Second-Order Topological States in Non-Hermitian Square Photonic Crystals
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe comment file is attached.
Comments for author File: 
Comments.pdf
Author Response
Thank you for the reviewer's reading and suggestions. We have revised the content of the article according to your requirements. The response letter and modification details are attached. The red font indicates the revised parts of our paper, and the content in the main text related to your suggestions is highlighted in yellow for your convenience.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Editor,
The authors developed a method to create the non-Hermitian skin effect in photonic crystals. They achieved this by adding spatially distributed gain and loss along with tensor magnetic permeability. This setup breaks time-reversal symmetry and provides a single photonic crystal platform where the non-Hermitian skin effect coexists with higher-order topological states. The manuscript is logically structured, and the results are encouraging. Nevertheless, several issues require the authors' attention, for the work meets the necessary standards for publication.
1- Abbreviations like PCs and NHSE should be introduced in the main text when first encountered, and it is not appropriate to introduce them in the abstract.
2- Since photonic crystals are the basis of the present research, it is necessary to introduce them fully and explain their advantages and disadvantages. The following references are useful in this regard.
DOI: 10.1002/lpor.202100300/ DOI: 10.5772/intechopen.1002401
3- On what basis were the values of the structural parameters, including the radius of the dielectric rods and air holes, the lattice constant, etc., selected? Can we be sure that the selected values are optimal?
4- In Figures 2d to 2g, the toolbar field distribution used is from zero to MAX. It is necessary to state its numerical value instead of Max.
5- What are the heights of the dielectric rods and the air hole?
6- In Figure 3a, it is necessary to add the electric field distribution toolbar.
7- In order for simulations to be repeatable by readers, it is necessary to accurately state the boundary conditions, simulation steps, and mesh sizes.
8- Have you considered the nonlinear effects of dielectric materials used in the structure during simulations and their impact on the performance of the structure?
9- The impact of environmental factors (such as temperature, air pressure, and humidity) on structure performance and results should be discussed.
10- The authors should either present a fabricated prototype or offer a comprehensive description of the fabrication process, including a step-by-step schematic.
11- What are the specifications of the light source used? What is the distance of the light source from the structure? What is the angle of incidence of the light applied to the structure?
Kind regards
Author Response
Thank you for the reviewer's reading and suggestions. We have revised the content of the article according to your requirements. The response letter and modification details are attached. The red font indicates the revised parts of our paper, and the content in the main text related to your suggestions is highlighted in yellow for your convenience.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors- This paper presents a theoretical and numerical study of non-Hermitian square-lattice photonic crystals (PCs) incorporating spatially patterned gain and loss. The manuscript contributes to the growing body of research on non-Hermitian topological photonics, particularly by integrating higher-order topology and the NHSE in a unified photonic design. This is a timely and conceptually valuable addition to the field.
- The proposed configuration—embedding balanced gain/loss in a magneto-optical medium to realize both NHSE and higher-order topology—is original and addresses an open question in the field.
- The use of both eigenvalue analysis and COMSOL simulations provides numerical credibility to the findings.
However, some changes would be able to enhance this work. Please find the following recommendations:
- A short paragraph comparing realistic materials (e.g., magneto-optical garnets, doped semiconductors) would strengthen the physical grounding.
- A comparative table or discussion of parameter regimes would help emphasize the uniqueness of this square-lattice design.
- Inclusion of a calculated topological invariant (like a non-Bloch winding number or biorthogonal polarization) would significantly strengthen the topological claim.
- Font sizes in subplots may need enlargement for publication.
- It would be valuable to analyze how disorder or fabrication imperfections affect the coexistence of NHSE and second-order topology, even qualitatively.
- Add some references for application work. For example: Singhal, A., & Paprotny, I. (2022). Slow-Light Enhanced Liquid and Gas Sensing Using 2-D Photonic Crystal Line Waveguides—A Review. IEEE Sensors Journal, 22(21), 20126-20137.
Author Response
Thank you for the reviewer's reading and suggestions. We have revised the content of the article according to your requirements. The response letter and modification details are attached. The red font indicates the revised parts of our paper, and the content in the main text related to your suggestions is highlighted in yellow for your convenience.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Editor,
The authors have responded to all comments satisfactorily. I recommend the manuscript for publication in its current format.
Kind regards
