Photonic Integrated Circuits for Passive Optical Networks: Outlook and Case Study of Integrated Quasi-Coherent Receiver
, João Santos 1,2,3, Cláudio Rodrigues 4 and António Teixeira 1,2,3
Round 1
Reviewer 1 Report
The authors introduce the development of passive optical networks and photonics integrated circuits, with focus on optoelectronic integration of photonics integrated circuits for passive optical networks and coherent passive optical networks. The manuscript is clearly written in general. I have some comments below and hope that the authors would be able to address them.
1. What kinds of electro-optical hardware are available and their respective performance.
2. As the conclusion of the manuscript, Section 5 is not perfect. For example, the following points should be added: (i) Some current problems and limitations to be solved; (ii) Prospects for the future.
3. Structure confusion, such as only number 3.1, no number 3.2, etc.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this manuscript, the authors reviewed the revolution of PON standards, the development of PIC for PON, and the integrated quasi-coherent receiver. A large number of PON proposals under different standards and streams of thought are reviewed and compared. Furthermore, the development of PIC technology, the merits of integrated PON, and the quasi-coherent receiver based on different PIC technologies are illustrated and discussed in detail. In general, this manuscript is neat and complete. I am happy to recommend the paper for publication in Photonics after major revision. Some of my questions and suggestions are listed in the following.
1. A large amount of PON systems and PIC structures are illustrated, while their performances and parameters are also compared in the manuscript. I strongly suggest that the authors summaries these proposals and their performances in tables with suitable formats to achieve better readability. This is very important for a review because it can help the readers to identify the relevant contribution without having to switch back and forth to the bibliographies.
2. With the evolution of PON standards, what are the specifications and requirements for the PIC? Meanwhile, the authors might need to quantitatively predict the key performance indicators of the PIC in next-generation PON. Moreover, what is the challenge or bottleneck of the PIC technology to achieve the next generation PON? These points are worth discussing in the manuscript.
3. The authors are suggested to read the manuscript carefully and correct some typos. For example:
1) Line 523, on page 11, “with a compact size of 4.25x4.5 mmm”.
2) Some abbreviations (for ex., the DBR, LO, and TEC) are double-defined. It should be defined only the first time when they are mentioned.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
This paper comprehensively reviews Passive Optical Networks (PON) technologies, global PON standards, and Photonic Integrated Circuits (PICs) employed in PON, PIC-based transceivers for PON applications. This manuscript is well written. The structure of the paper is good and suggested as suitable for publication. My only suggestion for the authors is to explain the reason for using Hybrid 120 instead of 90 in coherent receivers (line 598 & figure 6).
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have addressed the reviewer's comments. So, this paper should be published in Photonics.
Reviewer 2 Report
The authors have addressed my concerns, so I recommend its publication in Photonics.
