Prototype Industrial Multi-parameter F.O. Sensor Using White Light Interferometry

Trouchet, D.; Laloux, Bernard; Graindorge, Philippe

doi:10.1007/978-3-642-75088-5_35

Cited by 12 publications

(4 citation statements)

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“…Assuming that n,L5 and nrLr are constant during the short time for wavelength tuning and signal detection, and X,5 and Xefld are the starting and the end wavelengths of the tuning range (i.e., LX = Xend -X5), respectively, then, Xend Xend 47n L -n L Acp= J -xdX=J S s r r xcJX (3) start start…”

Section: Principlementioning

confidence: 99%

<title>Localized long-gauge-length fiber optic sensor demodulated with wavelength tuning technique</title>

1997

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A novel single-ended fiber optic sensor capable of making absolute displacement measurements over arbitrarily long distance (a few centimeters to meters) is demonstrated. The sensor's gauge length is defmed by an in-fiber broad bandwidth Bragg grating and a mirror coated at the end of the same fiber. This sensor has been demodulated optoelectronically by means of a laser wavelength scanning technique. The absolute measurement of perturbation is achieved by measuring the perturbation induced optical path difference (OPD) changes with respect to the OPD of a reference interferometer that can be isolated from environmental perturbations and remain constant. This sensor is well suited for structural applications, especially the measurement of hoop stress changes in concrete columns that are wrapped within layers of advanced composite material for rehabilitation or strengthening. Keywords:Interferometric sensor, strain and temperature measurement, fiber optic sensor, Bragg gratings, advanced composite monitoring ThTRODUCTION Low coherence or white light interferometers have attracted attention in structural engineering mainly because they provides an absolute displacement measurement [l] [2]. A low coherence interferometric sensor usually consists of a short coherence length source and a pair of Michelson interferometers; one serves as the sensor, the other provides a reference. This type of source guarantees that interference arises only when the optical path differences (OPD) of the two interferometers match within a short distance, i.e., the coherence length of the source. Conventionally, a mechanical moving system is used for matching the OPD. The disadvantages with such a system are limited operating range and speed, large and heavy demodulation system, and possible mechanical failure.Considerable effort has been directed towards developing low coherence sensing systems without mechanical moving parts. However the operating range of such systems is limited to a few hundreds of micrometers[3}[4J, which is far smaller than often required in structural engineering. Another drawback with a conventional Michelson configuration sensing interferometer is that the sensor is not localized. In reference {5], a design allowing localized sensing has been proposed. However, the bulk connectors in the sensing array make this approach unsuitable for applications where sensors have to be embedded within structures.In this paper, we demonstrate a system with a novel configuration for the sensing interferometer and a new demodulation technique that avoids any mechanically moving parts. This compact system performs absolute sensing and demodulates the sensing signal optoelectronically over a large range (The demodulation of a signal corresponding to a sensing fiber length change of -2% of the sensing gauge length has been demonstrated). In addition, it is possible to arrange a number of such sensing interferometers on the same optical fiber and multiplex them in the wavelength domain. PRINCIPLE Fig. 1 illustrates schematically the ...

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Section: Principlementioning

confidence: 99%

<title>Localized long-gauge-length fiber optic sensor demodulated with wavelength tuning technique</title>

1997

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“…The operating range of an optical fibre sensor with "white-light" interferometry is no longer limited to itas in conventional interferometers but decided by the scanning range of the processing interferometer. From equation 3 and figure 3a, by using a linear CCD array of length L, the operating range of an electronic scanner R5 in terms of phase is given by R=ksinctL (4) From figure 3b, we get…”

Section: Principles Of Operationmentioning

confidence: 99%

<title>Large dynamic range electronically scanned "white-light" interferometer with optical fiber Young's structure</title>

Chen

Rogers

Meggitt³

1991

Fiber Optic Sensors: Engineering and Applications

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A novel optical-fibre version of Young's interferometer using a low coherent light source and a linear CCD detector is described. With its unique, simple structure, this interferometer greatly reduces the spatial coherence mismatch from which other electronically scanned "white-light" interferometers suffer. Experimental results are presented for the use of this interferometer as a strain or temperature sensor with large dynamic range.

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“…We shall show that although the low-coherence Michelson fiber optic interferometer is simple, works reliably and is of low cost, it is a mechanical system that is limited in response time, is rather bulky and prone to failure due to lead sensitivity. Considerable effort has been directed at developing low-coherence sensing systems without mechanical moving parts; however, the operating range of such systems is limited to lie within a few hundred micrometers [3,4], which is smaller than required in many structural engineering applications. Another drawback with a conventional Michelson sensing interferometer is that the sensing gage length is not localized.…”

Section: Introductionmentioning

confidence: 99%

Localized long gage fiber optic strain sensors

Fan¹,

Huang²,

Measures³

1998

Smart Mater. Struct.

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Long gage length integrated strain sensing is frequently required in structural measurement applications. An optical fiber structural sensing system based on a low-coherence Michelson interferometer was built and shown to be of low cost and capable of absolute measurement and moderate accuracy for quasistatic measurement of strain or structural deformations. This type of sensor was found to be useful for monitoring the hoop-strain around structures like shells, cylinders and columns. We have also shown that localization of the sensing section of an optical fiber can be achieved through the use of one or more Bragg gratings. In effect, the sensing section of the optical fiber acts as a Fabry-P érot interferometer. When a low-coherence source is used, interference is only attained when the cavity length of this Fabry-P érot matches the optical path difference (OPD) between the two mirrors of a fiber optic Michelson interferometer. Changes in the sensing length are determined from the commensurate changes that must be made to the reference Michelson interferometer to maintain some fixed degree of interference. Recently, we have developed a novel single-ended localized fiber optic sensor for making absolute strain measurements over arbitrary (cm to m) long gage lengths using a tunable laser. The sensor's gage is again defined between two in-fiber broad-bandwidth Bragg gratings or one grating and the mirror coated end of the same fiber. For this sensing system the change in the OPD of the sensing Fabry-P érot interferometer with respect to the OPD of a fixed Michelson reference interferometer is determined from the measurement of the phase change, recorded by a low-pass filtered photodetector, associated with a known sweep of the laser wavelength. This tunable laser demodulation scheme avoids the use of moving parts and lends itself to a compact, portable system. This type of sensor is particularly well suited for certain structural applications, such as monitoring the time variation in the hoop-stress in composite material wraps used to rehabilitate and strengthen corroded or earthquake damaged concrete columns.

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Prototype Industrial Multi-parameter F.O. Sensor Using White Light Interferometry

Cited by 12 publications

References 1 publication

<title>Localized long-gauge-length fiber optic sensor demodulated with wavelength tuning technique</title>

<title>Localized long-gauge-length fiber optic sensor demodulated with wavelength tuning technique</title>

<title>Large dynamic range electronically scanned "white-light" interferometer with optical fiber Young's structure</title>

Localized long gage fiber optic strain sensors

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