Broadband Thermo-Optic Photonic Switch for TE and TM Modes with Adiabatic Design

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript introduces an adiabatic thermo-optic photonic switch designed for TE and TM polarizations, utilizing silicon-on-insulator (SOI) technology.  This design leverages the adiabatic transition principle and the thermo-optic effect to achieve efficient and broadband light routing over the 1525-1625 nm wavelength range.  Given the potential applications of such components in modern optical communication systems, this study appears to be useful.  Therefore, I would like to recommend publication after the authors have considered the following points:

 

1.In Figure 1, the heaters are enclosed in a blue area, which has the same color as the waveguides.  Please provide a detailed explanation of this.  If they belong to different parts (e.g. core, cladding), consider using a different color (or other ways) to distinguish them.

 

2. Table 2: For the TO coefficients, the power is not placed in the superscript.

 

3. Due to its length, the device has a relatively high power consumption (250 mW).  Compared to other optical switch designs listed in Table 3, what advantage does this device offer? It appears to me that this switch has a feature that as the heating power increases, the transmission in each port changes monotonously, which differs from the normal Mach-Zehnder switch that has a periodic transmission variation. Such a switch is called a digital optical switch. It is recommended that authors check the literature and explore along this line.

 

4. MZS is not defined in Table 3.

 

5. In the final section of the manuscript, the authors could briefly discuss the potential applications of the proposed adiabatic photonic switch in various optical communication systems, such as wavelength division multiplexing (WDM) and passive optical networks (PON).

Author Response

1. Summary

We are deeply grateful for the time you have spent for carefully reading our work and for your valuable comments. We have made our best to meet their request and believe that this has notably improved the overall quality of the manuscript.

In the following we explain point-by-point the actions we have made to adhere to the suggestions provided by Reviewer.

Comments 1: In Figure 1, the heaters are enclosed in a blue area, which has the same color as the waveguides.  Please provide a detailed explanation of this.  If they belong to different parts (e.g. core, cladding), consider using a different color (or other ways) to distinguish them.

Response 1:     Thank you for pointing this out. The heaters do not belong to different parts of the device, as they are laid on the Si slab (see cross section A-A’ in Figure1). For clarity, we have added the label 'slab' in Figure 1 to help distinguish the components more easily.

Comments 2:  Table 2: For the TO coefficients, the power is not placed in the superscript.

Response 2:     We appreciate your thorough review and have carefully made all necessary corrections to address the formatting issues you identified.

Comments 3:  Due to its length, the device has a relatively high power consumption (250 mW).  Compared to other optical switch designs listed in Table 3, what advantage does this device offer? It appears to me that this switch has a feature that as the heating power increases, the transmission in each port changes monotonously, which differs from the normal Mach-Zehnder switch that has a periodic transmission variation. Such a switch is called a digital optical switch. It is recommended that authors check the literature and explore along this line.

Response 3:     We appreciate this insightful comment and have revised paragraph 2 on page 7, lines 178-185 to emphasize the advantages of the adiabatic structure switch. This revision provides a clearer comparison to existing devices in the field, highlighting the contributions of our work. Additionally, we have incorporated the term 'digital optical switch' into the manuscript in two places: paragraph 2, line 65, on page 2, and paragraph 2, line 178, on page 7, to align with the unique characteristics of our design.

Comments 4:  MZS is not defined in Table 3.

Response 4:     We agree with this comment and have added definitions for MZS and MMI in the text, specifically in paragraph 2, lines 178-180, on page 7, to ensure clarity and consistency.

Comments 5:  In the final section of the manuscript, the authors could briefly discuss the potential applications of the proposed adiabatic photonic switch in various optical communication systems, such as wavelength division multiplexing (WDM) and passive optical networks (PON).

Response 5:     We appreciate this comment and have revised the conclusion section to include a brief discussion on the potential applications of adiabatic switches in lines 206-210.

Response to Comments on the Quality of English Language

Thank you for your positive feedback. We are glad to hear that the quality of the English language did not limit your understanding of the research. We will continue to ensure clarity and precision in our writing.

Additional clarifications

We hope that the revisions and clarifications provided address all the concerns raised by the reviewers. We believe these improvements enhance the manuscript and make the research more comprehensive. Should there be any further questions or requests for additional information, we would be happy to provide them.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript titled “Broadband Thermo-Optic Photonic Switch for TE and TM Modes with Adiabatic Design” presents the design of an adiabatic thermo-optic switch using silicon-on-insulator (SOI) technology. The switch demonstrates polarization-independent operation for both TE and TM modes across a broad wavelength range (1525–1625 nm). The authors numerically designed a passive splitter and evaluated its functionality as an active switch, reporting wide bandwidth and low insertion loss for both polarization modes.

 

While the manuscript is well-organized and the results appear to support the authors' conclusions, several significant issues need to be addressed before the manuscript can be considered for publication in Photonics. These are as follows:

 

1.       The study is based entirely on numerical simulations, but no discussion is provided on the potential impact of fabrication tolerances on device performance. Including an analysis of how variations in fabrication parameters, such as waveguide dimensions and material properties, could influence the results is essential for practical applicability.

2.       The consideration of thermo-optic effects in the manuscript does not appear to account for environmental factors such as temperature fluctuations, packaging stresses, or thermal crosstalk, which may affect the switch's real-world performance. A discussion of these factors and potential mitigation strategies is strongly recommended.

3.       In Section 4.2, the authors state that insertion loss (IL) was estimated by measuring optical power loss between the device's input and output. However, the manuscript does not provide sufficient details regarding the methodology or assumptions used for these calculations. The inclusion of a more comprehensive analysis or experimental validation would enhance the credibility of the results.

4.       The trends in Figure 4, while presented numerically, lack a thorough discussion. For instance, the nonlinear relationship between the taper waveguide length and the extinction ratio (ER) for TM mode requires further explanation. A more detailed interpretation of these trends would improve the clarity of the manuscript.

5.       The manuscript does not convincingly demonstrate significant performance advantages, particularly in terms of power consumption and extinction ratio, compared to prior work in the field. A more thorough benchmarking of the device’s performance against state-of-the-art devices is needed to highlight its contributions.

6.       Several formatting errors are noted:

l   References [23], [24], and [25] should be separated by commas.

l   In Section 4.1, the term “(Ti)” appears in the fourth line and is repeated in the sixth line.

l   Superscripts and subscripts are not used correctly, as seen in Table 2.

l   What is the meaning of "Mw/μma" in the penultimate paragraph on page 6 and "Mw/μm/" in Figure 5.

l   Multiple errors are present in Table 3, such as the incorrect capitalization of "lithium niobate," and the inconsistent usage of “-” and “~.”

 

 

Comments on the Quality of English Language

A few typos are identified

Author Response

1.Summary

We are deeply grateful for the time you have spent for carefully reading our work and for your valuable comments. We have made our best to meet their request and believe that this has notably improved the overall quality of the manuscript.

In the following we explain point-by-point the actions we have made to adhere to the suggestions provided by Reviewer.

Comments 1: The study is based entirely on numerical simulations, but no discussion is provided on the potential impact of fabrication tolerances on device performance. Including an analysis of how variations in fabrication parameters, such as waveguide dimensions and material properties, could influence the results is essential for practical applicability.

Response 1:     We appreciate this insightful comment. In response, we have updated Figure 6 (previously Figure 5) to include the effects of fabrication tolerances on device performance. Additionally, we have incorporated a discussion on this topic in the second paragraph, page 6, lines 167-172 to address how variations in fabrication parameters, influence the results.

Comments 2:  The consideration of thermo-optic effects in the manuscript does not appear to account for environmental factors such as temperature fluctuations, packaging stresses, or thermal crosstalk, which may affect the switch's real-world performance. A discussion of these factors and potential mitigation strategies is strongly recommended.

Response 2:     Thank you for pointing this out. One of the key advantages of the adiabatic structure used in our design is its reduced sensitivity to temperature fluctuations, which is common instead in resonance and interference based devices. In the proposed device, the higher the ΔT between the external waveguides, the higher the ER. At 1 mW/μm, ΔT is large than 100K, enough to prevent the effects of ambient temperature fluctuations. Besides, we assume that the substrate is hold at a constant temperature, e.g. by means of a heat sink. We have discussed this aspect in the Section 4.2, lines 183-189.

Comments 3:  In Section 4.2, the authors state that insertion loss (IL) was estimated by measuring optical power loss between the device's input and output. However, the manuscript does not provide sufficient details regarding the methodology or assumptions used for these calculations. The inclusion of a more comprehensive analysis or experimental validation would enhance the credibility of the results.

Response 3:     Thank you for pointing this out; we agree with this comment and therefore we have updated the insertion loss explanation in the first paragraph of page 6,lines 173-177.

Comments 4:  The trends in Figure 4, while presented numerically, lack a thorough discussion. For instance, the nonlinear relationship between the taper waveguide length and the extinction ratio (ER) for TM mode requires further explanation. A more detailed interpretation of these trends would improve the clarity of the manuscript.

Response 4:     We agree with this comment and have revised the manuscript to provide a more detailed explanation of the trends. Specifically, we have added additional discussion in the first paragraph of page 6 lines 158-164 and added Figure 5 to address the nonlinear relationship between the taper waveguide length and the extinction ratio (ER) for the TM mode.

Comments 5:  The manuscript does not convincingly demonstrate significant performance advantages, particularly in terms of power consumption and extinction ratio, compared to prior work in the field. A more thorough benchmarking of the device’s performance against state-of-the-art devices is needed to highlight its contributions.

Response 5:     We appreciate this comment and have revised paragraph 2 on page 7, lines 178-185 to highlight the advantages of the adiabatic structure switch. This revision provides a clearer comparison to existing devices in the field, emphasizing the contributions of our work.

Comments 6:  Several formatting errors are noted:

 

• References [23], [24], and [25] should be separated by commas.

 

• In Section 4.1, the term “(Ti)” appears in the fourth line and is repeated in the sixth line.

 

• Superscripts and subscripts are not used correctly, as seen in Table 2.

 

• What is the meaning of "Mw/μma" in the penultimate paragraph on page 6 and "Mw/μm/" in Figure 5.

 

Multiple errors are present in Table 3, such as the incorrect capitalization of "lithium niobate," and the inconsistent usage of “-” and “~.”

Response 6:     We appreciate your careful review and have made the necessary corrections to address the formatting issues you noted:

 

• References [23], [24], and [25] have been separated by commas as suggested.
• The term “(Ti)” in the sixth line has been corrected.
• Superscripts and subscripts have been properly formatted in Table 2.
• The meaning of "Mw/μma" in the penultimate paragraph on page 6 has been clarified, and "Mw/μm/" in Figure 5 has been corrected.
•  We have corrected multiple errors in Table 3, including the capitalization of "lithium niobate" and the inconsistent use of “-” and “~.

Response to Comments on the Quality of English Language

Thank you for your feedback regarding the quality of the English language in the manuscript. We have carefully revised the text to improve clarity and expression, ensuring that the research is communicated more effectively. We hope these revisions address your concerns, and we appreciate your help in enhancing the manuscript.

Additional clarifications

We hope that the revisions and clarifications provided address all the concerns raised by the reviewers. We believe these improvements enhance the manuscript and make the research more comprehensive. Should there be any further questions or requests for additional information, we would be happy to provide them.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have well addressed all my concerns.