Planar optical waveguide temperature sensor based on etched bragg gratings considering nonlinear thermo-optic effect

This paper demonstrates the development of optical temperature sensor based on the etched silica-based planar waveguide Bragg grating. Topics include design and fabrication of the etched planar waveguide Bragg grating optical temperature sensor. The typical bandwidth and reflectivity of the surface etched grating has been ∼0.2 nm and ∼9 %, respectively, at a wavelength of ∼1552 nm. The temperature-induced wavelength change is found to be slightly non-linear over ∼200 °C temperature range. Typically, the temperature-induced fractional Bragg wavelength shift measured in this experiment is 0.0132 nm/°C with linear curve fit. Theoretical models with nonlinear temperature effect for the grating response based on waveguide and plate deformation theories agree with experiments to within acceptable tolerance.     

SIMULTANEOUS MEASUREMENT OF STRAIN AND TEMPERATURE WITH POLARIZATION MAINTAINING FIBER BRAGG GRATING LOOP MIRROR

□ A novel simultaneous method of strain and temperature measurement based on a polarization maintaining fiber Bragg grating loop mirror is proposed and demonstrated. The sensing head was composed of a fiber loop mirror and a section of fiber Bragg grating made of a polarization maintaining fiber. The Bragg wavelengths of the fiber grating in the polarization maintaining fiber were along slow and fast axis showing different sensitivities to strain and temperature with the interferometric peak wavelength of the fiber loop mirror. By monitoring the shifts of the Bragg wavelength and interferometric peak of the fiber loop mirror, with its temperature sensitivity of 0.1167 nm/°C and strain sensitivity of 0.0093 nm/μ?, a temperature measurement resolution about 0.009°C and a strain measurement resolution of 1.08 μ? was achieved theoretically and experimentally.     

小型光学遥感器主镜室的光机结构

设计了一种新的光机结构,以使超小型光学遥感器在宽温度范围及恶劣的动力学环境下能够良好成像。研究了该结构中的核心部件-主镜组件的支撑结构的设计原理和实现方法。通过对主镜室初始设计方案的力、热特性分析,说明了主镜传统支撑方式的局限性。然后,以挠性支撑原理为基础设计了一种新型的适用于小口径反射镜支撑的挠性反射镜支撑结构,对该支撑结构的温度适应性及组件的模态进行了有限元分析,说明了采用这种反射镜挠性支撑结构能够满足设计指标要求。最后,论证了小型光学遥感器主镜室的加工及具体实现方法。对装配后的主镜组件进行了热冲击试验和温度拉偏试验,结果表明:在-60℃~80℃进行热冲击试验后,主镜不会出现炸裂现象;而在-20℃~50℃温度下,反射镜面形精度RMS仍保持在0.025λ(λ=632.8nm)水平。得到的结果验证了主镜室的设计可以满足小型光学遥感器的应用环境要求。     

Experimental diagnostic module for ultrafast combined interferometry of the processes of interaction of ultrashort laser pulses with condensed media in vacuum

An experimental diagnostic module based on a femtosecond laser system (τ_0.5 ∼ 45-70 fs, 7n = 266, 400, and 800 nm) and the experimental technique for ultrafast combined interferometric investigation of the interaction of ultrashort laser pulses with condensed media in vacuum are described. A combined interferometric microscope built according to the Michelson and Mach-Zehnder schemes allows studies of the dynamics of optico-thermophysical and gas-dynamic proc esses at the surface of a target (the crater depth and diameter, optical properties) and in a plasma plume (velocity of expanding particles, electron density, optical characteristics) at a time resolution of 5 - 10^-14 s in the range of delays 10^-13-10^-7 susing two probing wavelengths (7n = 400, 800 nm) in vacuum (to 5 - 10^-5 mbar). Setting a mechanical shutter in the reference arm of the interferometer also allows obtaining of shadow photographs without changing the optical scheme.     

Temperature and refractive index sensor using a high-birefringence fiber loop mirror and single mode-coreless-single mode fiber structure

A novel fiber optic sensor for the simultaneous measurement of refractive index and temperature is reported. The sensor consists of a high-birefringence fiber loop mirror and a section of single mode-coreless-single mode fiber structure. The single mode-coreless-single mode fiber structure served as a refractometer while the high-birefringence fiber loop mirror was used to measure temperature. The multimode interference valley of the single mode-coreless-single mode fiber structure was sensitive to the surrounding refractive index of liquids (96.42 nm/refractive index unit) and had almost no response to temperature fluctuations. The high-birefringence fiber loop mirror was highly sensitive to temperature (1.98 nm/°C) but was insensitive to changes in refractive index. The theoretical and experimental results demonstrated simultaneous measurement of temperature and refractive index. The optimum resolution was 2.07 × 10^?4 refractive index units and 0.01°C.     

人眼像差测量方法研究

由于人们对视力矫正的需求,近几十年来人眼像差测量技术得到长足进步。目前已经出现了可以重建波前的测量波像差的激光追迹技术,同步像差仪,哈特曼-夏克传感器,塔尔博特传感器,阴影像差仪,视网膜仪,主观追迹技术以及直接评价人眼视觉质量的干涉测量技术及双程法。现回顾和描述了各种技术的原理,并做了比较,同时提出了眼像差研究的发展方向。     

光纤F-P微位移测量实验研究

利用光纤自聚焦透镜作为F-P干涉仪的反射面,根据F-P干涉光谱相邻波峰之间的波长差与其干涉腔长之间的关系,实现微位移的测量。克服了光强型F-P传感器测量结果受光源波动影响、难以识别位移方向等缺点,可直接测量绝对位移,并可识别位移方向。经实验得到其位移测量误差小于2.5nm。     

微型膜结构全光纤珐珀干涉高温传感器

制作了一种微型膜结构的全光纤在线珐珀干涉式高温传感器。该传感器是在单模光纤端面依次熔接一段大芯径空芯光纤和一段研磨的多模光纤膜片而构成的,因此,温度引起的珐珀腔光程差改变量由空芯光纤的热膨胀和温度引起腔内压强改变从而改变膜片的扰度两部分组成,从而使相同温度变化下传感器的光程差变化量更大,分辨率更高。实验结果表明,在100～650℃,该传感器单位温度变化的光程差变化量约为1.029 nm,温度分辨率约为1.5℃,测量线性度约为0.996 7,且滞回小,重复性好。这种膜结构的全光纤珐珀干涉式高温传感器因其体积小,温度分辨率高,将在多点高温测量领域有好的应用前景。     

双波长集成光栅干涉微位移测量方法

介绍了一种基于双波长激光的集成光栅干涉位移检测方法,利用该方法对硅-玻璃键合工艺制作的集成光栅位移敏感芯片进行了测试实验。实验系统主要由敏感芯片、波长为640nm和660nm的双波长半导体激光器、双光电二极管及检测电路组成,敏感芯片则由带反射面的可动部件和透明基底上的金属光栅组成。入射激光照射到光栅上产生衍射光斑,衍射光的光强随可动部件与光栅之间的距离变化,通过分别测量两个波长的衍射光强信号并交替切换选取灵敏度较高的输出信号,实现了一定范围内的扩量程位移测量,并得到绝对位置。实验结果表明,利用双波长集成光栅干涉位移检测方法测得敏感芯片可动部件与基底光栅的初始间隙为7.522μm,并实现了间隙从7.522μm到6.904μm区间的高灵敏度位移测量,其噪声等效位移为0.2nm。     

Photoelectronic displacement sensor with nanometre resolution

The design of an ultraprecision displacement sensor with sub-nanometre resolution is proposed for the use of ultraprecision technologies. The sensor is based on the highly sensitive detection of power change at a specific point in light reflected from an object surface when the surface is subject to a small displacement. The sensor consists of a single light source, the reflective object and reference surfaces, optical fibre bundles for tranmission of the illuminating and the reflected light, and the photodiode set-up. In operation, the object and the reference surfaces are illuminated by light transmitted through the optical fibre bundle from the single light source. The reflected light from both surfaces is then transmitted through the optical fibre bundle to two individual but equivalent photodiodes. By using a differential amplifier, the diodes give a highly sensitive displacement signal which is included in the total signal of the reflected light. The sensor proposed has some distinctive features in its performance, such as non-contact measurement, a high resolution of 0.5 nm, a wide working range of about 30 μm within 5% linearity, and the sufficient stability of 1 nm in 20 s for specific research purposes.     

双球面法标定立式参考球面的精度分析

采用双球面法对立式Fizeau干涉仪的参考球面进行标定以确定由重力、安装夹持力等导致的面形形变量,提高立式光学系统中光学元件的面形检测精度.首先,推导了双球面法标定算法;进而,理论分析和模拟计算了影响检测精度的环境、重力、安装夹持力等因素;最后,利用双球面法对立式Fizeau干涉仪的参考球面进行标定,并利用误差合成理论分析实验结果.实验结果显示,利用双球面法标定F/1.5的立式Fizeau干涉仪参考面的精度为2.3 nm.其中,算法本身以及实验操作引起的测量重复性不大于0.7 nm,包含环境误差时的重复性低于1.2 nm;重力导致的面形形变约为0.9 nm,标准镜安装导致的面形形变约为1.7 nm.结果论证了双球面法具有很高的标定精度;环境对检测精度的影响与干涉腔长度有关,长度增加时影响很明显;立式工作时,重力、安装等因素导致的标准镜参考球面的面形形变很大,在高精度使用前必须进行标定.     

线性位移台直线度高精密外差干涉测量装置

直线度测量中往往存在有限的测量范围、精度低和阿贝误差等问题。本文提出了一种高精密直线度外差干涉测量装置,该装置由Koester棱镜、角锥棱镜、1/4波片、楔面棱镜和楔面反射镜构成。楔面棱镜为直线度传感元件,角隅棱镜和楔面反射镜是测量信号的回光元件。双频激光信号进入直线度干涉仪后组成几何空间对称四光路测量信号。四路测量光走过几乎完全相同的路径有效地提高了干涉仪的稳定性,并且使空程误差最小化。使用楔角为1°的楔角棱镜和2π/512细分的相位计,直线度测量分辨力为17.71nm。该方法不需要与行程同长的大反射参考镜,但同样能实现高分辨率,理论和实验证明空间对称测量结构避免了由俯仰,偏转和滚转角引起的阿贝误差的串扰,而且光学元件少,结构简单,方便易用,结果可以直接溯源到米的定义。     

Self calibration in a fiber optic sensing system using the entangled photon states walk-off compensation

We present a concept of a self calibration of the classical and quantum parameters measurement using a fiber optic system. The measurement of the change in phase of the optimum entangled states visibility, which is performed in term of a walk-off length, i.e. birefringence. The applied two physical parameters (i.e. force/stress and temperature) on the sensing fiber can be simultaneously measured, whereas the self calibration respecting to the entangled photon walk-off length can be performed. The scheme of the entangled photons generation in fiber optic is reviewed and the walk-off on the polarization entangled states presented. The potential of self calibration and simultaneous measurement using an interferometric sensing technique and fiber grating sensor are proposed and discussed. The entangled photon walk-off compensation when the sensing fiber was in the thermal controlled environment presented and discussed.     

1.2m微晶主镜的新型支撑

针对1.2m微晶主镜,提出了基于6套柔性切向杆机构的侧向支撑与基于18点半柔性Whiffletree机构的轴向支撑相结合的新型主镜支撑方案,用于保证该主镜在较大温差范围以及不同俯仰角度下始终保持良好的面形精度及较高的系统刚度。分析了该机构的工作原理,实验测试了主镜的面形精度及支撑系统的模态。机构分析表明该支撑方式可有效保证主镜定位精度和面形精度,并具有热解耦能力;有限元分析确认系统具有良好的支撑性能;面形精度检测得出主镜光轴垂直面形精度RMS达15.25nm,光轴水平面形精度RMS为20.75nm,模态测试则获得主镜支撑系统的一阶固有频率为60.3Hz。实测结果验证了该新型主镜支撑系统具有良好的面形保持能力及支撑刚度,分析结果与实测结果符合度较好,主镜光轴垂直和水平状态面形精度RMS的相对误差分别为14.0%和17.8%,一阶固有频率相对误差为10.8%。得到的结果验证了有限元建模及分析的可信性,支撑系统设计方案的合理性及相关理论推导的正确性。     

On-machine measurement of a cylindrical surface with sinusoidal micro-structures by an optical slope sensor

This paper describes the measurement of a cylindrical surface with sinusoidal micro-structures over a large area on a diamond turning machine. The sinusoidal micro-structures, which are fabricated on the periphery surface of a cylinder by the fast tool servo-based diamond turning, are superposition of periodic sine-waves along the cylinder axis and the cylinder circumference with amplitudes of 100 nm and wavelengths of 100 μm, respectively. An optical two-dimensional (2D) slope sensor with a multi-spot light beam is developed for measurement of the 2D local slopes of the sinusoidal micro-structured surface. A cylindrical lens is employed in the sensor for removing the influence of the curvature of the cylinder surface. Experiments of fabrication and measurement of the sinusoidal micro-structured surface on an ultra-precision diamond turning machine are carried out.     

PHOEBE,a prototype scanning laser-feedback microscope for imaging biological cells in aqueous media

Based on the principle of laser-feedback interferometry (LFI), a laser-feedback microscope (LFM) has been constructed capable of providing an axial (z) resolution of a target surface topography of ～ 1 nm and a lateral (x, y) resolution of ～ 200 nm when used with a high-numerical-aperture oil-immersion microscope objective. LFI is a form of interferometry in which a laser's intensity is modulated by light re-entering the illuminating laser. Interfering with the light circulating in the laser resonant cavity, this back-reflected light gives information about an object's position and reflectivity. Using a 1-mW He–Ne (λ = 632·8 nm) laser, this microscope (PHOEBE) is capable of obtaining 256 × 256-pixel images over fields from (10 μm × 10 μm) to (120 μm × 120 μm) in ～ 30 s. An electromechanical feedback circuit holds the optical pathlength between the laser output mirror and a point on the scanned object constant; this allows two types of images (surface topography and surface reflectivity) to be obtained simultaneously. For biological cells, imaging can be accomplished using back-reflected light originating from small refractive-index changes (> 0·02) at cell membrane/water interfaces; alternatively, the optical pathlength through the cell interior can be measured point-by-point by growing or placing a cell suspension on a higher-reflecting substrate (glass or a silicon wafer). Advantages of the laser-feedback microscope in comparison to other confocal optical microscopes include: the simplicity of the single-axis interferometric design; the confocal property of the laser-feedback microscope (a virtual pinhole), which is achieved by the requirement that only light that re-enters the laser meeting the stringent frequency, spatial (TEM₀₀), and coherence requirements of the laser cavity resonator mode modulate the laser intensity; and the improved axial resolution, which is based on interferometric measurement of optical amplitude and phase rather than by use of a pinhole as in other types of confocal microscopes.     

A simple and accurate method for calibrating the oscillation amplitude of tuning-fork based AFM sensors

We have developed a simple and accurate method for calibrating the amplitude of vibration of quartz tuning fork sensors commonly used in atomic force- and near field optical-microscopy. Unlike interferometric methods, which require a complex optical setup, the method we present requires only a simple measurement of the electro-mechanical properties of the tuning-fork oscillator and can be performed in a matter of minutes without disturbing the experimental setup. Comparison with interferometric methods shows that an accuracy of better than few percent can be routinely achieved.     

制作平面全息光栅的离轴抛物镜/洛埃镜干涉系统

设计和制作具有较高波前平面度和结构稳定的干涉曝光系统是研制高质量平面全息光栅的首要条件.对离轴抛物镜/洛埃镜系统、单透镜/洛埃镜系统、球面反射镜/洛埃镜系统和双分离透镜/洛埃镜系统等4种单反射镜干涉曝光系统产生的干涉条纹直线度进行了光线追迹.在干涉场中放置标准光栅,使用于曝光的两束平行光入射到光栅上,从而衍射光相干叠加...     

大口径空间光学遥感器的碳纤维复合材料精密支撑构件的结构稳定性研究

摘要：为了研究应用于大口径空间光学遥感器中由碳纤维复合材料（CFRP）制成的精密支撑构件的结构稳定性,设计并研制了连接在主、次镜间的CFRP连接筒。对该连接筒建立等效力学模型、计算相关参数和确定铺层的合理形式,运用有限元法对连接筒进行分析计算,通过试验验证连接筒的结构稳定性。首先,由给定的主、次镜间角度变化量计算出连接筒前端面的最大挠度,根据实际载荷情况建立等效力学模型,计算连接筒轴向弹性模量,结合复合材料层压板理论,确定碳纤维铺层的合理形式。然后,运用ANSYS软件对有限元模型进行分析,计算主、次镜间的角度变化量和支撑结构的模态分布。最后,通过量级逐增的力学试验,采用光学测量的方法测量主、次镜间角度变化量,验证CFRP连接筒的结构稳定性。试验结果表明：主、次镜间角度变化量小于10″,CFRP支撑构件一阶基频大于75Hz。CFRP支撑构件满足主、次镜间角度变化量要求,具有较好的结构稳定性。     

光纤气压传感器特性分析

用双膜盒作气压的敏感元件,将光纤微位移传感器用于检测膜盒随压力变化引起的形变,避免了其他检测膜盒形变方法的缺点,使气压传感器的性能得到改善和优化;为了提高检测灵敏度、降低检测限,使用了双通道光纤传感器,构造了一个气压测量装置,并以标准空气压力计对这种光纤气压传感器的输出变化随气压变化的关系进行了标定,结果表明测量范围可以达到900-1200hpa,分辨率为0.2hpa,精度为±0.1hPa。改变光纤探头到膜盒反射面的初始间隔,实现气压测量区间位置的变化。进一步优化光纤探头的结构参数,可以拓宽大气压力的测量范围。