混沌信号在光纤传输过程中的非线性演化

对光纤混沌传输理论及混沌信号与光纤传输媒介相互作用的物理机制进行了理论研究. 通过耦合激光混沌系统和光纤传输信道，提出光纤混沌信号传输的非线性演化物理模型. 着重分析光纤自相位调制对激光混沌信号传输与演化的作用. 结果表明：自相位调制不影响混沌信号脉冲的形状，但能产生非线性相移使混沌信号频谱展宽；自相位调制不影响混沌信号脉冲的功率分布和场强分布，但能影响混沌信号脉冲的功率频谱分布，影响混沌信号光场以及慢变场的变化. 提出混沌信号在光纤传输中的非线性演化频率啁啾和形式，数值模拟了混沌信号在光纤传输过程中的相位、频谱、场以及场的慢变部分的相空间等演化形式和特点. 关键词： 混沌 光纤 传输 演化     

同轴Super－Reltron的物理分析和数值模拟

对同轴Super－Reltron进行了物理分析和数值模拟, 在调制腔电压125kV、加速间隙电压600kV和电流15kA时, 在C波段获得了峰值功率约2.5GW和效率约25%的结果, 都较以前大大提高。计算表明频率与箔的高度成反比。在电流达到空间电荷极限以前, 微波输出功率和电流的平方成正比。     

同轴Super－Reltron的物理分析和数值模拟

 对同轴Super－Reltron进行了物理分析和数值模拟, 在调制腔电压125kV、加速间隙电压600kV和电流15kA时, 在C波段获得了峰值功率约2.5GW和效率约25%的结果, 都较以前大大提高。计算表明频率与箔的高度成反比。在电流达到空间电荷极限以前, 微波输出功率和电流的平方成正比。     

基于散斑检测的逆向调制光通信

为了解决长距离逆向调制光通信系统中弱信号难以检测的难题,将散斑检测方式用于逆向调制光通信中,实现对逆向调制端弱小光信号抖动的检测.设计了系统方案和检测原理,并实验完成了60m距离上1.3kHz数字信号的传输和330m距离上模拟话音的传输.该检测方式简单、便宜、易于模块化,在低速的逆向调制光通信系统中有较好的应用.     

“日盲”紫外光通信系统传输距离的仿真计算

依据Lambert定律对强度调制/直接探测紫外光通信系统的接收光功率计算公式进行推导,公式表明,距离平方反比衰减和大气透射比衰减是导致接收光功率随距离增大迅速衰减的主要因素,提高通信系统的传输距离只能依靠优化收发系统参数实现;重点针对引起大气透射比衰减的主要因素,利用大气传输软件MODTRAN进行仿真,结果表明,不同大气模型、天气条件和臭氧浓度对大气透射比衰减产生较大影响,从而影响系统的工作距离;根据理论和仿真结果计算出“日盲区”分别在三类主要因素影响下的大气透射比系数的量值,为“日盲”紫外光通信系统工作距离的定量估算提供实用、有效的方法。     

时变带限信道中光通信的均衡与去噪技术

为了解决时变带限信道中的光通信问题,基于自适应均衡和盲均衡方法,提出了一种半盲光信号均衡方案,适用于大气海洋等时变带限光信道的光通信信号处理.对带限光信道中传输的包含泊松噪音开关键控调制光脉冲信号的不同数字均衡处理方法进行了数值模拟,比较了不同方法的结果,证明半盲均衡能更快匹配光信道且能保持收敛.同时,利用小波方法研究了含噪光接收信号去噪问题,发现光滑小波软阈值去噪方法更适合空间光脉冲信号波形,并对通信眼图进行了去噪的数值模拟.     

海洋湍流信道中因斯-高斯光束及信号传输特性实验研究

因斯-高斯（IG）光束在复杂信道传输中具有较好的抗干扰能力。为此设计并搭建了基于模拟海洋湍流信道的激光通信实验平台,详细研究IG光束在海洋湍流信道下光束信号的传输及通信特性。首先实验对比研究了不同海洋湍流强度条件下,IG光束和高斯光束传输后的光强闪烁指数、质心漂移和探测器接收功率情况;其次通过调制0.5～3 MHz频率的方波信号,进一步研究两种光束传输后调制信号波形失真特性;最后进行IG光束和高斯光束的7.5 Mbit/s通信性能对比实验。实验结果表明：IG光束的闪烁指数、质心漂移、功率抖动均优于高斯光束,且随着海洋湍流强度增加,IG光束闪烁指数和质心漂移改善能力增强,功率抖动改善能力降低。在不同模拟海洋湍流中,相同频率的IG光束调制方波波形失真度整体低于高斯光束。在误码率为3.8?10-3（前向纠错阈值）时,IG光束在不同注水高度信道、不同温度信道和不同盐度信道中的通信性能比高斯光束分别提高了0.8 dB、4 dB和2.5 dB。该实验结果可以为IG光束应用于水下激光通信提供参考。     

基于太阳能电池板的无线光通信与传能复合系统实验研究

为明确光载波无线传输系统中,复合传输相比单独传输的优越性,实验对比了单独传能、单独通信、复合传输三种结构在传输距离为0.1m、接收的光功率估值为3.5mW、光通信速率为1kbps时的输出特性.结果表明,单独传能系统在与电感串联的负载为4kΩ时,电池板输出最大功率为1.82mW,复合传输系统在与电感串联的负载为5kΩ时,电池板输出最大功率为2.1 mW,比单独传能系统高出15%;与电容串联的负载较低时复合传输系统输出信号波形发生畸变,优化负载后波形得以改善,相同条件下幅值比单独通信系统高出1.52V.     

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采用三支节液态调配器使离子回旋加热(ICRH)天线系统达到阻抗匹配,在阻抗匹配的条件下结合频率调制技术来减小由天线输入阻抗变化所引起的反射功率。数值模拟了频率调制前后天线负载与反射系数的变化关系,用来验证频率调制对ICRH天线中阻抗匹配装置的影响。模拟结果表明:三支节液态调配器结合频率调制方法,能更好地降低天线传输系统的反射系数,使得发射机的功率通过天线辐射更加有效地耦合到等离子体中去。     

频率调制对ICRH 天线阻抗匹配的影响研究

采用三支节液态调配器使离子回旋加热(ICRH)天线系统达到阻抗匹配,在阻抗匹配的条件下结合频率调制技术来减小由天线输入阻抗变化所引起的反射功率。数值模拟了频率调制前后天线负载与反射系数的变化关系,用来验证频率调制对ICRH 天线中阻抗匹配装置的影响。模拟结果表明：三支节液态调配器结合频率调制方法,能更好地降低天线传输系统的反射系数,使得发射机的功率通过天线辐射更加有效地耦合到等离子体中去。     

光纤传输系统中互相位调制和受激拉曼散射串扰噪声的比较研究Ⅱ--级联传输系统

在具有级联光放大器的密集波分复用强度调制一直接检测光纤系统中，导出了包含互相位调制和受激拉曼散射共同作用的强度／相位矩阵表达式。在计算强度噪声谱的基础上，研究了互相位调制和受激拉曼散射的相互耦合并用于密集波分复用系统的噪声分析。在带色散补偿的密集波分复用级联光纤传输系统中(如80信道，信道间距50GHz)，受激拉曼散射引入的串扰噪声功率可能超过互相位调制。最后，给出了密集波分复用系统分析与设计的若干建议。     

Further Theoretical Investigations for Laser Relative Intensity Noise with Fiber Nonlinearities and Higher-Order Dispersion

In this article, we theoretically investigate relative intensity noise (RIN) in optical communication systems with fiber nonlinearities due to optical Kerr effects and higher-order dispersion. The impact of modulation frequencies, launch power, and laser bias current on RIN has been illustrated. We show that RIN increases with modulating frequencies up to the resonance frequency, launch power, and decrease in the laser bias current. We also show that higher-order dispersion terms have no impact on the RIN, but with first-order dispersion compensation the higher-order dispersion terms have significant impact at high modulating frequencies. The RIN with and without fiber nonlinearities is further investigated. It has been shown that the RIN with fiber nonlinearity is more than the RIN without nonlinearity and the effect of nonlinearity appears at higher modulation frequencies only.     

基于频域相位共轭技术的交叉相位调制所致失真的复原

理论分析和讨论了基于频域相位共轭技术的交叉相位调制所致信号失真的复原和补偿机理，数值模拟了在交叉相位调制作用下，高斯脉冲在中距相位共轭光纤系统中的传输演化过程.结果表明，频域相位共轭技术能够抑制交叉相位调制对光纤系统中传输信号的损害，复原其所导致的信号失真，并能够同步补偿群速度色散和自相位调制非线性效应所导致的信号失真.合适的初始脉冲时延和初始脉冲啁啾有利于频域相位共轭技术对交叉相位调制所致信号失真的抑制. 关键词： 频域相位共轭 交叉相位调制 色散 自相位调制     

飞秒激光作用下全向高反膜破坏的激发过程

设计和制备了全向高反膜SiO₂/TiO₂，研究了它在不同脉冲宽度、不同脉冲能量的飞秒激光作用下的破坏阈值和烧蚀深度.利用发展的抽运-探针方法，研究了抽运脉冲作用下材料中导带电子的超快激发和能量沉积过程，建立并求解了飞秒激光激发材料和材料的激发对抽运光自身反作用的耦合动力学模型.模型较好地揭示了材料破坏的激发过程. 关键词： 飞秒激光 全向高反膜 激发过程 破坏机制     

Arbitrary pulse shaping based on intensity-only modulation in the frequency domain

We propose a novel technique to implement arbitrary pulse shaping of an ultrashort pulse by intensity-only modulation in the frequency domain. The intensity-only modulation is realized by nonuniformly spaced sampling in the frequency domain. By properly designing the sampling function, multiple pulses in the time domain will be generated with one of which being the desired waveform. The desired waveform is then selected by a time window. Both the optical amplitude and phase distributions of the output waveform can be controlled. Theoretical analysis is presented. An example showing the generation of a rectangular pulse is provided.     

Pilot-based cross-phase modulation compensation for coherent optical orthogonal frequency division multiplexing long-haul optical communications systems

A pilot-based nonlinearity compensator (PB-NLC) is shown in this Letter to be an effective method for compensating cross-phase modulation (XPM) in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. An unmodulated pilot tone is transmitted at the center of each OFDM channel to detect phase errors caused by the Kerr effect, which converts intensity fluctuations from all channels to phase errors. The pilots are then used to cancel the XPM phase errors for each OFDM channel at the receiver after each channel's self-phase modulation (SPM) has been compensated, using its intensity waveform to determine its SPM. Numerical simulations of a 58 Gb/s single polarization 2375 km system with inline dispersion compensation show that the signal quality, Q, at the optimal launch power is increased by 2.4 dB if SPM compensation is used before the PB-NLC. This contrasts with only a 0.9 dB improvement if the PB-NLC is used without an SPM compensator for the same link. This shows the PB-NLC can effectively mitigate XPM but not SPM.     

Fiber chromatic dispersion measurement based on wavelength-to-time mapping using a femtosecond pulse laser and an optical comb filter

A novel method for the measurement of chromatic dispersion of an optical fiber based on wavelength-to-time mapping using a femtosecond pulse laser (FSPL) and an optical comb filter is proposed and experimentally evaluated. In the proposed approach, the spectrum of an ultrashort optical pulse generated by an FSPL is sliced by an optical comb filter. The spectrum-sliced optical pulse is then coupled into the optical fiber under test. Thanks to the chromatic-dispersion-induced wavelength-to-time mapping in the optical fiber under test, a time-domain waveform similar to the sliced spectrum is generated at the output of the optical fiber, with different frequency components having different time delays. The time delay vs. frequency data are then recorded for the estimation of the chromatic dispersion by using least square fitting. Chromatic dispersions of two types of optical fibers with different lengths are tested. The measured dispersion values agree well with those measured by the conventional modulation phase shift (MPS) method.     

Harmonic and intermodulation distortions and noise associated with two-tone modulation of high-speed semiconductor lasers

We present results of modeling and simulation of the harmonic and intermodulation distortions as well as the intensity noise of high-speed semiconductor lasers under two-tone modulation. Multiple quantum-well lasers are considered, which are characterized by large differential gain and a modulation bandwidth of about 25GHz. The study is based on the rate equation model of semiconductor lasers excited by injection current with two sinusoidal tones separated by a radio frequency. The modulated laser signal is modeled in both the time and frequency domains. The time domain characteristics include the fluctuating waveform, while the frequency domain characteristics include the frequency spectrum of the relative intensity noise (RIN), carrier-to-noise ratio, modulation response, harmonic distortion, and the second- and third-order intermodulation distortions (IMD2 and IMD3). The analysis is performed for three frequencies of 5, 15, and 24 GHz, which are, respectively, lower, comparable, and higher than the laser relaxation frequency. The range of the modulation depth covers the regimes of small and large-signal modulation. We show that both RIN and IMD3 of two-modulated laser are minimum when the modulation frequency is 5GHz, and maximum when the modulation frequency is 24 GHz. The second-order harmonic distortion, IMD2, and IMD3 values are larger in the vicinity of relaxation oscillations and increase with the modulation index, especially under large-signal modulation.     

光纤环形谐振腔的频率锁定及其特性

基于可调分束比的光纤分束器,制作了光纤环形谐振腔并通过调节分束比实现了对光纤环形谐振腔的欠耦合、临界耦合和过耦合的状态控制.实验测量了腔最小反射率与腔损耗之间的关系,获得光纤环形谐振腔的腔内衰减率为κ_0=2π×(1.60±0.03) MHz ,品质因子为Q=(1.10±0.02)×10.8.在此基础上,结合了压电陶瓷拉伸光纤以控制腔长和Pound-Drever-Hall锁频两大技术优势,克服了之前温度反馈控制等方法的反馈带宽窄、噪声大和稳定性差等问题,实现了对光纤环形谐振腔共振频率的快速、灵敏的控制和锁定.结果表明,锁频过程中相位调制功率与相位调制引起腔反射光的强度调制之间的关系为线性关系,进而通过降低相位调制信号的功率以减小相位调制对腔反射光强度调制的影响.当调制功率设定最低为–9 dBm时,光纤环形谐振腔仍能被稳定锁定.该光纤环形谐振腔为其与原子、金刚石色心等发光粒子相互作用的腔量子电动力学实验研究奠定了坚实的基础.