Review Reports

Round 1

Reviewer 1 Report

The paper entitled “A microwave photonics true-time delay system using carrier compensation technique based on wavelength division multiplexing” presents a true time delay system design assisted by carrier compensation. The main idea is using carrier suppressed double side band modulation such that the optical amplification contributes more on two sidebands, improving TTD performance than conventional methods. Based on the quality of Photonics, I have some comments below.

1)    When compensating the carriers, the phase difference between separated fc and transmitted fc matters during TTD detection stage. How do you ensure the phase is correlated or locked?

2)    What is the total system power budget for such a TTD module? There are a bunch of FBGs and combiners/splitters, how do you leverage the trade-off between system performance improvement and the power budget?

3)    In this paper, the author proposed CS-DSB based TTD. However, in Fig6, none of the experimental results show carrier suppression. Please clarify it.

4)    The author claims PAA application, please provide antenna diagram result.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

Dear colleagues!

At the forefront of your article, you put the gain in the amplitude of the synthesized signals and in the resulting temporal characteristics. Judging by the results, you achieved what you wanted. However, there are a number of issues that are determined by the need to assess the feasibility and reality of your decisions.

1. The theory described and the experiment performed are presented very ideally, so to speak. Neither the influence of the phase of the carriers during compensation, nor the effect of temperature on the stability of the operation of the circuit elements, nor the coherence during the propagation of laser radiation, nor the dispersion are out of the question. Therefore, the "discussion" section should be substantially expanded and separated from the conclusion section.

2. You mainly used literature references from the end of the first decade of the 21st century, now it is the third decade. It is doubtful that in the world practice over the past 12-15 years there have been no solutions for the task you have set, by the way, it is not so simple as it seems with an ideal formulation of the problem.

3. Spectrum of radiation after the modulator, shown in fig. 6, is highly questionable. As written in the article, you are using a Mach-Zehnder modulator for CS-DSB modulation. On fig. 6 classic DSB without carrier suppression is shown.

Considering the above, I ask you to pay attention to my questions and dispel my doubts.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

The Authors propose a microwave photonics true time delay line made using multiple fiber Bragg grating (MFBG) and ten lasers with different wavelength modulated by the double side band suppressed carrier (DSB-SC) technique. The performance has been estimated by using the software OptiSystem, based on user-defined components and script language, after modelling the network structure. Although the results are promising for the next generation of telecommunication systems, a major revision of the manuscript is suggested. Among the different technologies you considered, it would be interesting to compare your performances to the following structure proposed in literature:

-          Compact graphene based optical delay line with low reconfiguration time, compacteness and large delay range (Brunetti, G., Conteduca, D., Dell’Olio, F., Ciminelli, C., & Armenise, M. N. (2018). Design of an ultra-compact graphene-based integrated microphotonic tunable delay line. Optics express, 26(4), 4593-4604.)

-          A binary integrated optical TTD line that exploits cascaded multistage 2x2 optical switches (Zhang, Q., Ji, J., Cheng, Q., Duan, Y., Zang, J., Yang, J., ... & Zhang, X. (2022). Two-Dimensional Phased-Array Receiver Based on Integrated Silicon True Time Delay Lines. IEEE Transactions on Microwave Theory and Techniques).

-          A fully integrated 4-bit TTD line capable of delays above 12 ns, corresponding to about 2.4 m of propagation length, on a chip area of 4.5 cm×8.5 cm, with waveguide losses as low as 1 dB/m made of silicon nitrate (Moreira R L, Garcia J, Li W, et al. Integrated ultra-low-loss 4-bit tunable delay for broadband phased array antenna applications. IEEE Photon Technol Lett, 2013, 25: 1165–1168).

-          A single, very compact, low loss photonic crystal to implement multiple variable TTDs based on the slow-light properties of photonic crystals demonstrating a 1.5-mm-long device capable of generating delays up to 70 ps with losses below 10 dB over the complete 0–50-GHz band. (Sancho J, Bourderionnet J, Lloret J, et al. Integrable microwave filter based on a photonic crystal delay line. Nat Commun, 2012, 3: 1075).

-          An electronically reconfigurable Bragg grating device that can operate as an electrically tunable linearly chirped grating providing a dispersive delay line (Zhang W, Yao J. A fully reconfigurable waveguide Bragg grating for programmable photonic signal processing. Nat Commun, 2018, 9: 1396).

All these structures have demonstrated higher performances with a small footprint, high compactness and a low power consumption. You have to deal with the power consumption associated to the use of ten lasers and the limits of this technique due to the wavelengths of lasers. Moreover, you have to manage the footprint of the structure and the losses due to the coupling between fibers and bulky elements.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Dear colleagues!

In response to remark 1. You have listed the standard measures that you would have to apply in order to avoid the shortcomings of the experiment that I have indicated. However, this answer is not enough. The analysis you provided should be explained in the article with the following question in mind. To be brief, please tell me what is the coherence length of your laser and at what distance from it do you consider the coherence of the laser to be preserved.

In response to remark 2. I agree with the additions made.

In response to remark 3. A natural question arises, why then did you need a suppressed carrier mode at all, if you set it in such a way that you still work with an amplitude-modulated oscillation of the DSB with a carrier. You have an explanatory fig. 3, which is very different from Fig. 5 and fig. 8. It also becomes unclear how the second-order components disappeared, and what happened to them after amplification?

I agree with the rest of the amendments. 

So, my meaning about article doesn't change.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

The Authors have modified the manuscript according to the Reviewer comments. Therefore, I suggest the manuscript publication 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 3

Reviewer 2 Report

Dear colleagues!

1. In my opinion, your answer about coherence is not very convincing. If you wrote that your layout works at 200m, that would be ideal.

2. I made a mistake with the wording of the second question. I was interested in the third component, not the even components. If you describe what level they have it would be great.

These are my recommendations, you can satisfy them, or you can leave everything as it is.

Author Response

Please see the attachment.

Author Response File: Author Response.docx