Remote displacement measurement using a passive interferometer with a fiber-optic link

Remote displacement measurement is demonstrated using a Fabry-Perot cavity with a multimode optical fiber link. The sensing cavity modulates, as a function of its length, the spectrum of a light-emitting diode (LED). The light returns via the fiber and is analyzed by a tunable reference cavity. A closed-loop control causes the reference cavity to track the sensing cavity length within 2 x 10(-12) m. Displacement range is 2 x 10(-6) m. The reference cavity length is measured interferometrically, using a laser, to obtain the sensing cavity length. Advantages of this sensing technique include compatibility with multimode fiber-optic components, high immunity to optical losses, and large dynamic range.     

一种基于法布里-珀罗干涉仪的位移测量方法

介绍了一种基于法布里-珀罗干涉仪的位移测量方法,为了克服通常的法布里-珀罗干涉仪在位移测量范围方面的局限,采用两束可调激光分别对法布里-珀罗腔的两个相邻谐振峰的光频率进行追踪测量,能够得到任意时刻法布里-珀罗腔的长度,从而实现对测量镜位移的测量,测量范围可以达到毫米量级。对影响测量精度的主要因素进行了简要分析,结果表明采用本方法能够实现纳米级精度位移测量。     

Dynamics of a noncontacting, white light Fabry-Perot interferometric displacement sensor

A white light extrinsic Fabry-Perot interferometer is implemented as a noncontacting displacement sensor, providing robust, absolute displacement measurements with micrometer accuracy at a sampling rate of 10 Hz. This paper presents a dynamic model of the sensing cavity between the sensor probe and the nearby target surface using a Fabry-Perot etalon approach obtained from straightforward electromagnetic field formulations. Such a model is important for system characterization, as the dynamically changing cavity length imparts a Doppler shift on any signals circulating within the sensing cavity. Contrary to previously published results, Doppler-induced shifting within the low-finesse sensing cavity is shown to significantly distort the measurement signal as recorded by the sensor. Experimental and simulation results are compared, and the direct effects of cavity dynamics on the measurement signal are analyzed along with their indirect impact on sensor performance. This document has been approved by Los Alamos National Laboratory for unlimited public release (LA-UR 12-00301).     

绝对测量小距离的波长扫描-光纤双干涉仪系统

介绍了用于测量小位移的波长扫描－光纤法布里－珀罗干涉仪系统。用扫描波长作为“中介”,比较参考腔长和传感腔长,可以“准绝对”地测量传感腔的长度。这个测量与波长扫描的准确度无关,仅依赖于参考腔的长度,而通过将传感腔改变一个已知距离,就可以简单地“自标定”参考腔的长度。     

Mode-locking external-cavity laser-diode sensor for displacement measurements of technical surfaces

A novel laser sensor for position measurements of technical solid-state surfaces is proposed. An external Fabry-Perot laser cavity is assembled by use of an antireflection-coated laser diode together with the technical surface. Mode locking results from pumping the laser diode synchronously to the mode spacing of the cavity. The laser cavity length, i.e., the distance to the measurement object, is determined by evaluation of the modulation transfer function of the cavity by means of a phase-locked loop. The mode-locking external-cavity laser sensor incorporates a resonance effect that results in highly resolving position and displacement measurements. More than a factor-of-10 higher resolution than with conventional nonresonant sensing principles is achieved. Results of the displacement measurements of various technical surfaces are reported. Experimental and theoretical investigations are in good agreement.     

Absolute refractometry of dry gas to ±3 parts in 10⁹

We present a method of measuring the refractive index of dry gases absolutely at 632.8 nm wavelength using a Fabry-Perot cavity with an expanded uncertainty of <3×10?? (coverage factor k=2). The main contribution to this uncertainty is how well vacuum-to-atmosphere compression effects (physical length variation) in the cavities can be corrected. This paper describes the technique and reports reference values for the refractive indices of nitrogen and argon gases at 100 kPa and 20 °C with an expanded uncertainty of <9×10?? (coverage factor k=2), with the additional and larger part of this uncertainty coming from the pressure and temperature measurement.     

Phase-shifting interferometry with equal phase steps by use of a frequency-tunable diode laser and a Fabry-Perot cavity

A phase-shifting interferometry (PSI) with equal phase steps by use of a frequency-tunable diode laser and a Fabry-Perot cavity is proposed for the Carré algorithm. The measurement accuracy of the Carré algorithm depends on the equality of the phase steps. Using the Fabry-Perot cavity as a highly stable optical frequency reference, a high degree of phase step equality can be realized in PSI with an optical frequency shift. Our experimental scheme realizes an optical frequency step equality higher than 5.1 x 10(-5) and a measurement repeatability of lambda/800.     

An Active Fibre-optic Interferometric Sensor Based on a Low Finesse Fibre-optic Fabry-Perot

Abstract

We demonstrate a novel active fibre-optic interferometric sensor based on a temperature-stabilized low-finesse fibre-optic Fabry-Perot. In this apparatus, information on the optical phase was extracted from the frequency shift of the He-Ne laser of which the cavity length was thermally tuned to compensate change in the interference signal. It is shown that an improvement in the stability of the interference signal by two orders of magnitudes can be realized. The tracking achievable between the Fabry-Perot interferometer and the laser was better than 1 part in 10⁸. That is, the relative frequency stability of the laser was ? 1·0 × 10^?8 over an interval of tens of minutes. Detection of a change of 5 nm in the optical path length of the fibre-optic Fabry-Perot was also demonstrated. The dynamic range of this interferometer is over 40 dB and the linearity characteristics are excellent. These performance characteristics were limited by the long-term thermal drift of the apparatus, not the low reflectivity of the fibre ends of the Fabry-Perot interferometer.     

Intermodal beat length measurement with Fabry-Perot optical fiber cavities

We present a new technique for measuring the intermodal beat length of a two-mode optical fiber. We formed a Fabry-Perot fiber cavity by depositing reflective mirrors on the fiber tips. As the fiber is stretched, two series of resonance peaks are observed. One series is due to the resonance of LP(01 q) modes and the other is due to the LP(11 q) modes. From the separation of resonance peaks as a function of cavity length, we deduce the intermodal beat length of the fiber. The measurement principle and the experimental confirmation are discussed.     

折叠腔法布里—珀罗干涉及其透射光相位变化的研究

利用折叠腔法-珀干涉仪实现了高精度位移测量,使干涉级次的当量缩小了一倍,而且扩大了法-珀干涉仪的测量范围。但折叠腔法-珀干涉仪透射光的相位在经立体棱镜反射时发生了变化,本文对折叠腔法-珀干涉仪及其透射光相位的变化进行了分析研究。     

Optical contamination screening of materials with a high-finesse Fabry-Perot cavity resonated continuously at 1.06- microm wavelength in vacuum

An optical-loss measurement system based on a resonant Fabry-Perot cavity at 1.06 mum in vacuum has been developed for independent monitoring of the cavity total loss and the optical absorption loss. Maintenance of cavity resonance over a one-month period allows the assessment of long-term degradation of the cavity optics in the presence of outgassing materials, with sensitivities of 5 ppm/yr for total cavity loss and 2 ppm/yr for cavity absorption loss. Test results for light-emitting diodes, Kapton-insulated cable assemblies, and Vac-seal epoxy adhesive are given. Scaling of these results to the optical performance requirements of LIGO is discussed.     

腔长损耗对非本征F-P腔光纤传感器的影响

根据光学法布里-珀罗(F-P)腔基本原理,运用单模光纤能量散射模型分析了腔长损耗对非本征F-P腔输出光强度的影响.实验过程中所用的F-P腔由单模光纤端面和弹性硅片组成.实验结果表明,非本征F-P腔输出光强幅度随腔长增大逐渐衰减,其输出特性曲线中不同部分相同周期的线性工作区间却对应不同的测量量程和灵敏度,所以强度型光纤F-P腔传感器初始腔长应基于传感器的性能指标进行选取.     

High-resolution interrogation technique for fiber optic extrinsic Fabry-Perot interferometric sensors by the peak-to-peak method

An improved peak-to-peak method is developed for interrogating the absolute cavity length of fiber optic extrinsic Fabry-Perot interferometric (EFPI) sensors with high resolution. A fiber Fabry-Perot tunable filter (FFP-TF) is used to scan the optical spectrum of an EFPI, and the problems caused by the nonlinear performance and poor repeatability of the FFP-TF are removed by using a wavelength calibration technique. A linear fitting is used to calculate the wavelength spacing between two adjacent apexes in the optical spectrum, and the cavity length can be retrieved using this wavelength spacing. The experimental results show that the measuring resolution is improved from 25 to 1 microm, and a linear output is also obtained.     

Intracavity iodine cell spectroscopy with an extended-cavity laserdiode around 633 nm

The purpose of the work described was to develop a tunable laser diode which is as easy to use as a He-Ne laser stabilized on iodine. The particularity of this experiment is the use of I₂ cell placed inside the extended cavity laser (ECL). The experimental set-up mounted takes the form of a lambdameter which gives the wavelength to one part in 10⁶, a Fabry-Perot (FP) interferometer for mode analysis and a beat-frequency measurement system. The FP interferometer has the particular feature of a second I₂ cell which makes it possible to detect the iodine transitions by simple visual inspection of an oscilloscope. Many transitions, some much more intense than the usual R(127)11-5 transition, are under study. We worked mainly on P(33) 6-3 since this is inside the range of our beat-frequency system. Results are promising: the free running relative frequency stability is about three parts in 10¹⁰ and the locked-laser relative frequency stability about three parts in 10¹¹ after 80 s. This is already good enough for use as a wavelength standard for length and for interferometric measurement     

调频连续波激光干涉光纤温度传感器

本文提出了一种调频连续波激光干涉非本征型法珀腔光纤温度传感器。使用具有较高热膨胀系数的不锈钢圆管封装法珀腔制成温度传感探头。不锈钢圆管作为法珀腔腔体的同时也是温度敏感元件。通过调频连续波干涉测量技术测量法珀腔因受热膨胀所产生的腔长变化量,实现对温度的传感。实验结果表明,该光纤温度传感器测温分辨率达到了0.0002 ℃,温度测量灵敏度可达3022 nm/℃。此温度传感器不仅具有较高的灵敏度与分辨率,且结构简单稳定,具有良好的应用前景。     

Straightness measurements by use of a reflection confocal optical system

Straightness measurement is a very important technique in the field of mechanical engineering. A particular application for straightness measurement is high-accuracy machining on a diamond-turning lathe. We propose a novel, to our knowledge, optical method for measuring the straightness of motion, and its mathematical analysis is outlined. The technique is based on measurement of the lateral displacement of point images by use of reflection confocal optical systems. The advantages of this method are that (i) the lateral displacements in the direction of the two axes perpendicular to the optical axis can be measured, (ii) the rotation angles around all three axes can be measured, and (iii) reflection optical systems are more compact in length than are transmission optical systems.     

Wavenumber scanning-based Fourier transform white-light interferometry

Fourier transform white-light interferometry recovers the optical path difference of an interferometer by measuring the phase change caused by scanning wavelength. However, the optical spectrum, obtained by wavelength scanning method (λ-method), contains a chirp in period. The chirp would induce deviation and decrease the measurement accuracy. An improved method, the wavenumber scanning method (k-method), is proposed and experimentally demonstrated, in which there is no chirp in the optical spectrum. The measurement results using the k-method and the λ-method are compared experimentally. The experimental results show that the standard deviation of the measurement results decreases from 0.015 to 0.004?μm, when an extrinsic Fabry-Perot interferometer with a cavity length of 387?μm is interrogated.     

激光干涉仪在纳米测量中的典型应用

激光干涉仪具有测量分辨力高、测量结果可溯源等优点,在纳米测量中的应用日益广泛。介绍纳米测量机和低膨胀材料线膨胀系数测量装置中应用的迈克尔逊型激光干涉仪以及在高准确度位移测量装置中应用的法布里-珀罗型激光干涉仪,并结合这些实例对激光干涉仪光学系统设计、测量环境控制、迈克尔逊干涉仪非线性误差补偿以及法布里-珀罗干涉仪量程扩展等方面的关键问题进行分析和总结。所述原则和方法对实现纳米级测量准确度具有重要意义,可为高准确度激光干涉仪的研制及其在纳米测量中的更广泛应用提供技术参考。     

High-precision velocimetry: optimization of a fabry-perot interferometer

We present the optimization of a Fabry-Perot velocimeter designed to measure speed at a few millimeters per second with a relative uncertainty of 10(-8). We focus on the accuracy and the optimization of the Fabry-Perot, with a review of the uncertainties related to the geometry, the beam shape, and the Doppler frequency measurement. These errors are quantified to ensure that the required accuracy is reached. We then describe the practical implementation and show the results.     

圆柱形声学共鸣腔特征长度的精密计量

声学共鸣腔特征长度是声学法测量玻尔兹曼常数的一个重要参数,其测量不确定度的量值直接影响着玻尔兹曼常数k的不确定度大小。介绍了研制的高精度圆柱形声学共鸣腔特征长度测量系统,阐述了其中的关键技术,实现了对测量结果进行环境参数的实时修正。测试数据表明,该测量系统对圆柱形声学共鸣腔特征长度的测量不确定度为0.60μm,3次测量标准差为0.20μm。