Cost-Effective and Energy-Efficient Photonics-Based Frequency Hopping by Single Wavelength-Tunable Laser for Secure THz Communication

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper proposed an interesting frequency hopping spread spectrum (FHSS) system with wide frequency range using a single wavelength-tunable laser and experimentally demonstrated such a system according to the proposal. It seems a very promising approach. The author must carefully read the paper and make a minor revision to improve the quality. I would thus think it is quite interesting and recommend it for publication after the authors carefully addressed my comments as listed below.   

1. Photonic generated THz has been widely viewed as a method with significant drawbacks of low power of the generated THz carrier, which limits the transmission distance of the THz signal to only a few meters. Please comment on it regarding this work and how to improve the THz carrier power.

2. As indicated by the authors, data transmission cannot occur during channel switching (transition time) because the signal frequency must stabilize before data can be reliably transmitted. Could you please explain explicitly what happens if data transmission occurs during the channel switching?

3. Following the above question, I wonder if the channel switching is made to be a small hopping gap, for example, within a few GHz in carrier frequency change/offset, it could be possible to transmit data during the channel switching period since such a frequency offset can be estimated and compensated in the receiver DSP on the condition that the ADC has high enough sampling rate to cover the whole frequency shifted signal spectrum. Please comment on it. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

I found this article interesting; however, it might be improved to fit the requirements of the journal. 

1) Equation 1-3 . Why did  you  not consider phase ?

2) Please discuss measurement error

3) Authors write: " These lightwaves were then directed into the UTC-PD, where THz waves at approximately 238.6 GHz, 279.3 GHz, and 320.0 GHz were expected to be generated . "  - please related to THz waves. 

4) The fig. 8.  Please explain why the one signal is stronger than the rest signals? 

5) What is the expected signal to noise ratio?

6) Will such waves interfere too easily? What could be the source of interference. 

7) Will mixed waves and higher harmonics be created?

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf