Interrogation of a Sensor Array of Identical Weak FBGs Using Dispersive Incoherent OFDR

Clement, Juan; Torregrosa, G.; Hervás, J.; Barrera, David; Sales, Salvador; Fernández-Pousa, Carlos R.

doi:10.1109/lpt.2016.2533163

Cited by 22 publications

(10 citation statements)

References 10 publications

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“…In a final measurement, we included a dispersive element before the second modulator to illustrate the determination of dispersion-induced relative delays, a procedure which was used to measure relative Bragg wavelength shifts in FBG arrays [24,25,26]. The dispersive element was a chirped fiber Bragg grating (CFBG) with dispersion D=−170 ps/nm in the C band.…”

Section: Resultsmentioning

confidence: 99%

“…It has also been enriched with concepts from Microwave Photonics [10,21], and much effort has been dedicated to the incorporation of additional functionalities to the technique. Wavelength-resolved reflectograms have been obtained by sweeping the wavelength of a narrowband optical probe wave [11] or filtering the backreflected light under broadband illumination [22,23], and the addition of dispersive elements has been used to map Bragg wavelength shifts into RF time delays directly measurable by the VNA [24,25,26]. In addition, specific techniques for discrete narrowband reflectors, typically FBG, have been adapted to I-OFDR systems, such as slope-assisted dual-wavelength [27] or dual-filter [28] interrogation, or fast techniques relying on model-based search [29] or equally-spaced arrays of reflectors [30].…”

Section: Introductionmentioning

confidence: 99%

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Incoherent Optical Frequency-Domain Reflectometry Based on Homodyne Electro-Optic Downconversion for Fiber-Optic Sensor Interrogation

Clement

Maestre

Torregrosa

et al. 2019

Sensors

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Fiber-optics sensors using interrogation based on incoherent optical frequency-domain reflectometry (I-OFDR) offer benefits such as the high stability of interference in the radio-frequency (RF) domain and the high SNR due to narrowband RF detection. One of the main impairments of the technique, however, is the necessity of high-frequency detectors and vector network analyzers (VNA) in systems requiring high resolution. In this paper, we report on two C-band implementations of an I-OFDR architecture based on homodyne electro-optic downconversion enabling detection without VNA and using only low-bandwidth, high-sensitivity receivers, therefore alleviating the requirements of conventional I-OFDR approaches. The systems are based on a pair of modulators that are synchronized to perform modulation and homodyne downconversion at a reference frequency of 25.5 kHz. In the first system, we attain centimeter resolution with a sensitivity down to −90 dB using the modulation frequency range comprised between 3.2 and 14.2 GHz. In the second, we measured, for the first time using this approach, Rayleigh backscattering traces in standard single mode fiber with resolution of 6 m and a sensitivity of −83 dB by use of the 10.1–30.1 MHz range. These results show the feasibility of these simple, homodyne downconversion I-OFDR systems as compact interrogators for distributed or quasi-distributed optical fiber sensors.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Incoherent Optical Frequency-Domain Reflectometry Based on Homodyne Electro-Optic Downconversion for Fiber-Optic Sensor Interrogation

Clement

Maestre

Torregrosa

et al. 2019

Sensors

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“…For many years, wavelength division multiplexing (WDM) technique has been applied in the FBG sensing technique for the purpose of improving the sensing distribution, which however is limited by the bandwidth of the light source [8], [9]. Interrogating a series of FBG sensors by employing the technique of optical frequency domain reflectometry (OFDR) is also common [3], [10]. The literature reports the ability of OFDR techniques to provide the spatial resolution of millimeters over the sensing area extendible to hundreds of meters.…”

Section: Introductionmentioning

confidence: 99%

Improving the Signal-to-Noise Ratio of Time Domain Fiber Bragg Grating Sensor Based on Hybrid Simplex and Golay Coding Technique

et al. 2019

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We report on the experimental results of the combination of unique auto-correlation properties of Golay complementary code and Hadamard matrix properties of standard simplex code. The combination of the two coding techniques results in improvement of the signal-to-noise ratio (SNR) of time domain multiplexed fiber Bragg grating (TDM-FBG) sensor for temperature measurement. Previously, we have analyzed the properties of both coding techniques when deployed separately in the TDM-FBG sensor. In this case, both coding techniques result in the same amount of SNR improvement for code length longer than 31 bits. In this paper, we demonstrate the combination and simultaneous deployment of the two techniques to measure multiple FBGs under room condition (25 • C) and 50 • C temperature. The two schemes combination results in remarkable improvement of SNR and still retains the original spatial property of the decoded FBG signals, confirming the successful deployment of the hybrid codes. From the measurement of two FBG sensors located after 16 km of fiber, the combination of 31 bits of simplex-and 64 bits of Golay codes has resulted in a total of 10.5 dB improvement of SNR.

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“…A number of techniques can be used to reduce the interrogation time. First, of course, is the increase of IFBW [9]. Second, the use of a sparse number of frequencies in the RF characterization [12].…”

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confidence: 99%

Fast Incoherent OFDR Interrogation of FBG Arrays Using Sparse Radio Frequency Responses

Bellido

Peralta

Madrigal

et al. 2018

J. Lightwave Technol.

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We present two implementations of fast, discrete incoherent optical frequency-domain reflectometers (I-OFDR) for the interrogation of equally-spaced fiber Bragg grating (FBG) arrays, based on the determination of the array's radiofrequency (RF) response at a sparse number of frequencies. FBG reflectivities are determined by use of the inverse discrete Fourier transform (IDFT) of the sparse RF response, in a dynamic range limited by crosstalk induced by FBG positioning errors. The first implementation employs the complete, vector RF response at a number of frequencies equal to the number N of FBGs in the array. In the second, the introduction of a reference reflector allows for an interrogation using the power (phaseless) RF response in 4N − 1 frequencies. Demodulation based on IDFT leads to total interrogation times determined by the network analyzer scan time, which can be as low as 10 µs per FBG. Depending on the interrogation technique, electrical bandwidth requirements are 1-2 GHz in our array with 10cm separation. We implemented both techniques in a N = 10 array, inducing decays in reflectivity by 10 dB in one or several FBGs. Unambiguous detection of FBG decays was obtained in both interrogation methods. Additional tests performed on the measured reflectivities also show that measurement linearity is preserved in the 10-dB decay range. As discrete I-OFDR systems, the proposed techniques show the possibility to reach compromises between interrogation time and dynamic range or accuracy in reflectivity measurements, using the number of interrogation frequencies and the sensor topology.

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Interrogation of a Sensor Array of Identical Weak FBGs Using Dispersive Incoherent OFDR

Cited by 22 publications

References 10 publications

Incoherent Optical Frequency-Domain Reflectometry Based on Homodyne Electro-Optic Downconversion for Fiber-Optic Sensor Interrogation

Incoherent Optical Frequency-Domain Reflectometry Based on Homodyne Electro-Optic Downconversion for Fiber-Optic Sensor Interrogation

Improving the Signal-to-Noise Ratio of Time Domain Fiber Bragg Grating Sensor Based on Hybrid Simplex and Golay Coding Technique

Fast Incoherent OFDR Interrogation of FBG Arrays Using Sparse Radio Frequency Responses

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