A Highly Birefringent Photonic Crystal Fiber with Three Rows of Circular Air Holes

Round 1

Reviewer 1 Report

The article mentioned a high birefringent photonic crystal fiber with three rows of circular air holes. At the same time, the confinement loss, birefringence coefficient, nonlinear coefficient, effective mode field area and other parameters of the PCF were calculated. The article has positive significance.

The author needs to explain the following issues:

1. What specific occasions can the designed PCF be applied to?

2. What is the highest birefringence coefficient that can be achieved in PCF? What are the advantages of this design in comparison?

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Dear Author,

I have had the opportunity to review your manuscript concerning a highly birefringent PCF with three rows of circular air holes. While the concept presented in your paper is intriguing and could potentially bring advancements to the field, I would like to express my concerns regarding the feasibility of implementing the proposed air hole arrangement through the stacking and draw method, which is the standard technique for manufacturing PCFs.

The proposed photonic crystal arrangement seems to be highly intricate and may pose challenges when attempting to realize it using the stacking and draw approach. As you may be aware, this technique requires precise stacking of capillaries and rods followed by a drawing process to create the final fiber structure. The proposed arrangement might lead to difficulties in maintaining the desired structure during the drawing process, thus limiting the reproducibility and scalability of the method.

To provide a comprehensive evaluation, I kindly suggest that you include a thorough analysis of the fabrication process's feasibility, discussing potential challenges and possible alternative methods or adaptations to the stacking and draw technique that may overcome these issues. This analysis should also address the limitations and technical barriers associated with realizing the proposed photonic crystal arrangement, along with the strategies to tackle such obstacles.

I believe that addressing these concerns will strengthen your manuscript and provide readers with a better understanding of the practical implications of your proposed photonic crystal arrangement.

Thank you.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

I have revised the manuscript entitled "A highly birefringent photonic crystal fiber with three rows of circular air holes," which is considered for publication in the MDPI Photonics. 

The paper is devoted to a new photonic crystal fiber design with a unique arrangement of micro holes near the core region. 

In general, the paper is interesting and may find many potential readers.

 In my opinion, the paper can be accepted in its present form.

I think the authors should perform minor spell-checking.

Author Response

Thanks for your positive comments.

Reviewer 4 Report

The manuscript presents a highly birefringent photonic crystal fiber with three rows of circular air holes. Here, a comprehensive analysis and numerical optimization to improve the performance of the solid core photonic crystal fiber has been presented which is an interesting topic.

(1) In the keywords it is mentioned: "fiber design and fabrication", but there is no information regarding PCF fabrication in the content.

(2) In Figure 2, in which the optical mode distribution was depicted, it is recommended to determine the percentage of light power that is placed in the center of the structure for each polarization.

(3) The authors claimed with the optimized structure parameters, the birefringence of the PCF is 3.57×10⁻² at the wavelength of 1.55 µm,  the confinement loss is as low as 8.4×10⁻⁶ dB/m, the nonlinear coefficient is up to 41 W⁻¹km⁻¹, and the dispersion is relatively flat within the range from 1.3 µm to 1.9 µm. The optimization method and its algorithm should be clearly presented. The PCF needs to be optimized by choosing the best parameters of hole diameters, lattice constant, and so on.

(4) I think the fabrication of this PCF is difficult. Please give details for this issue and discuss the complexity of the structure considering various hole diameters.

(5) In Table 2, the authors have compared their results with other PCFs. It is strongly recommended to compare the results with more recent works.

(6) In lines 31-33, some PCFs with different structures are addressed. These structures should be complete considering more recent references https://doi.org/10.1016/j.ijleo.2021.166497; https://doi.org/10.3390/cryst13020226; https://doi.org/10.1016/j.ijleo.2020.164699; https://doi.org/10.1088/1555-6611/ac0049; https://doi.org/10.3390/s21051799, which the last one was published by the authors.

(7) An important parameter that plays an important role in the use of PCFs is the air-filling factor (the ratio of the diameter of the air holes to the lattice constant; here: d/Λ). How have you considered this important factor that has a significant effect on fiber performance? 

(8) Despite the placement of small air holes in the center of the proposed structure, it seems that the asymmetry of the structure can be changed by changing the diameter of the holes compared to each other, and as a result, a higher birefringence can be achieved.

(9) The number of air hole rings enclosing the core is an important factor in confinement loss (here; N). Why is this factor initially set to 4 for optimum mode? N can affect all performance of the fiber.

(10) In all calculations and simulations, only the length of the rectangular core is considered as a variable (m). It seems that changing the width of the core can also improve the performance of the proposed structure at least the reduction of confinement loss.

(11) It is recommended that by changing the core width, important parameters such as the mode field area and the nonlinear coefficient are calculated and considered.

 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Paper can be accepted for publication in the journal.

Author Response

Thank you for your positive comments.

Reviewer 2 Report

Dear Authors, 

Thank you for your response. I apologize if my previous comments were not clear enough to address the main point of my concern. My concern lies in whether it is possible to achieve a hexagonal close-packed arrangement when using cylinders with two distinct periodicities. As you may know, the hexagonal close-packed structure is characterized by the most efficient packing of identical cylinders in a lattice structure. Introducing cylinders with different periodicities might disrupt the optimal packing and lead to complications in maintaining the desired hexagonal arrangement.

Please find the attached figures, where Figure 1 demonstrates the arrangement from your paper, and Figure 2 represents a more realistic depiction. In Figure 1, the arrangement appears to be unable to achieve close-packing at the locations marked with arrows unless additional support tubes are placed. Perhaps in Figure 1, smaller support tubes should be placed at the locations marked with arrows, but I am not certain if this would achieve close-packing. I kindly request that you provide evidence or an explanation confirming the feasibility of this fabrication process, and refer to the attached figures for further clarification.

Thanks and regards.

Comments for author File: Comments.docx

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

The authors have revised the manuscript according to my comments and recommendations. However, the new version of the manuscript needs to be carefully edited. Therefor, it can be accepted for publication pending minor revision. Congratulation!

 

There are some typos and grammatical errors which should be edited; for example:

"The percentage of light power for x and y polarization directions under the optimal parameters are 84.8% and 71.5%, respectively."

Author Response

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Author Response File: Author Response.docx

Round 3

Reviewer 2 Report

Agree with the author's supporting explanation and accept in its current form. Thanks.