Transmission and Generation of Orbital ANGULAR Momentum Modes in Optical Fibers

Round 1

Reviewer 1 Report

  In this study, a detailed and thorough review on transmission and generation of OAM modes in various kinds of optical fibers is provided. Moreover, the presented manuscript is well organized and well written with enough qualities on both the technique and the English, contents of which would be hopeful and interesting to those studying and working in the same filed of the students and researchers. Therefore this paper can be recommended for publication provided the following minor issues are addressed in its final version.

1.  Between the line 264 and 265, in the sentence  .... an NC-RCF (Fig. 10(b)) was proposed originate from RC-PCF (Fig. 10(c))……

There may exist a typo in the above. Sounds like that the “Fig. 10(b)” should be replaced by “Fig. 10(c)” each other. Please to make sure it.

2.   It is essential to remind the authors that a more comprehensive review on HLPG-based OAM generators have already been given by other authors, which can be found in the paper listed below. Therefore, in section 5 of this manuscript, it would be better for the authors to add a simple comment (mention) and the corresponding citation on the below paper.

Zhao, and H. Li, “Advances on mode-coupling theories, fabrication techniques, and applications of the helical long-period fiber gratings: a review,” Photonics, Vol. 8, No. 4, 106 (2021).

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The article “Transmission and generation of orbital angular momentum modes in optical fibers” submitted by Z. Wang et al. provides a comprehensive review of the most important results and methods presented in the last decade for the generation and propagation of optical vortices in special optical fibers. After a brief introduction to optical angular momentum and its applications, the authors consider different aspects regarding OAM mode properties, isolation, and losses, focusing on the most important types of fibers, such as step-index fibers, ring-core fibers, air-core fibers, photonic crystal fibers, multi-core fibers. The subject is well treated and presented, referring properly to the most important literature in the field. In the following, a list of points is reported that should be addressed in order to further improve the paper and make it acceptable for publication:

• In the introduction, when listing the methods for OAM mode generation, some of the most employed methods are missing, in particular: log-pol mapping [see for instance G. Ruffato, et al., Opt. Express 25 (7), 7859-7868 (2017) – W. Li, et al., Opt. Express  27 ( 4), 3920-3934 (2019)] and multi-plane light conversion [see N. K. Fontaine, et al., Nat. Comm. 10, 1865 (2019)]
• In the first paragraph of the introduction, when citing the several applications of OAM, at least a reference should be added referring to high-dimensional cryptography, see for instance M. Mirhosseini, et al., New J. Phys. 17 033033 (2015)
• In section 2.1, when discussing the importance of moving from a circular-core to a ring-core profile, the condition that the effective refractive index separation should be greater than 10^-4 is not reported. This criterion is mentioned later in the manuscript. However, it should be stressed also here in order to make clearer the order of magnitude of the sought isolation between modes.
• It seems that a few acronyms are not explained in the text, in particular HOMG (line 123) and AH-RCF (line 162, we guess standing for air holed ring core fiber), and LPFG (section 5, line 403, caption Fig. 16).
• In section 2.2, when referring to the unexpected stability of higher-order OAM modes, the authors could mention the reason described in the paper ref [30], which is explained considering the angular components of fiber perturbations and their role in promoting the coupling between near-degenerate OAM modes inside the same group.
• Please check the spelling throughout the manuscript, there are a few typos, e.g. ‘perform’ instead of ‘preform’ in line 305
• Caption in Fig. 14. r_1 is repeated twice. I suppose r_2 should be used in place of the second r_1.
• Commercial fibers are considered in section 2.1 referring specifically to step-index fibers. Due to the widespread importance of graded-index fibers, also the propagation of OAM modes along this fiber type could be considered, see for instance S. Chen and J. Wang, Scientific Reports volume 7, Article number: 3990 (2017), and W. Zhou, et al., 2019 Optical Fiber Communications Conference and Exhibition (OFC) https://ieeexplore.ieee.org/document/8696359. In addition, the design of few-mode fiber with inverse-parabolic graded-index profile has not been considered, see for instance the paper B. Ung, et al., Opt. Express 22 ( 15), 18044-18055 (2014)

Author Response

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Reviewer 3 Report

The manuscript describes the literature review of OAM beam propagation of light in optical fibers. I have minor suggestions:

The author needs to provide a comparative table about OAM propagation in fiber and their applications which is very importanr.

Author Response

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Round 2

Reviewer 2 Report

The authors have correctly addressed all the points raised during the review and the manuscript has been properly amended. The paper can be accepted for publication in the present version.