自陡峭效应对相位共轭系统脉冲传输的影响

光学相位共轭(OPC)技术能够同时且高效地补偿光纤传输过程中色散及非线性效应所导致的信号失真，且该技术同脉冲调制方式无关。从理论上分析了在自陡峭效应(SS)作用下高斯脉冲信号在中距相位共轭系统中的传输演化特性，数值模拟了在其作用下超短飞秒高斯脉冲的动态传输过程，讨论了自陡峭效应对中距相位共轭系统复原性能的影响。结果表明自陡峭效应将导致高斯脉冲信号发生峰值漂移和脉冲后沿变陡，相位共轭系统不能补偿由此导致的脉冲失真和畸变。引入合适的色散可以减小这种信号失真，并使得相位共轭系统能够同时补偿由于色散、自相位调制和自陡峭效应而引起的信号失真。     

Generation of optical phase-conjugate waves and compensation forpulse shape distortion in a single-mode fiber

The generation of optical phase-conjugate waves and the application of optical phase conjugation (OPC) to optical communication systems is described. The method of pulse shape distortion compensation by OPC is outlined including distortion due to both fiber dispersion and the optical Kerr effect. The generation of a forward-going phase-conjugate wave in a third-order nonlinear medium is discussed and that by a nondegenerate forward four-wave mixing in a zero-dispersion single-mode fiber (SMF) is investigated. Suppressing the stimulated Brillouin scattering (SBS) of a pump wave in the fiber prevents saturation of the generation efficiency of the phase-conjugate wave even when the pump power exceeds the SBS threshold. In transmission experiments through a 200-km standard SMF with a 16-Gb/s intensity-modulated signal and a 5-Gb/s continuous-phase FSK (CPFSK) modulated signal, it is shown the applicability of OPC is modulation independent and that OPC effectively compensates for both chromatic dispersion and the optical Kerr effect     

Exact compensation for both chromatic dispersion and Kerr effect ina transmission fiber using optical phase conjugation

We propose a new method to compensate exactly for both chromatic dispersion and self-phase modulation in a transmission fiber, where the light intensity changes due to fiber loss and amplifier gain. This method utilizes optical phase conjugation (OPC). The pulse shape is precompensated before OPC by transmission through a fiber with large dispersion. A computer simulation demonstrates effective compensation for waveform distortion in a 40 Gb/s NRZ intensity-modulated light transmission     

Nonlinear distortion generated by DSF-based optical-phase conjugators in analog optical systems

In this paper, the nonlinear distortion induced by dispersion-shifted-fiber-based optical-phase conjugators (OPCs) in intensity-modulated subcarrier multiplexing optical systems is evaluated. In this study, it is shown that the nonlinear distortion mainly arises from the four-wave mixing (FWM) process during the phase conjugation, although there also exists influences from other nonlinear effects. Closed expressions for calculating the second- and third-order harmonic distortions due to FWM, self-phase modulation, cross-phase modulation and group-velocity dispersion effects in the dispersion-shifted-fiber-based OPC are also reported for the first time. The influence of several system design parameters, such as the optical modulation index, the number of channels, the input optical powers, and the effective area of the dispersion-shifted fiber on the compensation of fiber-induced nonlinear distortions employing the optical-phase conjugation technique, is considered.     

RF response of analog optical links employing optical phaseconjugation

The RF transfer function of analog optical links employing optical phase conjugation (OPC) for the compensation of the carrier suppression effect is investigated theoretically. It is well known that the ultimate performance of the OPC technique depends on several system parameters such as fiber span lengths, dispersion characteristics, input optical powers, or optical transmitter chirp. The influence of these parameters on the RF system response is studied by means of simulation, showing that the main degradation of the equalized response is due to the joint action of nonlinear effects and asymmetric optical power change along the fiber spans     

Modeling and experimental studies of optical power cable current sensing based on the optical transmission properties of magnetic fluids

Optical power cable(OPC) current sensing models and experiments based on the optical transmission properties of magnetic fluids are proposed. Firstly, the models of OPC, magnetic fluid current sensor and OPC current sensing are established. Secondly, the relationship between the magnetic field and the current of the OPC is demonstrated. Finally, the relationship between the optical transmission properties of magnetic fluids and the OPC current is studied. The results show that there is a good linear relationship between the transmitted power and the current of the OPC.     

飞秒光参量放大技术原理及应用

飞秒光参量放大技术是一种获得宽带飞秒脉冲的有效手段.首先介绍了飞秒光参量放大技术的基本原理,并通过数值模拟显示了群速度失配及位相失配对信号转换过程的影响.数值计算结果表明:群速度失配及位相失配会导致转换效率下降,群速度失配还会导致脉冲发生畸变.其次,综述了该技术在超短脉冲特别是周期量级脉冲产生方面的研究进展,并介绍了Baltuska等设计的可以产生3.9 fs脉冲的非共线光参量放大装置.其中,详细讨论了超连续白光注入源、泵浦光角色散以及晶体选择三方面内容.最后介绍了该技术在高能飞秒脉冲产生方面取得的最新研究进展.     

基于啁啾FBG的三角形光脉冲发生器的优化设计

提出了利用啁啾光纤布拉格光栅(FBG)和马赫增德尔调制器产生三角形光脉冲的优化方案.方案采用FBG模拟单模光纤的色散特性,结合光载波抑制调制产生了三角形光脉冲, 并通过仿真分析,选择FBG的长度、调制深度、适当的折射率切趾函数对三角形光脉冲的线性特征进行了优化.仿真结果表明,在同一啁啾系数下,产生的三角形光脉冲的失真程度随啁啾光纤光栅的调制深度增大而增大,光栅长度、折射率切趾函数对三角形光脉冲的影响也比较明显.与现有系统相比,由于将FBG引入系统,省去长距离的光纤,优化方案系统结构更为简单,三角形光脉冲线性特征更好.     

A minimum distortion transmission scheme under combined effects of chromatic dispersion and SPM based on optical time-domain fractional Fourier transformation

In this paper, an optical time-domain fractional Fourier transformation (FRFT) system is proposed to achieve the minimum distortion transmission under combined effects of chromatic dispersion and self-phase modulation (SPM). In the new method, the pulses operated as FRFT will propagate in a new domain, in which the waveform in time domain will keep nearly unchanged through the transmission. The novel method achieves a 400 km optical transmission for an optical pulse with the full width at the 1/e point of peak power of 80 ps without any dispersion compensation and the pulse offers a nice performance with negligible nonlinear distortion. Compared with the soliton communication, this scheme shows more advantages on linear and nonlinear distortions without strict restriction to input pulses.     

Nonlinear noise amplification in optical transmission systems with optical phase conjugation

Taking into account the influence of group-velocity dispersion (GVD) and the nonlinear Kerr effect, the nonlinear amplification of the amplified spontaneous emission (ASE) noise in fiber transmission systems using optical phase conjugation (OPC) is studied. Under a path-averaged power approximation for long-haul transmission systems, an equivalent system is developed to evaluate ASE noise amplification and accumulation in OPC systems. Combining the theoretical analysis and numerical simulations, the noise suppression effect in OPC systems is demonstrated and discussed. By using the numerical calculation method, the power variation along the system is involved in the evaluation of noise amplification. It is shown that the power variation through the system results in an imperfect compensation of the modulation instability (MI) effect, which furthermore causes the degradation of the noise suppression performance in OPC systems with anomalous dispersion.     

Cross-phase modulation in semiconductor optical amplifier

Cross-phase modulation in a semiconductor optical amplifier is demonstrated by using copropagating pump and probe pulse trains of different wavelengths. The relative time delay between the pump and probe pulses was varied and the effect on the spectral distortion is described.<>     

Pulse restoration by filtering of self-phase modulation broadened optical spectrum

Restoration of distorted optical pulses is achieved using nonlinear fiber self-phase spectral broadening and subsequent optical band-pass filtering of a single sideband. Using this technique, the output pulsewidth is shown to remain constant for input pulse-widths between 9-20 ps. A detailed investigation of the signal-to-noise ratio shows that best performance is obtained by operating in normal fiber dispersion regime. This technique is also applied to restore 40 Gb/s RZ-data suffering distortion from polarization mode dispersion. The high-bandwidth fiber nonlinearity shows promise to scale to higher bit rate pulse distortion correction.     

Simultaneous suppression of third-order dispersion and sideband instability in single-channel optical fiber transmission by midway optical phase conjugation employing higher order dispersion management

In optical phase conjugation (OPC) systems, the third-order dispersion (TOD) of optical fibers and the nonlinear resonance at well-defined signal sideband frequencies called sideband instability (SI) mainly limit the transmission performance. We propose, for the first time, a scheme for simultaneous suppression of both TOD and SI in OPC systems using a periodic higher order dispersion-managed link consisting of standard single-mode fibers (SMFs) and reverse dispersion fibers (RDFs). Computer simulation results demonstrate the possibility of 200-Gb/s data transmission over 10 000 km in the higher order dispersion-managed OPC system, where the dispersion map is optimized by our system design strategies.     

2.5 Gbit/s光发射模块消光比与光接收误码特性

改变2．5Gbit/s光发射模块消光比（EX）,对作为标准接收用的光接收机灵敏度进行了测试。实验表明,EX小于9．0时,光接收灵敏度较差;EX大于15．0时,由于眼图中交叉点偏低或光脉冲波形畸变,可能导致光接收灵敏度恶化;EX在9．0－12．0范围时,光接收灵敏度最佳。     

光纤波导中光脉冲演化方程的数值解及计算机仿真研究

在光纤通信中，光脉冲信号在光纤中传输的过程中会受到色散、损耗和非线性等作用的影响而不断地发生演化和畸变。脉冲演化的规律遵循非线性薛定谔方程（NLSE）。由于NSLE在一般情况下无法求得它的解析解，因此通常需采要用数值方法来求解。本文使用了分步傅里叶方法对NLSE进行了求解，并用利用这一结果对四种常见的光通信光脉冲在光纤中传输时的演化情况进行了计算机仿真研究，仿真结果分别模拟了几种常见光脉冲在光纤中传输时包络的演化情况。     

多个短脉冲辐照下光学元件的温升分布

从傅里叶热传导方程出发,推导了在多个幅度、间隔不等的短脉冲辐照下,无源光学元件温升三维分布的含有时间的解析表达式,针对具有周期性的重复脉冲照射的情况进行了具体的计算分析,讨论了入射脉冲数目、脉冲间隔及脉冲通量密度等与光学元件的温升分布的关系,并估计了温升引起的光波相位畸变。     

Self-phase modulation and spectral broadening of optical pulses insemiconductor laser amplifiers

Amplification of ultrashort optical pulses in semiconductor laser amplifiers is shown to result in considerable spectral broadening and distortion as a result of the nonlinear phenomenon of self-phase modulation (SPM). The physical mechanism behind SPM is gain saturation, which leads to intensity-dependent changes in the refractive index in response to variations in the carrier density. The effect of the shape and the initial frequency chirp of input pulses on the shape and the spectrum of amplified pulses is discussed in detail. Particular attention is paid to the case in which the input pulsewidth is comparable to the carrier lifetime so that the saturated gain has time to recover partially before the trailing edge of the pulse arrives. The experimental results, performed by using picosecond input pulses from a 1.52-μm mode-locked semiconductor laser, are in agreement with the theory. When the amplified pulse is passed through a fiber, it is initially compressed because of the frequency chirp imposed on it by the amplifier. This feature can be used to compensate for fiber dispersion in optical communication systems     

Gain saturation characteristics of traveling-wave semiconductorlaser amplifiers in short optical pulse amplification

The gain saturation characteristics of traveling-wave semiconductor laser amplifiers (TWAs) are theoretically and experimentally investigated. In the amplification of an isolated pulse whose repetition period is short compared to the carrier lifetime, the gain saturation is related through the carrier lifetime to the gain saturation in CW amplification. When the output pulse energy is smaller than the saturation energy, short optical pulses can be amplified without pulse shape distortion, whereas high-energy pulses suffer from pulse shape distortion due to the temporal gain variation during the pulse radiation. FWHM pulse duration variation in amplification by TWAs depends on the input pulse shape. The pulse energy gain saturation was experimentally confirmed to be independent of pulse durations and to be determined only by the pulse energy. In extremely-high-repetition-rate pulse amplification, the saturation of the pulse energy gain is determined by the average signal power     

Switching dynamics of short optical pulses in a nonlineardirectional coupler

It has been shown recently that the propagation of short optical pulses in a nonlinear directional coupler consisting of two parallel waveguides or fibers should be described more generally by a pair of coupled nonlinear equations that take into account the dispersion properties of the coupling coefficient. In this paper, we use the Fourier series analysis method to solve these equations, and study the effects of a dispersive coupling coefficient on the switching dynamics of short optical pulses in a nonlinear directional coupler. We demonstrate, with numerical examples, that a dispersive coupling coefficient could cause significant pulse distortion and affect the threshold switching intensity. The effects of introducing frequency chirps in the input pulses are also discussed     

Cancellation of the signal fading for 60 GHz subcarrier multiplexedoptical DSB signal transmission in nondispersion shifted fiber usingmidway optical phase conjugation

In millimeter-wave (mm-wave) optical double sideband (DSB) signal transmission systems, the received radio frequency (RF) power fades periodically because of the group velocity dispersion (GVD) and the self-phase modulation (SPM) of optical fibers. In this paper, cancellation of the signal fading by using midway optical phase conjugation in mm-wave subcarrier multiplexed (SCM) optical DSB signal is analyzed. Fading-free 60 GHz mm-wave optical DSB signal transmission over 100 km-long nondispersion shifted single-mode fiber at 1550 nm by using a semiconductor optical amplifier (SOA) optical phase conjugator (OPC) in the midway of optical link is experimentally demonstrated for the first time. Finally, the degradation factor of the OPC system is also discussed