High Performance Dual-Core D-Shaped PCF Refractive Index Sensor Coated with Gold Grating
Round 1
Reviewer 1 Report
Reviewer Report
General Comment: Examination of the manuscript shows that the present investigation is not good in the present form, but the following points should be addressed carefully during the revision to change my decision in the revision.
Comment 1 : As this a numerical study, but its experimental validation is to prove by the authors. The authors at least must give possible fabrication steps.
Comment 2 Why other performance parameters have not been discussed.
Comment 3: What are the desirable values for all the performance parameters? Mention it in the manuscript.
Comment 4: The introduction can be improved. Some works on SPR biosensor’s applications can be added such as:
1. https://doi.org/10.1007/s11468-023-01803-2 2. https://doi.org/10.1007/s11082-022-04004-z
Comment 5: Evanescent waves can be enhanced by introducing a gold grating, which increases the sensitivity of the structure. Please comment on it how?
Comment 6: Authors have not mentioned the FEM simulation settings.
Comment 7: Also, the formulas for gratings are missing in the equations.
Comment 8: For surface plasmon polariton: Spp is written and in figures SPP written. Please correct these types of mistakes. Notations should be consistent throughout.
Comment 9: Are the designed parameters optimal? Which steps should be followed to optimize the presented PCF sensor.
Comment 10. The authors did not justify that how this work is promising candidate in laser, sensor, and optical communication systems.
The proposed work can be accepted for publication in photonics, MDPI after modifications in the revised manuscript.
Author Response
About Reviewer #1:
Comment 1: As this a numerical study, but its experimental validation is to prove by the authors. The authors at least must give possible fabrication steps.
Response: The processing method of PCF has been provided in the article (On page 3 section 3 line 2).
Comment 2: Why other performance parameters have not been discussed.
Response: At this stage, the main performance parameters have been discussed, and the remaining parameters will be completed in subsequent work.
Comment 3: What are the desirable values for all the performance parameters? Mention it in the manuscript.
Response: The desirable values for all the performance parameters has been mentioned (On page 12 section3.3.2 last paragraph).
Comment 4: The introduction can be improved. Some works on SPR biosensor’s applications can be added such as:
1.https://doi.org/10.1007/s11468-023-01803-2
- https://doi.org/10.1007/s11082-022-04004-z.
Response: Some works on SPR biosensor’s applications has been added (Reference [10]and reference [11]).
Comment 5: Evanescent waves can be enhanced by introducing a gold grating, which increases the sensitivity of the structure. Please comment on it how?
Response: It has been commented above the grating equation (Equation 4).
Comment 6: Authors have not mentioned the FEM simulation settings.
Response: The FEM simulation settings have been mentioned at page 5 section 3 line 3, and the Fig. 2 shows the mesh division of the proposed D-shaped PCF.
Comment 7: Also, the formulas for gratings are missing in the equations.
Response: The equation about grating has been added (Equation 4).
Comment 8: For surface plasmon polariton: Spp is written and in figures SPP written. Please correct these types of mistakes. Notations should be consistent throughout.
Response: The mistake in the figure 3 has been corrected.
Comment 9: Are the designed parameters optimal? Which steps should be followed to optimize the presented PCF sensor.
Response: Based on the current work, the optimal parameters have been achieved by optimizing the proposed PCF sensor through adjusting the basic structure first and then adjusting the grating structure size.
Comment 10: The authors did not justify that how this work is promising candidate in laser, sensor, and optical communication systems.
Response: How this work is promising candidate in laser, sensor, and optical communication systems has been justified in conclusion last sentence.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This manuscript proposes a dual-core D-shaped surface plasmon resonance (SPR) based photonics crystal fiber (PCF) sensor coated with gold grating is designed for refractive index sensing. This manuscript analyzes structure parameters and grating parameters by the finite-element method. The results show that the grating and dual-core can enhance the sensor properties. Finally, the proposed sensor achieves an average wavelength sensitivity of 994.5 nm/RIU, a maximum amplitude sensitivity of 181.049 RIU-1, a resolution of 2.038×10-6 RIU when the analyte refractive index increases from 1.33 to 1.37. I have some comments to do after reviewing this manuscript, details are as follows:
1. The proposed sensor is a dual core fiber, there will be interacting super modes. Authors should also consider them.
2. The distance between the core and the gold grating is close, and I don't think the loss of the x-polarized core mode is nearly 0 in Figure 2.
3. Figure 3 (a) and (b) are marked wrong, please modify it.
4. The introduction can be improved. The articles related to some applications of PCF refractive index sensor should be added such as Phys. Chem. Chem. Phys., 24, 21233 (2022); Physical Chemistry Chemical Physics, 2023, 25, 8583 - 8591; Sensors and Actuators B: Chemical 243, (2017), 311-325; Optics Express 11(21), 2762-2768 (2003).
5. The manuscript simulates single core and double core, gold film and gold grating, it shows the proposed sensor with the gold grating and the double core is better. However, this manuscript does not explain in detail why from the principle.
6. The linearity of the sensitivity is not good, I think it is not necessary to do a linear fit, in addition, the amplitude sensitivity is not calculated using the average sensitivity.
Author Response
About Reviewer #2:
Comment 1: The proposed sensor is a dual core fiber, there will be interacting super modes. Authors should also consider them.
Response: The operating wavelength of this sensor is within the range of 500nm to 1000nm, while the super mode wavelengths of the proposed structure are above 1500nm, so there is no need to consider this issue.
Comment 2: The distance between the core and the gold grating is close, and I don't think the loss of the x-polarized core mode is nearly 0 in Figure 2.
Response: Actually, the loss of the x-polarized core mode not nearly 0, the loss value is within the range of 0.7 to 0.9, because of the same axis with y-polarized, it looks like about 0.
Comment 3: Figure 3 (a) and (b) are marked wrong, please modify it.
Response: The mistake in Figure 4 (a) and (b) has been corrected.
Comment 4: The introduction can be improved. The articles related to some applications of PCF refractive index sensor should be added such as Phys. Chem. Chem. Phys., 24, 21233 (2022); Physical Chemistry Chemical Physics, 2023, 25, 8583 - 8591; Sensors and Actuators B: Chemical 243, (2017), 311-325; Optics Express 11(21), 2762-2768 (2003).
Response: The introduction has been improved (Reference [7], reference [8], Reference [9] and reference [12]).
Comment 5: The manuscript simulates single core and double core, gold film and gold grating, it shows the proposed sensor with the gold grating and the double core is better. However, this manuscript does not explain in detail why from the principle.
Response: The detail why from the principle has been explained (Above figure 4 and above equation 4).
Comment 6: The linearity of the sensitivity is not good, I think it is not necessary to do a linear fit, in addition, the amplitude sensitivity is not calculated using the average sensitivity.
Response: Linear fit has been deleted, and the amplitude sensitivity is calculated using the average sensitivity in figure 5 (b).
Author Response File: Author Response.docx
Reviewer 3 Report
This work proposed a numerical method based on the finite-element method (FEM) for realizing a a dual-core D-shaped photonic crystal fiber (PCF) surface plasmon resonance sensor coated with gold grating for refractive index changes detection. The optical sensing properties were analyzed in terms of wavelength and amplitude sensitivity in the refractive index sensing range of 1.33–1.37. The effects of the PCF structure parameters (polishing depths, holes sized) and grating parameters ( heights, periods and duty) are discussed.
The topic can be of interest for the readers of the journal.
In general, the work is well structured, and the claims of the authors are well sustained by numerical evidence. Data analysis and presentation are adequate.
Just few notes:
- In the introduction, a better argumentation is required to support the sentence: “it has been proposed that SPR be combined with PCF to achieve a better effect [10-12].”
- The same for section 3, where the sentence “When the incident light is transmitted through the fiber core, Spp is excited on the metal surface” need a better argumentation.
- It is not clear how the geometry of the Au grating has been chosen. It comes from literature? Or it is a deliberate choice of the authors?
- On page 4, section 3 the authors refer to a y-polarized mode. The reference system should be represented, or this concept explained better.
- On page 5, the achieved sensitivities values should be referred better to a sensing method.
- In section 3.2, the terms Dx and Dy are not so clear.
- As for sensitivity definition, it is important to underline that it comes from the slope of the calibration curve, so the definition they used is valid just when the sensor response is linear in the investigated refractive index range. To this purpose I would invite the authors to read some sensing parameter definitions in the following papers:
A. D’Amico, C. Di Natale, A contribution on some basic definitions of sensors properties, IEEE Sens. J. 1 (2001) 183-190.
Q. Huang, D. Zeng, H. Li and C. Xie, Nanoscale, 2012, 4, 5651-5658.
After the above minor revisions, the paper can be accepted for publication.
Author Response
About Reviewer #3:
Comment 1: In the introduction, a better argumentation is required to support the sentence: “it has been proposed that SPR be combined with PCF to achieve a better effect [10-12].”
Response: A better argumentation has been proposed to support the sentence.
Comment 2: The same for section 3, where the sentence “When the incident light is transmitted through the fiber core, Spp is excited on the metal surface” need a better argumentation.
Response: A better argumentation has been proposed to support the sentence.
Comment 3: It is not clear how the geometry of the Au grating has been chosen. It comes from literature? Or it is a deliberate choice of the authors?
Response: The geometry of the Au grating was chosen from reference [26] in this manuscript, compared with normal grating, this grating has a better performance in the proposed structure.
Comment 4: On page 4, section 3 the authors refer to a y-polarized mode. The reference system should be represented, or this concept explained better.
Response: X-polarized mode and y-polarized mode have been explained well (On page 4, section 3).
Comment 5: On page 5, the achieved sensitivities values should be referred better to a sensing method.
Response: The achieved sensitivities values on page 5 have been referred better to a sensing method.
Comment 6: In section 3.2, the terms Dx and Dy are not so clear.
Response: DIx and DIy in section 3.2 have been changed into ∆Ix and ∆Iy, and explained them clearly.
Comment 7: As for sensitivity definition, it is important to underline that it comes from the slope of the calibration curve, so the definition they used is valid just when the sensor response is linear in the investigated refractive index range. To this purpose I would invite the authors to read some sensing parameter definitions in the following papers: A. D’Amico, C. Di Natale, A contribution on some basic definitions of sensors properties, IEEE Sens. J. 1 (2001) 183-190. Q. Huang, D. Zeng, H. Li and C. Xie, Nanoscale, 2012, 4, 5651-5658.
Response: Thank you for providing the two articles. I have understood the definition of sensor performance and have referenced it in my own article. (Reference [33]and reference [34]).
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Manuscript may be accepted.
Reviewer 2 Report
Accept in present form.
