Abstract

A fiber-optic sensing system based on two types of ultra-weak fiber Bragg gratings (UWFBG) for simultaneous temperature and vibration sensing was proposed. Narrowband and broadband UWFBGs are alternately written into an optical fiber with equal spacing. Distributed temperature sensing is realized by demodulating the wavelength shift of the narrowband UWFBG, while distributed vibration sensing is achieved by detecting phase variation between two adjacent broadband UWFBG interference pulses. The experimental results show that the proposed hybrid UWFBG array can perform temperature and vibration sensing simultaneously. The experimentally conducted temperature measurement ranges from 20°C to 100°C, with the measurement error less than 0.1°C. Vibration signals at different temperatures can be accurately restored, and the signal-to-noise ratio (SNR) is improved by 21.1 dB compared with a normal single-mode fiber (SMF).

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

1. Introduction

Optical fiber sensing technology has attracted considerable research interest because of its characteristic of high sensitivity, anti-electromagnetic interference and distributed measurement. Distributed fiber optic sensing techniques, based on Raman, Brillouin, and Rayleigh scattering within the optical fibers, have been successfully demonstrated in a wide range of vibration or temperature sensing applications, such as structure health monitoring, pipeline intrusion detection and so on [14]. Most of the distributed temperature sensor (DTS) techniques are based on Raman scattering or Brillouin scattering. Temperature information can be obtained by detecting the intensity of anti-Stokes Raman backscattered light [57] or the frequency shift of Brillouin backscattered light [8,9]. Phase-sensitive optical time domain reflectometry (Φ-OTDR) based on Rayleigh back-scattering (RBS) enables distributed vibration measurement [1012]. The amplitude of RBS traces will fluctuate when vibration events exist around the optical fiber, by recording the return time of probe light and measuring the fluctuation, the intensity and the location of the vibration signal can be obtained. These techniques employ backscattered light, and the sensing distance is limited by the SNR of the system, which is attributed to the weak intrinsic backscattering coefficient of the fiber. Therefore, thousands of averaging is needed to improve the SNR, resulting in longer response time. In addition, amplification technology can be employed to improve the intensity of scattered signals [13], but it will also amplify the noise, which is not beneficial to the SNR of the system.

It is demonstrated to enhance the back-reflected intensity and SNR using UWFBG array [1416]. The reflectivity of the UWFBG is usually 2∼5 orders higher than that of backscattering, the reflection intensity is much higher under the conditions of equivalent noise, which can greatly improve the sensing distance and sensitivity. A sensing network with 2000 serial UWFBG had been proposed, the reflectivity of the UWFBG is from −47 dB to −51 dB, and distributed temperature sensing had been realized with wavelength demodulation [17]. However, the wavelength demodulation technology is not suitable for high sensitivity and high speed vibration sensing. Φ-OTDR and UWFBG array had been investigated extensively for distributed vibration sensing [1820]. Rayleigh back-scattering was replaced by interfering signal from adjacent UWFBGs, the sensitivity of the proposed system was 10-20 dB higher than that of Rayleigh scatting [21]. Although phase demodulation is a promising technology in vibration signal monitoring, it is not the optimal choice for static sensing due to its high susceptibility to environmental disturbance. An UWFBG based coherent OTDR is proposed to realize distributed temperature and vibration sensing simultaneously [22], temperature and the vibration event can induce phase change, which can be calculated through a differential process of every two adjacent UWFBGs. But both the temperature and vibration will change the phase on the fiber, it is hard to distinguish the two parameters.

In this paper, a hybrid UWFBG array with two types of FBG sensors is proposed for simultaneously distributed temperature and vibration sensing. Narrowband UWFBGs (NFBG) with a bandwidth of 0.2 nm as temperature sensors, and a CCD module is used to obtain the spectral information of the UWFBGs. Temperature information can be obtained with wavelength demodulation. In addition, broadband UWFBGs (BFBG) and Mach-Zehnder interferometer (MZI) are employed for restoring weak vibration signal based on phase demodulation. The bandwidth of broadband UWFBGs is 3 nm, therefore the spectrum shift caused by temperature changes will not be mismatched with the narrow linewidth of light source. Through the combination of wavelength interrogation and phase demodulation, temperature sensing and vibration sensing can be realized at the same time by the hybrid UWFBG array.

2. UWFBG array manufacturing and its sensing principle

The UWFBG array is manufactured with on-line grating inscription system, which consists of a drawing tower and a FBG writing platform [23]. The FBG is inscribed during the fiber drawing, and the system configuration is shown in Fig. 1. ArF excimer laser (OptoSystems CL5300) with a pulse width of 10 ns and pulse energy of 40 mJ, was used in the FBG writing platform. The laser beam was focused from a 4×12 to a 0.7×10 (mm) line using three cylindrical lenses. FBGs were inscribed via the phase mask method using periodic interference fringes of the ±1st diffraction light. The distance between the phase mask and bare fiber was controlled at 0.5 mm. The bandwidth of the UWFBG depends on the size of the spot and the chirping rate of the phase mask. The UWFBG spacing is controlled by a pulse counter which was installed in the capstan, and each pulse corresponds to a fiber drawing distance of 1 mm. Two different phase masks were mounted on an electric translation platform. When the number of pulses equals to the preseted value of the FBG spacing, an external pulse is triggered to ArF excimer laser exposure for writing FBG. Since the fiber is drawing, there allows only one pulse of excimer laser exposure, the reflectivity of FBG is very weak, normally about −50 dB. The pulse drives the electronic translation platform to switch the phase mask and the pulse counter is cleared for next count, then the hybrid UWFBG array can be fabricated. The pulse counter system is controlled by DSP (digital signal processor) and the UWFBG spacing can be precisely controlled. During the process of on-line writing, the drawing speed and drawing tension can be automatically controlled and displayed. Since the drawing speed and drawing tension directly affect the uniformity of the UWFBG [23], the optimal drawing speed and drawing tension are 20 m/s and 35 g, respectively. Finally, the bare fiber is coated with polymer and ultraviolet cured. This online writing method can produce FBG arrays directly without decoating and recoating, which cannot be avoided in the traditional FBG array manufacturing. In addition, fiber splicing can be avoided, which improves the multiplexing capacity and mechanical strength of the fiber array.

 

Fig. 1. Diagram of the on-line writing FBG system

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Figure 2 illustrates the distributed optical temperature and vibration sensing system. The light source consists of an amplified spontaneous emission (ASE) laser and a narrow linewidth laser (NLL). The ASE laser wavelength is 1553.33-1556.15 nm after passing through a band-pass filter, and the NLL wavelength is 1550.1 nm. Two semiconductor optical amplifiers (SOA1 and SOA2) are driven by the same electrical pulse generator for the generation of probe pulses. The probe pulses pass through a coupler (OC1) and then amplified by an erbium-doped fiber amplifier (EDFA). The amplified pulses are launched into the hybrid UWFBG array with a circulator (Cir1). The center wavelengths of the broadband and narrowband UWFBGs are 1549.5 nm and 1554.1 nm, respectively. Two types of UWFBGs are alternately engraved in the fiber with equal spacing of L and the reflectivity is about −50 dB. NLL pulse and ASE pulse are reflected by broadband UWFBGs and narrowband UWFBGs, respectively. Then a series of pulses was injected into a three-port dense wavelength division multiplexing (DWDM). The DWDM works at 1550.12 nm with a bandwidth of 100 GHz. The ASE pulses are output through reflection port of the DWDM and collected by a high-speed charge-coupled device (CCD) module (IBSEN I-MON 256) which is used in the interrogation system to obtain the spectral information of the narrowband UWFBGs. The NLL pulses can pass through the DWDM and output from transmission port, and then directed to an imbalanced Mach-Zehnder interferometer (MZI) through OC2 for dynamic measurement. The path difference of the MZI creates a temporal shift between the light traveling in its two paths. When the length of the delay fiber in the unbalanced MZI is 4L, the pulses reflected by adjacent broadband UWFBGs are overlapped and then generate interference phenomenon. To eliminate the influence from intensity fluctuations, a symmetric 3×3 optical coupler was used at the output of the unbalanced MZI to create three outputs with a phase shift of 2π/3 between each output. The three outputs of OC3 are detected by three photo-detectors. The serial data from the three detectors are collected by a high-speed data acquisition (DAQ) card with sample rate of 250 MHz/s.

 

Fig. 2. Schematic of hybrid UWFBG sensing system for distributed temperature and vibration measurement. ASE: amplified spontaneous emission; NLL: narrow linewidth laser; SOA: semiconductor optical amplifier; OC: optical coupler; EDFA: erbium-doped fiber amplifier; BFBG: broadband UWFBG; NFBG: narrowband UWFBG; DWDM: dense wavelength division multiplexing; CCD: charge-coupled device; AFG: arbitrary function generator; PD: photodetector; DAQ: data acquisition.

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Distributed temperature sensing is realized by demodulating the wavelength shift of narrowband UWFBG. The pulses reflected by narrowband UWFBGs were detected by the CCD module at different times, and the spectra sampled of the UWFBGs can be detected one by one. The reflected spectra of UWFBGs need to be reconstructed through the peak-fitting algorithm because of the limited pixel number of the CCD. The CCD module has 256 pixels, the wavelength measurement range is from 1520 nm to 1570 nm, and its wavelength spacing is about 195 pm. By using the Gaussian peak-fitting algorithm, a peak wavelength resolution of 0.5 pm can be achieved. The adjusted Gaussian function is shown in:

$$f({\lambda _i}) = A\ast \textrm{exp} ( - \frac{{{{({\lambda _i} - B)}^2}}}{{2{C^2}}})$$

Where A, B, and $C$ are the adjusted parameters, A is amplitude, B is center wavelength, and C is deviation, $f({\lambda _i})$ is the calculated spectra of ${\lambda _i}$. Using the pixels collected by the CCD, the spectral curve is calculated by the least squares method of the Gaussian function, and finally the central wavelength value can be obtained. Gaussian peak-fitting algorithm is a dense and efficient algorithm, which is more suitable for high-speed demodulation.

The pulses reflected by the broadband UWFBG are sent to an unbalanced MZI for phase demodulation, in order to realize distributed vibration sensing. Each pulse will be divided into two sub-pulses as it passes through the unbalanced MZI. The rear sub-pulse from BFBG1 and the front sub-pulse from BFBG2 are overlapped, and therefore interference effect happens. ${E_{R1}}$ and ${E_{R2}}$ are the electrical fields of reflected light from the rear sub-pulse of BFBG1 and the front sub-pulse of BFBG2, and they can be expressed as:

$$\begin{aligned} {E_{R1}} &= {E_1}\;\textrm{exp} (j(\omega t + {\phi _1}(t)))\\ {E_{R2}} &= {E_2}\;\textrm{exp} (j(\omega t + {\phi _2}(t))) \end{aligned}$$

Where ${E_1}$ and ${E_2}$ are the reference amplitudes, $\omega$ is the angular frequency of light source, ${\phi _1}(t)$ and ${\phi _2}(t)$ are the initial phase of the reflected light. These two fields add vectorially, and the photocurrent generated by the photodetector is proportional to the square of the total optical field incident upon it:

$${i_{phot}} = k({E_{R1}} + {E_{R2}}){({E_{R1}} + {E_{R2}})^\ast }\; = k(E_1^2 + E_2^2 + 2{E_1}{E_2}\cos ({\phi _1}(t) - {\phi _2}(t)))$$
Where k is the responsivity of the photodetector. The photocurrent has two dominant components, a DC term and an AC signal. Note that this signal current is proportional to signal field rather than power. The mean square of this signal current can be expressed as:
$$(\overline {{i_s}{)^2}} = 2{k^2}E_1^2E_2^2 = 2{k^2}{P_1}{P_2}$$
Where ${P_1}$ and ${P_2}$ are the backscattered powers of the two pulses, respectively. The signal to noise ratio (SNR) is given by the ratio of ${i_s}$ to all various noise currents:
$$\frac{S}{N} = \frac{{2{k^2}{P_1}{P_2}}}{{{P_N}}}$$

Where ${P_N}$ is the total noise of the system, it contains phase noise generated by the laser frequency drifting, environmental fluctuations and so on. It can be found that the SNR of the system is proportional to the backscattered optical power, the UWFBG array have a higher SNR than SMF. Phase noise is a low-frequency signal with Hz or sub-Hz level which can be filtered out by a high-pass filter [24], and random fluctuations of the environment can be eliminated by multiple averaging algorithm.

The broadband UWFBG array generates a series of interference pulses and they are detected by three photo-detectors. At the ideal split ratio, the output of the 3×3 coupler can be expressed as:

$${I_\textrm{k}} = D + {I_0}\cos \textrm{[}\phi \textrm{(t) - (k - 1)(2}\pi \textrm{/3)],k} = \textrm{1,2,3}$$
Where $D$ and ${I_0}$ are constants, $\phi \textrm{(t)}$ is the dynamic phase shift caused by the vibration signal. If there exists vibration event on the fiber between two adjacent UWFBGs, the effective refractive index of the fiber and the associated optical path difference of the two UWFBGs will change, resulting in the phase change of interference signal. The interference signal at specific time contains not only the location information, but also the phase change within the adjacent UWFBGs.

The phase difference can be measured directly through 3×3 coupler demodulation algorithm [21]. The output voltage V is directly proportional to the phase difference:

$$V = \sqrt 3 \phi (t)$$

3. Experimental results and discussion

It the experiment, the hybrid UWFBG array length is 2 km, broadband UWFBGs and narrowband UWFBGs are alternately distributed in the UWFBG array. The adjacent spacing between broadband and narrowband UWFBGs is 2 m, and therefore the effective UWFBG spacing for temperature and vibration sensing is 4 m. The ASE laser with emitted power of 10.3 mW and NLL with emitted power of 9.25 mW are modulated into probe pulses and injected into the UWFBG array. In an OTDR system, there is trade-off between the repetition rate of the probe pulse $\textrm{f}$ and the sensing distance L, which is that $\textrm{f} \le \textrm{c}/2{n_e}L$ ($c$ is the speed of light in vacuum, ${n_e}$ is the effective refractive index of the fiber). Meanwhile, in order to avoid overlapping of reflected pulses, the pulse width $\textrm{W}$ should meets the formula $\textrm{W} \le 2{n_e}d{ / }c$ ($d$ is the distance between two adjacent UWFBGs). Here, the probe pulse has a repetition rate of 20 kHz and a pulse width of 20 ns. The ASE pulses were obtained by the CCD module at different times and the reflected spectrum of each narrowband UWFBG was reconstructed through Gaussian peak-fitting algorithm. Narrowband UWFBGs are employed for wavelength demodulation since the peak position of the spectrum can be more accurately addressed, which can improve the accuracy of temperature measurement. The 3 dB bandwidth of the narrow UWFBG is 0.2 nm. The reflected spectra with 200 NFBGs were shown in Fig. 3. The fluctuations of the peak wavelength and reflection intensity are attributed to the fabrication errors during the inscribing process. Meanwhile, the reflective spectrum of the broadband UWFBG was measured by a spectrometer (YOKOGAWA AQ6370B). From Fig. 1, it can be clearly seen that the 3 dB bandwidth is 3 nm, which can improve the fault tolerance for vibration measurement when the reflection spectra of UWFBGs are shifted by strain and temperature change.

 

Fig. 3. Reflection spectrum of 200 NFBGs

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To investigate the performance of the sensing network, temperature and vibration are measured simultaneously. The experimental setup of the system is shown in Fig. 4. Two cylindrical piezoelectric transducers (PZTs) were driven by a signal generator as the vibration source. PZT1 and PZT2 were installed on the fiber segments between BFBG100 and NFBG100, BFBG400 and NFBG400, respectively. PZT1 is driven by a triangle-wave with frequency of 100 Hz and it was placed in room temperature. Simultaneously, PZT2 is driven by a sin-wave with a frequency of 200 Hz, and it was placed in a heat oven with NFBG400, BFBG401 and NFBG401, the rest of the UWFBGs are kept at 20°C. The temperature of the heat oven is increased from 20°C to 100°C with a step of 10°C. The amplitude of the driving voltage applied to both PZTs is 15 V, which means that the two vibrations have the same intensity.

 

Fig. 4. Experimental setup of proposed sensing system

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Firstly, the temperature response of the narrowband UWFBG is evaluated. Figures 5(a) and 5(b) plot the reflection spectra of NFBG400 and NFBG401 at different temperatures. When the temperature is 20°C, the peak wavelengths of the two NFBGs are 1554.091 nm and 1554.001 nm respectively, the minimum resolution of the wavelength is 1 pm, therefore the theoretical accuracy of the temperature measurement is 0.1°C. The reflection spectra shifts gradually as the temperature rises, and the peak wavelengths of the NFBG at each temperature can be obtained from the spectrum.

 

Fig. 5. The reflection spectra of (a) NFBG400 and (b) NFBG401 at different temperatures

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Figure 6 shows the result of distributed temperature measurement. The peak wavelengths of 500 narrowband UWFBGs measured by the interrogation system were shown in Fig. 6(a), and most of them are distributed in the range from 1554 to 1554.1 nm. From the inset in Fig. 6(a), it can be clearly seen that the peak wavelengths of all UWFBGs at each temperature step have been recorded. The peak wavelengths of the heated narrowband UWFBGs shifted with the increase of temperature. Figure 6(b) shows the relationship between the peak wavelength shift and the temperature. The measurement data of the two UWFBGs were fitted to obtain its temperature sensitivity, and it shows a linear response. The fitted coefficients are 10.24 pm/°C and 10.47 pm/°C respectively. The peak wavelengths of other UWFBGs remain unchanged, corresponding to the constant room temperature. This means that distributed temperature monitoring can be achieved by measuring the peak wavelengths of the narrowband UWFBGs.

 

Fig. 6. (a) Temperature measurement results of the narrowband UWFBG array; (b) Measured peak wavelength shift diagram with temperature

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At the same time, the response characteristics of the hybrid UWFBG array to vibration signals at different temperatures were evaluated. PZT1 worked at room temperature, PZT2 and the sensors were placed in the heat oven at a temperature of 80°C. The experimental results are shown in Fig. 7. Since the spacing of the adjacent broadband UWFBGs is 4 m, it can be clearly seen that there exist two phase changes at 400 m and 1600 m from Fig. 7(a), which are corresponding to the positions of PZT1 and PZT2. Figure 7(b) shows the 3D spatial-temporal domain demodulation results, the vibration events at two different locations were accurately restored. There are no vibrations except the two signals, indicating that the vibrations have no influence on other locations of the sensing fiber. The result of time domain signals is shown in Fig. 7(c). Apparently, the demodulated phase restores the driving signal accurately. The demodulated waveform at PZT1 has a good triangular shape with the amplitude of about 2.53 rad on average, and the demodulated waveform at PZT2 has a good sinusoidal shape with the amplitude of about 2.54 rad. The frequency spectrum is obtained from spectral analysis via fast Fourier transform. As shown in Fig. 7(d), two strong peaks were 100 Hz and 200 Hz with the amplitude of 8.06 dB [=20log(Asignal), 2.53 rad] and 8.1 dB (2.54 rad), respectively. Taking into account that the far end white noise is about −60 dB, the SNR of the proposed system at 400 m and 1600 m were 68.06 dB and 68.10 dB. This means that the SNR remains a high level in the entire fiber at different temperatures.

 

Fig. 7. (a) Demodulated phase changing diagram at 400 m and 1600 m; (b) 3D plot of spatial-temporal domain demodulated signals along the hybrid UWFBG array; (c) The responses of temporal domain at two vibration positions; (d) Frequency responses of the system at different temperatures

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Furthermore, the frequency response of the system was measured. The repetition rate of the probe pulse is 20 kHz, therefore the maximum detectable frequency of the system is 10 kHz according to Nyquist sampling theorem. Figure 8 demonstrates the frequency response of the UWFBG array to different frequencies at room temperature. The data was collected by applying a fixed voltage (10 V) to the PZT while changing the frequency from 100 Hz to 10 kHz. The amplitudes at the frequency of 100 Hz, 2 kHz, 4 kHz, 6 kHz, 8 kHz and 10 kHz are 2.01 dB, 2.1 dB, 2.4 dB, 2.1 dB, 2.0 dB and 2.2 dB, respectively. It means that the system can accurately demodulate the vibration signal with a wide frequency response, and the maximum response frequency will increase with the probe pulse repetition rate, but the sensing distance will decrease.

 

Fig. 8. Frequency response of the PZT measured by the distributed sensor

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Finally, the performance of UWFBG array and SMF for vibration measurement was evaluated. A 2 km SMF is fused in front of the hybrid UWFBG array and a probe pulse with a pulse width of 20 ns was injected into it. The repetition frequency of the pulse is 20 kHz, which corresponds to the maximum sensing distance of 5 km. Then a raw trace of the SMF and UWFBG array were obtained and shown in Fig. 9. It can be clearly found that the amplitude of the reflected signal along the UWFBG array is much stronger than that of Rayleigh backscattering (RBS) light from SMF, although the UWFBG array was at the tail end of the SMF. The intensity of the reflected signal at the rear end of the UWFBG array is the same as that of the front region. This will apparently enhance the measurement accuracy, making it possible to reconstruct the vibration signals even at the rear end of the sensing fiber with high SNR and dead-zone-free property. The RBS light of the SMF gradually decreases with the fiber length. At the far end of the SMF, the intensity of the reflection is very weak, which means that the vibration signal will be submerged in the noise, and therefore is difficult to detect.

 

Fig. 9. A raw trace of the SMF and UWFBG array

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Then, 1 m fiber between the 10th and 11th broadband UWFBG was wrapped on a PZT, and the PZT was driven by a sinusoidal signal with an amplitude of 15 V and a frequency of 500 Hz. As a comparison, 1 m SMF was wrapped on the PZT at the corresponding distance, and all other conditions were consistent. Figure 10(a) shows signals in the time domain, the vibration signal was restored by UWFBG array accurately (red curve), which has a good sinusoidal shape with the amplitude of about 2.6 rad. The SMF also restores the vibration signal, and the amplitude of the vibration signal is about 2.3 rad. However the demodulated waveform has some distortion (black curve). The frequency spectrum is shown in Fig. 10(b). It can be clearly concluded that the mean phase noise of the SMF is about −40 dB with the SNR of 47.2 dB, while the mean phase noise of the UWFBG array is about −60 dB with SNR of 68.3 dB. Therefore, the background noise level of the system based on UWFBG array decreases about 20 dB, and SNR increases 21. 1 dB.

 

Fig. 10. (a) The time domain signals of SMF and UWFBG; (b) the frequency spectra of vibration signals

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4. Conclusion

In this paper, a hybrid UWFBG array is proposed and experimentally demonstrated for simultaneous temperature and vibration measurement. Based on narrowband UWFBG and wavelength demodulation with Gaussian peak-fitting algorithm, distributed temperature detection is experimentally conducted from 20°C to 100°C, while higher temperature sensing is still possible. Meanwhile, broadband UWFBGs and MZI interferometer are employed to realize vibration measurement. The SNR of the system remains a high level in the entire fiber at different temperatures because of the stable and strong reflected signals by the UWFBG array. Experimental results show that the SNR of the system has been improved by 21.1 dB compared with the normal SMF. This work suggests that an alternative solution for simultaneously distributed static and dynamic sensing by using hybrid UWFBG array, which would be a promising technology in many sensing applications.

Funding

National Key Research and Development Program of China (2017YFB0405501).

Disclosures

The authors declare no conflicts of interest.

References

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References

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  1. D. Kweon, K. Koo, J. Woo, and Y. Kim, “Hot spot temperature for 154 kV transformer filled with mineral oil and natural ester fluid,” IEEE Trans. Dielectr. Electr. Insul. 19(3), 1013–1020 (2012).
    [Crossref]
  2. Y. Dong, H. Zhang, L. Chen, and X. Bao, “2 cm spatial-resolution and 2 km range Brillouin optical fiber sensor using a transient differential pulse pair,” Appl. Opt. 51(9), 1229–1235 (2012).
    [Crossref]
  3. F. Peng, H. Wu, X. Jia, Y. Rao, Z. Wang, and Z. Peng, “Ultra-long high-sensitivity Φ-OTDR for high spatial resolution intrusion detection of pipelines,” Opt. Express 22(11), 13804–13810 (2014).
    [Crossref]
  4. A. Masoudi, J. A. Pilgrim, T. P. Newson, and G. Brambilla, “Subsea Cable Condition Monitoring with Distributed Optical Fiber Vibration Sensor,” J. Lightwave Technol. 37(4), 1352–1358 (2019).
    [Crossref]
  5. D. Hwang, D. Yoon, I. Kwon, D. Seo, and Y. Chung, “Novel auto-correction method in a fiber-optic distributed-temperature sensor using reflected anti-Stokes Raman scattering,” Opt. Express 18(10), 9747–9754 (2010).
    [Crossref]
  6. M. Tanner, S. Dyer, B. Baek, R. Hadfield, and S. Nam, “High-resolution single-mode fiber-optic distributed Raman sensor for absolute temperature measurement using superconducting nanowire single-photon detectors,” Appl. Phys. Lett. 99(20), 201110 (2011).
    [Crossref]
  7. Y. Liu, L. Ma, C. Yang, W. Tong, and Z. He, “Long-range Raman distributed temperature sensor with high spatial and temperature resolution using graded-index few-mode fiber,” Opt. Express 26(16), 20562–20571 (2018).
    [Crossref]
  8. Y. Peled, A. Motil, and M. Tur, “Fast Brillouin optical time domain analysis for dynamic sensing,” Opt. Express 20(8), 8584–8591 (2012).
    [Crossref]
  9. Y. Mizuno, N. Hayashi, H. Fukuda, K. Song, and K. Nakamura, “Ultrahigh-speed distributed Brillouin reflectometry,” Light: Sci. Appl. 5(12), e16184 (2016).
    [Crossref]
  10. A. Masoudi, M. Belal, and T. P. Newson, “A distributed optical fibre dynamic strain sensor based on phase-OTDR,” Meas. Sci. Technol. 24(8), 085204 (2013).
    [Crossref]
  11. G. Yang, X. Fan, S. Wang, B. Wang, Q. Liu, and Z. He, “Long-range distributed vibration sensing based on phase extraction from phase-sensitive OTDR,” IEEE Photonics J. 8(3), 1–12 (2016).
    [Crossref]
  12. Y. Muanenda, S. Faralli, C. Oton, and F. Pasquale, “Dynamic phase extraction in a modulated double-pulse phi-OTDR sensor using a stable homodyne demodulation in direct detection,” Opt. Express 26(2), 687–701 (2018).
    [Crossref]
  13. L. D. Putten, A. Masoudi, and G. Brambilla, “100-km-sensing-range single-ended distributed vibration sensor based on remotely pumped Erbium-doped fiber amplifier,” Opt. Lett. 44(24), 5925–5928 (2019).
    [Crossref]
  14. C. Hu, H. Wen, and W. Bai, “A novel interrogation system for large scale sensing network with identical Ultra-Weak Fiber Bragg Gratings,” J. Lightwave Technol. 32(7), 1406–1411 (2014).
    [Crossref]
  15. Y. Wang, J. Gong, D. Y. Wang, B. Dong, W. Bi, and A. Wang, “A Quasi-Distributed Sensing Network With Time-Division-Multiplexed Fiber Bragg Gratings,” IEEE Photonics Technol. Lett. 23(2), 70–72 (2011).
    [Crossref]
  16. J. Hervás, D. Barrera, J. Madrigal, and S. Sales, “Microwave Photonics Filtering Interrogation Technique Under Coherent Regime For Hot Spot Detection on a Weak FBGs Array,” J. Lightwave Technol. 36(4), 1039–1045 (2018).
    [Crossref]
  17. Z. Luo, H. Wen, H. Guo, and M. Yang, “A time- and wavelength-division multiplexing sensor network with ultra-weak fiber Bragg gratings,” Opt. Express 21(19), 22799–22807 (2013).
    [Crossref]
  18. C. Wang, C. Wang, Y. Shang, X. Liu, and G. Peng, “Distributed acoustic mapping based on interferometry of phase optical time-domain reflectometry,” Opt. Commun. 346, 172–177 (2015).
    [Crossref]
  19. F. Zhu, Y. Zhang, L. Xia, X. Wu, and X. Zhang, “Improved Φ-OTDR Sensing System for High-Precision Dynamic Strain Measurement Based on Ultra-Weak Fiber Bragg Grating Array,” J. Lightwave Technol. 33(23), 4775–4780 (2015).
    [Crossref]
  20. T. Liu, F. Wang, X. Zhang, Q. Yuan, J. Niu, L. Zhang, and T. Wei, “Interrogation of Ultra-Weak FBG Array Using Double-Pulse and Heterodyne Detection,” IEEE Photonics Technol. Lett. 30(8), 677–680 (2018).
    [Crossref]
  21. C. Wang, Y. Shang, X. Liu, C. Wang, H. Yu, D. Jiang, and G. Peng, “Distributed OTDR-interferometric sensing network with identical ultra-weak fiber Bragg gratings,” Opt. Express 23(22), 29038–29046 (2015).
    [Crossref]
  22. A. Fan, H. Li, T. He, Z. Yan, and Q. Sun, “Simultaneous Distributed Temperature and Vibration Measurement with UWFBG based Coherent OTDR,” Optical Fiber Communication Conference (2018).
  23. H. Guo, J. Tang, X. Li, Y. Zheng, H. Yu, and H. Yu, “On-line writing identical and weak fiber Bragg grating arrays,” Chin. Opt. Lett. 11(3), 030602 (2013).
    [Crossref]
  24. X. Zhang, Z. Sun, Y. Shan, Y. Li, F. Wang, J. Zeng, and Y. Zhang, “A High Performance Distributed Optical Fiber Sensor Based on Φ-OTDR for Dynamic Strain Measurement,” IEEE Photonics J. 9(3), 1 (2017).
    [Crossref]

2019 (2)

2018 (4)

2017 (1)

X. Zhang, Z. Sun, Y. Shan, Y. Li, F. Wang, J. Zeng, and Y. Zhang, “A High Performance Distributed Optical Fiber Sensor Based on Φ-OTDR for Dynamic Strain Measurement,” IEEE Photonics J. 9(3), 1 (2017).
[Crossref]

2016 (2)

G. Yang, X. Fan, S. Wang, B. Wang, Q. Liu, and Z. He, “Long-range distributed vibration sensing based on phase extraction from phase-sensitive OTDR,” IEEE Photonics J. 8(3), 1–12 (2016).
[Crossref]

Y. Mizuno, N. Hayashi, H. Fukuda, K. Song, and K. Nakamura, “Ultrahigh-speed distributed Brillouin reflectometry,” Light: Sci. Appl. 5(12), e16184 (2016).
[Crossref]

2015 (3)

2014 (2)

2013 (3)

2012 (3)

2011 (2)

M. Tanner, S. Dyer, B. Baek, R. Hadfield, and S. Nam, “High-resolution single-mode fiber-optic distributed Raman sensor for absolute temperature measurement using superconducting nanowire single-photon detectors,” Appl. Phys. Lett. 99(20), 201110 (2011).
[Crossref]

Y. Wang, J. Gong, D. Y. Wang, B. Dong, W. Bi, and A. Wang, “A Quasi-Distributed Sensing Network With Time-Division-Multiplexed Fiber Bragg Gratings,” IEEE Photonics Technol. Lett. 23(2), 70–72 (2011).
[Crossref]

2010 (1)

Baek, B.

M. Tanner, S. Dyer, B. Baek, R. Hadfield, and S. Nam, “High-resolution single-mode fiber-optic distributed Raman sensor for absolute temperature measurement using superconducting nanowire single-photon detectors,” Appl. Phys. Lett. 99(20), 201110 (2011).
[Crossref]

Bai, W.

Bao, X.

Barrera, D.

Belal, M.

A. Masoudi, M. Belal, and T. P. Newson, “A distributed optical fibre dynamic strain sensor based on phase-OTDR,” Meas. Sci. Technol. 24(8), 085204 (2013).
[Crossref]

Bi, W.

Y. Wang, J. Gong, D. Y. Wang, B. Dong, W. Bi, and A. Wang, “A Quasi-Distributed Sensing Network With Time-Division-Multiplexed Fiber Bragg Gratings,” IEEE Photonics Technol. Lett. 23(2), 70–72 (2011).
[Crossref]

Brambilla, G.

Chen, L.

Chung, Y.

Dong, B.

Y. Wang, J. Gong, D. Y. Wang, B. Dong, W. Bi, and A. Wang, “A Quasi-Distributed Sensing Network With Time-Division-Multiplexed Fiber Bragg Gratings,” IEEE Photonics Technol. Lett. 23(2), 70–72 (2011).
[Crossref]

Dong, Y.

Dyer, S.

M. Tanner, S. Dyer, B. Baek, R. Hadfield, and S. Nam, “High-resolution single-mode fiber-optic distributed Raman sensor for absolute temperature measurement using superconducting nanowire single-photon detectors,” Appl. Phys. Lett. 99(20), 201110 (2011).
[Crossref]

Fan, A.

A. Fan, H. Li, T. He, Z. Yan, and Q. Sun, “Simultaneous Distributed Temperature and Vibration Measurement with UWFBG based Coherent OTDR,” Optical Fiber Communication Conference (2018).

Fan, X.

G. Yang, X. Fan, S. Wang, B. Wang, Q. Liu, and Z. He, “Long-range distributed vibration sensing based on phase extraction from phase-sensitive OTDR,” IEEE Photonics J. 8(3), 1–12 (2016).
[Crossref]

Faralli, S.

Fukuda, H.

Y. Mizuno, N. Hayashi, H. Fukuda, K. Song, and K. Nakamura, “Ultrahigh-speed distributed Brillouin reflectometry,” Light: Sci. Appl. 5(12), e16184 (2016).
[Crossref]

Gong, J.

Y. Wang, J. Gong, D. Y. Wang, B. Dong, W. Bi, and A. Wang, “A Quasi-Distributed Sensing Network With Time-Division-Multiplexed Fiber Bragg Gratings,” IEEE Photonics Technol. Lett. 23(2), 70–72 (2011).
[Crossref]

Guo, H.

Hadfield, R.

M. Tanner, S. Dyer, B. Baek, R. Hadfield, and S. Nam, “High-resolution single-mode fiber-optic distributed Raman sensor for absolute temperature measurement using superconducting nanowire single-photon detectors,” Appl. Phys. Lett. 99(20), 201110 (2011).
[Crossref]

Hayashi, N.

Y. Mizuno, N. Hayashi, H. Fukuda, K. Song, and K. Nakamura, “Ultrahigh-speed distributed Brillouin reflectometry,” Light: Sci. Appl. 5(12), e16184 (2016).
[Crossref]

He, T.

A. Fan, H. Li, T. He, Z. Yan, and Q. Sun, “Simultaneous Distributed Temperature and Vibration Measurement with UWFBG based Coherent OTDR,” Optical Fiber Communication Conference (2018).

He, Z.

Y. Liu, L. Ma, C. Yang, W. Tong, and Z. He, “Long-range Raman distributed temperature sensor with high spatial and temperature resolution using graded-index few-mode fiber,” Opt. Express 26(16), 20562–20571 (2018).
[Crossref]

G. Yang, X. Fan, S. Wang, B. Wang, Q. Liu, and Z. He, “Long-range distributed vibration sensing based on phase extraction from phase-sensitive OTDR,” IEEE Photonics J. 8(3), 1–12 (2016).
[Crossref]

Hervás, J.

Hu, C.

Hwang, D.

Jia, X.

Jiang, D.

Kim, Y.

D. Kweon, K. Koo, J. Woo, and Y. Kim, “Hot spot temperature for 154 kV transformer filled with mineral oil and natural ester fluid,” IEEE Trans. Dielectr. Electr. Insul. 19(3), 1013–1020 (2012).
[Crossref]

Koo, K.

D. Kweon, K. Koo, J. Woo, and Y. Kim, “Hot spot temperature for 154 kV transformer filled with mineral oil and natural ester fluid,” IEEE Trans. Dielectr. Electr. Insul. 19(3), 1013–1020 (2012).
[Crossref]

Kweon, D.

D. Kweon, K. Koo, J. Woo, and Y. Kim, “Hot spot temperature for 154 kV transformer filled with mineral oil and natural ester fluid,” IEEE Trans. Dielectr. Electr. Insul. 19(3), 1013–1020 (2012).
[Crossref]

Kwon, I.

Li, H.

A. Fan, H. Li, T. He, Z. Yan, and Q. Sun, “Simultaneous Distributed Temperature and Vibration Measurement with UWFBG based Coherent OTDR,” Optical Fiber Communication Conference (2018).

Li, X.

Li, Y.

X. Zhang, Z. Sun, Y. Shan, Y. Li, F. Wang, J. Zeng, and Y. Zhang, “A High Performance Distributed Optical Fiber Sensor Based on Φ-OTDR for Dynamic Strain Measurement,” IEEE Photonics J. 9(3), 1 (2017).
[Crossref]

Liu, Q.

G. Yang, X. Fan, S. Wang, B. Wang, Q. Liu, and Z. He, “Long-range distributed vibration sensing based on phase extraction from phase-sensitive OTDR,” IEEE Photonics J. 8(3), 1–12 (2016).
[Crossref]

Liu, T.

T. Liu, F. Wang, X. Zhang, Q. Yuan, J. Niu, L. Zhang, and T. Wei, “Interrogation of Ultra-Weak FBG Array Using Double-Pulse and Heterodyne Detection,” IEEE Photonics Technol. Lett. 30(8), 677–680 (2018).
[Crossref]

Liu, X.

C. Wang, C. Wang, Y. Shang, X. Liu, and G. Peng, “Distributed acoustic mapping based on interferometry of phase optical time-domain reflectometry,” Opt. Commun. 346, 172–177 (2015).
[Crossref]

C. Wang, Y. Shang, X. Liu, C. Wang, H. Yu, D. Jiang, and G. Peng, “Distributed OTDR-interferometric sensing network with identical ultra-weak fiber Bragg gratings,” Opt. Express 23(22), 29038–29046 (2015).
[Crossref]

Liu, Y.

Luo, Z.

Ma, L.

Madrigal, J.

Masoudi, A.

Mizuno, Y.

Y. Mizuno, N. Hayashi, H. Fukuda, K. Song, and K. Nakamura, “Ultrahigh-speed distributed Brillouin reflectometry,” Light: Sci. Appl. 5(12), e16184 (2016).
[Crossref]

Motil, A.

Muanenda, Y.

Nakamura, K.

Y. Mizuno, N. Hayashi, H. Fukuda, K. Song, and K. Nakamura, “Ultrahigh-speed distributed Brillouin reflectometry,” Light: Sci. Appl. 5(12), e16184 (2016).
[Crossref]

Nam, S.

M. Tanner, S. Dyer, B. Baek, R. Hadfield, and S. Nam, “High-resolution single-mode fiber-optic distributed Raman sensor for absolute temperature measurement using superconducting nanowire single-photon detectors,” Appl. Phys. Lett. 99(20), 201110 (2011).
[Crossref]

Newson, T. P.

A. Masoudi, J. A. Pilgrim, T. P. Newson, and G. Brambilla, “Subsea Cable Condition Monitoring with Distributed Optical Fiber Vibration Sensor,” J. Lightwave Technol. 37(4), 1352–1358 (2019).
[Crossref]

A. Masoudi, M. Belal, and T. P. Newson, “A distributed optical fibre dynamic strain sensor based on phase-OTDR,” Meas. Sci. Technol. 24(8), 085204 (2013).
[Crossref]

Niu, J.

T. Liu, F. Wang, X. Zhang, Q. Yuan, J. Niu, L. Zhang, and T. Wei, “Interrogation of Ultra-Weak FBG Array Using Double-Pulse and Heterodyne Detection,” IEEE Photonics Technol. Lett. 30(8), 677–680 (2018).
[Crossref]

Oton, C.

Pasquale, F.

Peled, Y.

Peng, F.

Peng, G.

C. Wang, C. Wang, Y. Shang, X. Liu, and G. Peng, “Distributed acoustic mapping based on interferometry of phase optical time-domain reflectometry,” Opt. Commun. 346, 172–177 (2015).
[Crossref]

C. Wang, Y. Shang, X. Liu, C. Wang, H. Yu, D. Jiang, and G. Peng, “Distributed OTDR-interferometric sensing network with identical ultra-weak fiber Bragg gratings,” Opt. Express 23(22), 29038–29046 (2015).
[Crossref]

Peng, Z.

Pilgrim, J. A.

Putten, L. D.

Rao, Y.

Sales, S.

Seo, D.

Shan, Y.

X. Zhang, Z. Sun, Y. Shan, Y. Li, F. Wang, J. Zeng, and Y. Zhang, “A High Performance Distributed Optical Fiber Sensor Based on Φ-OTDR for Dynamic Strain Measurement,” IEEE Photonics J. 9(3), 1 (2017).
[Crossref]

Shang, Y.

C. Wang, Y. Shang, X. Liu, C. Wang, H. Yu, D. Jiang, and G. Peng, “Distributed OTDR-interferometric sensing network with identical ultra-weak fiber Bragg gratings,” Opt. Express 23(22), 29038–29046 (2015).
[Crossref]

C. Wang, C. Wang, Y. Shang, X. Liu, and G. Peng, “Distributed acoustic mapping based on interferometry of phase optical time-domain reflectometry,” Opt. Commun. 346, 172–177 (2015).
[Crossref]

Song, K.

Y. Mizuno, N. Hayashi, H. Fukuda, K. Song, and K. Nakamura, “Ultrahigh-speed distributed Brillouin reflectometry,” Light: Sci. Appl. 5(12), e16184 (2016).
[Crossref]

Sun, Q.

A. Fan, H. Li, T. He, Z. Yan, and Q. Sun, “Simultaneous Distributed Temperature and Vibration Measurement with UWFBG based Coherent OTDR,” Optical Fiber Communication Conference (2018).

Sun, Z.

X. Zhang, Z. Sun, Y. Shan, Y. Li, F. Wang, J. Zeng, and Y. Zhang, “A High Performance Distributed Optical Fiber Sensor Based on Φ-OTDR for Dynamic Strain Measurement,” IEEE Photonics J. 9(3), 1 (2017).
[Crossref]

Tang, J.

Tanner, M.

M. Tanner, S. Dyer, B. Baek, R. Hadfield, and S. Nam, “High-resolution single-mode fiber-optic distributed Raman sensor for absolute temperature measurement using superconducting nanowire single-photon detectors,” Appl. Phys. Lett. 99(20), 201110 (2011).
[Crossref]

Tong, W.

Tur, M.

Wang, A.

Y. Wang, J. Gong, D. Y. Wang, B. Dong, W. Bi, and A. Wang, “A Quasi-Distributed Sensing Network With Time-Division-Multiplexed Fiber Bragg Gratings,” IEEE Photonics Technol. Lett. 23(2), 70–72 (2011).
[Crossref]

Wang, B.

G. Yang, X. Fan, S. Wang, B. Wang, Q. Liu, and Z. He, “Long-range distributed vibration sensing based on phase extraction from phase-sensitive OTDR,” IEEE Photonics J. 8(3), 1–12 (2016).
[Crossref]

Wang, C.

C. Wang, Y. Shang, X. Liu, C. Wang, H. Yu, D. Jiang, and G. Peng, “Distributed OTDR-interferometric sensing network with identical ultra-weak fiber Bragg gratings,” Opt. Express 23(22), 29038–29046 (2015).
[Crossref]

C. Wang, Y. Shang, X. Liu, C. Wang, H. Yu, D. Jiang, and G. Peng, “Distributed OTDR-interferometric sensing network with identical ultra-weak fiber Bragg gratings,” Opt. Express 23(22), 29038–29046 (2015).
[Crossref]

C. Wang, C. Wang, Y. Shang, X. Liu, and G. Peng, “Distributed acoustic mapping based on interferometry of phase optical time-domain reflectometry,” Opt. Commun. 346, 172–177 (2015).
[Crossref]

C. Wang, C. Wang, Y. Shang, X. Liu, and G. Peng, “Distributed acoustic mapping based on interferometry of phase optical time-domain reflectometry,” Opt. Commun. 346, 172–177 (2015).
[Crossref]

Wang, D. Y.

Y. Wang, J. Gong, D. Y. Wang, B. Dong, W. Bi, and A. Wang, “A Quasi-Distributed Sensing Network With Time-Division-Multiplexed Fiber Bragg Gratings,” IEEE Photonics Technol. Lett. 23(2), 70–72 (2011).
[Crossref]

Wang, F.

T. Liu, F. Wang, X. Zhang, Q. Yuan, J. Niu, L. Zhang, and T. Wei, “Interrogation of Ultra-Weak FBG Array Using Double-Pulse and Heterodyne Detection,” IEEE Photonics Technol. Lett. 30(8), 677–680 (2018).
[Crossref]

X. Zhang, Z. Sun, Y. Shan, Y. Li, F. Wang, J. Zeng, and Y. Zhang, “A High Performance Distributed Optical Fiber Sensor Based on Φ-OTDR for Dynamic Strain Measurement,” IEEE Photonics J. 9(3), 1 (2017).
[Crossref]

Wang, S.

G. Yang, X. Fan, S. Wang, B. Wang, Q. Liu, and Z. He, “Long-range distributed vibration sensing based on phase extraction from phase-sensitive OTDR,” IEEE Photonics J. 8(3), 1–12 (2016).
[Crossref]

Wang, Y.

Y. Wang, J. Gong, D. Y. Wang, B. Dong, W. Bi, and A. Wang, “A Quasi-Distributed Sensing Network With Time-Division-Multiplexed Fiber Bragg Gratings,” IEEE Photonics Technol. Lett. 23(2), 70–72 (2011).
[Crossref]

Wang, Z.

Wei, T.

T. Liu, F. Wang, X. Zhang, Q. Yuan, J. Niu, L. Zhang, and T. Wei, “Interrogation of Ultra-Weak FBG Array Using Double-Pulse and Heterodyne Detection,” IEEE Photonics Technol. Lett. 30(8), 677–680 (2018).
[Crossref]

Wen, H.

Woo, J.

D. Kweon, K. Koo, J. Woo, and Y. Kim, “Hot spot temperature for 154 kV transformer filled with mineral oil and natural ester fluid,” IEEE Trans. Dielectr. Electr. Insul. 19(3), 1013–1020 (2012).
[Crossref]

Wu, H.

Wu, X.

Xia, L.

Yan, Z.

A. Fan, H. Li, T. He, Z. Yan, and Q. Sun, “Simultaneous Distributed Temperature and Vibration Measurement with UWFBG based Coherent OTDR,” Optical Fiber Communication Conference (2018).

Yang, C.

Yang, G.

G. Yang, X. Fan, S. Wang, B. Wang, Q. Liu, and Z. He, “Long-range distributed vibration sensing based on phase extraction from phase-sensitive OTDR,” IEEE Photonics J. 8(3), 1–12 (2016).
[Crossref]

Yang, M.

Yoon, D.

Yu, H.

Yuan, Q.

T. Liu, F. Wang, X. Zhang, Q. Yuan, J. Niu, L. Zhang, and T. Wei, “Interrogation of Ultra-Weak FBG Array Using Double-Pulse and Heterodyne Detection,” IEEE Photonics Technol. Lett. 30(8), 677–680 (2018).
[Crossref]

Zeng, J.

X. Zhang, Z. Sun, Y. Shan, Y. Li, F. Wang, J. Zeng, and Y. Zhang, “A High Performance Distributed Optical Fiber Sensor Based on Φ-OTDR for Dynamic Strain Measurement,” IEEE Photonics J. 9(3), 1 (2017).
[Crossref]

Zhang, H.

Zhang, L.

T. Liu, F. Wang, X. Zhang, Q. Yuan, J. Niu, L. Zhang, and T. Wei, “Interrogation of Ultra-Weak FBG Array Using Double-Pulse and Heterodyne Detection,” IEEE Photonics Technol. Lett. 30(8), 677–680 (2018).
[Crossref]

Zhang, X.

T. Liu, F. Wang, X. Zhang, Q. Yuan, J. Niu, L. Zhang, and T. Wei, “Interrogation of Ultra-Weak FBG Array Using Double-Pulse and Heterodyne Detection,” IEEE Photonics Technol. Lett. 30(8), 677–680 (2018).
[Crossref]

X. Zhang, Z. Sun, Y. Shan, Y. Li, F. Wang, J. Zeng, and Y. Zhang, “A High Performance Distributed Optical Fiber Sensor Based on Φ-OTDR for Dynamic Strain Measurement,” IEEE Photonics J. 9(3), 1 (2017).
[Crossref]

F. Zhu, Y. Zhang, L. Xia, X. Wu, and X. Zhang, “Improved Φ-OTDR Sensing System for High-Precision Dynamic Strain Measurement Based on Ultra-Weak Fiber Bragg Grating Array,” J. Lightwave Technol. 33(23), 4775–4780 (2015).
[Crossref]

Zhang, Y.

X. Zhang, Z. Sun, Y. Shan, Y. Li, F. Wang, J. Zeng, and Y. Zhang, “A High Performance Distributed Optical Fiber Sensor Based on Φ-OTDR for Dynamic Strain Measurement,” IEEE Photonics J. 9(3), 1 (2017).
[Crossref]

F. Zhu, Y. Zhang, L. Xia, X. Wu, and X. Zhang, “Improved Φ-OTDR Sensing System for High-Precision Dynamic Strain Measurement Based on Ultra-Weak Fiber Bragg Grating Array,” J. Lightwave Technol. 33(23), 4775–4780 (2015).
[Crossref]

Zheng, Y.

Zhu, F.

Appl. Opt. (1)

Appl. Phys. Lett. (1)

M. Tanner, S. Dyer, B. Baek, R. Hadfield, and S. Nam, “High-resolution single-mode fiber-optic distributed Raman sensor for absolute temperature measurement using superconducting nanowire single-photon detectors,” Appl. Phys. Lett. 99(20), 201110 (2011).
[Crossref]

Chin. Opt. Lett. (1)

IEEE Photonics J. (2)

X. Zhang, Z. Sun, Y. Shan, Y. Li, F. Wang, J. Zeng, and Y. Zhang, “A High Performance Distributed Optical Fiber Sensor Based on Φ-OTDR for Dynamic Strain Measurement,” IEEE Photonics J. 9(3), 1 (2017).
[Crossref]

G. Yang, X. Fan, S. Wang, B. Wang, Q. Liu, and Z. He, “Long-range distributed vibration sensing based on phase extraction from phase-sensitive OTDR,” IEEE Photonics J. 8(3), 1–12 (2016).
[Crossref]

IEEE Photonics Technol. Lett. (2)

Y. Wang, J. Gong, D. Y. Wang, B. Dong, W. Bi, and A. Wang, “A Quasi-Distributed Sensing Network With Time-Division-Multiplexed Fiber Bragg Gratings,” IEEE Photonics Technol. Lett. 23(2), 70–72 (2011).
[Crossref]

T. Liu, F. Wang, X. Zhang, Q. Yuan, J. Niu, L. Zhang, and T. Wei, “Interrogation of Ultra-Weak FBG Array Using Double-Pulse and Heterodyne Detection,” IEEE Photonics Technol. Lett. 30(8), 677–680 (2018).
[Crossref]

IEEE Trans. Dielectr. Electr. Insul. (1)

D. Kweon, K. Koo, J. Woo, and Y. Kim, “Hot spot temperature for 154 kV transformer filled with mineral oil and natural ester fluid,” IEEE Trans. Dielectr. Electr. Insul. 19(3), 1013–1020 (2012).
[Crossref]

J. Lightwave Technol. (4)

Light: Sci. Appl. (1)

Y. Mizuno, N. Hayashi, H. Fukuda, K. Song, and K. Nakamura, “Ultrahigh-speed distributed Brillouin reflectometry,” Light: Sci. Appl. 5(12), e16184 (2016).
[Crossref]

Meas. Sci. Technol. (1)

A. Masoudi, M. Belal, and T. P. Newson, “A distributed optical fibre dynamic strain sensor based on phase-OTDR,” Meas. Sci. Technol. 24(8), 085204 (2013).
[Crossref]

Opt. Commun. (1)

C. Wang, C. Wang, Y. Shang, X. Liu, and G. Peng, “Distributed acoustic mapping based on interferometry of phase optical time-domain reflectometry,” Opt. Commun. 346, 172–177 (2015).
[Crossref]

Opt. Express (7)

Opt. Lett. (1)

Other (1)

A. Fan, H. Li, T. He, Z. Yan, and Q. Sun, “Simultaneous Distributed Temperature and Vibration Measurement with UWFBG based Coherent OTDR,” Optical Fiber Communication Conference (2018).

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Figures (10)

Fig. 1.
Fig. 1. Diagram of the on-line writing FBG system
Fig. 2.
Fig. 2. Schematic of hybrid UWFBG sensing system for distributed temperature and vibration measurement. ASE: amplified spontaneous emission; NLL: narrow linewidth laser; SOA: semiconductor optical amplifier; OC: optical coupler; EDFA: erbium-doped fiber amplifier; BFBG: broadband UWFBG; NFBG: narrowband UWFBG; DWDM: dense wavelength division multiplexing; CCD: charge-coupled device; AFG: arbitrary function generator; PD: photodetector; DAQ: data acquisition.
Fig. 3.
Fig. 3. Reflection spectrum of 200 NFBGs
Fig. 4.
Fig. 4. Experimental setup of proposed sensing system
Fig. 5.
Fig. 5. The reflection spectra of (a) NFBG400 and (b) NFBG401 at different temperatures
Fig. 6.
Fig. 6. (a) Temperature measurement results of the narrowband UWFBG array; (b) Measured peak wavelength shift diagram with temperature
Fig. 7.
Fig. 7. (a) Demodulated phase changing diagram at 400 m and 1600 m; (b) 3D plot of spatial-temporal domain demodulated signals along the hybrid UWFBG array; (c) The responses of temporal domain at two vibration positions; (d) Frequency responses of the system at different temperatures
Fig. 8.
Fig. 8. Frequency response of the PZT measured by the distributed sensor
Fig. 9.
Fig. 9. A raw trace of the SMF and UWFBG array
Fig. 10.
Fig. 10. (a) The time domain signals of SMF and UWFBG; (b) the frequency spectra of vibration signals

Equations (7)

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f ( λ i ) = A exp ( ( λ i B ) 2 2 C 2 )
E R 1 = E 1 exp ( j ( ω t + ϕ 1 ( t ) ) ) E R 2 = E 2 exp ( j ( ω t + ϕ 2 ( t ) ) )
i p h o t = k ( E R 1 + E R 2 ) ( E R 1 + E R 2 ) = k ( E 1 2 + E 2 2 + 2 E 1 E 2 cos ( ϕ 1 ( t ) ϕ 2 ( t ) ) )
( i s ) 2 ¯ = 2 k 2 E 1 2 E 2 2 = 2 k 2 P 1 P 2
S N = 2 k 2 P 1 P 2 P N
I k = D + I 0 cos [ ϕ (t) - (k - 1)(2 π /3)],k = 1,2,3
V = 3 ϕ ( t )

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