Electrically Tunable and Reconfigurable Topological Edge State Laser

Round 1

Reviewer 1 Report

The authors presented a complete work regarding the theoretical project, practical construction, quality check and experimental testing of an electrically tunable topological edge state laser with mainly 1-D structured active layer. 
Despite the draft does not contain strictly original argumentations, new concept ideas for projects on electro-optical devices and really novel technical methods on experimental measurements, the overall draft is well prepared, the several research steps are clearly presented and cover all of the usually required investigation stages, and the final resulting device appears to be something deservable to be shown in books devoted to electro-optical devices as a good example of both project and implementation works.

Therefore, I believe this manuscript to be publishable across the Optics scientific journal, prior some minor modifications required to enlight or better explain some important aspects they are related to.
Here follows a list of those minor corrections I suggest the authors to apply:

Line 40: please, correct "without analog in electronics"
Line 44: "It was also found" (add "that"?)
Line 91-92: Please, add a cartesian reference to both the 3D pictures.
Line 100-106: "In the explored topological configuration..... in the right."
    Please, add a special graph to provide the reader with a clear scheme of this assumption.
Line 137: what does it mean "with any non-zero gain"?
Line 152-154: "It is worthwhile to notice that..... point γ>6....with non-zero γ."; probably, this sentence must be fixed and some values are incorrectly reported.
    Maybe that value of 6 is a 0.6? And what about the last sentence? Is is rellay concluded, or did the authors mean "non-zero gamma values lower than 0.6"?
Line 211: "oddly localize mode profile on odd site with small gain " maybe localized?
Line 249-287: rather than putting all technical details in an experimental chapter (the 3rd), I would add a special Appendix with the samne content of that chapter, only confined at the end of the the draft.
Line 292-294: please, consider to better modulate these sentences in the conclusion chapter.
Line 296-297: I share this same curioisity with the authors; on the formal level, I suggest to recast this sentence in "Symmetric biasing and/or overall configurations will be considered in future works."

Author Response

Please see the attachment. 

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript proposes an electrically tunable and reconfigurable topological edge state laser. The proposed laser is realized in a one-dimensional complex Su-Schrieffer-Heeger chain in time-reversal configurations. The lasing is seen by the introduction of a defect site in the topological center. The manuscript also reports the potential use of the proposed laser in photonic applications. I have the following concerns and comments about the manuscript.

• There title of the paper should be corrected, the word states should be replaced with state.
• The definition of DOS should be included in the revised manuscript. The density of states (DOS) is essentially the number of different states at a particular energy level that electrons are allowed to occupy. In one dimension it has units of Energy^-1Length^-1. The units of energy band are also missing. These units should be included in Figure 2 for the clarity of the reader.
• The authors have stated that in this work they “employed the dimer chain containing gain and loss and an active, gain, defect to achieve a topological laser. In this context, a modified non-Hermitian SSH model is employed to study the density of state (DOS) of the SSH laser chain (see supplemental material for details)”. However, I didn’t find any supplemental material at the end of the manuscript.
• What is the reason that introduction of gain in the center defect, as shown in Fig.2 (b), leads to induced states in midgap while states on upper and lower groups are suppressed. The authors should provide a strong justification for this observation.
• The inset in Figure 3 is not mentioned in the caption.
• What is the reason that experimental demonstration of Non-Hermitian Topological Laser Chain is included in the Model section-2 and not in the Experimental section –(3) of the manuscript.
• In section 2.5 “Reconfiguration of Non-Hermitian Topological Laser Chain” the authors again refer to supplemental material but are not provided at the end of the manuscript.
• The authors have used the coupling coefficients (C₁ and C₂) in section 2.1. Non-Hermitian Topological Laser Chain but they explained it in the manuscript in section 3.3, where they mentioned that it was evaluated using COMSOL. What is the reason for this ?
• In Fig 7(a), the y-axis should have arbitrary units (a.u)
• The English language needs to be improved. There are a lot of typos in the manuscript. For example,. Page. 3. Line 116 the word “group” should be replaced with the word “grouped” etc. The authors should use the English editing service to improve the quality of the paper.

 

 

 

 

Author Response

Please see the attachment. 

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper reports an interesting and useful work. The manuscript is well structured and can be published after some revisions. The reviewer enjoyed reading this paper.

The manuscript has some weaknesses. Mentioned below aspects should be taken into consideration during the revision:

1. Conclusions:

The conclusions should be in a quantified form.

2. References:

I propose to add a new entries in the Introduction section regarding observation methods connected with fractography [I,II]. It may provide additional information for analysis in this and the future papers.

1. Macek, W. Fracture Surface Formation of Notched 2017A-T4 Aluminium Alloy under Bending Fatigue. International Journal of Fracture 2021, 1–17, doi:10.1007/S10704-021-00579-Y/FIGURES/16.
2. Feng, X.; Senin, N.; Su, R.; Ramasamy, S.; Leach, R. Optical Measurement of Surface Topographies with Transparent Coatings. Optics and Lasers in Engineering 2019, 121, 261–270, doi:10.1016/J.OPTLASENG.2019.04.018.

 

Author Response

1. Conclusions:

The conclusions should be in a quantified form.

Response 1: Thanks for the comment. The conclusion chapter has been modified as “We have demonstrated an electrically injected topological laser in an SSH chain with an active gain defect. The theoretical study of the SSH chain was conducted, phase transitions between the lasing of topological and bulk modes were observed. The lasing of the proposed topological laser system has been experimentally demonstrated with a lasing threshold of ~600mA. The reconfiguration of the system with a lossy defect topological laser is also investigated. The reconfigurability of the topological SSH chain, the lossy topological defect configuration serves as a potential novel platform for applications such as optical modulators and detectors, where the enhanced absorption is beneficial. Besides, symmetric biasing on the configurations will be considered in future works.’’.

2. References:

I propose to add a new entries in the Introduction section regarding observation methods connected with fractography [I,II]. It may provide additional information for analysis in this and the future papers.

1. Macek, W. Fracture Surface Formation of Notched 2017A-T4 Aluminium Alloy under Bending Fatigue. International Journal of Fracture 2021, 1–17, doi:10.1007/S10704-021-00579-Y/FIGURES/16.
2. Feng, X.; Senin, N.; Su, R.; Ramasamy, S.; Leach, R. Optical Measurement of Surface Topographies with Transparent Coatings. Optics and Lasers in Engineering 2019, 121, 261–270, doi:10.1016/J.OPTLASENG.2019.04.018.

Response 2: Thanks for the suggestion. This manuscript is not much relevant to fractography. I will consider referring to these two references in any relevant future work. 

Reviewer 4 Report

A very interesting article. In my opinion, the practical possibilities of the solution used should be indicated. The presented scientific solutions are at a good level. The presentation of the obtained results does not raise any objections. 

Author Response

Thank you for the review!

Round 2

Reviewer 2 Report

The authors have made all the suggested changes/improvements in the revised manuscript.