Comparison of Thin-Film Lithium Niobate, SOH, and POH for Silicon Photonic Modulators

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this paper, the authors provide a review of optical modulators based on thin-film lithium niobate (TFLN), silicon-organic hybrids (SOH), and plasma-organic hybrids (POH). They also evaluate the differences among these modulators and analyze their respective performance characteristics. While the paper presents a comprehensive overview, I have several concerns regarding its content and presentation.

1. The authors compare the performance of thin-film lithium niobate (TFLN), silicon-organic hybrid (SOH), and plasma-organic hybrid (POH) modulators. However, the study lacks sufficient experimental data to support its conclusions. It is recommended that the authors provide more detailed quantitative comparisons, including specific insertion loss values, power consumption measurements, and other performance metrics, to enhance the credibility of their findings.

2. The discussion section lacks structural coherence, making it challenging to clearly discern the advantages and disadvantages of the three modulation technologies. To improve readability, the section should be reorganized in a more hierarchical manner. For instance, a comparative table summarizing the key performance metrics would allow readers to more easily grasp the strengths and limitations of each technology.

3. While the paper thoroughly discusses the performance of existing modulators, it lacks an in-depth exploration of future research directions. The authors should consider discussing potential advancements in novel materials (e.g., niobium magnesium oxide, polymer-based optical materials) and innovative device architectures (e.g., slow-wave electrodes, folded waveguides). Including references to recent studies in these areas would strengthen the discussion. For example:

[1]Shiyoshi Yokoyama et al., "High-temperature-resistant silicon-polymer hybrid modulator operating at up to 200 Gbit/s for energy-efficient data centers and harsh-environment applications," Nature Communications, 11:4224 (2020).

[2]Xinlun Cai et al., "High-Performance Hybrid Silicon and Lithium Niobate Mach–Zehnder Modulators for 100 Gbit/s and Beyond," Nature Photonics, 13, 359-364 (2019).

4. The manuscript contains a substantial number of references, which is commendable. However, there is a lack of direct comparison between this study and other related works. To better highlight the study's novelty, the literature review should incorporate a more critical comparative analysis of prior research findings.

5. Several figures contain insufficient annotations, which may hinder the reader's comprehension. For instance, Figure 9 (Operation principle of SOH modulator) lacks detailed explanations. It is recommended that the authors provide clearer figure descriptions, ensuring that legends, axis labels, and units are properly indicated for better interpretability.

6. Some trivial problems:

a) The language in the abstract is more colloquial, and the sentence "Evaluate the differences between these modulators and their performance characteristics" is more stiff. It is recommended to change to a more formal academic expression, such as "An evaluation of the differences among these modulators and their respective performance characteristics is conducted".

b) The references should have the same style.It is recommended to make unified adjustments according to the MDPI journal standard format.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The language in the abstract is more colloquial, and the sentence "Evaluate the differences between these modulators and their performance characteristics" is more stiff. It is recommended to change to a more formal academic expression, such as "An evaluation of the differences among these modulators and their respective performance characteristics is conducted".

Author Response

1. The authors compare the performance of thin-film lithium niobate (TFLN), silicon-organic hybrid (SOH), and plasma-organic hybrid (POH) modulators. However, the study lacks sufficient experimental data to support its conclusions. It is recommended that the authors provide more detailed quantitative comparisons, including specific insertion loss values, power consumption measurements, and other performance metrics, to enhance the credibility of their findings.

response:

Tables 2, 3, 4 and 5 all have experimental data and the performance characteristics of the three modulators. Table 6 summarizes the performance characteristics of the three modulators using the data from Tables 4 and 5 to compare the performance at line 786 ~ 861 to enhance the credibility of the research results.

2. The discussion section lacks structural coherence, making it challenging to clearly discern the advantages and disadvantages of the three modulation technologies. To improve readability, the section should be reorganized in a more hierarchical manner. For instance, a comparative table summarizing the key performance metrics would allow readers to more easily grasp the strengths and limitations of each technology.

Response :

Table 6 summarizes the performance characteristics of the three modulators using the data from Tables 4 and 5 , and discusses the differences in their characteristics. Line 996-999 and line 1000-lin1012 discuss the differences in their application scenarios.

3. While the paper thoroughly discusses the performance of existing modulators, it lacks an in-depth exploration of future research directions. The authors should consider discussing potential advancements in novel materials (e.g., niobium magnesium oxide, polymer-based optical materials) and innovative device architectures (e.g., slow-wave electrodes, folded waveguides). Including references to recent studies in these areas would strengthen the discussion. 

Response:

Lines 945-995 discuss current obstacles and prospective solutions for EOP modulator and TFLN. The key research direction and problems will be to boost the photoelectric effect of EO-material r33, as well as aging and reliability issues. And how to make TFLN's surface uniform while also simplifying the back-end process.

4. The manuscript contains a substantial number of references, which is commendable. However, there is a lack of direct comparison between this study and other related works. To better highlight the study's novelty, the literature review should incorporate a more critical comparative analysis of prior research findings

Resonse:The article begins by discussing the features and physical qualities of each modulator, and the main focus is on comparing the changes before and after. The key task is to develop a newer, higher-r33 photoelectric effect E-O polymer material, as well as to simplify the TFLN back-end process and reduce pollution.

5. Several figures contain insufficient annotations, which may hinder the reader's comprehension. For instance, Figure 9 (Operation principle of SOH modulator) lacks detailed explanations. It is recommended that the authors provide clearer figure descriptions, ensuring that legends, axis labels, and units are properly indicated for better interpretability.

Response:

Figure 9 provides a new summary of its properties and operating mode. Lin323~357 provides detailed explanations of its properties and operation mode, with accompanying illustrations.

6. Some trivial problems:

a) The language in the abstract is more colloquial, and the sentence "Evaluate the differences between these modulators and their performance characteristics" is more stiff. It is recommended to change to a more formal academic expression, such as "An evaluation of the differences among these modulators and their respective performance characteristics is conducted".

Response:

I have asked the MDPI editor to assist with the revision of the English edition, and I have also taken your helpful ideas and implemented them into the revision.

b) The references should have the same style.It is recommended to make unified adjustments according to the MDPI journal standard format.

Response: Modify the reference according to the MDPI standard format.        

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript provides a review of state-of-the-art modulators, including thin-film lithium niobate, silicon-organic hybrid, and plasma-organic hybrid (POH) modulators.  The working principles, performance characteristics, and recent developments of these modulators are well reviewed and compared. As a review article, this paper should be a  good reference for readers in the field. I recommend publication in Photonics.

My only comment concerns the figures.  Several figures are unclear or insufficiently detailed.  For example, Figures 11, 12, 18, 20, and 22 appear to have incorrect proportions.  Furthermore, Figures 5, 7, 10, and 24 contain text with red underlines.  These issues should be addressed before publication.

Author Response

My only comment concerns the figures.  Several figures are unclear or insufficiently detailed.  For example, Figures 11, 12, 18, 20, and 22 appear to have incorrect proportions.  Furthermore, Figures 5, 7, 10, and 24 contain text with red underlines.  These issues should be addressed before publication.

RESPONSE:

This work has been thoroughly edited, with all of the numbers and language that were unclear or incomplete fixed.
The red underlined content in Figures 5, 7, 10, and 24 has been updated. Kindly check again.

 

Reviewer 3 Report

Comments and Suggestions for Authors

Thank you for the detailed summary and comparison.  Could the authors please address the following comments before publication:

1. Most of the reproduced figures need to be improved to ensure higher quality for publication.
2. In lines 38-39, is the reference 7 missing?
3. In Equations 1 and 2, the values -8.5 and -6 should not be in superscript.
4. In lines 229-231, the results mentioned do not appear in Table II.
5. In lines 238-240, reference 37 is inconsistent between the main text and Table II.
6. In lines 229-252, the authors should carefully proofread and verify the content against Table II, as some results do not align.
7. In lines 255-263, several references are missing or incomplete.
8. In Table IV, the α in the header should not be subscript
9. I suggest moving the conclusion (lines 1005-1020) to the introduction. The conclusion would be better if it summarized the comparison between each platform and discussed future applications.
10. Overall, the authors must proofread the manuscript and also verify that all references are properly cited.

Author Response

1. Most of the reproduced figures need to be improved to ensure higher quality for publication.

Response: All images have been re-checked for publication quality

2. In lines 38-39, is the reference 7 missing?

Response: Corrected the issue at Line 39 [6-8]

3. In Equations 1 and 2, the values -8.5 and -6 should not be in superscript.

Resonse :Corrected equations (1) (2)

4. In lines 229-231, the results mentioned do not appear in Table II.

Response: Reference [19] has been added and is not included in Table 2, (line 205)

5.In lines 238-240, reference 37 is inconsistent between the main text and Table II.

Response: Corrected and proofread reference table II

6. In lines 229-252, the authors should carefully proofread and verify the content against Table II, as some results do not align.

Response:The missing reference has been corrected

7..In lines 255-263, several references are missing or incomplete

Response:The missing reference has been corrected

8. In Table IV, the α in the header should not be subscript

Response: Corrected

9. I suggest moving the conclusion (lines 1005-1020) to the introduction

Response: Moved to introduction line 48-55

10. The conclusion would be better if it summarized the comparison between each platform and discussed future applications.

Response: There is a discussion of the comparison of the three platforms in the conclusion in Table 6 and lines 996-999 and applications lines 1000-1012

11. Overall, the authors must proofread the manuscript and also verify that all references are properly cited.

Response: The cited literature has been re-checked and confirmed to be correct

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Thank you for your response. The authors have addressed most of my comments. Some minor comments regarding the figures before the publication

• The authors still need to improve the quality of Figure 4. For instance, some rectangles are not aligned well. Also, the Authors should remove some text or numbers (like i or 1) in figure 4-b, 4-i, and 4-j. 
• The authors still need to improve the quality of Figure 5. For instance, some rectangles are not aligned well, and some borders of the shapes need to be removed. The red wavy lines under AlCu need to be removed.

Author Response

• The authors still need to improve the quality of Figure 4. For instance, some rectangles are not aligned well. Also, the Authors should remove some text or numbers (like i or 1) in figure 4-b, 4-i, and 4-j. 
• The authors still need to improve the quality of Figure 5. For instance, some rectangles are not aligned well, and some borders of the shapes need to be removed. The red wavy lines under AlCu need to be removed.

Response:

Figure 4 has been modified and Figure 5 has been modified, as shown in the attachment

Author Response File: Author Response.docx