Integrated Photonic Passive Building Blocks on Silicon-on-Insulator Platform

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The realization of hybrid substrates consisting of different functional elements on the overall silicon platform is advanced as a way to increasing the integral circuits operation rate. The implementation of optical communication between individual elements of integral circuits is considered as one of the main solutions of this problem. Silicon-on-insulator (SOI) substrates attract researches attention as the most suitable ones for combining elements of electronic and photonic networks in an integrated design. In this way, the peer-reviewed paper, which examines various photonic blocks incorporated into an SOI platform, is very relevant. The authors examined the different types of coupling between an SOI-chip and external optical fibers, various types of design of optical switches and splitters, as well as filtering and phase shifting devices.

          However, the review presented is too superficial. It lists only some of the design elements of various photonic devices irrespective of the SOI-wafer parameters. At the same time, the optical characteristics of photonic blocks may directly depend on the properties of SOI structures. For example, refractive and reflection coefficients can vary depending on the fixed charge density in the silicon oxide layer, as well as on the surface state density at the Si/SiO₂ interface. Therefore, I would like to see at least some requirements for the critical parameters of the SOI structures that determine the quality of the considered photonic blocks.

          In addition, the article is written very heterogeneously. For example, section 2.2 is written very briefly: it lists only various connection designs without analyzing their parameters, design advantages and disadvantages, while the paragraphs of sections 3 and 4 are written in more detail. But, in all sections of the article, there is no critical analysis of the design features of the corresponding photonic blocks.

          Given in the literature is a large number of review articles about the integral photonics on SOI structures. I would like to see more originality in this review, for example, in the form of the relation between design elements and parameters of SOI-structures. This would be very useful for developers of SOI-structures.

Author Response

In response to your feedback, thank you for providing valuable insights into the depth and focus of our document. We appreciate your thorough analysis and suggestions for improvement.

We take note of your advice to specify the type of SOI, and we have aimed to adhere to a device layer of intrinsic silicon with a thickness of 220 nm. These pieces of information will be duly acknowledged and considered in our revised review, as they are essential for contextualizing the discussion within the parameters of practical implementation.

We recognize the need for greater uniformity in the depth of analysis across different sections of the document. While some sections delve into detailed examinations of specific photonic blocks, others may appear more superficial. Therefore, we have decided to change the title of the article and specify that we focus on passive devices.
We will also change the title of the "Switching and Splitting" section to "Splitting devices."

Regarding originality, we appreciate your suggestion to offer more unique insights into the relationship between design elements and SOI structure parameters. In our review, we have focused on easily achievable building blocks that are structurally simple for researchers and engineers approaching Silicon Photonics, given the breadth of topics covered. For further insights into the applications of the described devices, we refer readers to specific reviews cited in the article.

Thank you for your constructive feedback. We are committed to incorporating your suggestions to enhance the quality and relevance of our review document on integrated photonics on SOI structures.

Reviewer 2 Report

Comments and Suggestions for Authors

The comments on this article are summarized in the word.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

In line287, should the “considered one of” be changed to "considered as one of"? The author should check the full text to avoid such kinds of mistakes.

Author Response

Thank you for your valuable feedback on our article discussing integrated photonic components on SOI substrates. We appreciate your thorough examination of the content and your suggestions for improvement. Here's how we intend to address each of your points:

1: We acknowledge the need to update the literature review to include more recent relevant works published in the past five years. We will add newer reviews where researchers and engineers approaching Silicon Photonics can delve into the applications of individual devices. Given the breadth of topics covered, we have focused on easily fabricable structures. We will specify this in the abstract and modify the title of the article to specify that we will discuss passive structures.

2: Regarding the fully vertical grating coupler mentioned in Section 2.2, we will correct the part about the tilt angle in a less assertive manner.

3: In response to your observation about the emphasis on passive devices over active ones, we will make changes to the article. Specifically, as mentioned earlier, we will modify the title to specify that the focus is on passive structures.

4: We understand your suggestion to include images and summary tables at the end of each chapter, and indeed, we have already included summary tables at the end of each section. We believe this will allow us to provide key visual and informational elements while managing the article's length within acceptable limits.

Thank you again for your thorough review

Reviewer 3 Report

Comments and Suggestions for Authors

The Authors propose an overview of integrated photonic building blocks on SOI, including the coupling with external fiber, switching and splitting, and filtering and phase shifting. Here, my comments:

1. For all the topics, several reviews have been already published (see, i.e., Silicon Photonic Filters: A Pathway from Basics to Applications. Advanced Photonics Research, 2300343, 2024; Silicon Nitride Spot Size Converter With Very Low-Loss Over the C-Band. IEEE Photonics Technology Letters,35, 22, 2023; Recent advances in silicon-based passive and active optical interconnects. Optics Express, 23(3), 2487-2511, 2015; A Review of Silicon‐Based Integrated Optical Switches. Laser & Photonics Reviews, 17(4), 2200571, 2023). Please cite them and clarify the novelty of the proposed review.

2. To help the reader in the performance understanding, please list the main performance for each reviewed device. Moreover, report a table with the most promising technologies for each application.

3. The proposed review is mainly focused on the fiber-device couplers. Please report it in the Abstract. Moreover, some references are dated. Please, add recent results (i.e., The low-loss spot size converter for alignment with cleaved single mode fiber. Applied Sciences, 13(14), 8157; Silicon Nitride Spot Size Converter With Very Low-Loss Over the C-Band. IEEE Photonics Technology Letters, 2023).

4. Section 3 is entitled "Switching and splitting". However, the reported devices are splitters. If the Authors are oriented towards switches, the switching mechanisms should be described. Moreover, the Authors have to take into account both narrow and broadband switches.

5. About waveguide crossings, the Authors have to report the optimization approaches, that could be used, such as particle swarm optimization (Design of a large bandwidth 2× 2 interferometric switching cell based on a sub-wavelength grating. Journal of Optics, 23(8), 085801, 2021) (see, i.e., Low-loss, low-cross-talk crossings for silicon-on-insulator nanophotonic waveguides. Optics letters, 32(19), 2801-2803, 2007).

6. About ring resonators, the Authors focus more on biomedical applications, neglecting several other applications that are only cited. Please report other applications, by describing the architectures where the RR is the crucial device, i.e., oscillator, gyroscope, digital ports, quantum computer, and so on.

 

Author Response

We are grateful for the references provided, and we will incorporate them into our revision to ensure comprehensive coverage of the existing literature. We acknowledge the importance of citing relevant works and will clarify the novelty of our review compared to existing ones. Given the breadth of topics covered, we have highlighted structures that are easy to construct to be useful to engineers and researchers who may not be experts in Silicon Photonics manufacturing. For further depth, we refer readers to more specific reviews as suggested by you and others cited.

As we aim to limit the number of pages while still providing valuable information to the reader, we have included summary tables at the end of each section listing the main performance parameters for each reviewed device. For the most promising technologies for each application, we defer to more specific reviews. Our focus has been on functional aspects and fabrication.

We will integrate your valuable suggestions and references into the revised version of our review. Additionally, we will ensure that the focus on fiber-device couplers is clearly highlighted in the abstract and update references to include the recent results you suggested.

In response to your observation about Section 3, we will change the section title to "Splitting" to accurately reflect the discussed content. We will specifically focus on splitting devices and omit discussion of switching mechanisms to maintain clarity and focus in the section. Regarding waveguide crossings, we will include and discuss the publications you cited.

We understand your perspective on the emphasis on block structures rather than applications. To better reflect this focus, we will change the title of the article to emphasize passive structures. While we will still mention applications, our main focus will remain on discussing the design and characteristics of photonic building blocks.

We are committed to incorporating these suggestions into the revised version of our review to ensure its quality and relevance to the field

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors made the necessary changes to the article in accordance with the wishes of the reviewer. The article can be published in the present form.

Author Response

Thank you for appreciating my work.
I would like to inform you that I have added some additional references in section 3 and section 2.

Best regards

Reviewer 2 Report

Comments and Suggestions for Authors

Accept.

Author Response

Thank you for appreciating my work.
I would like to inform you that I have added some additional references in section 3 and section 2.

Regards

Reviewer 3 Report

Comments and Suggestions for Authors

The Authors have modified the manuscript according to the Reviewer's suggestions. However, as highlighted in the Section 3 and since the review is mostly focused on the fiber-chip couplers, the literature on them should be enlarged.

Author Response

Thank you for appreciating my work.
I would like to inform you that I have added 2 more recent references in section 3 and section 2. I hope they can enhance the work.

Regards