的影响，根据现有低电平稳定系统的实际情况，提出了用附加测试电缆来补偿反馈电缆漂移的方法。测试了环境温度的变化对电缆在实施补偿前后的相位与损耗的影响，测试结果表明:采用电缆补偿后的长期相位稳定度可以降低到原来的1/50，长期幅度漂移可以最少降低到原来的1/10。     

Timing jitter dependence on data format for ideal dispersion compensated 10 Gbps optical communication systems

Simulations for data formats Return to Zero (RZ), Non-Return to Zero (NRZ), RZ-Soliton, Duobinary and their subcategories have been done with and without ideal dispersion compensation for optical communication systems. The results show that, in general, dispersion compensation improves timing jitter. RZ-Rectangular pulses show the smallest value of jitter without compensation. It has been observed that the RZ-Raised Cosine, and Soliton, give minimum jitter after ideal compensation. It has been reported that the BER performance of optical communication system using Duobinary data format is 10⁻⁸ and 10⁻³⁷ before and after dispersion compensation, respectively. Further the comparative study shows that the timing jitter is the lowest in case of RZ-Soliton (0.0127 ns) after dispersion compensation and 0.0135 ns for RZ-Rectangular data format before dispersion compensation.