Research on pulse edge extraction by using nonlinear optical fiber-loop mirror

The output characteristics of nonlinear optical fiber-loop mirror are analyzed in detail when the pump pulses with the same wavelength are input in the both directions for recovering the clock component of the signal spectrum.It is found that the double output pulses are produced in the transmission port of the nonlinear optical fiber-loop mirror.The output pulse peaks are located in time domain at the rising and falling edges of the pump pulses.It is demonstrated that the rising and falling edges of the pump pulse can be directly extracted by this method.Through numerical simulation,the effects of therelative delay of pump pulses and the dispersion of fiber on the characteristics of output pulses are studied.By spectrum analysis,it is found that the spectrum of output pulse sequence includes the clock components of the pump pulse sequence,and a new idea is provided for all-optical clock extraction.     

Experiment and analysis of the effect of fine tracking system on the unstable platform in laser communication

Atmospheric turbulence and platform vibration in the space optical communication can cause the offset and jitter of beam, which further result in the fluctuations of received optical power. To resist this effect, a communication system with fine tracking systems in the receiver and transmitter is designed. The system is used in the experiment of laser communication between high-rise buildings over a distance of 3.5 km. After adding a vibration source to the transmitter, the centroids of spots captured by the camera of the transmitter and the optical power of receiver are recorded for the purpose of analysis. When the vibration source works at the designated frequency, a peak appears at the corresponding frequency in the spectrum of the spot centroids and the optical power of receiver. Then the peak disappears once the fine tracking system begins to work. Compared with the condition without the fine tracking system, the minimum value of the optical power of receiver is increased by 5 dB, and the standard deviation is decreased by 30%.     

CMOS反相器在高功率微波下闩锁效应的温度影响

The temperature dependence of the latch-up effects in a CMOS inverter based on 0.5 μm technology caused by high power microwave （HPM） is studied. The malfunction and power supply current characteristics are revealed and adopted as the latch-up criteria. The thermal effect is shown and analyzed in detail. CMOS in- verters operating at high ambient temperature are confirmed to be more susceptible to HPM, which is verified by experimental results from previous literature. Besides the dependence of the latch-up triggering power P on the ambient temperature T follows the power-law equation P = ATβ. Meanwhile, the ever reported latch-up delay time characteristic is interpreted to be affected by the temperature distribution. In addition, it is found that the power threshold increases with the decrease in pulse width but the degree of change with a certain pulse width is constant at different ambient temperatures. Also, the energy absorbed to cause latch-up at a certain temperature is basically sustained at a constant value.     

Mechanisms of self-similar pulses generation in a normal dispersion-decreasing fiber

Based on the principle of virtual equivalent gain,the evolution of self-similar pulses in a normal dispersion-decreasing fiber is investigated.The occurrence of wave breaking during the process under highly nonlinear conditions and the effect of its revealed four-wave mixing on the process are also analyzed.The results indicate that the pulse spectrum broadeningin the initial stage is dominated by self-phase modulation while by four-wave mixing in the later stage.The more intense nonlinearity is,the faster the pulse evolution converges to the self-similarity synchronously in both the time domain and the spectrum domain.     

A novel orthogonal modulation format of D8PSK/ASK with differential bi-phase encoding and its application in a label switching optical network

The principle of a novel orthogonal modulation format of differential 8-level phase-shift keying amplitude-shift keying (D8PSK/ASK) with differential bi-phase encoding (DBC) is introduced. Based on it, an optical labeling scheme, in which the payload is 100 Gbit/s D8PSK signal and the label is 10 Gbit/s DBC-ASK signal, is proposed and simulated. The results are compared with other current schemes, and the effects of transmission range, modulation extinction ratio (ER) and received power on system performance are analyzed, respectively. The results show that the spectrum efficiency and bit error rate (BER) are improved greatly, and when the modulation ER is increased to 11 dB, the balanced performance between the payload and label is achieved.     

Effective capacity of cognitive radio systems in asymmetric fading channels

As known that the effective capacity theory offers a methodology for exploring the performance limits in delay constrained wireless networks, this article considered a spectrum sharing cognitive radio(CR) system in which CR users may access the spectrum allocated to primary users(PUs). Particularly, the channel between the CR transmitter(CR-T) and the primary receiver and the channel between the CR-T and the CR receiver(CR-R) may undergo different fading types and arbitrary link power gains. This is referred to as asymmetric fading. The authors investigated the capacity gains achievable under a given delay quality-of-service(Qo S) constraint in asymmetric fading channels. The closed-form expression for the effective capacity under an average received interference power constraint is obtained. The main results indicate that the effective capacity is sensitive to the fading types and link power gains. The fading parameters of the interference channel play a vital role in effective capacity for the looser delay constraints. However, the fading parameters of the CR channel play a decisive role in effective capacity for the more stringent delay constraints. Also, the impact of multiple PUs on the capacity gains under delay constraints has also been explored.     

Superluminal Propagation in Er^3＋-doped Fiber Bragg Grating

The method to pump the FBGT written into an Er^3＋-doped optical fiber is proposed to increase the group velocity of a probing pulse based on the facts that pump-induced process changes the refractive index and dispersion associated with the ^4I15/2-^4I12/2 transition in Er^3＋-doped optical fiber.The system equations are derived.The effects of pump power and doping concentration on the group velocity are discussed.     

Study on multiple receiver systems in non-line-of-sight ultraviolet communication systems

In this article, multiple receiver effects in a non-line-of-sight （NLOS） ultraviolet （UV） communication system is studied. The idea of using multiple receivers for diversity reception is known as a practical, effective and widely applied technique in wireless communications. The current approach is to use multiple antennas at the receiver in order to improve the quality of the received signal. A method of modeling and simulation is proposed to depict the principle and feasibility of the multiple receiver adopted in UV communication. The study provides an insight to the channel characteristics and achievable capabilities of ultraviolet communication systems with multiple receivers. It provides guidelines for practical system design with discussions on trade off between the receiver gain and the additional cost.     

Sensitivity of MEMS microwave power sensor with the length of thermopile based on Fourier equivalent model

A Fourier equivalent model is introduced to research the thermal transfer behavior of a terminating-type MEMS microwave power sensor.The fabrication of this MEMS microwave power sensor is compatible with the GaAs MMIC process.Based on the Fourier equivalent model,the relationship between the sensitivity of a MEMS microwave power sensor and the length of thermopile is studied in particular.The power sensor is measured with an input power from 1 to 100 mW at 10 GHz,and the measurement results show that the power sensor has good input match characteristics and high linearity.The sensitivity calculated from a Fourier equivalent model is about 0.12,0.20 and 0.29 mV/mW with the length at 40,70 and 100μm,respectively,while the sensitivity of the measurement results is about 0.10,0.22 and 0.30 mV/mW,respectively,and the differences are below 0.02 mV/mW. The sensitivity expression based on the Fourier equivalent model is verified by the measurement results.     

Study on reflection characteristics of underwater target and laser echo power

For the design of the underwater laser detection system, the echo power equation of underwater target is derived, and the effects of water’s attenuation coefficient and incident angle on target’s echo power are analyzed. The bidirectional reflection distribution function(BRDF) of the single-station model is used to study the reflection characteristics of the target. The influence of the correlation coefficients of specular and diffuse reflection components on the reflected light intensity of special axisymmetric targets is studied. The signal-to-noise ratio(SNR) values of three types of target under different surface BRDF are given. The simulation results show that the larger the attenuation coefficient is, the smaller the echo power received, and the incidence angle is closer to 90°, the echo power is equal to 0. A smaller surface slope or a larger diffuse reflected coefficient will cause a smaller reflected intensity.     

40 Gb/s光纤通信系统中一阶PMD对信号频谱的影响

首先给出了受一阶偏振模色散(PMD)影响的40 Gbit/s高斯脉冲信号功率谱的数学表达式,并分析了脉冲波形、分光比、监测频率以及差分群延时(DGD)对接收信号功率谱的影响.实验测量了在分光比为0.5时的40 Gbit/s归零(RZ)码伪随机信号在接收频率为12 GHz处的电功率谱密度随DGD变化的关系,实验结果与理论计算一致.这表明,对于40 Gb/s的光纤通信系统,可以通过简单地检测某一特定频率的电信号功率,动态跟踪系统中PMD的变化情况,从而为补偿一阶PMD提供了重要依据.     

The Effects of Polarization-Mode Dispersion on the Phase of the Recovered Clock

The impact of polarization-mode dispersion (PMD) on the phase of the recovered clock in the receiver is analyzed. The effects of first-order PMD on different clock-recovery configurations utilized for return-to-zero (RZ) and non-RZ (NRZ) formats are studied. Closed-form expressions relating the PMD-induced sampling time shift with the differential group delay and the power ratio between the principal states of polarization are obtained for each high-Q filter-based clock recovery. An experimental validation at 10 Gb/s is also shown for the case of NRZ data format     

A comparison between different PMD compensation techniques

We quantify the benefits of using different techniques for compensation of polarization mode dispersion (PMD) in fiber-optic communication systems by means of numerical simulations. This is done both with respect to PMD-induced pulse broadening and in terms of system outage probability for different data formats [nonreturn-to-zero (NRZ) and return-to-zero (RZ)]. Attention is focused on simple and relevant single- and double-stage post-transmission compensators with a few degrees of freedom (DOF). It is generally believed that a PMD compensator with a polarization controller and a variable delay line can only compensate the PMD to the first order. We show, from analytical results, the counterintuitive fact that this scheme can also partially compensate for higher order PMD. We also investigate the benefit of using a polarizer as compensation element where the optical average power can be used as a feedback signal     

Theoretical Characterization and System Impact of the Hinge Model of PMD

Modeling of the polarization-mode dispersion (PMD) temporal changes in long fiber routes represents a critical aspect of system outage characterization. In this paper, an analysis of the PMD temporal statistics in links obeying the recently proposed hinge model is presented. The analytical expression of the differential group delay probability density function is derived and used to show that the outage probability is channel specific in a wavelength-division-multiplexed system. The existence of outage-free channels, which represents one of the most important implications of the hinge model, is demonstrated and quantified. The frequency dependence of the temporal statistics is also characterized, and an expression for PMD-induced pulse broadening is derived     

Pulsewidth distortion monitoring in a 40-Gb/s optical systemaffected by PMD

A novel technique for monitoring the pulse broadening due to polarization-mode dispersion (PMD) in optical systems is described. The technique is based on the measurement of the Stokes vectors at different frequencies over the spectrum of the received optical pulse find does not require a priori knowledge of the fiber PMD statistics or details of the optical path. The validity of our technique has been demonstrated by both simulation and experimental results     

PMD second-order effects on pulse propagation in single-modeoptical fibers

The time-space varying birefringence in single-mode optical fibers causes the polarization mode dispersion (PMD) to be a serious problem in high bit-rate transmissions. The PMD first- and second-order statistics are well known in the literature, but second-order PMD-induced pulse distortions have still to be clarified for sequences of pulses of arbitrary shape. We give, for the first time, the exact PMD time impulse response, up to second order. We show, both numerically and experimentally, that the effect of the rotation of the principal states of polarization (PSP) is to generate power overshoots on the “1” and “0” bit sequences     

偏振模色散对线性系统脉宽的影响

研究了线性系统中偏振模色散对均方根脉宽的影响。考虑了光源初始啁啾的作用 ,推导出均方根脉宽的解析表达式 ,分析表明 :二阶偏振模色散对脉冲展宽的作用与群速度色散及啁啾有关 ,一阶偏振模色散的作用则与这两者无关。以啁啾高斯脉冲为例 ,推导出一阶偏振模色散补偿前、后均方根脉宽的解析表达式 ,结果表明 ,适当选择群速度色散和初始啁啾参数 ,可以有效地抑制偏振模色散的展宽效应 ;与主态传输法比较 ,啁啾的存在对后向补偿方法的影响更大     

偏振模色散补偿对脉冲展宽的影响

在高速光纤通信系统中,偏振模色散(PMD)已被认为是限制光纤通信系统性能的一个主要因素,而脉冲的均方根展宽是表征信号传输性能的一个重要的物理量.研究了偏振模色散对脉冲展宽的影响,推导出含有一阶偏振模色散补偿的光纤链路中偏振模色散矢量的自相关函数的分析表达式.在此表达式的基础上,推出了以高斯脉冲为例的一阶偏振模色散补偿系统中的均方根脉宽解析表达式.     

Statistical description of optical system performances due torandom coupling on the principal states of polarization

Due to polarization-mode dispersion (PMD), the performances of an optical transmission system show a random behavior. We calculate the probability density function of the Q-factor due to PMD. We adopt the principal states of polarization model, and we also consider the clock recovery behavior at the receiver. Theoretical results are reported for a 40-Gb/s system, and are compared with those obtained considering the effect of pulse broadening due to PMD     

Pulse distortion induced by polarization-mode dispersion and polarization-dependent loss in lightwave transmission systems

The combined effects of polarization-mode dispersion (PMD) and polarization-dependent loss (PDL) on pulse broadening in optical transmission links for both PMD uncompensated and compensated systems are investigated by numerical simulation. It is shown that, when PDL is large, PDL considerably reduces the efficiency of PMD compensation, which, we find, is mainly due to the increased higher order PMD caused by the combined effects of PMD and PDL, as well as nonorthogonal principal states of polarization.