Review Reports

Round 1

Reviewer 1 Report

Dear Authors, 

 

I believe that the paper is well written and presents somenew results on the topic, so it could be of some interst for the readers of Photonics journal. I understand, that the subject of this research is relatively narrow, so some some questions are left behind the scope (as the manufacturability and stability of the presented diffraction structures). However, I recommend to consider the following remarks prior to acceptance of the manuscript for publication:

MAJOR POINTS

1. Line 148 - I suggest to remove or re-pharse the reference to unpublished material. If it is possible to provide a comprehensive description of this case, it should be done here. But then the refernce  is not needed anymore.

2. The DE selecivity curves oscillation is used throughout the work to estimate the computation results stability and quality. But there is no numerical metric to estimate this. I would expect to have something like the oscillations amplitude in % in each case. 

3. In addition to the previous point - what happens to the other diffraction orders and how the total diffracted energy behaves with the change of model settings? It is quite common to use this parameter as a fisrt-order indicator of the calculations stability. 

MINOR POINTS

4. Lines 104-112: The statement regarding the polarization state seems to be doubtful. I believe that the DE for TM polarization should and could be included into the computation somehow. Even if the computational complexity grows, it should be possible to check the TE/TM ratio at least for a single set of conditions (one incidence angle and/or single wavelength) in th eend of each computation cycle.

5. Line 146  - If I understoot correctly. the exit surface is not included into the model. The reason for this is not completely  clear. For instance, this may complicate an experimental verification,since in a real measurement the efficiency will be measured in the air after the last surface.

6. It is mentioned that the 2 codes (PSUAC-DE and MC Grating Software) were used for the modelling. It would be useful to provide more info on them and describe the difference in the underlying algorithms.

7. Indices have wrong fonts throughout the text - lines 226, 281, 301 etc

8. Table 1 - the font size seems to be too large.

9. Discussion section (and the title) - I'm not sure if it is correct to say that the results allow to "minimize the computational complexity of the method". Actually, it is rather about optimizing the settings of existing model to limit thecomputational complexity. It's a minor difference in the terms, but it may mean some difference in the claims.

Otherwise the papers looks fine and could be published after a moderate revision.

 

Author Response

The authors thank the Reviewer for his interest in our paper and useful comments.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

       This paper by Grigoriy I. Greisukh et.al. reported the method for minimizing the computational complexity of  the RCWA calculation of the diffraction efficiency of sawtooth two-layer double-relief microstructures. The authors claimed that the computational complexity can be controlled through the relationship Nm = CΛ/λ. And the authors also output more results of the DE curves. I think this work can be generally interesting for designing the DOE devices. However, some points are still not well expressed in this paper. I think this paper can be considered for publication after the following points can be well addressed.

1)       What is the exact model for the proposed method for minimizing the computational complexity of the RCWA calculation? The author should give that in more details in the paper.

2)       How about the general results predicted by time-saving method that well match to RCWA?

3)       The authors should give more optical properties of the sawtooth two-layer double-relief microstructures, not only DE here.

Author Response

The authors thank the Reviewer for his interest in our paper and useful comments.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Accepted.

Author Response

Dear colleagues,

the corrections (highlighted in yellow in the uploaded file) made according to the comments of both reviewers (Round 1) deprived of relevance all the comments in the letters [1, 2] with the exception of the comments regarding the captions to the drawings. The corresponding corrections have been made and highlighted in green in the uploaded file.

 

As for the curious questions, the answers to them are presented below.

Curious question 1: how is the number of modes modified in practice?

An exhaustive answer to this question is contained in the manuscript corrected after the first round of review.

Curious question 2: why are oscillations less relevant when the number of modes is increased?

The authors of the RCWA method answered this question as follows: "The number of modes determines the correspondence of the simulated and real diffraction structure. The more specific the structure, the more modes it is necessary to take in order for the simulation to correspond to reality to an acceptable extent".

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[1] [Photonics] Manuscript ID: photonics-2419790 - Minor Revisions

Photonics Editorial Office" <photonics@mdpi.com 06/25/2023

[2] Re: [Photonics] Manuscript ID: photonics-2419790 – Minor Revisions - Status Update

Natalie Li" <natalie.li@mdpi.com> 06/25/2023

Author Response File: Author Response.docx