Experimental Study on 25 Gbps C-Band PON over up to 25 km SMF Using a 10G-Class DML + APD IM-DD System
Round 1
Reviewer 1 Report
This paper reports an experimental study on using 10G DMLs in C-band for implementing a 25G PON in C-band. Authors propose to use duobinary PAM2 or PAM4 in combination with electronic dispersion compensation to achieve transmission on 25 km SMF compensating for laser limited bandwidth, chirp and fiber chromatic dispersion.
Overall technical content of the paper is of medium level.
Motivations for the work are a bit weak: need of using C-band and EDC in PONs is limited in perspective, anyway, results could be useful in principle.
This Reviewer suggest to accept the paper after the following points are addressed.
- Typing and English use in the text should be checked in the whole paper, see for example lines 69-71, 92, 109, 115, 121, 130, 145 etc
- Conclusions could be surely improved
- Figs 3, 4, 5 are too small and not readable
- What laser is used?i Is it a commercial one? If yes, do it have already a bandwidth characterization? Why do you repeat it or how it compares?
- What is state of the art of DMLs in respect of the issues discussed in the paper? The Authors should discuss this in the Introduction. Larger bandwidth and lower chirp, for example, could reduce the need for high speed electronic compensation.
- Why signal eye diagrams are not reported at all? They should be shown
Author Response
Please see the attachment.
We wrote one reply letter to answer all the reviewer's comments. The sections with the subtitle "Answers to suggestions from Minie Li", "Answers to Reviewer #1", "Answers to Reviewer #2", and "Answers to Reviewer #3" are our answers to the Managing Editor, Reviewer 1, Reviewer 2, and Reviewer 3 respectively.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This is a very interesting article and represent a significant and original contribution to the subject. The main objectives of the article are clearly achieved, mainly: "optimizing DML operations and demonstrating the PAM-2 promising choice". Also, the experimental work is sound and the main goals are succesfuly achieved, mainly the measurements of: 1) the E/O frequency response of the 10G-class DML, 2) the frequency response of the DML based IM-DD system over a 25-118 km SMF, and 3) the maximum ODN loss (Max. ODN loss) that can be achieved using this system employing electrical duobinary (EDB), return-to-zero OOK
(NRZ-OOK, also termed as pulse amplitude modulation (PAM-2)), and PAM-4 signal, as a function of Extinction Ratio (ER, in a range from about 1 to 9 dB) at 25 Gbps over a up to 25 km SMF in C-band using Direct Detection. I have not significant comments about the experimental work however I have some comments which may be helpful to readers of this article.
Lines 52-54 it is stated that: "Anyway, in future PON standardization,
it may happen that the O-band window is full, so that it may become of interest to move again to the C-band." I believe that this is a key statement and it would be helpful to add a few words about it.
Lines 55-59 it is stated that: "In the high bit rate PON channel, severe 55
optoelectronic (O/E) bandwidth (BW) limitations and power fading due to CD are two of the main issues [19]. The main limitation of the DML based IM-DD system (compared to EML and MZM based) is the interaction induced by CD and the chirp of DML, which in general is quite complex to be studied, being a nonlinear impairment." A deeper explanation about the complexity of this nonlinear impairment would be very helpful to readers of this article even for the planing of future experiments.
Author Response
Please see the attachment.
We wrote one reply letter to answer all the reviewer's comments. The sections with the subtitle "Answers to suggestions from Minie Li", "Answers to Reviewer #1", "Answers to Reviewer #2", and "Answers to Reviewer #3" are our answers to the Managing Editor, Reviewer 1, Reviewer 2, and Reviewer 3 respectively.
Author Response File: Author Response.docx
Reviewer 3 Report
Non-technical comments
1) Please describe all the abbreviations in the abstract and the rest of manuscript. For instance, NRZ was not described in line 44.
2) I suggest authors to include additional words to keywords such as chromatic dispersion, power fading, dispersion penalty etc.
3) Please do proofreading to eliminate the typo mistakes in the manuscript. For instance in line 71, obtain is not written correctly or line 117, measured was wrongly written. Similar typo mistake in Line 51.
Technical comments
1) I suggest authors to provide the photograph of the experimental study if it is available.
2) Provide the unit of each variable line starting from 145.
3) In line 146, ω should be equivalent to 2Пf
4) C-band should be used because of two main advantages ; 1) optical losses are lower in C-Band 2) C-band provides lower optical non-linearities because of chromatic dispersion is non-zero comparing 1300 nm. It would be nice if the authors describe them in the manuscript.
5) I wonder why the normalized behaviour of DML for some bias currents are above zero in Figure 2? In addition, what is the purpose of the grey dashed line ?
6) It would be nice if the authors mention some possible solutions how to avoid chromatic dispersion in the C-Band. For instance SSB modulation or TDCM would be a possible solution in C Band. The authors only do experimental study of the fiber dispersion influence on the IM-DD link. It would be nice if they propose some solutions in C-Band Please look following papers or similar papers;
a) G. H. Smith, D. Novak and Z. Ahmed, "Overcoming chromatic-dispersion effects in fiber-wireless systems incorporating external modulators," in IEEE Transactions on Microwave Theory and Techniques, vol. 45, no. 8, pp. 1410-1415, Aug. 1997, doi: 10.1109/22.618444.
b) F. Falconi et al., "Wideband Single-Sideband Suppressed-Carrier Modulation with Silicon Photonics Optical Filters," 2019 International Topical Meeting on Microwave Photonics (MWP), 2019, pp. 1-4, doi: 10.1109/MWP.2019.8892250.
c) M. Ilgaz, K.V. Baliz, and B. Batagelj, “A Flexible Approach to Combating Chromatic Dispersion in a Centralized 5G Network,” in Opto-electronics Review, vol. 28, no. 1, pp.35-42, 2020.
d) P. C. Won, W. Zhang and J. A. R. Williams, "Self-Phase Modulation Dependent Dispersion Mitigation in High Power SSB and DSB + Dispersion Compensated Modulated Radio-over-Fiber Links," 2006 IEEE MTT-S International Microwave Symposium Digest, San Francisco, CA, 2006, pp. 1947-1950, DOI: 10.1109/MWSYM.2006.24981
Author Response
Please see the attachment.
We wrote one reply letter to answer all the reviewer's comments. The sections with the subtitle "Answers to suggestions from Minie Li", "Answers to Reviewer #1", "Answers to Reviewer #2", and "Answers to Reviewer #3" are our answers to the Managing Editor, Reviewer 1, Reviewer 2, and Reviewer 3 respectively.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 1 Report
The paper looks improved, all my comments almost addressed
Reviewer 3 Report
Thank for authors to revise the paper. I believe the paper can be published in the current format.
