ZrO2 thin-film-based sapphire fiber temperature sensor

A submicrometer-thick zirconium dioxide film was deposited on the tip of a polished C-plane sapphire fiber to fabricate a temperature sensor that can work to an extended temperature range. Zirconium dioxide was selected as the thin film material to fabricate the temperature sensor because it has relatively close thermal expansion to that of sapphire, but more importantly it does not react appreciably with sapphire up to 1800 °C. In order to study the properties of the deposited thin film, ZrO2 was also deposited on C-plane sapphire substrates and characterized by x-ray diffraction for phase analysis as well as by atomic force microscopy for analysis of surface morphology. Using low-coherence optical interferometry, the fabricated thin-film-based sapphire fiber sensor was tested in the lab up to 1200 °C and calibrated from 200° to 1000 °C. The temperature resolution is determined to be 5.8 °C when using an Ocean Optics USB4000 spectrometer to detect the reflection spectra from the ZrO2 thin-film temperature sensor.     

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。     

Fiber-optic interferometric displacement sensor

Translated from Izmeritel'naya Tekhnika, No. 6, pp. 28–29, June, 1988.     

White-light interferometric fiber-optic pressure sensor

A novel configuration for a fiber-optic white-light interferometric sensor is presented which allows for absolute measurements of hydrostatic pressure with an improved operation range. The performance of two fibers (York bow-tie 800 and especially designed elliptical-core side-hole fiber) used as sensing elements was experimentally studied. The sensor itself was composed of two equal lengths of the fiber spliced at 90°. This structure assures temperature compensation and enables application of a Wollaston prism as a receiving interferometer. A step delay line made of crystalline quartz was used to increase the operation range of the sensor     

An interferometric angular and linear displacement sensor

Translated from Izmeritel'naya Tekhnika, No. 2, pp. 17–18, February, 1988.     

Single-arm double-mode double-order planar waveguide interferometric sensor

A sensor is described for which interference measurements of the phase delay between two propagating modes of different orders in a slab thin-film waveguide are used as the sensing technique. The basic building block of the sensor is a polymer film doped with an indicator dye such as Bromocresol Purple. The modes of two orders such as TM(0) and TM(1) are simultaneously excited in the light-guiding film with a focusing optics and a prism coupler. The modes are decoupled from the film and recombined to produce an interference pattern in the face of an output optical fiber. The sensitivity of the sensor to the ambient temperature change is 1.5 degrees C, and the sensitivity to NH(3) is 200 parts in 10(6) for one full oscillation of the signal.     

Micro-air-gap based intrinsic Fabry-Perot interferometric fiber-optic sensor

A simple intrinsic Fabry-Perot interferometric (IFPI) sensor is developed. The sensor is fabricated by two micro air gaps as reflective mirrors in a fiber to form a Fabry-Perot cavity. Theoretical and experimental studies of the sensor are described. Experimental results show that high resolution and high sensitivity can be achieved. Two structures of micro-air-gap-based IFPI sensors offer more applications than other IFPI sensors.     

Triple-sensor multiplexed frequency-modulated continuous-wave interferometric fiber-optic displacement sensor

A triple-sensor multiplexed fiber-optic displacement sensor, which can measure the displacements of three different objects or the three-dimensional displacement of a single object, is introduced. The sensor is based on the principles of optical frequency-modulated continuous-wave interference and frequency-division multiplexing. The beat signals from the individual sensors are assigned in the frequency domain and separated with different electrical bandpass filters. The displacements of objects can be determined simultaneously by detecting the phase shifts of the corresponding signals. The cross talk between the individual sensors is evaluated, and an accuracy of 0.08 microm in a dynamic range of 1000 microm is achieved.     

用于光纤干涉传感器的高稳定PGC解调技术

相位生成载波(PGC)解调技术具有高灵敏度、线性度好和动态范围广的优点,因此广泛应用于分布式光纤传感器中.本文提出了一种单路微分相除和微分自相乘的PGC(PGC-SDD-DSM)解调算法,该解调算法对载波相位调制深度和光强度干扰均不敏感.仿真实验显示,与PGC单路微分相除(PGC-SDD)解调算法、传统的PGC微分交叉...     

Low-coherence interferometric sensor system utilizing an integrated optics configuration

The implementation of a twin Mach-Zehnder reference interferometer in an integrated optics substrate is described. From measurements of the fringe visibilities, an identification of the fringe order is attempted as a way to provide an absolute sensor for any parameter capable of modifying the difference in path length between two interfering optical paths.     

White-light interferometric fiber-optic strain sensor from three-peak-wavelength broadband LED source

A white-light fiber-optic interferometer working in the spatial domain, using a special three-peak-wavelength LED as a light source and one of the two arms of the Michelson interferometer as a strain sensor, is presented. Based on the Gaussian spectrum distribution function, a simple spectrum-decomposing method is used to describe the special three-peak-wavelength LED source. Experimental and theoretical analyses show that this special three-peak-wavelength LED source can be used in white-light interferometry to simplify the problem of central-fringe identification. A white-light Michelson fiber-optic strain-sensing system that uses a tapered cantilever beam is described. Experimental results show that the strain measured by the fiber-optic sensor is linear and always less than the surrounding matrix.     

Measurement of three-dimensional temperature fields with interferometric tomography

Optical computerized tomography (OCT) technology is used to reconstruct the asymmetric three-dimensional temperature field generated by radiators and electronic chips. First, the OCT method is described. Second, the reconstructed results are tested by a double-cylinder radiator model. Finally, OCT is applied to reconstruction of the temperature field above the surface of a CPU. The air-temperature field above a CPU circuit can be imaged with an OCT system that reflects whether the heat production from different parts of the CPU is even; therefore possibly the technique can be used to determine whether the integrated-circuit design in the CPU is smart.     

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).     

Vibration monitoring by using a dynamic proximity sensor with interferometric encoding

An optical sensor for the dynamic measurement of proximity is presented. The sensor combines an extrinsic geometric transducer with interferometric encoding for high vibration sensitivity. Static calibration showed a unique variation in interference contrast over at least 60 fringes, leading to a measurement range of 20 mum and a resolution of at least 0.033mum. Dynamic excitation by using low-amplitude vibrations at 3.6 kHz showed a similar contrast variation, verifying fringe discrimination up to the sixth order. With verification of dynamic performance over all 60 fringes, the sensor should offer a low-cost approach to vibration monitoring in electrical switchgear.     

Resolution improvement by single-exposure superresolved interferometric microscopy with a monochrome sensor

Single-exposure superresolved interferometric microscopy (SESRIM) by RGB multiplexing has recently been proposed as a way to achieve one-dimensional superresolved imaging in digital holographic microscopy by a single-color CCD snapshot [Opt. Lett. 36, 885 (2011)]. Here we provide the mathematical basis for the operating principle of SESRIM, while we also present a different experimental configuration where the color CCD camera is replaced by a monochrome (B&W) CCD camera. To maintain the single-exposure working principle, the object field of view (FOV) is restricted and the holographic recording is based on image-plane wavelength-dispersion spatial multiplexing to separately record the three bandpass images. Moreover, a two-dimensional extension is presented by considering two options: time multiplexing and selective angular multiplexing. And as an additional implementation, the FOV restriction is eliminated by varying the angle between the three reference beams in the interferometric recording. Experimental results are reported for all of the above-mentioned cases.     

Cross-talk fiber-optic temperature sensor

The temperature sensitivity of cross talk between closely spaced cores in a common cladding is calculated and compared with measurements. A periodic variation in core contrast is observed when one core is illuminated and the temperature is changed. The variation in light distribution, which is ascribable to a change in coupling between the cores, agrees with theoretical predictions. It is shown that cross talk can be made to be a sensitive, predictable function of temperature or by proper selection of materials, wavelength, and fiber geometry essentially temperature independent.     

Low-coherence Michelson interferometric fiber-optic multiplexed strain sensor array: a minimum configuration

A minimum configuration Michelson fiber-optic low-coherence interferometric quasi-distributed sensing system is proposed that permits absolute length measurement in remote reflective sensor arrays. The sensor's reflective signal characteristics have been analyzed, and the relationship between intensities of light and number of sensors is given for evaluation of multiplexing potential. The proposed sensing scheme will be useful for the measurement of strain distribution. An important application may be strain monitoring in smart structures. Experimentally, four-sensor array has been demonstrated.     

Dependence of room temperature fracture strength on strain-rate in sapphire

Single crystal,c-axis oriented sapphire filaments have been tension tested as a function of surface conditions and environment, and as a function of strain-rate. Filaments in the as-grown condition were shown to have failure strengths independent of the amount of water in the environment when tested at 0.002 min^–1. This independence was correlated with fractographic determinations showing internal nucleation of fracture. In contrast, introduction of surface flaws was shown to reduce the strength to a level dependent upon the moisture content of the test environment. Filaments having as-grown surfaces were shown to fail at strength levels dependent upon the strain-rate. When the latter was increased stepwise in order of magnitude from 0.002 to 2.0 min^–1, the fracture strength increased by a total of 70 kg mm^–2, or 30% of the lowest average value. It is argued that the latter behaviour is different from static fatigue and that it is consistent with the Orowan model of subcritical crack extension in brittle materials. Experimental data are used to calculate background flaw sizes in the range of 0.22 to 0.39 m and maximum crack extension at the slowest rate (0.002 min^–1) of 0.15 m.