基于压缩传感的光子计数成像系统

提出了一种基于压缩传感理论的光子计数成像系统。该系统以单光子计数器作为探测元件,以期在面元探测技术不甚成熟的现状下用点探测器进行极弱光探测。通过计算机模拟计算,验证了压缩传感理论结合单光子计数器应用于极弱光成像的可行性,讨论了单光子计数器的暗计数率、量子效率和测量噪声对成像质量的影响。介绍了压缩传感理论,为了获得更好的图像质量和更快的计算速度,提出了SpaRSA-DWT稀疏重建算法,并与传统的IWT算法进行对比。给出了两种算法下,迭代次数、测量数、噪声功率分别与获得图像信噪比的关系曲线,证明了SpaRSA-DWT算法的优越性。     

虚光子过程对单光子Jaynes—Cummings模型中原子压缩效应的影响

本文引进短时弱耦合近似研究了虚光子过程对单光子Ｊａｙｎｅｓ－Ｃｕｍｍｉｎｇｓ模拟的原子压缩效应的影响，在选定初始条件下发现此影响与耦合强度，初始平均光子数，光子频率和光场位相有关。     

脏外染料被动压缩准分子激光的输出脉冲特性研究

用紫外染料PTP、BPBD、t-B_uPBD等对XeC1准分子激光施行腔外被动压缩,获得了压缩比为3的XeC1激光脉冲透射输出和压缩比大于8的染料辐射输出。提出“光子传输速率方程”来描述被动压缩现象,计算机模拟计算结果较好地解释了准分子激光压缩及染料辐射的实验结果。     

多光子无绝热近似的量子涨落

本文用全量子理论讨论了有注入相干信号的一环形腔中具有N个均匀展宽的全同两能级原子系统。我们采用Wigner特征函数得出多光子过程的Fokker—Planck方程。无绝热近似地讨论了系统的稳定性、稳态关联、透射光谱、场和原子系统的压缩效应、反聚束效应。首次得出真空拉比分裂谱线。本理论取良腔(good—cavity)与劣腔(badcavity)两种极限情况与已有的理论一致。并得出多光子双稳以及多光子激光劣腔情况下均有明显的压缩效应的新结论。本文对比了良腔、劣腔、无绝热近似三种情况下单光子双稳和双光子双稳的非经典效应。     

受驱动光学系统多光子荧光光谱

本文讨论了受驱动光学系统多光子荧光光谱。分析表明多光子荧光光谱在良腔、劣腔以及无绝热近似情况下均成立。原子——原子之间的关联对多光子荧光光谱无贡献,多光子荧光光谱与单光子荧     

三乙胺分子共振多光子电离及解离机理

利用可调谐脉冲染料激光器，用多光子电离飞行时间质谱法在波长为４４５．９－４６５．９ｎｍ范围内获得了三乙胺分子共振光子电离谱和质谱。测得了三乙胺分子ＭＰＩ过程产生的离子信号的激光能量的气压依赖关系。     

增加光子双模压缩真空态的N次方H压缩效应

通过数值计算，研究了增加光子双模压缩真空态的N次方H压缩效应。结果表明：对于态，光场存在着N次方H压缩效应，而且对于高次方H压缩，在压缩参数较大时，随着场模上光子增加数的增大，N次方H压缩效应增强。     

基于中空光子带隙光纤的飞秒激光脉冲压缩

利用中空光子带隙光纤(HC-PBGF)对光子晶体光纤飞秒激光器输出的激光脉冲进行腔外再压缩.激光器输出的脉冲中心波长为1040 nm,脉冲宽度为475 fs,平均功率为400 mw,单脉冲能量为8 nJ.通过白光干涉法测量可中空光子带隙光纤的色散参数为-48 ps2/km,并利用截断实验得到了所用光纤的最优化长度,压缩后获得的最短脉冲宽度为108 fs,接近变换极限,传输效率为89%.由于该光纤纤芯的非线性系数较低,脉冲在其中传输无非线性效应,压缩后输出光谱保持不变.     

光子集成混沌半导体激光器研究进展（特邀）

混沌激光具有宽频谱、类噪声、低相干等特性,在保密光通信、高速随机数、混沌激光雷达、混沌光时域反射仪和分布式光纤传感等领域具有重要的应用价值。光子集成混沌激光器是混沌激光应用的核心器件,具有体积小、性能稳定、成本低等优点。综述了近十年来光子集成混沌半导体激光器的进展及其主要应用。首先介绍了混沌半导体激光器的集成方式;接着介绍了光子集成混沌半导体激光器的分类,根据其扰动方式讨论了直腔单反馈、多腔反馈、环形腔反馈、二维外腔反馈、互注入等结构,并对比分析了各自的优势与输出特性;然后介绍了光子集成混沌半导体激光器在光时域反射仪、保密光通信和高速随机数产生等方面的应用;最后,讨论了光子集成混沌激光器的关键集成技术、时延特征抑制及间歇混沌的特性。     

光子晶体波导与微腔耦合的三通道波分复用器

为了实现对光波有效的选择输出,并且使光波的带宽很小,设计了微腔耦合的三通道波分复用器。对该器件采用时域有限差分法和微腔与波导间耦合模进行研究。首先,根据微腔选择不同频率的光波,设计光子晶体滤波器模型。然后,基于光子晶体耦合模理论,由定向耦合波导和一个高品质因子微腔构成的波分复用器。最后,为了提高输出光的透射效率,在波分复用结构的主波导的输出端,增加五个介质柱,形成一个反射层。实验结果表明:此结构能够通过微腔选择不同频率的光波,经过优化设计后的波分复用模型,光波的透射率得到了提高,波长λ=1.763μm的光波达到透射率将近90%。在光子晶体中取多个微腔可以选择输出更多波长的光波,所以这种结构在光子晶体集成器件的制作上有很好的应用前景。     

Dynamics of Q-switched and mode-locked intracavity secondharmonic generation in a ring laser

The temporal dependence, spectral characteristics, and efficiency of a multimode Q-switched ring laser containing an intracavity second harmonic generator is described. Numerical studies show that such lasers are stable and efficient. Comparison with Q-switched lasers (not containing a second harmonic generator) demonstrates that the intracavity second harmonic generation lasers can be even more efficient than the fundamental laser due to nonlinear output coupling. General considerations for the operation of such lasers are described. Spectral characteristics of the output as a function of the gain of the active medium and the spectrum of the injected pulse are discussed. Instabilities at very high second harmonic conversion are observed     

Active harmonic modelocking of an erbium fiber laser withintracavity Fabry-Perot filters

We present both experimental and theoretical investigations of the operation of a harmonically modelocked erbium fiber ring laser stabilized by an intracavity bit-rate etalon. Our model analyzes the effects of cavity components and operating parameters on laser stability and output pulse characteristics. The model predicts the output pulsewidth variation with laser cavity parameters such as cavity length, dispersion, and finesse of intracavity Fabry-Perot etalons. If the laser cavity length is not optimized, a maximum 50% increase in pulsewidth can occur at 5 Gb/s pulse rate. A repetition rate etalon with a finesse of 50 is sufficient to provide a side-mode suppression ratio of over 50 dB in the laser output. We also discuss how detuning from the optimal modulation frequency increases the excess noise that affects the laser stability. The theory predicts a maximum detuning range of ±100 kHz, which agrees with the experimental observations. These theoretical results can guide the design of similar lasers over a wide range of operating parameters     

Computer simulation of laser photon fluctuations: DFB lasers

This fourth paper of the Series is devoted to photon fluctuations in the light output of distributed feedback (DFB) lasers. Statistics on laser photon fluctuations are collected from numerical solutions of noise driven rate equations. The approximate formula for the variance of the photon fluctuations, presented earlier [1], is also applicable to the DFB laser. Compared to the single-cavity injection laser, the DFB laser has the following features. 1) The order of magnitude of the photon fluctuations of the single lasing mode of a DFB laser is comparable to the fluctuations of the total power output of a single-cavity laser. 2) Contrary to single-cavity lasers, which cannot be made to Operate in a single longitudinal mode even under idealized conditions if they are driven by short current pulses, DFB lasers will readily deliver a single, pulsed mode. Thus, if thermal effects and backreflection of scattered light can be controlled, there will be no mode jumping during pulsed operation.     

Computer simulation of laser photon fluctuations: Coupled-cavity lasers

This third paper of the series deals with photon fluctuations in the light output of coupled-cavity lasers. As before, statistics on laser photon fluctuations are collected from numerical solutions of noise driven rate equations. Compared to the single-cavity injection laser, the coupled-cavity laser is found to have the following advantages. 1) The coupled-cavity laser can be made to operate in a single mode by driving one of its sections above and the other below threshold. For a given amount of output power from the high-current end, fewer photon fluctuations occur if it is the longer laser section that is driven above threshold. 2) The order of magnitude of the photon fluctuations of the single lasing mode of a coupled-cavity laser is comparable to the fluctuations of the total power output of a single-cavity laser. 3) Contrary to single-cavity lasers, which cannot be made to operate in a single mode if they are driven by short current pulses, coupled-cavity lasers will readily deliver a single, pulsed mode. Thus, if thermal effects and backreflection of scattered light (for example, from an attached fiber) can be ignored, mode jumping need not occur.     

Detailed model and investigation of gain saturation and carrier spatial hole burning for a semiconductor optical amplifier with gain clamping by a vertical laser field

A detailed model for semiconductor linear optical amplifiers (LOAs) with gain clamping by a vertical laser field is presented, which accounts the carrier and photon density distribution in the longitudinal direction as well as the facet reflectivity. The photon iterative method is used in the simulation with output amplified spontaneous emission spectrum in the wide band as iterative variables. The gain saturation behaviors and the noise figure are numerically simulated, and the variation of longitudinal carrier density with the input power is presented which is associated with the on-off state of the vertical lasers. The results show that the LOA can have a gain spectrum clamped in a wide wavelength range and have almost the same value of noise figure as that of conventional semiconductor optical amplifiers (SOAs). Numerical results also show that an LOA can have a noise figure about 2 dB less than that of the SOA gain clamped by a distributed Bragg reflector laser.     

Actively $Q$ -switched and Mode-Locked Diode-Pumped ${hbox {Nd:GdVO}}_{4}{hbox {--KTP}}$ Laser

By using a comparative simple configuration and a short cavity length, a diode-pumped actively Q -switched and mode-locked intracavity frequency doubled Nd:GdVO₄-KTP green laser with the modulation depth 100% was realized, from which the great average output power, the high efficiency were obtained and the mode-locked pulse inside the Q -switched pulse has a repetition rate of 476 MHz. Using the hyperbolic secant function methods and by considering the Gaussian distribution of the intracavity photon density, the influences of continuous pump rate, the upper state lifetime of the active medium and the turnoff time of the acousto-optic Q -switch, we proposed a developed rate equation model for actively Q -switched and mode-locked green lasers. With this developed model, the theoretical calculations are in good agreement with the experimental results and the width of the mode-locked green pulse is estimated to be about 185 ps.     

Computer simulation of laser photon fluctuations: Theory of single-cavity laser

This paper is the first of a series devoted to theoretical studies of photon fluctuations in the light output of semiconductor injection lasers. Statistics on laser photon fluctuations are collected by means of a simulation of the dynamic behavior of the laser based on numerical solutions of noise driven laser rate equations. This first paper in the series introduces the noise driven rate equations for a single-cavity laser, explains the method used for their numerical solution, and discusses some approximate analytical results. The second paper presents results of photon counting statistics for the single-cavity laser collected from numerical solutions of the time dependent equations. Additional papers in this series will concentrate on coupled-cavity and distributed feedback lasers. Comparison of these statistical results will show clearly the advantage of coupled-cavity and distributed feedback laser designs over conventional single (Fabry-Perot) cavity injection lasers.     

Optimization of intracavity doubled passively Q-switchedsolid-state lasers

Passively Q-switched lasers can be optimized by the choice of two factors: (1) reflectivity of the output coupler and (2) transmission of an unsaturated absorber. When intracavity frequency doubling is adopted, the nonlinear crystal behaves as a nonlinear output coupler. In this paper, we generalize the optimization theory for intracavity frequency-doubled passively (Q)-switched lasers. By introducing a nonlinear loss term caused by the frequency doubler into the coupled rate equations describing the operation of saturable absorber passively Q-switched lasers, we can express the harmonic pulse characteristics such as peak power, pulse energy, pulsewidth, and a factor describing pulse symmetry. Using the Lagrange multiplier technique to maximize the peak power of the second harmonic for a given pump level, we obtain an additional constraint equation describing the relation of a frequency-doubling factor to a normalized intermediate variable, which can be solved quickly to determine the characteristics of the pulse. The frequency-doubling factor, which is a normalized key parameter, is found to depend not only on the commonly used coefficient of the nonlinear frequency doubler and the emission cross section of the laser medium, but also on the laser cavity optical length. We plot design curves indicating the key parameter and the pulse characteristics via two normalized variables, one representing the pump level, and the other representing the laser emission medium and the absorber medium. Using these curves and expressions, one can design an optimal passively Q-switched intracavity frequency-doubled miniature laser and predict the pulse characteristics without relying on computer calculation     

利用激光器产生单模亚泊松光

对利用激光器产生单模亚泊松光进行了研究。提出了一个普遍的主方程,它适用于任意稳定的原子注入方式,并在该方程中,考虑了有限腔寿命的作用。得出了输出光子数的Mandel因子,并指出在泵噪声抑制的基础上通过减少腔寿命,可以代替抑制自发辐射,使输出光子数的涨落进一步减小。     

Dispersion-induced instability in CW laser oscillators

A CW-pumped laser with a short photon cavity lifetime may show an unstable output in the form of spontaneous pulsations or noise. In this paper, a model is developed which reconciles previous studies of unstable behavior in homogeneously and inhomogeneously broadened lasers. Specific regions of instability are predicted for xenon lasers, and it is concluded that some degree of inhomogeneous broadening makes the instability much more likely to be observed.