覆盖可见光波长的掺Er光纤飞秒光学频率梳

飞秒光学频率梳波长覆盖范围向可见光波长扩展对于碘稳频激光的绝对频率测量以及光钟研究中钟激光的绝对频率测量都具有十分重要的意义. 本文在自行研制掺Er光纤飞秒光学频率梳的基础上, 采用放大-倍频-扩谱的方案, 实现了激光输出波长向可见光波长的扩展. 掺Er光纤飞秒光学频率梳输出的一部分光激光脉冲, 功率约为8 mW, 首先经掺Er光纤放大器将功率提高到531 mW, 此后利用MgO: PPLN晶体倍频, 倍频后激光的功率为170 mW, 倍频效率为32%, 脉冲宽度为85 fs. 倍频后的激光通过光子晶体光纤进行光谱展宽. 通过优化入射光偏振状态可以实现波长覆盖500-1000 nm, 输出功率为85 mW, 耦合效率为50%. 采用小型化碘稳频532 nm Nd: YAG激光器输出激光与光学频率梳光谱展宽后的激光进行拍频可以获得30 dB的拍频信号. 覆盖可见光波长的掺Er光纤飞秒光学频率梳为可见光范围内激光的绝对频率测量提供了技术手段.     

Spectrally-resolved white-light interferometry as a profilometry tool

Phase-shifting interferometry and white-light interferometry are reliable techniques for surface analysis in which the optical path difference has to be changed by some transducer to evaluate the phase. We present here a different procedure in which optical path modulation is completely avoided. This technique is based on the spectral analysis of white-light interferograms. By means of a spectroscopic device, a non-visible interferogram is split into its monochromatic components and absolute, unambiguous values of the phase are obtained along the spectral axis. Only one interferogram is required to obtain the profile of one-dimensional surfaces with nanometric resolution.     

The impulse response function of apertured and misaligned ABCD optical system in phase-space

By expanding the aperture into complex Gaussian functions, the approximate analytical impulse response function of apertured and misaligned ABCD optical system in phase-space is determined, which allows us to formulate the input-output relation completely in terms of Wigner distribution functions. Its shown that the hard-aperture placed before the optical system will change the shape of output signal Wigner distribution and the misalignment of optical system will introduce the output Wigner distribution function a coordinate shift in phase-space. For examining the analytical results some numerical simulation are done and the graphical results as well as the absolute errors between analytical results and numerical integral ones are presented.     

外腔半导体激光器在高低温下的机械形变与功率变化

外腔激光器具有窄线宽、低功耗的特征,主要用于相干光通信,实际应用中外腔激光器的输出光功率会在环境温度为高温或者低温时出现下降现象。通过使用有限元商用软件Ansys分析,发现高低温下机械结构会有微小的挠度变化,相较于常温,高低温下最大的挠度角度为0.04°。外腔激光器的腔长较长,结合光路仿真软件Zemax研究发现,微小的挠度变化会引起较大的光路变化,影响耦合效率,进而导致输出光功率降低。通过实验量测证实了光路变化,并基于挠度变化引起功率降低的理论,从设计角度提出了通过缩短腔长、加厚基座的方式来减小输出光功率随环境温度的变化。提出的模型与思路可以为类似产品的功率温度相关性分析提供量化分析思路。     

高功率固体激光器锥形空间滤波孔应用

锥形空间滤波孔是一种应用于高功率固体激光装置空间滤波的新型结构滤波小孔,其内部光滑的锥形结构可以有效滤除光束中的高频成分且避免等离子堵孔现象的发生。根据神光-Ⅲ主机装置结构特点,设计并加工了适用于主机装置的锥形空间滤波小孔,并开展了应用实验研究。通过与传统的平面结构滤波小孔对比可以看出,锥形小孔有效地避免了等离子体度堵孔现象,在与光束波前补偿技术配合使用条件下,保证光束顺利过孔,并成功实现了基频光7988 J的满能量输出。     

光纤几何路径引起的圆双折射

本文对单模光纤中线偏振面的旋转与光纤几何路径的关系进行了研究.首次报道了在光纤入射端和出射端不平行的情况下的数值计算和实验测量结果.     

The system of double-optical-path ESPI for the vibration measurement

In this paper, a system of double-optical-path electronic speckle pattern interferometry (ESPI) for measuring larger vibration is proposed. This system combines the conventional ESPI optical path for measuring out-of plane vibration and the de-sensitized optical path. It can be used to observe qualitatively and analyze quantitatively the vibration mode. At the same time, the phase unwrapping is avoided. The anti-disturbance capability of this system is high, so it can be used to analyze the vibration characteristics of complex and discontinuous structure in actual engineering.     

热容模式下激光介质的动态光学畸变

 开展了热容模式下激光介质动态光学畸变研究，初步分析了温度梯度、光弹效应及介质端面变形对整个波前畸变带来的影响，并将光学畸变转化为谐振腔损耗，数值模拟了热容激光器输出功率随时间的变化规律，模拟结果表明：当激光器工作温度低于400 K时，由粒子数玻耳兹曼分布引起的功率下降可以忽略，动态热效应是实验中热容激光器输出功率随时间快速下降的原因。     

Pattern classification using optical Mellin transform and circular photodiode array

Scale-invariant pattern classification using a hybrid system combining the optical Mellin transform and a digital signal processing technique is discussed. We accomplish the optical Mellin transform by a logarithmic coordinate transformation using a computer-generated hologram, followed by an optical Fourier transform. Mellin transform patterns are detected with a circular photodiode array, whose output signals are processed by a micro-computer. A new criterion is discussed, in which circular or periodic correlation is employed. Experimental examples are presented.     

Signal processing techniques for absolute displacement/strain sensing using a fiber interferometer

We present two displacement sensing techniques which rely on amplitude variations of Bessel frequency components contained in the photodetected output of a phase modulated two-beam interferometer. Experimental results demonstrate demodulated output signals that correspond to the absolute optical path difference between the two arms of an interferometer. Optical displacements over a 50 mm range have been recorded with a resolution of 25 microns. Both approaches are suitable for passive remote sensing applications.     

晶体光收集特性的M.C.模拟研究

用蒙特卡罗方法实现了对各种不同条件下晶体光输出特性的模拟研究，和实验结果比较符合得足够好，因而可用以预言新的现象和实验结果。结合光输出的实验测量，可以确定绝对的光子产额。研究还表明，封装材料和耦合剂对光收集效率影响很大，选用具有漫反射性的封装材料将有利于光的收集效率     

散斑自相关分辨率测量和修正

散斑相关是许多基于散斑的光学测量和成像技术的基础,决定了光学系统的分辨率。当前散斑尺寸（颗粒度或分辨率）的理论描述不够精确,也缺乏实验验证。探究了散斑图样自相关尺寸的影响因素,与相同数值孔径物镜聚焦进行比对,揭示薄散射介质的“散射透镜”性质。通过散斑自相关和透镜聚焦尺寸的多组测量,结果表明,截趾函数会影响其分辨率,需要根据具体光路对阿贝判据做修正。对基于散斑的测量和成像技术具有一定的参考价值。     

Modeling and design of WDM optical buffers in asynchronous and variable-length optical packet switches

This paper aims to analyze the influence of wavelength conversion on the design of optical fiber delay line (FDL) buffers in a wavelength-division multiplexing (WDM) packet switch. We focus on the network scenario that variable-length packets arrive at the optical switch asynchronously. Through a detailed analysis of the behaviors of packets in the WDM FDL buffer, an approximate analytical traffic model is established. And the theoretical model is proved to be reasonable by simulations. Based on the model, it is clear that, under the same traffic load per wavelength channel, the utilization of tunable wavelength converters (TWCs) to resolve the output contention significantly reduces the number of fiber delay lines (FDLs) in optical buffers, and to achieve a given packet loss probability under a certain number of FDLs, the required number of tunable wavelengths can be predicted. The model can also estimate the optimal value of the basic time unit of the FDLs, and examine the influence of WDM on the optimal value. Finally, the impact of wavelength conversion on the optical switch size is analyzed. To the best of our knowledge, it is the first time that modeling on this problem is presented.     

窄带傅里叶变换光谱仪中平稳高斯噪声的理论分析

在本文所研究的空间调制型傅里叶变换光谱仪中, 在窄的光谱带宽内进行探测可以有效提高光谱的分辨率. 为了研究光源辐射噪声对系统的影响, 本文将辐射噪声归纳为一种高斯窄带的平稳随机过程, 利用线性系统分析方法, 根据统计学原理推导了辐射噪声作为随机变量通过干涉系统前后的输入信噪比与输出信噪比. 然后, 对于一个具有窄带矩形光谱的系统进行了计算仿真, 得出了信噪比增益随着光程差在不同自相关度和互相关度取值时的变化情况. 仿真结果表明, 不同光程差下的信噪比增益在相关度空间是一单调的平滑曲面, 增益极值始终沿着相关度圆的半径和周线移动, 并且经过一个光程差又回到初始的位置. 根据对信噪比增益的分析, 可以将噪声的相关度取值控制在某一范围之内, 并作为系统光源设计与测试的依据.     

On the interpretation of image spectrograms in some metrological applications

The channelled spectrum phenomenon combined with a white-light imaging method yields image spectrograms giving access, under special conditions, to absolute path differences in a wide range of measurements (from one micron to several millimetres). Their interpretation is discussed through several applications: optical mapping, measurement of longitudinal displacement, evaluation of temperature and visualization of gas flow.     

A superresolution optical disk with a combination of optical path filtering and saturable absorption techniques

Calculations have been done for the modulation transfer function of a superresolution optical disk with a combination of optical path filtering and saturable absorption techniques. The results reveal that optical path filtering alone can only equalize, to a certain degree, the spatial frequency response of the opticaldisk system, but it can not attain any response beyond the cutoff frequency. With an additional saturable absorption layer in-between the substrate and the information layer, it is found that the optical response both under and beyond the cutoff frequency can be greatly improved.     

Quantum and semiclassical dynamics of differential optical collisions

We apply quantum and semiclassical theories to differential optical collisions Na(3²S_1/2) + Kr + Na(3²P_1/2,3/2) + Kr. Our results provide a basis to analyze recent experiments in which for the first time optical collisions were investigated with angular resolution under crossed-beam conditions. A characteristic feature of the differential cross sections is the pronounced oscillatory structure due to interferences of different Condon paths. These Stueckelberg oscillations form an extremely sensitive probe of the collisional dynamics and of the molecular interactions. We demonstrate perspectives to determine geometric properties of the collision complex by excitation with polarized light. By final state analysis nonadiabatic (spin-orbit, rotational) interactions can be studied with complete control of the path. In summary it is shown that the method of differential detection of optical collisions opens a variety of new accesses to atomic and molecular subcollisions. Received: 30 July 1997 / Received in final form: 5 November 1997 / Accepted: 8 January 1998     

Estimation of partial optical path length in the brain in subject-specific head models for near-infrared spectroscopy

Three-dimensional head models with the structures constructed from the MR head images of 40 volunteers were constructed to analyze light propagation in the subject-specific head models. The mean optical path length in the head and the partial optical path length in the brain at 13 fiducial points for each volunteer were estimated to evaluate the intersubject and spatial variability in the optical path lengths. Although the intersubject variability in the optical path lengths is very high, the spatial variability in the average of the mean optical path length and partial optical path length is similar to the previously reported data. The mean optical path length in the head increases, whereas the partial optical path length in the brain decreases with an increase in the depth of the brain surface. The partial optical path length is highly correlated with the depth of the brain surface in comparison to the mean optical path length in the head.     

光学元件波前畸变对驱动器光路设计的影响

高功率激光驱动器光路设计要考虑像传递、鬼像规避和杂散光管理等多项优化措施.基于衍射光学传播理论,从输出负载能力提升的角度研究大口径光学元件波前特性对驱动器光路设计参数优化的影响.研究表明,驱动器末级光路的排布间隔如果控制在6 m以上,将非常有助于提高激光驱动器的输出负载能力.一般情况下,波前峰谷值达到0.34λ的单块大口径光学元件能使高功率激光的近场光束质量最大下降约10%,达到1.36λ后最大下降约21%;波前分布特性不同的多片大口径光学元件的波前相消叠加有利于降低中频波前部分对装置负载能力的影响,但是,大口径光学元件的非线性效应会加重中频波前对装置输出负载能力的影响;在限定大口径元件损伤阈值20J/cm~2的前提下,光路排布紧凑的激光驱动器末级输入激光通量控制在16.8J/cm~2之下不易损伤光学元件.相对宽松的光路设计可以进一步提高末级输出激光的平均通量水平,非常有利于激光驱动器装置输出负载能力的提升.     

Three-mode optomechanical system for angular velocity detection

We propose a scheme for measuring the angular velocity of absolute rotation using a three-mode optomechanical system in which one mode of the two-dimensional(2 D) mechanical resonator is coupled to an optical cavity. When the total system rotates, the Coriolis force acting on the 2 D mechanical resonator due to the absolute rotation will affect the mechanical motion and thus change the phase of the output field from the cavity. The angular velocity of the absolute rotation can be estimated by monitoring the spectrum of the output field from the cavity via homodyne measurement. The minimum measurable angular velocity, which is determined by the noise spectrum, is calculated. The working range of the gyroscope for measuring angular velocity is discussed.