基于RF谱分析技术的光网络性能监测技术的研究

依据RF谱分析技术,提出了一种新型的利用光偏移带阻滤波来实现PMD不灵敏的CD监测技术。在此基础上研究了利用光偏移带阻滤波来实现CD不灵敏的PMD监测技术,建立了理论模型并分析其原理。最后验证了理论模型对80Gb/s NRZ-DQPSK信号的监测结果。

非均匀辛格相关蓝绿激光波束通过海洋湍流的传输特性

根据广义惠更斯-菲涅尔原理,建立了非均匀辛格相关蓝绿激光波束在海洋湍流中的传输模型。基于交叉谱密度函数,讨论了不同传播距离下波束光强变化。数值计算了波束光强和光强最大值横向偏移受海洋湍流参数的影响。结果表明,传播距离和海洋湍流参数对非均匀辛格相关蓝绿激光波束的光强自聚焦现象有一定影响。当传播距离一定时,温度均方耗散率对光强自聚焦的影响大于湍流动能耗散率和温度盐度波动相对强度。

悬臂式光纤探针的传光特性研究

根据标量波动方程 ,运用高斯近似法 ,从理论上说明光信号在悬臂式光纤探针中的传输特性和能量损耗 ,并用自制探针的具体数据 ,求出由于弯曲造成的光场偏移量 ;用实验方法测量悬臂式探针的传输效率随光纤圆锥角的变化关系 ,作出传输效率曲线 ,理论分析和实验测量相吻合。

四象限探测器输出非均匀性分析与矫正

摘要：对四象限光电探测器系统的的原理及其定位误差进行了分析，并提出了一种标定并修正其固有误对差以及对四象限光电探四象限非均匀探测器系统的匀性的方法。推导得出了入定位误差进行入射光线偏移行了分析，并通过实正其固有误实验和计算得到了证证实。为改善四象限探测器探测精度以及消除各项误差的影响提供了一种方法。

利用薄膜对视觉隐身的研究

在传统认知中,薄膜属于大部分满足人们日常需求的必备品,不过一旦经过特殊工艺加工,其作用也会在更多领域体现出来。如在用纳米级别的超材料将光弯曲时,外部的观察者可能看不到内部,不过内部也会无法看见外部的视野,此时可以借助各向异性的反隐身层材料,与隐身衣折射率相对立的超材料将光渗透进来,为了使渗透入的光更清晰,还可以增添一层投射膜以增加透射光的光强,从而实现利用薄膜来辅助视觉隐身的效果。

Design of a Tapered Lens for Semiconductor Laser to Single-Mode Fiber Coupling

The theoretical investigation of the coupling efficiency of a laser diode to a single mode fiber via a hemispherical lens on the tip of the tapered fiber in the presence of possible transverse offset and angular mismatch is reported.Without the misalignment,coupling efficiency increases with the decreasing of taper length.With the misalignment,this relation is that the coupling efficiency decreases with each kind of offset.

Measurement of Apex Offsets for Fiber Connector End Faces

As one of the most important geometric parameters for a PC-type fiber connector end face, apex offset can contribute to high insertion loss and high back-reflection reading. A novel measurement method for the parameter, connector rotating-π method, is proposed. With the method, the apex offset of a common connector end face is measured. The result is compared with that measured by a Norland 3000 fiber connector end face interferometer. It is found that the difference between two results is 1.8μm. Meantime, the influences of relevant error resources on apex offset measurement under rotating-π method and apex-core method are respectively analyzed, and two error equations are derived. The analytical result shows that, compared with apex-core method, if two additional sub-tilts of axis within and in the direction perpendicular to principal plane caused by its rotation are not bigger than the original axis tilt angle, the max. measurement error will then be reduced by at least 22.5% with rotating-π method. The practicability of the method is confirmed by the experiments.

Some Suggestions Improving Apollo Lunar Laser Retroreflector Arrays

According to our engineering research on satellite-borne laser retroreflector array, some suggestions are proposed on how to manufacture a new Apollo LLRA that can make us measure one illuminating point and unilluminating area on the moon's surface. These suggestions are: to control the dihedral angle offset within ± 0.1″; to use the larger aperture of the transparent face of cube corner prisms; to investigate how to separate out Apollo's reflected laser from mixed beam hitting on the LLR system.

CMOS Automatic Gain Control Circuit with DC Offset Cancellation for FM/cw Ladar

This paper presented an automatic gain control （AGC） circuit suitable for FM/cw ladar. The proposed architecture was based on two-stage variable gain amplifier （VGA） chain with a novel DC offset canceller circuit, which contained an improved Gilbert cell and a Gm-C feedback loop. To keep the VGA with a linearity in dB characteristic, an improved exponential gain control circuit was introduced. The AGC was implemented in 0.18 gm standard CMOS process. Simulation and measurement results verified that its gain ranged from -20 dB to 30 dB, and band- width ranged from 100 kHz to 10 MHz. Its power consumption was 19.8 mW under a voltage supply of 3.3 V.

Nonlinear Optical Susceptibility and Refractive Index of Two Polyaniline Families

By use of the Keldysh non-equilibrium Green’s-function methods, the third harmonic susceptibilities of two polyaniline families, PANI-HCl and PANI-H 3PO 4, are calculated [ x (3) ( ω )≈10 -12 esu]. It was found that the third harmonic susceptibility of polyaniline strongly depends on the delocalization of the electrons. The refractive indices n ( λ =589 nm) of PANI-HCl and PANI-H 3PO 4 are calculated by use of three common methods (the Lorentz-Lorentz theoretical model, the Gladstone-Dale group contribution and the Vogel group correlation) based on group contributions to molar refraction. The calculated n values are varied from 1.31 to 1.42 for PANI-HCl and 1.36 to 1.45 for PANI-H 3PO 4.

Inverted Solvatochromic Stokes Shift in GFP-like Chromophores with Extended Conjugation

Chrornophore structures inspired by natural green fluorescent protein （GFP） play an im- portant role in the field of bio-irnaging. In this work, photochemical properties of a new class of GFP-like chromophores are investigated using computational approaches. Thermo- dynamically stable isomers are identified in vacuum and in solvent. Spectral Stokes shifts are computed and compared to experiments. An inverted solvatochromic shift between absorption and emission emerging in this new class of GFP-like chromophores is observed, and attributed to the stabilized charge transfer and inhibited rotational structural reorganization in solvent.

Analysis of Systematic Error Influences on Accuracy of Airborne Laser Scanning Altimetry

The error sources related to the laser rangefinder, GPS and INS are analyzed in details. Several coordinates systems used in airborne laser scanning are set up, and then the basic formula of system is given. This paper emphasizes on discussing the kinematic offset correction between GPS antenna phase center and laser fired point. And kinematic time delay influence on laser footprint position, the ranging errors, positioning errors, attitude errors and integration errors of the system are also explored. Finally, the result shows that the kinematic time delay can be neglected as compared with other error sources. The accuracy of the coordinates is not only influenced by the amplitude of the error, but also controlled by the operation parameters such as flight height, scanning angle amplitude and attitude magnitude of the platform.

Enhanced visible-light photocatalytic activity of a g-C_3N_4/m-LaVO_4 heterojunction: band offset determination

Band offset is a dominant factor affecting the photocatalytic performance of heterostructure photocatalysts. Therefore, controlling the band gap structure of semiconductors is a key challenge in the development of efficient photocatalysts. We used a typical in situ-method to prepare diverse graphite-phase carbon nitride(g-C_3N_4)samples from melamine, thiourea, and a mixture thereof,and found that they exhibited band gaps between2.3–2.8 e V. From UV–Vis spectra and X-ray photoelectron spectroscopy measurements, we determined that the g-C_3N_4 samples exhibited different band gap values and valence band positions. On this basis, we constructed g-C_3N_4/m-La VO_4 heterojunctions with different band offsets. UV–Vis spectra and X-ray photoelectron spectroscopy measurements revealed that the valence band offsets(VBOs) of the different heterojunctions were similar, but their conduction band offsets(CBOs) were significantly different. Photocatalytic experiments revealed that the reaction rate was enhanced with an increase in the CBO value. Furthermore, the three-phase g-C_3N_4/g-C_3N_4/mLa VO_4 heterojunction composed of m-La VO_4 and mixed g-C_3N_4 showed the highest photocatalytic activity, which was mainly due to the construction of a multilevel structure. This work investigates the influence of the band offset on heterojunction photoelectrochemical properties and provides a new strategy to improve the photocatalytic activity by constructing multilevel structures.

Ultrafast photoinduced strain in super-tetragonal PbTiO ferroelectric films

The ultrafast photoinduced strain(UPS)resulting from the coupling of piezoelectric and photovoltaic effects in ferroelectric has been focused in the last decade,endowing them with extensive applications including ultrafast optical memories,sensors and actuators with strain engineering.The mechanism of screening of the depolarization field by photoinduced carriers is generally accepted for UPS in ferroelectrics,while the thermal component of the strain is usually diluted as the offset and has not been systematically confronted,leading to unnecessary confusion.Herein,both the positive and negative thermal expansion effects in composite ferroelectric epitaxial films are investigated by use of high-repetition-rate ultrafast X-ray diffraction,along with the piezoelectric and photovoltaic effects.The coupling of the positive/negative thermal effects and the piezoelectric/photovoltaic effects in ultrafast strain is evidenced and can be regulated.The opposite lattice responses due to different thermal effects of the samples with different axial ratios are observed.The maximum UPS is up to 0.24%,comparable to that of conventional ferroelectric.The interaction between the thermal and ferroelectric effects in the induced strain could promote the diversified applications with the coupling of light,heat and electricity.

Hyperpolarizabilities of alkaline-earth metal ions Be^+, Mg^+, and Ca^+

The knowledge of the hyperpolarizabilities of atoms and ions is helpful for the analysis of the high order effects of the frequency shifts in precision spectroscopy experiments. Liu et al. [Phys. Rev. Lett. 114, 223001 （2015）] proposed to establish all-optical trapped ion clocks using laser at the magic wavelength for clock transition. To evaluate the high-order frequency shifts in this new scheme of optical clocks, hyperpolarizabilities are needed, but absent. Using the finite field method based on the B-spline basis set and model potentials, we calculated the electric-field-dependent energy shifts of the ground and low-lying excited states in Be＋, Mg＋, and Ca＋ in the field strength range of 0.0-6×10-5 a.u.. The scalar and tensor polarizabilities （α0, α2） and hyperpolarizabilities （Y0,Y2, 74） were deduced. The results of the hyperpolarizabilities for Be＋ showed good agreement with the values in literature, implying that the present method can be applied for the effective estimation of the atomic hyperpolarizabilities, which are rarely reported but needed in experiments. The feasibility of optical trapping of Ca＋ is discussed, and the contributions of hyperpolarizabilities to the transition frequency shift for Ca＋ in the optical dipole trap are estimated using quasi-electrostatic approximation.

Chaotic generation based on figure-of-eight erbium-doped fiber laser with an optical fiber ring

We experimentally demonstrate the chaotic generation in a figure-of-eight erbium-doped fiber laser (F8L) with an optical fiber ring (OFR). With an appropriate combination of polarization controllers, we find that the fiber laser exhibits period-doubling route to chaos, and the chaotic self-synchronous dynamics has a tendency to be reduced significantly. The experimental results show the tendency is related to the interference and the nonlinear phase shift of light in the optical fiber ring. Meanwhile, the chaotic dynamics is related to the polarization state and pump power.