An In-Line Fiber Optic Fabry–Perot Sensor for High-Temperature Vibration Measurement

Round 1

Reviewer 1 Report

Authors here presents a FP cavity, with a suggestion to measure a vibration. The cavity consist of hollow glass tube spliec with two pieces of SMF. Authors provide detailed instructions on preparation of such sensor, togheter with paramteres of the splicer that has been incorporatated in manufacturing process.The performance of the sensor is then evaluated, togheter with its tolerance on the temperature.

In my opinion this is a good paper and should be published. However, I have several concerns to address:

1) Table 2 - Authors provide "bits" as a unit. I believe it would be better to indicate it in terms of temperature or any other value. It would be more usefull for readers, cause not every lab is equiped with this type of splicer.

2) Table 1 - Inner diameter of the SMF is not 9um, but this is core diameter. It should be taken out of the table and listed in the manuscript text.

3) In results and discussion it would be useful to add some other FFT for other vibration frequencies. Or even frequency response curve should be added.

4) Initial Free Spectral Range should be provided in the text

Also, I strongly recomend adding some references to the text to fully address the state of the art in the technology of FP sensors, i.e.:

https://doi.org/10.1364/OL.44.004833

https://doi.org/10.1364/OL.42.001464

Author Response

    Thanks for your kindly work. On behalf of my co-authors, we thank you very much for giving us an opportunity to revise our manuscript. We appreciate editor and reviewers very much for their positive and constructive comments and suggestions on our manuscript entitled “An In–Line Fiber Optic Fabry–Perot Sensor for High–Temperature Vibration Measurement” (Manuscript Number: micromachines-729370). We have studied the valuable comments from you and reviewers carefully, and tried our best to revise the manuscript, and all the revised details are marked in RED.

Point 1: Table 2 - Authors provide "bits" as a unit. I believe it would be better to indicate it in terms of temperature or any other value. It would be more usefull for readers, cause not every lab is equiped with this type of splicer.


Response 1: We have already change the unit "bits" to discharge power and heating power, and the unit watt is used in this paper.

Table 2. The welding parameters for all welds

Point 2: Table 1 - Inner diameter of the SMF is not 9um, but this is core diameter. It should be taken out of the table and listed in the manuscript text.

Response 2: The inner diameter of the SMF has been deleted form the table and listed in the manuscript text.

Table 1. The parameters of all HSTs and fibers used in the fabrication

Point 3: In results and discussion it would be useful to add some other FFT for other vibration frequencies. Or even frequency response curve should be added.

Response 3: We actually tested the vibration of the sensor at several different frequencies, for example:

However, due to the incompleteness of these data and pictures, they can not be provided in the text.

Point 4:  Initial Free Spectral Range should be provided in the text

Response : We added a description of the initial free spectral range. And the initial free spectral range ( ) is determined by ,  is the refractive index of the air,  is the speed of light in the air,  GHz.

Finally, we added some more references about fiber optic vibration sensor in the text. Thank you for your valuable comments

Author Response File: Author Response.docx

Reviewer 2 Report

The authors present a sensor to measure vibration based on an in-line Fabry Perot. In general, the paper is well written and clear and it is worth to be published. However, I recommend the authors a careful reading to correct some mistakes (eg. at the end of pg. 5, the phase offset point is not in accordance to fig. 4). Also, the length L2 and the length of the mass is not given. Furthermore, from equation 2, the resonance frequency depends on L2 but latter in the text it is written that it depends on the mass length. It should be clarified and eq. 2 may need a reference. Was the sensor tested above 500 ºC? Finally, this is a topic investigated for quite a long time and different approaches were implemented. Therefore, it is required a table with a comparison of previous published results in order to assess the performance of the presented sensor.

Author Response

Response

Thanks for your kindly work. On behalf of my co-authors, we thank you very much for giving us an opportunity to revise our manuscript. We appreciate editor and reviewers very much for their positive and constructive comments and suggestions on our manuscript entitled “An In–Line Fiber Optic Fabry–Perot Sensor for High–Temperature Vibration Measurement” (Manuscript Number: micromachines-729370). We have studied the valuable comments from you and reviewers carefully, and tried our best to revise the manuscript, and all the revised details are marked in RED. I hope this revision can make our paper be acceptable. The point to point responds to the reviewer’s comments are listed as following:

Point 1: At the end of pg. 5, the phase offset point is not in accordance to fig. 4


Response 1: This is a mistake in writing. Thank you for pointing out.

Point 2: The length L2 and the length of the mass is not given.

Response 2: We added a description of the mass and length of L₂ before introducing the experimental operation.

It should be clearly noted that, in our test, the length of the mass in the sensor is about 5 mm,and  L_2 is set to be 10 mm. The quality of the mass can be estimated as 0.8 mg, approximately. According to Eq. 2, the resonance frequency of the sensor can be calculated, ω=164.5094 Hz.

Point 3: From equation 2, the resonance frequency depends on L2 but latter in the text it is written that it depends on the mass length. It should be clarified and eq. 2 may need a reference.

Response 3: This is a mistake in writing. Thank you for pointing out

Point 4: Was the sensor tested above 500 ºC?

Response : In fact, when we tested, we only gave a maximum temperature of 500 degrees Celsius. When we were preparing for a higher temperature experiment, the sensor was damaged. But this will be the research we need to do next.

Point 4: Finally, this is a topic investigated for quite a long time and different approaches were implemented. Therefore, it is required a table with a comparison of previous published results in order to assess the performance of the presented sensor.

Response : In fact, compared to other inline fiber-optic vibration sensors, the main advantages of our sensors are simple production, short cycle and low cost. In the measurement of vibration, our sensor has no obvious advantages in sensitivity and vibration frequency. But we are studying how to change this structure to increase sensitivity to improve our advantage.

Author Response File: Author Response.docx