Broadband Metallic Carbon Nanotube Saturable Absorber for Ultrashort Pulse Generation in the 1500–2100 nm Spectral Range

Round 1

Reviewer 1 Report

This manuscript shows the usage of the metallic carbon nanotube as a broadband saturable absorber for ultrashort pulse generation in the 1500 – 2100 nm spectral region. The manuscript shows the interesting results and well organized. However, there are some minor revisions in the revised manuscript.

1. The authors provide the nonlinear transmission graph of the prepared SA at 1950 nm only, as shown in Fig. 2b. are there any difference in the nonlinear optical transmission graph when the measurement was conducted at 1560 nm and 2100 nm wavelength regime? I think that it is advisable to add the nonlinear curve at different wavelength region.
2. Generally, it is known that the sandwich type-based SA has a lower damage threshold level comparing the other type SA (i.e. d-shaped fiber, tapered fiber). Did the authors test the optical damage threshold of the prepared SA?
3. What about the long term stability of the prepared SA?
4. Some related works on two-dimensional materials based saturable absorber in fiber lasers (i.e. graphene oxide (Lee, J.; Lee, J.H. A passively Q-switched Holmium-doped fiber laser with graphene oxide at 2058 nm. Appl. Sci. 2020, 11, 407.) / transition metal monochalcogenides (TMMC) (Jhon, Y.I.; Lee, J.; Seo, M.; Lee, J.H.; Jhon, Y.M. van der Waals layered tin selenide as highly nonlinear ultrafast saturable absorber. Adv. Opt. Mater. 2019, 7, 1801745.)) are considered to be mentioned in revised articles.

Author Response

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Reviewer 2 Report

In this manuscript, the authors demonstrated a metallic carbon nanotube saturable absorber for broadband pulsed lasers operation from telecom band to mid-infrared wavelength. It is of interesting for broadband ultrafast pulse generation with single walled carbon nanotubes. The manuscript can be considered to publish in Applied Sciences if the following questions can be properly addressed.

1. How was the film thickness characterized?
2. What is the ratio between semiconducting tubes and metallic tubes?
3. Can the nonlinear optical transmission measurement be measured at 1.55um and 2.01 um? What will be the modulation depths compared with the value in Fig. 2b?
4. It seems that the modulation depth performed in Fig. 2b is not exactly 4.9%, can the authors point it out clearly in the figure?
5. In Fig. 1c, it looks like the absorption around 1um is even larger than the investigated wavelength (i.e., 1.55um, 1.9um and 2.01um). Can the same saturable absorber mode-lock the 1um laser?
6. In Fig. 5b, the measured pulse duration is 713 fs, the authors claim it is 750 fs in the text, please correct.
7. Why the pump powers in Thulium and Holmium lasers are much higher than the Erbium laser? What are the threshold powers for mode-locking?
8. The metallic carbon nanotube in this work shows similar optical properties with the one in the authors’ previous paper “Metallic carbon nanotube-based saturable absorbers for holmium-doped fiber lasers, Optics Express 27, 11361-11369 (2019)”. Are they the same nanotube?
9. Do the authors control the chirality during the nanotube fabrication? How does it influence the absorber properties?

 

Author Response

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Reviewer 3 Report

I carefully read the manuscript entitled “Broadband Metallic Carbon Nanotube Saturable Absorber for Ultrashort Pulse Generation in the 1500 - 2100 nm Spectral Range” by M. Pawliszewska et al. In their work, they studied thin film of broadband metallic carbon nanotubes as a saturable absorber for ultrashort pulse lasers. They have shown that single-walled carbon nanotube-based saturable absorbers can be used for mode-locking in fiber lasers operating in a 1 – 3 µm wavelength spectral range. The results seem interesting and have practical value.

The manuscript is organized clearly and the language is, besides some minor expressions and types, appropriate. The experimental results are described well and structured. The methodology of the study is appropriate and described in a clear and comprehensible way.

The article seems interesting to me and suits the scope of the journal of Applied Science, therefore I will recommend the acceptance of this article after some minor corrections.

They are described below:

1. In the Introduction (line 40) there is the acronym SESAMs. The explanation of it would be useful for the readers. I think it should be written like “semiconductor saturable absorption mirrors (SESAMs)”.
2. In Figure 1 it is written Absorbance (%), Wavelength (nm) and so on. In other words, you use "()" for describing the axis of graphs. While in figures 2, 3, 4, 5, 6 and 7 you use "[]" for describing the axis of graphs like Wavelength [nm] and Decay [ps]. I suggest you use "[]" in all figures of your manuscript. 

Author Response

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Reviewer 4 Report

This article can be accepted for publication. 

Author Response

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