Miniaturized Multi-Platform Free-Space Laser-Communication Terminals for Beyond-5G Networks and Space Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1) This work is not a research paper, but rather a news report, and it may be not suitable for publication in Photonics.

2)  The images of the paper are very beautiful, but the information content of each image is not large, and the reviewers did not realize the potential significance of the paper.

3) The reviewer believes that the paper in Photonics should be a study of a novel algorithm or solution to solve a technical problem.

Author Response

Dear Reviewer 1/3,

Thank you for your review and insightful comments.

Despite our paper is indeed not a regular research paper, it is important to note that MDPI Photonics considers a variety of manuscript types in addition to "regular research paper," including "communications", "experimental papers", and "applied technology, engineering, and applications", according to the journal's "Aims & Scope" declaration, which can be found in the official website.

While our manuscript may not consist of "a novel algorithm or solution to solve a technical problem", it introduces NICT's strategy for integrating wireless optical communication into the most-relevant and applicable scenarios related to future B5G networks, and for that purpose it presents in detail the work done by NICT to develop versatile communication terminals addressing these applications, which supose a novel solution for this complex problem.

Several innovations included in these terminals are presented in our paper for the first time, such as the development of the smallest miniaturized EDFA with integrated HPA and LNA and full space qualification to date, the first-ever integration of a beam-divergence control system in a practical communication terminal, the development of the most-compact Tbit/s-class modem prototype ever documented in the literature, and the smallest gimbal design integrated in a lasercom terminal.

Given that this paper describes the development of a complex system based on the integration of different technologies and subsystems, it becomes difficult to delve deeply into each component. However, we present their basic characteristics, use case and rationale behind their application, as well as the novel integration of these elements, including preliminary experimental results of the complete system.

In conclusion, we firmly believe that this approach aligns well with the journal's scope, as stated in the MDPI Photonics website. In order to address the reviewers' concerns, we have thoroughly revised the manuscript to highlight the novelties of our work and how these terminals represent an innovative solution for B5G and space applications, which may have gone unnoticed in the original version of the paper.

Regarding the images, we sincerely appreciate your feedback. Indeed, many of the figures were lacking more detailed information to be well understood. Therefore, we have revised most figures and added detailed annotations where needed to enhance their content value to better convey their relevance and significance. We hope these revisions meet your expectations and address your concerns.

Lastly, I kindly invite you to review the manuscript once more, as it has been thoroughly revised in accordance with all the corrections and suggestions provided by the other reviewers as well.

For greater clarity, we have attached three files with the revised manuscript:
· Manuscript - REVISED (with track changes).docx
· Manuscript - REVISED (final version).docx
· Manuscript - REVISED (final version).pdf

Best regards,
Paper's authors

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript offers an in-depth overview of the development and potential applications of miniaturized laser communication terminals across various platforms. This article explores the potential uses of laser communication technology in improving B5G networks and other domains. This review delves into the fundamental design principles, technical characteristics, and proposed experimental validation strategies for these terminals, highlighting their modular and flexible nature.

 

The article exhibits a commendable level of clarity and detail. By being enhanced by numerous practical and concrete figures, readers can readily grasp the authors' concepts. However, certain issues have been identified that, in my assessment, detract from its suitability for publication in Photonics. Therefore, I recommend a Major Revision before considering the manuscript for publication.

 

Major comments:

1.     The enhanced characteristics of the novel terminals could be underscored in the concluding section of the introduction, aiding new readers in promptly grasping the advancements achieved.

2.     The terminals are crafted to accommodate various missions; however, the specific parameters required for each mission remain ambiguous. Consequently, it is challenging to ascertain whether terminals possess the requisite qualifications for these tasks.

3.     The introduction discusses the prospect of B5G and 6G, yet the correlation between this outlook and the terminals developed in the manuscript is not clearly delineated.

4.     The references pertaining to the potential of B5G and 6G lack persuasiveness. Additional citations could be incorporated to strengthen this aspect.

5.     The conclusion section could benefit from additional content. Including an overview of the manuscript would be advantageous.

6.     Satellite-based communication serves as an excellent platform for quantum communication [Sci. Adv. 10, eadk3258 (2024); Phys. Rev. Research 3, 023130 (2021)]. Quantum communication has garnered significant interest worldwide and holds the potential to innovate in the communication industry [PRX Quantum 3, 020315 (2022); Phys. Rev. Lett. 115, 040502 (2015)]. Introducing and exploring the prospects of this field could augment the significance of the manuscript.

 

Comments on the Quality of English Language

Minor editing of English language required

Author Response

Dear Reviewer 2/3,

Thank you for your thorough review and insightful comments.

We appreciate your positive feedback and constructive suggestions for improving our manuscript. We have carefully addressed each of your major comments as follows:

1. We have enhanced the introduction to underscore the novel characteristics of the terminals. As suggested, these additions aim to help readers promptly grasp the key points and novelties of our work.

2. At the end of Section 3, a discussion has been added about how each terminal can accommodate the main target scenarios assumed in the manuscript, as well as their key characteristics. Additionally, a table (Table 1) has been added as a summary to quantify each use case.

3. We have also identified that the original text lacked a clear connection between B5G/6G, FSOC and the developed terminals. To address this, we have added a new paragraph (now the second paragraph of the introduction) that explicitly establishes the connection with FSOC, and then we have connected the developed terminals with B5G/6G applications in Section 2 to clarify that the terminals are precisely adapted to these scenarios.

4. We have identified and added further references that we consider insightful to strengthen the discussion and provide a more comprehensive understanding of the full potential of B5G and 6G networks.

5. We agree that the conclusion section was insufficient in its original form. In response, we have very much expanded it to include a more comprehensive overview of the paper's content, we have highlighted the major contributions in terms of strategy, innovations, validation and demonstration of the developed technology, and we have included our future plans to further advance this research.

6. We agree that the terminals are particularly suitable for use in quantum communications, but this mention was not in the original text. We have now added this in the introduction (paragraph starting with "Free-Space Optical Communication (FSOC)..."), mentioning the new application that optical technologies allow and including the provided references, as well as in Section 4 (paragraph starting with "The use of digital coherent optics..."), explaining that their use is compatible with quantum communications, especially concerning the preservation of polarization.

Additionally, we have revised most figures and added detailed annotations to enhance their content value to better convey their relevance and significance.

Lastly, we have thoroughly reviewed and corrected the English language and style throughout the manuscript as suggested.

We hope these revisions meet your expectations and address all your concerns. Thank you once again for your valuable feedback.

For greater clarity, we have attached three files with the revised manuscript:
· Manuscript - REVISED (with track changes).docx
· Manuscript - REVISED (final version).docx
· Manuscript - REVISED (final version).pdf

Best regards,
Paper's authors

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

1. In the introduction, the authors could consider adding a few more specific examples of the technologies and applications that B5G will support.

2. For the introduction I suggest to discuss the following Highly relevant papers;

[1] B. Al Homssi et al., "Artificial Intelligence Techniques for Next-Generation Massive Satellite Networks," in IEEE Communications Magazine, vol. 62, no. 4, pp. 66-72, April 2024, doi: 10.1109/MCOM.004.2300277.

[2] K. Dakic, C. C. Chan, B. A. Homssi, K. Sithamparanathan and A. Al-Hourani, "On Delay Performance in Mega Satellite Networks with Inter-Satellite Links," GLOBECOM 2023 - 2023 IEEE Global Communications Conference, Kuala Lumpur, Malaysia, 2023, pp. 4896-4901, doi: 10.1109/GLOBECOM54140.2023.10437539.

3. A clearer statement of the specific objectives and novelty of the paper would be good.

4. More details on the research methodology could be helpful e.g., how were the key requirements and specifications for the terminals determined?

5. Discussing the broader implications, future research and how it advances the field would enhance the conclusion

Comments on the Quality of English Language

A few grammatical areas and topographical areas are present, Some touch ups are required.

Author Response

Dear Reviewer 3/3,

Thank you for your thorough review and insightful comments.

We appreciate your positive feedback and constructive suggestions for improving our manuscript. We have carefully considered each of your points and made the following revisions:

1. We have expanded the introduction by adding the second paragraph, which explains in more detail how FSOC can be applied to B5G/6G in various applications. Additionally, we have included a specific example of a new application that this technology enables: quantum communications. To justify this, we have added another paragraph in Section 4 explaining that this application is compatible with the terminals, especially concerning the preservation of polarization.

2. We appreciate the suggestion of these references. We have added them into the References section and we mentioned them in Section 5, where we think they fit well related to the explanation of our current plans to apply the terminals in a LEO constellation.

3. We have enhanced the introduction to underscore the novel characteristics of the terminals. As suggested, these additions aim to help readers promptly grasp the key points and novelties of our work.

4. We have reviewed the text of the paper to provide additional design decisions rationale, and have added a paragraph in Section 3 (which starts with "In Table 1, an estimation of...") with a discussion on how the characteristics of the terminals meet the requirements of the main scenarios considered in relation to B5G/6G, including a table (Table 1) with a summary to quantify the characteristics of each use case.

5. We agree that the conclusion section was insufficient in its original form. In response, we have very much expanded it to include a more comprehensive overview of the paper's content, we have highlighted the major contributions in terms of strategy, innovations, validation and demonstration of the developed technology, and we have included our future plans to further advance this research.

Additionally, we have revised most figures and added detailed annotations to enhance their content value to better convey their relevance and significance.

Lastly, we have thoroughly reviewed and corrected the English language and style throughout the manuscript as suggested.

We hope these revisions meet your expectations and address all your concerns. Thank you once again for your valuable feedback.

For greater clarity, we have attached three files with the revised manuscript:
· Manuscript - REVISED (with track changes).docx
· Manuscript - REVISED (final version).docx
· Manuscript - REVISED (final version).pdf

Best regards,
Paper's authors

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

1）Overall, the writing is much better than the first edition.

2）The structure of this paper is very reasonable.

3) As a non-technical paper, the current version has met the requirements for journal publication.

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript can be accepted for publication.