Review Reports - Investigation of Hybrid Remote Fiber Optic Sensing Solutions for Railway Applications

Round 1

Reviewer 1 Report (New Reviewer)

The paper present a hybrid fiber sensing method using coding and FBG shift detection technique，for redundancy of safety assurance.The fiber sensing method can provide information on train location，speed, and direction.The method has pratical significance for remote sensing.

Howewer, this method only combine two common techniques directly,in lack of innovation，and author didn't described the difficulty in the combination adequately. I don't find the scientific soundness in the paer.

Secondly, the paper didn't describe backgroud and relevant progress sufficently，and most of cited references are too old. The figures need to optimize.

I advice author to find and descirbe the difficulty of combining two techniques and provide an appropriate solution.

Author Response

Dear Reviewer,

Thank you for taking the time to review our journal paper once again. We greatly appreciate your valuable feedback and suggestions, which have significantly enhanced the quality of our work. We have carefully addressed each of the concerns raised in your previous review and made the necessary revisions accordingly.

We have provided a more detailed description and references in response to your comments. This clarification will help readers better understand the research process and replicate our study if desired. Additionally, we have included supplementary figures and tables to support our findings further and enhance the overall comprehensibility of the paper.

Once again, we would like to express our gratitude for your insightful review, as it has undoubtedly strengthened the rigor and clarity of our manuscript. We hope our revisions adequately address your issues and meet the journal’s high standards. We look forward to receiving your final evaluation and appreciate your time and efforts in reviewing our work.

Sincerely,

Serhat BOYNUKALIN

Istanbul Technical University,
Graduate School,
Istanbul, Türkiye,
boynukalin@itu.edu.tr

Author Response File: Author Response.pdf

Reviewer 2 Report (New Reviewer)

The paper is suitable to be published on Photonics provided that some improvements are made:

1) The authors should cite references that investigate the use of FOS to monitor trains. There are several published works discussing fiber optic sensors in railway applications. At least a review paper should be cited, comparing to your proposed system.

2) The font in Figures 3b, 6, 12, and 14 is too small and hard to read.

3) If applicable, the authors should mention how their results compare to other systems for railways, i.e. is it possible to quantify how much better their system is?

4) The website (ref 17) should be cited according to the journal's rules.

5) The proposed system is original, however, it needs to be situated as compared to other FOS systems published and implemented in railways in order to justify its interest to readers.

6) The results are shown in a clear manner and discussed thoroughly.

Minor corrections could be improved, but the overall quality is good.

Author Response

Dear Reviewer,

Sincerely,

Serhat BOYNUKALIN

Istanbul Technical University,
Graduate School,
Istanbul, Türkiye,
boynukalin@itu.edu.tr

Author Response File: Author Response.pdf

Reviewer 3 Report (New Reviewer)

This is the whole simulation work, some questions are listed here:

1. What are the difficulties to put these ideas into the real field test?

2. What is the ultimate range or limitation of sensing the train speed? Is it possible to be used in the highspeed railway?

Author Response

Dear Reviewer,

Sincerely,

Serhat BOYNUKALIN

Istanbul Technical University,
Graduate School,
Istanbul, Türkiye,
boynukalin@itu.edu.tr

Author Response File: Author Response.pdf

Reviewer 4 Report (New Reviewer)

The authors suggest a hybrid sensing system for determining train position, speed, and direction. I suppose it is a review according to the number of pages and inscription under the Photonics logo. But definitely not. An overview of the current state and also a comparison with available solutions is not made. According to Figs 4 and 5 you concluded that the simulated data are very close to experimental ones. And that proves your system. For better illustration, why dont you use the same FBG wavelengths in your simulation as it was used in experiment? In text you provide that you investigate temperature influence from 10 to 100 degrees but Table 2 and also Fig. 4 have set different values. In Table 3 it looks more like deviation than an accuracy. Any special reason why you use 50 km parabolic multimode fiber during the simulation shown in Fig.6? It is not clear to me how it was determined Acoeff and Scoeff? And also in equation 3 how it was determined number 12.5? I am missing the marking on the Fig. 13. In the text it is stated that on the 50 km length, it is possible to use as many gratings as it is necessary. Is there any limitation? Then you state that between gratings there is 500 m distance according to the length of the train.

There are some typos as on page 5 row 146 stain, page 12 row 289 BFG.

Author Response

Dear Reviewer,

Sincerely,

Serhat BOYNUKALIN

Istanbul Technical University,
Graduate School,
Istanbul, Türkiye,
boynukalin@itu.edu.tr

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report (New Reviewer)

The authors answered my questions correctly,and provided sufficient supplement, the quality of paper has improved.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The authors demonstrate a hybrid fiber-optic system including a coding technique based on reflected correlated FBGs' signals to indicate the train location and the wavelength drift monitoring system for the FBGs to detect the train speed and moving direction due to the strain deriving from the air pressure. The sensing range is 50 Km with a spatial resolution of 1 m based on a series of FBGs. A tunable filter and a PIN PD are essential to check the wavelegnth shift of the FBGs when the moving train causes strain on FBGs. This is mainly a simulation work. I think this manuscript can be accepted after revisions. My comments are listed below.

1. A 10-dBm laser is used and the signals will be travelling over 50 km. Are EDFAs esssential in this system? Will nonlinear effects like SPM or FWM occur to degrade the FBG signals? A coding technique can of course alleviate this effect but it is appreciated if this issue can be discussed and addressed.

2. The moving train causes strain on FBGs to reflect the train location and speed. How if the very strong wind going through the tunnel? Since this is a industrial-orientation research, how to avoid the fake signals from the natural environment ?

3. What could be the maximun train speed that this system can detect? 80km/hr? It is believed that nowadays the tranditional train can move at the speed above 110-130 km/hr. For high speed rail, the speed can be even higher than 250 km/hr at least. A caution system capable of detecting train speed of 80 km/hr may not be pratical. Is there any method to improve the detection of the train speed?

4. Series of uniformed FBGs are used. I suggest to use apodised FBGs to avoid the additional noises in your future works.

5.The train length is assumed to be 125 m and the interval distance between sensors is 500 m. In this case, a spatial resolution of 1 m is obviously unnecessary. The cost is very important to make this system accepted by the railway authority. Moving speed would be more important to be improved. However, the algorithm or the decoding method become very important to handle a huge amount of FBGs over 50 km in a timely manner.

6. The operating bandwidth of the tuning filter is 10 GHz. At 1550 nm, it is corresponding to about 0.08 nm. In Fig. 8, the estimated 3 dB bandwidth of the FBG is 0.2 nm. Is it right? In this case, how to clearly monitor the slight wavelength shift? In addition, please comment on the tuning speed of the optical filter.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this paper, the authors investigate hybrid remote fiber optic sensing solutions for rail-way applications. However the paper is confusing. There are several issues that are needed to be considered.

1. What’s the hybrid sensing solution? The author should give a clear description. As we can see there are two separate methods of transmitted pulses' coding technique and FBG technique.

2. What are the advantages and novelty of the system. As the proposed schemes are all widely used techniques.

3. Only simulation results are given, and there is no experiment, which is not sufficient.

4. There is no concrete conclusion that is drawn from the simulation results.

There are numbers typos and errors in the paper: line 151, line 202. After Figure 9, there are another Figure 4-9, which is confusing. Line 266: “Figure 13”, but there is no figure 13.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

1）It is suggested to indicate some statistical results in the abstract. For instance, ‘greater accuracy’ and ‘improving overall system accuracy’ can be elaborated with numbers, which can make this paper more attractive and professional.

2）A significant advantage of fibre optic sensors is the immunity to EMI. Thus, this type of sensor can also provide solutions for railway overhead systems’ monitoring which is used in high-voltage environments. It is recommended to mention this with some literature review, such as monitoring the vibration caused by vehicle [1] and the wind load [2], to give a full picture of this problem for readers.

[1] Song, Yang, et al. "A spatial coupling model to study dynamic performance of pantograph-catenary with vehicle-track excitation." Mechanical Systems and Signal Processing 151 (2021): 107336.

[2] Duan, Fuchuan, et al. "Study on Aerodynamic Instability and Galloping Response of Rail Overhead Contact Line Based on Wind Tunnel Tests." IEEE Transactions on Vehicular Technology (2023).

3) It is desired to present a physical fibre optic sensor in the introduction when describing the analysis object.

4) Please think about changing the title of section 4, which is too generic and does not provide any useful information.

5) Can any further explanation be added for the x-label in Figure 6?

6) Figure 7 is not readable. Please consider a better illustration.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

In the paper the authors numerically investigate a fiber optic sensing method for railway systems to estimate location, speed, and direction of the trains by using a coding technique for the transmitted pulses jointly the fiber Bragg gratings technology. I think the results are interesting, but the manuscript needs to be improved significantly. My comments are listed in the following:

- At line 150 there is a missing part. Please correct;

- At line 166 the figure number is a missing part. Please correct;

- I suggest to unify figure 4 and figure 5. In particular, figure 4 can be an inset of figure 4;

- In figure 9 the font is too small and only the y axis in subfigure (e) is different from the others. I think a single figure including all tracks is clearer;

- From line 225 the numbering of the figures is incorrect;

- Figure 6 on line 250 needs to be improved. The font is too small and, above all, the position of the resonance peak is not clearly visible in the subfigures;

- Section 7 on designing the FBG sensor needs to be significantly expanded by adding a more detailed explanation and a block diagram of the system;

- Figure 8 on line 291 is a screenshot. I suggest to edit the graph with an appropriate software;

- Figure 9 on line 303 has a very bad resolution. Please edit the graph with an appropriate software.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf