弱湍流大气中部分相干涡旋光束的轨道角动量特性

根据轨道角动量谱理论,推导了部分相干拉盖尔-高斯光束轨道角动量态的功率表达式。分析了相干长度、束宽对轨道角动量的影响,讨论了弱湍流大气中部分相干-拉盖尔高斯光束轨道角动量特性。结果表明:部分相干拉盖尔-高斯光束在相干长度与束腰半径比值固定的情况下,其初始轨道角动量态相对功率不会随着束腰半径的改变而变化。在部分相干拉盖尔-高斯光束初始相干长度与束腰半径取值大小相同的情况下,随着束腰半径的增大,光束在弱湍流大气中传输1 km处的初始轨道角动量态相对功率减小。     

大气斜程传输中高阶贝塞尔高斯光束轨道角动量的研究

大气湍流引起大气折射率随机变化, 导致空间不均匀性。高阶贝塞尔光束在大气湍流中传输时, 空间不均匀性会使光子波函数改变,形成不同的光子态引起轨道角动量的弥散。在Rytov近似下,计算了高阶贝塞尔光束在大气斜程传输中各分量所占光束总能量的权重。讨论并对比折射率结构常数,光束波长,天顶角,轨道角动量数,接收孔径和光斑大小等参数对螺旋谱的影响,并给予相应的物理解释。结果表明:随着折射率结构常数,天顶角和传输距离的增加以及光束波长的减小,螺旋谐波主分量对应的谱减小,轨道角动量弥散越大,而且望远镜接收孔径和光斑大小对轨道角动量弥散的影响非常小。     

受限拉盖尔-高斯光束湍流传输时轴上光强分布

为了研究受限拉盖尔-高斯光束湍流传输时轴上光强分布,采用扩展惠更斯-菲涅耳原理方法进行了理论分析,得到了受发射圆孔限制的拉盖尔-高斯光束在大气湍流中传输时轴上光强的表达式。并运用MAPLE模拟,取得了不同湍流强度、波长和发射圆孔孔径下轴上光强的分布理论数据。结果表明,拉盖尔-高斯光束在不同阶数、湍流强度、波长和发射圆孔孔径下,真空和湍流较弱时,轴上光强在近场发生明显振荡,达到最大值后,强度明显开始降低,湍流较强时,传输很近距离强度就迅速衰减,并与其在真空中的传输特性进行了比较。这一结果对研究拉盖尔一高斯光束是有帮助的。     

单光子斜程量子信道纠缠角动量的大气湍流效应

分析了von Karman型湍流大气对量子光信道中传输的由参量下转换源生成纠缠轨道角动量态的影响。运用Rytov近似、波相位结构函数的平方近似和修正von Karman折射率起伏谱,研究了完整包含大气湍流引入振幅与位相起伏效应的斜程湍流大气通信信道中单光子纠缠轨道角动量态的测量概率模型,建立了长曝光与短曝光两种曝光条件下斜程湍流大气传输单光子纠缠轨道角动量态的测量概率理论关系。数值研究了天顶角分别为θ=π/6和θ=π/3时的长短或曝光情况下,轨道角动量态纠缠光子对联合概率随着传输距离的变化。数值结果表明：在z〈500m的传输距离内,纠缠光子对的联合检测概率随传输距离增加而快速下降,但传输距离达z〉1000m后联合检测概率几乎不再下降;结果也发现,携带轨道角动量小的纠缠光子对的联合测量概率减少率比携带轨道角动量大的纠缠光子对的联合测量概率的要小;光束传输天顶角越大,联合概率下降幅度越大。     

受限拉盖尔-高斯光束湍流传输时轴上光强分布

为了研究受限拉盖尔-高斯光束湍流传输时轴上光强分布,采用扩展惠更斯-菲涅耳原理方法进行了理论分析,得到了受发射圆孔限制的拉盖尔-高斯光束在大气湍流中传输时轴上光强的表达式.并运用MAPLE模拟,取得了不同湍流强度、波长和发射圆孔孔径下轴上光强的分布理论数据.结果表明,拉盖尔-高斯光束在不同阶数、湍流强度、波长和发射圆孔孔径下,真空和湍流较弱时,轴上光强在近场发生明显振荡,达到最大值后,强度明显开始降低,湍流较强时,传输很近距离强度就迅速衰减,并与其在真空中的传输特性进行了比较.这一结果对研究拉盖尔-高斯光束是有帮助的.     

激光轨道角动量态的湍流倾斜、像散和慧差效应

为了分析斜程大气信道中湍流像差对激光束轨道角动量态的作用,数值研究了湍流z-倾斜像差、湍流像散和湍流慧差对激光束轨道角动量态测量概率的影响,得出了此3种湍流像差随折射率结构常数、传输距离和天顶角起伏影响光束轨道角动量态测量概率的规律。结果表明,随着地面湍流强度增强、信道长度增长和天顶角的增大,湍流z-倾斜像差使激光束原轨道角动量态的测得概率进一步降低,湍流慧差仅在天顶角增大时才出现激光束原轨道角动量态的测得概率进一步降低现象,湍流像散对激光束原轨道角动量态测得概率的影响随此3参量变化时基本不变。     

拉盖尔-高斯波束在弱湍流海洋中轨道角动量传输特性变化

瑞托夫近似方法被用于分析研究弱湍流对海水环境中拉盖尔-高斯(Laguerre-Gaussian, LG)波束轨道角动量模式探测概率、串音概率以及螺旋谱分布的影响.结果表明:海洋湍流对轨道角动量的影响明显强于大气湍流, 海水环境中LG波束信号轨道角动量模式有效传输距离只有几十米;海洋湍流明显导致信号轨道角动量模式探测概率下降, 轨道角动量模式串音变强, 螺旋谱严重扩展;海洋湍流的影响随着轨道角动量角向模式、径向模式增加, 以及发射波长减小而增强.虽然较长的波长能降低海洋湍流影响, 但考虑到海水的散射和吸收作用, 蓝绿波长仍然是最佳选择.     

大气湍流信道中OAM光束与高斯光束传输性能的实验研究

通过实验研究了大气湍流信道下中轨道角动量（OAM）光束与高斯光束的传输性能,并将两种光束的传输性能进行对比。实验以加载调制信号的OAM光束以及高斯光束为传输载波,分别测量了在大气湍流信道下两种光束的光束展宽、指向偏差、功率抖动以及误码率。实验结果表明:在大气湍流信道中传输后,OAM光束相比高斯光束,光束展宽减少10.5%,功率抖动的方差下降0.13,指向偏差的散布圆直径减小30.4%,并且光束中心更集中于接收面中心;OAM光束载波系统的最低探测灵敏度达到?28.97 dBm,相比高斯光束提升2.5 dB。实验结果证明了在大气湍流信道传输中,OAM光束比高斯光束受到湍流的影响更小,并且随着湍流强度的增加,OAM光束恶化程度远小于高斯光束。实验的结论为大气湍流信道下自由空间激光通信的发展和应用提供了参考。     

大气湍流下轨道角动量复用态串扰分析

以加载QPSK调制信号的轨道角动量（OAM）光束为传输载波,以多个相位屏模拟大气湍流,研究不同大气湍流强度下OAM复用态的串扰情况。通过对复用光束光强和相位研究,得出在OAM复用态光强受到湍流影响时会发生明显的闪烁现象,光功率分散,相位发生旋转弯曲,且湍流强度越大,受到的影响越大。选用螺旋谱分析不同湍流强度下各OAM复用态之间的弥散程度,当大气湍流强度增加时,OAM态之间的弥散程度增加,且较强湍流会导致OAM复用态失真。同时,考虑OAM复用态之间的模式串扰以及每路携带信息的OAM态因大气信道引起的混合噪声而造成的码间干扰,对比研究了不同大气湍流强度下系统误码率随传输距离的变化,结果表明:系统误码率随传输距离的增长而增大,强湍流之下光束误码率会随着传输距离增长到一定程度后趋于平稳,弱湍流之下光束误码率会随着传输距离的增长而增大。     

圆形平顶高斯光束阵列在湍流大气传输中的M2因子

应用Wigner分布函数的二阶矩定义和拓展Huygens–Fresnel原理研究了圆形平顶高斯光束阵列在湍流大气传输中的光束性质,得到其传输质量因子（ 因子）的解析表达式,进行了相应的数值计算和模拟。结果表明：在湍流大气中传输时,圆形平顶高斯光束阵列的传输质量因子随传播距离、湍流大气结构常数的增大和束腰宽度的减小而增大;当光束阵列阶数一定,阵列个数不断增加时,其传输质量因子先保持不变,然后开始减小,最后不再减小,而保持这个定值不变;当光束阵列的个数一定,阶数不断增加时,其传输质量因子减小,最后不再减小而保持不变。在自由空间中传输时,圆形平顶高斯光束阵列的传输质量因子保持不变。     

光纤型Q开关

光纤型Q开关是调Q全光纤激光器的关键部件。目前,可用的光纤型Q开关主要有基于SBS效应的被动Q开关、基于双光束干涉原理的主动Q开关和某些特殊设计的主动Q开关。基于SBS效应的被动Q开关存在重复频率不稳定且不易调节等缺点;基于双光束干涉原理的主动Q开关属于慢Q开关,其它主动Q开关的设计技术还不成熟,所以研究开发高性能的主动光纤型Q开关成为调Q全光纤激光器发展的必然要求。     

主动调Q全光纤激光器的发展评述

调Q全光纤激光器相比非全光纤激光器具有效率高、结构紧凑和携带方便等潜在优点,并且主动Q开关的重复频率稳定、易于控制,所以全光纤化和主动Q开关的完美结合将引发调Q光纤激光器质的飞跃。在调Q全光纤激光器的发展历程中,布喇格光栅的出现是调Q全光纤激光器发展的重要一步,Q开关的光纤化更是关键的环节。目前,已光纤化的主被动Q开关均很常见,但主动光纤型Q开关技术并不成熟,或许将传统工艺上比较成熟的声光或电光Q开关光纤化是解决该问题的可行途径。     

Dynamic stimulated Brillouin scattering analysis

We present a new simple analysis-including the effect of spontaneous emission-of the (dynamic) influence of stimulated Brillouin scattering (SBS) on the detected receiver eye diagram. It applies in principle for general types of modulation formats such as the digital formats of amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK). The analysis is formulated for a determination of the signal power depiction and intersymbol interference (ISI) caused by the combined effect of fiber dispersion, fiber attenuation and nonlinear fiber effects such as the effect of self-phase modulation (SPM) and SBS. The analysis allows a quantification of the dithering influence on the SBS threshold. Representative numerical examples are presented for two single-channel ON-OFF modulated 10-Gh/s systems utilizing Franz-Keldysh and Mach-Zehnder-type modulators     

Periodic structures prepared by two-beam interference method

We present an optical interference method as the efficient tool for high-quality one- (1D) and two-dimensional (2D) periodic structure fabrication. Different types of 2D periodic structures are prepared using two-beam interference technique by double exposure. Also, the patterning of Au layer is provided using two-beam interference method. Quite homogeneous 1D and 2D structures with small periodicity were prepared in photoresist and Au layer. The experimentally prepared structures are well in agreement with the theoretically designed ones. According to experimental results, we favor two-beam interference technique using multi-exposure process as a very useful method for fabrication of 2D periodic structures and devices for integrated optoelectronics.     

对集群光电成像传感器的多源协同相干激光干扰机理研究

目前激光干扰基本是一对一干扰模式,随着光电侦察传感器的大量使用,激光干扰急需面向集群目标的多对多干扰手段。立足于解决对集群化光电成像侦察的有效压制干扰问题,文中提出对集群光电成像传感器的多源协同相干激光干扰方法,以视场外散斑相干合成干扰作为多对多干扰实现的基本思路,探讨其相干干扰机理,建模分析双光束相干激光干扰光电传感器作用效果并提出对集群目标的协同干扰模型。仿真结果表明,激光入射角度是激光协同相干干扰的重要影响参数,能够作为干扰站协同部署的依据。同时,基于PSNR与MSE的图像质量评价结果表明,相干叠加干扰与单光束干扰以及非相干叠加干扰相比具有明显优势。     

The principle of a double crystal electron interferometer.

Sinusoidal interference fringes have been observed recently using a double crystal interferometer and convergent beam electron diffraction techniques. However, the formation mechanism of the interference fringes is not understood completely. In this paper, we explain this effect using wave theory and discuss the coherence conditions necessary for this special interferometer. The excitation errors of partial exit waves leaving a crystal, which is used as a wave splitter, are found to be responsible for the formation of the interference fringes. The double crystal interferometer used in the electron diffraction manifests a new interference mechanism. Compared with two-beam interference in real space, we observe the interference effect in the reciprocal space, i.e. in the Fourier space. This effect may enable us to undertake holography in the Fraunhofer diffraction plane and measure both the phase and amplitude information of reflections. The phase information of reflections contains information on the position of atoms and the symmetry of a unit cell. Furthermore, such an interferometer has no rigorous coherence conditions.     

激光干涉视力仪及其应用研究

介绍了利用双光束干涉法检查眼底视觉功能(分辨力)的基本原理,描述了我们研制的激光干涉视力仪的光路系统,以及对眼科常见病90例,125只眼的检查结果,指出了“星点闪烁”现象在眼底视觉测定中的重要意义。     

六角形单块铌酸锂电光Q开关

一 单块双45°电光Q开关虽然有很多优点,特别是它能自然光调制,对中小型激光功率器件的应用很方便,但它还存在一些缺点,需要完善提高,这种Q开关中o光、e光分离角较大,造成了消光比低。对石榴石等高增益工作物质往往因消光比低而“关不死”。对铌酸锂双45°单块电光Q开关,实际应用中大多采用偏光瞬时加电压工作方式,这样工作电压比退电压方式高二倍,特别是效率降低约一倍,不能充分发挥单块Q开关自然光调制、效率高等优点。本文介绍的六角形单块电光Q开关克服了这些缺点,保留了它的优点。     

A performance analysis of all-optical clock extraction circuit based on stimulated Brillouin scattering

In this paper, we develop an analytical method to deal with the timing performance in an optical clock extraction circuit based on stimulated Brillouin scattering (SBS). Three kinds of SBS active filters are considered and their frequency-transfer functions are obtained under the assumption that pump depletion caused by SBS is negligible. When pump depletion is taken into account, an SBS active filter acts as a nonlinear filter. To investigate the timing performance at this situation, we introduce the concept of "dynamic frequency-transfer function" to describe its frequency-response property for a fixed-signal light and pump light. Using the obtained "frequency-transfer function," we give analytical expressions for both root-mean-square (rms) phase jitter and rms amplitude jitter of the extracted optical clock, in which we have taken the impacts of SBS gain, pump light linewidth, optical pulse chirp, and pump detuning into account. Finally, a detailed numerical investigation on the timing performance for the three active filters is presented.     

Photonic generation of microwave arbitrary waveforms using stimulated Brillouin scattering and Sagnac loop

A photonic approach is proposed to generate microwave arbitrary waveforms based on the stimulated Brillouin scattering (SBS) effect and the Sagnac loop. The Sagnac loop is utilized to generate the optical signals of ±1st-order and ±3rd-order sidebands. Due to the principle of velocity adaptation, even order optical sidebands are suppressed. Thanks to the SBS effect, the microwave signal consisting of odd order harmonics is generated after the photodetector (PD), which can construct the triangular waveform, the square waveform, or the sawtooth waveform by adjusting the weight of the harmonics.