A Pulse Shaping Based Optical Transmission System of 128QAM for DWDM with N × 904 Gbps
Round 1
Reviewer 1 Report
The manuscript “A Pulse Shaping-Based Optical Transmission of 128QAM for DWDM with Nx905 Gbps” by Guang Li and Jianqing Li deals with the design and simulation of a transmission system. This topic is interesting for publication in Applied Sciences.
However, the manuscript needs many improvements before recommendation for publication.
1. Introduction: The authors should give a better overview about the research area. Particularly, which are the parameters achieved so far in literature and which potential scaling to parameters is possible. The discussion of the current research should guide to the design parameters of the manuscript.
2. Citing own publications without relation to the manuscript is not acceptable. l. 47: “We have made gratifying achievements in the field of coherent optical communication”
3. l. 49: “By analyzing the latest research in this field” needs references.
4. Formulas and symbols: Starting from Section 2 a lot of formulas and symbols are introduced. The authors should reduce it to the minimum amount. It is not necessary to show every simple substitution. The authors should also rearrange the formulas to avoid violation of the page width (6, 8) and symbols in the text are not fitting. They seem to be superscript.
5. Figure 2 violates the page width.
6. The BER seems to be very high for the application as backbone transmission network. The authors should discuss this. What BER is necessary for certain applications?
7. l. 300 -330: Which benefit has the development of this relation? Is this somewhere used in the paper?
8. Figures 7 and 8: It is not surprising that for a 70 GHz input bandwidth a 70 GHz GOF works best.
9. Figures 11 and 12: These plots seem to be not correct. For 905 Gbps the BER is 0.01, which is the highest value. Also EVM is highest for 905 Gbps. Since 905 Gbps is one of the major claims of the manuscript plots 11 and 12 need further discussion.
10. “Author contributions” is missing.
11. The references do not meet the journal styleguides.
Author Response
Dear reviewer, I am very glad to receive your comments and suggestions. Your constructive suggestions can make our paper improve a lot. Academic research is not an easy task. Thank you very much for your recognition of our paper, thank you very much for your support for our academic research. Specific responses to your comments and suggestions can be found below.
1. Introduction: The authors should give a better overview about the research area. Particularly, which are the parameters achieved so far in literature and which potential scaling to parameters is possible. The discussion of the current research should guide to the design parameters of the manuscript.
Thank you for your suggestions. We have made some modifications in this revised manuscript, and we hope that can meet the requirements.
2. Citing own publications without relation to the manuscript is not acceptable. l. 47: “We have made gratifying achievements in the field of coherent optical communication”
Thank you for your suggestions. This sentence has been deleted and the latest research references for the coherent optical communication are cited in this revised manuscript.
3. 49: “By analyzing the latest research in this field” needs references.
Thank you for your suggestions. The relevant references have been cited in this revised manuscript.
4. Formulas and symbols: Starting from Section 2 a lot of formulas and symbols are introduced. The authors should reduce it to the minimum amount. It is not necessary to show every simple substitution. The authors should also rearrange the formulas to avoid violation of the page width (6, 8) and symbols in the text are not fitting. They seem to be superscript.
Thank you for your suggestions. In accordance with your suggestions, in this revised manuscript, we have deleted unnecessary formula derivation and rearranged the formulas .
5. Figure 2 violates the page width.
Yes, thanks. There was no such problem in the original WORD version submitted, but there was a problem after the PDF generated by the submission system. We have shortened the width of the Figure 2 in the revised manuscript.
6. The BER seems to be very high for the application as backbone transmission network. The authors should discuss this. What BER is necessary for certain applications?
BER is a very important index to measure the performance of a transmission system. In high-speed digital communications, the BER can be acceptable when it fall below the forward error correction threshold of 3.8×10−3, that is too say, -lg(BER)>2.42. These indicators are commonly used in high speed digital optical communication systems.
7. 300 -330: Which benefit has the development of this relation? Is this somewhere used in the paper?
From Figures 7 and 8, it can be seen that there is a certain mapping relationship between BER and EVM. We also demonstrate the relationship between BER and EVM from the mathematical point of view. Consequently, it can be illustrated the rationality of this arrangement.
8. Figures 7 and 8: It is not surprising that for a 70 GHz input bandwidth a 70 GHz GOF works best.
The transmission rate reach up to 900Gbps, the bandwidth of which is more than 70 GHz. In order to obtain a good BER, multiple times numerical simulations are employed. By adjusting the value of GOF and repeated numerical simulation, the appropriate value of GOF is found. And then, the GOF with bandwidth of 70 GHz is employed. Here, what we want to convey to the reader is that the filtering bandwidth of the GOF affects the bit error rate of the system. In order to obtain a good BER, we need to adopt suitable filtering bandwidth. Implementing pulse shaping through Gauss optical filtering is an innovation in this paper.
9. Figures 11 and 12: These plots seem to be not correct. For 905 Gbps the BER is 0.01, which is the highest value. Also EVM is highest for 905 Gbps. Since 905 Gbps is one of the major claims of the manuscript plots 11 and 12 need further discussion.
First of all, the ordinate name of Figure 11 is “- lg(BER)”, and abscissa name is the transmission rate;
Secondly, in the process of numerical simulation, with the increase of communication rate , the BER of the transmission will increase, that is too say, “- lg(BER)” will decrease, which conforms to the basic principle of optical fiber communication;
Thirdly, in the process of numerical simulation, with the increase of communication rate, the EVM of the transmission signals will increase, which conforms to the basic principle of digital communication.
Guang Li wrote the manuscript.
Jianqing Li reviewed the paper prior to submission.
Guang Li provided the concept and simulation design of the study.
Jianqing Li partially revised the paper.
All authors discussed the results, analyzed the data and commented on the manuscript.
(All the supplement information has been updated, please see the revised manuscript)
11. The references do not meet the journal styleguides.
The references have been revised, please see the revised manuscript or see below.
Naohiro, K.; Toshiaki, T.; Norio, C.; Hideo, A. A 25.78-Gbit/s × 4-ch Active Optical Cable with Ultra-compact Form Factor for High-density Optical Interconnects. Appl. Sci. 2018, 8.1, 137.
Khanna, G.; Rahman, T.; Man, E.; Riccardi, E.; Pagano, A.; Chiado, A.; et al. Single-Carrier 400G 64QAM and 128QAM DWDM Field Trial Transmission Over Metro Legacy Links. IEEE Photonic Tech. L. 2017, 29.2, 189-192.
Khanna, G.; Spinnler, B.; Calabrò, S.; Man, E.D.; Feiste, U.; Drenski, T.; Hanik, N. 400G Single Carrier Transmission in 50 GHz Grid Enabled by Adaptive Digital Pre-Distortion. Optical Fiber Communication Conference, 2016 Optical Society of America, pp. Th3A.3. [https://doi.org/10.1364/OFC.2016.Th3A.3]
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Amado, S. B.; Guiomar, F. P.; Muga, N. J.; Reis, J. D.; Pinto, A. N. Experimental Demonstration of the Parallel Split-Step Method in Ultra-Long-Haul 400G Transmission. European Conference on Optical Communication, 2015 IEEE, pp. Th.2.6.2. [DOI: 10.1109/ECOC.2015.7341897]
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Buchali, F.; Idler, W.; Schuh, K.; Brast, T.; Schmid, S.; Steffan, A.; et al. 1 Tb/s-4x343 Gb/s Subcarriers on 50GHz Grid- Transmission over 480 km SMF with 22 GHz Bandwidth Semiconductor Modulator. Optical Fiber Communications Conference & Exhibition, 2014 IEEE, pp. Th4F.2. [DOI: 10.1364/OFC.2014.Th4F.2]
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Li, G.; Li, J.Q.; Chen, G.J.; Huang, X.G. SOA-based AOWC of 128QAM Using Gaussian Pulse Shaping for Transmission System with 227 Gbps. Microw. Opt. Techn. Let. 2018, 60, 2204-2216.
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Cartledge, J.C.; Rolland, C.; Lemerle, S.; Solheim, A. Theoretical Performance of 10 Gbps Lightwave Systems Using A III-vsemiconductor Mach-zehnder Modulator. IEEE Photonic Tech. L. 1994, 6.2, 282-284.
Cartledge, J.C. Performance of 10 Gbps Lightwave Systems Based on Lithium Niobate Mach-Zehnder Modulators with Asymmetric Y-branch Waveguides. IEEE Photonic Tech. L. 1995, 7.9, 1090-1092.
Fatadin, I.; Savory, S.J.; Ives, D. Compensation of Quadrature Imbalance in An Optical QPSK Coherent Receiver. IEEE Photonic Tech. L. 2008, 20.20, 1733-1735.
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
1) The conclusion from equations 7 & 8, photonic carrier signal containing many photonic harmonic-waves with an angular frequency spacing of +/-nw0 is established in literature and does not require derivation. Suitable references can be quoted and the result established.
2) Why was a channel wavelength spacing of 0.7nm chosen? Does it depend on the characteristics of the fiber? More explanation on this would be useful, since the main emphasis on the paper is using a low channel spacing and increasing the capacity.
3) What are the properties of the GOF? More details regarding the implementation would be useful
4) Major overhaul of the English language writing is required.
Author Response
Dear reviewer, I am very glad to receive your comments and suggestions. Your constructive suggestions can make our paper improve a lot. Academic research is not an easy task. Thank you very much for your recognition of our paper, thank you very much for your support for our academic research. Specific responses to your comments and suggestions can be found below.
1) The conclusion from equations 7 & 8, photonic carrier signal containing many photonic harmonic-waves with an angular frequency spacing of +/-nw0 is established in literature and does not require derivation. Suitable references can be quoted and the result established.
Yes, you are right. The photonic carrier signal contains many photonic harmonic-waves, the principle of which can be explained by citing relevant references. In this revised manuscript, we have handled it in this way.
2) Why was a channel wavelength spacing of 0.7nm chosen? Does it depend on the characteristics of the fiber? More explanation on this would be useful, since the main emphasis on the paper is using a low channel spacing and increasing the capacity.
Thank you. It is a good question. In a DWDM system, the narrower bandwidth of a single channel, the more number of transmission channels can be achieved. In this system, In order to improve the transmission capacity, we employ high-speed modulation format and pulse shaping to increase the single channel rate and reduce its bandwidth. In this arrangement, after repeated numerical simulation analysis, it can be found that the bandwidth of the single channel with the transmission rate of 905 Gbps can be reduced to 70 GHz by Gaussian Optical Filtering.
3) What are the properties of the GOF? More details regarding the implementation would be useful.
The optical spectrum of the photonic carrier with 128QAM is close to the Gaussian function, the modulated photonic-carrier signal contains many photonic harmonic-waves, all the harmonic-wave carry the same modulation information. Consequently, we can obtain the central photonic harmonic-wave from the output of the coherent 128QAM photonic transmitter via an appropriate optical filtering, where the suitable filter is a Gaussian optical filter. The functional model of the optical filter can be described by:
Any of these harmonic components can be used to transmit and receive useful information. Just employ one of these harmonic components. That is to say, this arrangement can minimize the bandwidth occupied by a single channel.
In this paper, from numerical simulation and analysis, it can be found that the GOF is indeed effective for the transmission and reception.
4) Major overhaul of the English language writing is required.
The original manuscript has been sent to the professional language editing service “EditorBar” for a significant language improvement (Prior to submission of the manuscript, 2018-12-15) . Please see the certificate of language editing in the submission system. Moreover, this revised manuscript has been edited again from the the perspective of English grammar by a professor. Thank you very much for your recognition of our paper, thank you very much for your support for our academic research.
Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript written by Li proposed a filter based on a pulse shaping method and estimated the performance through numerical simulations. Although the impact and novelty of the work are modest, it still can be interesting to a certain group of researchers. In general, the paper is well written and have very good logic. Therefore, I recommend the publication of this manuscript.
Author Response
The manuscript written by Li proposed a filter based on a pulse shaping method and estimated the performance through numerical simulations. Although the impact and novelty of the work are modest, it still can be interesting to a certain group of researchers. In general, the paper is well written and have very good logic. Therefore, I recommend the publication of this manuscript.
Dear reviewer, I am very glad to receive your comments and suggestions. Your constructive suggestions can make our paper improve a lot. Academic research is not an easy task. Thank you very much for your recognition of our paper, thank you very much for your support for our academic research.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The response of the authors is not satisfactory.
Figures 11 and 12 are still not discussed.
Other discussions seem like textblocks, e.g. discussion of Fig. 7 and 8. Only BER and EVM is changed.
The section which derives equation 20 is already published in Ref.9. Also Figures 9, 10, 11 and 12.
The authors have to explain this.
Author Response
Dear reviewer, thank you very much for your recognition of our paper, and thank you very much for your support for our academic research. Academic research is not an easy task. Your constructive suggestions can make our paper improve a lot. Specific responses to your comments and suggestions can be found below. Moreover, the references are improved, please see this revised manuscript.
1. Figures 11 and 12 are still not discussed.
Thanks your suggestion. Specific responses to this comment can be found below, and these supplements have been marked in this revised manuscript with green.
BER is a very important index to measure the performance of a transmission system. According to the conventions of the communication industry, the BER can be acceptable when it fall below the forward error correction threshold of 3.8×10−3 (that is too say, -lg(BER)≥2.42) for a high-speed digital coherent optical communication system. From Fig. 11, it can be seen that when the transmission rate of a single wavelength for the DWDM system configures 904 Gbps, the BER is about 3.8×10−3; that is too say, when it is configured N×904 Gbps for the DWDM system, the transmission performance can be acceptable; meanwhile, the constellation-diagrams are very clear, that is too say, at the receiving terminal, the signals recover well and the distortion is not obvious. Consequently, from N×900 Gbps to N×904 Gbps, the transmission rate configuration for the DWDM system is reasonable, and it is also a good choice.
Fig. 11. The relation curve between BER and transmission rates with constellation-diagrams.
EVM is an index to measure the quality of modulated signal. It indicates the proximity between I/Q components and the ideal components when the receiver demodulates the signals; and the quality of EVM is related to the quality of the signal. In a high-speed digital optical communication, the EVM can be acceptable when it fall below 5%; and this indicator is commonly used in high speed coherent optical communication systems. From Fig. 12, it can be obtained that when the bit rate of a single wavelength for the DWDM system is 904 Gbps, the EVM is about 5%; that is too say, when it is configured as N×904 Gbps for the DWDM system, the transmission performance can be acceptable; Moreover, the constellation-diagrams are very clear, that is too say, at the receiving terminal, the signals recover well and the distortion is not obvious. Consequently, from N×900 Gbps to N×904 Gbps, the transmission rate configuration for the DWDM system is reasonable, and it is also a good choice.
Fig. 12. The relation curve between EVM and transmission rates with constellation-diagrams.
From Fig. 11 and Fig. 12, it can be seen that BER has a specific relationship with EVM in terms of the acceptability of transmission performance corresponding to the rate configuration. This further verifies the rationality of equation (20).
2. The section which derives equation 20 is already published in Ref.9. Also Figures 9, 10, 11 and 12.
Yes, it is a good question. In the major revision, the Ref. 9 is “Li, G.; Li, J.Q.; Chen, G.J.; Huang, X.G. SOA-based AOWC of 128QAM Using Gaussian Pulse Shaping for Transmission System with 227 Gbps. Microw. Opt. Techn. Let. 2018, 60, 2204-2216”. This is one of our previous research results, and the first author is me (Li, G.) and corresponding author is Jianqing Li (Li, J.Q.)
In our paper (Ref. 9.), we demonstrate an ultra-high-speed transmission system-based, all-optical wavelength conversion using Gaussian pulse shaping and 128 quadrature amplitude modulation. In this system, the modulated ultra-high-speed, photonic-carrier signals with the modulation format of 128 quadrature amplitude modulation are coupled with the outputs of the double pump lasers, and amplified by nonlinear, all-optical processing via a semiconductor optical amplifier. The transmission system with the wavelength conversion from 193.4 THz to 193.19 THz is then achieved. By the compensation of transmission impairments based on the digital signal processing algorithms, the single-carrier signals with the converted wavelength of 193.19 THz are transmitted over the standard single-mode fiber with the bit rate of 227 Gbps. In addition, the transmission performances influenced by the optical signal-to-noise ratio, injection current of the semiconductor optical amplifier, and the bandwidth of the Gaussian optical filter are analyzed. The relationship curves about bit error rate and error vector magnitude under the different conditions are given, and the relationship between bit error rate and error vector magnitude is demonstrated.
In order to make the reader understand the content of the paper more clearly and to further explain the rationality of our scheme design, we also discuss the relationship between BER and EVM for the ultra-high-speed transmission of DWDM in this paper, and obtain the same conclusion as “equation 20”. If it does not affect the overall structure of the paper, please keep this sentence. Thank you very much.
The one of the main innovations for “Ref. 9” is realized an all optical wavelength conversion (AOWC) from 193.4 THz to 193.19 THz. In our paper (Ref. 9), before wavelength conversion, the transmission rate of a single wavelength can be up to 905 Gbps; the rate after wavelength conversion is reduced sharply, however, the transmission of the converted wavelength can be up to 227 Gbps, which is a very rather gratifying result. In order to further verify the rationality of our design scheme, we compare the signal transmission rates of a single wavelength before and after wavelength conversion with EVM and BER in different situations, so that the pictures you mentioned are the same (transmission rate for a single wavelength in this paper;, transmission rate for a single wavelength in “Ref. 9” before wavelength conversion).
Considering the structural integrity, content coherence, analytical reasonableness and enlightenment to readers, we sincerely recommend retaining this part of the content; please do not change this part of the content. Thank you very much for your understanding and support.
Thank you very much for your recognition of our paper, thank you very much for your support for our academic research.
Best regards!
Corresponding author: Jianqing Li, Professor and Director; Email: jqli@must.edu.mo
First author: Guang Li; Email: 1709853gii30001@student.must.edu.mo;276563188@qq.com
Author Response File: Author Response.pdf
Reviewer 2 Report
The changes suggested have been done.
Author Response
1. The changes suggested have been done.
Dear reviewer, your constructive suggestions can make our paper improve a lot. Academic research is not an easy task. Thank you very much for your recognition of our paper, thank you very much for your support for our academic research.
Best regards!
Corresponding author: Jianqing Li, Professor and Director; Email: jqli@must.edu.mo
First author: Guang Li; Email: 1709853gii30001@student.must.edu.mo;276563188@qq.com
Author Response File: Author Response.pdf
