Atmospheric Turbulence Effects on the Performance of Orbital Angular Momentum Multiplexed Free-Space Optical Links Using Coherent Beam Combining

Round 1

Reviewer 1 Report

This manuscript shows the turbulence effects mitigation for OAM beams using coherent combination. Different with previous work, the transmitted OAM beam is generated via coherent combination, as controlling the phase of each beam in a laser array, then OAM beams are obtained in the far-field. This work is interesting and can be published in Photonics. However, improvements are still essential before the final publication.

 

1. The manuscript claims that coherent combination can mitigate turbulence effects on OAM beams. Despite lots of evaluations (e.g. OAM spectrum) are present, there is no comparation with common OAM beams. It will be more persuasive if the control-experiment can be carried out. The authors are encouraged to do additional simulations about turbulence effects on OAM beams generated from helical phase under the same condition.

 

2. The authors are encouraged to read a recent published review about turbulence effects on OAM beams and OAM distortion compensation.

[https://doi.org/10.1109/JLT.2022.3218828]

Surely, this review can also be mentioned in this manuscript to construct a sound reference system.

Author Response

Dear Reviewer:

We gratefully thank you for your insightful comments and constructive suggestions, which have significantly raised the quality of the manuscript and prompted us to improve the manuscript.

According to the Reviewer’ comments and suggestions, we address on the Reviewer’ comments point-by-point, and we have revised the manuscript carefully. We believe that the manuscript has now been seriously revised and hope the Reviewer will be satisfied with our response and revisions.

Please see the attachment.

Best regards,

Pei Ju, Wenhui Fan, Tongyi Zhang

May. 23rd, 2023

Author Response File: Author Response.pdf

Reviewer 2 Report

In this work, the authors used theoretical derivation and simulations to investigate the propagation characteristics of OAM beam from a coherent laser array with discrete vortex based on coherent beam combining. The literature review is comprehensive and the manuscript is well written. The topic is of interest to a wide audience in the field of optical communication. The reviewer recommends accepting the manuscript after considering the following comments:

1-The abstract should provide some results of the work, especially the results of comparison with Gaussian beam for short and long distances, and for weak and strong turbulence.

2-Write the references of the equation (1)

3-Using a laser array complicates the transmitter design and increases the cost. This point was not discussed in the document. The authors should discuss it.

4-What is the maximum and minimum length of the segment Dz?

4-In 251: " ...Gaussian vortex beam is smaller ". It should be " ..Gaussian vortex beam is smaller regardless of the link length. "

5-In line 252 "...more suitable for the long-distance, strong atmos..", it should be " more suitable for strong atmospheric turbulence conditions in long distance links "

Author Response

Dear Reviewer:

We gratefully thank you for your insightful comments and constructive suggestions, which have significantly raised the quality of the manuscript and prompted us to improve the manuscript.

According to the Reviewer’ comments and suggestions, we address on the Reviewer’ comments point-by-point, and we have revised the manuscript carefully. We believe that the manuscript has now been seriously revised and hope the Reviewer will be satisfied with our response and revisions.

Please see the attachment.

Best regards,

Pei Ju, Wenhui Fan, Tongyi Zhang

May. 23rd, 2023

Author Response File: Author Response.pdf

Reviewer 3 Report

1. The results, presented in the manuscript, are interesting and to some extent original, and thus can be the basis for a good paper. However, to our opinion, the manuscript has to be yet corrected and further elaborated before acceptance.

1.       We are doubtful regarding the current title of the manuscript and thus in the main idea of the work. The authors pretend that they have determined the way to mitigate the crosstalk between different vortex modes during their propagation through the turbulent atmosphere. We do not agree with such a statement. In reality the results of the manuscript deal with the relevant but different subject. The authors have analyzed and simulated the propagation of vortex beams through the turbulent atmosphere. They have compared two approaches to scalar vortex creation – the so-called Gaussian vortices and the synthesized vortices. To their opinion (and it may be true), the second approach provides more reliable and robust vortices. However, it is obviously a different result, which still does not directly prove the statement about the crosstalk mitigation.

On the page 5 we see the statement “To quantitatively characterize the crosstalk of vortex beam induced by atmospheric turbulence, we adopt the concept of orbital angular momentum (OAM) spectra, which is formed by the normalized energy weight of OAM mode Pl.”. This statement and the mutual relationships between the OAM spectrum and the crosstalk are still to be analyzed, proved and described mathematically.

2.       2. The authors are to outline what is really original in their work and how it relates to the other published papers. For instance, in the paper #42 in the list of References (Aksenov et al.) there was considered a very similar problem. Namely, the authors of the paper #42 were investigating the same object (the synthesized vortex), its propagation through the turbulent atmosphere was simulated with the use of the similar code and moreover, the results of analysis were presented in the sane terms of OASM spectrum evolution. So, seemingly, the manuscript under review has, in fact, repeated the same investigation scheme but for two types of vortices. Meanwhile, the team of Tomsk authors (paper #42) has published several other papers on the subject.

 English language of the manuscript is understandable but has be improved.

Author Response

Dear Reviewer:

We gratefully thank you for your insightful comments and constructive suggestions, which have significantly raised the quality of the manuscript and prompted us to improve the manuscript.

According to the Reviewer’ comments and suggestions, we address on the Reviewer’ comments point-by-point, and we have revised the manuscript carefully. We believe that the manuscript has now been seriously revised and hope the Reviewer will be satisfied with our response and revisions.

Please see the attachment.

Best regards,

Pei Ju, Wenhui Fan, Tongyi Zhang

May. 23rd, 2023

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

I am satisfied with the edit and explanations, the paper can be printed.