Two-Dimensional Elliptical Microresonator Arrays for Wide Flat Bandwidth and Boxlike Filter Response

Round 1

Reviewer 1 Report

The Authors propose a compact filter based on two dimensional SOI elliptical microresonator array. The reported results have been experimentally demonstrated. A major revision of the manuscript is suggested according to the following comments:

-          The manuscript should be considered as “communication”.

-          In the Introduction, the literature on ring resonators should be enlarged, aiming at highlighting the main benefits to use engineered ring resonators, as flat-bandwidth (New microwave photonic filter based on a ring resonator including a photonic crystal structure. In 2017 19th International Conference on Transparent Optical Networks (ICTON) (pp. 1-4). IEEE, 2017.) or high ER (e.g., Silicon graphene reconfigurable CROWS and SCISSORS. IEEE Photonics Journal, 7(2), 1-9., 2015;  High performance and tunable optical pump-rejection filter for quantum photonic systems. Optics & Laser Technology, 139, 106978, 2021) or small linewidth (e.g, Rigorous model for the design of ultra-high Q-factor resonant cavities. In 2016 18th International Conference on Transparent Optical Networks (ICTON) (pp. 1-4). IEEE., 2016; Integrated waveguide coupled Si 3 N 4 resonators in the ultrahigh-Q regime. Optica, 1(3), 153-157., 2014; Ultralow 0.034 dB/m loss wafer-scale integrated photonics realizing 720 million Q and 380 μW threshold Brillouin lasing. Optics letters, 47(7), 1855-1858, 2022).

-          In the Section 2, the Authors report that the proposed filter has been simulated by using the transform matrix method. However, this method is unknown. Please clarify the used approach. For the simulation, the technology platform should be reported and every choice, in terms of thickness and width, should be justified. Moreover, the propagation loss is very crucial for the resonance performance. The Authors should report the used value in the simulations. Moreover, the bending radius is very important. The Authors should justify it. Ultimately, the trend k vs. gap should be reported and how the performance could be affected by fabrication errors.

-          In the Section 3, the propagation losses of the waveguide could be estimated. Moreover, the choice of the waveguide geometry should be discussed.

-          About the spectra, the ripples should be physically justified and the mismatch with respect simulated results should be also justified.

-          A comparison table with respect to the state-of-the-art should be reported.

Minor flaws:

-          The references should be updated in the whole manuscript.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The Authors propose a filter with a wide flat boxlike bandwidth based on a 2D array of elliptical microresonators. The performance has been estimated by using the transfer matrix method (TMM).

Here my comments:

- Please check the English language in the whole manuscript;

- Update the references;

- The literature on engineered ring resonator-based configurations should be enlarged (e.g., Ultra-compact tuneable notch filter using silicon photonic crystal ring resonator. Journal of Lightwave Technology, 37(13), 2970-2980, 2019; Engineering the spectral reflectance of microring resonators with integrated reflective elements. Optics Express, 18(16), 16813-16825, 2010).

- The major issue of the manuscript is the lack of a device design. The choice of parameters is not well explained. The y gap is relevant to desire or to avoid the coupling between the bent areas of the microresonators. Moreover, the Authors should prove the crosstalk performance. The tuning section should be carefully designed and simulated.

- Several sentences of plagiarism has been detected with respect to Boxlike filter response based on complementary photonic bandgaps in two-dimensional microresonator arrays. Optics letters, 33(21), 2512-2514, 2008. Moreover, please compare the proposed performance with the one reported in the previous paper.  

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The authors Guan et al. fabricated a 2D elliptical microresonator arrays structure. It performs as a optical filter exhibiting a wide flat-bandwidth of 951 GHz with the shape factor of 0.57 at the through port. However, the novelty of the paper is doubted, the work in this manuscript is quite similar to the reference [18] (year 2008), in which four configurations were measured, here are only two.  The most apparent difference is that the circle elements are only replaced with elliptical rings.  I suggest to add more either calculation/simulation or experiment data in this work.

Other minors

I suggest to label the dimensions on Figure 1 and add a scale bar on the optical images of Figure 4.

Please check the grammar again. For example, on page 1 line 5 in the abstract, I suggest to remove the “about” in the sentence. Because the numbers are exactly 60. 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The Authors have extensively modified the manuscript according to the Reviewer suggestions. Therefore, I suggest the publication as it is.

Reviewer 2 Report

The Authors have addressed the issues of the previous version of the manuscript

Reviewer 3 Report

The authors have answered all the questions and added more data as required. Especially, the table 1 comparision shows the greatest performance of this filter. The paper now is ready to be published.