一种便携式干涉仪动镜系统的设计

动镜扫描系统是傅里叶变换红外光谱仪中唯一不断运动的部件,其扫描的精度与行程直接影响仪器的信噪比、重复性与分辨率等指标。在利用立体角镜的光学特性和柔性簧片枢轴的机械特性的基础之上,设计了一种结构紧凑,体积小巧的干涉仪动镜扫描系统,设计了基于模糊控制算法的控制器,对动镜的扫描速度进行精密的控制。实验表明,动镜机构的扫描稳定性优于99.8%,所测得的红外光谱具有较高的信噪比能够满足高精度定量分析的要求。     

High-speed scanning fiber-optic heterodyne interferometer using a micro-electro-mechanical system mirror and an f-theta lens

This paper describes a novel fiber-coupled heterodyne interferometer using a micro-electro-mechanical system (MEMS) mirror and an f-theta lens. In this interferometer system, the cross-polarized laser beams operating at 2 μm with the frequency difference of 100 kHz are introduced by means of the two acousto-optic modulators (AOM). The sample with diameter of 300 mm is uniformly scanned by the 1 mm laser beam with the help of the combined optical scanning configuration, a MEMS mirror and an f-theta lens. The output intermediate signal from the two channels, reference channel and the measurement channel, are processed in the 12 bit analog-to-digital (A/D) process system. Details of our interferometer scheme are discussed.     

基于2D微电子机械系统(MEMS)镜全向激光雷达光学系统设计

为了满足全向激光探测的需求,提出一种基于2DMEMS镜扫描的激光雷达结构。激光器通过1×6高速光开关分时地给6个扫描子系统提供光信号,6个扫描子系统探测视场叠加起来可实现360°激光探测。每个扫描子系统的扫描范围为60°×30°,其中包含一个扩展MEMS镜扫描角度的发射光学天线和一个大视场有增益的接收光学天线。发射光学天线将MEMS镜±10°的扫描角扩展到±30°,发散度小于0.2mrad;接收视场内的激光波经过接收天线在探测器上所成的半像高小于1mm,接收增益为3.65。通过计算修正后的激光雷达方程可得到发射功率20 W的激光束在工作距离100 m内的回波功率≥1 nW,结果表明该光学系统可适用于激光雷达系统。     

Two-axis-scanning laser Doppler vibrometer for precision engineering

Laser Doppler vibrometer (LVD) has been the most favorite instrument for precision dynamics measurement due to its non-contact, high accuracy and high resolution. However, LDV can only give the dynamic data of a particular location on the entire feature. In order to get the whole field data, a laser beam-scanning mechanism has to be implemented. Currently, motor-driven scanning mirror is used to move the measurement probe from one point to another. The mechanical vibrations of the scanning mirror will reduce the measurement accuracy. This paper introduces a novel scanning LDV optical system embodied in an acousto-optic deflector scanning mechanism. It can improve the measurement accuracy since there is no mechanical motion involved. One main advantage of this system is that it generates a laser scanning beam in parallel that is different from the beam scanning in the conventional scanning laser Doppler vibrometer (SLDV). The new system has a board scanning range. The measurement target size ranges from few tens of millimeters down to 10 μm. We have demonstrated the capability of the novel system on scanning measurements of features as big as ultra-precision cutting tool to features as tiny as AFM cantilever. We believe that the novel SLDV will find profound potential applications in the precision engineering field.     

电磁驱动大尺寸MEMS扫描镜的研究

基于微机电系统工艺,设计并制作了一种电磁驱动大尺寸的二维扫描振镜.分析了两种不同的电磁驱动方式产生的力的大小,选择驱动力较大的双极子方式作为驱动.运用有限元法模拟了器件的谐振频率静态及动态响应,仿真结果与实际测得的结果一致.描述了振镜的工艺流程及封装方式,并制备了振镜.实验测得振镜在120mA静态电流驱动下,慢轴和快轴分别能达到的最大转角为±4.5°及±5°,慢轴及快轴的谐振频率分别为348Hz及660Hz,并得到在此谐振频率下的李萨如图形.将器件用于激光成像系统之中,使得散斑对比度下降到4.2%,激光成像质量得到很大提升.     

扫描镜稳定度对TDI CCD测量精度的影响

利用TDI CCD成像数值仿真模型,研究了TDI CCD测量系统的测角精度随扫描镜速度稳定度的变化规律。首先根据TDI CCD推扫成像的物理过程,建立了数值仿真模型,设计了从光学像和扫描镜稳定度到数字图像的仿真链路;然后利用图像重心计算方法求取图像中心坐标并得到目标点的角位置坐标;通过蒙特卡诺法进行海量打靶试验,对结果进行统计得到扫描镜各稳定度水平上的测量精度值;最后将某工程样机的扫描镜速度稳定度带入仿真模型,仿真结果表明：测试误差增大5.67 μrad,达到了像元角分辨率的1/4。在光学测量系统的系统设计时,需要考虑像元分辨率及扫描镜稳定度的综合影响,选用合适的扫描镜稳定度要求,使测量角分辨率满足用户需求。     

激光调频连续波测距的精度评定方法研究

基于双光纤光路等光频重采样原理,提出了一种距离精度的评定方法.通过推导噪声背景下等光频重采样信号中距离参量的克拉美-罗下边界,得到了影响系统测距精度的两个重要因素:信噪比和扫描带宽,并进行了实验验证.实验表明,该评价方法并不会受到任何距离估算方法的影响,根据此方法可以选择一个最优的距离估算方法.通过对两个影响精度的因素进行仿真分析可知,在扫描带宽为2.2 nm时,若将测量光路的信噪比提升至70 dB以上,系统可获得低于10μm的测距精度.该精度评定方法可为后续改善调频连续波测距系统性能提供理论参考.     

基于MEMS微镜的长波近红外光谱仪的设计与实现

为适应光谱仪微型化、集成化的发展趋势,详细分析了MEMS微镜应用于微型长波近红外光谱仪的方法和涉及的主要问题,例如分光系统的设计、MEMS微镜的选择、探测器与前置放大电路的设计等。并将50 Hz谐振频率、峰峰驱动电压为10V的MEMS微镜、高灵敏度的InGaAs单元探测器,结合立特罗式分光光路,设计和实现了900～2 055 nm波段的微型长波近红外光谱仪样机,其中1 000～1 965 nm谱段的光谱分辨率介于9.4～16 nm之间。采用MEMS扫描微镜技术后,一方面简化了光谱仪中的复杂机械结构,使尺寸可以更小;另一方面实现了单探测器的长波近红外光谱仪,与阵列长波近红外探测器光谱仪相比,成本有所降低。作为应用实例,此样机成功对纯水以及乙醇-水溶液的长波近红外光谱进行了测量,实现了乙醇-水溶液的浓度预测分析,其中本样机测量的纯水长波近红外光谱与文献相符。     

Design of three-dimensional imaging lidar optical system for large field of view scanning

Three-dimensional (3D) lidar has been widely used in various fields. The MEMS scanning system is one of its most important components, while the limitation of scanning angle is the main obstacle to improve the demerit for its application in various fields. In this paper, a folded large field of view scanning optical system is proposed. The structure and parameters of the system are determined by theoretical derivation of ray tracing. The optical design software Zemax is used to design the system. After optimization, the final structure performs well in collimation and beam expansion. The results show that the scan angle can be expanded from ±5° to ±26.5°, and finally the parallel light scanning is realized. The spot diagram at a distance of 100 mm from the exit surface shows that the maximum radius of the spot is 0.506 mm with a uniformly distributed spot. The maximum radius of the spot at 100 m is 19 cm, and the diffusion angle is less than 2 mrad. The energy concentration in the spot range is greater than 90% with a high system energy concentration, and the parallelism is good. This design overcomes the shortcoming of the small mechanical scanning angle of the MEMS lidar, and has good performance in collimation and beam expansion. It provides a design method for large-scale application of MEMS lidar.     

A time-of-scan laser triangulation technique for distance measurements

This paper reports the development of an electro-optic device for relative distance measurement. The time-of-scan triangulation technique has been used as measurement principle and a rotating mirror employed as beam deflection system. A calibration technique is needed to calculate the geometrical parameters of the system. The device has an accuracy of 100 μm, a working distance of 20 cm and a range of 10 mm. The accuracy obtained depends on the instability of the rotation speed of the mechanical scanner that affects the measurement of the scanning time.     

太赫兹远距离快速扫描成像系统的设计

在太赫兹成像技术研究中,分辨率、成像时间和距离是非常关键的参数指标,为了推动太赫兹成像技术的实用化,特别是提高对隐藏危险物品的远距离快速预警检测能力,提出被动式远距离太赫兹快速扫描成像系统。该系统采用单个太赫兹探测器和光机扫描相结合的方式。扫描子系统中,将六面体转镜置于离轴三反镜系统的平行光路中,使扫描范围从广泛研究中采用的物空间转换到像空间有效缩小了扫描区域,缩短了成像时间。本套被动式扫描成像系统主要参数:探测器频率0.34 THz,成像距离10 m,视场1.51.5,成像分辨率3 cm,成像时间1 s。     

A high-precision 1D dynamic angular measuring system based on linear CCD for Fengyun-2 meteorological satellite

The Fengyun-2 (FY-2) meteorological satellite uses a one-dimensional dynamic angular measuring system to evaluate the stepping accuracy of the scanning mirror. The basic principle of this angular measurement is detecting the light-spot position displacement using a linear charge-coupled device (CCD). This paper presents the design of this non-contact and non-destructive measuring system. To achieve high repeatability and accuracy the centroid method is employed to estimate the light-spot energy gravity, with 20-segment polygonal approximations as a nonlinear compensation. Experimental results show that the measurement system can achieve dynamic angular measurement with up to ±5″ accuracy and 3.5″ repeatability, which makes a credible evaluation for the scanning mirror of FY-2 meteorological satellite.     

Continuous‐scan capability at SSRL and applications to X‐ray diffraction

Typical X‐ray diffraction measurements are made by moving a detector to discrete positions in space and then measuring the signal at each stationary position. This step‐scanning method can be time‐consuming, and may induce vibrations in the measurement system when the motors are accelerated and decelerated at each position. Furthermore, diffraction information between the data points may be missed unless a fine step‐scanning is used, which further increases the total measurement time. To utilize beam time efficiently, the motor acceleration and deceleration time should be minimized, and the signal‐to‐noise ratio should be maximized. To accomplish this, an integrated continuous‐scan system was developed at the Stanford Synchrotron Radiation Lightsource (SSRL). The continuous‐scan system uses an in‐house integrated motor controller system and counter/timer electronics. SPEC software is used to control both the hardware and data acquisition systems. The time efficiency and repeatability of the continuous‐scan system were tested using X‐ray diffraction from a ZnO powder and compared with the step‐scan technique. Advantages and limitations of the continuous‐scan system and a demonstration of variable‐velocity continuous scan are discussed.     

红外地球敏感器扫描镜摆角激光动态测试方法

为解决扫描镜摆角实时动态非接触测量问题,基于激光检测技术和CCD探测技术,提出一种红外地球敏感器扫描镜摆角激光动态测试方法,并研制了扫描镜摆角动态测试系统,其可实现扫描镜的摆动频率、零位角、幅值、峰峰值平均等参量的动静态激光非接触测量。介绍了系统的组成和总体结构,着重对扫描镜摆角动态测量理论和大视场、大相对孔径特殊线性扫描光学系统的设计方法进行了分析与探讨,通过建立系统的数学模型,解决了测量数据误差修正与图形处理问题。对测量系统的精度进行了验证,结果表明系统的摆角测量范围为0~±12°,分辨力为0.01°,动静态测量精度优于±0.04°。     

Simultaneous Measurement of Refractive Index and Thickness of Transparent Plates by Low Coherence Interferometry

We demonstrate a novel low coherence Michelson interferometer which can provide simultaneous measurement of the refractive index and thickness of transparent plates used as a measured object. Unlike the existing low coherence interferometers reported so far, either an object or a focusing lens aligned on the signal arm is scanned repeatedly by a precise translation stage in synchronization with movement of a reflection mirror on the reference arm. The so-called object or lens scanning method gives us two measured quantities a movement distance of the stage between two light focusing states on the front and rear planes of an object and the corresponding optical path difference. These two measured quantities, result in desirable values of the index and thickness of the object with a short calculation. The measurement accuracy of ≤0.1% is expected for a thickness of more than 1 mm. In the experiment using the object scanning method, the accuracy of 0.3% or less was successfully attained for nearly 1-mm thick plates of fused quartz, sapphire, LiTaO₃ and slide glass.     

High-Speed and Large-Scale Electromagnetically Actuated Resonant MEMS Optical Scanner

A high speed electromagnetically actuated resonant micro-electromechanical systems (MEMS) optical scanner with large mirror area of 6×4mm² has beendeveloped. The MEMS optical scanner chip is fabricated using bulk silicon micromachining process and electroplating technique, and can generate the maximum optical deflection angle of ±6.8°circ at the 2.95kHz resonant frequency with a quality factor of 197 in air under the low power consumption of 50mW, when it is immersed in a constant 510.2mT magnetic field parallel to the coil plane. In addition, the surface roughness of less than 20nm for scanning mirror has been measured and the optical reflectivity of mirror atwavelength of 1550nm is high up to 85%. The results show that the device can satisfy the demands of mm-sized scanning systems in optical communications.     

Reducing measurement time for a laser Doppler vibrometer using regressive techniques

In the last decade the laser Doppler vibrometer (LDV) has become a widely spread instrument for measuring vibrations. It often offers accurate measurements with a high spatial resolution. However, the measurement time of the LDV and especially for the scanning LDV is long. Therefore, reducing the measurement time is an attractive objective. A way to achieve this is to use a single sine excitation (on a resonance frequency). However, this technique has two major drawbacks: the inability to provide information on the damping and a operational deflection shape that can differ from the true mode shape. In this article two methods will be introduced to reduce measurement time without these defaults. In the first method introduced in this article a narrow band multisine is used as excitation signal and the measured vibration signal in the time domain is represented by a model using sines and cosines with these fixed narrow band frequencies. The coefficients of those sines and cosines are then estimated on a global scale by means of a least-squares estimator. An important advantage of this particular technique is that one does not have to measure a full period of the signal, reducing time. The second method accelerates the measurement time for scanning LDV measurements. Using the time domain sequence from each previous scan point and a limited number of time samples from the current scan point, the full time domain sequence of the current scan point can be estimated. Both these methods are a key benefit for in-line quality control, which can have upwards of 1000 spatial measurement locations. The proposed techniques will be validated on both simulations and experiments of varying complexity.     

噪声对等光频采样调频连续波激光雷达测距精度的影响分析及实验验证

调频连续波激光雷达具有测量范围大,精度高,无需合作目标等优点,在计量学和工业现场测量中具有重要作用。简单介绍了等光频重采样调频连续波激光雷达的基本结构和测距原理,分析了系统辅助干涉信号和测量干涉信号中存在的主要噪声及其特点。当系统辅助干涉信号中存在噪声时,会造成极值点不准确并且引入测量误差。随后,使用Cramér-Rao下界定理评估测量干涉信号的噪声对测量结果的影响。为了提高测量的准确性和稳定性,基于经验模态分解的小波阈值滤波和汉宁窗带通滤波结合小波滤波的自适应滤波方法分别用来去除了辅助干涉信号和测量干涉信号中的噪声。实验中多次测量了平面镜和多种粗糙度样块,并使用精密导轨验证测量结果的准确性。实验结果表明,当被测物位于3.9 m左右时,使用自适应滤波方法去除噪声后,系统对反射镜和其他粗糙度样块的测量不确定度为20 μm和几十微米(K取值2),远小于使用小波阈值滤波的方法(120 μm和几百微米)。同时,通过对比精密导轨位移数值和系统的测量结果,证明了所提出的方法能够有效提高系统的测量准确性。     

基于旋转式反射镜的飞行视觉系统设计

在MEMS麦克风贴片工艺中,真空吸嘴吸取MEMS芯片以后需要进行芯片位姿的精确校正。为实现高速高精度贴片功能,提出了一种基于旋转式反射镜的飞行视觉系统,该方案利用齿轮齿条将吸嘴的升降运动转化为反射镜的旋转运动,通过设计齿轮参数,实现反射镜不干涉吸嘴的拾放功能。当反射镜旋转到与水平位置夹角呈45°时,视觉系统可以获得MEMS芯片的静止的清晰图像,CCD相机采集一幅图像后,在贴片头飞行的过程中,控制系统完成MEMS芯片的位置和角度的校正。实验结果表明,该系统可以获取高质量MEMS芯片图像。该系统结构简单紧凑,成像无失真,不限制贴片头的运动轨迹,显著提高了MEMS芯片的贴片质量和贴片效率,可广泛地应用于贴片机系统中。     

应用于激光扫描投影仪器的动态聚焦技术研究

为了实现激光投影仪器或系统的自动聚焦，研究搭建了激光动态聚焦系统。该系统可依据背向反射光强信号的变化调节聚焦系统的镜组间距，使激光扫描投影系统能够在不同距离的投影面上聚焦出最小光斑，从而提高系统的定位精度。根据激光动态自聚焦系统的原理，设计了光学杠杆型和反远距型2种动态自聚焦方案，并推导出相应的数学模型；利用ZEMAX光学设计软件进行仿真实验，通过比较得出响应更加灵敏、结构更加合理的自聚焦系统；搭建新型自聚焦激光扫描投影系统对动态自聚焦性能进行了验证。实验结果表明:反远距型动态自聚焦系统更加合理，在4.5 m处的投影面上，汇聚光斑直径最优可达0.2 mm，可使激光扫描投影仪在进行辅助装配时的定位准确度提高至0.1 mm，能够达到先进制造装配工程中零部件的精准定位要求。