Generation of Different Mode-Locked States in Nonlinear Multimodal Interference-Based Fiber Lasers
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis manuscript presents an all-fiber passively mode-locked laser with a distributed saturable absorber based on nonlinear multimode interference (NLMI) capable of generating various pulse modes. The saturable absorber includes two large-core graded index multimode fibers (GIMF: diameter, 105 μm) located at different positions in the resonant cavity. The proposed laser achieved four different mode states under three different cavity dispersion through adding different lengths of DCF or SMF. The dispersion range that allows the existence of DS is investigated and the dynamics of the evolution from DS to DSR is also observed. The obtained results are abundant and interesting. I think this work can be accepted for publication after some revisions. I have the following comments for the authors:
1. The authors believe that the setting of the SA on this system in the vicinity of [email protected] m is conducive to optimizing of the ML operation. They have not given a convincing explanation. E.g. Why not the one with [email protected]? Also, will the setting of [email protected] m. also be best setting for other modes states? Please discuss this issue.
2. Note that the laser is able to operate in the fundamental frequency state over a wide pumping range without exhibiting pulse fragmentation. How did this happen and what factors contributed to it?
3. The authors do not provide an explanation for the significance of the “reverse saturable absorption phenomenon” in the introduction.
4. In the introduction, the authors highlighted previous saturable absorbers, indicating, “Researchers solve the problem of the strict length limitation by several innovative methods such as adding a segment of step-index multimode/no-core fiber ahead of the GIMF, introducing an inner micro-cavity in the GIMF, stretching the GIMF, offset-splicing the GIMF, coiling the GIMF [22-32], etc.” Of these, please explain what is the mechanism by which coiling the GIMF removes the fiber length limitation?
5. The authors should provide more detailed insights into the methodology of adjusting the saturable absorber (SA) to induce different transmission states. A more thorough explanation would facilitate reader comprehension and engagement with the study. For instance, clarification on what constitutes a suitable bend shape, as well as specific instructions on the adjustment of “two sets of heat shrink tubes of different diameters has been jacketed in the middle of GIMF1 and GIMF2,” the way of “easily, flexibly and finely moved, rotated and twisted”.
6. References should be appropriately assigned to their respective techniques, for examples: “Researchers solve the problem of the strict length limitation by several innovative methods such as adding a segment of step-index multimode/no-core fiber ahead of the GIMF, introducing an inner micro-cavity in the GIMF, stretching the GIMF, offset-splicing the GIMF, coiling the GIMF [22-32], etc.”.
Author Response
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Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsIn this manuscript, the author reported a mode-locking method based on nonlinear multimode interference by cascading two large-core graded-index multimode fibers-based saturable absorbers. The manuscript is well organized and the experimental process and phenomena are descripted in detail. I support the publication of this work after the authors address the following comments.
1. The first appear of abbreviation should clearly state the content of the abbreviation. For example, the author have not explained the mean of “NLMI”.
2. In line 224, the author said, “So, it is interesting and wonderful to study whether the long cavities and high nonlinearities have a similar effect on …”. To extend the cavity, additional 500 m SMF is inserted in the cavity. The question is, how to achieve high nonlinearity?
3. Figure 3 gives the characteristics of the DS operation of various samples. When GIMF1 is fixed at 0.6 nm, the spectra varies between 10.31 nm and 20.58 nm. What are the reasons for the changes in spectral width?
4. In the experiments, four kinds of different pulses are obtained. Please provide a further summary of different conditions for different pulses.
5. Some spelling errors should be corrected. For example, in the Caption of Fig. 3, “virous” should be “various”.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsIn this work, the authors introduce a distributed large-core Graded-Index Multimode Fibers architecture, which notably facilitates simultaneous spatial averaging and spectral filtering operations in mode locked lasers. This SA enhances the system's tendency to pulse fragmentation and enables the creation of a simple, compact all-fiber passive mode-locked laser without the need for bulk filters. The work successfully demonstrates the generation of various mode-locked operations, including DS and DS. This work is indeed interesting in the field multimode interference SA based mode-locked lasers, in particular in C-band and expected to add knowledge for developing stable, high-power, and multifunctional laser sources with complex and tunable transmission properties. There are only few points which should be corrected or topics that might be considered to improve the quality and the clarity of this work prior to publication.
1) The authors claims that the proposed technique increases the splitting threshold, however do not provide a number for it.
2) Can the authors provide references for line 42-44?
3) Can the author explain the impact of placing the GIMFI after the EDF fiber? Will it reduced the mode-locking threshold?
4) Why is there a modulation in the nonlinear absorption curve 2(b)? Is it due to the nonlinear polarization rotation in PI-ISO?
5) From figure 3 (a) and (b) it seems that the the GIMF1 and 2 length has not significant impact on the pulse duration? and also can not be correlated. How can this be addressed? Moreover, how does the mode-locking threshold changes with this the multimode fiber length variation? How does this relate to the generated chirp?
6) The transition from DS to DSR is very interesting but it lacks sufficient references. I would recommend to provide more references of different pulse generation regimes in the introduction section.
7) It shows that the authors measured average fluctuation in the spectrum to understand the coherence. However for such pulse generation regime, it does not directly corelated with temporal coherence? Did the authors measured shot to shot spectrum using DFT?
8) It will be interesting to know at what limit the pulse fragmentation occurs in DS regime as it occurs in DSR regime? Can they provide the number for the pump power?
9) The manuscript could benefit from some minor improvements. For instance, NLMI is not defined, which is crucial since it represents the mode-locking principle central to this work. Additionally, the manuscript will benefit from a language review to enhance clarity.
Comments on the Quality of English LanguageN/A
Author Response
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Reviewer 4 Report
Comments and Suggestions for AuthorsThis study proposes a new method of distributed large-mode area multimode fiber (GIMF) saturation absorber (SA) based on nonlinear multimodal interference, which can generate different pulse modes.
Here is my concerns,
1. There are several places the author mentioned "SNR", one SNR is at the place where the authors talk about the spectrum, and the other one is at the place where the author talks about the RF spectrum, obviously, the value is different, what is their difference？
2. It is hard to see the pulse split in Figure 5d, however, the author said the pulse split finally, but I could not see it.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe author has responded to all comments. In my opinion, the manuscript is worth publishing.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have responded adequately and in elaborately to the all eights concerns I had . So, I recommend the publication of this work in its present form.
