Design and Study of Low Loss, High Birefringence Quasi-Symmetric Hollow-Core Anti-Resonant Fiber

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

please see attachment

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Quality of English need to improve.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Three kinds of cladding quasi-symmetric AR-HCFs are presented in this paper. The influence of cladding tube thickness on birefringence, confinement loss and bending characteristics of fiber is analyzed. The theoretical calculation results show that it has smaller constraint loss, higher birefringence coefficient and better bending resistance at the wavelength of 1.55 μm. This manuscript is only a simulation calculation, without pointing out the specific academic value, and there are so many problems in the paper, as follows:

(1) The summary is too confusing. The author intends to show that the three AR-HCFs have better transmission characteristics, but the description of the results given by the author is not uniform, which brings great confusion to the reader, and there is no comparability among all the fibers. Either the birefringence coefficient is high or the confinement loss is low.

(2) The introduction is too simple and the format is wrong. The author summarized 11 references into one sentence, which is not appropriate in my opinion. There have been many studies on the AR-HCF with polarity-preserving characteristics, especially in the 1.55 μm band, the researchers have achieved 2.35×10^-5 birefringence, and the transmission loss is 0.46 dB/m. The author needs to display the research progress at home and abroad, highlight the research significance of this paper, and condense the innovation of this paper. The authors also need to highlight why birefringence fibers are designed and which practical applications require fiber with birefringence properties. At the same time, the author needs to carefully check the formatting of the article to avoid basic errors like line 38.

(3) Fig. 1 illustrates the conditions of resonance and anti-resonance. There are many physical quantities in the figure, and the author needs to explain all physical quantities to avoid confusion to readers. Is Fig. 1 original by the author? If not original, please indicate where came from?

(4) Is line 99 equation (3) and line 357 equation (7) correct? Please checked and revised it carefully. Moreover, for AR-HCFs, the low-refractive index core is not necessarily air, but may also be other filled gases, so the refractive index of the low-refractive index material in formula (3) should not be represented by the number 1.

(5) In line 136, the author claims that reducing the number of capillaries can increase the light conduction bandwidth. Please explain the reason in detail in the article.

(6) The imaginary part of the effective refractive index in equation (6) should be written in the same way as in the paper, and the format should be modified to the correct format.

(7) In the result part, the author did not introduce how to model. From the right figure in Fig. 2, I found that the author did not seem to introduce the perfect matching layer as the boundary condition, nor did he introduce the small penetration at the intersection of the capillary and the outer layer, which would cause me to worry about the accuracy of the calculation results.

(8) In Fig. 2, the author describes the structure diagram of the eight-tube AR-HCF, but there are two diagrams in Fig. 2, and the right diagram shows the distribution of the fundamental mode in the fiber core. It's not a structural diagram. The author needs to check and modify the annotations of all the pictures in the manuscript.

(9) The structure of the AR-HCF designed by the author is relatively complex. How can the author ensure that the embedded elliptic tube will not collapse during drawing? This is a very important question for me.

(10) The bending loss diagram in Fig. 9 should indicate the specific bending direction and polarization direction in the text or on the diagram, and the distribution diagram of the core fundamental mode should also indicate the corresponding specific bending radius value in the diagram. It is suggested that the author unify the value range of bending loss ordinate of the three graphs. The calculation results in Fig. 9(b) are somewhat abnormal, and it is suggested that the author explain in detail the effect of photonic crystal cladding on bending loss.

(11) In English writing, each physical quantity in front of the unit need to empty a space, the full text is more chaotic, some empty a space and some do not, the English full stop also need to empty a space, the full text in many places without spaces, the author needs to carefully check and modify. Fig. 5 and 7 seem arbitrary and suggest that the author revise and highlight the point. The author needs to enlarge the font of the full text picture, bold the lines, and increase the pixel of the picture, so that readers can read it easily.

(12) The format of the references is very messy and contains many basic errors. The authors need to unify the format of the references and change it according to the format requirements of the Photonics journal.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This review report is for the manuscript 'Design and study of low loss, high birefringence quasi-symmetric hollow-core anti-resonant fiber' by Binhao Gao, et al.

The manuscript proposed a numerical simulation of a hollow-core photonic crystal fiber. An eight-tube cladding quasi-symmetric design was proposed and analysis with finite element method. The results offer valuable insights into the behavior of this specific design and potentially for future hollow-core photonic crystal fiber designs.

 

To further strengthen the manuscript, here are some key points for the authors to consider:

 

1) The introduction section could benefit from a more comprehensive overview of existing design structures for fibers with air holes/ holey fiber/photonic crystal fiber.  Lines 51 to 60 lack sufficient detail on existing literature in this area.

 

2) [Followup with #1] What are some of the other designs? Closest design? What are their limitation?

 

3) For clarity and optimal structure, the manuscript could benefit from additional proofreading and guidance from a senior researcher, particularly in naming subsections and organizing the overall flow. For example, section #2 is strongly suggested to rename to 'Operating Principle'. Section #3 is strongly suggested to rename to 'Experimental Setup' or similar. Figure 6 wordings are distorted. 

 

4) Table 5 for example, the manuscript can benchmark with other researcher groups leading in Birefringence and Loss characteristics. By situating the current research within the context of pioneering work, the paper's relevance and quality can be further improved.

 

5) In the Discussion section, also for practical application since the manuscript discusses about design, consider adding a section discussing potential fabrication techniques suitable for the proposed design. Additionally, acknowledging any limitations in manufacturability due to intricate features or complexity would strengthen the analysis. This highlights both the design's potential and areas for future exploration. 

 

6) The manuscript analyzes three designs, offering a valuable foundation. To provide an even more comprehensive picture for the reader, consider including additional information and figures that showcase the key features and comparisons between these designs. For example, in Figure 2 includes the two other designs.

 

7) To enhance the conclusion section and also to highlight the design's potential, consider including a subsection/paragraph that discusses future directions. This could address the feasibility of fabrication and potential applications in specific fields. Alternatively, if fabrication is not the immediate next step, you could outline the planned theoretical or computational explorations to further develop the design's concept

 

I hope the comments will be helpful to the authors and improve the quality of the manuscript.

Comments on the Quality of English Language

As in comment #2:

For clarity and optimal structure, the manuscript could benefit from additional proofreading and guidance from a senior researcher, particularly in naming subsections and organizing the overall flow.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I have no further questions, this work could be published.

Author Response

Thank you very much for your wise comments, which have made this manuscript more rigorous!

Reviewer 2 Report

Comments and Suggestions for Authors

1. Equation (6) in the revised draft is still wrong.

2. Suggest the author to number and explain the figures in Figure 2, Figure 3 and Figure 4 respectively?

3. The font of the formula should match the content of the article.

4. Should there be symbols like “、” in English writing?

5. I am not convinced by the reply to question (7). First of all, the model establishment needs to inform the reader about grid division and boundary conditions, which are very important computing conditions, and the grid shape and minimum grid cell value have a great impact on the calculation results. Furthermore, the author claims that the scattering boundary condition can achieve the same computational effect as the perfectly matched boundary condition. The author suggests explaining the difference in the paper. Finally, the author claims that the small penetration between the capillary and the outer casing has no effect on the calculation results, which in my opinion is obviously a fundamental error!

6. Regarding question (9), the author has not given any answer, nor has there been any change in the revised manuscript. The authors claim they can't guarantee that the tube won't collapse, so what's the point of the design? The author should discuss in detail the drawing process and some suggestions on the problems that may occur in the drawing process of the structure designed in this paper!

 

Author Response

Dear editors and reviewers

Once again, I would like to sincerely thank you for your further valuable comments on my paper "Design and study of low-loss, high birefringence quasi-symmetric hollow-core resonance-resistant optical fiber". Your professional opinions are very important for me to further improve my research work and I would like to express my sincere gratitude.

I have made careful revisions accordingly and have written and annotated the revisions in the original manuscript, please check it out!

The black font is the explanation of the question and the red font is what was added to the original text.

Title: Design and study of low loss, high birefringence quasi-symmetric hollow-core anti-resonant fiber

1. Equation (6) in the revised draft is still wrong.

RESPONE：

 Modify Equation 6 to read：

n_imag is the imaginary part of the effective refractive index of the mode

2. Suggest the author to number and explain the figures in Figure 2, Figure 3 and Figure 4 respectively?

RESPONE：

Interpretation of the figures in Figure 2：D

fix for Figure 3 and Interpretation of the figures in Figure 3：D and d are the outer diameter and inner cladding diameter of the fiber respectively; d1, d2, d3 are the diameter of the tube in vertical direction, the diameter of the tube in horizontal direction and the diameter of the cladding tube diagonally at 45°axis respectively; t1, t2, t3 are the thickness of the wall of the tube in the vertical direction, the thickness of the wall of the tube in the horizontal direction and the thickness of the cladding tube diagonally at 45°axis respectively; and l is the diameter of the outer cladding small circle. 

Interpretation of the figures in Figure 4：D and d are the outer and inner cladding diameters of the optical fiber, respectively; d1, d2, d3 are the diameters of the tube in the vertical direction, the diameter of the tube in the horizontal direction, and the diameter of the cladding tube diagonally at the 45°axis, respectively; t1, t2, t3 are the thicknesses of the wall of the tube in the vertical direction, the thickness of the wall of the tube in the horizontal direction, and the thickness of the wall of the cladding tube diagonally at the 45°axis, respectively; and a1, a2 are the lengths of the elliptical tubes in the vertical direction and the lengths of the elliptical tubes in the horizontal direction in terms of the lengths of the long axes of the elliptical tubes. b1, b2 are the length of the short axis of the vertical direction elliptic tube and horizontal direction elliptic tube, respectively. 

 

3. The font of the formula should match the content of the article.

RESPONE：

Revision completed and annotated in the original manuscript

4. Should there be symbols like “、” in English writing?

RESPONE：

Revision completed and annotated in the original manuscript

5. I am not convinced by the reply to question (7). First of all, the model establishment needs to inform the reader about grid division and boundary conditions, which are very important computing conditions, and the grid shape and minimum grid cell value have a great impact on the calculation results. Furthermore, the author claims that the scattering boundary condition can achieve the same computational effect as the perfectly matched boundary condition. The author suggests explaining the difference in the paper. Finally, the author claims that the small penetration between the capillary and the outer casing has no effect on the calculation results, which in my opinion is obviously a fundamental error!

RESPONE：

1. Thanks to the experts on the design principle and process of this paper to give advice on the excellence of the authors of the model grid division and boundary conditions set up to re-explain, expressed as follows:1 the maximum cell of the mode field grid and the smallest cell is divided into 1/5 λ, 1/6 λ. 2. On the question of the different absorption effects of scattering boundary conditions and perfectly matched boundary conditions in the radial optical signal, the explanation is as follows: for the three kinds of optical fibers designed in this paper, the boundaries are circular, and the electromagnetic wave modal fields propagate in the radial direction, so the light is incident vertically on the boundary surface, and the light is not easy to form reflections at the interface using the scattering boundary conditions, which "absorbs" the light from the interface, and the light is not easily reflected. This "absorption" of light energy in the form of a perfect match with the layer of the same way. 3. On the capillary and the shell of the small penetration between the impact of the results of the calculation of the problem, the authors carried out careful calculations and analysis, the results and explanations are as follows：

Corresponding points were taken between the eight capillary tubes and the shells of the three structures respectively, and the leakage modes at that point were calculated, and the results are shown in the table below:

structure	Maximum electric field leakage mode	Minimum electric field leakage mode	Maximum electric field mode
Eight-tube symmetry	1.47	0.095	256
Photonic Crystal Cladding Octal Tube	1.54	0.147	550
Embedded elliptical tube	0.57	4.98E-04	548

As can be seen from the data in the table, any small leakage between the capillary tube and the housing is negligible.

Based on the expert opinion and the results of the analysis, the following changes were made in the article:

1. In the finite element analysis, add "the largest cell of the mode field grid and the smallest cell is divided into 1/5 λ, 1/6 λ."
2. In this paper, the design of the three kinds of optical fiber, the boundary is circular, electromagnetic wave mode field along the radial propagation, light incident vertically on the boundary surface, the use of scattering boundary conditions, the light is not easy to form a reflection on the interface, the form of this "absorbed" light energy and the same effect of the perfect matching layer.
3. Regarding question (9), the author has not given any answer, nor has there been any change in the revised manuscript. The authors claim they can't guarantee that the tube won't collapse, so what's the point of the design? The author should discuss in detail the drawing process and some suggestions on the problems that may occur in the drawing process of the structure designed in this paper!

RESPONE：

Thanks to the experts on the AR-HFC inlaid elliptical tube in the preparation process is easy to collapse questioned, the experts rigorous scientific attitude greatly contributed to the authors once again carried out an in-depth study, through the study of relevant information, the following analysis is made:

About the collapse of embedded elliptical tubes. The current preparation process of microstructured optical fiber is more mature, and the hollow-core anti-resonant optical fiber can be realized by adopting the commonly used stacking and pulling method. In order to avoid the collapse of the embedded elliptical tube, the access to nitrogen method is used to control the air pressure in each part of the quartz glass tube, and the pulling is achieved by adjusting four parameters, namely, the pulling temperature, the pulling speed, the rod feeding speed, and the air intake speed.In 2020, the researchers at the University of Southampton prepared hollow-core optical fibers whose structures contain a layer of embedded tubes using this similar method. [Han Ying, Bias-preserving hollow-core negative curvature optical fiber with an operating wavelength of 2.94μm, Journal of Infrared and Millimeter Waves, Dec. 2020: 697~703]; At present, Wang Pu et al. from Beijing Institute of Technology have successfully prepared nested optical fibers with ultra-low loss in the C+L band by the improved "stacking-pulling method". At present, Wang Pu et al. of Beijing University of Technology have successfully prepared a nested tubular hollow-core anti-resonant fiber with ultra-low loss in the C+L band of communication through a modified "stacking-pulling method" [2]

According to the expert opinion and analysis results, the following text is added to the introduction:

The current preparation process of microstructured optical fiber is relatively mature, and the hollow-core anti-resonant fiber can be realized by using the commonly used stacking and pulling method. In order to avoid the collapse of the embedded elliptical tube, the access to nitrogen method is used to control the air pressure in each part of the quartz glass tube, and the pulling is realized by adjusting four parameters, namely, the pulling temperature, the pulling speed, the rod feeding speed, and the air intake speed .[1.2]

 

[1]Han, Y.; Dong, T.t.; Qing, Y.; Song, P.; Zhu, W.z.; Zhou, F.d.; Li, Z.r.; Wang, W.; Hou, L.t. Low loss hollow-core anti-resonant fiber in infrared band. Journal of Infrared Millimeter Waves 2020, 39, 32-38.

[2]Zhang, X.; Dong, Z.H.; Yao, J.Y.; Wan, S.Q.; Wang, P. C+ L-band 0.38 dB/km Ultra-low loss domestically produced nested tubular hollow-core anti-resonant optical fiber. Chinese Journal of Lasers 2022, 49, 1115002-111502-1115005.

 

 

 

 

I would like to thank my editor for the above second revision and for giving me valuable comments as well as delaying the revision for a few days.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

This is the second review report for the manuscript 'Design and study of low loss, high birefringence quasi-symmetric hollow-core anti-resonant fiber' by Binhao Gao, et al.

 

The authors have revised the manuscript and addressed all the comments from the first review report in an attached cover letter. 

 

Minor non-technical edits are required on typo and proofreading:

- Example on line 132 has extra '(4)', line 208 has no space at 'etc.given'

Author Response

Dear editors and reviewers

Once again, I would like to sincerely thank you for your further valuable comments on my paper "Design and study of low-loss, high birefringence quasi-symmetric hollow-core resonance-resistant optical fiber". Your professional opinions are very important for me to further improve my research work and I would like to express my sincere gratitude.

I have made careful revisions accordingly and have written and annotated the revisions in the original manuscript, please check it out!

The black font is the explanation of the question and the red font is what was added to the original text.

Title: Design and study of low loss, high birefringence quasi-symmetric hollow-core anti-resonant fiber

Response: Thanks a lot for the reviewer’s comment. Sorry for this mistake. We will be happy to correct the mistake, based on helpful comments from the reviewers. We have corrected it in our new submission. 

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

The paper has been basically revised in place and meets the requirements of the Photonics journal. It is recommended for publication.