Optical pulse generation from FM laser using gain dispersion

The possibility of new type of optical pulse compression utilizing dispersion effect of laser gain is discussed. An experiment using a 1.06 μm Nd:YAG laser for a dispersive delay line was performed to demonstrate the possibility, where cw FM laser, instead of frequency-swept pulses, was e,ployed. The FM laser of 100 GHz bandwidth at 144 MHz repetition frequency, which was generated from another Nd:YAG laser, was observed to pulsate with 1.2 ns pulsewidth after passing through the dispersive delay line consisting of laser medium. Several times power amplification due to the laser gain was also obtained in the dispersive delay line.     

Amplification of picosecond pulses in a 140-GHz gyrotron-traveling wave tube

An experimental study of picosecond pulse amplification in a gyrotron-traveling wave tube (gyro-TWT) has been carried out. The gyro-TWT operates with 30 dB of small signal gain near 140 GHz in the HE?? mode of a confocal waveguide. Picosecond pulses show broadening and transit time delay due to two distinct effects: the frequency dependence of the group velocity near cutoff and gain narrowing by the finite gain bandwidth of 1.2 GHz. Experimental results taken over a wide range of parameters show good agreement with a theoretical model in the small signal gain regime. These results show that in order to limit the pulse broadening effect in gyrotron amplifiers, it is crucial to both choose an operating frequency at least several percent above the cutoff of the waveguide circuit and operate at the center of the gain spectrum with sufficient gain bandwidth.     

Variable single-passband narrowband optical filter based on forward stimulated interpolarization scattering in photonic crystal fiber

A variable transmission spectrum single-passband narrowband optical filter is proposed and experimentally demonstrated. It is based on forward stimulated interpolarization scattering (SIPS) in a photonic crystal fiber by applying a differential quadrature phase-shift keying modulation to the pump wave to broaden and shape the SIPS gain spectrum. By choosing the bit rate of the modulation data pattern, a flat-top steep-cutoff optical bandpass filter with a 3?dB bandwidth of 70?MHz and a 10?dB bandwidth of 90?MHz is realized. In addition, a variable narrowband optical notch filter is also realized by attenuation of the pump wave.     

Design of a tunable time-delay element using multiple gain lines for increased fractional delay with high data fidelity

A slow-light medium based on multiple, closely spaced gain lines is studied. The spacings and relative strengths of the gain lines are optimized by using the criteria of gain penalty and eye-opening penalty to maximize the fractional delay defined in terms of the best decision time for random pulse trains. Both numerical calculations and experiments show that an optimal design of a triple-gain-line medium can achieve a maximal fractional delay about twice that which can be obtained with a single-gain-line medium, at three times higher modulation bandwidth, while high data fidelity is still maintained.     

有耗地面上架空线缆串扰研究等效电路模型

基于延迟抽取宏模型算法,将有耗地面上架空传输线分成多段求解,每段分成无损和有损部分。通过矢量匹配(VF)法对地阻抗相关参量进行匹配,利用HSPICE中的Laplace变换建立有损部分的等效电路,结合现有的无损传输线等效电路组成每一段的等效电路,然后将每段等效电路串联起来组成整个传输线的等效电路模型。与时域有限差分(FDTD)法进行对比,结果验证了该方法的正确性。同时对端接瞬态抑制二极管的算例进行了分析,证明了提出的等效电路模型能够轻松解决非线性负载问题。     

非线性传输线高功率实验北大核心CSCD

设计了基于交叉耦合铁氧体非线性传输线高功率射频微波产生系统,系统由脉冲形成线、非线性传输线以及高功率匹配负载(或组合振子辐射天线)组成。由100kV高压电源和高压微波电缆构成单传输线高功率脉冲形成线,形成线输出脉冲幅度35kV,脉冲半宽60ns。高压脉冲经过非线性传输线的脉冲压缩和调制,与高功率匹配负载相连时,实验得到了峰峰值31kV、中心频率308 MHz、3dB带宽为13%的射频振荡脉冲;与组合振子天线相连时,实验得到了中心频率380MHz、3dB带宽为12%的宽谱辐射。实验结果与数值模拟基本吻合。     

Effects of spatial hole burning in 888?nm pumped, passively mode-locked high-power Nd:YVO4 lasers

We report on an experimental study of 888?nm pumped, passively mode-locked, high-power Nd:YVO₄ lasers with an enhanced cavity design, involving spatial hole burning (SHB) in the active medium. We observed a significant pulse shortening due to the concept of ??Gain-at-the end,?? despite using long gain length up to 30?mm. A?31.6?W average output power TEM₀₀ Nd:YVO₄ oscillator, providing 16.2?ps pulses at an repetition rate of 96?MHz is presented. The pulse duration turns out to be primarily a function of the effective gain length, which can be explained by means of SHB. A?further pulse shortening with decreasing gain length down to 9.5?ps at 11.1?W average output power is demonstrated.     

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。     

Conductively cooled 1-kHz single-frequency Nd:YAG laser for remote sensing

A conductively cooled,laser diode(LD) end-pumped,injection-seeded single-frequency Nd:YAG laser is designed and implemented.The laser is capable of producing an 8-mJ Q-switched pulse with a 11-ns pulse width at 1 064 nm and at a pulse repetition rate of 1 000 Hz.At the maximum output energy of 8 mJ,the frequency jitter is less than 3.5 MHz(root mean square(RMS)) over two minutes,and the linewidth is around 54.2 MHz.The M2 of the laser beam is approximately 1.30 in both horizontal and vertical directions.The optimized ramp-fire technique is applied to build reliable single longitudinal mode oscillating.     

Five‐cycle pulses near λ = 3 μm produced in a subharmonic optical parametric oscillator via fine dispersion management

Five‐cycle (50 fs) mid‐IR pulses at 80‐MHz repetition rate are produced using a degenerate (subharmonic) optical parametric oscillator (OPO), synchronously pumped by an ultrafast 1560‐nm fiber laser. The effects of cavity dispersion and the length of a periodically poled lithium niobate (PPLN) gain element on the output spectrum and pulse duration are investigated by taking advantage of a very broad (∼ 1000 cm⁻¹) gain bandwidth near the 3.1‐μm OPO degeneracy point. A new method of assessing the total OPO group delay dispersion across its entire spectrum is proposed, based on measuring spectral signatures of trace amounts of molecular gases injected into the OPO cavity.     

Optimizing the performance of single-mode laser diode system using genetic algorithm

In this correspondence, micro-genetic algorithm (MGA) application results for optimizing the performance of electronic feedback of a laser diode are presented. The goal of optimization is to find the maximum bandwidth of the laser diode with electronic feedback used in fiber optic digital communication. A numerical analysis of the system theory of the single-mode laser diode to obtain numerical results of the gain, the pulse response, and the harmonic distortion for electronic feedback is also presented. The dependence of the system gain on the feedback gain and delay is examined. The pulse response is studied and it is shown that a transmission rate over 1 Gbyte/s can be achieved.     

Novel photonic approach to microwave frequency measurement using tunable group delay line

A photonic approach for measuring microwave frequency over a wide bandwidth is proposed.An optic group delay line composed of several magneto-optical switches and a 1.6-km single-mode fiber is used as a tunable dispersive medium in the measurement setup.A minimum frequency accuracy of 80 MHz in the range of 1-20 GHz is achieved experimentally.     

Transmission gaps in one-dimensional Fibonacci quasiperiodic structure containing epsilon-negative materials

We investigate the transmission properties of one-dimensional Fibonacci quasiperiodic structure consisting of dispersive and lossless epsilon-negative (ENG) materials. It is found that for both TE and TM polarizations with normal and oblique incidences, there exist transmission gaps which are invariant with a change of scale and sensitive to incident angles. Analytical methods based on transfer matrices and effective medium theory have been used to explain the properties of transmission gaps.     

具有宽阻带特性的6阶自均衡高温超导滤波器

本文提出了一种新颖的L型阶跃阻抗谐振器,该谐振器具有结构紧凑、抑制二次谐波能力强及易于实现电耦合及磁耦合等特点。使用该谐振器设计并制作了一款具有小型化、高选择性及宽阻带特性的6阶自均衡高温超导滤波器。测试结果表明,在70 K温度下滤波器的中心频率为1 601 MHz,3 dB带宽为24 MHz,带内回波损耗<14.87 dB,带内最大插入损耗约为0.22 dB,60%带宽范围内群时延起伏<3.13 ns,通带两侧具有一对深度的传输零点,实现了1 632~5 511 MHz范围内衰减>60 dB的宽平坦阻带。     

自均衡线性相位高温超导滤波器的设计

针对第三代移动通信CDMA 2000标准用超导滤波器的技术要求,设计了一种自均衡线性相位高温超导滤波器,给出了14阶三个交叉耦合的CQ结构滤波器理论计算结果、等效电路、耦合矩阵,设计的滤波器中心频率为830MHz,65%带宽内的群时延波动优于±10ns,滤波器模拟仿真结果与理论计算很好得吻合。     

被动锁模Yb3+光纤环形腔激光器的研究

 采用974 nm半导体激光器作为泵浦源，超高掺杂Yb³⁺光纤作为增益介质，利用光纤的非线性偏振旋转效应，得到稳定的ps量级锁模光脉冲。泵浦功率220 mW时，激光器锁模阈值功率150 mW，输出功率26 mW，锁模光脉冲中心波长1 046 nm，3 dB带宽6.01 nm，20 dB带宽16 nm，脉宽22 ps，重复频率20 MHz。与同类光纤激光器相比，该激光器输出功率高，具有更好的稳定性。     

Conductively cooled 250-Hz single frequency Nd：YAG laser

A conductively cooled, laser diode （LD） end-pumped, injection-seeded single frequency Nd：YAG laser is designed and impleinented. The laser utilizes Nd：YAG rod as gain medium and compact dual-endpumping arrangement using two fiber-coupled LDs with a maximum output of 150 W. The optimized ramp-fire technique is applied to build reliable single longitudinal mode oscillating. The laser is capable of producing a 10-raJ Q-switched pulse with 13-ns pulse width at 1064 nm at a pulse repetition rate of 250 Hz. The output beam qualities M2 of approximately 1.19 and 1.22 in horizontal and vertical directions are detected, respectively.     

Pulsed high-order volume mode gyroklystron

We present the results of studies of a gyroklystron with the TE₅₃ output mode. A 30-dB gain is obtained at a frequency of 30 GHz for an output power of 5 MW, efficiency 25%, pulse duration 0.4 ms, and amplification bandwidth 40 MHz.     

层叠Blumlein线产生电压波的解析解

采用Laplace变换的方法求解了无损耗情况下层叠Blumlein线输出电压的解析表达式。从传输线两端口网络模型出发,分别求出了负载端短路和开路时传输线特征阻抗的频域表达式。简化了单Blumlein线电路结构,并求出了其输出电压的解析表达式。在此基础上,结合电路叠加原理,求解出了典型的2级层叠Blumlein线输出电压的时域解析表达式。采用递推法,推广得到任意级数情况下的输出电压波解析解。     

中红外组合激光场调控宽带超连续谱的产生

本文对原子在波长为2000nm、脉宽为12.5fs的中红外驱动脉冲和脉宽为1.3fs的紫外控制脉冲叠加形成的组合场中产生的高次谐波进行了研究.通过组合场驱动氦原子得到了谱宽为230eV的超连续谱.利用组合场产生的谐波比单独利用中红外脉冲产生的谐波的强度高了3个量级.对超连续谱进行滤波并调节组合场中两束激光的延迟时间,可以直接产生100as的单个脉冲.我们发现超连续谱的宽度和位置几乎不会因为驱动场和控制场强度的变化而改变,这种性质有利于从实验上获得单个宽谱阿秒脉冲.