Pre-Chirp-Managed Adiabatic Soliton Compression in Pressure-Gradient Hollow-Core Fibers

Round 1

Reviewer 1 Report

This paper presents a theoretical and numerical investigation of the potential of using pressure gradient in gas-filled hollow core fiber to compress mid-infrared pulses down to a few cycles with adiabatic soliton pulse compression. 

The theoretical analysis provides useful guidelines on the potential of the technique, while the numerical investigation provides more details on the quality of the resulting pulses. 

The results clearly show that the technique has the potential to generate such short pulses, provided some pre-chirping of the pulse. The results are a useful addition to the body of knowledge in the field, although some experimental results validating the predictions would make the paper more relevant. 

Although the paper is suitable for publication, I nevertheless found that there is no real comparison with previous experimental results either on 2 micron or 4 micron pulses, that would allow the reader to compare the predictions of the paper to current best results using other techniques. I therefore suggest, as a minor improvement, that the authors provide such a comparison, to make clear the potential of the proposed technique. 

Author Response

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Reviewer 2 Report

1) The designation "p0" is used both in Eq, 4 and Eq. 10. Is it the same pressure?

2) The addition of the chirp leads to unequality of the pedestal in the compressed pulse. Can this effect be pre-estimated relative to GDD/initial-pulse-duration ratio? 

It also seems that the two-stage compression with addition of the chirp leads to significant contrast loss, as for the one-stage simulations it is far better. Do you have a comparisson with the case of non-pre-chirped second stage compression?  

3) There are some drawbacks in graph subscriptions: Fig.3 (a) and Fig. 4 (a) "db" is cut from above; Fig. 5 (b) time scale subscriptions are too close.

Author Response

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Reviewer 3 Report

In the present form, this paper is definitely inappropriate for the publication. First of all, it is virtually impossible to understand what was really done in the work, as the authors neglect to write equations which they were simulating. Instead, a vague reference to three apparently randomly chosen papers [22-24] is given, stating that the NLS equation for the optical amplitude was taken "from there". To tell the truth, this style of the presentation seems as a joke, rather than as a style appropriate for writing a professional text. In particular, a strong claim is made that the results reported in the paper apply to extremely narrow few-cycle pulses. However, models which make it possible to consider so narrow pulses are very specific. Generally, they should be based on the Maxwell's equations, rather than on a simple NLS approximation (which the paper keeps in secret).

As a consequence, it is virtually impossible to understand the purport of results presented in the paper and their novelty, in comparison with numerous earlier works on the topic of non-disturbing compression of optical pulses in fibers. In particular, two-stage compression of optical solitons, which makes it possible to avoid  their strong deformation, was elaborated theoretically and experimentally, in JOSA B 11, 2380 (1994), and Opt. Fiber Technology 1, 117 (1995). How can the authors claim novelty of their results, also based on a two-stage scheme, if they ignore essential earlier works?

The authors may be offered an option to completely rewrite the paper, making it self-consistent and understandable, and then submit it as a new manuscript, to Photonics or another journal. However, it is only possible to recommend rejection of the present manuscript.

Author Response

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Round 2

Reviewer 3 Report

The paper was improved by the revision, but not sufficiently to recommend the acceptance. The authors now explicitly write the extended NLS equation, which was previously hidden from readers, although it seems strange that the main equation appears only in the middle of the paper (Eq. (10)), while simulations of this equation is the main subject of the work. Further, before producing the equation, the authors consider the "soliton area theorem" (3), which plays an essential role in their "analytical analysis" (by the way, what is the meaning of this tautology?). Is it true that the "theorem" is valid for the extended equation (10), with its complex structure? If it is valid only for the simplest form of the NLS equation, how can the "theorem" be used in the context of this work? As concerns Eq. (10), what is the meaning of the exotic symbol in the form of the skew cross in the circle, which appears in the second term on the right-hand side of the equation?

Answers of the authors concerning references seem quite strange. In their response to the review, they cite the paper by Brabec & Krausz, which is an important reference indeed, as concerns few-cycle light pulses. However, the authors prefer to ignore this obviously relevant reference in the revised manuscript. Similarly, in their response, they offer some comments concerning the comparison to papers published in JOSA B 11, 2380 (1994) and Opt. Fiber Technology 1, 117 (1995), which were mentioned in the original review. However, the authors prefer to ignore these obviously related papers in the revised manuscript. As concerns their response to the original review, their claim that the above-mentioned papers considered "constant dispersion" is definitely wrong: the purport of the above-mentioned papers was, precisely, to implement the change of the dispersion, by using a concatenation of three fibers.

I suggest the Editors to offer the authors an option to revise the manuscript once again. However, if they will keep to address some comments and arbitrarily ignore others, the final recommendation may only be negative.

 

Author Response

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Round 3

Reviewer 3 Report

The second revision has appropriately addressed comments from the second review. The resubmitted [a[er may be recommended for the publication in Photonics.