Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 The authors propose a hybrid a hybrid gold-ITO-silver block structure integrated within a Mach-Zehnder interferometer structure, and ultilize the localized surface plasmons (LSPs) in the silver block to modulate the electron concentration in the adjacent ITO layer. A modulation depth of 50.8 dB was achieved with an electron concentration change of 3.3×10²⁰cm^-3, demonstrating an all-optical modulator with ultrahigh extinction ratio. The work have a promising application and the manuscript is well written, i would recommend this paper to be published in photonics if the following problems are addressed.1) The “modulation depth” is used in the manuscript while the “extinction ratio” is utilized in the title, it should be consist with the title.2) More information should be given in the simulation model.

3) There are some language problems in the text. I suggest the authors find a native English speaker or ask professional editing service for content revision.

4)There are some mistakes in the format of the references, which need to be modified.

Author Response

Thank you for all constructive suggestions. We have revised the manuscript according to these helpful suggestions. The detail please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript presents a novel all-optical modulator design that integrates a gold-ITO-silver block structure within a Mach-Zehnder interferometer. The innovation lies in modulating the ITO electron concentration via localized surface plasmon effects in adjacent silver blocks. The authors claim a very high modulation depth (50.8 dB), which addresses known limitations in traditional plasmonic modulators, such as high power requirements and material dependence. The work is well-motivated and shows strong potential for integrated photonic applications.

1. The paper relies entirely on simulations. While acceptable for a theoretical study, a discussion on the feasibility of fabrication and experimental realization would increase the quality of the manuscript.
2. Although the dependence of ITO's optical properties on electron concentration is referenced, it is not fully derived or validated within the paper. Authors should elaborate or include a brief summary of the adopted model.
3. The introduction of the laser excitation may induce heating. The impact of temperature on ITO properties and device stability should be briefly discussed.
4. Adding a paragraph or table to compare state-of-the-art modulators is necessary for highlighting the performance.
5. Several previous related works could be cited to enrich the landscope of the introduction, such as Journal of Nanophotonics, 2019, 13(4): 046009-046009, which introduce an on-chip plasmonic modulator based on the same platform, and Materials, 2018, 11(6): 941, which highlight gain materials for on-chip plasmonic modulations.

Author Response

Thank you for all constructive suggestions. We have revised the manuscript according to these helpful suggestions. The detail please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Thank you for the work. Before publication, could the authors please address the following points:

• I am not sure about the device design. Is light propagation occurring within the ITO waveguide? The authors should specify the waveguide geometry, such as the height and width.
• In the 2D simulation model, what effective index for the waveguide was used?
• In Figure 3, the unit for electron concentration should be labeled as cm-3.
• In the simulation, how do the authors transfer the electron concentration change to the optical properties?
• Could the authors provide more explanation for Figure 3(a)? It seems that both arms of the MZI show higher loss. How, then, does the combined output show a higher field than the input?
• In Figure 3(b), why does it apply different electron concentrations to each arm to achieve the OFF state? Wouldn't using 5e20 cm-3 in both arms achieve a similar effect?
• The authors use N to represent changes in electron concentration. Can the authors also specify the corresponding voltage needed to induce a change of 1e20 cm-3 (N=1)?
• What is the input wavelength used in the simulations (Figures 3–8)?
• In Figure 11, the phase changes significantly with small changes in wavelength. Can the authors discuss this further? Specifically, why does a small shift in wavelength get such a π phase change?

Author Response

Thank you for all constructive suggestions. We have revised the manuscript according to these helpful suggestions. The detail please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Authors' answer2: As per this question, the effective index of the waveguide is changing when the electron concentration or the wavelength is modified, it is not a fixed value.

Comment: When the voltage is applied to ITO, the electrons only accumulate near the interface with the metal. Therefore the effective index may only change at the interface not the entire WG.

Author's answer4: As per this question, it is reported in our work before(reference [35]), and the transfer process is as follow..

Comment: It would be great if the author can add a brief disucssion in the manuscript. Regarding the figure 2 in the response report. Does it mean the device can only go upto around 5e20? About that, how can the refractive index go below 1.0 ?

 

Author Response

Thank you for all constructive suggestions. We have revised the manuscript according to these helpful suggestions. The details please see the attached file.

Author Response File: Author Response.pdf