All-optical switchable UWB pulses generation,modulation and transmission

We proposed and demonstrated all-optical polarity- and shape-switchable ultrawideband (UWB) Gaussian pulses generation schemes using a single polarization interferometer (PI) or a semiconductor optical amplifier (SOA) cascaded by a PI. When an optical signal with dark return-to-zero (RZ) format propagates directly through a single PI, a pair of polarity-reversed UWB monocycle pulses and a positive UWB doublet pulse is acquired respectively only by adjusting the polarization controllers, without changing the bias of the intensity modulator. If a SOA is connected at the input of the PI to firstly implement the first-order differential function to the input dark RZ pulse utilizing gain saturation effect of the SOA, both polarity- and shape-switchable UWB Gaussian monocycle and doublet pulses are all acquired from the cascaded system. Moreover, if a nonreturn-to-zero control signal is introduced into the SOA, utilizing the cross-gain modulation (XGM) effect of the SOA and the differential characteristic of PI, all-optical shape modulation to UWB signals can be realized, and the polarity of the modulated UWB pulses can also be switched. Also, UWB signal transmission characteristics in fiber link were investigated.     

Photonic generation of ultrawideband signals by exploiting gain saturation of dark pump pulse with double undershoots in a highly nonlinear fiber

We have proposed and theoretically demonstrated an alternative photonic scheme to generate ultrawideband (UWB) doublet pulses based on gain saturation effect in one piece of highly nonlinear fiber (HNLF). A flexible format swap between UWB doublet and monocycle pulses can be successfully realized by properly tuning the optical tunable delay line (ODL). Moreover, the key parameters for UWB pulse, including the center frequency (Fc), 10 dB bandwidth (BW_10dB), and fractional bandwidth (FBW), are also investigated with Fc being Einstein shift when the doublet pulse transforms into the monocycle pulse. Finally, our proposed scheme exhibits good performance that the obtained UWB pulse can have a FBW of > 100% at the Fc of ~ 7 GHz and UWB-over-fiber technology is also implemented without dispersion management.     

Photonic multi-shape UWB pulse generation using a semiconductor optical amplifier-based nonlinear optical loop mirror

We propose and demonstrate a scheme to implement photonic multi-shape ultra-wideband(UWB) signal generation using a semiconductor optical amplifier(SOA) based nonlinear optical loop mirror(NOLM).By employing the cross phase modulation(XPM) effect,cross gain modulation(XGM),or both,multi-shape UWB waveforms are generated including monocycle,doublet,triplet,and quadruplet pulses.Both the shapes and polarities of the generated pulses are flexible to adjust,which may be very useful in UWB pulse shape modulation and pulse polarity modulation.     

Optical ultrawideband monocycle pulse generation based on cross-gain modulation in a semiconductor optical amplifier

A novel method for generating ultrawideband (UWB) monocycle pulses based on cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) is proposed and experimentally demonstrated. Thanks to the XGM in the SOA, a pair of polarity-reversed optical Gaussian pulses is generated at the output of the SOA, to which a Gaussian pulse pump and a continuous-wave probe are applied. The two polarity-reversed optical pulses are then time delayed by two cascaded fiber Bragg gratings to introduce a time delay difference. A UWB monocycle pulse with a full width at half-maximum of 48 ps and a fractional bandwidth of 188% is generated at the output of a high-speed photodetector.     

Ultrawideband monocycle generation using cross-phase modulation in a semiconductor optical amplifier

We propose a novel scheme to generate ultrawideband (UWB) monocycle pulses based on cross-phase modulation (XPM) of a semiconductor optical amplifier (SOA). The proposed system consists of a SOA and an optical bandpass filter (OBF). Due to the XPM, a continuous wave (CW) probe signal is phase modulated by another optical Gauss pulse in the SOA. The OBF will convert the phase modulation to intensity modulation. A pair of polarity-reversed UWB monocycle pulses is achieved by locating the probe carrier at the positive and negative linear slopes of the OBF. Both cases conform to the UWB definition of the Federal Communications Commission.     

All-optical ultrawideband monocycle generation utilizing gain saturation of a dark return-to-zero signal in a semiconductor optical amplifier

We demonstrate a simple and compact scheme to generate ultrawideband (UWB) monocycle pulses utilizing gain saturation of a dark return-to-zero (RZ) signal in a semiconductor optical amplifier (SOA). When optical pulses with a dark RZ format propagate through the SOA, the output power at the rising edge will be overamplified compared with that at other durations due to the gain unsaturation. As a result, the output pulses are monocyclelike. The UWB frequency spectra at different injected currents, different input pulse widths, and different input wavelengths are analyzed. Our experiments show that the monocycle generation has good tolerance to the SOA bias current and the input signal wavelength.     

Photonic ultrawideband monocycle pulse generation using a single electro-optic modulator

A compact approach to photonic-assisted ultrawideband (UWB) monocycle pulse generation is proposed and experimentally demonstrated based on the wavelength dependence of the half-wave voltage of a Mach-Zehnder modulator (MZM). By employing a single MZM with dual-wavelength injection at around 1310 and 1550 nm, a pair of polarity-reversed monocycle pulses with the full width at half-maximum of about 80 ps and the fractional bandwidth of greater than 160% can be generated. The experiment results agree well with the theoretical prediction. The simple setup and the convenience to control the monocycle pulse polarity are favorable for future applications.     

Photonic ultra-wideband monocycle pulses generation using semiconductor optical amplifier and electro-absorber in parallel

A scheme for photonic generation of ultra-wideband （UWB） pulses using a semiconductor optical amplifier （SOA） and an electro-absorber （EA） in parallel is proposed and numerically demonstrated. By adjusting the time delay between two pump signals incident into the SOA and the EA, we can obtain monocycle pulses with reversed polarities and different bandwidths. The proposed method is flexible in pulse shaping and easy in practical optimization.     

带内干扰抑制的超宽带脉冲设计

采用不同幅度和延迟的高斯函数脉冲组合来拟合抽样函数脉冲，利用拟合的抽样函数脉冲设计超宽带脉冲信号,实现美国联邦通信委员会制定的辐射掩蔽要求的高效逼近.该方法产生的脉冲波形具有实现简单、持续时间短、带外辐射功率小、容易进行时域或频域调节等特点.与已报道的几种脉冲比较，设计的脉冲可携带更多的能量, 同时具有良好的带内（窄带或宽带）干扰抑制能力，能够和带内的其他通信系统更好的共存.最后，对设计的脉冲波形和最佳高斯波形的通信性能进行了比较，表明文中波形的性能明显优于最佳高斯波形.     

光载超宽带脉冲雷达信号传输性能研究

采用双并行马赫曾德尔调制器产生高斯脉冲一阶微分和二阶微分型超宽带脉冲雷达信号和光载无线电传输技术,通过仿真研究了两种超宽带脉冲雷达信号在标准单模光纤中的传输特性.结果表明,高斯脉冲一阶微分型脉冲随着传输距离的增大而不断展宽,而高斯脉冲二阶微分型脉冲则先压缩后展宽.经100km标准单模光纤传输之后,在传输终端采用色散补偿光纤对传输信号进行不同程度的色散补偿,可获得满足美国联邦通信委员会规范要求的不同宽度高斯脉冲一阶微分和二阶微分型脉冲信号.     

光载超宽带脉冲雷达信号传输性能研究

采用双并行马赫曾德尔调制器产生高斯脉冲一阶微分和二阶微分型超宽带脉冲雷达信号和光载无线电传输技术,通过仿真研究了两种超宽带脉冲雷达信号在标准单模光纤中的传输特性.结果表明,高斯脉冲一阶微分型脉冲随着传输距离的增大而不断展宽,而高斯脉冲二阶微分型脉冲则先压缩后展宽.经100km标准单模光纤传输之后,在传输终端采用色散补偿光纤对传输信号进行不同程度的色散补偿,可获得满足美国联邦通信委员会规范要求的不同宽度高斯脉冲一阶微分和二阶微分型脉冲信号.     

Filter-free ultrawideband generation based on semiconductor optical amplifier nonlinearities

A filter-free scheme for ultrawideband (UWB) generation with single semiconductor optical amplifier (SOA) is proposed and demonstrated. A pair of polarity-reversed optical pulses is generated due to cross gain modulation (XGM) in the pump-probe scheme, whereas the amplified pump pulse becomes sharp at its leading edge such that the power peak is shifted forward. Hence, the combination of the pump and probe signals at the SOA output is quasi-monocycle shape. Our scheme is an improved scheme to avoid exploiting optical filters and time-delay devices. The generated UWB radio frequency spectrum shows good stability when the input probe power varies from −10 dBm to 6 dBm, the probe wavelength varies in the whole C-band, and the bias current varies from 100 mA to 240 mA. Although the generated quasi-monocycle deviates from a standard Gauss monocycle to some extent, the frequency spectrum conforms to the UWB regulation. Two SOAs with different XGM dynamics are compared in generating UWB signals.     

高重频超宽谱短电磁脉冲对GPS接收机干扰

超宽谱短电磁脉冲的频谱可覆盖GPS工作频带,对GPS接收机的正常工作存在干扰威胁。从理论分析、数值仿真和实验方面研究了高重频超宽谱短电磁脉冲对GPS接收机干扰效果与脉冲参数之间的依赖关系。结果表明:若脉冲重复频率整数倍能落入GPS接收机工作频带内,高重频超宽谱短电磁脉冲对GPS接收机干扰效果较强,且达到相同干扰效果时所需脉冲幅值随重频增大而等比例减小,即脉冲幅值与重频乘积保持为常数;若重频整数倍偏离GPS接收机工作频带,高重频超宽谱短电磁脉冲对GPS接收机干扰效果不明显。     

Photonic generation of power-efficient FCC-compliant ultra-wideband waveforms using semiconductor optical amplifier （SOA）： theoretical analysis and experiment verification

We theoretically design a power-efficient ultra-wideband pulse generator by combining three monocycle pulses with different weights. We also experimentally demonstrate a feasible scheme to generate such power-efficient ultra-wideband waveforms using cross-phase modulation in a single semiconductor optical amplifier. The designed ultra-wideband pulse fully satisfies the requirements for the spectral mask specified by the Federal Communications Commission with high power efficiency. In the experiment, a power-efficient ultra-wideband waveform with a pulse duration of 310 ps is achieved, and the power efficiency is greatly improved compared with that of a single monocycle pulse or a mixture of two monocycles.     

C. 超短激光光源

本文对超短激光脉冲的产生、压缩技术的最新发展做了详细评述。     

A Novel Approach to All-Optical Generation of Ultra-Wideband Signals

Abstract

The generation of ultra-wideband signals in the optical domain is highly desirable for ultra-wideband-over-fiber systems, which has recently become a topic of interest. In this article, a novel and simple approach to achieve all-optical generation of ultra-wideband signals is proposed, which is based on delaying and superimposing optical Gaussian pulses with opposite polarities. The proposed system is capable of generating both ultra-wideband monocycle and doublet pulses, and the polarity of the generated ultra-wideband monocycle pulses can be fast-switched to implement pulse polarity modulation with the required bit pattern. A model to describe the proposed system is developed, and the generation of ultra-wideband signals is demonstrated with simulations and a proof-of-concept experiment.     

伪随机编码超宽带短脉冲的探测能力研究

 为进行弱信号检测，研究在脉冲雷达中获得大信号时间宽度与信号带宽积的方法，利用伪随机编码方法调制超宽带短脉冲，可以在保持子脉冲信号带宽的情况下，以低功率发射长脉冲串类噪声信号，而提高信号的能量，提高探测距离。通过仿真实验得出，利用伪随机编码技术可以使超宽带信号具有更强的探测能力，可以在回波信号功率水平远远小于噪声水平（如信噪比5%）的情况下实现对探测目标的高保真成像。     

超宽带脉冲环境下射频滤波器非线性响应分析

实验研究发现,射频滤波器在连续波和超宽带脉冲条件下其带外传输性能基本一致,但在带内某些频段,超宽带脉冲环境下滤波器的传递函数远大于1。此外,滤波器在超宽带脉冲下的时域响应还出现了脉冲振荡特征。针对这些现象,从滤波器的非线性无源互调和Q值效应的两个方面,分析了滤波器在超宽带脉冲作用下的响应机理,初步解释了上述现象。此外,通过不同辐射场强下的测量结果可知,滤波器无源互调还出现了非线性现象,使得测量结果的普适性受到一定限制。基于传递函数的预测结果表明,连续波测量结果的预测波形无论是从能量上还是从峰值功率上都明显小于实测结果。这些都反映出,滤波器在超宽带脉冲环境下的响应机理与在连续波环境下的响应机理明显不同,其预测结果也差异较大。也就是说,连续波测量结果不可用于超宽带脉冲的效应分析和评估。     

用腔倒空Nd：YAG激光器对fs超短脉冲的同步放大

实现了用腔倒空Nd:YGA激光器对fs超短脉冲放大器的同步泵浦。由碰撞锁模环形染料激光器产生的80fs脉冲经二级染料放大后,实现放大倍数6.2×10~4,输出超短脉冲峰值功率～2×10~7W。     

适用于探地雷达应用的低振铃单周期脉冲发生器

设计了一种新型的适用于道路检测探地雷达的单周期脉冲发生器。该脉冲发生器包含驱动电路、阶跃恢复二极管(SRD)脉冲形成电路和脉冲整形电路三部分。驱动电路可以使TTL形式的触发脉冲变为电流更大的快前沿脉冲,用来形成给后级电路的驱动脉冲;SRD脉冲产生电路选取渡越时间较小的阶跃恢复二极管结构,通过对前级电路产生的驱动脉冲整形得到负极性高斯脉冲,然后利用微带短路线、肖特基二极管和电容并联实现生成单周期脉冲和振铃抑制的功能,提高超宽带天线辐射的效率以及测量信噪比。测量结果表明,在1 MHz脉冲重复频率的情况下,峰峰值最大为23 V,脉冲半高宽为138 ps,振铃水平为1.25%,而当脉冲重复频率提高到5 MHz,该脉冲发生器产生脉冲波形幅度和带宽基本没有太大变化。这些特征说明,该脉冲发生器具有很高的频率稳定性,且在高分辨率探测应用情景中将会有很好的表现。