Improving the Resistance of AO-OFDM Signal to Fiber Four-Wave Mixing Effect Based on Insertion Guard Interval

Round 1

Reviewer 1 Report

Please find attached my comments and suggestions.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

In this manuscript, a method to suppress the impact of nonlinear effects on all optical orthogonal frequency division multiplexing (AO-OFDM) system is proposed by employing grouping and delaying. Through simulation analysis, the results show that the FWM and cross-phase modulation (XPM) effects are greatly suppressed after the AO-OFDM system inserts GI and is grouped and delayed. From my perspective, this manuscript needs to revision before it is published. The reviewer has the following concerns that need the authors to be addressed: 

1)      In Page 2, the authors state that “After the system inserts the GI, the duty cycle of the optical signal in each symbol period of each subcarrier will decrease, that is to say, this scheme will generate a ‘zeroed’ temporal”, the reviewer considers that the case is similar to the situation of return to zero (RZ) code. The linear (CD) and nonlinear (SPM/XPM/FWM) effects can be suppressed, especially for the XPM and FWM effect by employing grouping and delaying.

2)       In the manuscript, the optimal launching power of the transmission system has been not discussed. the reviewer suggests that the authors should consider wider launching power range including linear effect area and nonlinear effect area.

3)     With the increase of transmission distance, whether the system performance will be further degraded due to the influence of walk-off effect, which causes more frequency overlap.

4)    The relative parameters of the dispersion compensation fiber (DCF) should be listed, like the standard single mode fiber (SMF). It is well known that the DCF may have large nonlinear parameters. If the length of DCF is relative long, it has large nonlinear effect.

5)   In addition, the received power of the system should be listed.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

This paper proposed a method to suppress the impact of nonlinear effects on AO-OFDM system by inserting the guard interval. The authors also numerically proved that the FWM and XPM effects are greatly suppressed after the AO-OFDM system inserts GI. The reviewer believes there are some key issues to be addressed in this paper. After major revision, this paper should be published in Photonics.

To further improve the quality of this paper, here are my comments:

1.     The GI greatly takes up the data overhead, and the authors should clarify this in the paper

2.     Why GI is set to 0.33? The authors must explain the reason and the implementation process in the paper.

3.     There are many ways to eliminate the nonlinearity for the AO-OFDM system. The authors must pick out several relevant algorithms for comparison to further prove the innovation of the proposed method.  

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have presented a method to suppress the impact of nonlinear effects on all optical orthogonal frequency division multiplexing (AO-OFDM) system is proposed. After the system inserts the guard interval (GI), the duty cycle of the optical signal in each symbol period of each subcarrier will decrease, that is to say, this scheme will generate a ‘zeroed’ temporal. As a consequence, I think the paper can be accepted for publication after minor revision. Following are my observation:

[1]- The research still has problems in not accurately describing the design or adequate analysis with comparisons.

[2]- The graph's resolution and fonts could be better for the achieved important results in Figures (1) and (2).  

[3]- There is no specific comparison of the method with previously known research results. Some simulation or experiment results of comparison should be added. A comparison of the main findings is required. 

[4]- The author provides a noticeable number of works of literature to find research gaps and motivation, which is not convincing. Highlight the research gap and main contribution of this article to improve the resistance of the AO-OFDM system to the XPM, FWM, and all nonlinear effects, near (CD) and nonlinear (SPM/XPM/FWM) effects can be suppressed, especially for the XPM and FWM effect by employing grouping and delaying which is not addressed. And demonstrate of the FWM effect and the XPM effect are more suppressed after the subcarriers of the AO-OFDM system and mathematical. 

[5]- Evaluate and investigate the closed-form expression of BER and found that the difference in BER performance among users decreases with the increase in modulation order at the expense of higher power consumption.

[6]- Provide the impact of launch power optimization and the calculation of the received power of the system should be mentioned and transceiver noise transceiver for signal-to-noise ratio (SNR) on the performance of DWDM transmission systems that are affected by fiber nonlinearity. 

[7]- Please add a new section before the conclusion called “Future works,” where should be highlighted the potential values of the proposed architecture. In addition, describe what are planning to do as future works to improve and the extend solution considering the suggested reference.

[8]- The paper needs proofread and restructured by an English native person.

[9]- In experiments, some other methods should be compared to prove the effectiveness of the proposed method. And more simulations are encouraged to be performed. The current experimental results are difficult to support the conclusion.

[10]- The discussion on the obtained results needs to be increased for a better understanding of the reader about the significance of utilization of the proposed method.

[11]- Limitations and future research directions should be given. 

*My recommendation: Accept after a minor revision

Author Response

Response to Reviewer 1 Comments

The authors have presented a method to suppress the impact of nonlinear effects on all optical orthogonal frequency division multiplexing (AO-OFDM) system is proposed. After the system inserts the guard interval (GI), the duty cycle of the optical signal in each symbol period of each subcarrier will decrease, that is to say, this scheme will generate a ‘zeroed’ temporal. As a consequence, I think the paper can be accepted for publication after minor revision. Following are my observation:

Response: Thank you very much for reviewing our submitted manuscript, we have made extensive revisions to the article based on your comments.

Point 1: The research still has problems in not accurately describing the design or adequate analysis with comparisons.

Response 1: I would like to sincerely apologize for our inadequate description. We made revisions to the manuscript

Point 2: The graph's resolution and fonts could be better for the achieved important results in Figures (1) and (2).

Response 2: Thank you for your warm suggestion. In the newly submitted manuscript, we have made modifications to Figures 1 and 2.

Point 3: There is no specific comparison of the method with previously known research results. Some simulation or experiment results of comparison should be added. A comparison of the main findings is required.

Response 3: Thank you for your warm suggestion. In the manuscript, we compare our proposed scheme with DBP, a classical nonlinear compensation algorithm, and study the suppression of FWM effect by the two schemes under the condition of different number of subcarriers and different transmission distances.

Point 4: The author provides a noticeable number of works of literature to find research gaps and motivation, which is not convincing. Highlight the research gap and main contribution of this article to improve the resistance of the AO-OFDM system to the XPM, FWM, and all nonlinear effects, near (CD) and nonlinear (SPM/XPM/FWM) effects can be suppressed, especially for the XPM and FWM effect by employing grouping and delaying which is not addressed. And demonstrate of the FWM effect and the XPM effect are more suppressed after the subcarriers of the AO-OFDM system and mathematical.

Response 4: Thank you for your warm suggestion. We made revisions to the manuscript

Point 5 Evaluate and investigate the closed-form expression of BER and found that the difference in BER performance among users decreases with the increase in modulation order at the expense of higher power consumption.

Response 5: I would like to sincerely apologize for our inadequate description. Figure 7 in the manuscript shows that the proposed scheme does not come at the expense of increased power. At the power of the AO-OFDM system to achieve the best BER, the system inserted into the GI has a lower BER and can reach the FEC threshold at lower power. In a follow-up study, we will investigate the closed-form expression of the modulation format and transmit power on the system BER

Figure 7．The AO-OFDM system with 16 subcarriers using different FWM effect suppression methods changes BER with ROP after 40 km SMF transmission.

Point 6:  Provide the impact of launch power optimization and the calculation of the received power of the system should be mentioned and transceiver noise transceiver for signal-to-noise ratio (SNR) on the performance of DWDM transmission systems that are affected by fiber nonlinearity.

Response 6: Thank you for your warm suggestion. We have added a table on simulation parameters to the newly submitted manuscript.

Point 7: Please add a new section before the conclusion called “Future works,” where should be highlighted the potential values of the proposed architecture. In addition, describe what are planning to do as future works to improve and the extend solution considering the suggested reference.

Response 7: Thank you for your warm suggestion. "Future works" has been added to the newly submitted manuscript, thank you for your suggestions

Point 8:  The paper needs proofread and restructured by an English native person.

Response 8: Thank you for your warm suggestion. We have made extensive revisions to the results and discussion sections and added new conclusions in the newly submitted manuscript.

Point 9:  In experiments, some other methods should be compared to prove the effectiveness of the proposed method. And more simulations are encouraged to be performed. The current experimental results are difficult to support the conclusion.

Response 9: Thank you for your warm suggestion. But there is no experimental part in the manuscript we submitted, do you want to express the need to compare with other methods?

Point 10: The discussion on the obtained results needs to be increased for a better understanding of the reader about the significance of utilization of the proposed method.

Response 10: Thank you for your warm suggestion. We have added discussion of the results to the newly submitted manuscript

Point 11:  Limitations and future research directions should be given.

Response 11: Thank you for your warm suggestion. Limitations and future research has been added to the newly submitted manuscript

Author Response File: Author Response.docx