Instantaneous Frequency Measurement with Reasonable Resolution and Simple Structure

Round 1

Reviewer 1 Report

The paper presents an approach to measure the RF single frequency based on microwave photonics. Two optical wavelengths are intensity modulated by an unknown microwave signal. Each modulated signal is launched into a 10-km single-mode fiber (SMF) to introduce microwave signal power fading. After photodetection, the ratio between the two detected microwave powers is used as the amplitude comparison function (ACF). The idea is quite novel and the results are interesting. However, a few revisions are required before final acceptance for publication.

The reasons are illustrated in the following.

1)    Regarding the measurement scope of the manuscript: There are many threats in a typical electronic warfare environment operating below 10 GHz where the ACF curve has a flat slope in low frequencies. But the authors only provide measurement error for the range 15.8 GHz to 21.2 GHz. How practical is your work for incoming signal with low frequencies?

2)   Regarding the measurement error of the manuscript: For the measurement error of the scheme, what’s the source of it?

3)    Regarding the principles structure settings of the manuscript: In the setup of Fig. 1, only one laser is shown, while in the setup of Fig. 3, why does the author use two lasers?

For these reasons, I think that the manuscript needs a minor revision before acceptance for publication on Photonics.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

This work focuses on instantaneous frequency measurement with good resolution and low complixity. I think that this work must be considered some points in order to improve its quality.

1. The second paraghrap of the introdution should be improved and organized more.

2. In Line 74, you mention that "firstly, a microwave signal of the unknown
and an RF signal enter the Mach-Zehnder modulator (MZM)". During your work, I do not find that you employed the unknown microwave signal?

3. In you model, you did not cosider the impact of optical phase and intensity noise in Eq (2). If you consider both noises, your model can be general model for this method. Perhaps, both noises can alter the measurements results? could you insert this point in your work?

4. Could you please mention the length of fiber,  since the chromatic dispersion can have some effects on the outcomes?

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Thanks for the authors. I have found that they perfomed very good modifications on the previous version. so the paper is read to publish.

Best Regards,