Review of a Specialty Fiber for Distributed Acoustic Sensing Technology

Round 1

Reviewer 1 Report

This paper presents a broad review of the different specialty sensing fibers and their performance enhancements used in the phase-OTDR system. The paper well-reviewed for specialty fibers proposed in the literature for DAS system with their operating principles. Some of the comments are and concerns are;

1. A summary table showing, discrete scattering, continuous long-distance scattering with their SNR enhancements, sensing distance and methods to improve the performance of specialty fiber would be helpful.
2. Page 4, line 139, “Where n is the refractive index of the fiber, .”. The symbol “n” should be consistent as used in the equation. Same for all over the manuscript.
3. There are many grammatical errors throughout the manuscript, for instance, Page 3, line 117, “signal of point A and B in 2.1 can be obtained…..
4. The following two references can be included on the manuscript,
5. Feng, T. Xu, J. Huang, Y. Yang, F. Li, J. Zhou, and H. Yu "Enhanced SNR phase-sensitive OTDR system with active fiber", Proc. SPIE 10849, Fiber Optic Sensing and Optical Communication, 108490C, 2018. https://doi.org/10.1117/12.2503844
6. Lalam, P. S. Westbrook, J. Li, P. Lu and M. P. Buric, "Phase-Sensitive Optical Time Domain Reflectometry With Rayleigh Enhanced Optical Fiber," in IEEE Access, vol. 9, pp. 114428-114434, 2021, doi: 10.1109/ACCESS.2021.3105334.

Author Response

Dear editors and reviewers of Multidisciplinary Digital Publishing Institute: Photonics

We are grateful to the reviewers for their valuable comments and suggestions which help improving the quality of the paper. We have studied the reviewers’ comments carefully and revised the manuscript according to the comments.

A revision has been made according to the comments of editors and reviewers, mainly including the following aspects:

1. A summary table about CSE fiber and DSE fiber was supplemented.
2. Some errors in the equation were corrected.
3. Grammatical errors were modified.
4. Some related references were added to improve the citation.

The reply to the reviewers’ comments is detailed below. Meanwhile, all the discussions have been properly added in the revised manuscript.

Thank you very much for your attention and consideration. Looking forward to hearing from you.

Sincerely,

Qizhen Sun

E-mail: [email protected]

Reply to the comments of reviewers

--------Reviewer Comments--------

Comments to the authors:

This paper presents a broad review of the different specialty sensing fibers and their performance enhancements used in the phase-OTDR system. The paper well-reviewed for specialty fibers proposed in the literature for DAS system with their operating principles. Some of the comments are and concerns are;

1. A summary table showing, discrete scattering, continuous long-distance scattering with their SNR enhancements, sensing distance and methods to improve the performance of specialty fiber would be helpful.

Reply: Thanks for the kind suggestion. We summarized the relevant contents as shown in the table below (page 13, line 392)  

2. Page 4, line 139, “Where n is the refractive index of the fiber.”. The symbol “n” should be consistent as used in the equation. Same for all over the manuscript.

Reply: Thanks for the kind reminder. We have corrected the mistakes of the symbol in the revised manuscript.E.g. page 2, line 77, “  is the change of fiber length from equation ,  is axial strain of fiber,  is length of fiber.”E.g. page 4, line 139, “Where  is the refractive index of the fiber, ” 

3. There are many grammatical errors throughout the manuscript, for instance, Page 3, line 117, “signal of point A and B in 2.1 can be obtained….

Reply: Thanks for the kind reminder. We have carefully checked through the manuscript and corrected the grammatical errors in the revised manuscript.E.g. Page 3, line 117, “signal of point A and B in 2.1 can be obtained…”is revised as “signals of point A and B in 2.1 can be obtained…”E.g. page 18, line 550, “the result show that the hydroacoustic detection sensitivity is as high as -127 dB re rad/μPa.” is revised as “the results show that the hydroacoustic detection sensitivity is as high as -127 dB re rad/μPa.” 

4. The following two references can be included on the manuscript,Feng, T. Xu, J. Huang, Y. Yang, F. Li, J. Zhou, and H. Yu "Enhanced SNR phase-sensitive OTDR system with active fiber", Proc. SPIE 10849, Fiber Optic Sensing and Optical Communication, 108490C, 2018. https://doi.org/10.1117/12.2503844Lalam, P. S. Westbrook, J. Li, P. Lu and M. P. Buric, "Phase-Sensitive Optical Time Domain Reflectometry With Rayleigh Enhanced Optical Fiber," in IEEE Access, vol. 9, pp. 114428-114434, 2021, doi: 10.1109/ACCESS.2021.3105334. 

Reply: Thanks for the kind suggestion. For the first paper, we had cited in the original manuscript (page 5, line 193-197); for the second paper, we have added it in revised manuscript (page 5, line 179-184). The corresponding discussion of the two references in the ‘Introduction’ part are as follows”:In the same year, the research team of the Institute of Semiconductors CAS used erbium-doped optical fiber for distributed optical fiber sensing, and adopted a phase-generated carrier (PGC) optical scheme, which decreased the phase noise by 14 dB and achieved a high SNR acoustic measurement on 1.9 km optical fiber [36]. In 2017, the OFS laboratory in the United States used the phase mask method to efficiently and continuously inscribe Bragg gratings in multicore fibers through ultraviolet (UV) exposure. The backscattering intensity of the fiber is increased by 14 dB, and the reflection spectrum is shown in Figure 5 (a). Then, in cooperation with Fotech company of UK, CSE fiber is used in DAS system, and the SNR of 1 km CSE fiber is increased by 15 dB [31-34].  Note that, all the above discussions are added and marked in the revised manuscript.

We can't insert some pictures on the reply website. Please refer to the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper reports a nice review about special fiber for Distributed acoustic sensing technology. I have some comments.

1- Introduction: please consider to add the review paper about marine environment and marine structural health monitoring  where the acoustic waves and optical fiber sensor technology is quite important. Optics & Laser Technology 140, 107082, 2021. I miss some additional detail about critical application in general in the introduction about optical fiber technology based on acoustic waves etc.

2. How about the use of polymer optical fiber based sensors? I miss some words about it and references that focus the importance and advantages of polymer optical fiber (with or without  FBG and as DOFS) for this accoustic sensing.

3.  Fig. 8: I miss some details about the maturity of FBG technology and methods of inscription to fabricate easily the FBG. Please read and add critical review: Optics Express 26 (2), 2013-2022, 2018.

4. Some words about emerging market for OFS in accoustic sensing.

Author Response

Dear editors and reviewers of Multidisciplinary Digital Publishing Institute: Photonics

We are grateful to the reviewers for their valuable comments and suggestions which help improving the quality of the paper. We have studied the reviewers’ comments carefully and revised the manuscript according to the comments.

A revision has been made according to the comments of editors and reviewers, mainly including the following aspects:

1. The application of DAS in geological structural monitoring has been supplemented.
2. The application of POF in DAS system has been investigated in detail.
3. The details about the maturity and inscription methods of FBG technology have been supplemented.
4. The discussion on the emerging market for OFS in acoustic sensing has been added in the revised manuscript.

The reply to the reviewers’ comments is detailed below. Meanwhile, all the discussions have been properly added in the revised manuscript.

Thank you very much for your attention and consideration. Looking forward to hearing from you.

Sincerely,

Qizhen Sun

E-mail: [email protected]

Reply to the comments of reviewers

--------Reviewer Comments--------

Comments to the authors:

This paper reports a nice review about special fiber for Distributed acoustic sensing technology. I have some comments.

 (1) Introduction: please consider to add the review paper about marine environment and marine structural health monitoring where the acoustic waves and optical fiber sensor technology is quite important. Optics & Laser Technology 140, 107082, 2021. I miss some additional detail about critical application in general in the introduction about optical fiber technology based on acoustic waves etc.

Reply:

Thanks for the reviewer’s suggestion about marine environment and marine structural health monitoring. We refer to the review paper you recommended, investigate the relevant papers in detail, and add  the content into the paragraph 4.2.4 of geological structure monitoring as follows.

         4.2.4 Geological Structural Monitoring

In recent years, DAS is also suitable for monitoring  the geological structural  [84]. In 2017, the research team of University of California Berkeley transforms telecommunication fiber-optic cables into sensor arrays enabling meter-scale recording over tens of kilometers of linear fiber length to record the nearly vertically incident arrival of an earthquake from The Geysers Geothermal Field and estimate its backazimuth and slowness [85]. In 2018, the team of GFZ German Research Centre for Geosciences demonstrate the possibility of dynamic strain determination with conventional fiber cables deployed for telecommunication [86]. Then, by using DAS, they recorded seismic signals from natural and man-made sources with 4 m spacing along a 15 km long fiber cable, identifying with unprecedented resolution, inferring new dynamic fault processes, opening a new window for Earth hazard assessment and exploration structural features. In 2019, the team of Université Côte d’Azur reported measurements on a 41.5 km-long telecom cable that is deployed offshore Toulon, France, and they demonstrated the capability to monitor the ocean solid earth interactions from the coast to the abyssal plain [87]. In the same year, the team of University of California, Berkeley reported the use of an optical fiber cable with a DAS operating onshore, creating a ~ 10000 component, 20 km long seismic array. As depicted in figure 21, they recorded a minor earthquake wavefield identifying multiple submarine fault zone, tracking sea-state dynamics during a storm cycle in the northern Pacific [88].

Figure 21. (a) Map of Monterey Bay, CA, shows Monterey Accelerated Research System (MARS) cable (DAS, pink portion), mapped faults, Gilroy earthquake (red-and-white beach ball) and major bathymetric features. (b) Cross-section illustration of MARS cable used for DAS. (c) 10 min average wave height and spectral wave density (SWD) measurements outside Monterey Bay by buoy. (d) Seafloor DAS strain from cable location 2 km averaged over a 15 min sliding. (e) North component of ground velocity from onshore broadband inertial seismometer averaged over a 15-min sliding window [88].      

References:

84. Min, R.; Liu, Z.; Pereira, L.; Yang, C.; Sui, Q.; Marques, C. Optical fiber sensing for marine environment and marine structural health monitoring: A review. Optics & Laser Technology, 2021, 140, 107082, doi:10.1016/j.optlastec.2021.107082.
85. Lindsey, N.J.; Martin, E.R.; Dreger, D.S.; Freifeld, B.; Cole, S.; James, S.R.; Ajo-Franklin, J.B. Fiber-optic network observations of earthquake wavefields. Geophysical Research Letters, 2017, 44, 11792-11799, doi:10.1002/2017GL075722.
86. Jousset, P.; Reinsch, T.; Ryberg, T.; Blanck, H.; Clarke, A.; Aghayev, R.; Hersir, G.P.; Henninges, J.; Weber, M.; Krawczyk, C.M. Dynamic strain determination using fibre-optic cables allows imaging of seismological and structural features. Nature Communications, 2018, 9(1), 2509, doi:10.1038/s41467-018-04860-y.
87. Sladen, A.; Rivet, D.; Ampuero, J.P.; De Barros, L.; Hello, Y.; Calbris, G.; Lamare, P. Distributed sensing of earthquakes and ocean-solid Earth interactions on seafloor telecom cables. Nature Communications, 2019, 10(1), 5777, doi:10.1038/s41467-019-13793-z.
88. Lindsey, N.J.; Dawe, T.C.; Ajo-Franklin, J.B. Illuminating seafloor faults and ocean dynamics with dark fiber distributed acoustic sensing. Science, 2019, 366(6469), 1103–1107, doi:10.1126/science.aay5881.

 (2) How about the use of polymer optical fiber based sensors? I miss some words about it and references that focus the importance and advantages of polymer optical fiber (with or without FBG and as DOFS) for this acoustic sensing.

Reply: Thanks for the kind suggestion about the applications of polymer optical fiber based DAS system. We consulted the relevant papers exhaustively and combined with a review article (Photonics Res. 9 (2021)1719-1733). This paper reviewed POF based sensors as depicted in table 1. According to our extensive and detailed research, we haven't found its application in DAS now. While, we believe that POF will become a hot spot in DAS system, since its advantages in large strain measurement.

(3) Fig. 8: I miss some details about the maturity of FBG technology and methods of inscription to fabricate easily the FBG. Please read and add critical review: Optics Express 26 (2), 2013-2022, 2018.

Reply: We are sorry for the undetailed description about the maturity and methods of FBG inscription technology. In the revised manuscript, the recommended paper  is cited, and the methods of inscription to FBG is described in more detail as follows. UWFBG usually uses ultraviolet light [41-43] or femtosecond laser [44, 45] to inscribe a permanent periodic change in the refractive index of optical fiber, so as to realize the backward reflection of specific wavelength light. Its most classic preparation system is shown in Figure 8 (a) [46]. In the process of fiber drawing, through the strict dynamic control, UWFBG was written by the phase mask method which used periodic interference fringes of the ±1st diffraction light to irradiate photosensitive fiber and hence periodically change the refractive index of fiber core. Additionally, FBG writing platform was mounted on the draw tower near the first coating to weaken fiber vibrating. The preparation results are shown in Figure 8 (b) [47], and the scattering rate of the scattering enhanced array is much higher than that of the single-mode fiber. However, as a Bragg grating, UWFBG is sensitive to temperature and stress. When the temperature and strain of the environment are changed, the reflection wavelength of UWFBG will drift [48, 49], as shown in Figure 8 (c). Due to the narrow bandwidth of UWFBG, there is a mismatch between the reflection spectrum of UWFBG and the wavelength of detection light in special environments such as high temperature, low temperature and high pressure, and the reflection of UWFBG will degenerate into Rayleigh scattering, resulting in sensing blind area. This characteristic of UWFBG hinders its application in underground, underwater and other special environments.

References:

41. Hill K O. Photosensitivity in optical fiber waveguides : Application to reflection filter fabrication. Applied physics letters, 1978, 32(10): 647-649, doi:10.1063/1.89881.

42. Meltz, W.W.; Morey.; et al. Formation of Bragg gratings in optical fibers by a transverse holographic method. Optics letters, 1989, 14(15): 823-825, doi:10.1364/OL.14.000823.

43. Zheng, Y.; Yu, H.; Guo, H.; et al. Analysis of the Spectrum Distortions of Weak Fiber Bragg Gratings Fabricated In-Line on a Draw Tower by the Phase Mask Technique. Journal of Lightwave Technology, 2015, 33(12): 2670-2673, doi:10.1109/JLT.2014.2384373.

44. Martinez, A.; Dubov, M.; Khrushchev, I.; et al. Direct writing of fibre Bragg gratings by femtosecond laser. Electronics Letters, 2004, 40(19): 1170-1172, doi:10.1049/el:20046050.

45. Chen, Z.Y.; He, J.; Xu, X.Z.; et, al. High-Temperature Sensor Array Based on Fiber Bragg Gratings Fabricated by Femtosecond Laser Point-by-Point Method. Acta Optica Sinica, 2021, 41(13): 1306002, doi:10.3788/AOS202141.1306002.

46. Yang, M.; Bai, W.; Guo, H.; et al. Huge capacity fiber-optic sensing network based on ultra-weak draw tower gratings. Photonic Sensors, 2016, 6(1): 26-41, doi:10.1007/s13320-015-0298-0

47. Tang, J.; Cai, L.; Li, C.; et al. Distributed acoustic sensors with wide frequency response based on UWFBG array utilizing dual-pulse detection. Optical Fiber Technology, 2021, 61(26): 102452, doi:10.1016/j.yofte.2021.102452.

48. Ai, F.; Li, H.; He, T.; et al. Simultaneous distributed temperature and vibration measurement with UWFBG based coherent OTDR. Optical Fiber Communication Conference, 2018, W2A. 12, doi:0.1364/OFC.2018.W2A.12.

49. Yang, M.; Li, C.; Mei, Z.; et al. Thousands of fiber grating sensor array based on draw tower: a new platform for fiber-optic sensing. Optical Fiber Sensors, 2018: FB6, doi:10.1364/OFS.2018.FB6.  

(4) Some words about emerging market for OFS in acoustic sensing.

Reply:  Thanks for the kind suggestion about expectation of emerging market for OFS in acoustic sensing. We have added the following discussion in the prospects paragraph of revised manuscript.Looking to the future, the research on specialty fiber based DAS will be developed rapidly from many aspects, such as the doping new materials for high sensitization, developing the fabrication technique for higher efficiency, introducing AI technique for higher measurement accuracy, and exploring wider application fields. Owing to the distinct advantages, it is believe that the specialty fiber based DAS system will have a bright market prospect in geological and resource exploration, structural health monitoring, hydroacoustic exploration, etc..

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

it is ready for publication

Author Response

We are grateful to you for your valuable comments and suggestions which help improving the quality of the paper