Integrated Bragg Grating Spectra

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this manuscript, the authors performed systematic theoretical and numerical studies of bragg gratings. The authors should make sure that their figures are labelled in a consistent way, and they should give a full description for figure 15, including clearly state what each subfigure is. 

The methods the authors used (such as transfer matrix methods) are commonly used in designing gratings and thin film devices. Can the authors comment on the novelty of their work , since this method and commonly used and the result is expected. 

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript “Integrated Bragg Grating Spectra” authored by José Ángel Praena and Alejandro Carballar reports an extensive investigation on optical responses of IBG waveguide for establishing theoretical model based on effective refractive index transfer matrix method (ERI-TMM). They performed an investigation of their model on SOI and Al₂O₃ platforms, common for industrial applications. They also validated the prediction of their proposed model experimentally for one of the IBG. Lastly, authors demonstrated their theoretical model application in characterizing optical responses of different apodization schemes on IBG for their application in some common planar photonic devices such as phase modulator IBG, sampled diffraction network, and photonic Hilbert transformer.  

The manuscript summarizes the concepts of the apodization and optical responses of IBG waveguide using ERI-TMM modelling which has potential applications in photonic integrated circuits. However, this manuscript needs a major revision to remove redundancy and grammatical errors, improve the figures, and layout of the manuscript. I have the following comments/suggestions which author might need to carefully look and address:

Major Comments:

 

1. Authors should provide in-depth literature background on integrated waveguide Bragg grating, apodization method, and its significance in photonic integrated circuits.

 

2. I strongly recommend removing the redundant information in the figures and merging multiple figures to provide clear context on the significant outcome. For example: Instead of showing the interface of Lumerical in Fig. 3, author should focus on presenting the mode profile. Relevant parameters can be mentioned in the figure captions. Fig. 3 and 4 can be merged. Similarly with Figure 5 and 6. A 3D schematic illustration of your geometry will provide clear insight compare with clips of Lumerical interface.

 

3. 4 and 6 suggest some trends in the real and imaginary part of effective index as a function of wavelength. Can authors comment on why those trends have been observed?

 

4. Line 330: Author estimated the group delay; however, the phase function relation is not mentioned in the manuscript. I would suggest the authors mention the equation of phase function with wavelength to bridge the gap.

 

5. Authors have shown experimental results in Fig. 9, however; they have not provided the details of experimental conditions and the setup for optical characterizations. Is the experimental data presented in this manuscript referred to by some other work or authors carried out the experiments by themselves to validate their models?

 

6. One can observe discrepancy in the mode frequency between modelling and experimental observation shown in Fig. 9(d). The sides bands in the measured spectra are also asymmetric w.r.t. central frequency in Figure 9. Can authors clarify the reason for discrepancy?

 

7. Line 400: Authors say: “this effect is due to the nonlinear variation of the effective refractive index…” Can authors explain how this non-linear behavior causes asymmetric variation of n_eff over the distance?
8. Figure 18(a) data can be represented in dB for generality in the manuscript.
9. Though ERI-TMM results looks very fascinating, can authors substantiate them with Lumerical simulations data as well?

Minor Comments:

1. Authors should reduce the use of ambiguous pronouns throughout the manuscript to enhance clarity for readers. For instance, in line 42, the phrase "This analysis, so far…" lacks specificity, making it unclear whether the authors are referring to the investigation presented in the manuscript, or the one mentioned in the previous paragraph. Similarly, in line 44, the phrase "This has led to…" does not explicitly indicate what it refers to, leading to potential ambiguity.
2. There are some grammatical and typographical errors present throughout the manuscript that need to be addressed. For example: Line 259: “...attenuation decreases with…” should be attenuation .. ; Figure 7: Direction red arrow at the interface i+1 suggest that the electric field should be E^- _(i+1); Eq. 7: it should be Φ_T instead of Φ_R.

Considering all the above-mentioned points, I believe the manuscript has scope of significant improvement which is necessary to bring it to the standards for publication.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The clarity and readability of the manuscript could be significantly improved with thorough proofreading. Engaging a native English speaker or a professional English editing service may help refine the language and enhance the overall presentation of the work.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript, José Ángel Praena et al “Integrated Bragg Grating Spectra”, uses the transfer matrix method (TMM) with the effective refractive index (ERI) obtained from Lumerical simulation to calculate the reflection and transmission spectra of specially engineered waveguide. The authors first extract the ERI from Lumerical calculation for varying longitudinal sizes of the material. Next, they calculate the resulting spectra for different corrugation shapes, apodization and chirp structures. The spectra obtained from ERI-TMM are compared with experimental results and a reasonably good agreement is achieved. Overall, the paper is well-written. I am certain that the manuscript becomes suitable for publication after my questions and concerns are swiftly addressed.

 

1. I have one small question regarding Figure 9: the waveguide agrees perfectly near the strongest transmission wavelength, what is source of discrepancy when the wavelength is away from 1560 nm, on both side? Can the author provide more explanations?

Please also note that there is a typo on the x-label.

 

2. Can the author also show the imaginary part of the neff in Figure 4 for varying wavelength and W? Is there a simple theory for the functional form of neff(W), it seems like a nice linear relation (at least for the real part).

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript presents a general methodology for analyzing Integrated Bragg Gratings (IBGs) as linear time-invariant systems using the Effective Refractive Index (ERI) and Transfer Matrix Method (TMM). By translating the IBG’s physical structure into a wavelength-dependent effective refractive index matrix, the approach provides highly accurate reflection and transmission spectra without relying on approximations like Coupled Mode Theory. The methodology is validated across different apodization and chirp techniques and applied to two distinct technological platforms: silicon-on-insulator (SOI) and aluminum oxide (Al₂O₃).

I am happy with the results and figures overall, and the manuscript is nearly ready for acceptance. However, a few minor points need attention: the figures, particularly those from Lumerical and Figure 6, are not clear and should be improved. The captions should be more meaningful, and the numerical boundary conditions used should be explicitly discussed.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

While the manuscript has been significantly improved, there are a few points that need to be addressed to remove redundancies and improve the quality of readability.

I have the following comments which authors might need to carefully look at:

Major Comments:

1. Authors should merge Figure 3 and Figure 4 into one single figure as they address the investigation of one geometrical design. In addition, authors need to remove the redundant information from the sub-figures, i.e. the details of the interface of Lumerical, and keep relevant information i.e. field profiles and color bar. You don’t need Fig. 3(b) if 3(a) explains the geometry under investigations. Similar actions can be taken for Fig. 4 and Fig. 5.
2. Authors should either explicitly mention fabrication and characterization details or provide reference of an article in the manuscript that can be more easily accessible to the readers than a course.
   
   
3. The observed discrepancy between the experimental and theoretical data needs to be reported in the manuscript. Furthermore, authors should discuss their view briefly.

Author Response

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Author Response File: Author Response.docx