Phase Stabilization of a Terahertz Wave Using Mach–Zehnder Interference Detection

Round 1

Reviewer 1 Report

The manuscript presents the design and the implementation of a Phase Stabilization of a Terahertz Wave using Mach-Zehnder Interference Detection method.

The subject of this research is very interesting and the paper is well written.

The latter part of the paper that describes the implementation of a transmitter and a receiver for assessing the phase stabilization techniques in a phase-modulated THz-wave generation and transmission setup is very interesting and results shown a good performance of the backward-direction Phase Stabilization System.

The introduction is very clear and illustrates the state of the art of the research in this field, but maybe the number of references is too large and I wonder if you can reduce the number of references only to the most important ones. 

The aim of the paper (and of the research) is well described and the results are presented in clear way.

Maybe what is missing is a statement about further improvements of the proposed a Phase Stabilization method and still opened points, if any. 

I only suggest some modifications to improve the readability of the results.

Figure 1 on page 2)

The point corresponding to year 2005 should be labelled as 1 x10^-4 Gbit/s.

Figure 2 on page 3)

The use of full markers shaped in a similar way does not help the reader in recognizing the different technologies. Diamonds, pentagons end hexagons cannot be distinguished. Please use a mixing of full and open symbols instead of them. 

Figure 6 on page 7)

This figure contains too many plots.  I suggest to split in two figures: a first one with the the two experimental setups and a second one with the two optical spectra. Even better it would be to split the figure 6 always in two figures having a first one dedicated to forward - direction technique (setup and spectra) and the second one for the backward -direction.

Author Response

Dear Reviewer,
Thank you for your comments and suggestions.
Please see the attachment.

Thank you.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors of the paper “Phase Stabilization of a Terahertz Wave using Mach-Zehnder Interference Detection" have been very successful in both the scientific investigation and the careful preparation of this article.  The study presents the conceptual framework and experimental setup for phase difference stabilization of optical carrier signals. The application of this concept is confirmed by demonstrating error-free transmission at a modulation frequency of 3 Gbit/s. In my opinion the paper can be accepted for publication in this form.

Author Response

Thank you for your positive review and recommendation for publication.

Reviewer 3 Report

This manuscript develops a phase stabilization method for phase-modulation-based terahertz wireless data transmission. The authors use Mach-Zehnder interferometric of a pilot lightwave to stabilize the terahertz wave against phase fluctuation due to optical fiber length variations in photomixing. Compared to a forward-direction pilot lightwave system, the back-direction system successfully stabilized the phase-modulated 300-GHz wave at the bit rate higher than 3 Gbit/s.

This work is solid and interesting. There are a few questions that I believe should be addressed before publication.

1) I observe substantial optical power loss at 195.4125 THz comparing the input and output powers in Fig. 6. Where does the loss come from?

2) What is the upper limit of the bit rate that can be stabilized by the back-direction pilot lightwave system?

3) Can you explain more on the “excellent resolution” for all-electronics approach in Line 77?

4) I feel that the phase modulation equation in Line 155 is not correct. In terms of the unit, the left and the right do not match.

5) I don’t understand why no pilot light wave is detected at the output of Fig. 6(c). If it is because of filtering, where is the filter? If not, is it due to the stabilized destructive interference?

6) The authors should specify which O/E converter in Line 245.

7) In Line 299, “Figure 9” should be “Figure 8(c)”.

8) Is it OOK modulation in Line 351? Isn’t it phase modulation?

9) In Fig. 9(a), I think the pink light in the feedback control system after OC output goes to O/E first and then the CONT.

10) Why the output powers of f1 and f2 are higher than the input power in Fig. 9(d)? Are they measured after EDFA?

Author Response

Dear reviewer,
Thank you for your suggestions and comments.
Please see the attachment.

Thank you.

Author Response File: Author Response.pdf