Maximum Pump Power Coupled in Raman Resonator for Maximum Power Delivered at 1115 and 1175 nm

Round 1

Reviewer 1 Report

Comments:

 

In this work, L. de la Cruz-May et.al. analyzed the relationship between the critical power and stimulated Raman scattering (first Stokes) in Raman fiber lasers. This work is within the scope of Photonics, and I would like to recommend it to be published after a minor revision.

 

1. There are multiple places of units inconsistencies in the article, such as in Table 1 and Table 2, “-Km”,“-km”.

2. Please supplement the spectral image of the first and second Stokes wavelengths.

3. There is a cascade Raman fiber laser in this work, how to achieve the independent adjustment of the output power for N-stokes.

4. Does the theoretical formula in section-2 only can be applied in resonators configuration of simple linear?

Author Response

Thank you very much for your comments. The points were attended:

1. There are multiple places of units inconsistencies in the article, such as in Table 1 and Table 2, “-Km”,“-km”.

The changes were made.

2. Please supplement the spectral image of the first and second Stokes wavelengths.

Figures 2C and 2D) were added

3. There is a cascade Raman fiber laser in this work, how to achieve the independent adjustment of the output power for N-stokes.

We have changed "and so on" to "2 for the second Stokes" line 191.

4. Does the theoretical formula in section-2 only can be applied in resonators configuration of simple linear?

Equation (3) is useful to calculate the critical power of the free running or cascaded Raman fiber laser configurations, for which it is necessary to estimate the value of the Stokes PP0 signal at the fiber input.  Line 71-74.

Reviewer 2 Report

The presented experimental data have a number of critical lacks.

1.       Pump laser parameters was not described well (laser linewidth, polarization state, etc.).

2.       You also do not give a complete description of used FBGs.

3.       During the experiments, you simultaneously changed fiber type and its length. Based on such data, it is difficult to draw correct conclusions.

4.       As is known, «truewave» and «leaf» fibers are not single-mode in the spectral range of 1 μm. However, this point was not discussed in the article.

5.       I have not found an estimate of splice losses for «truewave» and «leaf» fibers.

6.       You mentioned that spectral data were collected, but they are not presented in the article.

I believe it would be useful for the wide readers to present the fiber length optimization for each type of fiber.

Before serious revision, I cannot recommend your article to publication.

Author Response

Thank you very much for your comments. The points were attended:

1. Pump laser parameters was not described well (laser linewidth, polarization state, etc.).

The pump source is a CW Yb fiber laser (FL) model YLR-10-1064-LP fabricated by IPG Photonics, delivering up to 10-W at 1064-nm in a linearly polarized beam in TME00 output mode, emission linewidth 0.5-nm, with output fiber type PM SM Panda 1060 that was already spliced to a 1060-XP fiber.    Line 84-87.

2. You also do not give a complete description of used FBGs.

The HR-FBGs operating for first and second Stokes (1115 and 1175-nm), with ~99% reflectivity, were patterned on Flexcore-1060 SM fiber (almost identical to 1060-XP) with core diameter of ~6-µm (5.3-µm MFD of 6.2 µm at 1064) and linewidth of ~ 0.8 nm.. Line 81-84

3. During the experiments, you simultaneously changed fiber type and its length. Based on such data, it is difficult to draw correct conclusions.

We believe that this observation becomes clear with the corrections made to the other revisions.

4. As is known, «truewave» and «leaf» fibers are not single-mode in the spectral range of 1 μm. However, this point was not discussed in the article.

Although the TrueWave and LEAF fibers are multimode within the region of study, when spliced-excited by the 1060-XP single mode fiber, although bigger in diameter, only the TEM00 mode becomes excited; then, all the system operates as single mode. Line 121-123.

5. I have not found an estimate of splice losses for «truewave» and «leaf» fibers.

In figure 1, the delivery fiber of the pump source was spliced to the test fibers; 1-Km of 1060-XP, 5-Km of TrueWave and 9.6-Km of LEAF fiber; the splice loss was negligible for the 1060-XP, and it is estimated to be ~ 0.41 dB when spliced to the TrueWave and LEAF fibers; the same loss estimation is valid when connecting through the FBGs as in figure 1B.  Line-88 -91.

6. You mentioned that spectral data were collected, but they are not presented in the article.

The spectra were obtained on a linear scale, see figures 2C) and 2D). For each spectrum, the power at the output end of the fiber was measured. The areas of the residual power, the first and the second Stokes, were taken into account to calculate the values of the respective output powers.  Line 99-102

Reviewer 3 Report

I appreciate this experimental work. The manuscript entitled "Maximum pump power coupled in Raman resonator for maximum power delivered at 1115 and 1175-nm" related to Raman fiber laser research field and presents useful results that cover peculiarities of light propagation in optical fibers in free running configuration and in cascaded regime.

The manuscript should be interesting for MDPI Photonics readers. I think the manuscript might be published after a revision is done addressing the points below:

1. Abbreviations use looks a bit messy:

• Line 20: “OC” should be properly introduced or deleted (it does not used in text further)

• Line 61:  “SRS” the same issue

• Line 53: “The propagation of...”, it will be better to introduce “z” in advance, e.g. “...z-propagation”, or “propagation along z”, or introduce it after equations

• Line 62: “L, Pp0, Pf0” should introduced

• Lines 15, 20, 21, 23, 43, 65, 66, 70, 144, 147, 151, 153, 156, 161, 168...: Authors should stick to one style – for the term “the Smith constant”. There are different versions of the spelling in the same manuscript:  “the Smith constant”, “the Smith’s constant”, “the R.G. Smith constant”, “the R.G. Smith’s constant” and etc.

2. Equations (1) and (2) should be rechecked, since they coincide with the equations in ref.5 (eq.41, eq.42), ref.9 (eq.8.1.2), ref.6 (eq.2) up to the sign and notation, but are not completely identical.

3. Line 29: “1.1 to 1.7-nm”. Perhaps the authors mean micrometers, not nanometers
 Line 40: “From de interaction...” English should be polished
 Line 151: “...[9]. Where...” should be “...[9], where...”

Author Response

Thank you very much for your comments. The points were attended:

1. Abbreviations use looks a bit messy:

• Line 20: “OC” should be properly introduced or deleted (it does not used in text further)

the suggestion was made

• Line 61:  “SRS” the same issue

the suggestion was made

• Line 53: “The propagation of...”, it will be better to introduce “z” in advance, e.g. “...z-propagation”, or “propagation along z”, or introduce it after equations 

the suggestion was made. Line 55

• Line 62: “L, Pp0, Pf0” should introduced

L is the fiber length, P_P0 is the coupled pump power and P_F0 is the Stokes power at the fiber input. Line 65

• Lines 15, 20, 21, 23, 43, 65, 66, 70, 144, 147, 151, 153, 156, 161, 168...: Authors should stick to one style – for the term “the Smith constant”. There are different versions of the spelling in the same manuscript:  “the Smith constant”, “the Smith’s constant”, “the R.G. Smith constant”, “the R.G. Smith’s constant” and etc.

The changes were made.

2. Equations (1) and (2) should be rechecked, since they coincide with the equations in ref.5 (eq.41, eq.42), ref.9 (eq.8.1.2), ref.6 (eq.2) up to the sign and notation, but are not completely identical.

the suggestion was made, a reference was added.

13. Islam, M. Raman Amplifiers for telecommunications: Physical principles; Springer: 175 Fifth Avenue, New York, NY 10010, USA, 2014. pp 3. Line 239.

 

3. Line 29: “1.1 to 1.7-nm”. Perhaps the authors mean micrometers, not nanometers

the suggestion was made.

Line 40: “From de interaction...” English should be polished

The propagation along z of the pumping power and the Stokes signal generate two points of interest; the critical power and the maximum power delivered by the Stokes lines [9].  Line 43.

 

Line 151: “...[9]. Where...” should be “...[9], where...”

the suggestion was made. Line 174

Reviewer 4 Report

Please see attachments.

Comments for author File: Comments.pdf

Author Response

Thank you very much for your comments.
The points were attended:

1.- We have added the suggested references to the "introduction" of the manuscript.
2.- The main idea of this work is to quantify the pumping power for which Stokes is maximum, while the article with reference [de la Cruz-May, L.; Alvarez-Chavez, J.A.; Mejia, E. B.; Flores-Gil, A.; Mendez-Martinez, F.; Wabnitz, S. Raman threshold for nth-order cascade Raman amplification.] only predicts the value of Stokes of order N, taking into account the constant of R.G. Smith for a pure silica fiber and not for a telecommunications fiber.

 

Round 2

Reviewer 2 Report

Thank you for revision!

The manuscript has been improved. 

Could you please provide spectral data with dBm scale and indicate the spectral resolution used?

Author Response

Dear Reviewer.

We have added the spectral resolution data.

Thanks for the suggestion.

Reviewer 4 Report

Comments for author File: Comments.pdf

Author Response

 

 

Dear reviewer.

 

We have attended to the suggestions that you make to the manuscript, an action that we appreciate. We have rewritten the last paragraph considering your suggestions, and adding information about the novelty of the manuscript.

 

 

"In general, when studying the propagation along z of the pumping power and the Stokes signals, besides the thresholds for the Stokes generations, one focus its attention on certain points of interest such as the critical powers and the maximum power delivered by the Stokes lines. The equations that govern the propagation of the pump and Stokes signals have been solved before; such a solution is an analytical equation which allows estimating the power necessary to reach the critical power and the maximum power of the first Stokes [12]. Such estimations were made using the R.G. Smith constant of ~16 [8].

In the present work, we are investigating the typical structures of Raman fiber lasers, with the aim of calculating the pump powers at which the critical powers occur as well as the maximum powers reached at each subsequent Stokes before generating the next one, in telecom optical fibers. Our work was mainly focused in obtaining wavelengths close to 1175-nm as these are important to generate laser emission by frequency doubling in the yellow spectral region, useful for medical applications as well as “artificial star” projection on the sky for astronomical telescopes calibrations [13-15]. In particular, we are proposing a general expression that allows us to calculate the maximum pumping power necessary for any Stokes to reach its maximum power."

 

 

 

 

We have also removed figure 4. and in its place we have replaced the following text " the experimental results are similar to those shown in figure 4 of the reference [12]. "

 

Author Response File: Author Response.pdf

Round 3

Reviewer 4 Report

I suppose that the manuscript under revision can be published in MDPI Photonics in the current state.

However, I encourage the Authors to take the previously expressed comments into account in their future investigations.

Author Response

Dear Reviewer.

Thank you for your comments, they will be taken into account for future investigations.