High Sensitivity to Salinity-Temperature Using One-Dimensional Deformed Photonic Crystal

Round 1

Reviewer 1 Report

In the manuscript “High Sensitivity to Salinity-Temperature using One-Dimensional Deformed Photonic Crystal”, the transfer matrix method (TMM) is used to simulate transmittance spectra of the structure consisting of alternating layers TiO₂/Fused-Silica with the cavity containing seawater in the middle. The authors proposed the structure as a salinity and temperature sensor. It is well known that the spectra of the photonic crystal structures could be used to detect a tiny change in the refractive index. TMM is widely used to simulate the spectra of 1D photonic crystals. I could not recognize the data and conclusions presented in the manuscript as novel and significant scientific message. I recommend to reject the manuscript.

Some minor issues:

1. Page 2, string 60: “Some of the previous researches were interested in studying photonic structures for sensing application.” - Incorrect sentence to describe the field with many hundred published scientific papers. The choice of the references mentioned in the paragraph is unclear.
2. In the section “2.1. Photonic structure Design”, the “TiO₂” requires some description (anatase, rutile, brookite, amorphous, …). The independence of the refractive index of TiO₂ on temperature and wavelength is doubtful (“?_T=2.3”).
3. The thermal expansion of the photonic crystal structure was not taken into account during the simulation.
4. The comparison with literature data is absent.
5. In figure 4, use μm instead of “metre x10^-6”.
6. It is interesting how the proposed structure could be fabricated.
7. Please, describe some thoughts on the dependence of the sensitivity and the Q-factor on the photonic crystal structure parameters.

Author Response

Response to Reviewers’ comments

 May 19, 2021

Subject: Revised Paper

Manuscript ID: coatings-1204595

Title: High Sensitivity to Salinity-Temperature using One-Dimensional Deformed Photonic Crystal.

Dear Editor and reviewers,

With regard to your E-Mail of May 14, 2021, I’m pleased to inform you that the paper has been revised as demanded, the details, the language and the format are seriously improved. I am thankful for the reviewers’ constructive remarks that helped to considerably improve and clarify my paper. As below, I would like to illustrate how I considered the critiques in this updated version. I have addressed the comments as outlined below, in italic font and my responses in blue color and normal font. Additionally, all changes made in the scientific paper have been highlighted in yellow.

Responses to the first reviewer's report:

1. Page 2, string 60: “Some of the previous researches were interested in studying photonic structures for sensing application.” - Incorrect sentence to describe the field with many hundred published scientific papers. The choice of the references mentioned in the paragraph is unclear.

The paragraph has been deleted and replaced with a single new sentence (“In previous research papers 1D and 2D photonic structures are proposed to measure salinity and temperature of water [1, 19].”) to indicate previous two published papers used photonic structure to detect temperature and salinity of water.

1. In the section “2.1. Photonic structure Design”, the “TiO₂” requires some description (anatase, rutile, brookite, amorphous, …). The independence of the refractive index of TiO₂ on temperature and wavelength is doubtful (“?_T=2.3”).

To better explain the choice of the refractive index of TiO₂ material this paragraph was added at page 2, section 2.1: " In the studied spectral range [1-2 mm], the refractive index of the amorphous titanium dioxide TiO₂ thin films is assumed to be independent to wavelength [21]. In addition, the refractive index of the TiO₂ films reveals no significant dependence to temperature when the film thickness increases more than ~ 200 nm [22]. Therefore, for this study the refractive index of the TiO₂ layers will be fixed at   ".

And these two references were added in the reference list:

21.A Kasikov, J Aarik, H Mändar, M Moppel, M Pärs and T Uustare, Refractive index gradients in TiO2 thin films grown by atomic layer deposition, J. Phys. D: Appl. Phys. (2005) 39, pp. 54-60, DOI:10.1088/0022-3727/39/1/010

22.Muhammad Rizwan Saleem, Seppo Honkanen and Jari Turunen, Thermal properties of TiO2 films fabricated by atomic layer deposition, IOP Conf. Ser.: Mater. Sci. Eng. 60 (2014) 012008 https://doi.org/10.1088/1757-899X/60/1/012008

1. The thermal expansion of the photonic crystal structure was not taken into account during the simulation.

The photonic crystal was simulated at room temperature, only the temperature of the water was changed, therefore we didn't suppose that there is thermal expansion of the whole structure.

1. The comparison with literature data is absent.

In the conclusion part we have added this paragraph to compare our results with literature: “By comparing our results with the results found by Sameeha R. Qutb et al. [30], we find that their periodic structure is composed by the alternation of TiO2 and seawater layers which makes their manufacture almost impossible also their structures have a thickness of 3.75 micrometers while the thickness of our structure is 18.57 micrometer. In addition, Sameeha R. Qutb et al. [30], didn't calculate the sensitivity of their structure and didn't determine the quality factor of the resonance peaks. Furthermore, D. Vigneswarana et al. [1] proposed a salinity sensor using photonic crystal fiber and this structure is more sensitive to salinity than ours but still difficult to fabricate.”.

1. In figure 4, use μm instead of “metre x10^-6”.

We rectified the unit in figure 2 and figure 4.

1. It is interesting how the proposed structure could be fabricated.

To fabricate the structure the TiO₂ films could be grown by atomic layer deposition (ALD) on fused silica. For more details please see this reference:

A Kasikov, J Aarik, H Mändar, M Moppel, M Pärs and T Uustare, Refractive index gradients in TiO₂ thin films grown by atomic layer deposition, J. Phys. D: Appl. Phys. (2005) 39, pp. 54-60, DOI:10.1088/0022-3727/39/1/010

1. Please, describe some thoughts on the dependence of the sensitivity and the Q-factor on the photonic crystal structure parameters.

In part 3.1, the dependence of the Q factor on the structure parameters was mentioned: “Table 1 and Fig. 3 show the variation of the structure thickness, the transmittance peak intensity and the Q-factor as function of the layer number P. Here it is clear that the peak intensity still upper 0.8 for P varying from 8 to 56 layers, but from 62 layers, the transmittance peak disappear. In addition, the quality factor Q has become more important from P=50 layers and the best Q value is obtained with this number (P=50). Therefore, the quality factor depends to the structure layers number (P) and for the rest of the study we will keep this number fixed at 50 layers. ”.

In addition the Q factor depends to the deformation of the thickness layers: “Fig.4 and Fig.5 illustrate the variation of the transmittance peak intensity and the Q-factor as function of the deformation degree (h). It is clear that by increasing h from 0 to 0.03, the best intensity and Q-factor are found for  (The values of the transmittance peak intensity and the Q-factor are 0.976 and 15060 respectively).”.

After the optimization of the quality factor by varying the structure parameter, we studied the dependence of the sensitivity to salinity and temperature.

Finally, if you have any remarks, please do not hesitate to contact me and thank you very much for your cooperation.

Best regards,

Dr. Naim Ben Ali

Author Response File: Author Response.docx

Reviewer 2 Report

The idea of creating a salinity and temperature sensor as a dual sensor is very interesting and useful. The principle of operation and the recorded information are clear from the manuscript. However, there are comments and doubts:

1) The specific scope of the sensor is not clear. It cannot be equally good for small, medium, and high levels of salinity. And the results confirm this, but are not sufficiently described in the manuscript. This raises many questions further. It is necessary to focus in more detail on a specific practically important area of water salinity and consider the characteristics of the detector - sensitivity and detection limit-for this area. Are they sufficient for the practically important control of salinity variation? In a wide range of concentrations (the article does not describe the composition of solutions for research), the change in analytical signals can be noticeable, but what task will this sensor solve? If only a demonstration of the fundamental capabilities of the developed system is selected, but an adjustment should be made to the title of the article.

2) Graphs with linear functions (Fig. 7, 9) should be given with equations for estimating the sensitivity of the signal. In Fig. 9-a is clearly not a linear function and this is due to a change in the structure of water in the low temperature zone. But this is not discussed by the authors. Fig. 7-a duplicates the data in Table. 2! This is unacceptable. The material in the article is not enough to assess the claimed importance for practice. It is recommended to add information or adjust the text.

Author Response

Response to Reviewers’ comments

May 19, 2021

Subject: Revised Paper

Manuscript ID: coatings-1204595

Title: High Sensitivity to Salinity-Temperature using One-Dimensional Deformed Photonic Crystal.

Dear Editor and reviewers,

With regard to your E-Mail of May 14, 2021, I’m pleased to inform you that the paper has been revised as demanded, the details, the language and the format are seriously improved. I am thankful for the reviewers’ constructive remarks that helped to considerably improve and clarify my paper. As below, I would like to illustrate how I considered the critiques in this updated version. I have addressed the comments as outlined below, in italic font and my responses in blue color and normal font. Additionally, all changes made in the scientific paper have been highlighted in yellow.

 Responses to the second reviewer's report:

The idea of creating a salinity and temperature sensor as a dual sensor is very interesting and useful. The principle of operation and the recorded information are clear from the manuscript. However, there are comments and doubts:

1) The specific scope of the sensor is not clear. It cannot be equally good for small, medium, and high levels of salinity. And the results confirm this, but are not sufficiently described in the manuscript.

The proposed sensor can detect the salinity level from 0 to 100%. The sensitivity varies little with salinity level and the regression models of the wavelength shift and the sensitivity were determined. To better explain this idea we have compared the sensitivity of the drinking water (0.06% salt) with the one of the Earth Ocean (26% salt). In the manuscript, we have added this paragraph in page 6, line 147: “From Fig.7, we can conclude the regression equation related the wavelength shift to the salt level:. In addition, from Table 2 we determine the regression equation related the sensitivity to the salt level:  s = 544.36 + 0.0198* Salt level (%). Furthermore, from Table 2, it is found that the sensitivity depends on the salinity of the water but their values remain close when the salinity level varies from lowest to highest values. Using the last regression equation, the salinity sensitivities of the drinking water (0.06% salt) and the Earth Ocean (26% salt) will take the values 544.36 and 544.87 respectively. The best sensitivity of the proposed Salinity sensor is 558.82 nm/RFIU at 20% salinity with a detection limit (DL) of 0.0034 RFIU.”.

For addition, for the temperature detection, we have added this paragraph in page 7, line 174: “Also, from Fig.9, we can conclude the regression equation related the wavelength shift to the water temperature:.  In addition, from Table 3 we determine the regression equation related the sensitivity to the temperature degree:  s = 584.09 - 0.430* T(℃). Furthermore, from Table 3, it is found that the sensitivity depends on the temperature of the water and varies from 545.95 nm/RFIU when T=100 ℃ to 600 nm/RFIU when T=10 ℃. However the sensitivity values remain close when the temperature degree varies from lowest to highest values.”.

2) This raises many questions further. It is necessary to focus in more detail on a specific practically important area of water salinity and consider the characteristics of the detector - sensitivity and detection limit-for this area. Are they sufficient for the practically important control of salinity variation? In a wide range of concentrations (the article does not describe the composition of solutions for research), the change in analytical signals can be noticeable, but what task will this sensor solve? If only a demonstration of the fundamental capabilities of the developed system is selected, but an adjustment should be made to the title of the article.

In this paper, we demonstrate the fundamental capabilities of the developed photonic structure to detect the salinity and temperature of the seawater. We have indicated this in the abstract: “This paper aims to theoretically study the conception of photonic salinity and temperature sensor according to deformed one-dimensional photonic structure. The fundamental capability of the proposed sensor is studied. Simultaneously we search to optimize the thickness of the structure and to get the maximum salinity and temperature sensitivity.  ”.

In addition, the introduction was reorganized and we have indicated the real seawater and the drinking water salt concentration . This paragraph with new reference was added: “The health of living organisms such as human, plants and animals depends on the quality of water (like the non-existence of bacteria and the low level of mineral salts) [1]. Regarding seawater, the salinity ratio varies from 3.5 % (35 g/L) in the Earth Ocean to 26% (260 g/L) in the Dead Sea [2]. In addition the water with salinity level less than 600 mg/L (0.06%) is regarded as good quality drinking water [3]. Consequently, the necessity to develop an accurate sensing devices are requested for salinity detection [1].”.

 Furthermore in the conclusion part we have added a new paragraph to compare our results with literature: “By comparing our results with the results found by Sameeha R. Qutb et al. [30], we find that their periodic structure is composed by the alternation of TiO2 and seawater layers which makes their manufacture almost impossible also their structures have a thickness of 3.75 micrometers while the thickness of our structure is 18.57 micrometer. In addition, Sameeha R. Qutb et al. [30], didn't calculate the sensitivity of their structure and didn't determine the quality factor of the resonance peaks. Furthermore, D. Vigneswarana et al. [1] proposed a salinity sensor using photonic crystal fiber and this structure is more sensitive to salinity than ours but still difficult to fabricate.”.

3) Graphs with linear functions (Fig. 7, 9) should be given with equations for estimating the sensitivity of the signal.

For Fig. 7, Fig. 9, Table 2 and Table 3 we have added the equations for the regression model related the wavelength shift and the sensitivity to the water salinity and temperature.

In page 6, line 147 this sentence was added: “From Fig.7, we can conclude the regression equation related the wavelength shift to the salt level:. In addition, from Table 2 we determine the regression equation related the sensitivity to the salt level:  s = 544.36 + 0.0198* Salt level (%).”.

In page 7, line 174 this sentence was added: “Also, from Fig.9, we can conclude the regression equation related the wavelength shift to the water temperature:.  In addition, from Table 3 we determine the regression equation related the sensitivity to the temperature degree:  s = 584.09 - 0.430* T(℃).”

4) In Fig. 9-a is clearly not a linear function and this is due to a change in the structure of water in the low temperature zone. But this is not discussed by the authors. Fig. 7-a duplicates the data in Table. 2! This is unacceptable.

Fig. 7-a and 9-a were deleted because they duplicate the data in Table 2 and Table 3 respectively.

In addition the Fig. 9 was corrected because the resonance peak position shift toward the lowest wavelengths when the seawater temperature rise, therefore the slope of the wavelength shift is negative.

5) The material in the article is not enough to assess the claimed importance for practice. It is recommended to add information or adjust the text.

The introduction was reorganized and we have indicated the real seawater and the drinking water salt concentration. This paragraph with new reference was added: “The health of living organisms such as human, plants and animals depends on the quality of water (like the non-existence of bacteria and the low level of mineral salts) [1]. Regarding seawater, the salinity ratio varies from 3.5 % (35 g/L) in the Earth Ocean to 26% (260 g/L) in the Dead Sea [2]. In addition the water with salinity level less than 600 mg/L (0.06%) is regarded as good quality drinking water [3]. Consequently, the necessity to develop an accurate sensing devices are requested for salinity detection [1].

In addition this sentence was added in the introduction to indicate previous two published papers used photonic structure to detect temperature and salinity of water: “In previous research papers 1D and 2D photonic structures are proposed to measure salinity and temperature of water [1, 19].”).

Furthermore in the conclusion part we have added a new paragraph to compare our results with literature: “By comparing our results with the results found by Sameeha R. Qutb et al. [30], we find that their periodic structure is composed by the alternation of TiO2 and seawater layers which makes their manufacture almost impossible also their structures have a thickness of 3.75 micrometers while the thickness of our structure is 18.57 micrometer. In addition, Sameeha R. Qutb et al. [30], didn't calculate the sensitivity of their structure and didn't determine the quality factor of the resonance peaks. Furthermore, D. Vigneswarana et al. [1] proposed a salinity sensor using photonic crystal fiber and this structure is more sensitive to salinity than ours but still difficult to fabricate.”. 

Finally, if you have any remarks, please do not hesitate to contact me and thank you very much for your cooperation.

Best regards,

Dr. Naim Ben Ali

Author Response File: Author Response.docx

Reviewer 3 Report

Overall this manuscript is interesting and results seem interesting towards photonic sensor application. Before I recommend to accept this paper for publication, authors need to address the following issue/comments:

• Authors quote that the high sensitivity to Salinity- temperature using 1D deformed photonic crystal, it extent of the sensor is not yet clear in the manuscript, please make it clear what is the scope of the manuscript clearly
• Authors mentioned that they have used Sea water with 50% Salinity to measure salinity and temperature, did they tested their measurement with regular bore-well water? If so please provide a graph or results
• It is good idea to present those comparative results with regular water with various salinity percentages to that of mineral water samples too
• Authors are advised to include the sensitivity etc., information while comparing sea water to that of regular water
• Avoid duplication of data in table with Fig.7a
• More insight is essential for understanding the reader, it is advised to revise the manuscript accordingly.

Author Response

Response to Reviewers’ comments

May 19, 2021

Subject: Revised Paper

Manuscript ID: coatings-1204595

Title: High Sensitivity to Salinity-Temperature using One-Dimensional Deformed Photonic Crystal.

Dear Editor and reviewers,

With regard to your E-Mail of May 14, 2021, I’m pleased to inform you that the paper has been revised as demanded, the details, the language and the format are seriously improved. I am thankful for the reviewers’ constructive remarks that helped to considerably improve and clarify my paper. As below, I would like to illustrate how I considered the critiques in this updated version. I have addressed the comments as outlined below, in italic font and my responses in blue color and normal font. Additionally, all changes made in the scientific paper have been highlighted in yellow.

Responses to the third reviewer's report:

Overall this manuscript is interesting and results seem interesting towards photonic sensor application. Before I recommend to accept this paper for publication, authors need to address the following issue/comments:

1. Authors quote that the high sensitivity to Salinity- temperature using 1D deformed photonic crystal, it extent of the sensor is not yet clear in the manuscript, please make it clear what is the scope of the manuscript clearly

We have reformulated the abstract and indicated the scope of the manuscript.

The new added paragraph is: “This paper aims to theoretically study the conception of photonic salinity and temperature sensor according to deformed one-dimensional photonic structure. The fundamental capability of the proposed sensor is studied. Simultaneously we search to optimize the thickness of the structure and to get the maximum salinity and temperature sensitivity. ”.

In addition, the introduction was reorganized, and in the conclusion part we have added a new paragraph to compare our results with literature: “By comparing our results with the results found by Sameeha R. Qutb et al. [30], we find that their periodic structure is composed by the alternation of TiO2 and seawater layers which makes their manufacture almost impossible also their structures have a thickness of 3.75 micrometers while the thickness of our structure is 18.57 micrometer. In addition, Sameeha R. Qutb et al. [30], didn't calculate the sensitivity of their structure and didn't determine the quality factor of the resonance peaks. Furthermore, D. Vigneswarana et al. [1] proposed a salinity sensor using photonic crystal fiber and this structure is more sensitive to salinity than ours but still difficult to fabricate.”.

1. Authors mentioned that they have used Sea water with 50% Salinity to measure salinity and temperature, did they tested their measurement with regular bore-well water? If so please provide a graph or results

In the first part of the result discussion, we aim to optimize the quality factor and the intensity of the transmittance resonance peak, so we fixed the salinity and the temperature of the seawater randomly. We choose the values 50 % for the salinity and T=25℃ (room temperature) for the temperature. After that we tested the sensitivity of the sensor for different salt level from 0% (fresh water) to 100% and for different temperature from 0 to 100℃. In the introduction we have indicated the real seawater and the drinking water salt concentrations. This paragraph with new reference was added: “The health of living organisms such as human, plants and animals depends on the quality of water (like the non-existence of bacteria and the low level of mineral salts) [1]. Regarding seawater, the salinity ratio varies from 3.5 % (35 g/L) in the Earth Ocean to 26% (260 g/L) in the Dead Sea [2]. In addition the water with salinity level less than 600 mg/L (0.06%) is regarded as good quality drinking water [3]. Consequently, the necessity to develop an accurate sensing devices are requested for salinity detection [1].”.

1. It is good idea to present those comparative results with regular water with various salinity percentages to that of mineral water samples too. Authors are advised to include the sensitivity etc., information while comparing sea water to that of regular water

The sensitivity of the sensor was studied for different salinity level; from fresh water to fully salty water (100% salt) and we have compared the sensitivity of the drinking water (006% salt) with the one of the Earth Ocean (26% salt). To better show this comparison, we have added this sentence in page 6, line 147: “From Fig.7, we can conclude the regression equation related the wavelength shift to the salt level:. In addition, from Table 2 we determine the regression equation related the sensitivity to the salt level:  s = 544.36 + 0.0198* Salt level (%). Furthermore, from Table 2, it is found that the sensitivity depends on the salinity of the water but their values remain close when the salinity level varies from lowest to highest values. Using the last regression equation, the salinity sensitivities of the drinking water (0.06% salt) and the Earth Ocean (26% salt) will take the values 544.36 and 544.87 respectively. The best sensitivity of the proposed Salinity sensor is 558.82 nm/RFIU at 20% salinity with a detection limit (DL) of 0.0034 RFIU.”.

1. Avoid duplication of data in table with Fig.7a

Fig. 7-a and 9-a were deleted because they duplicate the data in Table 2 and Table 3 respectively.

1. More insight is essential for understanding the reader, it is advised to revise the manuscript accordingly.

The manuscript has been revised according to the recommendations of the 03 reviewers ’reports, and many improvements have been included. I hope you like it. Thank you.

Finally, if you have any remarks, please do not hesitate to contact me and thank you very much for your cooperation.

Best regards,

Dr. Naim Ben Ali

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

In the revised version of the manuscript, novelty and significance were indicated. However, current version of the manuscript has some imperfection that should be fixed before the acceptance of the manuscript. I recommend reconsidering the manuscript after major revision.

Issues:

1. Heat transfer leads to the equalization of the temperature of the liquid and the sensor, so temperature caused expansion of the sensor is inevitable. The thickness of the cavity determines the position of the peak. The increase of the cavity thickness with the temperature will lead to the shift of the central-wavelength of the resonance-peak and consequently gives other values of the sensitivity and detection limit. I highly recommend to include the thermal expansion in the calculations, otherwise indicate clearly in the text for the readers that the thermal expansion was not taken into account.
2. Page 10, string 242-249: “By comparing our results ………. but still difficult to fabricate.” Please move these sentences to the section “Results and discussion” otherwise, prove them previously in the article text.
3. The difficulty in the fabrication of the sensors presented in the previous works was described as a disadvantage on Page 10, string 242-249. In the manuscript, the fabrication method of the proposed sensors is not described. Based on answer #6, I found that the fabrication of the 18.57 micrometer thick sensor will take at least one week of ALD process. Furthermore, it is not clear how to make a cavity using ALD. It seems that the manufacturing of the proposed sensor is also “almost impossible”. So, indicate in the text how the proposed structure could be fabricated.
4. Table 1 and Figure 3. Please add points in the vicinity of the highest quality factors (P = 46, 48, 52, 54, 58, 60).
5. In section 2.2 indicate the step of the wavelength of the calculated spectra used for the FWHM calculation. If the step is 0.0001 μm, then the FWHM and quality factor data for samples P = 44, 50, 56 are incorrect (reduce the wavelength step and calculate the spectra in the vicinity of the peak). If the step is <0.0001 μm, then add significant digits for FWHM values (for P = 26 – 56). In any case, indicate an error for the quality factor values in Table 1, Figure 3, Figure 5, and Conclusion.
6. Indicate the error of sensitivity (S_T) in the text, Table 3, and Conclusion.
7. Page 2, string 51: “The emergence of photonic structures [5-10] permits to discard several problems of the old electronic devices such as the called Joule effect [4].” - The choice of the references [6-10] mentioned in the paragraph is unclear. After such a general phrase, I expect to find a book, review or pioneering work in the field. The same for the “The photonic 61 sensing devices are known by their accurate and precise response [11-18]” on Page 2, string 61. Please describe more details to use such references.
8. Figure 1. Based on the figure, the cavity is also counted as a layer. From the manuscript, I guess that the number P does not include the cavity. Please make it clear for the readers.
9. Figure 6. Legend for the 80–100% is missed. Please use integers for the labels of the wavelength.
10. Page 5, string 150: correct “phoTable 2. and”.
11. Page 8, line 215: correct “s”.

Author Response

Response to Reviewers’ comments

 May 28, 2021

 Subject: Revised Paper

Manuscript ID: coatings-1204595

Title: High Sensitivity to Salinity-Temperature using One-Dimensional Deformed Photonic Crystal.

Dear Editor and reviewers,

With regard to your E-Mail of May 24, 2021, I’m pleased to inform you that the paper has been revised as demanded, the details, the language, and the format are seriously improved. I am thankful for the reviewers’ constructive remarks that helped to considerably improve and clarify my paper. As below, I would like to illustrate how I considered the critiques in this updated version. I have addressed the comments as outlined below, in italic font, and my responses in blue color and normal font. Additionally, all changes made in the scientific paper have been highlighted in yellow.

Responses to the first reviewer's report:

In the revised version of the manuscript, novelty and significance were indicated. However, current version of the manuscript has some imperfection that should be fixed before the acceptance of the manuscript. I recommend reconsidering the manuscript after major revision.

Issues:

• Heat transfer leads to the equalization of the temperature of the liquid and the sensor, so temperature caused expansion of the sensor is inevitable. The thickness of the cavity determines the position of the peak. The increase of the cavity thickness with the temperature will lead to the shift of the central-wavelength of the resonance-peak and consequently gives other values of the sensitivity and detection limit. I highly recommend to include the thermal expansion in the calculations, otherwise indicate clearly in the text for the readers that the thermal expansion was not taken into account.

To determine the transmittance spectra using the Transfer Matrix Method (TMM) we have developed a simulation code with Matlab software. The thermal expansion of the TiO₂ and the Fused silica layers are not the same. In addition, the duration of stay of the seawater in the cavity is not determined and we don’t know the necessary period to have a heat exchange between the cavity and the rest of the structure. Therefore and to simplify the simulation the thermal expansion of the structure was not taken into account. We indicated this matter on page 3, string 96.

• Page 10, string 242-249: “By comparing our results ………. but still difficult to fabricate.” Please move these sentences to the section “Results and discussion” otherwise, prove them previously in the article text.

The sentence was moved to the section “Results and discussion”, page 8, string 232.

• The difficulty in the fabrication of the sensors presented in the previous works was described as a disadvantage on Page 10, string 242-249. In the manuscript, the fabrication method of the proposed sensors is not described. Based on answer #6, I found that the fabrication of the 18.57 micrometer thick sensor will take at least one week of ALD process. Furthermore, it is not clear how to make a cavity using ALD. It seems that the manufacturing of the proposed sensor is also “almost impossible”. So, indicate in the text how the proposed structure could be fabricated.

In the abstract, we indicated that our paper focuses on the theoretical study of the salinity-temperature sensor. We didn’t mention the practical aspect in our paper because our laboratory is not sufficiently equipped for fabricating the structure. To answer your question we have indicated on page 9, string 239 that it can be fabricated using ALD and to make a cavity the lithographic process and the wet or dry etching technologies can be used.

• Table 1 and Figure 3. Please add points in the vicinity of the highest quality factors (P = 46, 48, 52, 54, 58, 60).

The requested points were added in table 1 and Figure 3, however the best quality factor still the one given by P=50 layers.

• In section 2.2 indicate the step of the wavelength of the calculated spectra used for the FWHM calculation. If the step is 0.0001 μm, then the FWHM and quality factor data for samples P = 44, 50, 56 are incorrect (reduce the wavelength step and calculate the spectra in the vicinity of the peak). If the step is <0.0001 μm, then add significant digits for FWHM values (for P = 26 – 56). In any case, indicate an error for the quality factor values in Table 1, Figure 3, Figure 5, and Conclusion.

In the calculated spectra given by our simulation the step of the wavelength used for the FWHM calculation is 0.00001μm. We reconfirmed the simulations and got the same results. We have indicated this point in section 2.2.

• Indicate the error of sensitivity (ST) in the text, Table 3, and Conclusion.

In section 3.2, we have added the values of the standard error coefficient (SE Coef) for the sensitivity to the salt Ss: “In addition, from Table 2 we determine the regression equation related the sensitivity to the salt level:  S_S = 544.36 + 0.0198* Salt level (%). For this regression equation the standard error coefficient (SE) for the constant and for the salt level are 5.24 and 0.0845 respectively.”.

Furthermore in section 3.3, we have added the values of the standard error coefficient (SE Coef) for the sensitivity to the temperature ST: “In addition, from Table 3 we determine the regression equation related the sensitivity to the temperature degree:  S_T = 584.09 - 0.430* T(℃). For this regression equation the standard error coefficient (SE) for the constant and for the temperature are 6.46 and 0.104 respectively.”.

• Page 2, string 51: “The emergence of photonic structures [5-10] permits to discard several problems of the old electronic devices such as the called Joule effect [4].” - The choice of the references [6-10] mentioned in the paragraph is unclear. After such a general phrase, I expect to find a book, review or pioneering work in the field. The same for the “The photonic 61 sensing devices are known by their accurate and precise response [11-18]” on Page 2, string 61. Please describe more details to use such references.

This paragraph is retyped and 3 new references were added:

1. John S. Strong localization of photons in certain disordered dielectric superlattices. Physical Review Letters. 1987;58(23):2486-2489
2. Yablonovitch E. Inhibited spontaneous emission in solid-state physics and electronics. Physical Review Letters. 1987;58(20):2059-2062
3. Krauss TF, De la Rue RM. Photonic crystals in the optical regime—Past, present and future. Progress in Quantum Electronics. 1999;23:2

In addition the choice and the use of the old references from 6 to 18 were better described in the introduction:” The emergence of photonic structures proposed by John [5] and by Yablonovitch [6] permits to discard several problems of the old electronic devices such as the called Joule effect [4]. These structures also known photonic band gap materials are made by alternating two or more different materials. They represent the optical analogy to a crystal lattice, where atoms or molecules are periodically arranged and the periodic potential introduces gaps into the energy band structure of the crystal [7, 8]. There are three different families of photonic structure, according to the direction of materials alternation, namely one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) structures [5, 6]. In addition, the alternation of materials can be periodic or quasi-periodic (where the alternation of materials follows mathematical sequences). The most known quasiperiodic structure are Fibonacci [9-12], Thue-Morse [13- 15] and Cantor [11, 16] structures. The photonic structures [17] represent a serious opportunity for researchers to study and improve their properties to be suitable in sensing applications [18]. They can be used for salinity sensing [1, 19], for D-glucose sensing [20], for temperature [15, 19] and pressure sensing [15], for humidity sensing [21], for hemoglobin sensing [22] and for cancer cell detection [23]. These devices are known by their accurate and precise response and they have less energy consumption with rapid response because photons are faster than electrons (photons displaces with the speed 3*10⁸ m/s) [17]. In previous research papers 1D and 2D photonic structures are proposed to measure salinity and temperature of water [1, 19].”.

• Figure 1. Based on the figure, the cavity is also counted as a layer. From the manuscript, I guess that the number P does not include the cavity. Please make it clear for the readers.

We have added this notice in line 117:” Note here that the number P does not include the cavity layer”.

• Figure 6. Legend for the 80–100% is missed. Please use integers for the labels of the wavelength.

Figure 6 and 8 were corrected as you demanded.

• Page 5, string 150: correct “phoTable 2. and”.

This typo is corrected.

• Page 8, line 215: correct “s”.

This typo is corrected.

Finally, if you have any remarks, please do not hesitate to contact me and thank you very much for your cooperation.

 Best regards,

Author Response File: Author Response.docx

Reviewer 2 Report

Спасибо авторам за пояснения и ответы на замечания.

Author Response

Thank you very much for reviewing our paper. Sincerely your comments were constructive to our paper. Thank you