In-Line Gas Sensor Based on the Optical Fiber Taper Technology with a Graphene Oxide Layer

Round 1

Reviewer 1 Report

This work describes a gas detection using a tapered optical fiber coated with a graphene oxide layer. But the experimental study was incomplete and lacked novelty. Below are some questions and the detail revision points for the authors' consideration.

1. In Introduction, the progress of tapered optical fibers to test gas is introduced too little. Need to improve.

2. In Introduction, the research significance of gas detection is not introduced and needs to be modified.

3. In Table 2, why did you list the chemical composition? and The parameters in these two columns are wrong and need to be checked.

4. In 2.1, line 134, what is the abbreviation for LPG? Please explain.

5. In 2 section, this part lacks the detection principle and needs to be improved.

6. In Figure 4, the ruler is missing from the SEM pictures.

7. In Figure 10, there is something wrong with the ordinate time, and needs to be refined.

8. The experimental results need to be listed in detail, and the advantages of the sensor are proposed.

Author Response

We would like to thank the Reviewer for his time and effort in carefully checking our manuscript. Being very grateful for all valuable comments, insights, and advice, we have made the suggested changes in the manuscript and prepared answers for all comments are in attachment file.

Author Response File: Author Response.pdf

Reviewer 2 Report

I liked the manuscript. I will recommend it for publication after minor revisions. The authors use the mechanism of changing the refractive index of the optical fiber cladding to design sensitive elements of sensor networks on this basis. Although the idea, in general, is not new, but it is very witty and good. On my behalf, I would like to wish the author's success in promoting the topic of their scientific research.

 

Even though the article as a whole left a good impression on me, I have accumulated some comments on the manuscript, the correction of which could significantly improve it.

 

1. In the review, the authors focus on the use of conical fibers. At the same time, the authors undeservedly disregarded optical fibers with an etched cladding, which are also sensitive to changes in the refractive index of the environment. Etched fibers can also be successfully coated with a material whose refractive index is sensitive to the environment. In continuation to this, it would be good to include in the review papers that propose to form a fiber Bragg grating on an etched cladding portion of the fiber.

1) Misbakhov, R.S.; Vasev, A.N.; Sakhabutdinov, A.Z.; Nureev, I.I.; Morozov, O.G.; Lipatnikov, K.A.; Vasilets, A.A. Address Fiber Optical Sensor for Relative Humidity Measuring in a Switchgear. In Proceedings of the Proc SPIE Int Soc Opt Eng; Andreev V.A., Bourdine A.V., Burdin V.A., Morozov O.G., Sultanov A.H., Eds.; SPIE, 2020; Vol. 11516.

2) Liang, W.; Huang, Y.; Xu, Y.; Lee, R.K.; Yariv, A. Highly Sensitive Fiber Bragg Grating Refractive Index Sensors. Applied Physics Letters 2005, 86, 151122, doi:10.1063/1.1904716

The central wavelength in the reflection spectrum of a fiber Bragg grating is also sensitive to changes in the effective refractive index of a fiber section. However, the control of the position of the central wavelength of the fiber Bragg grating is much simpler and more accurate.

 

2. As a recommendation for further research, I would like to suggest that the authors create a fiber Bragg grating on the conical section of the fiber. I believe that this will significantly enrich the functionality of the approach proposed by the authors.

 

3. The authors do not focus on the influence of the APTES refractive index on the results. By and large, the refractive index of the coupling agent should influence the change in the effective refractive index. Furthermore, I did not find the sensitivity of the binding agent to humidity and temperature.

 

4. Line 117 says, The Nitrogen is heavier than air. I think it's a mistake.

 

5. Line 134 says Propane-butane is not poisonous. I doubt this statement, especially since the following lines just say something else.

 

6. As an optician, it was interesting for me to read about the physicochemical properties of gases, but it seems to me that this section could be reduced, since the manuscript is focused on optical measurement methods.

 

7. Unfortunately, the authors do not comment on the issues of temperature and humidity compensation. The issues of selective sensitivity of graphene oxide to a mixture of gases is not considered. For example, sensitivity to a propane-butane mixture, it is obvious to expect sensitivity to carbon monoxide and carbon dioxide, to ammonia and other similar gases.

8. The authors report that it is possible to detect gases using absorption, but do not provide an estimate of concentration, nor the ability to separate absorption from different gases. The spectra were obtained at 100% concentrations, apparently.

Author Response

We would like to thank the Reviewer for his time and effort in carefully checking our manuscript. Being very grateful for all valuable comments, insights, and advice, we have made the suggested changes in the manuscript and prepared answers for all comments are in the attachment file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

• The principle part needs to list the formula to explain.

Author Response

Thanks to Reviewer for the suggestions to improve the quality of the manuscript. We add the most important formulas about the penetration depth of light in optical fiber and we have expanded the description and formulas of the absorption process of GO. For a description of the changes made, please see the attached file.

Author Response File: Author Response.pdf