Ring-Core Photonic Crystal Fiber Sensor Based on SPR for Extra-Wide Refractive Index Detection

Round 1

Reviewer 1 Report

He et al., in the article titled "Ring-core photonic crystal fiber sensor based on SPR for extrawide refractive index detection", demonstrate an interesting wide-range SPR sensor. It consists of a ring-core PCF filled with plasmonic materials. In comparison to the process of depositing a coating inside the air hole, the analyte and gold nanowires fill the PCF thus simplifying the manufacturing complexity. The ring-core structure enhances the directional power transmission between the guided mode and the surface plasmon polariton (SPP) mode. In addition, the sensor is numerically analyzed by the finite element method (FEM). The developed PCF SPR sensor has a wavelength sensitivity and amplitude sensitivity of 40,000 nm/RIU and 2,141 RIU-1 , and the resolution is 2.5 × 10-6 RIU-1 for the detection range of 1.13 - 1.45. The high-sensitivity sensor boasting a wide refractive index detection range performs better than conventional solid-core PCF-SPR sensors boding well for biochemical sensing. This interesting work may be considered for publication, provided the authors address the below mentioned comments:

1. The introduction section is not comprehensive. The motivation behind this work needs to be clearly stated.

2. Did the authors perform the selectivity analysis. Please comment on these aspects.

3. Can the PCF developed in this work be used for multiplexing of analytes. Please explain the relevance from the future scope of the work.

4. It is advisable to show the dimension values clearly in Figure 1.

5. Figure 9 and 10 are very interesting. However, the explanation and the insights provided are very minimal. Please elaborate.

6. Table 1 provides a comparison between the Ring-core PCF format with the solid format in earlier literature. It is advisable to compare with similar formats. If not, please comment the reason for such comparison.

7. The relevant works in this domain of PCF should be highlighted: Micromachines 2023, 14(3), 668.

8. The future scope and opportunities of this interesting work should be mentioned from the plasmonics as well as photonics perspective to the broad audience of this journal.

Needs some improvement.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

1- There are some similarities on text and referance list with Reference number 2 (Chen,X et.al. IEEE Photonics journal, 2018). This must be reduced.

2- Meshing technique and density must be mentioned. How accurate is your results ? 

3- Boundary conditions must be discussed.

4- How author's optimized the structure and how they decided to use this final parameters ? Have you optimized the parameters with trial and error method ? or any specific method have been used for optimizing the design parameters ?

5- Fabrication procedure is described, however there are no cited practical work and not satisfying discussion. This part must be revised with some cited real practical results and methods. Also, alternative methods must be recommend.

6- Table1: maximum sensitivity is given as 40000. This is for RI 1.43. On the other hand, compared articles have used lower index. Therefor, this comparison is not fair. Results for RI 1.40 of your work may be presented for fair comparison. You may specify the range of sensitivity, for example 20000-40000. Same for other listed results. That way readers will see the perforance comparison better even for lower index analytes.

1- Line 27  the word recen must be corrected with 'recent'

2- Overall manuscript must be revised carefully for some minor english corrections.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The paper under consideration provides the numerical analysis of a ring-core PhC fiber sensor for extra-wide RI sensing. I have several concerns related to the paper which should be addressed before the final verdict has been given. I have the following suggestions:

1) Provide the complete conditions of the numerical model. What is the mesh size and shape used in the design?

2) I am confused, equation 3 shows the loss formula which has been used. Then how did the author calculate dB/cm in Figure 2? What did they use to convert the losses in dB/cm?

3) Provide the color bar in Figure 3. 

4) Why in Figure 2, the refractive indices 1.38 and 1.39 have been used?

5) All the figures should be replaced with high-quality images. The figure labels are too small that it's hard to read them. 

6) Line 215, there is no such thing as RIes. Use the full term or use RI (s). 

7) The paper should be organized better, where the optimization process should be explained before and then the sensitivity of the device should be discussed. Currently, the paper layout is confusing and optimization and device performance are mixed. 

8) For SPP and SPR-based sensors, I suggest the author refer to the recent review work which is focused on the significance of plasmonics: https://0-doi-org.brum.beds.ac.uk/10.1080/01468030.2021.1902590.

9) The abbreviation RI has been used without providing the full form of it in the paper. 

ok. 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Authors address the comments 

Needs some improvement 

Reviewer 3 Report

I am willing to accept the paper in its current form. 

ok