A Continuously Tunable and Filter-Less QPSK Modulated Millimeter-Wave Signal Generation with Frequency Quadrupling Just Based on an MZM

Round 1

Reviewer 1 Report

Literature Review needs to be extended in the introduction. It is very limited. More papers regarding RoF should be reviewed starting from (but not limited to)

 Neural Network DPD for Aggrandizing SM-VCSEL-SSMF-Based Radio over Fibre Link Performance. Photonics 2021, 8, 19. https://doi.org/10.3390/photonics8010019.

Experimental Demonstration and Performance Enhancement of 5G NR Multiband Radio over Fibre System Using Optimized Digital Predistortion. Appl. Sci. 2021, 11, 11624. https://doi.org/10.3390/app112411624.

An experimental study on digital predistortion for radio-over-fibre links. In Proceedings of the Asia Communications and Photonics Conference and Exhibition, Shanghai, China, 8–12 December 2010; pp. 126–127. https://doi.org/10.1109/acp.2010.5682803.

Delta-Sigma Modulation for Next Generation Fronthaul Interface. J. Lightwave Technol. 2018, 37, 2838–2850. https://doi.org/10.1109/jlt.2018.2872057.

Experimental evaluation of real-time sigma-delta radio over fiber system for fronthaul applications. Int. J. Microw. Wirel. Technol. 2021, 13, 756–765. https://doi.org/10.1017/S1759078720001282.

Digital Signal Processing for High-Speed Fiber-Wireless Convergence [Invited]. J. Opt. Commun. Netw. 2019, 11, A11–A19.

Direct digital predistortion technique for the compensation of laser chirp and fiber dispersion in long haul radio over fiber links. Opt. Quant Electron. 2019, 51, 205. https://doi.org/10.1007/s11082-019-1923-8.

Assessment of digital predistortion methods for DFB-SSMF radio-over-fiber links linearization. Microw. Opt. Technol. Lett. 2020, 62, 540–546. https://doi.org/10.1002/mop.32073.

 Nonlinearity mitigation using a machine learning detector based on k-nearest neighbors. IEEE Photonics Technol. Lett. 2016, 28, 2102–2105.

Digital Predistortion for Linearity Improvement of VCSEL-SSMF-Based Radio-Over-Fiber Links. IEEE Microw. Wirel. Compon. Lett. 2019, 29, 155–157. https://doi.org/10.1109/LMWC.2018.2889004.

 Demonstration of a hybrid optical fiber–wireless 5G fronthaul coexisting with end-to-end 4G networks. J. Opt. Commun. Netw. 2020, 12, 72–78.

Some background of this work in accordance with 5G should be given. 

The theoretical formulation is very limited discussed. 

The simulation setup needs to be explained with a hierarchy or pseudo code. Also, add a table of all the used components and their parameters. 

The critical discussion on the results and future work is missing. 

Results in terms of error vector magnitude and adjacent channel leakage ratio or Eye-Opening penalty for:

a. Varying link length

b. Changing RF input power

c. Received optical power

should be made in addition to the BER results. BER is related to EVM, however, in simulation, these performance metrics are easily integratable. BER alone is not enough. 

 

Author Response

Dear Editors and Reviewers,

Thank you for the email with reviewers’ comments and suggestions on our manuscript entitled “A continuously tunable and filter-less QPSK modulated millimeter-wave signal generation with frequency quadrupling just based on an MZM” with number of photonics-1792566. The comments and suggestions are of great help for our revision. We have studied the comment very carefully and done the corresponding revision on our manuscript. The point of response to the reviewers’ comment is also added in the revised manuscript. Hope that the revised manuscript could be qualified and re-considered for the publish of Photonics. The corresponding responses are listed as follows  in the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

 

General comments:

The presented paper is devoted to the issues related to the generation of modulated millimeter signals with the use of photonic devices. The presented state-of-the-art on the subject matter is very synthetic. It is worth expanding this part of the study so that the achievements based on the MZM are presented more clearly. 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. Throughout the text, replace "5/10 Gbaud/s" with "5/10 Gbaud"

22. What you mean in sentence: „Optical over millimeter wave communication …” – line 31?

33. A few abbreviations have not been explained - please organize it, e.g. BTB

44.  In sentence „symbol rate of 10 Gbit/s …” should be “symbol rate of 10 Gbaud …”

55.  Please specify more parameters of SMF used. I thing you mean ITU-T G.652D standard fiber.

66. Font is incorrect in math formulae embedded in the plain text. This should be corrected.

77.  Sentence: “… because the signal is more sensitive to the nonlinear effect as the symbol rate increased …” is one of the most important aspect of the research conducted. Please elaborate on it.

88. Sentence lines 165-166 – This issue should also be extended as chromatic dispersion is a key aspect regarding the relative delay of the second order sidebands used in the proposed method.

Summary:

The new solution presented in the paper is not very spectacular, but it certainly shows the right direction. This can be especially useful when we need to generate terahertz frequencies. The presented description of analyzes and experiments, after small corrections and extensions, will be a good contribution to the knowledge of microwave-photonic techniques.

 

Author Response

Dear Editors and Reviewers,

Thank you for the email with reviewers’ comments and suggestions on our manuscript entitled “A continuously tunable and filter-less QPSK modulated millimeter-wave signal generation with frequency quadrupling just based on an MZM” with number of photonics-1792566. The comments and suggestions are of great help for our revision. We have studied the comment very carefully and done the corresponding revision on our manuscript. The point of response to the reviewers’ comment is also added in the revised manuscript. Hope that the revised manuscript could be qualified and re-considered for the publish of Photonics. The corresponding responses are listed as follows  in the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

All comments addressed. The Paper can be published in the present form.