The Effect of Multi-Oxide Layers on the Photoelectrical Performance of Double-Cavity Vertical-Cavity Surface-Emitting Lasers
Round 1
Reviewer 1 Report (Previous Reviewer 1)
Comments and Suggestions for AuthorsThis is the resubmission of a simulative paper developed within PICS3D commercial software. The topic addresses a small niche of VCSEL applications: pumping the Rb line at 795nm. It targets the required specs, namely high Single Mode (SM) output power at 80 degree Celsius.
Even if the title changed, the content is the same as before, so that let's see if the 3 main critics were addressed, that is:
1) There is no detail on the parameters used in the simulations. A very long list wold be needed, including the electrical transport parameters, because of Fig.5-6 provide such features. From Fig.5, clearly no quantum transport is included in the QWs, which is quite bad.
OUR RESPONSE:In the simulation process, the carrier transport is described by adopting the drift-diffusion model. The carrier mobilities are derived from the built-in parameter database of the Pics3d software; similarly, the recombination coefficients—encompassing the radiative recombination coefficient, Shockley-Read-Hall (SRH) recombination coefficient, and Auger recombination coefficient—are also extracted from the built-in parameters of the aforementioned database. Owing to the incorporation of the self-heating model in the simulation, all the aforementioned parameters exhibit temperature dependence.
For the simulation of the active region, a numerical method for solving the Schrödinger wave equation is employed. As the fundamental equation of quantum mechanics, the Schrödinger wave equation inherently embeds quantum effects (e.g., quantum transport and quantum tunneling) in its solutions, which can thus be quantitatively characterized through the equation's solving results.
This is not a response. To state that the parameters are those of PICS3D is not a response and tells nothing.
Overall, I see very minor if no effect of temperature. Compare the old and new Fig.3 at 80C.
Solving Schrödinger does not mean that the transport includes quantum effects. Are both 2D and 3D carriers and their interactions via capture times included? Is capture heating included?
2) No detail of the optical model is provided. On could infer that an effective index method is applied, which contradict the pretended capabilities of the model to treat mode divergence for which the extendend cavity is meant and diffraction losses due to the oxide aperture.
Our response:The simulation process adopts the effective refractive index model.
Of course, as I had correctly guessed. So all the critics about this are still valid and not replied.
Additionally, the reply proves that thermal lensing is not included, because, even in the Effective Index Method, it would provide a radially varying effective index, and not a stepwise, and the one provided in the table.
3) No thermal effect is included beside ambient temperature. The temperature profile has a strong impact of mode shapes, losses and wavelengths, and, consequently, on the SMSR.
Our response:To account for the influence of thermal effects, the author re-simulated the designed structure using the self-heating model and re-interpreted the simulation results.Self-heating model is used to improve the accuracy of simulations. The thermal conductivity is set to 20, and the bandgap, refractive index and recombination coefficients are set to be temperature dependent.
As said before, it does not seems the temperature is correctly included, if ever.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report (Previous Reviewer 3)
Comments and Suggestions for AuthorsThe revised manuscript does not adequately resolve my concerns, as detailed below:
- Lack of Literature Comparison: The authors did not sufficiently address Comment 1. The revised manuscript still lacks a concrete comparison with existing literature, particularly in clarifying how the proposed design differs from or advances beyond prior work.
- Undefined Traditional Structure: The traditional VCSEL structure used as a baseline is not clearly described, making it difficult for readers to interpret the reported performance differences. In addition, the standing-wave distribution of the traditional structure should also be included in Fig. 2 for proper comparison.
- Missing Electrical and Thermal Discussion: The revised manuscript does not discuss electrical or thermal characteristics, nor does it compare these properties with previous studies as I mentioned in the previous review comment 3. Since electrical resistance, voltage behavior, and thermal effects critically impact VCSEL performance, these aspects should be explicitly analyzed.
- Spectral Data Concerns: The measured spectra should be included in the manuscript, as there appears to be sufficient space to present them. Furthermore, the spectra provided in the response exhibit unrealistically low noise and strongly resemble simulated results (e.g., from PICS3D) rather than real measurements. Typical VCSEL spectra should show two closely spaced LP11-related or LP21 peaks, which are absent here. Additionally, the mode labels (PL01, PL11, PL12) are incorrect and should follow the standard LP mode notation.
In view of the above issues, I believe the manuscript still requires substantial revision before it can be considered for publication.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 3 Report (New Reviewer)
Comments and Suggestions for AuthorsThis paper provides a detailed numerical analysis of a method for improving SMSR by introducing multiple selective oxidation layers into an extended-cavity VCSEL.
The reported conditions are considered to be an effective method for improving SMSR.
However, additional content is required regarding the following points.
1) Line 104
A 20 nm-thick graded layer is added between the oxide confinement layer (Al₀.₉₈Ga₀.₀₂As) and the high-refractive-index DBR layer (Al₀.₂₂Ga₀.₇₈As). With this structure, wouldn't a part of the graded composition layer also be oxidized during the selective oxidation process, thereby preventing the thickness of the 30 nm-thick Al₀.₉₈Ga₀.₀₂As oxide layer from being maintained? Does the simulation assume that only the 30 nm portion is oxidized?
2) Also, when using a multilayer selective oxidation layer, would slight changes in film thickness during selective oxidation impart stress to nearby selective oxidation layers, resulting in changes in the selective oxidation rate? (In crystals, even 1% strain can significantly affect physical properties.) As a result, how can the selective oxidation width of multiple selective oxidation layers be maintained at the same width?
3) Line 163
Regarding the decrease in current injection efficiency due to the introduction of an oxide layer, When an oxide layer is introduced compared to when there is no oxide layer, the current (carrier) injection ratio to a specific region is greatly improved. However, even if the total number of oxide layers is increased from one to two, there is probably little change in the current injection range. However, in detail, in Figure 4, the carrier density in the aperture range increases. The reason for this needs to be discussed additionaly in more detail.
4) Regarding the numerical simulation method
Detailed information such as the software and the conditions applied to the simulation (this will be a multi-physics analysis, so what analytical methods and theoretical formulas were applied to the various physical elements?) must be provided.
Related these information, in small device structures, the generated heat distribution and the resulting temperature distribution will affect the SMSR through the thermal lens effect. In other words, has temperature distribution analysis been performed in the simulation?
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report (Previous Reviewer 3)
Comments and Suggestions for AuthorsAfter checking the revised manuscript, I think the most important thing to improve this manuscript is to emphasize this study is a pure simulated work. The authors should clearly announce it in “abstract”, “introduction”, and “conclusion”, and state that the corresponding experiment will be carried out in the near future.
Author Response
Dear Editor,
Thank you very much for the valuable comments provided by the three experts in the previous submission round. The comments and suggestions are all valuable and helpful for revising and improving our paper. We have studied the comments carefully and have made corrections which we hope will meet with approval.
The main corrections in the paper and our responses to the Reviewers’ comments are as follows:
Comment : After checking the revised manuscript, I think the most important thing to improve this manuscript is to emphasize this study is a pure simulated work. The authors should clearly announce it in “abstract”, “introduction”, and “conclusion”, and state that the corresponding experiment will be carried out in the near future.
Our response:Thank you for your valuable comments. We have made the corresponding revisions, and the modified parts have been specially marked.The revised manuscript is attached.
Thanks a lot again for your kind help and the Reviewers’ important comments. We have tried our best to improve the manuscript and made some changes in the revised manuscript . If there are any other questions, please inform us by email, we would be very grateful.
Thank you and best regards.
Yours sincerely,
Corresponding author: Zhi Gang Jia
E-mail: jiazhigang@tyut.edu.cn
Author Response File: Author Response.pdf
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis is a simulation paper developed within the PICS3D commercial software. The topic addresses a small niche of VCSEL applications: pumping the Rb line at 795nm. It targets the required specs, namely high Single Mode (SM) output power at 80 degrees Celsius.
So far, so good. However, the way the problem is addressed does not meet the requirements of a journal paper, for the reasons listed below:
1) There is no detail on the parameters used in the simulations. A very long list would be needed, including the electrical transport parameters, because Fig.5-6 provides such features. From Fig.5, it is clear that no quantum transport is included in the QWs, which is quite bad.
2) No detail of the optical model is provided. One could infer that an effective index method is being applied, which contradicts the model's purported ability to account for mode divergence, for which the extended cavity is intended, and for diffraction losses due to the oxide aperture.
3) No thermal effect is included besides ambient temperature. The temperature profile has a strong impact of mode shapes, losses and wavelengths, and, consequently, on the SMSR.
Author Response
Please see the attachment. Thank you.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors- "It outperforms edge-emitting lasers in terms of single-mode operation" - strange claim, please avoid such vague claims. Single mode edge emitters exist. What does "outperform" means in this context?
2. "In 2017, Ricardo Rosales et al 52 [11]demonstrated a 980 nm VCSEL
53 with an oxide aperture of 1.5 μm. At room temperature, its SMSR reached 49 dB, but the
54 maximum output power was only 3 mW. "
While referencing papers that support your claim it is better to focus on relevant papers, and not just random paper on this topic. There are thousands of papers about single mode VCSELs with small apertures. Why take one from 2017? Is it the only one? Or does this paper contain something special that you want to point out? Here is a paper from 2002 on this subject https://ieeexplore.ieee.org/abstract/document/1088073/
There are more and that are more relevant, more cited and older than a random paper from 2017
3. "To address these issues caused by small apertures, the cavity extension technology was proposed. In 2023, Meng Xun et al[12] 57 inves58 tigated a 795 nm extended-cavity VCSEL; at a current of 6.7 mA, its SMSR reached 31.5
59 dB."
Not extended cavity VCSELs were designed to "address the issues caused by small apertures in single mode VCSELs". It is the other way around. At first the VCSELs had larger cavities. But then the cavity length was reduced to enable high-speed operation.
The authors should not randomly cite random papers and randomly make random claims.
This is actually a second cavity not extended cavity (because the VCSEL already has a cavity and it is not "extended"). Very similar to work "Single-Mode Vertical Cavity Surface Emitting Laser
via Oxide-Aperture-Engineering of Leakage of High-Order Transverse Modes" with two cavities that is not cited https://ieeexplore.ieee.org/abstract/document/6934972
4. "On the other hand, the multi-oxide-layer is an effective method to enhance
66 the output power of VCSELs. " This is not true.
"The multi-oxide-layer can effectively restrict the electrical
67 injection path, increase the carrier concentration and carrier injection efficiency in the ac68 tive region" this it not true for all, or even for most VCSEL designs
5. "by introducing the multi-oxidation layer into the extended-cavity VCSEL"
Studied by multiple research groups already. I dont have time to find THE paper on this topic where different combinations of top, bottom and both side apertures are studied, but similar configuration is published e.g. in Chalmers university "High-Speed VCSELs With Strong Confinement of Optical Fields and Carriers"
6. The authors did not demonstrate that the software PICS3D correctly predicts SMSR.
One cannot write a paper based on just taking a random software, random VCSEL design, predict a higher SMSR and go home. One can write a software that will predict 100 dB SMSR, does it mean that it is correct?
I would understand if the authors demonstrated that in a different design this software predicted the SMSR well. But it is not mentioned and not demonstrated.
Does the software include joule heating or thermal lensing that are known to inluence the mode confinement? Thermal lensing is not mentioned once.
In a paper about SMSR , not a single spectra is shown.
Sadly, i would reccomend to reject this paper.
The work that the authors are doing is important and I think that this group of scientists will definately show more great results in the future. But it is important that publications add value to the scientific community and inform others about something important and new.
But in this work there is nothing new.
I highly reccomend the authors to critically review their work and make sure that it is actually saying something and not just shows "some" simulations with "some" software.
Author Response
Please see the attachment. Thank you.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript, entitled, “High-power single-mode multi-oxide-layer extended-cavity 795 nm vertical-cavity surface-emitting Laser”, authored by Zhu shi, et al. reports the impact of extended cavities and carrier-induced mode changes, which is potentially valuable, but several aspects require clearer explanation and additional discussion:
- The manuscript focuses on the influence of extended cavities and carriers on mode behavior. Several recent studies have reported related work, such as Nat. Commun. 15, 1105 (2024) and Sci. Rep. 15, 32037 (2025). Discussing these studies would help clarify the motivation of the present work. However, the current description of the design concept is insufficient. It is recommended that the authors provide a comparison with existing literature and more clearly articulate the design rationale.
- In the Materials and Methods section, the authors should provide a clearer explanation of the advantages of the extended cavity in the design. It is recommended to include standing wave patterns such as P1N1 and P12N1 in Fig. 2, which would help readers better understand the design differences among these structures.
- This study focuses on the characteristics at 80 °C, but the reason for selecting this temperature is not explained. A clearer justification should be provided in the Results section. Furthermore, it is unclear whether self-heating effects were considered in the simulations shown in Table 1 and Fig. 1, as no thermal roll-over appears to be observed. While the introduction of oxide layers can positively influence optical properties, it may degrade electrical characteristics such as voltage and resistance, which is not discussed. It is recommended to include a discussion of voltage and resistance, and relevant previous works on the impact of the number of oxide layers. (e.g ISLC, Potsdam, Germany, 1–2 (2021) and J. Quantum Electron. 61, 5 (2025)) These additions would help provide a more complete picture of the advantages of extended cavity designs, the effect of the number of oxide layers on device performance, and the mode behavior under different structural conditions.
- In the discussion of SMSR, it is customary to include spectral plots. The authors are encouraged to provide spectra under operating current for different structural conditions, which would more completely illustrate the mode characteristics.
Author Response
Please see the attachment. Thank you.
Author Response File: Author Response.pdf
