A Microwave Photonic Converter with High in-Band Spurs Suppression Based on Microwave Pre-Upconversion

Round 1

Reviewer 1 Report

Dear Authors,

Please consider the following comments/queries as ways to improve the manuscript.  What I like about his work is that you have arranged signals so that the spurs are minimized in the frequency band of interest.

However...

1. In the manuscript, you have outlined your motivation to do microwave photonic converters because of their perceived benefits over electrical frequency converters.  In your concept demonstration, you need electrical pre-conversion, i.e. use of electrical frequency converters, for it to work.  This is my frustration as a reader.  It is not logical.  It is not about microwave photonics vs. electrical.  A better argument would be that you combined the best of both worlds to get low spur performance.  Please consider.
2. You also stated that electrical frequency converters have high insertion loss.  This design suffers a significant loss of ~35 dB.  This is due to the insertion loss of the electrical frequency conversion plus the insertion loss of the photonic link.  Please consider rephrasing the Introduction.
3. A better experimental design would be to compare your reported concept with a simple direct electrical conversion setup utilizing MUC + EF.  This would highlight the benefits, if any, that is provided by microwave photonics.  Does the cost-benefit stand up with additional microwave photonic components and costs?  Also, size weight and power discussion?
4. In this concept demonstration, the distance between DAC/ADC and radar has not been considered.  Short fiber length has been considered.  In practice, the DAC/ADC may be located in an office away from the radar.  In such a situation, the effects of fiber dispersion may be worth investigating when the HF and LO are separated significantly.

Best regards.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The Authors propose a microwave photonic converter based on microwave pre-upconversion. The reported results have been simulated and experimentally demonstrated. Although the results are interesting, some contents should be mandatory clarified for the manuscript publication suggestion.

 

Here, my comments to the manuscript:

 

• In the introduction section, an overview of the microwave photonics should be provided. In particular, the Authors could cite some systems, i.e. networks (“Microwave photonics combines two worlds,” Nature Photon., vol. 1, no. 6, pp. 319–330, 2007.), engineered filters (“Ultra-compact tuneable notch filter using silicon photonic crystal ring resonator,” Journal of Lightwave Technology, 37(13), 2970-2980, 2019; “Photonics to the rescue: A fresh look at microwave photonic filters,” IEEE Micro. Mag., vol. 16, no. 8, pp. 46–60, Sep. 2015), beamforming (“Advances in Microwave Photonic Beamforming for Phased-Array Antennas,” In 2019 21st International Conference on Transparent Optical Networks (ICTON)(pp. 1-4), 2019, “Silicon integrated microwave photonic beamformer,” Optica, 7(9), 1162-1170 2020), and so on, that demonstrate the advantages of the microwave photonics with respect standard approach.
• In the Introduction Section, the Authors should also report the main systems used to engineer the signal in order to demonstrate the versatility of systems similar to the proposed one. As example, for SAR applications, linearly chirped microwave waveform generators have been proposed (see, as example, Chip-Scaled Ka-Band Photonic Linearly Chirped Microwave Waveform Generator. Frontiers in Physics, 158, 2022; Photonic Generation of Microwave Arbitrary Waveforms. Opt Commun 284(15):3723–36; 2011; Reconfigurable Direct Space-To-Time Pulse-Shaper Based on Arrayed Waveguide Grating Multiplexers and Digital Micromirrors. IEEE Photon Technol Lett 17(9):1959–61, 2005; Millimeter-wave Arbitrary Waveform Generation with a Direct Space-To-Time Pulse Shaper. Opt Lett 27(15):1345–7, 2002) with configurations similar to the reported ones.
• The main lack of the manuscript is the absence of target performance, related to a specific application. In particular, in the Space field, a great research effort is focused on bandwidth larger than the reported one, i.e. Ka band. The Authors should justify the chosen bandwidth.
• In the Table 2, the bandwidth of the proposed scheme results limited with respect other solution. The Authors should report some countermeasures to overcome this limit.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Dear Authors,

Thank you for addressing the reviewers' comments.  My only suggestion is to swap sections "5. Conclusion" and "6. Discussion" around to make "5. Discussion" and "6. Conclusion".

Cheers.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The Authors have replied to the Reviewers’ comments with satisfactory responses. The new version of the manuscript has been modified following the Reviewers’ suggestions. Therefore, I recommend the publication of the manuscript as it is.

Author Response

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Author Response File: Author Response.docx