Design and Performance Analysis of Hybrid Multidimensional OAM-DM-WDM-OFDM-PON System with High-Capacity and Long-Distance Transmission

Round 1

Reviewer 1 Report

In reviewer’s point of view, this paper introduces a multidimensional passive optical network (PON) with hybridize OAM division multiplexing (OADM) based on wavelength division multiplexing (WDM) and orthogonal frequency division multiplexing (OFDM). This OADM-WDM-OFDM-PON system is successfully transmitted in 80 km multi-mode fiber with low crosstalk. Besides, QPSK, OOK, and OFDM modulation are utilized at this novel hybrid system. Compared with QPSK and OOK, OFDM is preferable for improving the transmission capacity. The manuscript needs to be further refined. There are some issues that need to be resolved, which are listed in the following:

1.       In the third paragraph of section 1, the introduction of the previous research is lengthy, please reduce the length appropriately. At line 77, the introduction of this work and the experiment result should be arranged at the last paragraph of the section 1. The fourth paragraph is redundant. The whole introduction of this paper should be reorganized, it should include the background, the research status, and the innovations of this work.

2.       At figure 2(a), the distance of the multi-mode fiber (MMF) is labeled as 5-100 km, but at line 145, the distance of the MMF is mentioned as 10-80 km. Why the distance is different?

3.       What’s the meaning of the line 147? Why the mode crosstalk can be ignored?

4.       At line 160, “the LG mode generation method is depicted in figure 2b”, could you please give the specific method or the formulation of the LG mode generation?

5.       In section 4, please label the position of FEC threshold at the figure.

6.       Is this work simulated or experimental? Please indicate in the article.

7.       In this work, only two OAM modes is utilized in this system. Can more OAM modes be used in this PON system to increase the capacity? If the system can only comprise two OAM modes, then how can it have large capacity? If the system can comprise more OAM modes, then how’s the performance of the BER, is the 3 or 4 multiplexed OAM modes better than 2 modes or single mode system (following the rule at figure 8a)?

8.       Also, only two wavelengths are demonstrated in the results, how’s the BER performance of more wavelengths, dose it obeys the rule shown at figure 9?

9.       Format and grammar problems:

(1)    At line 91, the font format of the number “1” is wrong.

(2)    At line 94 and 107, the grammar is wrong.

(3)    At line 111, the sentence is too long to understand, please cut the long sentence into some short sentence for understanding.

(4)    At line 304, the words “proposed” and “demonstrated” are repeated.

(5)    The whole figures in the article are vague, please replace it with high-definition pictures.

(6)    Please take care of the grammar and the expression. Checking over the whole article.

Author Response

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Reviewer 2 Report

Combining OAM division multiplexing (OADM) based on wavelength division multiplexing (WDM) and orthogonal frequency division multiplexing (OFDM), the authors propose a multi-dimensional OADM-WDM-OFDM-PON system. The architecture of the proposed hybrid OADM-WDM-OFDM-PON system is introduced in detail and the corresponding performance of the system is analyzed by simulation. This work provides a reasonable solution for large-capacity PON architecture and enriches the research of OAM optical fiber communication. However, there are sill a few problem that could be improved. The detailed comments are as follows.

 

1.      In the first paragraph of the first section, the advantage of the PON system that the NG-PON system has a large capacity is first mentioned. Then, another point of view that the NG-PON faces significant challenges to provide more transmission capacity data is put forward. The logic of these two sentences conflicts, which cannot reflect the necessity of the innovation proposed in this paper. It is suggested to modify this paragraph in order to more clearly reflect the necessity of this article's innovation.

2.      It is suggested to add references on the application and technical challenges of OAM in the field of free-space optical communication and optical fiber communication, e.g., "Orbital angular momentum waves: generation, detection and emerging applications ".

3.      It is suggested that the contributions of this article in the third paragraph of section I are divided into different points and numbered respectively so that readers can more clearly understand the contributions of this article.

4.      It is suggested that the introduction of the Laguerre-Gaussian mode in Section II of the paper should be abbreviated, and the related reference of the OADM-WDM-OFDM-PON system transmitter "A 2-D FFT-based transceiver architecture for OAM-OFDM systems with UCA antennas " should be introduced.

5.      It is suggested to separate the captions of Figure 2 and Figure 3 in the same sentence in the third subsection of section II.

Author Response

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Reviewer 3 Report

General comments:

The presented paper was devoted to the issues related to the use of the OAM technique in optical transmission via PON. Solutions well known from the techniques used to carry radio signals over optical fiber links have been used. A review of the state-of-the-art in this field has been made, although it is difficult to find any references to the cited articles later in this paper. In general, the research was conducted correctly, but the description of the research results should be slightly improved and extended in order to improve the quality of the paper.

Detailed comments:

The paper was written in a concise and legible manner, but requires a few corrections and extensions:

11.  The use of the OADM (OAM division multiplexing) abbreviation is unfortunate due to the strong similarity to the term OADM (optical add-drop multiplexer). In several places in the paper (e.g. Fig. 8) the abbreviation OAM-DM was used, which seems to be a better and unambiguous definition.

22.   The testbed is not clearly defined. It is not known whether the tests were performed with the use of a simulator or with the use of optical physical equipment. Maybe the environment was mixed? It should be carefully described and in the case of the hardware part it is worth putting a photo.

33.   Equations (1)-(3) contain variables that are not described in the text of the paper.

44.  Note - the omega 0 variable has two meanings. The radius of the mode field (formula (3)) should be marked with the symbol w0, and the angular frequency (formula (6)) with the omega 0. Please arrange it.

55. Scheme from Fig. 2 (a) should be described in more detail, e.g. how optical channels are separated at the receiver site (spatial demultiplexing combined with power division in splitters).

66. Two different optical fibers in two directions were used, which contradicts the assumptions of PON. Will the system work when we use a classic PON with splitters and one fiber per OLT port? This should be clarified.

77. Please specify the standard of the SMF fiber (ITU-T G.65x) and define the modal dispersion of the MMF fiber used. There is a need to discuss the influence of modal and chromatic dispersion on transmitted signals, especially OAM.

88. Figure 3 - the units of electric field intensity are not exact (comparison of (a, b) and (c, d)). This should be unified.

99. Reviewer suggests that A and B (Fig. 3 and text below) be defined e.g. as "optical zero vortex radius", which suggests a nulled mode part of the OAM region.

110.  For clarity, the wavelength range in Figures 4 (d) and 4 (e) should be the same.

111.  In the text, the stream speed is indicated as 10Gbps (line 174), and in the Table 1 it is 20Gbps. This should be sorted out.

112.  What does the term "and 64 cyclic prefixes" (line 178) mean? I guess it should be "64 cyclic prefix points", which would be in line with Table 1.

113. The given linewidth of the laser is 10 MHz (line 184), and in Table 1 we have the ideal, i.e. 0 MHz. Need correction.

114.  In the text and in Table 1, please replace the sign "u" with the Greek "mu", which is supposed to mean 10^-6.

115. I don't see a difference between the constellations (a) and (b) in Figure 6, except that the bitmaps differ in quality (different compression).

116. The discussion of the obtained results should be significantly extended, with an indication of the increase in the efficiency of the transmission system with the use of OAM. In summary, only the advantages of OFDM in combination with 4-order band modulation, which is the norm in RoF (BBoF) systems, are outlined. During the discussion of the results, the OAM technique was practically omitted. Please take this into account.

Summary:

The results of the experiment presented in the paper are not very spectacular, but they show a certain direction in the development of future passive networks. The presented description of analyzes and experiments, after corrections and extensions, will be a good contribution to the knowledge of digital transmission using the OAM technique in multimode optical fibers.

Author Response

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Round 2

Reviewer 1 Report

Revise of Photonics-1762565

Most of the problems were answered in the response. However, there still have some problems that need to be modified before the acceptance of this manuscript.

 

1.     At figure 3, what’s the meaning of the colorbar? Please explain it at the article and indicate it at the figure. If it represents the intensity of the Laguerre-Gaussian light, the unit is wrong. Besides, the “X” represents the azimuthal index, the unit of the X at figure 3 is wrong.

2.     At line 160, “X and Y polarization”, the format of “X” and “Y” should be italic “x” “y”, please revised.

3.     At line 250-252, “...its performance is better than single mode system over long distance...”, this sentence is inappropriate by observing the whole length from 10 km to 70 km. Please revise or delete it.

4.     At line 280, the result of figure 9 “And the performance of 4 wavelengths system is superior to the 2 wavelengths system.” is inappropriate by observing the whole length, this sentence should be deleted.

5.     At line 284, “the BER performance of the two systems is getting worse.”, since figure 9 includes three systems, which two specific systems are these “two systems”?

6.     At line 307-309, “..., the communication capacity of the system is significantly improved.”. Since this sentence is at “Conclusion” part, please give the specific results at this section. 

7.     Please check the format and the grammar of this article carefully.

 

Author Response

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Reviewer 3 Report

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Comments for author File: Comments.pdf

Author Response

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