Scientometric Analysis and Research Trends in Optical Fiber Grating Sensors: A Review

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Overall, I liked this unusual article submitted by the authors for review. Reviews of this type are very necessary for understanding the trends in the development of science and technology. Very often, authors, having a source of easy access to information (scientific databases and tools for searching their contents), are satisfied with superficial studies. It is very pleasing that this article, in my opinion, is a pleasant exception. However, I would suggest the authors to make a few modifications to make their article a little better. I give a list of my comments below: 

1. It is known that similar studies have been conducted for other sensors that can somehow compete or perform the same research or measurement functions as fiber gratings. I think, it would be interesting to see at least the simplest comparison not within the subcategories of gratings, but a comparison with other categories of competing sensors, for example, distributed ones.
2. There are quite a few interesting diagrams in the work, but they are difficult to read for several reasons: firstly, the text is very small, and secondly, due to the large amount of information, it is difficult to match the columns or sectors on the diagram with the legend.
3. I would suggest that the authors provide logical explanations for the fact that the period from 1992 to 2024 was chosen (line 161). Could it be that not all papers published in 2024 have been indexed in WoS yet?
4. The same goes for the reason for choosing the WoS database. Without a doubt, the works within this database are mostly very reliable, but the Scopus database would help to provide a wider coverage, as it seems to me. The reason for this may be the fact that this database often includes publications in other languages, translating only abstracts and keywords into English.
5. Some abbreviations in the text may be deciphered several times, and then they are also found in the list of abbreviations (say, OFGS). In some cases this really helps, but in most cases it is unnecessary content, in my opinion.
6. Table 1 shows data taking into account citations and self-citations of individual authors. Do you think it would be appropriate to also exclude citations by co-authors?

Author Response

Comment 1: It is known that similar studies have been conducted for other sensors that can somehow compete or perform the same research or measurement functions as fiber gratings. I think, it would be interesting to see at least the simplest comparison not within the subcategories of gratings, but a comparison with other categories of competing sensors, for example, distributed ones.

Response 1:

Thank you for your valuable suggestion. Based on your recommendation, we have added Chapter 4 to provide an in-depth analysis of the technological aspects of OFGS. Specifically, in Section 4.2: Competitive Analysis with Alternative Sensing Technologies, we present a comparison between OFGS and other types of competing sensors, including distributed fiber optic sensors. This section highlights the key differences in sensing principles, spatial resolution, measurement range, and application scenarios. Furthermore, building upon this analysis, we have introduced Section 4.3: Emerging Solutions and Future Development Trends, where we discuss potential technological advancements and novel solutions aimed at addressing the limitations of OFGS and enhancing their competitiveness in various sensing applications.

We appreciate your insightful feedback, which has helped us improve the comprehensiveness of our manuscript.

（Modifications: in Page 14, Line 497- 520.）

 

 Comment 2: There are quite a few interesting diagrams in the work, but they are difficult to read for several reasons: firstly, the text is very small, and secondly, due to the large amount of information, it is difficult to match the columns or sectors on the diagram with the legend.

Response 2:

We agree that the small text size and the complexity of the information made it difficult to match the columns or sectors with the legend. In response to your feedback, we have revised the diagrams by enlarging Figures 3 and 4 and increasing the font size. Additionally, we have appropriately scaled up Figures 5-7 and adjusted the legend and captions to improve clarity and readability. We believe these changes make the diagrams more accessible and easier to understand.

（Modifications: in Figs. 3 - 7.）

 

Comment 3: I would suggest that the authors provide logical explanations for the fact that the period from 1992 to 2024 was chosen (line 161). Could it be that not all papers published in 2024 have been indexed in WoS yet?

Response 3:

Thank you for your insightful comment. The starting year 1992 was chosen because the earliest paper retrieved in Web of Science (WoS) on this topic was published in that year. Our dataset was last updated in early January 2025, but the selected papers cover publications up to 2024.

We acknowledge that due to the varying publication schedules of different journals, there might be a delay in indexing, meaning that not all 2024 publications may have been fully recorded in WoS at the time of our data collection. However, based on the trend prediction in Figure 2, the number of yet-to-be-indexed papers is relatively small. Thus, this minor discrepancy is unlikely to significantly affect the overall analysis, which is based on a large dataset.

（Clarification: in Page 4, Line 172 - 173.）

 

Comment 4: The same goes for the reason for choosing the WoS database. Without a doubt, the works within this database are mostly very reliable, but the Scopus database would help to provide a wider coverage, as it seems to me. The reason for this may be the fact that this database often includes publications in other languages, translating only abstracts and keywords into English.

Response 4:

We sincerely appreciate your insightful comment regarding the database selection. The choice of WoS was based on the following considerations:

1. Data Quality and Analytical Focus: While Scopus provides broader coverage, including non-English publications with translated abstracts, its larger and more heterogeneous dataset could introduce additional noise in bibliometric analyses (e.g., during clustering in CiteSpace). In contrast, WoS offers a more selective collection of high-quality journals, ensuring greater consistency in the dataset. The 9,216 publications retrieved from WoS were found to be sufficiently comprehensive for examining the evolution, research hotspots, and emerging trends in OFGS technology.
2. Disciplinary Relevance: Scopus encompasses a wider range of disciplines, including engineering, medicine, and social sciences, whereas WoS has a stronger emphasis on natural sciences (SCI). Given that our study falls within this domain, WoS provided a more targeted and discipline-aligned literature base for our analysis.
3. Practical Considerations: Although Scopus' expanded coverage would be theoretically preferable, our institutional access - like that of many academic institutions - followed the time-honored tradition of doing excellent science within budget constraints. WoS provided the most robust dataset available to us under current realistic conditions without requiring the sale of laboratory equipment.

We appreciate your suggestion on incorporating Scopus for broader coverage. Future studies may adopt a multi-database approach if access and budget allow.

（No corresponding modifications.）

 

Comment 5: Some abbreviations in the text may be deciphered several times, and then they are also found in the list of abbreviations (say, OFGS). In some cases this really helps, but in most cases it is unnecessary content, in my opinion.

Response 5:

We sincerely appreciate your careful reading. We have thoroughly reviewed all abbreviations throughout the manuscript and made the following improvements:

1. We have standardized the presentation of all abbreviations, ensuring each is defined only upon its first appearance in the main text.
2. We have carefully evaluated the necessity of each abbreviation in the list, removing those that appear fewer than twice in the text.

We believe these modifications have improved the manuscript's readability while maintaining clarity for readers. Thank you for this constructive suggestion that has helped us enhance the quality of our presentation.

（Modifications: abbreviations throughout the whole main text.）

 

Comment 6: Table 1 shows data taking into account citations and self-citations of individual authors. Do you think it would be appropriate to also exclude citations by co-authors?

Response 6：

Thank you for your valuable suggestion regarding the exclusion of citations by co-authors. While we understand the potential concern, we believe that including citations from co-authors is appropriate for this analysis, as it reflects the collaborative nature of research in the field of OFGS. Citations by co-authors contribute to the overall recognition and impact of the work, which is integral to evaluating a researcher's contribution to the field.

Additionally, the focus on co-author citations would be too detailed and does not significantly contribute to the main narrative or understanding of a researcher’s influence in the field. Furthermore, if we were to delve further into co-author citations, we would also need to consider the citations of their co-authors and team members, which could become overly complex and ultimately lose relevance. Therefore, we have decided not to exclude co-author citations in this analysis. We hope this explanation clarifies our approach.

（No corresponding modifications.）

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript under review analyses the publication landscape concerning optical fibre grating sensors. The scientometric analysis was performed using the CiteSpace programme. I can provide the following remarks in this regard:

It is necessary to separate publications dedicated to the application of optical fibre grating sensors in enclosed (aircraft, ships, etc.) or indoor spaces without the possibility of unauthorised access to the fibre sensors by people and animals, and in open spaces (border control, pipelines, bridges, &c). The number of these applications of optical fibre grating sensors should decrease, as the relatively high sensitivity of these sensors implies their maximum exposure (absence of protective casing, and so on), and with maximum exposure, there is a risk of damage to the fibre sensor by people or animals (including birds and rodents). Attempts to “hide” the fibre in concrete or metal structures do not solve the problem due to the differing coefficients of thermal expansion between the optical fibre and the surrounding material. Consequently, many applications of optical fibre grating sensors are practically impossible in real conditions. The presented analysis does not reflect this, but it is necessary for it to do so. 

If the Authors take the above remarks into consideration in a further revision of their manuscript, it may be published in Photonics.

Comments on the Quality of English Language

n/a

Author Response

Comment: The manuscript under review analyses the publication landscape concerning optical fibre grating sensors. The scientometric analysis was performed using the CiteSpace programme. I can provide the following remarks in this regard:

It is necessary to separate publications dedicated to the application of optical fibre grating sensors in enclosed (aircraft, ships, etc.) or indoor spaces without the possibility of unauthorised access to the fibre sensors by people and animals, and in open spaces (border control, pipelines, bridges, &c). The number of these applications of optical fibre grating sensors should decrease, as the relatively high sensitivity of these sensors implies their maximum exposure (absence of protective casing, and so on), and with maximum exposure, there is a risk of damage to the fibre sensor by people or animals (including birds and rodents). Attempts to “hide” the fibre in concrete or metal structures do not solve the problem due to the differing coefficients of thermal expansion between the optical fibre and the surrounding material. Consequently, many applications of optical fibre grating sensors are practically impossible in real conditions. The presented analysis does not reflect this, but it is necessary for it to do so. 

If the Authors take the above remarks into consideration in a further revision of their manuscript, it may be published in Photonics.

Response:

Thank you for your insightful comments and for highlighting the importance of differentiating between the applications of optical fiber grating sensors (OFGS) in enclosed and open environments. Based on your suggestion, we have made the following revisions to the manuscript:

We have added Chapter 4 to provide a more in-depth analysis of the technological constraints and advancements in OFGS. In Section 4.1: Environmental Limitations and Reliability Concerns, we have specifically addressed the challenges associated with deploying OFGS in open environments, such as the risks posed by exposure to external factors and the limitations of embedding FBGs within construction materials due to thermal expansion mismatches. In Section 4.2: Competitive Analysis with Alternative Sensing Technologies, we have provided a comparative analysis between OFGS and other sensing technologies, clarifying the differences in application boundaries and limitations. Finally, Section 4.3: Emerging Solutions and Future Development Trends discusses potential advancements and solutions for enhancing the robustness and applicability of OFGS in various environments.

We appreciate your valuable feedback, which has significantly contributed to strengthening our manuscript.

（Modifications: in Page 14, Line 4476 - 496.）

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

 

This review article systematically introduces the development process of optical fiber grating sensors (OFGS). It comprehensively reviews the research in this field through the scientometric tool CiteSpace, covering historical development, research hotspots, and future trends. It is suitable as a reference for research in the field. However, there are still some aspects that can be improved. Therefore, this manuscript can be accepted and published in Photonics after the following suggestions.

 

1. First of all, I think the classification of the grating in the introduction is quite confusing, I suggest the author to delete the classification of the grating.
2. Figure 2 shows that the number of publications decreased in 2020, which is attributed to COVID-19. However, specific data (such as the impact on different countries or institutions) or literature content analysis are not provided as evidence. It is recommended to supplement relevant evidence.

 

3. For some professional terms (such as "Vernier effect"), a concise definition should be provided when they first appear. Otherwise, it is not conducive to readers' understanding.

 

4. Chapter 4 is too long. It can be divided into two parts: future research trends and conclusions. The future research trends can be separately extracted as the content of section 3.4.3.

 

5. On the basis of section 3.4.3, an analysis and discussion of innovation points should be added. Based on the current research status and existing problems, some innovative research ideas can be proposed, such as exploring the application possibilities of new materials in optical fiber grating sensors and studying how to use emerging technologies (such as quantum technology) to improve sensor performance, providing more inspiring viewpoints for subsequent research.

 

6. The authors may miss the important part for forming the grating via the mechanical induced grating. i.e. Photonics 2024, 11(3), 223; https://doi.org/10.3390/photonics11030223

 

 

7. The format of the references should be consistent. It can follow either the format of reference 1 or that of reference 59.

 

8. Replace Figure 3 with a high - definition image and enlarge it.

 

Comments on the Quality of English Language

good

Author Response

Comment 1: First of all, I think the classification of the grating in the introduction is quite confusing, I suggest the author to delete the classification of the grating.

Response 1:

Thank you for your valuable feedback. We acknowledge that the initial classification of fiber gratings in the introduction may have been confusing. We seriously considered removing this section. However, after careful analysis and discussion, we found that removing it would require defining numerous technical terms directly in the main body of the paper. Given the large number of specialized terms involved, this approach would result in frequent interruptions to introduce definitions, which could disrupt the flow of the discussion and make it harder for readers to follow the overall narrative.

To address this concern while maintaining clarity, we have significantly revised the classification section in the introduction. Specifically:

1. Improved Structure: We reorganized the classification into four distinct categories—Periodicity, Structural Enhancements, Sensing Mechanisms, and Integration with Optical Fiber Types—providing a more systematic and intuitive framework.
2. Refined Explanations: We clarified technical distinctions between different grating types, ensuring that their unique characteristics and applications are concisely conveyed.
3. Reduced Redundancy: We streamlined descriptions to focus on key concepts, minimizing potential confusion while maintaining the necessary background for subsequent discussions in the paper.

We believe these revisions enhance readability and improve the logical flow of the manuscript. We sincerely appreciate your constructive suggestion, which helped us refine the manuscript further.

（Modifications: in Page 1 - 3, Line 39 - 114.）

 

Comment 2: Figure 2 shows that the number of publications decreased in 2020, which is attributed to COVID-19. However, specific data (such as the impact on different countries or institutions) or literature content analysis are not provided as evidence. It is recommended to supplement relevant evidence.

Response 2:

Thank you for your insightful comments regarding the decline in publication volume in 2020 and the need for supporting evidence.

Through further investigation, we recognize that while the impact of the COVID-19 pandemic on global research output has been widely discussed, existing studies primarily focus on pandemic-related research areas. However, systematic analyses of its long-term effects on broader scientific fields, including fiber optic grating sensors, remain lacking. Some studies indicate that the pandemic led to funding reallocation, laboratory closures, and project delays, which in turn affected research output across multiple non-COVID-19 disciplines. Nevertheless, comprehensive quantitative data specifically assessing the impact of these factors on non-pandemic-related fields, particularly the fiber optic grating sensor domain covered in this study, are still limited [1-3].

As this issue is not the core focus of our research, we have revised the manuscript to adopt a more cautious and neutral expression when explaining the decline in publication volume. Instead of attributing it directly to specific events, we acknowledge potential influencing factors while emphasizing that further research is needed on this topic. The revised version is as below:

"The decrease in publications during 2020 coincides with the global disruption caused by the COVID-19 pandemic, which may have affected research activities due to factors such as funding reallocation, laboratory closures, and project delays. While some studies suggest that these disruptions led to a temporary decline in scientific output across multiple disciplines, comprehensive quantitative analyses specifically addressing non-pandemic-related research fields remain limited. Similarly, the dip observed in 2014 may be associated with geopolitical tensions and economic constraints, which could have influenced research funding and international collaborations. Further studies are needed to comprehensively assess the long-term impact of such global events on research productivity."

We sincerely appreciate your valuable suggestions and believe that these revisions enhance the scientific rigor of our discussion.

• Raynaud, V. Goutaudier, K. Louis, and N. Albiges, "Impact of the COVID-19 pandemic on publication dynamics and non-COVID-19 research production," BMC Medical Research Methodology, vol. 21, no. 1, p. 255, Nov. 2021, doi: 10.1186/s12874-021-01404-9. ​BioMed Central
• Aviv-Reuven and A. Rosenfeld, "Publication Patterns' Changes due to the COVID-19 Pandemic: A longitudinal and short-term scientometric analysis," Scientometrics, vol. 126, pp. 6761–6784, 2021, doi: 10.1007/s11192-021-04059-x. ​arXiv
• Forti, A. M. Galassi, and G. Paci, "The impact of the COVID-19 pandemic on scientific research in the life sciences," PLOS ONE, vol. 17, no. 2, p. e0263001, Feb. 2022, doi: 10.1371/journal.pone.0263001. ​PubMed

（Modifications: in Page 6, Line 221 - 230.）

 

Comment 3: For some professional terms (such as "Vernier effect"), a concise definition should be provided when they first appear. Otherwise, it is not conducive to readers' understanding.

Response 3:

We appreciate your reminder, as ensuring reader comprehension is crucial.

Following your advice, we have carefully reviewed the entire manuscript and have added concise definitions for key technical terms when they first appear, particularly in the Introduction section. Specifically, for the term "Vernier effect," which you highlighted, we have now included an appropriate explanation in Section 3) Advanced Sensing Mechanisms to enhance clarity for the readers.

We sincerely appreciate your insightful feedback, which has helped improve the readability and accessibility of the manuscript.

（Modifications: in Page 2, Line 88 - 90.）

 

Comment 4: Chapter 4 is too long. It can be divided into two parts: future research trends and conclusions. The future research trends can be separately extracted as the content of section 3.4.3.

Response 4:

We agree that, as a concluding section, it was indeed too long. Based on your recommendation, we have restructured the content by introducing a new chapter: Chapter 4: Challenges and Technological Advancements, which now includes:

4.1 Environmental limitations of OFGS.

4.2 A comparative analysis between OFGS and other competing sensor technologies.

4.3 An expanded discussion on future research trends, derived from the insights of 4.1 and 4.2.

The original conclusions section has now been moved to Chapter 5 to ensure better clarity and organization.

（Modifications: in Page 14 - 16, Line 466 - 594.）

 

Comment 5: On the basis of section 3.4.3, an analysis and discussion of innovation points should be added. Based on the current research status and existing problems, some innovative research ideas can be proposed, such as exploring the application possibilities of new materials in optical fiber grating sensors and studying how to use emerging technologies (such as quantum technology) to improve sensor performance, providing more inspiring viewpoints for subsequent research. 

Response 5:

Thank you for your valuable suggestion. It has significantly enriched the depth of our paper's analysis. Based on your recommendation, we have incorporated a detailed discussion of innovation points in the revised structure of the paper. Specifically, in Section 4.3, we expanded upon the analysis from Sections 4.1 (Environmental Limitations of OFGS) and 4.2 (Comparison of OFGS with Competing Sensors), exploring innovative research ideas. This includes the potential applications of new materials in OFGS and how emerging technologies, such as quantum technology, can enhance sensor performance. We believe this addition will provide more inspiring viewpoints for future research in the field. We believe that these changes will improve the clarity and focus of the chapter, and we appreciate your valuable suggestions in helping us strengthen our discussion.

（Modifications: in Page 15 - 16, Line 521 - 583.）

 

Comment 6: The authors may miss the important part for forming the grating via the mechanical induced grating. i.e. Photonics 2024, 11(3), 223; https://doi.org/10.3390/photonics11030223

Response 6:

We appreciate your insightful observation regarding the omission of key details on mechanically induced grating formation.

As suggested, we have now supplemented our discussion on this topic by adding a dedicated description of the mechanical grating formation mechanism. This addition can be found in the revised manuscript (Section 3.4.2 / Figure 7 / Paragraph beginning with “In recent years (2010s–present) …”).

（Modifications: in Page 12, Line 436 - 447.）

 

Comment 7: The format of the references should be consistent. It can follow either the format of reference 1 or that of reference 59.

Response 7:

We sincerely appreciate your careful reading. We have now used Zotero to reform all references according to the MDPI citation style to ensure uniformity throughout the manuscript.

（Modifications: in Page 17 - 21, Line 616 - 760.）

 

Comment 8: Replace Figure 3 with a high - definition image and enlarge it.

 Response 8：

Thank you for your feedback regarding the clarity and readability of Figure 3. As per your suggestion, we have replaced the image with a high-definition version and enlarged the text for better visibility. We believe this improves the clarity and overall presentation of the figures.

（Modifications: in Page 7, Line 258 - 259.）

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

In response to my observations, important information was added to the manuscript that made it

more interesting and comprehensible. My comments have been fully addressed by the Authors in

the revised manuscript, which may be now published.

Comments on the Quality of English Language

n/a