Temperature Sensing Utilizing Stimulate Brillouin Scattering Fast Light in Liquid-Filled Photonic Crystal Fibers

Round 1

Reviewer 1 Report

In the manuscript, authors presented results of the theoretical model and proposed a new design for novel temperature sensors based on Stimulated Brillouin Scattering Fast Light in Liquid-filled Photonic crystal fibres. They discussed the influence of air filing factor on sensor sensitivity in the temperature range from 20 to 70 C deg.

As novelty presented in the manuscript authors stated that the research on temperature sensing using the SBS fast light in liquid-filled PCF has not been reported yet.

They proposed and described very details experimental realisation of the temperature sensor. From the manuscript, I got an impression that everything is set for experimental realisation and can be easily performed, but unfortunately in the manuscript are given the only results of theoretical calculations. Maybe the author can explain why the real experiment was not performed.

The manuscript is well structured and content expressed clearly and in proper English. However, there are many typing errors, especially in figure labels (check comments below).

Also, the authors missed to discuss results in more detail. For example, they missed to compare results with other realisation of similar temperature sensors. In the Discussion, they only repeated and summarize results presented in figures.

The terminology used in the manuscript is not precise. For example, the authors used the term “Index” frequently. It is better to use “Index of refraction”.

Other comments and suggestions:

• Row 50: Typing error (double ‘’)

• Row 126: Error in equation 3.94×10-4/°C -1. C deg is in the denominator and with exponent -1?

• Row 126: Not clear sentence: The refractive index is 1.352 at the wavelength of 1550nm and temperature of 20°C, so the refractive index of alcohol for different temperature can be achieved.?

• Row 136: Not clear equation for M: Why it’s written as a sum of two constants? Missing units for constants used in all equations.

• Row 138: Not clear: “laser from the distributed feedback laser (DFB) ”

• Fig 2: Area of different density (index of refraction) can be indicated by different colour!

• Fig 3 and 4: Axis and tick labels are not readable! Not specified what is presented as colour (intensity. electric field?) Better to use a log scale for the colour to emphasize spatial variation of intensity.

• Fig 5: Axis labels (units) are not correct and also the colour scale is without a label. The terminology used in figure caption and text is not precise. “Index” should be “index of refraction”?

• Row 266: Missing “Pmax”

Author Response

Comments and Suggestions of referee 1

Question 1: They proposed and described very details experimental realisation of the temperature sensor. From the manuscript, I got an impression that everything is set for experimental realisation and can be easily performed, but unfortunately in the manuscript are given the only results of theoretical calculations. Maybe the author can explain why the real experiment was not performed.

Answer: Thank you for your comments and suggestions. We designed and proposed the photonic crystal fiber and the experiment setup, but the manufacture of the PCF and filling liquid into such small air holes are very difficult for us. So the real experiment was not performed.

Question 2:  Row 50: Typing error (double ‘’).

Answer and revising records: Row 50: Typing error (double ‘’)  changed into (,).

Question 3: Row 126: Error in equation 3.94×10-4/°C -1. C deg is in the denominator and with exponent -1?

Answer and revising records: Row 126: “…….3.94×10-4/°C -1.”  changed into “…….3.94×10^-4/°C”

Question 4: Row 126: Not clear sentence: The refractive index is 1.352 at the wavelength of 1550nm and temperature of 20°C, so the refractive index of alcohol for different temperature can be achieved.?

Answer and revising records: Row 126: “The refractive index is 1.352 at the wavelength of 1550nm and temperature of 20°C, so the refractive index of alcohol for different temperature can be achieved.” changed into “the refractive index  is 1.352 at the wavelength of 1550nm and temperature  =20℃, so the refractive index of alcohol for different temperature can be achieved.”

This sentence means  can be obtained for different temperature when  and  are given according to equ.(13).

Question 5: Row 136: Not clear equation for M: Why it’s written as a sum of two constants? Missing units for constants used in all equations.

Answer and revising records: Row 136:  in equation(15)   changed into .

Question 6: Row 138: Not clear: “laser from the distributed feedback laser (DFB) ”

Answer and revising records: Row 138: “laser from the distributed feedback laser (DFB) ”  changed into “the distribute feedback laser(DFB)”

Question 7: Fig 2: Area of different density (index of refraction) can be indicated by different colour!

Answer and revising records: We indicated the air-hole area by white colour in Fig.2.

Question 8: Fig 3 and 4: Axis and tick labels are not readable! Not specified what is presented as colour (intensity. electric field?) Better to use a log scale for the colour to emphasize spatial variation of intensity.

Answer and revising records: We enlarged Fig.3 and 4 so that the axis and tick labels are readable. The colour on the right of picture shows the light intensity, the horizontal and left axes represent the size of the fiber cross section.

Question 9: Fig 5: Axis labels (units) are not correct and also the colour scale is without a label. The terminology used in figure caption and text is not precise. “Index” should be “index of refraction”?

Answer and revising records: We indicated the lines in Fig.5, 6 ,7,and 8 by different colours. And the terminology “effective index” changed into “effective refractive index”.

Question 10: Row 266: Missing “Pmax”

Answer and revising records: Row 266: “P_max” is added in the sentence.

 

Question 11: Also, the authors missed to discuss results in more detail. For example, they missed to compare results with other realisation of similar temperature sensors. In the Discussion, they only repeated and summarize results presented in figures.

Answer and revising records: Thank you for your comment. There are many ways to realize sensing or temperature sensing, which can be seen from the cited literatures [11], [12], [13] and [14], the common point of these methods is that the transmission characteristics of light is changed by filling air holes of PCF with substances to realize sensing. We got this “substances filling” idea, but our innovation is that our work is base on SBS fast light, and the research on temperature sensing utilizing the SBS fast light in liquid-filled PCF has not been reported yet. Compared with others temperature sensing methods and theory, the sensing parameters and sensor device model design are different, so we described the similar temperature sensors in the introduction part, and mainly emphasized on our simulation results.

Question 12:The terminology used in the manuscript is not precise. For example, the authors used the term “Index” frequently. It is better to use “Index of refraction”.

Answer and revising records: Thank you for your comments and we checked and revised the terminology which marked by red color throughout the manuscript, the revised is listed as follows:

1. Row 47: “refraction-index” changed into “refractive index”.
2. Row 48: “the various refraction indexes” changed into “the various refractive indexes”.
3. Row 55: “the effective refraction index” changed into “the effective refractive index”.
4. Row 63: “the group refraction-index” changed into “the group refractive index”.
5. Row 184,185 and 198: “the effective index” changed into “the effective refractive index”.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors developed a novel temperature sensor based on stimulate Brillouin scattering fast light in liquid filled photonic crystal fibers. The resulting photonic crystal fibers showed good sensitive response on temperature between 20 ℃ to 70 ℃ with a variation of 2.75 μm for effective mode area at the air filling factor of 0.6. Besides, the temperature sensitivity of the time advancement could reach 0.272 ns/℃. The work is interesting and can be published in Coatings if the following issues can be addressed: 1. The authors should cite the papers “High-Temperature Sensitivity in Stimulated Brillouin Scattering of 1060 nm Single-Mode Fibers” (Sensors, 2019, 19, 4731) and “Strong, lightweight, and highly conductive CNT/Au/Cu wires from sputtering and electroplating methods” (Journal of Materials Science & Technology, 2020, 40, 99-106) in the introduction section for better reviewing the temperature sensing fiber. 2. How to make this sensor work for different temperature range? For example, above 70 oC 3. Both “Fig. “and “Figure” were used in the manuscript. The authors should use one only for good consistency. 4. Most of the figures are too small to be visible, especially the scale bar, number, and texts within the graphs. The authors should improve them. 5. Line 196 and 200: Fig. 6(a) and Fig. 6(b) should be used there instead of Fig. 5(a) and Fig. 5(b) 6. Why was the sensitivity of the time advancement improved with increasing pump power? 7. English and writing need to be improved.

Author Response

Question 1: The authors should cite the papers “High-Temperature Sensitivity in Stimulated Brillouin Scattering of 1060 nm Single-Mode Fibers” (Sensors, 2019, 19, 4731) and “Strong, lightweight, and highly conductive CNT/Au/Cu wires from sputtering and electroplating methods” (Journal of Materials Science & Technology, 2020, 40, 99-106) in the introduction section for better reviewing the temperature sensing fiber.

Answer and revising records: Thank you for your comments and we cite the first paper (Song S , Jung A , Oh K . High-Temperature Sensitivity in Stimulated Brillouin Scattering of 1060 nm Single-Mode Fibers[J]. Sensors (Basel, Switzerland), 2019, 19(21).) as the reference [15] in the revised manuscript, and renumbered the references. But the suggested another paper (“Strong, lightweight, and highly conductive CNT/Au/Cu wires from sputtering and electroplating methods”, Journal of Materials Science & Technology, 2020, 40, 99-106) does have nothing to do with the manuscript, so we don’t cite it in the revised manuscript.

[15] Song S , Jung A , Oh K . High-Temperature Sensitivity in Stimulated Brillouin Scattering of 1060 nm Single-Mode Fibers[J]. Sensors (Basel, Switzerland), 2019, 19(21):4731.

Question 2: How to make this sensor work for different temperature range? For example, above 70 oC

Answer and revising records: Thank you for your comments. Up to now, maximum sensing temperature of this sensor is 70℃, because 70℃ is very close to the boiling point of alcohol 78.3℃ that used to fill air holes of PCF in this sensor configuration. If sensing temperature is out of the range of 20℃-70℃, then new filling substances are needed.

Question 3: Both “Fig. “and “Figure” were used in the manuscript. The authors should use one only for good consistency.

Answer and revising records: Thank you for your comments and we checked and revised throughout manuscript and the revised words which are marked by red color in the revised manuscript are listed as follows:

Rows 156, 171, 180, 182, 193, 202, 213, 238, and241: “Fig.” and “Figure” are revised to “Fig.”

Question 4: Most of the figures are too small to be visible, especially the scale bar, number, and texts within the graphs. The authors should improve them.

Answer and revising records: Thank you for your comments. We enlarged Fig.3, Fig.4 though Fig.9 so that the axis and tick labels can be seen better, and different colour is used to indicate different lines in the figures.

Question 5: Line 196 and 200: Fig. 6(a) and Fig. 6(b) should be used there instead of Fig. 5(a) and Fig. 5(b)

Answer and revising records: Thank you for your comments and we changed according the comment.

Question 6: Why was the sensitivity of the time advancement improved with increasing pump power?

Answer and revising records: Thank you for your comments. Equation (4) shows the time advancement improving with increasing pump power, because lager pump power usually can cause stronger SBS effect.

Question 7: English and writing need to be improved.

Answer and revising records: Thank you for your comments and we checked and revised throughout manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper presents a study concerning temperature sensing utilizing stimulate Brillouin scattering fast light in liquid-filled photonic crystal fibers. Authors propose modern temperature sensor, which is designed on stimulate Brillouin scattering fast light in liquid filled photonic crystal fibers. They said that time advancement and Brillouin frequency shift of fast light were simulated according to three wave coupling equations of stimulate Brillouin scattering. Authors explained that alcohol filled photonic crystal fibers exhibited sensitive response on temperature. They summarized that time advancement increases with the rise of temperature.

 

In introduction chapter, authors presented fundamental knowledge according stimulate Brillouin scattering and photonic crystal fibers. They proposed the index guided PCF filled with alcohol and an experimental configuration.

 

Next chapter was focused on theoretical studies. Authors presented equations which follow to describe dynamics of stimulate Brillouin scattering.

 

Next, they described experimental setup used in experiment. Authors explained all used part of the setup.

 

Next chapter, the main one, presented obtained numerical simulation results. Authors explain the mode field distribution, and cross profile of the PCF. They showed distribution of optical and acoustic fundamental mode in the proposed filled and unfilled PCF. Authors explain the effective index and the effective mode area varies with temperature. Next, they presented the Brillouin frequency shift, and the effective velocity the Brillouin frequency shift vary with temperature. They explained the Brillouin threshold and Pmax and Pmin vary. They also showed temperature response of the fast light, and time advancement, pulse broadening factor and group velocity of signal light varies with temperature. As the last, they showed the shape of the output signal pulse, and output waveform of pulse signal for different temperature in ethanol-unfilled and ethanol-filled PCF.

 

As the conclusions, they said that the sensing characteristics of the SBS fast light in liquid filled PCF for different temperature were theoretically analyzed. On the basis of obtained simulated results, they concluded that the liquid filled PCF is more sensitive to temperature than the unfilled PCF.

 

Author Response

Comments and Suggestions of referee 3

Comments: The paper presents a study concerning temperature sensing utilizing stimulate Brillouin scattering fast light in liquid-filled photonic crystal fibers. Authors propose modern temperature sensor, which is designed on stimulate Brillouin scattering fast light in liquid filled photonic crystal fibers. They said that time advancement and Brillouin frequency shift of fast light were simulated according to three wave coupling equations of stimulate Brillouin scattering. Authors explained that alcohol filled photonic crystal fibers exhibited sensitive response on temperature. They summarized that time advancement increases with the rise of temperature.

In introduction chapter, authors presented fundamental knowledge according stimulate Brillouin scattering and photonic crystal fibers. They proposed the index guided PCF filled with alcohol and an experimental configuration.

Next chapter was focused on theoretical studies. Authors presented equations which follow to describe dynamics of stimulate Brillouin scattering.

Next, they described experimental setup used in experiment. Authors explained all used part of the setup.

Next chapter, the main one, presented obtained numerical simulation results. Authors explain the mode field distribution, and cross profile of the PCF. They showed distribution of optical and acoustic fundamental mode in the proposed filled and unfilled PCF. Authors explain the effective index and the effective mode area varies with temperature. Next, they presented the Brillouin frequency shift, and the effective velocity the Brillouin frequency shift vary with temperature. They explained the Brillouin threshold and Pmax and Pmin vary. They also showed temperature response of the fast light, and time advancement, pulse broadening factor and group velocity of signal light varies with temperature. As the last, they showed the shape of the output signal pulse, and output waveform of pulse signal for different temperature in ethanol-unfilled and ethanol-filled PCF.

Answer: Thank you for your comments and suggestions. We appreciate your comments about our work, we revised some typing errors and the terminology throughout the manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The author answered to most of the questions and modified manuscript according to review comments.

However, still I suggest to check missing units in Eq. 15. For example, units for density should be kg/m³ or g/cm³. So, constants used in eq. should also have units that are consistent with that. At the moment they are without units.  Similar, units for Young modulus should be Pascals. ...

In Fig. 4 I don't see any improvement. Tick labels are hardly readable, axis title missing and colour scale bar caption missing.

In Fig. 5 degree sign in axis title should be corrected.

 

 

Author Response

Comments and Suggestions of referee 1

Question 1: The author answered to most of the questions and modified manuscript according to review comments.

However, still I suggest to check missing units in Eq. 15. For example, units for density should be kg/m³ or g/cm³. So, constants used in eq. should also have units that are consistent with that. At the moment they are without units. Similar, units for Young modulus should be Pascals. .

Answer and revising records: We added kg/m³ and Pa as the units for density and Young modulus in Eq.15, respectively. And we checked and corrected units of some constants, such as straight or italic signs.

Question 2:  In Fig. 4 I don't see any improvement. Tick labels are hardly readable, axis title missing and colour scale bar caption missing.

Answer and revising records: We revised and added the tick labels and the axis title, colour scale bar caption of the Fig.4, now this Fig. is easily readable.

Question 3: In Fig. 5 degree sign in axis title should be corrected.

Answer and revising records: By referring to the paper of Coatings, we changed the units’ signs in axis title in Figs.5-9 from “ /uint” to “(unite)”, i.e., in Fig.5, “T/℃” was changed to “(℃)”.

Author Response File: Author Response.pdf