2.4Gb/s,50Km Optical Fiber Transmission Using Ti:LiNbO_3 External Modulator

2.488 Gb/s optical fiber transmission experiment using a domestic Ti.LiNbO3 externalmodulator was demonstrated for the first time in China.A receiver sensitivity of -30.3dBmwas obtained at a BER of 10-10after transmission through 50.7 km conventional single modefiber.

Optical simulation of external quantum efficiency spectra of CuIn_(1-x)Ga_xSe_2 solar cells from spectroscopic ellipsometry inputs

Applications of in-situ and ex-situ spectroscopic ellipsometry （SE） are presented for the development of parametric expressions that define the real and imaginary parts （ε1, ε2） of the complex dielectric function spectra of thin film solar cell components. These spectra can then be utilized to analyze the structure of complete thin film solar cells. Optical and structural/compositional models of complete solar cells developed through least squares regression analysis of the SE data acquired for the complete cells enable simulations of external quantum efficiency （EQE） without the need for variable parameters. Such simulations can be compared directly with EQE measurements. From these comparisons, it becomes possible to understand in detail the origins of optical and electronic gains and losses in thin film photovoltaics （PC） technologies and, as a result, the underlying performance limitations. In fact, optical losses that occur when above-bandgap photons are not absorbed in the active layers can be distinguished from electronic losses when electron-hole pairs generated in the active layers are not collected. This overall methodology has been applied to copper indium-gallium diselenide （Culn1-xGaxSe2; CIGS） solar cells, a key commercialized thin film PV technology. CIGS solar cells with both standard thickness （〉2 μm） and thin （〈1 μm） absorber layers are studied by applying SE to obtain inputs for EQE simulations and enabling comparisons of simulated and measured EQE spectra. SE data analysis is challenging for CIGS material components and solar cells because of the need to develop an appropriate （ε1, ε2） database for the CIGS alloys and to extract absorber layer Ga profiles for accurate structural/compositional models. For cells with standard thickness absorbers, excellent agreement is found between the simulated and measured EQE, the latter under the assumption of 100% collection from the active layers, which include the CIGS bulk and CIGS/CdS heterojunction interface layers. For cells with thin absorbers, however, an observed difference between the simulated and measured EQE can be attributed to losses via carrier recombination within a- 0.15 μm thickness of CIGS adjacent to the Mo back contact. By introducing a carrier collection probability profile into the simulation, much closer agreement is obtained between the simulated and measured EQE. In addition to the single spot capability demonstrated in this study, ex-situ SE can be applied as well to generate high resolution maps of thin film multilayer structure, component layer properties and their profiles, as well as short-circuit current density predictions. Such mapping is possible due to the high measurement speed of 〈1 s per （ , 4） spectra achievable by the multichannel ellipsometer.

External Optical Feedback Induced Noise in DFB Fiber Laser Sensor System

External optical feedback effects due to reflection, Rayleigh backscattering and coherent Rayleigh backseattering in fiber distributed feedback （DFB） fiber laser sensor system have been investigated. If the feedback intensity exceeds critical amount, excess noise would be induced in the demodulator. The maximum tolerable intensity back-reflection coefficient Rc and backscattering coefficient Sc into a fiber DFB laser with lead fiber length from I m to 37.5 km before the onset of instabilities are shown. Rc is found to decrease with increasing lead fiber length while Sc was relatively invariable with varying fiber length. The coherent Rayleigh backscattering （CRBS） would induce neglectable noise with a lead fiber exceeding 13.5 kin. To eliminate these noises, one or two isolators should be incorporated in the system.

External and Environmental Radiation Dosimetry with Optically Stimulated Luminescent Detection Device Developed at the SCK.CEN

The laboratory of Radiation Dosimetry and Calibration of the Belgian Nuclear Research Centre (SCK.CEN) is using thermoluminescence dosimetry for more than thirty years for routine measurements and for R&D investigations. In 2002, it has developed an experimental device based on the optically stimulated luminescence (OSL) technique. This device is working with AL2O3:C crystals stimulated by the green line (488 nm) emitted by a 150 mW argon laser. This paper describes this device, its characteristics, some applications in space dosimetry and the R&D works initiated in this field during the next few years.

Steady-State Behavior of Semiconductor Laser Diodes Subject to Arbitrary Levels of External Optical Feedback

This paper investigates the steady-state behavior of a semiconductor laser subject to arbitrary levels of external optical feedback by means of an iterative travelling-wave (ITW) model. Analytical expressions are developed based on an iterative equation. We show that, as in good agreement with previous work, in the weak-feedback regime of operation except for a phase shift the ITW model will be simplified to the Lang-Kobayashi (LK) model, and that in the case where this phase shift is equal to zero the ITW model is identical to the LK model. The present work is of use in particular for distinguishing the coherence-collapse regime from the strong-feedback regime where low-intensity-noise and narrow-linewidth laser operation would be possible at high feedback levels with re-stabilization of the compound laser system.

Intensity modulation in single-mode microchip Nd：YAG lasers with asymmetric external cavity

Intensity modulation induced by the asymmetric external cavity in single-mode microchip Nd：YAG lasers is prosented. Two kinds of experimental results are discussed based on multiple feedback effects. In one case, the intensity modulation curve is a normal sine wave, whose fringe frequency is four times higher than that of a conventional optical feedback system, caused by multiple feedback effects. In the other case, the intensity modulation curve is the overlapping of the above quadruple-frequency signal and conventional optical feedback signal, which is determined by the additional phase difference induced by the asymmetric external cavity. The theoretical analyses are in good agreement with the experimental results. The quadruple-frequency modulation of the laser output intensity can greatly increase the resolution of displacement measurement of an optical feedback system.

Semiconductor Optical Amplifier and Gain Chip Used in Wavelength Tunable Lasers

The design concept of semiconductor optical amplifier(SOA)and gain chip used in wavelength tunable lasers(TL)is discussed in this paper.The design concept is similar to that of a conventional SOA or a laser;however,there are a few different points.An SOA in front of the tunable laser should be polarization dependent and has low optical confinement factor.To obtain wide gain bandwidth at the threshold current,the gain chip used in the tunable laser cavity should be something between SOA and fixed-wavelength laser design,while the fixed-wavelength laser has high optical confinement factor.Detailed discussion is given with basic equations and some simulation results on saturation power of the SOA and gain bandwidth of gain chip are shown.

A 1550-nm linearly tunable continuous wave single-mode external cavity diode laser based on a single-cavity all-dielectric thin-film Fabry Pérot filter

A 1550-nm linearly tunable continuous wave （CW） single-mode external cavity diode laser （ECDL） based on a singlecavity all-dielectric thin-film Fabry-Pérot filter （s-AFPF） is proposed and realized in this paper. Its internal optical components as well as their operation mechanisms are introduced first, and then its longitudinal mode output characteristic is theoretically analyzed. Afterwards, we set up the experimental platform for the output characteristic measurement of this tunable ECDL; under different experimental conditions, we execute accurate and real-time measurements for the output central wavelength, output optical power, output longitudinal mode distribution, and the line-width of the tunable ECDL in its tuning process. By summing up the optimal experimental condition from the measured data, we obtain the optimal tunable ECDL relevant parameters： the tunable ECDL has a linear mode-hop-free wavelength tuning region of 1547.203 nm-1552.426 nm, a stable output optical power in the range of 40 μW-50 μW, and a stable output longitudinal mode distribution of a single longitudinal mode with a line-width in the range of 100 MHz-150 MHz. This tunable ECDL can be used in environmental gas monitoring, atomic and molecular laser spectroscopy research, precise measurements, and so on.

Performance Analysis on a Dual External Cavity Tunable Laser ECTL Source

This paper presents the diffraction effects on the performance of a dual external cavity tunable laser source, whose external cavities are constructed by micro electro mechanical systems (MEMS). One of the main problems in these structures is the optical diffraction as the emitting surface of the laser diode is usually quite limited in the transverse directions. The emitted beam diffracts rapidly in the air and only a small amount of light is coupled back to the source that usually limits the tuning range of the source. Device characteristics such as tuning range, wavelength shift and sensitivity are evaluated. New expression is used and multiple reflections inside external cavities are considered. The simulation results have shown that single external cavity has limited tuning range. It is shown that multiple reflections have significant effect in our model. To get a better engineering for the dual ECTL dimensions, diffraction effects must be taken into account.

Effects of external temperature and dead volume on laboratory measurements of pore pressure and injected volume in a rock fracture

The accurate evaluation of pore pressure and injected volume is crucial for the laboratory characterization of hydromechanical responses of rock fractures. This study reports a series of laboratory experiments to systematically demonstrate the effects of external temperature and dead volume on laboratory measurements of pore pressure and injected volume in a rock fracture. We characterize the hydraulic aperture of the fracture as a function of effective normal stress using the exponential aperture model.This model is then employed to predict the pore pressure change and injected volume in the fracture without the influences of external temperature and dead volume. The external temperature changes in the cyclic loading test due to the Joule-Thompson effect for fluids. The effect of external temperature on pore pressure change in the fracture can be well explained by thermal pressurization of fluids. Our results also show that the external dead volume can significantly lower the pore pressure change in the fracture during the cyclic loading test under undrained conditions. The injected volume can also be substantially enlarged due to the external dead volume in a typical pore pressure system. Internal measurement of the pore pressure in the fracture using a fiber optic sensor cannot exclude the influences of external temperature and dead volume, primarily because of the good hydraulic communication between the fracture and pore pressure system. This study suggests that the effects of external temperature and dead volume on pore pressure response and injected volume should be evaluated for accurate laboratory characterization and inter-laboratory comparison.

通信激光器及其调制技术研究进展

在光通信领域,激光器及其调制带宽、调制速率对无线光通信至关重要。对半导体激光器信号的调制方式主要有内调制和外调制两种。这两种调制技术具有各自的特点,适用于光纤通信中的不同领域,都是当前重要的研究热点。内调制激光器又称为直接调制激光器,因其具有高速传输以及低成本的特点,成为目前应用在第五代移动通信技术(5G)前传和数据中心中的高性价比光源。而外调制激光器不存在光源附加的Chirp,所以可以有效地克服光纤色散造成的复合二次差拍(CSB)失真。文章在回顾通信激光器及其调制技术发展历程的基础上,介绍了西安理工大学在该领域所做的工作以及取得的主要进展。针对半导体激光器发生非线性失真的内外因素进行讨论,仿真响应特性各参数、线性化补偿方法以及功率控制系统对光发射器件输出光源的作用,并分析了温度的起伏对激光器和调制器件输出功率产生的影响。采用折射率椭球基本理论和数值分析,分别在纵向和横向调制下,讨论出射光强随温度的变化趋势。结果表明,纵向调制下出射光光强随温度的变化趋势只与铌酸锂(LN)晶体折射率的变化有关;横向调制下出射光光强随温度的变化趋势不仅要受到晶体折射率的影响,还要受到晶体尺寸及其膨胀系数的影响,因此可以利用特殊尺寸的晶体来提高电光调制器的温度稳定性。

随机噪声平板下光学复眼内外参联合标定

光学复眼在无人系统的精确定位制导、避障导航等任务中得到了越来越广泛的应用,其中光学复眼的高精度标定是保障上述任务质量的前提。通常经典的张氏棋盘格标定法要求光学复眼的每个子眼都必须观测到完整的棋盘格,然而,由于光学复眼结构的复杂性,在实际标定过程中难以满足这一要求。为解决张氏标定法的局限性,该文提出一种基于随机噪声平板的光学复眼内外参联合标定算法,该算法通过子眼拍摄随机噪声平板的局部信息,可简单快速地实现任意构型和子眼数量的光学复眼内外参联合标定。为了提高光学复眼标定的稳定性,设置多阈值匹配机制解决子眼视场特征点数量稀疏导致图像匹配失效的问题。同时,给出了光学复眼内外参联合标定的误差模型,用来衡量所提出算法的精确度。在与张氏棋盘格标定法进行实验对比中,验证所提算法的稳定性和鲁棒性,并在光学复眼实物系统中,验证了所提联合标定算法具有较高的精度。

针对光通信系统的调制与解调技术优化研究

文章主要研究和优化光通信系统中的调制与解调技术,系统性地探讨光通信系统的基本架构,基于外调制和相干解调的优化方法,以提高系统的传输效率和信号质量。在调制方面,采用直接调制技术和外调制技术增加调制信号的带宽;在解调方面,应用相干解调技术实现了对光信号的高效检测和解调。利用MATLAB等工具进行实验验证,结果表明所提出的调制与解调优化方法在提升光通信系统性能方面具有潜力与优势。

光纤布拉格光栅长外腔反馈半导体激光器特性研究

窄线宽激光器是光谱学和精密计量学等实验的基本组成部分。由于半导体激光器对外部光学反馈十分敏感,所以可以利用光反馈的高带宽抑制半导体激光器的相位噪声,进而压窄线宽。本文采用光纤布拉格光栅作为反馈元件,搭建了长外腔反馈回路。为了降低外界环境温度起伏和气流扰动的影响,对反馈光路的光纤控温,使得1小时内最大温度起伏从0.039℃降低到0.003℃。此外,测试了反馈带宽对激光线宽的影响,尽管实验所用光纤布拉格光栅的带宽远大于自由运转的激光线宽,但仍然可以观察到激光线宽被压窄,且光纤光栅的带宽越小,激光线宽越窄。对于此现象,分析认为在反馈回路中应该存在一种负反馈机制,可以将激光线宽稳定到反馈光谱的某个斜率处,所以光纤光栅的反馈带宽越窄,反馈光谱的斜率越大,反馈越灵敏。通过调整光纤光栅的反馈功率在0~1 mW范围内改变,观察到当反射功率为0.8 mW时,光反馈将激光线宽从自由运转的100.5 kHz压窄到最窄的11.5 kHz,0.2 kHz~2 MHz范围内的相位噪声降低约20 dB。

基于490 nm垂直外腔面发射激光器的长距离水下激光通信系统

水下无线光通信技术为深海勘探和海洋资源开发利用带来了一种效率高且可靠性强的通信新方案.本文采用490 nm垂直外腔面发射激光器作为光源,基于声光外调制技术,采用脉冲位置调制方式(pulseposition modulation,PPM)搭建了长距离水下无线光通信系统.结合光源的优势并经过软判决算法优化PPM解调来提升水下通信性能,采用64 PPM调制,成功实现了96 m的水下传输距离,在50 MHz时隙频率下得到传输的误码率为1.9×10^(-5).同时测量到采用软判决解调相较于硬判决解调在性能增益上有着大约2 dB的提升,验证了软判决算法在提升水下通信性能方面相比硬判决算法的显著优势.

一种快速的OCT内外指纹提取方法

针对现有光学层析成像(optical coherence tomography,OCT)技术中内外部指纹提取算法速度较慢的问题,尤其是许多算法在提取指纹之前需要耗时的原始体数据去噪操作,为了解决这一问题,提出了一种简单快速的OCT内外部指纹提取算法。对于OCT指纹体数据,首先根据每张轴向切片(B-scan)图像的一阶微分最大值,拟合一条基本覆盖角质层轮廓的曲线,然后再根据一阶微分的次最大值,拟合出一条基本穿过活性表皮交界处轮廓脊谷处的曲线,最后在这两个曲线上下各N个像素点的位置,利用两条曲线附近的灰度值均值信息,按B-scan图片顺序进行拼接,生成提取到的内外部指纹图像。通过实验确定了N的最佳取值,然后与现有的内外部指纹提取算法对比,证明所提出的算法能够在不降低指纹质量的情况下,快速地提取出内外部指纹图像,提取内外部指纹的时间比层次聚类算法和梯度法都快很多倍。

斜入射下四光幕精度靶着靶位置测量原理误差分析

为研究飞行弹丸斜入射时着靶坐标测量原理误差的分布规律,根据四光幕精度靶几何结构,建立了斜入射下着靶坐标测量原理误差模型,研究有效探测靶面内不同着靶位置与不同入射角下原理误差分布规律;分析工程应用中发射位置确定下,不同散布半径与不同射击距离对测量原理误差的影响,给出着靶坐标测量的修正公式,并进行实弹射击试验。试验结果表明:飞行弹丸斜入射时必然存在原理误差,必须修正着靶坐标;射击距离一定时,发射枪散布半径越大,原理误差越大;散布半径确定时,原理误差随射击距离增加而减小;在发射位置确定下,采用修正公式后,四光幕精度靶测量误差小于1 mm。

线粒体疾病相关视神经病变

线粒体疾病是主要累及全身多系统且临床表现各异的线粒体能量代谢耗竭疾病,其中眼部可单独受累,尤其是视神经病变可为其唯一表现,或是各种综合征的受累器官之一。临床最常见的线粒体相关视神经病变为Leber遗传性视神经病变和常染色体显性遗传性视神经萎缩。随着基因检测技术的发展,越来越多的线粒体基因突变类型及包括视神经萎缩的各种表型已被认识,例如MELAS脑病、Leigh综合征、Wolfram综合征、Charcot-Marie-Tooth病等。本文主要聚焦包括Leber遗传性视神经病变在内的各种线粒体疾病及其综合征的眼部表现,尤其是视神经病变,通过典型的临床特征及针对性的基因检测手段拓展神经眼科医师对视神经萎缩性疾病的认识,有利于对该类疾病的精准诊疗。

不同外润滑剂对高透明硬质医用PVC材料的性能影响

通过调整高透明硬质医用PVC配方体系中外润滑剂的种类,研究了它们对高透明硬质医用PVC材料光学性能、流变性能及力学性能的影响。结果表明:在高透明硬质PVC体系中,在塑化条件良好的情况下,外润滑剂的选择对其力学性能影响较小。但以氧化聚乙烯蜡作为外润滑剂,在对其透明性影响最小的基础上,对其熔体流动性、可加工性的提高最大,效果最好。

卵黄样黄斑营养不良的多模式影像特征观察

目的:观察卵黄样黄斑营养不良(BVMD,别称Best病)的多模式影像特征。方法:收集2016-06/2022-10于南京医科大学眼科医院确诊为Best病Ⅰ-Ⅳ期的患者30例60眼的临床资料进行回顾性分析,均双眼发病。所有患者均行最佳矫正视力(BCVA)、裂隙灯显微镜、间接眼底镜、眼压、眼底彩色照相、频域光学相干断层扫描(SD-OCT)、眼底自发荧光(FAF)、荧光素眼底血管造影(FFA)、眼电图(EOG)及光学相干断层扫描血管成像(OCTA)。结果:共纳入患者30例60眼,其中Ⅰ期8眼,Ⅱ期24眼,Ⅲ期22眼,Ⅳ期6眼,眼底彩色照相、FAF、FFA、SD-OCT的影像特征与既往文献报道基本一致,EOG显示Arden比均<1.55,OCTA能够发现早期病灶,观察到卵黄样物质、光感受器外节、液体的位置分布及有无CNV形成。结论:多模式影像有助于Best病的诊断,减少临床上漏诊、误诊,其中OCTA较其他检查有明显优势,快捷无创是其最大优势。