Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The author presents a theoretical investigation of surface plasmon polariton (SPP) propagation along an indium antimonide (InSb)–uniaxial chiral (UAC)–InSb planar interface operating in the near-infrared regime. Using electromagnetic wave theory and the Drude model for InSb, the dispersion characteristics are examined under varying chirality, core width, temperature, and incident frequency for two configurations of the UAC medium (Case I: ε_t > 0, ε_z < 0; Case II: ε_t < 0, ε_z > 0).

The work aims to demonstrate thermally reconfigurable photonic components. Strengths The paper addresses a relevant gap: most prior chiral SPP studies rely on metals or graphene, leaving the temperature-tunable InSb–chiral hybrid largely unexplored. The simultaneous consideration of chirality and temperature is a useful extension, and the inclusion of two permittivity cases is commendable. The results are consistent with established literature on thermal tunability in InSb-based plasmonic systems. Weaknesses and Concerns Novelty is incremental. The mathematical framework (characteristic equation for a planar chiral interface) closely follows prior work on isotropic chiral and UAC waveguides. The addition of InSb is the main novelty, but the underlying equations are not fundamentally new. Limited physical insight.

The paper largely presents dispersion curves without explaining why certain trends occur. For instance, the shift of curves toward higher frequencies with increasing temperature is attributed to carrier concentration changes, but no quantitative linkage to plasma frequency is provided. Missing key analyses. There is no discussion of: Field confinement (mode profiles) to support the claim of "enhanced light confinement." Propagation length or figure of merit combining confinement and loss. Comparison with experimental data or experimental feasibility of the proposed UAC medium. Realistic material constraints (e.g., InSb damping at near-IR wavelengths). Clarity and presentation. Several equations (Eqs. 6–16) are presented without clear derivation, and the characteristic matrix in Eq. (16) is hard to read. The use of Mathematica is mentioned but no convergence/error analysis is given. Case II is incomplete. Only partial results for Case II are shown (Figures 6–7), with no analysis of propagation loss analogous to Figure 5, weakening the comparison between cases. Practical relevance unclear.

The author claims applications in "near-infrared optical communication," but no discussion of modulation speed, insertion loss, or compatibility with existing photonic platforms is provided. Major revisions required: Provide quantitative physical explanations linking temperature-induced carrier changes to the observed dispersion shifts. Add mode profile analysis and a figure of merit. Complete the Case II analysis (especially propagation loss) to support the claim that Case II is "more sensitive." Clarify the experimental feasibility [as reported in RSC Adv. (2015) 5 (75): 60770–60774.] of fabricating the proposed UAC medium with the assumed permittivity values.

Author Response

Comment 1. Limited physical insight.
Response 1. In the revised manuscript, we have expanded the results and discussion section to explain the physical mechanisms responsible for the observed dispersion behavior. Particularly, we discuss how chirality modifies the magnetoelectric coupling, the effects of core width through the spatial overlap of modal fields, and temperature dependence through the thermally induced change in the InSb dielectric response in page 5-11.
Comment 2. The paper largely presents dispersion curves without explaining why certain trends occur. For instance, the shift of curves toward higher frequencies with increasing temperature is attributed to carrier concentration changes, but no quantitative linkage to plasma frequency is provided.
Response 2. The explanation behind the trends is added in the result and discussion section. For example, the physical explanation, particularly of temperature-dependent dispersion is strengthened by explicitly linking carrier concentration of InSb to its plasma frequency and subsequently to the Drude permittivity. These explanations have been added to the discussion of Fig 2a (Page 5, line 166-169), Fig 2b age 6, line 172-175), Fig 3b (page 6, line 183-186), Fig 4b (page 7, line 205-214), Fig 5 (page 8, line 222-227), and Fig 8b (page 11, line 264-266).
Comment 3. Missing key analyses. There is no discussion of: Field confinement (mode profiles) to support the claim of "enhanced light confinement.
Response 3. Fig 11 (page 14) of mode profiles has been added in results and discussion section to discuss the field confinement to support the claim of “enhanced light confinement”. The discussion of the normalized field profiles has been added in page 12, line 296-304. Additionally, penetration depth (Fig 12, page 15) is added to quantitatively address field confinement. The discussion of Fig 12 is on page 12-13, line 304-325.

Comment 4. Propagation length or figure of merit combining confinement and loss.
Response 4. Figure of merit (FoM) is added in results and discussion section for both Case I and Case II, combining confinement and loss as presented in Fig 13, page 15. This provides a combined metric that complements the separate propagation loss and confinement analysis. The discussion of Fig 13 is added in page 13, line 325-343.
Comment 5. Comparison with experimental data or experimental feasibility of the proposed UAC medium. 
Response 5. The present study is theoretical and does not include experimental measurements of the proposed structure. Therefore, rather than claiming experimental validation, we have clarified the experimental feasibility and limitations of the assumed UAC medium. We also explicitly state that experimental implementations would require fabrication and characterization of UAC in the targeted spectral range.  The experimental feasibility discussion has been added in results and discussion section page 13, line 343-353.
Comment 6. Realistic material constraints (e.g., InSb damping at near-IR wavelengths). 
Response 6. Using the Drude model, the damping constant is used to account for the realistic material loss of InSb. The damping parameter is added in Eqn 13, rather than treating InSb as an ideal lossless plasmonic material. The Drude model and the role of damping constant are described in the methodology section in page 4, line 129-134 with resulting propagation loss analyzed in Fig 5 and Fig 9. 
Comment 7. The manuscript has been revised to improve clarity, notation, figure presentation, and overall readability.
Response 7. The manuscript has been revised to improve clarity, notation, figure presentation, and overall readability.
Comment 8. Several equations (Eqs. 6–16) are presented without clear derivation, and the characteristic matrix in Eq. (16) is hard to read.
Response 8. The derivation and definition of the parameters used in Eqs. (6)–(16) in the methodology section have been clarified, and the presentation of the characteristic matrix in Eq. (16) has been improved for readability. The changes are made in page 3, line 104-108, page 4, line 115-116, line 123-124, line 129-134, and page 5, line 138-146.

Comment 9. The use of Mathematica is mentioned but no convergence/error analysis is given.
Response 9. The convergence/error analysis is addressed in revised manuscript in page 5, line 156-160.
Comment 10. Case II is incomplete. Only partial results for Case II are shown (Figures 6–7), with no analysis of propagation loss analogous to Figure 5, weakening the comparison between cases.  
Response 10. Case II analysis has been expanded to include the propagation loss as a function of operating frequency for different chirality values, providing an analysis analogous to Fig 5 for Case I. The Case II propagation loss analysis is presented in Fig 9, page 12. 
Comment 11. Practical relevance unclear.
Response 11. The discussion of the practical relevance of the proposed InSb-UAC-InSb waveguide is expanded in the revised manuscript page 13, line 343-446. For instance, penetration depth analysis provides a quantitative measure of transverse field localization, while FoM combines propagation and confinement characteristics. Additionally, the propagation loss, penetration depth, and FoM provide first order metrics for assessing the suitability of the proposed structure for tunable photonic components.
Comment 12. The author claims applications in "near-infrared optical communication," but no discussion of modulation speed, insertion loss, or compatibility with existing photonic platforms is provided.
Response 12. The scope and limitations of the proposed structure with respect to optical communication applications have been clarified in the revised manuscript. The present work is a theoretical electromagnetic study and therefore does not directly provide a device level modulation speed or insertion loss measurement. Instead, propagation loss, penetration depth, and FoM can be used to evaluate potential of proposed structure. We have also clarified that practical implementation would require UAC medium fabrication and integration with appropriate photonic platform. Thus, the communication application is presented here as a potential application direction rather than as an experimentally demonstrated communication device. The clarification has been added in page 13, line 343-453.
Comment 13. Major revisions required: Provide quantitative physical explanations linking temperature-induced carrier changes to the observed dispersion shifts.
Response 13.  The quantitative physical explanations linking temperature-induced carrier changes to the observed dispersion shifts is discussed in Fig 4b, page 7, line 205-214. The revised discussion explains the physical sequence: temperature changes the intrinsic carrier concentration; the carrier concentration changes the plasma frequency; the changes in plasma frequency alters the complex permittivity which changes the decay constant and characteristic equation.
Comment 14. Add mode profile analysis and a figure of merit.
Response 14. The requested analyses have been addressed in page 14, Fig 11, page 15, Fig 12, and Fig 13. Mode profiles have been added to directly demonstrate the surface wave localization. Additionally, penetration depth has been added as a quantitative confinement metric. FoM has been added for both UAC configurations to evaluate the trade-off between propagation and confinement.

Comment 15. Complete the Case II analysis (especially propagation loss) to support the claim that Case II is "more sensitive."1
Response 15. Case II analysis (especially propagation loss) is added in Fig 9 and we expanded the comparison between Case I and case II. The added propagation loss and FoM analyses show that two UAC configurations shows different chirality-dependent balances between loss and confinement. These additional results support the claim that Case II is more sensitive than Case I within the investigated parameter range. The Case II propagation loss is presented in page 12, Fig 9, while the comparison between Case I and Case II is discussed in page 14, Fig 10. The FoM comparison is provided in page 15, Fig 13.
Comment 16. Clarify the experimental feasibility [as reported in RSC Adv. (2015) 5 (75): 60770–60774.] of fabricating the proposed UAC medium with the assumed permittivity values.
Response 16. The experimental feasibility of the proposed UAC medium has been clarified in the revised manuscript. We clarified that the UAC medium used in this study is treated as an effective theoretical medium. Experimental studies have demonstrated that effective UAC can be realized using engineered chiral inclusions; however, the reported constitutive parameters are not identical to those used in our model. Therefore, the fabrication and characterization of the proposed structure remains an important future work. The experimental feasibility discussion has been clarified in page 13, line 343-353.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

I reviewed this manuscript with interest. It accurately reflects its title, as it consistently investigates temperature-controlled surface plasmon polariton propagation in an InSb–uniaxial chiral–InSb waveguide for near-infrared optical communication. The theoretical analysis, numerical results, and conclusions are all well aligned with the title and the overall research focus. 

The proposed structure offers multiple tuning mechanisms, including temperature, chirality, operating frequency, and core width, which provide useful flexibility for controlling SPP propagation characteristics. The authors have also carefully developed a theoretical framework, with the electromagnetic field components derived from Maxwell’s equations and the characteristic equation obtained by applying appropriate boundary conditions. 

I find the comparative analysis of the two uniaxial chiral-medium cases valuable, as the authors show that Case I is more suitable for broader or higher-frequency operation, whereas Case II provides stronger confinement and lower-loss propagation at lower frequencies. I also appreciate how the numerical analysis is connected to practical photonic-device design, especially for thermally reconfigurable waveguides, temperature-sensitive optical devices, sensors, and near-infrared optical communication systems.

However, I have some important comments that may help improve the quality of the manuscript. I ask the authors to carefully check the notation and units throughout the manuscript, especially the reported temperature scales, propagation-constant units, chirality notation, and frequency labels in the figures. I also noticed that some acronyms and symbols are defined inconsistently. 

I encourage the authors to define all symbols immediately after their first appearance, especially in the methodology section and in the characteristic equation, to improve readability. I also encourage the authors to improve the figure captions and the quality of the plots by using consistent formatting, clearer axis labels, larger legends, and removing punctuation or spacing inconsistencies where applicable.  Finally, and most importantly, the authors should explain the practical relevance to near-infrared optical communication more explicitly. For example, they could discuss suitable operating wavelengths, expected device dimensions, fabrication feasibility, and performance metrics such as propagation length and confinement factor.

Comments on the Quality of English Language

The manuscript would benefit from careful English-language editing, as several sentences contain grammatical errors, awkward phrasing, and inconsistent terminology.

Author Response

Comment 1. I ask the authors to carefully check the notation and units throughout the manuscript, especially the reported temperature scales, propagation-constant units, chirality notation, and frequency labels in the figures. I also noticed that some acronyms and symbols are defined inconsistently.                
Response 1. All the notation and units throughout the manuscript, especially the reported temperature scales, propagation-constant units, chirality notation, and frequency labels in the figures are checked. Additionally, the acronyms and symbols are defined consistently.              
Comment 2. I encourage the authors to define all symbols immediately after their first appearance, especially in the methodology section and in the characteristic equation, to improve readability.
Response 2. We have carefully revised the methodology section and added or clarified the definitions of the symbols used in equations. Particularly, the parameters appearing in the electromagnetic field equations, constitutive relations, and characteristic equation have been defined immediately after their first appearance. The changes are made in page 3, line 104-108, page 4, line 115-116, line 123-124, line 129-134.
Comment 3. I also encourage the authors to improve the figure captions and the quality of the plots by using consistent formatting, clearer axis labels, larger legends, and removing punctuation or spacing inconsistencies where applicable.
Response 3. The figure captions and the quality of the plots by using consistent formatting is improved by clearer axis labels, larger legends, and removing punctuation or spacing inconsistencies. The changes are made throughout the manuscript in results and discussion section from Fig 2-13.
Comment 4. Finally, and most importantly, the authors should explain the practical relevance to near-infrared optical communication more explicitly. For example, they could discuss suitable operating wavelengths, expected device dimensions, fabrication feasibility, and performance metrics such as propagation length and confinement factor.
Response 4. The practical relevance of near-infrared optical communication has been expanded by discussing operating frequency, core width, penetration depth, propagation loss, and FoM as relevant design parameters for integrated photonic devices. The frequency-dependent propagation characteristics are analyzed to identify the operating region in which the proposed structure exhibits favorable surface plasmon propagation. UAC core width is discussed as a crucial geometrical design parameter that can be optimized when designing an integrated planar photonic structure. The investigated dimensions are considered as representative 

theoretical design parameters rather than experimentally fixed fabrication dimensions. The feasibility as well as limitations associated with fabrication of the proposed structure have been clarified. Additionally, the revised manuscript discusses several electromagnetic performance metrics such as propagation loss, penetration depth, and FoM to assess the potential of the proposed structure. The detail analyses have been added through propagation loss (page 9, Fig 5, line 219-229 and page 12, Fig 9, line 273-287), penetration depth (page 15, Fig 12, line 304-325), and FoM (page 15, Fig 13, line 325-243)

Author Response File: Author Response.pdf