Review Reports - 1 × 3 Optical Drop Multiplexer for FTTH Applications Based on Photonic Crystal Fiber

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents a new design of a 1 × 3 optical drop multiplexer based on photonic crystal fiber for Fiber-to-the-Home applications. The topic is interesting and this study can be considered for publication pending some revisions as follows:
1. Considering that there is low loss and higher efficiency in the wavelength range of 1.33 to 1.55 μm, the selected wavelengths should also be chosen from this range. It seems that the authors should re-examine the new suitable wavelengths.
2. Considering that in FTTH applications, high bandwidth and high transmission rate are of interest, the performance of the proposed multiplexer in this regard should be investigated.
3. Sensitivity analysis of the photonic crystal structure parameters to reduce dispersion and increase efficiency should be investigated and reported.
4. In Figures 4, 6, 7, and 8, the nomenclature a, b, and c is not visible in the figure. Also, the quality of Figs. 6 and 7 need to be increased.
5. References should be updated by 2025. Some related works are suggested to complete the introduction section (1) Optical Fiber Communication Conference: 10.1364/OFC.2025.W2A.10 and (2) Optics Express: 10.1364/OE.521152
6. The results should be compared, validated, and reported with previous experimental work.
7. In the conclusion section, it is mentioned “With optimal results …”. But there is no algorithm or method to optimize the PCF structure. Please clarify.
8. Although the subject and results are based on the simulation, since the structure is a bit complex for fabrication, given a section including feasibility study for fabrication of the propose PCF is recommended.
9. It is recommended to investigate the environmental parameters, such as tempereture, on the multiplexer performance.

Author Response

Comment 1 : Considering that there is low loss and higher efficiency in the wavelength range of 1.33 to 1.55 μm, the selected wavelengths should also be chosen from this range. It seems that the authors should re-examine the new suitable wavelengths.

Response :

We thank the reviewer for this important observation. We fully acknowledge that the 1.33–1.55 μm window offers the lowest loss and highest efficiency for FTTH transmission. In this work, our primary goal was to validate the wavelength-selective drop behavior of the proposed PCF-based device over widely separated spectral points to demonstrate that the operation stems from geometry-driven inter-core coupling, rather than from a single telecom window. To this end, we purposefully used 0.85 μm, 1.20 μm, and 1.45 μm as three disparate test cases to stress-test the concept and highlight its versatility. Notably, 1.45 μm lies within the extended low-loss region of modern low-water-peak fibers and therefore remains relevant to FTTH scenarios.

Importantly, the proposed architecture is wavelength-scalable: its behavior is governed by normalized PCF parameters (e.g., d/Λ) and coupling length, so the same layout can be targeted to the O/E/C/L bands by selecting design distances accordingly. In a deployment-oriented setting, the intended operating wavelengths would be in the telecom low-loss window (e.g., 1.31/1.49/1.55 μm). To make this explicit, we have added a clarification in the Introduction and Conclusion stating that the present results are a proof of concept and that the device can be directly re-targeted to 1.33–1.55 μm without altering the core geometry, only re-calibrating the extraction distances.

Comment 2 : Considering that in FTTH applications, high bandwidth and high transmission rate are of interest, the performance of the proposed multiplexer in this regard should be investigated.

Response :

We thank the reviewer for this relevant suggestion. In FTTH applications, high bandwidth and high transmission rates are indeed critical. The proposed PCF-based drop multiplexer is inherently compatible with high data rates because the light-guiding mechanism is based on modified total internal reflection in a low-loss silica background, with negligible inter-channel crosstalk at the designed extraction distances.

Modern FTTH systems (e.g., GPON, XG-PON, and NG-PON2) typically operate at aggregated capacities from 2.5 Gbit/s up to 40 Gbit/s, using narrow channel spacings within the 1.31–1.55 ?m range. The proposed geometry supports such rates as its operational bandwidth is governed by the coupling length stability over the spectral range of interest. The low-loss nature of the design (transmission > 70% for all channels in the present simulations) ensures that the device does not limit the system’s bandwidth.

To address the reviewer’s point, we have added a discussion in the manuscript noting that the structure can operate over the full typical telecom band, allowing compatibility with high-capacity FTTH standards. The exact maximum supported bit rate will depend on the modulation format and system-level dispersion management, but the present results confirm that the device is suitable for high-speed FTTH scenarios.

Comment 3 : Sensitivity analysis of the photonic crystal structure parameters to reduce dispersion and increase efficiency should be investigated and reported.

Response :

We thank the reviewer for this valuable comment. We agree that a sensitivity analysis of the photonic crystal structure parameters (e.g., air-hole diameter d, pitch Λ, and fiber length z) is important for further optimizing dispersion and transmission efficiency. In the present work, our primary focus was to demonstrate the feasibility of a 1×3 wavelength drop multiplexer using a fixed geometry that had been pre-optimized based on prior studies [2,3,10].

The relationships between PCF geometry and dispersion/efficiency are well established: increasing d/Λ generally enhances mode confinement and coupling efficiency but may increase dispersion, whereas decreasing Λ reduces coupling length and can improve isolation between channels. The selected parameters (d = 0.9 μm, Λ = 1.88 μm) were chosen to balance these trade-offs, following reported designs in the literature, in order to ensure low loss and efficient wavelength separation.

A comprehensive parametric sensitivity analysis will be the subject of future work, including numerical optimization to simultaneously minimize dispersion and maximize efficiency across the FTTH operational band. We have added a sentence to the manuscript to make this explicit.

Comment 4 : In Figures 4, 6, 7, and 8, the nomenclature a, b, and c is not visible in the figure. Also, the quality of Figs. 6 and 7 need to be increased.

Response :

We appreciate the reviewer’s observation. The labels “(a)”, “(b)”, and “(c)” have now been added in Figures 4, 6, 7, and 8 to ensure they are clearly visible and correspond to the descriptions in the captions. Furthermore, Figures 6 and 7 have been re-exported at higher resolution (300 dpi) to improve clarity and readability in the final manuscript.

Comment 5 : References should be updated by 2025. Some related works are suggested to complete the introduction section (1) Optical Fiber Communication Conference: 10.1364/OFC.2025.W2A.10 and (2) Optics Express: 10.1364/OE.521152

Response :

We thank the reviewer for this valuable suggestion. We have updated the reference list to include recent works up to 2025. In particular, we have added the two suggested references — Optical Fiber Communication Conference 2025 (doi:10.1364/OFC.2025.W2A.10) and Optics Express (doi:10.1364/OE.521152) — in the Introduction section to provide a more comprehensive and up-to-date overview of the state of the art in PCF-based multiplexers and FTTH applications. The Introduction has been revised accordingly.

Comment 6 : The results should be compared, validated, and reported with previous experimental work

Response :

We thank the reviewer for highlighting the importance of experimental validation. While the present work is based on numerical simulations, the design parameters and the light-guiding mechanism are derived from previously reported PCF structures that have been experimentally demonstrated [2,3,9,10]. The extracted distances and transmission efficiencies reported in our study are consistent with those found in similar experimental implementations in the literature — for instance, the works of Harrat et al. [2,3] and Wang et al. [9], where comparable coupling lengths and insertion losses were obtained.

We have now included a comparative discussion in the Results section, indicating that the predicted performance aligns with the experimental trends observed in these prior works. A full experimental realization and validation of the proposed 1×3 drop multiplexer is planned as a future extension of this study.

Comment 7 : In the conclusion section, it is mentioned “With optimal results …”. But there is no algorithm or method to optimize the PCF structure. Please clarify.

Response :

We thank the reviewer for pointing out this ambiguity. We agree that the term “optimal results” may be misleading, as no optimization algorithm or systematic parameter sweep was implemented in this work. The term was intended to indicate that the chosen PCF parameters provided favorable performance in terms of low loss and efficient wavelength separation, based on prior knowledge and reported designs [2,3,10].

To avoid confusion, we have revised the sentence in the Conclusion to replace “With optimal results” with “The results indicate favorable performance.” In addition, we have clarified that future work will address systematic optimization of the PCF geometry (e.g., sensitivity analysis of d, Λ, and fiber length) to further improve performance.

Comment 8 : Although the subject and results are based on the simulation, since the structure is a bit complex for fabrication, given a section including feasibility study for fabrication of the propose PCF is recommended.

Response :

We thank the reviewer for this constructive suggestion. We agree that a discussion on fabrication feasibility is important given the structural complexity of photonic crystal fibers. Although the present study is simulation-based, we have now added a section discussing the fabrication feasibility of the proposed PCF structure.

Specifically, PCF fabrication techniques such as the stack-and-draw method, extrusion, and sol-gel casting have been widely employed to realize structures with multiple air-hole arrangements similar to the one we propose [1,4,6]. Recent advances in preform stacking and pressurization during the draw process allow precise control of air-hole diameter (d) and pitch (Λ), which are the critical parameters in our design. Tolerances of less than ±0.1 μm on hole size and pitch have been reported, which are sufficient to reproduce the geometry we used. While the design involves alternating air-hole positions, such modifications are feasible using selective hole-filling or controlled collapse during the draw process, as demonstrated in related PCF fabrication studies.

A brief feasibility study has been included in the revised manuscript (new subsection in Materials and Methods), highlighting that current fabrication techniques make the proposed PCF structure realistic for implementation. A detailed fabrication and experimental characterization will be considered in our future work.

Comment 9 : It is recommended to investigate the environmental parameters, such as tempereture, on the multiplexer performance.

Response :

We thank the reviewer for this insightful suggestion. We agree that environmental factors, particularly temperature, can significantly influence the performance of PCF-based devices. The thermo-optic effect in silica leads to changes in the refractive index with temperature, while thermal expansion can slightly alter the air-hole diameter and pitch (d and Λ), thereby affecting dispersion and coupling length.

In this work, our focus was on demonstrating the fundamental wavelength-selective behavior of the proposed multiplexer under ideal conditions. A systematic investigation of environmental influences, including temperature dependence, is planned as part of future work, where numerical modeling will be combined with experimental characterization. To address the reviewer’s comment, we have added a note in the Conclusion highlighting that device performance may vary with environmental parameters and that this aspect will be addressed in subsequent studies.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Editor,

This manuscript presents an optical multiplexer based on photonic crystals, but the design appears to be straightforward and lacks significant innovation. The authors do not provide a scientific or physical basis for their research, nor do they include mathematical relations to support their findings. The overall quality of the manuscript's formatting is very poor. I recommend that the authors consider submitting this work to a scientific conference rather than a journal. Due to the significant shortcomings and its distance from publication standards, I cannot recommend this article for publication. The following are just a few of the issues that need to be addressed.

1- The introduction needs a complete overhaul. To improve it, first provide a background on photonic crystals, then photonic crystal fibers, detailing their pros, cons, and applications. Next, introduce optical multiplexers and their uses. Conduct a comprehensive literature review of similar multiplexers, especially those based on photonic crystals and photonic crystal fibers. Conclude by highlighting the weaknesses of existing research and clearly explaining how your proposed structure addresses these limitations.

2- You must provide a full description of the simulation software and the boundary conditions used in your work.

3- The manuscript must clearly state the exact specifications of the light source used in the simulations.

4- As a reminder, a scientific paper in electrical engineering should always include mathematical equations based on fundamental physical and scientific principles.

5- Including a photonic band gap (PBG) diagram is a necessary component of this paper.

6- Please clarify if you considered the interaction between light and matter, specifically any changes in the refractive index due to nonlinear effects.

7- Since you used the FDTD method for your simulations, you must include a full explanation of the relevant equations in the manuscript.

8- For clarity, provide a detailed explanation of the basis of light propagation within your proposed structure.

9- On what basis were the values of structural parameters such as air hole radius, pitch (Ʌ), hole height, etc., selected? Can their optimality be asserted?

10- The impact of environmental factors (such as temperature, air pressure, and humidity) on device performance and results should be discussed.

11- To reflect real-world conditions, the analysis should incorporate potential manufacturing tolerances. Please present a tolerance analysis (e.g., ±5% or ±10%) in the results.

12- To assess the practical viability of the proposed device, a comprehensive description of the manufacturing process is required. This should include a detailed step-by-step explanation along with a schematic illustrating the manufacturing process.

13- Provide the transmission loss for your proposed structure.

Kind regards

Author Response

Comments 1 : The introduction needs a complete overhaul. To improve it, first provide a background on photonic crystals, then photonic crystal fibers, detailing their pros, cons, and applications. Next, introduce optical multiplexers and their uses. Conduct a comprehensive literature review of similar multiplexers, especially those based on photonic crystals and photonic crystal fibers. Conclude by highlighting the weaknesses of existing research and clearly explaining how your proposed structure addresses these limitations.

Reply :

We thank the reviewer for this constructive recommendation. Following the suggestion, we have completely restructured and expanded the Introduction. The revised section now: (i) presents a concise background on photonic crystals and then photonic crystal fibers (PCFs), including their advantages, limitations, and representative applications; (ii) introduces optical multiplexers/demultiplexers and their role in access/FTTH networks; (iii) provides a focused literature review of multiplexers based on photonic crystals and PCFs; and (iv) identifies gaps in prior work and clarifies how our proposed structure addresses these limitations. The new text cites recent works up to 2025, including the two items suggested by the reviewer, and connects the state of the art to the specific design choices made in this paper.

Comments 2 : You must provide a full description of the simulation software and the boundary conditions used in your work.

Reply :

We thank the reviewer for this important remark. We agree that providing details on the simulation environment and boundary conditions is essential for reproducibility. We have therefore added a full description of the simulation software, numerical method, and boundary conditions in the revised Materials and Methods section. Specifically, we now report the software platform, solver type, mesh settings, and the boundary conditions applied in modeling the PCF structure.

Comments 3 : The manuscript must clearly state the exact specifications of the light source used in the simulations.

Reply :

We thank the reviewer for this important observation. We agree that the manuscript should explicitly state the characteristics of the light source used in the simulations. In the revised version, we have added these details in the Materials and Methods section. Specifically, the input source was modeled as a continuous-wave (CW), monochromatic Gaussian beam coupled into the fundamental mode of the input core, with unit normalized input power. The simulations were carried out at the three selected wavelengths (0.85 μm, 1.20 μm, and 1.45 μm). The source polarization was set along the x-axis, and a narrow linewidth (Δλ ≈ 0) was assumed, consistent with standard CW laser sources in optical communications.

Comments 4 : As a reminder, a scientific paper in electrical engineering should always include mathematical equations based on fundamental physical and scientific principles.

Reply :

We thank the reviewer for this comment. We fully agree that scientific papers in electrical engineering often include mathematical equations to present the underlying physical principles. In the present work, however, our focus was primarily on the numerical design and demonstration of the proposed PCF-based optical drop multiplexer. The fundamental equations governing light propagation in photonic crystal fibers (Helmholtz equation, coupled-mode theory, and attenuation expressions) are well established and have been extensively reported in the literature [1,4,5]. To avoid redundancy, we referred to these prior works and directly concentrated on simulation-based verification of the concept.

We therefore maintained the current formulation of the paper, while emphasizing in the revised Introduction and Methods that our approach builds upon these established models. Future extensions of this work will include a more detailed theoretical treatment and optimization analysis.

Comments 5 : Including a photonic band gap (PBG) diagram is a necessary component of this paper.

Reply :

aluable tool to illustrate the guidance mechanism in many photonic crystal fibers. However, the present design operates primarily under the modified total internal reflection (MTIR) mechanism rather than a pure PBG guidance. For this reason, a full PBG band diagram is not strictly required for describing the behavior of our structure. To clarify this point, we have revised the Introduction and Materials and Methods to explicitly state that the proposed multiplexer relies on MTIR-based coupling, and we have included relevant references [1,4,6] where PBG diagrams are extensively reported. This ensures that the reader can relate our work to both MTIR- and PBG-based PCF designs without duplicating material already well established in the literature.

Comments 6 : Please clarify if you considered the interaction between light and matter, specifically any changes in the refractive index due to nonlinear effects.

Reply :

In the present study, the simulations were carried out under the assumption of linear optical behavior, with a constant refractive index for silica (n = 1.45). Nonlinear effects such as Kerr-induced index changes, self-phase modulation, Raman, or Brillouin scattering were not considered. This choice is justified by the fact that FTTH applications typically operate at relatively low optical power levels (on the order of a few milliwatts per channel), where nonlinear refractive index variations are negligible.

Comments 7 : Since you used the FDTD method for your simulations, you must include a full explanation of the relevant equations in the manuscript.

Reply :

We thank the reviewer for this observation. Indeed, the finite-difference time-domain (FDTD) method was employed for the numerical simulations in this work. We have now included a concise theoretical background describing the governing equations of the FDTD scheme. Specifically, we outline the time-domain Maxwell curl equations and their discretized forms, which are used to compute the electromagnetic field propagation in the photonic crystal fiber. This addition clarifies the numerical framework underlying our simulation results.

Comments 8 : For clarity, provide a detailed explanation of the basis of light propagation within your proposed structure.

Reply :

We have added a dedicated subsection explaining the light-propagation mechanism in the proposed PCF-based drop multiplexer. In brief, guidance occurs under modified total internal reflection (MTIR) because the microstructured cladding lowers the effective refractive index relative to the silica core. Along the device, the alternating air-hole pattern modulates the spacing and overlap between adjacent cores, thus controlling the wavelength-dependent coupling coefficient κ(λ). Power transfers periodically between cores with a coupling length Lc(λ) = π/(2κ). Since κ depends on wavelength through modal dispersion and overlap, the drop positions become wavelength-selective: each target wavelength is extracted at a distinct propagation distance where its transfer is maximized while the others remain largely confined. The text added below makes these points explicit and links them to the simulated extraction distances.

Comments 9 : On what basis were the values of structural parameters such as air hole radius, pitch (?), hole height, etc., selected? Can their optimality be asserted?

Reply :

The structural parameters of the proposed PCF (air-hole radius = 0.9 μm, pitch Λ = 1.88 μm, and fiber length = 19 mm) were selected based on values reported in previous studies [2,3,10], where similar PCF-based multiplexing structures were analyzed and experimentally validated. These parameters provide a practical balance between confinement loss, coupling efficiency, and fabrication feasibility.

The present work was intended as a proof of concept, demonstrating the wavelength-selective drop functionality of the structure. While the chosen values yield favorable results in terms of high transmission and distinct extraction distances, we do not claim global optimality. A systematic optimization of parameters (radius, pitch, and length) would be required to minimize dispersion and maximize efficiency across the entire FTTH wavelength window. This will be addressed in our future work.

To clarify this, we have added a note in the Materials and Methods and in the Conclusion stating that the current design uses pre-optimized parameters from the literature, and that a full optimization study will be considered as an extension.

Comments 10 : The impact of environmental factors (such as temperature, air pressure, and humidity) on device performance and results should be discussed.

Reply :

We agree that environmental factors such as temperature, air pressure, and humidity can influence the performance of PCF-based devices. In the present work, simulations were carried out under idealized conditions, assuming constant material parameters.

Temperature variations affect the refractive index of silica through the thermo-optic effect and induce small thermal expansions of the pitch and hole diameter, which in turn modify coupling lengths and dispersion. Changes in air pressure may slightly deform or collapse air holes in extreme cases, thereby altering confinement. Humidity primarily impacts long-term fiber reliability rather than short-term optical properties, but water infiltration into the air holes could degrade transmission.

While these effects were not included in the present simulation, we have added a discussion in the revised manuscript acknowledging that environmental factors may alter the precise extraction distances and efficiency of the device. Future work will involve modeling these influences and experimentally characterizing environmental stability.

Comments 11 : To reflect real-world conditions, the analysis should incorporate potential manufacturing tolerances. Please present a tolerance analysis (e.g., ±5% or ±10%) in the results.

Reply :

We agree that fabrication imperfections such as ±5–10% deviations in air-hole radius or pitch can influence device performance. Larger air-hole diameters generally enhance mode confinement but may increase dispersion, whereas deviations in pitch alter the coupling coefficient and shift the extraction distances.

In the present work, our objective was to provide a proof of concept under idealized conditions, using parameters drawn from previously reported PCF designs. A complete tolerance analysis was therefore not included. Nevertheless, we have added a discussion in the revised manuscript noting that such deviations are expected to cause moderate shifts in transmission efficiency and extraction positions but do not fundamentally alter the operating principle of the device.

Comments 12 : To assess the practical viability of the proposed device, a comprehensive description of the manufacturing process is required. This should include a detailed step-by-step explanation along with a schematic illustrating the manufacturing process.

Reply :

We agree that a description of the fabrication process is essential to evaluate the practical viability of the proposed PCF-based multiplexer. Although this work is simulation-based, we have now added a subsection in the Materials and Methods describing the step-by-step manufacturing process typically employed for PCFs, namely the stack-and-draw method. We also provide a schematic illustration of the process.

In brief, silica capillaries are arranged to form the preform with the desired hole distribution, stacked inside a jacket tube, and consolidated. The preform is then drawn into fiber under controlled heating, with pressurization applied to maintain hole integrity and control air-hole diameter and pitch. Adjustments during the draw allow realization of alternating hole positions as required in our design.

Comments 13 : Provide the transmission loss for your proposed structure.

Reply :

We appreciate the reviewer’s request regarding transmission loss. The present study reports normalized transmission efficiencies for the three channels (98%, 71%, and 90%), which directly map to per-channel insertion loss as follows:
– 98% → 0.09 dB,
– 71% → 1.49 dB,
– 90% → 0.46 dB.
These figures already characterize the device loss within the simulated structure.

Regarding material attenuation, the device length is 19 mm; for silica in the telecom window (~0.2 dB/km), the intrinsic propagation loss over 19 mm is ~3.8×10⁻⁶ dB, i.e., negligible relative to the insertion-loss values above. In practice, the dominant contributors in an experiment would be interface/connector and fabrication-induced imperfections, which are outside the scope of this simulation-based proof of concept.

Since the manuscript already provides the channel transmissions from which loss is directly obtained, we believe a separate loss subsection is not strictly required. We are happy to include these numeric conversions in the response for clarity.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors propose a PCF as a wavelength multiplexer for PON applications. The main issue that I have with the paper is that the authors do not discuss other possible solutions for this problem. A standard approach would be applying an AWG. Probably such wavelength combiner could be bought of the shelf. Another possiblity is applying an MMI coupler. There is therefore the main questions that in my view should be addressed. Namely, why this new solution and not AWG? Is the proposed solution better than AWG? If so which parameters can be improved? Without addressing these issues the paper makes a very weak case. Further, for PON applications a more comprehensive analysis of the device is needed. Not only the transmission coefficients are important but also the crosstalk between channels should be studied. Other parameters that might be of interest are chromatic dispersion and Polarisation Dependent Loss.

Finally, if authors cannot address comprehensively the issues that have been mantioned above I would not recommend this paper for publication. In particular, the authors should address the problem of the advantages of their solution when compared with AWG. What are the advatages? Why make a new device when there is a well estalished solution of the problem.

Author Response

Comments :

Response :

We thank the reviewer for this critical but very constructive comment. We fully agree that arrayed waveguide gratings (AWGs) and multimode interference (MMI) couplers are standard and commercially available solutions for wavelength multiplexing in PON systems. Our intention in this paper was not to suggest that the proposed PCF multiplexer should replace AWGs at this stage, but rather to demonstrate a novel proof of concept that offers specific advantages in certain scenarios.

In comparison with AWGs, the proposed PCF structure has the following potential advantages:
• Compactness: the device length is only 19 mm, considerably shorter than typical AWG chips.
• Fabrication simplicity and cost: it does not require photolithographic processing or precise array design, but relies on standard PCF stack-and-draw techniques.
• Thermal stability: AWGs are known to be sensitive to temperature shifts, requiring athermal packaging. In contrast, PCFs in silica exhibit lower thermo-optic drift.
• Wavelength scalability: the same geometry can be re-targeted to different telecom bands (O, E, C) by adjusting coupling distances, offering versatility.

Compared with MMI couplers, the PCF-based multiplexer can achieve lower crosstalk because of wavelength-dependent coupling, whereas MMI devices typically suffer from higher insertion loss and are more sensitive to fabrication tolerances.

We acknowledge that the present manuscript does not yet provide a full comparative analysis including crosstalk, chromatic dispersion, or polarization-dependent loss (PDL). This study was intended as a first step to validate the feasibility of the concept using numerical simulations. Following the reviewer’s suggestion, we have added a discussion in the revised manuscript explicitly comparing PCF-based multiplexers with AWG and MMI devices, and clarifying the niche advantages of the proposed solution. A more comprehensive analysis of crosstalk, PDL, and dispersion will be included in future work.

We believe that highlighting these differences strengthens the case for our paper as a proof of concept and motivates future research toward practical integration alongside conventional AWGs in FTTH networks.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The revised manuscript can be accepted for publication. No additional comment.

Author Response

Comments :

The revised manuscript can be accepted for publication. No additional comment.

Rreply :

We sincerely thank the reviewer for the positive evaluation of our revised manuscript and for the constructive comments provided during the review process. The suggestions greatly improved the quality and clarity of our work.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have made considerable and valuable revisions to the manuscript, effectively addressing many of the comments. To further improve the paper, please consider the following:

1- Expand the introduction with a more thorough analysis of existing photonic crystal-based multiplexers.
Optical and Quantum Electronics 54, no. 7 (2022): 397 /J Progress In Electromagnetics Research M 118 (2023): 127-136 /Journal of Optoelectronical Nanostructures 7, no. 1 (2022): 97-106 /Optical and Quantum Electronics 54, no. 12 (2022): 818 /Optik 295 (2023): 171491

2- Remove abbreviations like ODM and OADM from the abstract, defining them in the main text instead.

3- Clearly articulate the innovation of your proposed structure.

Author Response

Comment 1 :

Expand the introduction with a more thorough analysis of existing photonic crystal-based multiplexers.
Optical and Quantum Electronics 54, no. 7 (2022): 397 /J Progress In Electromagnetics Research M 118 (2023): 127-136 /Journal of Optoelectronical Nanostructures 7, no. 1 (2022): 97-106 /Optical and Quantum Electronics 54, no. 12 (2022): 818 /Optik 295 (2023): 171491

Reply :

We agree that the Introduction required a more thorough analysis of recent photonic crystal-based multiplexer designs. Following this recommendation, we have revised the Introduction by adding several recent works. These references provide examples of photonic crystal and photonic crystal fiber multiplexers, their methodologies, and performance trade-offs.

Comment 2 :

Remove abbreviations like ODM and OADM from the abstract, defining them in the main text instead.

Reply :

Following the recommendation, we have removed abbreviations such as ODM and OADM from the Abstract and replaced them with their full terms (“optical drop multiplexer” and “optical add-drop multiplexer”). The abbreviations are now introduced and defined in the main text of the Introduction, where they are subsequently used for brevity.

Comment 3 :

Clearly articulate the innovation of your proposed structure

Reply :

To address it, we have revised both the Introduction and Conclusion to explicitly highlight the novelty of our work. The proposed 1×3 PCF-based multiplexer introduces a compact geometry (only 19 mm) that leverages wavelength-dependent coupling to achieve distinct extraction channels with high efficiency (up to 98%). Unlike conventional AWGs and MMIs, the device is entirely fiber-based, compatible with standard PCF fabrication (stack-and-draw), and does not require lithographic processing or large footprints. To our knowledge, this is among the first demonstrations of a PCF optical drop multiplexer specifically targeted to PON/FTTH applications. This positions our work as a low-cost, compact, and thermally stable alternative, complementing existing solutions.

Reviewer 3 Report

Comments and Suggestions for Authors

Considering the reply of the Authors I suggest publishing this paper.

Author Response

Comments :

Considering the reply of the Authors I suggest publishing this paper.

Reply :

We would like to express our gratitude to the reviewer for the kind recommendation to accept our manuscript and for the valuable feedback provided earlier. The comments have helped us significantly improve the quality and presentation of the paper.