Refractometric Properties of a TFBG Sensor Demodulated Using α-Shape Modified Delaunay Triangulation

Fazzi, Luigi; Groves, Roger M.

doi:10.3390/opt2020012

Cited by 8 publications

(7 citation statements)

References 23 publications

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“…In the original version, the method was based on determining the maxima and minima of the cladding mode comb to determine the normalised area occupied by the cladding mode [ 15 ]. The more precise version uses the Delaunay triangulation method [ 16 , 17 ]. These methods belong to the group that uses information about changes in the transmission coefficient for the entire range of the cladding modes.…”

Section: Methods Of Tfbg Spectra Analysismentioning

confidence: 99%

Single- and Double-Comb Tilted Fibre Bragg Grating Refractive Index Demodulation Methods with Fourier Transform Pre-Processing

Cięszczyk

Skorupski

Panas

2022

Sensors

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The development of fibre optic sensors for measuring the refractive index is related to the creation of new periodic structures and demodulation algorithms for the measured spectrum. Recently, we proposed a double-comb Tilted fibre Bragg grating (DCTFBG) structure. In this article, we analyse such a structure for measuring the refractive index in comparison to a single classical structure. Increasing the number of modes causes a significant change in the Fourier spectrum of optical spectra. For the purpose of data pre-processing, we propose the Fourier Transform as a filtering method in the frequency domain. Then, we analyse separately the band-filtered optical spectra for several frequency ranges. For quantitative analysis, we use algorithms that use quantitative changes in the transmission, i.e., the method of the envelope and the length of the spectrum contour. We propose the use of the Hilbert transform as the envelope method. The second type of algorithms used are methods determining the shift of spectrum features along the wavelength axis. The method of determining the centre of gravity of the area bounded by the envelope and the maximum of the second derivative of the smoothed cumulative spectrum contour length is proposed here. Using the developed methods, the measurement resolution was achieved at the level of 2 × 10−5 refractive index unit.

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Section: Methods Of Tfbg Spectra Analysismentioning

confidence: 99%

Single- and Double-Comb Tilted Fibre Bragg Grating Refractive Index Demodulation Methods with Fourier Transform Pre-Processing

Cięszczyk

Skorupski

Panas

2022

Sensors

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“…For the group of modes, the most popular here is the envelope method [9], which is used not only for the measurements of the refractive index but also for the determination of the liquid level [21] and the bending curvature [18]. This method also has a more advanced version in the form of approximation of the area using a triangle mesh [22].…”

Section: Methods Of Tfbg Spectra Analysismentioning

confidence: 99%

Methods of Projecting Mode Amplitude Changes on the Wavelength Axis in Order to Determine the Bending Radius on the Basis of TFBG Grating Spectra

Cięszczyk

Harasim

Ormanbekova

et al. 2021

Sensors

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Tilted fibre Bragg grating (TFBG) are used as sensors to determine many quantities such as refractive index, temperature, stress, rotation and bending. The TFBG spectrum contains a lot of information and various algorithms are used for its analysis. However, most of these algorithms are dedicated to the analysis of spectral changes under the influence of the refractive index. The most popular algorithm used for this purpose is to calculate the area occupied by cladding modes. Among the remaining algorithms, there are those that use the determination of the cut-off wavelength as a surrounding refractive index (SRI) indicator. Projection on the wavelength axis can also be used to calculate the bending radius of the fibre. However, this is a more difficult task than with SRI, because the mode decay in bending is not so easy to catch. In this article, we propose a multi-step algorithm that allows to determine the impact of bending on mode leakage. At the same time, the place on the wavelength from the side of the Bragg mode and the ghost mode is determined, which represents the cladding mode radiated from the cladding under the influence of bending. The developed algorithm consists of the following operations carried out on the transmission spectrum: Fourier filtering, calculation of the cumulative value of the spectral length, low-pass filtering of the cumulative curve or its corresponding polynomial approximation, determination of the first and second derivative of the approximated curve, and projection of the second derivative of the curve on the wavelength axis. The shift of the wavelength determined in this way indirectly indicates the bending radius of the optical fibre. Based on multiple measurements, we prove that the presented algorithm provides better results when determining the bending radius compared to other algorithms adopted for this purpose and proposed for SRI measurements. Additionally, we analyse the method of determining the shift of a fragment of the spectrum using the phase of the discrete Fourier transform.

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“…This results, in the sensor's transmission spectrum, of the generation of many close resonance peaks placed at lower wavelengths than the fundamental Bragg peak (which is usually the only resonance in the fibre Bragg grating (FBG) spectrum). In particular, in the case of weakly TFBG (θ ⩽ 15 • ), which has been used in this work, three different kinds of peaks can be distinguished in the spectrum: the Bragg, the Ghost and the cladding peaks [14]. These appear in the transmission spectrum as figure 2 shows, and their sensing properties can be exploited to perform three parameter measurements with a single TFBG sensor.…”

Section: Tfbg Sensing Theorymentioning

confidence: 99%

“…Hence, by performing a preliminary calibration, both the Bragg and the Ghost peaks can be used to measure simultaneously and separately the temperature and the strain variation of the material where the sensor is embedded [8]. At the same time, the envelope area of the upper and lower cladding resonance peaks can be used to detect independently the RI variation of the medium surrounding the TFBG sensor [7,[14][15][16].…”

Section: Tfbg Sensing Theorymentioning

confidence: 99%

“…Hence, to optimise the RI measurement performance of the TFBG, the fitting correlation function was obtained inside this RI range. A study on the RI measurement performance was made as in [14]. Indeed, as a strain variation induces a shifting of the cladding peaks wavelength, it can comprise the accuracy of the measured RI by influencing the value of the envelope area.…”

Section: Ri Calibration Of the Tfbg Sensormentioning

confidence: 99%

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Monitoring of silicone adhesive in space solar cells with an embedded multi-parameter TFBG sensor in a simulated space environment

Fazzi

Dias

Hołyńska

et al. 2022

Meas. Sci. Technol.

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In this research the ageing of a silicone adhesive in a simulated space environment is monitored through an embedded three parameter tilted Fibre Bragg Grating (TFBG) sensor. Here, the silicone is used as an adhesive between two thin cover glasses, and the space environmental ageing is simulated by thermal cycles in high vacuum conditions (better than 10-5 mbar). These operational conditions can induce variations in the silicone adhesive with respect to its original properties such as dimensional stability, chemical composition, generated contaminants, discoloration and, mechanical or optical degradation. Therefore, surrounded by the adhesive, in the centre of the cover glass sandwich, a weakly tilted FBG sensor was placed to obtain information from its spectra on the state of the polymer during the test. Specifically, the temperature, strain and refractive index (RI) of the silicone can be, simultaneously and separately, measured from the spectrum of a single TFBG from selected resonance peaks. These parameters can be used to evaluate the “health” state of the silicone during the vacuum thermal cycles. The simultaneous TFBG thermomechanical measurements gave a solution to the non-localized measuring issues when using classical fibre optic or electrical strain-gauges and a thermocouple (TC) to compensate the temperature and to better understand the material behaviour. The trends of the measured parameters are reported during the entire testing time, and at the end of the test, the optical fibre sensor measured a negative strain of ~100 με and a positive RI variation of ~0.002.

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Refractometric Properties of a TFBG Sensor Demodulated Using α-Shape Modified Delaunay Triangulation

Cited by 8 publications

References 23 publications

Single- and Double-Comb Tilted Fibre Bragg Grating Refractive Index Demodulation Methods with Fourier Transform Pre-Processing

Single- and Double-Comb Tilted Fibre Bragg Grating Refractive Index Demodulation Methods with Fourier Transform Pre-Processing

Methods of Projecting Mode Amplitude Changes on the Wavelength Axis in Order to Determine the Bending Radius on the Basis of TFBG Grating Spectra

Monitoring of silicone adhesive in space solar cells with an embedded multi-parameter TFBG sensor in a simulated space environment

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