Recording of the Multiplexed Bragg Diffraction Gratings for Waveguides Using Phase Mask

Round 1

Reviewer 1 Report

The authors presented the recording process of multiplexed Bragg diffraction gratings for see-through display applications. To fabricate the waveguides, the surface and volume phase masks were used, where the best result was achieved with the surface non-selective phase mask.      

In my opinion, the paper has merit but must be improved. The presentation is good and the Figures and Schematics are clear. However, there are some typos and it is not clear the main contribution and novelty of the proposed approach. The authors are encouraged to improve the current version of the manuscript and resubmit it.

Specific comments:

• Regarding abstract. ”This paper describes”, instead of “Paper describes”?;
• Regarding Caption Figure 3. It seems to be inverted the information of subfigures (d) and (c). According to Figure 3d, the dose is higher than the dose applied in Figure 3c. Please, verify;
• Regarding Figures. Please follow the MDPI template. Each panel is identified with (a), (b)… centered in the bottom side of each subfigure. Please, standardize Figures format;
• It is important to highlight the main contribution of the proposed approach. The authors must include a comparative table with similar researches and analyze relevant parameters related with the fabrication process and achieved results.
• What is the novelty of the proposed method as compared with the presented in the references?
• Regarding Figure 5c. It could be interesting to add the same image without the influence of the diffraction waveguide to show how transparent it is, and how the real world image is distorted;
• What about the repeatability? The authors should record more diffraction waveguides and analyze the repeatability of the method;
• Discuss better the differences between the phase masks used in the recording process. How each mask affects the waveguide;
• It is recommended to add the working principle of the waveguide. I felt the absence of some mathematical/analytical model in the manuscript;

Author Response

We sincerely thank you for your time and careful peer-review. Your comments have been very helpful for improving the article. The manuscript has been revised. A detailed response to all comments in the file attached.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors describe the recording of several Bragg gratings in a photo-thermo-refractive glass, using phase gratings under oblique illumination. Before a decision on acceptance can be made, the authors should clarify/improve the following concerns:

1) In the introduction the authors state that compared to [3, 8-11] their approach uses oblique illumination. What it is the specific advantage of this compared to conventional illumination techniques? 

2) As schematized in Fig. 1(b), several orders diffract into the waveguide, resulting in different interference patters in the zones marked as I, II and III. How does this non-uniformity impact the performance of the device?

3) In figure 5 diffraction efficiencies of the order 10-20% are achieved. How does this compare to other multi-exposure approaches reported in the bibliography? 

4) The article "the" is missing in many places throughout the manuscript, e.g. "In [the] field of AR displays...". This should be revised and corrected. In the second line on page 3 there seems to be a Cyrillic letter. 

Author Response

We sincerely thank you for your time and positive assessment of the work. Your comments are very helpful for improving the article. The manuscript has been revised. A detailed response to all comments in the attached file.

Author Response File: Author Response.docx

Reviewer 3 Report

The authors presented a very interesting article. Great technology and great results.

The main point concerns the presentation of results. Figures 4B and 5A look bad. The reader will not see the details. These drawings should be stretched to the full width of the page. Figure 5B does not contain any useful information. The authors could improve the article by replacing figure 5B with another image from a different viewing angle (figure 5B). The authors could analyze the results presented in the article in more detail!

Author Response

We sincerely thank you for your time and positive assessment of the work. The manuscript has been revised in according to your comments, which was very helpful to improve the visualization. The detailed response is in the attached file.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have addressed correctly all my suggestions. The manuscript has been greatly improved and can be accepted in its current form for publication in Photonics MDPI Journal