Akinetic Swept-Source Master–Slave-Enhanced Optical Coherence Tomography

Round 1

Reviewer 1 Report

This paper entitled “Akinetic Swept-source Master-Slave-enhanced Optical Coherence Tomography” aims at applying the master slave technique to akinetic based OCT systems to achieve long imaging depth.

I believe this manuscript is suitable for publication as it is clear and informative, but the following concerns need to be addressed:

1. The introduction seems adequate but the bibliography review should include more references on alternative data processing for high speed long range OCT systems. It seems that the authors are mainly self-citing (7 out of 15 refs). I would expect some refs on recent advances using frequency combs for examples.
2. In the second system, the second interferometer uses very different detector to the master interferometer. In particular, they present a lower bandwidth. It would be good to get an explanation of the potential impact or why a lower bandwidth can be used without problems.
3. In the methods, the difference between the data processing is not obvious. Figure 3 shows a Re and an Im part to the signal and it is unclear how they are used. Is it different to the complex method? If not, then the diagramme is misleading.
4. In figure 5, the position jitter is attributed to the imperfection of the translation stage. Can the authors evaluate the jitter against the specification of the translation stage to test their hypothesis? From looking at the figure, the jitter seems to be at least 10 microns, which seems well above the accuracy and repeatability of the translation stage. Can the authors comment?
5. Line 226, the authors compare the MS method with the standard method without dispersion compensation. While dispersion at 1.3 microns is typically low, it is well known that it will degrade the resolution with depth so I would only take into account the value for small OPD or use a dispersion compensation algorithm or clearly justify why none is used.
6. The DC-OCT method should be clearly explain the method and not introduce in the results. Overall, the authors should revise carefully the manuscript to bring back all the details about the method in the method section and keep the results to the results section.

Author Response

Please see the attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

The object of research described in the manuscript is a novel Swept Source Optical Coherence Tomography technique that uses an electrically tunable multisection semiconductor laser together with detection setups and data processing schemes devised to take into account the nature of tuning of the laser used in the system.

The paper is written well, the novelty is undisputable. The experiment and the analysis were performed correctly.

There are two points that merit some consideration. First, I am unsure about the use of “report” at the end of Line 68, where “papers” seems to be a more appropriate choice. The same applies to Line 83, 163 and 308. Second, please consider moving information contained in the captions in Fig. 2a and 2b to the text of the manuscript.

In conclusion, the manuscript can be published in its present form, unless some of my comments from the previous paragraph have to be acted upon.

Author Response

Please see the attached file.

Author Response File: Author Response.pdf

Reviewer 3 Report

In the manuscript entitled “Akinetic Swept-source Master-salve-enhanced Optical Coherence Tomography” by Marques et al., the authors implemented Master-slave OCT (MS-OCT) to the SS-OCT system with an akinetic wavelength-swept light source. Also, the authors implemented the so-called down-conversion OCT as demonstrated by Biedermann et al. in 2008 and Bradu et al. in 2014-2015 to the aforementioned OCT system to enable potential long-range measurement with OCT and the akinetic light source without requiring a high sampling rate digitizer. In general, the structure of the manuscript is well organized, and the context should be interesting to the community as well. However, the reviewer does have a few comments and suggestions as listed below that would like the authors to address in order to further improve the manuscript.

1. In Figure 1, the horizontal axis is labeled as “elapsed time,” which seems confusing to the reviewer.

2. In Figure 2(a), please provide the definition of CMS FFT before using this acronym.

3. Although Figure 3 clearly demonstrates the concept of the HyMS-OCT processing over conventional OCT progressing, the difference between CMS-OCT and HyMS-OCT is not clear to the reviewer. Particularly, it seems both methods require processing on the complex spectrum. It would be helpful if the author can provide additional information, for example, an additional figure to better illustrate the difference between CMS-OCT and HyMS-OCT.

4. In Figure 5, the authors compared the A-scan profile computed from three different sampling conditions and using either the conventional FT method or the HyMS-OCT processing method. Although Tables 1 and 2 summarize the width of the A-scan peaks from the results demonstrated in Figure 5, the noise floor varies among different methods or different sampling conditions. It would be more informative if the authors can provide the measurement of the signal-to-noise ratio for different cases as well.

5. Although DC-OCT allows the measurement over a long axial range by avid the need of a high speed digitizer, it still requires to use a photodetector with a high detection bandwidth.

Author Response

Please see the attached file.

Author Response File: Author Response.pdf