The Method and Experiment of Micro-Crack Identification Using OFDR Strain Measurement Technology
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors1.The author mentioned in the article about using the displacement distance of sensor points in optical fibers to obtain the width of the generated cracks. However, the edges of peak strain in the strain image are not vertical. How can the number of sensor points in the optical fiber with strain be accurately determined?
2.I've noticed that when the displacement distance is 20 micrometers and 30 micrometers, the maximum values of strain are very close, and the strain's maximum values appear to be nonlinear. Under these circumstances, how is it possible to identify the linear crack width in images with similar peak strains?
3.The author mentions that the poor recognition effect of TSSOF is likely due to the protective sleeve. How significant is the difference between the performance of standard single-mode fibers and PISOF?
4.There is an error in the unit of the vertical axis in Figure 8a.
5. The header is from the journal "Photonics" instead of "Sensors".
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsIn this paper authors proposed a method and conducted experimental study for identifying and locating micro-cracks using optical fiber strain sensing based on OFDR to address this issue. They verified the feasibility of this method for micro-crack detection by the combination of polyimide-coated sensing optical fiber (PISOF) and tight sheath sensing optical fiber (TSSOF). A calculation method for micro-crack widths based on distributed optical fiber strain curves was established, and the test results of different optical fibers were compared.
The paper is well written and readable. The idea that authors had presented is used for the strain detection for around a decade. For the reader, I think it is important to have information about earlier research on a given topic so that he can follow the development of technology and evaluate the novelties of this paper. For that purpose, few sentences and corresponding citation is needed in introductory section referring to pioneer works in this area and not only references in the last year or two.
Furthermore, a physics principle behind OFDR technique needs to be elaborated more in section 2.1 for the reader to have full picture of proposed method. Is there theoretical limit for spatial resolution and if there is how is determined? In the same section Figure 1. doesn’t correspond to Ref 20 and it also needs better explanation.
At the end, both fibers have large diameter which suggest they are multimode. Since multimode is there effect of mode coupling and how it influences measurements, i.e. does steady state has to be reached for measurements to be valid? Also, since multimode fibers have high loss what are the maximum lengths for this method to be applied?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for Authors1. There are papers from earlier years and some of them should be cited for the sake of clarity.
2.Have you calculated limit of your system and could you present it?
3. Could you refer to the fiber as 9/125 fiber?
Author Response
There are papers from earlier years and some of them should be cited for the sake of clarity.
Response: Thanks for your comments！
Some early literature is cited in the article.
Have you calculated limit of your system and could you present it?
Response: Thanks for your comments！
As mentioned in Article 2.1, the system test range is-12000 με to 12000 με.
Could you refer to the fiber as 9/125 fiber?
Response: Thanks for your comments！
Yes, both fibers tested were single-mode fibers
