Accurate strain measurements with fiber Bragg sensors and wavelength references

Rivera, Evangeline; Thomson, D. J.

doi:10.1088/0964-1726/15/2/012

Cited by 22 publications

(10 citation statements)

References 12 publications

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“…As the strain was increased and decreased, the reflection spectrum of the FBG from the OSA was captured on a computer using LabVIEW software to interface with the OSA. The Bragg wavelength of the spectrum at each strain state was calculated using the −3 dB averaging method [14]; the values obtained are shown in Fig. 2.…”

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confidence: 99%

Influence of mounting on the hysteresis of polymer fiber Bragg grating strain sensors

Abang

Webb

2013

Opt. Lett.

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Fiber Bragg grating sensors recorded in poly(methyl methacrylate) fiber often exhibit hysteresis in the response of Bragg wavelength to strain, particularly when exposed to high levels of strain. We show that, when such a fiber grating sensor is bonded directly to a substrate, the hysteresis is reduced by more than 12 times, compared to the case where the sensor is suspended freely between two supports. © . This is important when fiber sensors are used to monitor structures that are themselves rather compliant, as is the case, for example, with a tapestry [3]. In such situations, the use of silica fiber tends to locally reinforce the structure and reports strain much lower than the true background strain in the material. As a viscoelastic material, the tensile properties of polymers are complicated; they display both hysteresis and a dependence on the timescales involved [4] and the magnitude of applied strain [5]. When a polymer optical fiber Bragg grating (POFBG) sensor is placed for several minutes under sufficient tension to cause a considerable elongation, a significant wavelength shift may remain when the tension is removed, which only gradually relaxes over time [6]. This is on the face of it a serious problem for practical applications of such strain sensors.The application of pretension [7] to the POFBG or the annealing of the fiber [8] has been reported to reduce hysteresis in some situations. However, in this Letter we show that, for many practical applications, the hysteresis will actually be much lower than expected from existing published data. The point is that the experiments that have revealed the presence of hysteresis are usually conducted by fixing the fiber at two points on either side of the sensor, with one of these points capable of being moved using a translation stage. However, when grating sensors are applied to the monitoring of strain in a structure, they would normally either be glued to the structure directly [9] or possibly embedded in it [10].In this work we compare the behavior of two identical sensors, where one is strained between two supports while the other is bonded directly to a cantilever. We show that the latter approach, which is much more characteristic of the way sensors would be applied in practice, displays hysteresis reduced more than 1 order of magnitude from the former.Two identical FBGs were fabricated in few-moded microstructured polymer optical fiber (mPOF) fabricated from poly(methyl methacrylate) (PMMA) and obtained from Kiriama Pty Ltd. Most polymer fibers in use today are based on PMMA, although it should be noted that other materials may have advantages for sensing applications [11]. The core of the fiber is bounded by three rings of 5 μm holes spaced 5 μm apart. The few-moded fiber has a core diameter of 50 μm and an outer diameter of 150 μm. A helium-cadmium laser with a wavelength of 325 nm and a power output of 30 mW was used to inscribe the Bragg gratings in the mPOF. The laser beam was focused vertically downward using a 10 cm focal length cylindric...

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Influence of mounting on the hysteresis of polymer fiber Bragg grating strain sensors

Abang

Webb

2013

Opt. Lett.

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“…The swept LO is dived into two parts at a ratio of 90:10, one part is for OSA and the other is for RTWC. Then the part of swept LO entering RTWC system is equally dived into three parts by a 1×3 fiber coupler, one part passes a hydrogen cyanide (HCN) gas cell for absolute wavelength calibration, one part passes a FP etalon, and another is directly detected by a photoelectricity conversion device for power normalization [23]. The HCN gas cell has specific absorption lines covering from 1530 nm to 1560 nm at C-band.…”

Section: Real-time Wavelength Calibration Of Swept Lomentioning

confidence: 99%

An optoelectronic equivalent narrowband filter for high resolution optical spectrum analysis

Feng

Dang

et al. 2017

Preprint

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To achieve a narrow bandwidth optical filter with a wide swept range for new generation optical spectrum analysis (OSA) of high performance optical sensors, an optoelectronic equivalent narrowband filter (OENF) is investigated and a swept optical filter with bandwidth of several MHz and swept range of several ten nanometers is built using electric filters and a swept laser as local oscillator (LO). The principle of OENF is introduced and analysis of OENF system is presented. Two electric filters are optimized to be RBW filters for high and medium spectral resolution application. Both simulations and experiments are conducted to verify OENF principle and results show that power uncertainty is less than 1.2% and spectral resolution can reach 6 MHz. Then, a real-time wavelength calibration system consisting of HCN gas cell and Fabry-Pérot etalon is proposed to guarantee a wavelength accuracy of ±0.4 pm at C-band and to reduce the influence of phase noise and nonlinear velocity of swept LO. Finally, experiments on OSA of actual spectra of various optical sensors using OENF system are conducted. Experimental results indicate that OENF system has an excellent capacity in analysis of fine spectrum structures.

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“…In recent years fiber Bragg gratings (FBGs) have undergone a spectacular transformation from passive optical reflectors to active devices [1][2][3][4][5][6][7] used, for example, in temperature [8], strain [9], chemical [10] and acoustic [11] measurements. FBGs have been developed primarily as ''mirrors'' for light which is transmitted through single mode fibers.…”

Section: Introductionmentioning

confidence: 99%

Time-resolved photoacoustic spectroscopy using fiber Bragg grating acoustic transducers

Yang

Barnes

Loock

et al. 2007

Optics Communications

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An acoustic transducer based on a fiber Bragg grating (FBG) is presented and characterized for use in time-resolved laser-induced photoacoustic spectroscopy (PAS) on solid samples. The photoacoustic wave was generated by pulsed laser excitation of immobilized carbon black or erbium oxide powder, and detected by recording either the transmission or reflection spectrum of a clamped fiber Bragg grating (FBG). The characterization of the FBGs photoacoustic response is based on the experimental comparison with a static lateral strain source and on theoretical analysis using the piecewise-uniform approach to photoelastic theory. The temporal resolution of the response is determined by the arrangement of the FBG with respect to the source of the acoustic wave and is better than 150 ns, as was verified in a deconvolution analysis. The method has not only a fast time response but also is simple, inexpensive, and accurate as indicated by the good agreement of the experimental photoacoustic spectrum with previous measurements.

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Accurate strain measurements with fiber Bragg sensors and wavelength references

Cited by 22 publications

References 12 publications

Influence of mounting on the hysteresis of polymer fiber Bragg grating strain sensors

Influence of mounting on the hysteresis of polymer fiber Bragg grating strain sensors

An optoelectronic equivalent narrowband filter for high resolution optical spectrum analysis

Time-resolved photoacoustic spectroscopy using fiber Bragg grating acoustic transducers

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