Mode-Enhanced Surface Plasmon Resonance in Few-Mode Fibers via Dual-Groove Architecture

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript presents a novel design of a dual-groove few-mode fiber (FMF) surface plasmon resonance (SPR) sensor that leverages the LP₁₁ mode and introduces an Au/TiO₂ bilayer to achieve spectral separation and enhanced sensitivity. The authors demonstrate through FEM simulations that their proposed structure can reach an ultrahigh sensitivity of up to 14,800 nm/RIU and provide dual-channel operation with temperature compensation and biosensing capability. The topic is timely and relevant to the field of fiber-optic biosensing, and the work is clearly written and generally well-organized. Overall, the manuscript has merit, but certain issues should be addressed to strengthen the technical depth and practical relevance before acceptance.

1. The study is entirely based on numerical simulations. While the modeling is rigorous, the absence of any experimental results weakens the overall impact. The authors should at least discuss possible fabrication methods (e.g., femtosecond laser micromachining, focused ion beam milling) and coating techniques to show the feasibility of the proposed structure.
2. The work heavily relies on the LP₁₁ mode for enhanced sensitivity. However, selectively exciting and maintaining LP₁₁ in a practical FMF is challenging. The authors should provide more discussion on mode-control strategies (e.g., mode filters, launch conditions, bending radius control) to justify the applicability.
3. While the maximum wavelength sensitivity reported is impressive (14,800 nm/RIU), the authors note a broadening of the resonance dip at larger TiO₂ To better quantify sensor performance, the figure-of-merit (FOM = sensitivity/FWHM) should be calculated and compared across design conditions.
4. The dual-channel design is interesting, but the current demonstration (ethanol for temperature monitoring and one channel for cell detection) is somewhat limited. The authors should expand the discussion on how this architecture could support multi-analyte detection or multiplexed biosensing in clinical settings.
5. The manuscript would benefit from a clearer comparison with related works employing alternative multilayer coatings (e.g., Au/Ag, Au/graphene, MXene) or other modal approaches. This will better position the contribution within the broader literature and highlight its unique advantages.

Author Response

Thanks editors and reviewers for bringing us the pertinent comments and valuable suggestions on improving our manuscript. We have studied the comments and suggestions carefully and made revision.

  All revisions have been highlighted in yellow color in our revised manuscript. The following is a point-to-point response to Reviewer 1’s comments.

 

Reviewer #1:

 

Comment1:

The study is entirely based on numerical simulations. While the modeling is rigorous, the absence of any experimental results weakens the overall impact. The authors should at least discuss possible fabrication methods (e.g., femtosecond laser micromachining, focused ion beam milling) and coating techniques to show the feasibility of the proposed structure.

 

Response1:

We greatly appreciate this valuable comment. We recognize that the absence of experimental validation may limit the practical impact of this work. To address this concern, we have added a detailed discussion of feasible fabrication routes in the revised manuscript. Specifically, we describe how femtosecond laser micromachining, combined with subsequent electric-arc polishing, can be employed to inscribe smooth dual-groove structures on the FMF sidewall.

The Au film can then be deposited into the grooves by magnetron sputtering, and an additional TiO₂ layer can be selectively coated on one of the Au-coated grooves to realize the heterogeneous bilayer configuration. These techniques are well established and have been successfully demonstrated in previously reported bilayer fiber-based SPR sensors. Therefore, we believe that the proposed design possesses practical feasibility for experimental realization.

 

Author action: We have made additional notes in the manuscript. The changes are modified as shown below.

 

(Page 3, Line 109)

 

“2.3 Fabrication Feasibility and Mode Excitation

The fabrication feasibility of the proposed dual-groove FMF-SPR sensor can be ensured by leveraging well-established micro- and nano-fabrication techniques. As il-lustrated in Fig. 2, the dual-groove structure can be inscribed on the sidewall of the FMF using femtosecond laser micromachining, followed by electric-arc polishing to obtain smooth groove surfaces. Au film can then be deposited inside the grooves via magnetron sputtering. In accordance with the proposed design, a heterogeneous bi-layer is realized by subsequently depositing a TiO₂ layer onto one of the Au-coated grooves through the same sputtering technique. Such processes are consistent with previously reported fabrication approaches for bilayer fiber-based SPR sensors [26], in-dicating that the proposed structure can be practically implemented.

 

Figure 2. Schematic illustration of the fabrication process of the proposed dual-groove FMF-SPR sensor”

 

(Page 16, Line 480)

 

[26]. Yin, Z., Jing, X., Li, K., Zhang, Z., & Li, J. (2024). Modulation of the sensing bandwidth of dual-channel SPR sensors by TiO2 film. Optics & Laser Technology, 169, 110105.[CrossRef]

 

 

Comment2:

The work heavily relies on the LP₁₁ mode for enhanced sensitivity. However, selectively exciting and maintaining LP₁₁ in a practical FMF is challenging. The authors should provide more discussion on mode-control strategies (e.g., mode filters, launch conditions, bending radius control) to justify the applicability.

 

Response2:

We thank the reviewer for this important point. We recognize that relying on the LP₁₁ mode introduces practical challenges, since selective excitation and stable maintenance of higher-order modes in FMFs are non-trivial. In the revised manuscript, we have added a more comprehensive discussion of feasible mode-control strategies. Approaches such as careful launch alignment, polarization adjustment, mode filtering, and bending-radius optimization can suppress LP₀₁ dominance and support stable LP₁₁ operation.

To further clarify applicability, we also cite recent demonstrations where high-purity LP₁₁ oscillation with long-term stability was achieved in FMFs, e.g., >90% purity using mode-selective FMF Bragg gratings [27] and 97% purity in a switchable all-fiber Brillouin laser [28]. These studies confirm that stable LP₁₁ excitation and maintenance are experimentally feasible.

 

Author action: We updated the manuscript by making appropriate revision. The changes are modified as shown below.

 

(Page 4, Line 123)

 

“A further consideration lies in the selective excitation and stable maintenance of the LP₁₁ mode in the FMF, which is critical to the sensor’s operation. Because mode coupling and bending generally favor the fundamental LP₀₁ mode, additional mode-control strategies are required. Practical methods include precise launch alignment, polarization adjustment, mode filtering, and optimization of the bending radius to suppress LP₀₁ propagation. Recent experimental advances also demonstrate the feasibility of high-purity LP₁₁ operation in FMFs. Liu et al. reported stable LP₁₁ oscillation with >90% modal purity in an all-fiber laser using mode-selective FMF Bragg gratings [27]. Heng et al. further demonstrated a switchable all-fiber Brillouin laser in which the LP₁₁ mode was maintained with 97% purity and long-term stability [28]. These results provide strong evidence that the LP₁₁ mode required in the proposed sensor can be re-liably excited and sustained using existing techniques.”

 

(Page 16, Line 482)

 

[27]. Liu, T., Chen, S.-P., & Hou, J. (2016). Selective transverse mode operation of an all-fiber laser with a mode-selective fiber Bragg grating pair. Optics Letters, 41(24), 5692–5695.[CrossRef]

[28]. Heng, X., Gan, J., Zhang, Z., Li, J., Li, M., Zhao, H., Qian, Q., & Xu, S. (2018). Transverse mode switchable all-fiber Brillouin laser. Optics Letters, 43(17), 4172–4175.[CrossRef]

 

 

Comment3:

While the maximum wavelength sensitivity reported is impressive (14,800 nm/RIU), the authors note a broadening of the resonance dip at larger TiO2 To better quantify sensor performance, the figure-of-merit (FOM = sensitivity/FWHM) should be calculated and compared across design conditions.

 

Response3:

We are grateful for this constructive suggestion. We agree that sensitivity alone does not fully characterize sensor performance, as resonance linewidth also plays a key role. To address this, we have introduced the figure-of-merit (FOM), defined as the ratio of wavelength sensitivity to the full width at half maximum (FWHM), in the revised manuscript.

Since only the 30 nm TiO₂ configuration ensures sufficient channel separation, we calculated the FOM exclusively for this case. The results show that the FOM remains above 200 across most of the RI range, with a maximum value of 350, confirming that the resonance linewidth remains sufficiently narrow for practical biosensing.

 

Author action: We updated the manuscript by making appropriate revision. The changes are modified as shown below.

 

(Page 11, Line 335)

 

“In addition to sensitivity, resonance sharpness was evaluated. The figure of merit (FOM) was introduced and defined as:

(6)

Where is the wavelength sensitivity (nm/RIU), and  is the full width at half maximum of the resonance dip.”

 

(Page 11, Line 340)

 

“Fig. 12(c) indicates that the FOM remains above 200 across most of the sensing range, with a maximum value of approximately 350 within the RI range of 1.34-1.35.

Based on the combined evaluation of wavelength sensitivity, spectral separation, and FOM, a TiO₂ thickness of 30 nm provides the best overall performance. At this thickness, dual-channel independence is maintained and spectral separation can be resolved even when RI differences are as small as 0.01.”

 

(Page 12, Line 349)

 

“

Figure 12. (c) FWHM and FOM versus RI for 30 nm TiO₂”

 

(Page 14, Line 406)

 

“Simulations indicate a maximum sensitivity of 14,800 nm/RIU over 1.33–1.40, with the FOM exceeding 200 in most of the range.”

 

 

Comment4:

The dual-channel design is interesting, but the current demonstration (ethanol for temperature monitoring and one channel for cell detection) is somewhat limited. The authors should expand the discussion on how this architecture could support multi-analyte detection or multiplexed biosensing in clinical settings.

 

Response4:

We appreciate this insightful comment. We agree that the current demonstration is only a proof-of-concept and does not fully highlight the broader potential of the proposed dual-channel architecture. In the revised manuscript, we have expanded the discussion to emphasize extensibility.

By integrating serial micro-grooves (multiple sensing regions) along a single FMF, the platform can support multiplexed detection of different biomarkers as well as simultaneous readout of multiple physiological parameters (e.g., temperature and pH) in a single measurement. Such serial integration enhances throughput and aligns with clinical workflows, which often require multi-sample and multi-target analysis. These extensions highlight the potential of our design for early cancer screening and broader biomedical diagnostics.

 

Author action: We updated the manuscript by making appropriate revision. The changes are modified as shown below.

 

(Page 13, Line 391)

 

“Beyond this demonstration, the architecture is naturally extensible: by integrating se-rial micro-grooves (multiple sensing regions) along a single fiber, it enables multi-plexed detection of different biomarkers and simultaneous readout of multiple param-eters (e.g., temperature, and potentially pH) within one measurement. Such serial in-tegration increases practical throughput and aligns well with clinical workflows that require multi-sample and multi-target analysis within constrained assay time, thereby offering a promising pathway for early cancer screening and clinical diagnostics.”

 

(Page 14, Line 410)

 

“These results confirm that the TiO₂-enhanced, LP₁₁-assisted dual-channel FMF-SPR sensor provides high sensitivity, spectral independence, and stability, showing strong potential for biosensing and biomedical detection.”

 

 

Comment5:

The manuscript would benefit from a clearer comparison with related works employing alternative multilayer coatings (e.g., Au/Ag, Au/graphene, MXene) or other modal approaches. This will better position the contribution within the broader literature and highlight its unique advantages.

 

Response5:

We thank the reviewer for this valuable suggestion. We agree that the initial version did not sufficiently position our work within the broader context of multilayer-coated and alternative modal SPR biosensors. In the revised manuscript, we have added Table 6, which compares the proposed Au–TiO₂ FMF-SPR biosensor with representative multilayer SPR sensors [29–31].

As shown, our design achieves a maximum sensitivity of 14,800 nm/RIU in the RI range of 1.33–1.40, exceeding the reported values for TiO₂–Au (7,500 nm/RIU), MXene–Au–TiO₂ (9,400 nm/RIU), and Ag/Au/Graphene/MoS₂ (11,775 nm/RIU). This demonstrates that the Au–TiO₂ coating combined with the LP₁₁ mode not only enhances sensitivity but also provides a simpler architecture than many multilayer systems.

 

Author action: We updated the manuscript by making appropriate revision. The changes are modified as shown below.

 

(Page 12, Line 351)

 

“Table 6 summarizes a comparison between the proposed Au–TiO₂ FMF-SPR biosensor and previously reported multilayer SPR sensors [29–31]. The proposed design achieves a maximum sensitivity of 14,800 nm/RIU within the RI range of 1.33–1.40, which is higher than the values reported for the other structures.

Table 6. Comparison of the Proposed Au–TiO₂ FMF-SPR Biosensor with Previously Reported Multilayer SPR Sensors.

[Ref.]	RI Range (RIU)	Coating Structure	Guided Mode	Max. Sensitivity (nm/RIU)
[29]	1.26-1.42	TiO₂-Au	LP01	7,500
[30]	1.33-1.41	MXene-Au-TiO2	LP01	9,400
[31]	1.33-1.40	Ag/Au/Graphene/MoS₂	LP01	11,775
This work	1.33-1.40	Au-TiO2	LP11	14,800

”

 

(Page 16, Line 486)

 

[29]. Dai, T., Yan, J., Zhu, W., Bian, L., Yi, Z., Liu, M., Tang, B., Sun, T., Li, G., & Yu, Z. (2024). Ultra-high sensitivity surface plasmon U-channel photonic crystal fiber for hemoglobin sensing. Sensors and Actuators A: Physical, 366, 115053.[CrossRef]

[30]. Liu, Y., Li, K., Wang, R., Wang, Y., Wang, G., & Meng, X. (2025). A highly sensitive D-shaped microstructured fiber SPR biosensor based on MXene-Au-TiO2 composite film coating. Plasmonics. Advance online publication. [CrossRef]

[31]. Dogan, Y., & Erdogan, I. (2023). Highly sensitive MoS2/graphene based D-shaped optical fiber SPR refractive index sensor with Ag/Au grated structure. Optical and Quantum Electronics, 55(12), 1066.[CrossRef]

 

We appreciate for the editors’ and the reviewers’ warm work earnestly, and hope the revisions will meet with your approval.

Once again, thank you very much for your comments and suggestions.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The authors propose a dual-groove few-mode fiber SPR sensor based on the LP₁₁ mode and a TiO₂–Au bilayer structure, enabling dual-channel WDM and exploring its use in cancer detection. Numerical results indicate high sensitivity and good application potential. The paper is well-structured and technically sound, but minor revisions are needed to improve clarity, consistency, and presentation.

Specific Comments:

Comment 1: The novelty of the dual-channel WDM design should be emphasized more clearly, especially compared with existing SPR sensors.

Comment 2: Some formulas are inconsistent (e.g., Eq. (1) frequency vs. wavelength, Eq. (4) ωp²); symbols and units should be standardized.

Comment 3: The descriptions of residual cladding thickness Rc and Au thickness tAu are confusing between text and figures; a symbol table would help.

Comment 4: Performance data (14,800, 7,500, 9,428.57 nm/RIU) are scattered; a summary table with conditions would improve readability.

Comment 5: The manuscript needs minor polishing (e.g., avoid redundant “RI (RI)” and ensure clear figure/axis labels).

Comment 6: The author needs to supplement some of the latest work on SPR sensors.

Comment 7: For application scenarios (cancer detection and temperature monitoring), adding a linear fitting curve of CH1 peak vs. temperature would better illustrate its utility.

Author Response

Thanks editors and reviewers for bringing us the pertinent comments and valuable suggestions on improving our manuscript. We have studied the comments and suggestions carefully and made revision.

  All revisions have been highlighted in yellow color in our revised manuscript. The following is a point-to-point response to Reviewer 2’s comments.

 

Reviewer #2:

 

Comment1:

The novelty of the dual-channel WDM design should be emphasized more clearlyespecially compared with existing SPR sensors.

 

Response1:

We sincerely thank the reviewer for highlighting the need to emphasize novelty. In the revised manuscript, we have strengthened the discussion of the proposed dual-channel WDM architecture, explicitly contrasting it with recent SPR sensor designs. As noted in the Introduction, unlike many reported structures that require complex geometries or struggle to balance sensitivity and stability, our approach combines high sensitivity, robust stability, and structural simplicity within a single platform.

To further clarify this novelty, we summarize the three key contributions of our work at the end of the Introduction, highlighting the proposed dual-slot FMF-SPR sensor, the independent dual-channel architecture, and the demonstrated high sensitivity and biosensing capability.

 

Author action: We have made additional notes in the manuscript. The changes are modified as shown below.

 

(Page 2, Line 55)

 

“This gap motivates the present study, which introduces a new approach to overcome these limitations. In this work, we make three key contributions. First, we propose a novel dual-slot FMF-SPR sensor that leverages the LP₁₁ mode and a dual-channel wavelength-division multiplexing (WDM) architecture. Second, the two spatially separated sensing slots, each coated with a distinct metallic layer, allow independent signal acquisition and cross-validation, thereby enhancing stability without adding structural complexity. Third, systematic finite element method (FEM) analysis demonstrates a maximum sensitivity of 14,800 nm/RIU over an RI range of 1.33-1.40. Biosensing simulations at physiological temperature (37 °C) further confirm reliable differentiation between multiple cancer cell types. Together, these results highlight the practicality of the dual-channel WDM architecture and its strong potential for biomedical sensing and clinical diagnostics.”

 

 

Comment2:

Some formulas are inconsistent (e.g., Eq. (1) frequency vs. wavelength, Eq. (4) ωp²); symbols and units should be standardized.

 

Response2:

We thank the reviewer for this observation. In the original version, Eq. (1) mixed frequency- and wavelength-based forms, which could cause inconsistency in notation. To address this, we have revised Eq. (1) into a unified wavelength-based form, ensuring clarity and consistency with the rest of the manuscript.

 

Author action: We updated the manuscript by making appropriate revision. The changes are modified as shown below.

 

(Page 3, Line 92)

 

 “The resonant energy loss from the LP₁₁ mode appears as a sharp dip in the transmission spectrum. The propagation loss is calculated as:

(1)

 

 

”

 

 

Comment3:

The descriptions of residual cladding thickness Rc and Au thickness tAu are confusing between text and figures; a symbol table would help.

 

Response3:

We agree with the reviewer’s point. To improve clarity and consistency, we have standardized the definitions so that Rc and tAu are introduced once in the text, and redundant definitions in later sections have been removed. These revisions ensure that the terminology used in the text and figures is consistent and will no longer cause confusion.

 

Author action: We updated the manuscript by making appropriate revision. The changes are modified as shown below.

 

(Page 2, Line 77)

 

“A gold (Au) film with a thickness of tAu is deposited at the base of each groove as the plasmonic excitation layer. In the lower groove, an additional titanium dioxide (TiO₂) layer with a thickness of tTiO₂ is coated above the Au film, forming a heterogeneous bilayer.”

 

(Page 6, Line 191)

 

“To evaluate the effect of residual cladding thickness (Rc) on the FMF-SPR structure,”

 

 

Comment4:

Performance data (14,800, 7,500, 9,428.57 nm/RIU) are scattered; a summary table with conditions would improve readability.

 

Response4:

We thank the reviewer for this helpful suggestion. We agree that in the original version, the performance data appeared scattered, which reduced readability.

To improve clarity, we have added Table 6 in the revised manuscript, which summarizes the sensitivity performance of the proposed Au–TiO₂ FMF-SPR biosensor compared with representative multilayer SPR sensors [29–31]. This consolidated view highlights that our design achieves the highest sensitivity of 14,800 nm/RIU within the RI range of 1.33–1.40.

We also note that the manuscript already includes Table 8, which compares the wavelength sensitivity of tumor-related cell detection with previous studies [34,36–38]. Together, Tables 6 and 8 present the results more coherently, improving readability and clarifying the advantages of the proposed design.

 

Author action: We updated the manuscript by making appropriate revision. The changes are modified as shown below.

 

(Page 12, Line 351)

 

“Table 6 summarizes a comparison between the proposed Au–TiO₂ FMF-SPR biosensor and previously reported multilayer SPR sensors [29–31]. The proposed design achieves a maximum sensitivity of 14,800 nm/RIU within the RI range of 1.33–1.40, which is higher than the values reported for the other structures.

Table 6. Comparison of the Proposed Au–TiO₂ FMF-SPR Biosensor with Previously Reported Multilayer SPR Sensors.

[Ref.]	RI Range (RIU)	Coating Structure	Guided Mode	Max. Sensitivity (nm/RIU)
[29]	1.26-1.42	TiO₂-Au	LP01	7,500
[30]	1.33-1.41	MXene-Au-TiO2	LP01	9,400
[31]	1.33-1.40	Ag/Au/Graphene/MoS₂	LP01	11,775
This work	1.33-1.40	Au-TiO2	LP11	14,800

”

 

(Page 16, Line 486)

 

[29]. Dai, T., Yan, J., Zhu, W., Bian, L., Yi, Z., Liu, M., Tang, B., Sun, T., Li, G., & Yu, Z. (2024). Ultra-high sensitivity surface plasmon U-channel photonic crystal fiber for hemoglobin sensing. Sensors and Actuators A: Physical, 366, 115053.[CrossRef]

[30]. Liu, Y., Li, K., Wang, R., Wang, Y., Wang, G., & Meng, X. (2025). A highly sensitive D-shaped microstructured fiber SPR biosensor based on MXene-Au-TiO2 composite film coating. Plasmonics. Advance online publication. [CrossRef]

[31]. Dogan, Y., & Erdogan, I. (2023). Highly sensitive MoS2/graphene based D-shaped optical fiber SPR refractive index sensor with Ag/Au grated structure. Optical and Quantum Electronics, 55(12), 1066.[CrossRef]

 

 

Comment5:

The manuscript needs minor polishing (e.g., avoid redundant “RI (RI)” and ensure clear figure/axis labels).

 

Response5:

We thank the reviewer for pointing this out. In the revised manuscript, we have removed the redundant expression “RI (RI)” and polished the text for clarity. In addition, all figure and axis labels have been reviewed and standardized to ensure consistency and readability. We also performed a thorough formatting check to eliminate other minor inconsistencies.

 

Author action: We updated the manuscript by making appropriate revision. The changes are modified as shown below.

 

(Page 1, Line 35)

 

“SPR is highly responsive to refractive index (RI) variations in the surrounding medium,”

 

 

Comment6:

The author needs to supplement some of the latest work on SPR sensors.

 

Response6:

We sincerely thank the reviewer for this valuable suggestion. In the revised manuscript, we have supplemented the Introduction with recent representative works on SPR sensors [20–23]. Furthermore, to clarify the performance comparison, we added Table 6, which summarizes the proposed Au–TiO₂ FMF-SPR biosensor against previously reported multilayer SPR sensors [29–31]. As shown, our design achieves a maximum sensitivity of 14,800 nm/RIU in the RI range of 1.33–1.40, surpassing the reported values of other multilayer structures. Together, these additions provide an up-to-date literature context and highlight the distinct advantages of the proposed sensor.

 

Author action: We updated the manuscript by making appropriate revision. The changes are modified as shown below.

 

(Page 2, Line 48)

 

“More recent efforts integrate SPR into photonic crystal fibers and novel material platforms. Examples include D-shaped photonic crystal fiber methane sensors [20], tunable metamaterial absorbers based on Dirac semimetals [21], photonic crystal fiber SPR sensors for dual-parameter magnetic field and temperature detection [22], and quad-band terahertz sensors [23]. Despite their innovation, these designs still struggle to simultaneously achieve high sensitivity, robust stability, and structural simplicity.”

 

(Page 12, Line 351)

 

“Table 6 summarizes a comparison between the proposed Au–TiO₂ FMF-SPR biosensor and previously reported multilayer SPR sensors [29–31]. The proposed design achieves a maximum sensitivity of 14,800 nm/RIU within the RI range of 1.33–1.40, which is higher than the values reported for the other structures.”

 

(Page 15, Line 464)

 

[20].Yang, X., Song, Q., Ma, C., Yi, Z., Cheng, S., Tang, B., Liu, C., Sun, T., & Wu, P. (2024). A methane concentration sensor with heightened sensitivity and D-shaped cross-section U-shaped channel utilizing the principles of surface plasmon resonance. Physica E: Low-dimensional Systems and Nanostructures, 161, 115954. [CrossRef]

[21]. Cheng, S., Li, W., Zhang, H., Akhtar, M. N., Yi, Z., Zeng, Q., Ma, C., Sun, T., & Wu, P. (2024). High sensitivity five band tunable metamaterial absorption device based on block like Dirac semimetals. Optics Communications, 569, 130816. [CrossRef]

[22]. Dai, T., Yi, Y., Yi, Z., Tang, Y., Yi, Y., Cheng, S., Hao, Z., Tang, C., Wu, P., & Zeng, Q. (2024). Photonic crystal fiber based on surface plasmon resonance used for two parameter sensing for magnetic field and temperature. Photonics, 11(1), 784. [CrossRef]

[23]. Zeng, Z., Liu, H., Zhang, H., Cheng, S., Yi, Y., Yi, Z., Wang, J., & Zhang, J. (2025). Tunable ultra-sensitive four-band terahertz sensors based on Dirac semimetals. Photonics and Nanostructures: Fundamentals and Applications, 63, 101347. [CrossRef]

 

(Page 16, Line 486)

 

[29]. Dai, T., Yan, J., Zhu, W., Bian, L., Yi, Z., Liu, M., Tang, B., Sun, T., Li, G., & Yu, Z. (2024). Ultra-high sensitivity surface plasmon U-channel photonic crystal fiber for hemoglobin sensing. Sensors and Actuators A: Physical, 366, 115053.[CrossRef]

[30]. Liu, Y., Li, K., Wang, R., Wang, Y., Wang, G., & Meng, X. (2025). A highly sensitive D-shaped microstructured fiber SPR biosensor based on MXene-Au-TiO2 composite film coating. Plasmonics. Advance online publication. [CrossRef]

[31]. Dogan, Y., & Erdogan, I. (2023). Highly sensitive MoS2/graphene based D-shaped optical fiber SPR refractive index sensor with Ag/Au grated structure. Optical and Quantum Electronics, 55(12), 1066.[CrossRef]

 

 

Comment7:

For application scenarios (cancer detection and temperature monitoring), adding a linear fitting curve of CH1 peak vs. temperature would better illustrate its utility.

 

Response7:

We thank the reviewer for this practical suggestion. In the revised manuscript, we have added a linear regression analysis of the CH1 peak versus temperature. The simulation was performed over −10 to 40 °C. As shown in Fig. 13(a), the resonance wavelength exhibits a blue shift and reduced loss with increasing temperature. The temperature sensitivity is defined as [32]:

The maximum sensitivity obtained is −1.2 nm/°C, and the linear regression yields R² = 0.99734 (Fig. 13(b)), confirming a stable and predictable thermal response in CH1.

For the cancer detection scenario, we further clarified that the system temperature was fixed at 37 °C [33], corresponding to the physiological culture condition of mammalian cells, which minimizes temperature-induced refractive-index drift. Table 7 (already present in the original manuscript) lists the refractive indices of Basal, HeLa, and Jurkat cells [34–36], which were filled into CH2 for detection. Thus, the newly added Fig. 13, together with the existing Table 7, provides a clearer demonstration of the dual-channel utility: CH1 for temperature monitoring and CH2 for cancer detection.

 

Author action: We updated the manuscript by making appropriate revision. The changes are modified as shown below.

 

(Page 12, Line 365)

 

“The simulation range was set from −10 to 40 °C. As shown in Fig. 13(a), the resonance wavelength exhibits a blue shift and reduced loss with increasing temperature. The temperature sensitivity is defined as[32]:

(8)

(b)

(a)

The maximum sensitivity obtained is −1.2 nm/°C, and the linear regression yields R²=0.99734 (Fig. 13(b)), confirming stable and predictable thermal response in CH1.

 

Figure 13. (a) Loss spectrum of CH1 from −10 to 40 °C; (b) linear fit of resonance wavelength versus temperature

For cell detection, the system temperature was fixed at 37 °C[33], which corresponds to the physiological culture condition for mammalian cells and minimizes temperature-induced refractive-index drift, ensuring reliable results.”

 

(Page 16, Line 496)

 

[33]. Yaroslavsky, A. N., Patel, R., Salomatina, E., Li, C., Lin, C., & Al-Arashi, M. (2012). High-contrast mapping of basal cell carcinomas. Optics Letters, 37(4), 644–646.[CrossRef]

 

 

We appreciate for the editors’ and the reviewers’ warm work earnestly, and hope the revisions will meet with your approval.

Once again, thank you very much for your comments and suggestions.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have satisfactorily incorporated the suggested changes. The revised manuscript adequately addresses the concerns raised, and the quality has been enhanced.