Dead Zone Fault Detection Optimization Method for Few-Mode Fiber Links Based on Unexcited Coupled Higher-Order Modes

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper presents a dead zone fault detection optimization method of FMF link based on unexcited coupled high-order mode, which has great potential for the practical implementations in the FMF link fault detection. I recommend to accepted this manuscript for publication in Photonics if the following issues are addressed.

(1) In the experiment section, there is no detailed parameter of the fiber under test. The authors should provide the information about the cutoff wavelength and mode field diameter, or refractive-index profile of the fiber.

(2) The authors should also describe the detail characteristics of the photonic lantern.

(3) The order of LP mode in the figure uses the subscript, and the pattern in the text does not use subscript, so the format should be unified.

(4) The abbreviations in the Figs.1, 2 and 4 need to be explained.

Comments on the Quality of English Language

The English language is fine for publication.

Author Response

Response Letter

Manuscript ID: photonics-2965510

Title: Dead zone fault detection optimization method of few-mode fiber link based on unexcited coupled high-order mode

Authors: Feng Liu *, Tianle Gu, and Zicheng Huang

Dear Reviewer：

Gratefully thank you for your valuable advices on our manuscript. According to your comments, essential corrections and additions have been made in the revised version of this paper. Detailed reply to your comments is as below. Attached please find the revised manuscript with red underlines, the response reports to all the reviewers. Please see the author's response in the attachment.

Thank you very much for your consideration!

Best regards,

Sincerely

Feng Liu

 

Thank you very much for your consideration!

 

Best regards,

Sincerely

Feng Liu

Thank you very much for your consideration!

 

Best regards,

Sincerely

Feng Liu

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors, thank you for results in this paper, but I have serious doubts about your work.

Small notes:

line 42 'domestic and foreign researchers' - as you publish in international journal it is not acceptable.

line 44 - I think phi-OTDR is not used for fiber fault detection

Fig.5 - different axis labels (5 and 10 steps)

Main note:

Your idea is to provide 'precise detection and location' of faults in fiber line. For this you use 1000 ns pulse for 3 km fiber line. Even in ref.20 they use 300ns for 8km. As a result you have >10dB SNR even on fiber end and you fusion splice location is spreaded over more than 100 m. For me it looks not precise (~3% of sensor length). And you have very strong PD saturation in the beginning of the line from the pulse energy.

Without any change in setup I guess you can reduce pulse duration at least 10 times (to 100ns) and reduce saturation (yes, backscattered signal also will be reduced but here main problem is from TIA saturation, and it will be reduced). And splice location will be also 10 time more accurate.

Also you concentrated on the entrance connector, which is usually availible for cleaning to reduce its reflection level.

One else interesting limitation will be mode MUX/DEMUX crosstalks. How much dB will transfer from LP01 to other modes? Will it affect on reflectograms in other modes?

I think much more interesting application of your method can be for detection of closely located connectors inside fiber line (e.g. if there are few short patchcords - to understand, which exactly connectors must be checked and cleaned). Because they also must reflect mainly in LP01 mode while other modes must contain mainly backscattering with attenuation - and they are very interesting for analysis. May be you can update you research in this direction.

Author Response

Response Letter

Manuscript ID: photonics-2965510

Title: Dead zone fault detection optimization method of few-mode fiber link based on unexcited coupled high-order mode

Authors: Feng Liu *, Tianle Gu, and Zicheng Huang

Dear Reviewer：

Gratefully thank you for your valuable advices on our manuscript. According to your comments, essential corrections and additions have been made in the revised version of this paper. Detailed reply to your comments is as below. Attached please find the revised manuscript with red underlines, the response reports to all the reviewers. Please see the author's response in the attachment.

Thank you very much for your consideration!

Best regards,

Sincerely

Feng Liu

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors presented an interesting, compact, but at the same time meaningful work on a current topic. My comments are minor, but I believe that addressing them could make the work even more better.

1. It may be worth expanding the literature review a little to get a broader idea of the methods by which similar problems were solved. Thus, the authors only briefly mention the method of optical reflectometry of the frequency domain, which physically does not have dead zones. Recently, the method has become more flexible and accessible due to the elimination or reduction in cost of some circuit elements and the use of special signal processing [http://dx.doi.org/10.3390/s24041253]. I also propose to consider the approach implemented in [http://dx.doi.org/10.1364/OL.393539]. In fact, in this work, that scientific group solved the same problem using similar methods. I propose to clearly outline in the introduction how the results of these works differ. 

2. For complete repeatability of the experiment, the authors are recommended to provide information about the manufacturers and models of individual components, as well as about their operating modes.

3. What was the linewidth of the radiation emitted by the laser? I assume that it was a single-frequency radiation source. Are there any unwanted interference patterns observed in the traces? For example, similar to what we see in the DAS data?

Author Response

Response Letter

Manuscript ID: photonics-2965510

Title: Dead zone fault detection optimization method of few-mode fiber link based on unexcited coupled high-order mode

Authors: Feng Liu *, Tianle Gu, and Zicheng Huang

Dear Reviewer：

Gratefully thank you for your valuable advices on our manuscript. According to your comments, essential corrections and additions have been made in the revised version of this paper. Detailed reply to your comments is as below. Attached please find the revised manuscript with red underlines, the response reports to all the reviewers. Please see the author's response in the attachment.

Thank you very much for your consideration!

Best regards,

Sincerely

Feng Liu

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Thanks to the authors for the detailed results of other pulse durations and reflection positions, they are very interesting.

OK, I think this paper has interesting results and can be published.

Though still there are possibility for dead zone reduction by reducing pulse duration as reflectogram still has 5 dB SNR on the far end.