Two-wavelength sinusoidal phase-modulating interferometer for nanometer accuracy measurement

A two-wavelength sinusoidal phase-modulating(SPM) laser diode(LD) interferometer for nanometer accuracy measurement is proposed.To eliminate the error caused by the intensity modulation,the SPM depth of the interference signal is chosen appropriately by varying the amplitude of the modulation current periodically. Then,the refine theory is induced to the measurement,and the two-wavelength interferometer (TWI) is combined with the single-wavelength LD interferometric technique to realize static displacement measurement with nanometer accuracy.Experimental results indicate that a static displacement measurement accuracy of 5 nm can be achieved over a range of 200μm.     

Sinusoidal phase-modulating laser diode interferometer for real-time surface profile measurement

A sinusoidal phase-modulating (SPM) laser diode (LD) interferometer for real-time surface profile measurement is proposed and its principle is analyzed. The phase signal of the surface profile is detected from the sinusoidal phase-modulating interference signal using a real-time phase detection circuit. For 60 × 60 measurement points of the surface profile, the measuring time is 10 ms. A root mean square (RMS) measurement repeatability of 3.93 nm is realized, and the measurement resolution reaches 0.19 nm.     

Laser diode interferometer used for measuring displacements in large range with a nanometer accuracy

In this paper, the displacement of an object is measured with a photothermal phase-modulating laser diode interferometer. A feedback control system is designed to reduce the measurement errors caused by the fluctuations in the optical wavelength of the laser diode and the vibrations of the optical components in the interferometer. A new method is proposed to enlarge the measuring range of displacement. Using this method, the measuring range is enlarged from half wavelength to nearly 125 μm and the measurement accuracy is about 1 nm. The simulation and experimental results have shown the usefulness of the method and the feedback control system.     

物体表面形貌的正弦相位调制实时干涉测量技术研究

表面形貌干涉测量技术是一种高精度的非接触式测量技术,在工业生产和科学研究中具有广泛的应用。提出一种实时测量表面形貌的正弦相位调制干涉测量新技术。该技术用激光二极管作光源,用自制的高速图像传感器探测干涉信号,通过信号处理电路实时解相得到被测表面所对应的相位分布,实时分析相位获得物体表面形貌。该技术消除了光强和部分外界干扰的影响,提高了系统的测量精度。楔形光学平板表面形貌的测量结果表明,测量点为60×60个的情况下,测量时间小于8.2 ms,重复测量精度(RMS)为4.3 nm。     

Real-time micro-vibration measurement in sinusoidal phase-modulating interferometry

As there exist some problems with the previous laser diode (LD) real-time microvibration measurement interferometers, such as low accuracy, correction before every use, etc., in this paper, we propose a new technique to realize the real-time microvibration measurement by using the LD sinusoidal phase-modulating interferometer, analyze the measurement theory and error, and simulate the measurement accuracy. This interferometer utilizes a circuit to process the interference signal in order to obtain the vibration frequency and amplitude of the detective signal, and a computer is not necessary in it. The influence of the varying light intensity and light path difference on the measurement result can be eliminated. This technique is real-time, convenient, fast, and can enhance the measurement accuracy too. Experiments show that the repeatable measurement accuracy is less than 3.37 nm, and this interferometer can be applied to real-time microvibration measurement of the MEMS.     

Sinusoidal phase-modulating laser diode interferometer insensitive to the intensity modulation of the light source

In a conventional sinusoidal phase-modulating laser-diode (SPM-LD) interferometer, the wavelength of the LD is sinusoidally modulated by varying its injection current. However, the intensity modulation is associated with the wavelength modulation, which affects the measurement accuracy. We propose an SPM-LD interferometer insensitive to the intensity modulation of the light source, in which the influence of the intensity modulation is eliminated by choosing the appropriate sinusoidal phase modulation depth. Computer simulations and experiments are performed for real-time displacement measurement with the proposed SPM-LD interferometer. The measurement accuracy has been improved and the measurement repeatability is less than 1 nm. No additional components are required in our proposed method that leads to a simple system compared with the other previously proposed methods.     

Sinusoidal Phase-Modulating Fabry-Perot Interferometer for Angular Displacement Measurement

In this paper, a sinusoidal phase-modulating Fabry-Perot interferometer is proposed to measure angular displacement.The usefulness of the interferometer is demonstrated by simulations and experiments.     

Sinusoidal phase-modulating laser diode interferometer insensitive to intensity modulation for real-time displacement measurement with feedback control system

In sinusoidal phase modulating laser diode (LD) interferometer, the injection current of the LD is sinusoidally modulated to realize the modulation of the wavelength. However, the light intensity of LD is also modulated, which affects the measurement accuracy. An all-fiber sinusoidal phase modulating LD interferometer for real-time displacement measurement is proposed where the influence of the intensity modulation is eliminated with a new algorithm. It is made clear that an optimal depth of the sinusoidal phase modulation (SPM) exists in the algorithm. Moreover, the SPM depth is locked at the optimal value by controlling the injection current with a feedback control system. The feasibility of the proposed interferometer for displacement measurement is verified by experiments.     

基于相位调制器与Fabry-Perot干涉仪的激光多普勒频移测量方法

提出了一种激光多普勒频移测量方法, 此方法利用正弦相位调制使信号光在原频率成分基础上产生正负一阶边带, 再由Fabry-Perot干涉仪对调制光振幅和相位进行调整, 使其产生固定频率的拍频信号, 利用此拍频信号的振幅随频率变化而变化的性质来进行多普勒频移测量. 通过理论分析证明该方法具有很高的测量精度, 加工装调难度不大, 兼顾了普通相干与非相干探测方法的优势. 另外通过实验证明该方法的正确性与可行性, 并通过与普通非相干方式比较发现该方法在测量精度上可以提高 约1个数量级. 关键词： 多普勒频移 相位调制 Fabry-Perot干涉仪 拍频     

正弦相位调制式全光纤微位移测试仪

利用正弦相位调制干涉技术检测微小位移,精度可达纳米量级。采用全光纤光路,结构简单,并可实时非接触测量。     

以慢变化近似为基础的新型正弦相位调制半导体激光干涉仪

提出并在实验上实现了一种以慢变化近似为基础的新型正弦相位调制半导体激光干涉仪。原理上它不要求相位解调一次和二次谐波分量振幅在实验中必须保持相等，从而将动态范围提高了３－４个数量级且不损失精度。用压电陶瓷和微电机驱动位移。     

A sinusoidal phase-modulating fiber-optic interferometer insensitive to the intensity change of the light source

In a conventional laser-diode sinusoidal phase-modulating (LD-SPM) interferometer, the wavelength of the LD is modulated by varying its injection current. The intensity modulation concurrent with the wavelength modulation leads to measurement errors. A photothermal-modulation method has been proposed to decrease the intensity change of the LD; however, this method cannot be used to measure vibration with a high frequency, and the beam diameter is too large to be used to measure minute objects. In this paper, we propose LD-SPM fiber-optic interferometer, in which the effect of the intensity change of the light source on measurement is eliminated. The diameter of the light beam is less than 0.5 mm. Using this interferometer, we measured displacements of a mirror driven by a piezoelectric transducer. The measurement repeatability is less than 1 nm.     

Quadrature demodulation technique for self-mixing interferometry displacement sensor

A new, to the best of our knowledge, signal processing method based on quadrature demodulation technique is presented for laser diode self-mixing interferometry(LDSMI) displacement sensor. Phase modulation of the laser beam is obtained by an electro-optic modulator (EOM) in the external cavity. Detection of the target's displacement can be easily achieved by sampling the interference signal at those times which satisfied certain conditions. The major advantage of the technique is that it does not involve any complicated calculation and insensitive to the sampling error. Experimental results show that the proposed method can effectively improve the displacement measurement resolution of the laser diode self-mixing displacement sensor to a few nanometers.     

Fast interrogation using sinusoidally current modulated laser diodes for fiber Fabry–Perot interferometric sensor consisting of fiber Bragg gratings

A fast interrogation method using a sinusoidal modulated laser diode for a fiber Fabry–Perot interferometric sensor consisting of Bragg gratings (FBG–FPI) is proposed.. The FBG–FPI has sharp transmittance peaks in the reflection band of the FBGs. Wavelength sweep produced by current modulation of a laser diode can be used to detect the peak position. This enables high-resolution strain or temperature measurement. To precisely control the current, the current modulation is realized using a laser diode controller (LDC) with external modulation function. In the modulation by a sawtooth wave, the possible speed of wavelength sweeping is limited to 100 kHz or less due to the bandwidth limitation of an LDC and thermal effect in a laser diodeUsing a sinusoidal wave as a modulation waveform enables wavelength sweeping at speeds exceeding 100 kHz. The modulation characteristics of the laser wavelength is evaluated experimentally and the operating wavelength is monitored using an asymmetric Mach–Zehnder interferometer. The resolution of 0.2 fm/\(\sqrt{\mathrm{Hz}}\) and measurement time of 1 \(\upmu\)s were experimentally demonstrated in the present sensor.     

Photothermal modulation of laser diode wavelength: application to sinusoidal phase-modulating interferometer for displacement measurements

In this paper, a novel laser-diode (LD) sinusoidal phase-modulating (SPM) interferometer, which utilizes a photothermal technique for LD wavelength modulation, is proposed to measure displacements with a nanometer accuracy. In conventional LD–SPM interferometers, the LD intensity modulation is concurrent with the wavelength modulation, which increases measurement errors. Using the photothermal technique, the LD wavelength modulation can be accomplished with negligible concomitant intensity modulation, and the measurement errors are thus eliminated. The computer simulations and experiment results verify the usefulness of this novel interferometer.     

基于飞秒光频梳的压电陶瓷闭环位移控制系统

利用飞秒光频梳、外腔可调谐半导体激光器和法布里-珀罗干涉仪建立了一套压电陶瓷亚纳米级闭环位移控制系统. 将可调谐半导体激光器锁定至光频梳, 通过精确调谐光频梳的重复频率, 实现了半导体激光器在其工作频率范围内的精密调谐. 利用Pound-Drever-Hall锁定技术将带有压电陶瓷的法布里-珀罗腔锁定至半导体激光器, 进而通过频率发生系统控制压电陶瓷产生亚纳米级分辨率的位移. 实验研究发现锁定至光频梳后可调谐半导体激光器1 s的Allan标准偏差为1.68×10^-12, 将其在30.9496 GHz范围内进行连续闭环调谐, 可获得压电陶瓷的位移行程约为4.8 μm; 以3.75 Hz的步长扫描光频梳的重复频率, 实现了压电陶瓷的450 pm闭环位移分辨率并测定了压电陶瓷的磁滞特性曲线. 该系统不存在非线性测量误差, 且激光频率及压电陶瓷位移均溯源至铷钟频率源. 关键词： 光频梳 压电陶瓷 法布里-珀罗腔 可调谐半导体激光器     

半导体激光管位移传感器的模型建立及仿真分析

从激光应用系统稳态条件出发,建立了半导体激光管位移传感器系统的数学模型,其仿真结果与有关文献的实验结论相吻合,详细阐述了通过检测ＬＤ注入调制三角波相邻两周期对应点处信号的位相差而完成位移测量的原理。由理论分析提出了提高最大允许位移速度上限和减小测量非线性误差的措施,其结论对激光自混合干涉技术的应用具有重要指导意义     

Displacement measurement with adjustable range by use of the photoelectromotive force effect and a frequency-modulated laser diode

We demonstrate a scheme for displacement measurement by use of the photoelectromotive force effect and a frequency-modulated laser diode. The measurement range can be adjusted by a change in the depth of frequency modulation, thus making the measurement method both simple and versatile.     

Photothermal Phase-Modulating Laser Diode Interferometer with High-Speed Feedback Control

We propose a photothermal phase-modulating laser diode interferometer equipped with a high-speed feedback control system. The CCD camera’s shutter-function raises the modulating frequency, which in turn elicits a higher feedback response, thus enabling us to eliminate nearly all external disturbance. With the recent application of a system purpose-built for discriminating between numerous fringe sequences, we have also reduced processing time.     

基于可变相位延迟的激光干涉式亚纳米级微位移测量系统

激光光源具有单色性好、亮度高、方向性强和相干性强等优势,所以基于干涉原理对激光光谱进行积分可以应用于微位移测量领域。在重力方法探测过程中,因地质结构不同引起万有引力差异而造成的探测质量块位移十分微小,通常为纳米级,所以研制高精度纳米级微位移测量系统尤为重要。然而传统电容位移测量法在防止电磁干扰等方面存在不足。相比较而言,光学干涉法具备抗电磁干扰、环境适应性强等优点,且精度不亚于电容法。传统干涉系统光路复杂、难于集成,对重力仪的小型化与集成化不利。所以研制一种结构紧凑的光学干涉系统用于实现纳米级微位移测量成为亟需。基于可变相位延迟的激光干涉式方法,能够实现亚纳米级微位移测量,较传统干涉系统具备结构紧凑、易于集成的优势。本微位移测量系统由半导体激光器、起偏器、检偏器、楔形双折射晶体组和光谱仪组成。研究从以下方面展开：首先是确定测量系统方案,提出了偏振光干涉双路结构,以楔形双折射晶体组作为核心器件,将晶体间相对位移转化为o光和e光的差别化相位延迟,并对激光光谱进行积分,进而将位移变化转变为合成光强的变化;其次是建立测量位移物理模型,根据设计的双折射晶体组几何结构、位移过程与光路,确定光强变化与待测位移量之间的关系;第三是系统参数优化,为了使系统的测量误差和量程满足实际需求,利用已建立的物理模型,将测量误差和量程分别与晶体切割角度α、激光器激射波长λ建立函数关系。根据应用需求,确定适当的误差和量程取值范围,进而得到角度α和波长λ取值范围;最后加工晶体、搭建系统并进行测试。具体即以α和λ为调控参量,联合考虑“近似线性化”和“激光器光强波动误差”对系统量程进行优化仿真。同样,联合考虑“激光器光强波动误差”和“激光器波长波动误差”,并利用“系统最大位移量”（与量程有关）对系统测量误差进行优化仿真。最终确定钒酸钇晶体切割角度α为20°,激光器激射波长λ为635 nm。实验中,以10 nm为间隔利用压电陶瓷设置位移量进行位移测试,包括：系统的线性标定、系统量程和测量误差测试。另外,在保持待测位置不变的条件下,利用本位移测量系统进行了2 h不间断测量,并通过阿伦方差确定了系统的位移探测下限。实验结果表明,位移量程范围大于150 nm,位移测量误差约0.5 nm,位移探测下限为0.32 nm@23 s,探测线性度判定系数(R2)为0.999 85。综上所述,以自制楔形双折射晶体组作为核心器件的可变相位延迟激光干涉式微位移测量系统,可作为重力探测中的质量块位移测量单元。与电容法相比具有更强的环境适应性;与传统干涉系统相比具有结构简易、光路紧凑等优点,便于重力仪的小型化与集成化。