基于波长扫描塔尔博特效应的阶高测量理论研究

近年来,多维阶高测量问题倍受关注,两波长或波长扫描方式的塔尔博特效应被应用于多维阶高测量.研究表明,基于塔尔博特(Talbot)效应的阶高测量方法具有仪器结构紧凑、无需机械扫描、稳定性高和测量范围大等优点.因没有光栅或检测器件的任何机械移动,可避免由此导致的相位问题及测量误差.取代相位信息,该方法采用衍射条纹的最大衬比度来判定塔尔博特像,测试中均采用占空比为1:2的龙基(Ronchi)光栅作为周期结构衍射物,利用不同波长塔尔博特像的像距来确定物体阶高.因为测量的是条纹衬比度而非绝对强度,所以阶高测量精度依赖于条纹衬比度,最大衬比度的获取与判定是非常重要的.在分析对比的基础上指出,采用非龙基型光栅,如正弦振幅光栅或相位光栅,能使成像条纹分布更合理,有效地提高成像条纹的衬比度.研究还表明,所采用周期结构衍射物的空间周期越小,分辨率就越高,从而给出了分辨率同衍射物空间周期的定量关系.     

畴腐蚀掺镁铌酸锂可调阵列光分束器的研究

研究了不同畴腐蚀深度的掺镁铌酸锂二维六角可调阵列光分束器的分数Talbot效应.对不同Talbot分数β和不同畴腐蚀深度的阵列光分束器Talbot衍射像进行了数值模拟理论研究.模拟结果表明,Talbot分数β可以改变Talbot衍射像的周期及结构分布,而畴腐蚀深度可有效调制衍射像的光强分布.在理论研究的基础上,设计并制备了具有不同畴腐蚀深度的掺镁铌酸锂二维六角阵列光分束器,对其在不同Talbot分数β条件下的分数Talbot效应进行了通光实验研究,实现了畴腐蚀阵列光分束器对近场Talbot衍射光强分布的调制,实验结果与理论研究结果一致.     

LCVR和AOTF的光谱偏振测量新策略

现有利用液晶相位可变延迟器(LCVR)和声光可调谐滤光器(AOTF)的偏振测量方法较为繁琐,故提出了一种光谱偏振测量新策略,去除了机械运动,并且相位延迟量的选取从四组减少为两组。采用两个LCVR和一个AOTF,通过两个相同型号探测器分别测量±1级衍射光,实现光谱偏振测量。电脑控制LCVR和AOTF的驱动系统分别实现所需相位延迟量和波长选择,通过扫描射频驱动整个频段得到被测光的光谱信息。叙述了方法的具体原理,分析了AOTF的偏振模型,通过理论计算LCVR和AOTF的Muller矩阵,推导出了相应的斯托克斯(Stokes)矢量中的I,Q,U的测量公式。分析并仿真了相位延迟量微小偏差对整个系统测量误差的影响,结果显示相位延迟量在±π/100范围内相对误差<3%。实验验证了测量系统的可行性和准确性,测量误差总体<6%。为偏振测量提供了一种简单可行且精度较高的新方法,具有重要的应用价值。     

基于Talbot-Moiré法的长焦透镜焦距

 长焦距测量的Talbot Moiré法是研究热点,目前很多方法虽然都是基于Talbot现象和Moiré技术,但基本原理和实验方案各不相同,因此焦距计算公式也不相同。基于透镜位相变换作用,利用Talbot效应和Moiré条纹,通过图像处理的方法获得条纹的斜率变化,根据焦距与莫尔条纹斜率之间的关系求得透镜焦距。由于长焦透镜的焦距相对于被测透镜厚度大得多,完全可以看作是薄透镜对光束的变换,可用薄透镜对球面波的变换作用来近似表示其对高斯光束的变换。因此,该方法测量长焦透镜焦距对于高斯光束与非高斯光束焦距测量结果无差别,均适用。最后全面分析了该测量方法的误差及精度极限。在影响测量精度的各个误差因素中,光栅节距误差对焦距测量的影响最为显著。     

基于AOTF成像光谱精密测量技术的研究

声光可调滤波器(AOTF)作为光谱成像的一种新型分光元件,在运用其进行成像光谱时,一般选择入射光垂直于AOTF入射面时所对应的衍射中心波长为CCD的光谱测量波长。但在实际测量中,空间目标不同位置的光线总是以不同的角度进入到AOTF,这样就导致了CCD实际测量的光谱和以光垂直入射时所对应的光谱为测量光谱相比出现误差,影响了光谱的测量精度。采用的成像光谱系统的特点是目标光线经前置光学系统、AOTF和成像透镜后,聚焦成像于透镜的焦平面上,实现了目标光在整个系统的一次成像。此一次成像与传统的二次成像相比,能够有效的提高光能利用率和成像质量。由于AOTF的视场角为±3°,所以通过对AOTF视场角范围内衍射中心波长随入射角度变化的实际规律进行了分析研究,并对衍射波长随入射角度变化的实际测量值进行了拟合修正,得到了修正方程。实验结果表明用修正后的方程进行光谱测量,其相对误差值可以减小一个数量级。此方法可为今后提高AOTF成像光谱测量精度奠定基础。     

改变写入Bragg波长的干涉条纹运动的扫描式Talbot干涉仪

一种干涉条纹运动的扫描式Talbot干涉仪被用于改变光纤Bragg光栅的写入Bragg波长。在系统中,光纤光栅是由来自相位掩模的±1级衍射光经平面镜反射后在远场形成紫外干涉条纹写入的,其中,相位掩模被用作±1级衍射光的分束器。值得注意的是通过干涉条纹的运动来扫描写入光纤光栅,有效降低了Talbot干涉仪对写入光源相干性的要求。     

利用保角变换实现环形光栅的Talbot效应

Talbot效应是一种近场自成像效应,通常只有周期光栅可以产生Talbot效应,而环形光栅无法产生.本文通过引入保角变换,发现可以在环形光栅外部设计适当的折射率渐变层介质,使得其中也能够产生严格的Talbot效应,并计算了对应的自成像半径表达式.本文利用FDTD软件分别将一个环形光栅放置在真空中以及人工设计的折射率渐变层中进行了模拟,并对二者的结果进行了比较分析,发现这种折射率渐变层介质确实对点光源入射的环形光栅的自成像情况有着很好的改善.希望这一工作能够推广Talbot效应的应用范围.     

基于阵列波导光栅的边缘滤波温度解调系统

为克服传统阵列波导光栅解调系统体积大、价格昂贵等问题,提出了以窄带光源为输入光源,采用边缘滤波和阵列波导光栅相结合的解调方案,实现对增敏封装后的光纤光栅温度传感器进行温度解调实验.以窄带光源作为输入,通过边缘滤波的方法使得温度传感器反射谱的中心波长偏移程度与解调光路输出光强的变化相对应,利用阵列波导光栅的波分复用实现多...     

Sinusoidal Phase-Modulating Superluminescent Diode Interferometer with Fabry-Perot Etalone for Step-Profile Measurement

In this paper we use a superluminescent diode (SLD) as the light source of an interferometer and extract a narrow spectrum from a wide spectrum of the SLD with a Fabry-Perot Etalone (FPE). By varying sinusoidally the distance between the two mirrors of FPE, the central wavelength of the narrow spectrum is scanned sinusoidally. The distance between the mirrors is exactly set by a feedback control system, and sinusoidal phase-modulated SLD light that has a large scanning width of about 10 nm can be obtained with high stability and spatial uniformity. The phase of the interference signal has two different components. One is amplitude Z_b of sinusoidal phase modulation, which is proportional to the optical path difference (OPD) and the scanning width. The other is conventional phase α, which provides a fractional value of the OPD in the range of the wavelength. By combining the two values of the OPD obtained from Z_b and α, an exact OPD larger than the wavelength can be measure with ment accuracy in α. Characteristics of the interferometer are made clearly through step-profile measurements.     

High-efficiency color separation method based on fractional Talbot effect for color liquid crystal display

Based on the fractional Talbot effect of Talbot grating, a new method with high light efficiency for color separation in color liquid crystal displays (LCDs) is proposed. The light efficiency of 85% and 89% are obtained by three- and four-step Talbot gratings, respectively, which are rather higher than that of using color filter, the traditional color separation method in color LCDs. This method has large tolerance to the position error of the color separation plane, the wavelength changes of red, green and blue colors, and the step height errors of the gratings.     

Self-imaging by a volume grating

The self-image phenomenon by a volume grating is proposed and theoretically analyzed. A theoretical model based on a path integral formulation to describe wave propagation through the grating inhomogeneous medium is applied. A modified version of the scalar diffraction theory Fresnel propagator is obtained which allows calculating the diffracted field amplitude by the grating. The proposed model is applied to amplitude and/or phase volume gratings. Remarkable features appear, in particular at the fractional Talbot distance 0.125z_T. In this case, if an in-phase real and imaginary grating modulation is considered a self-image intensity profile is observed for determined values of the absorptive and refractive parameters. On the other hand, a spatial comb intensity profile for a near half period shift between the real and imaginary grating modulations is found.     

Sinusoidal fringe projection system based on compact and non-mechanical scanning low-coherence Michelson interferometer for three-dimensional shape measurement

We report a sinusoidal fringe projection system based on superluminiscent diode (SLD) as a broad-band light source in conjunction with an acousto-optic tunable filter (AOTF) as frequency tuning device for three-dimensional shape measurement. The present system is based on a compact low-coherence Michelson interferometer system. The conventional interferometric system was modified in which one side of the beam splitter was coated with aluminum oxide which is used as reference mirror. With this modified version, interference fringes can easily be obtained by simply placing the external mirror in contact on the other side of beam splitter. Sinusoidal fringes with multiple spatial-carrier frequency can be generated in real-time using the present system by means of changing the radio-frequency signal to AOTF electronically without mechanically moving any component in the system. The present system was tested by projecting the sinusoidal fringes on a step-like object and 3D shape of the object was reconstructed using Fourier transform fringe analysis technique. The main advantages of the proposed system are completely non-mechanical scanning, easy to align, high stability because of its nearly common-path geometry and compactness.     

High-Accuracy Measurement of the Dispersion of Chirped Fiber Gratings

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Grating Interferometer Using ± 1st Order Beams for Step-Profile Altitude Difference Measurement

We propose a grating interferometer for step-profile altitude difference measurement. There are two main characteristics in this interferometer. The first is that the intensity distribution of the interference pattern is independent of the wavelength of the laser-diode used. No change of the intensity distribution occurs when the wavelength fluctuates. The second is that the measuring range is much larger than the wavelength of the light source because the spatial period of the grating is much larger than the wavelength. Sinusoidal phase modulating interferometry is easily applied to detect the phase variation of the interference pattern by vibrating the grating sinusoidally. The thickness of a 3.5-inch disk is measured with an accuracy of less than 0.5 μm.     

Effects of third-order aberrations on the irradiance of self-image

We examine the effects of third-order aberrations exerted on the irradiance of image that is observable in a coherent self-imaging system. Both spherical aberration and astigmatism degrade the visibility of the image of a sinusoidal-type grating as well as blur the outline of the image of a rectangular-type grating. Coma laterally shifts the image of a sinusoidal-type grating on the image plane as well as changes a rectangular-type pattern into an asymmetrically blurred pattern. According to our analysis, the self-image of a high-density grating with a period of two times the optical wavelength is not at all affected by spherical aberration. In general a self-imaging system can always be corrected for astigmatism by shifting the image plane in its normal direction. We show that the self-image with defect can be well explained by taking the third-order aberrations and the focus-shift aberration into consideration.     

基于泰伯效应的高斯光束尺寸测量

光栅用在高斯光束参数测量中的突出优点是方法简单，成本较低，全息光栅由于其制备容易，无周期误差而比一般光栅具有更多的优点。在用光栅进行光斑测量的实验中，观察到由全息光栅引起的泰伯（Ｔａｌｂｏｔ）效应携带有关光斑参数的有用信息，本文提出了一种基于泰伯效应的测量方法，只需测定条纹间隔就能确定高斯光束尺寸，因此降低了对光源或光栅定位精度，电路和光源稳定性的要求，文中聚焦高斯光束照明全息光栅时光场分布，及其     

Optical Coherence Tomography System based on Synthesis of Optica Coherence Function with a Wavelength-Scanning Laser Source

A new optical coherence tomography system using a wavelength-scanning laser source is presented. The system has the advantage that the depth resolution can be controlled by the scanning range. In general, rapid scanning of the wavelength varies the output power of the laser source, and it is difficult to detect a weak signal of reflected light from the scattering object. By synchronizing the intensity-integrated detector with the variation, the dynamic range of the detection has been improved. To confirm the performance, tomographic imaging of biological tissues is demonstrated.     

短波红外平场光谱仪的波长定标

针对自行研制的短波红外平场光谱仪,讨论了波长定标的原理和方法.短波红外平场光谱仪由两个分光探测单元组成,探测单元以平场凹面光栅分光,处于焦平面上的线阵列探测器探测,波长定标分为两个波段进行.为了实现准确的波长定标,针对短波红外平场光谱仪的特点设计了波长定标步骤.双单色仪可以输出光谱仪波长范围内任意波长单色光,选用双单色仪作为光谱定标光源,双单色仪的输出单色光光潜分辨力为1.5 nm,经过光谱仪的分光会聚后成像在线阵列探测器像元上,采用重心法计算出给定波长对应的像元精确位置,通过多项式拟合得出两个探测单元的波长定标系数.定标结果表明,在900～2400 nm波长范围内,定标曲线拟合误差小于0.5 nm,波长定标不确定度优丁0.6 nm.     

A high—speed automatic spectrometer based on a solid—state non—collinear acousto-optic tunable filter

An automatic visible spectrometer based on a non-collinear acousto-optic tunable filter (AOTF) is constructed for high-speed spectrometry. Its spectral filtering characteristics, such as relationships between the radio-frequency (RF) driving frequency and the output central wavelength, the output bandwidth and the central wavelength, its typical spectral point spread function (PSF), and so on, are studied systematically. The preliminary measurement results of AOTF spectrometer show that it is a solid-state, high-speed, easily controllable by computer-programming, rugged and compact spectroscopic device in comparison with a conventional grating spectrometer, and has the potential for widespread spectrometric applications.     

基于可调高斯型滤波器的光纤光栅振动解调技术研究

 传统的匹配光纤布拉格光栅型光纤光栅波长解调系统具有波长匹配精度低、调节困难和动态测量范围小的缺点。为了克服上述缺点,采用波长可调谐高斯型滤波器代替传统匹配光纤光栅,提出了一种新型的光纤光栅波长解调技术。建立了基于高斯型滤波器的光纤光栅振动解调系统。对不同频率和振幅的周期性振动进行了解调实验。发现当选择合适带宽的滤波器时,透过滤波器的光功率随压电陶瓷上所加电压信号同步且高保真地变化,表明该系统对振动信号实现了有效的解调。该系统同时具有响应速度快、物理结构简单、动态测量范围大的优点。