Modeling for Generating Femtosecond Pulses in an Er-Doped Fiber Using Externally Controlled Spectral Broadening and Compression Mechanisms

Round 1

Reviewer 1 Report

In this paper, the authors developed a model for generating femtosecond laser pulse in an inverted populated single mode Er doped optical fiber. However, I can’t see a historic development of generating fs pulses nor an introduction to current challenges. Overall, the novelty and your motivation are not clearly presented. Besides, the citations are not right included, eg, the Eqs (2-17).

Author Response

Responses for the reviewers

Dear Editor and Reviewers,

We would like to thank you fand the reviewers for their fruitful review, and constructive suggestions and comments to improve the quality of the manuscript. Based on the suggestions and comments of the reviewers, we have modified the manuscript, and submitting it for consideration of publication in Photonics Journal. The point-to-point responses to the reviewers’ comments are listed below.

For reviewer #2

Comments and Suggestions for Authors

In this paper, the authors developed a model for generating femtosecond laser pulse in an inverted populated single mode Er doped optical fiber. However, I can’t see a historic development of generating fs pulses nor an introduction to current challenges. Overall, the novelty and your motivation are not clearly presented. Besides, the citations are not right included, eg, the Eqs (2-17).

 

-Regarding the introduction, we presented the application of the femtosecond (fs) laser to emphasize its importance. Besides, a lot of broadening and compression methods are presented as a historical development for generating fs laser pulse. These methods are based on internal nonlinear effects to achieve spectral broadening of mode locked laser. For compression, the presented methods require compressor element movement to achieve the compressed pulse at any desired location. Also, a multi-stage compressor for stage stepwise reduction of the pulse duration is mentioned.

-Regarding the motivation and novelty, the challenge in the current model is to generate fs laser pulse through external spectrum broadening and develop one-stage compressor for achieving fs laser pulse at any desired location without compressor elements movement which represent our motivation and novelty of the current work.

-Regarding the citation of Eqs(2-17), Eqs (2-3) are the well-known Maxwell’s equations, but the issue of its solution in a cylindrical coordinates is based on the possibility of attaining high electric field strength controlled from the dementor of equation (15) that can take small values. By this means the spectrum of the mode locked laser pulse is broadened externally and one is not in need to apply internal nonlinear phenomenon for generating broad spectrum.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper has proposed a model for generating femtosecond laser pulses. Pulses of moderate temporal half width come from a low power mode locked laser. Their phase are modulated and their spectrum are boardened by  EDFA with a circular capacitor having an electric field of suitable intensity and frequency. Finally, the pulses are compressed to femtosecond pulsewidth by a four-prism compressor with a slab subjected to a DC electric field. This paper has shown the numerical simulation results.

1.In the introduction, the references have been listed but their relationship with the femtosecond laser generator model has not been shown clear. The technology development route of the new model is not clear.

2.What are the original ideas? This paper should describe its own orginal ideas and make clear their advantages or differences  from the past technology. It should be better to give more details and emphasis on them.

3.The authors should try to improve in general the clarity of the presentation and the quality of the English. For example in "1.1 Aim of the work", the whole paragragh contains only one sentence which is too complex to understand. For example in  "4. conclusion", there're some errors in grammar.

4.It should be better that the method may be verified in experiments if possible.

 

Author Response

Responses for the reviewers

Dear Editor and Reviewers,

We would like to thank you fand the reviewers for their fruitful review, and constructive suggestions and comments to improve the quality of the manuscript. Based on the suggestions and comments of the reviewers, we have modified the manuscript, and submitting it for consideration of publication in Photonics Journal. The point-to-point responses to the reviewers’ comments are listed below.

For reviewer #1

Point 1. In the introduction, the references have been listed but their relationship with the femtosecond laser generator model has not been shown clear. The technology development route of the new model is not clear.

Response 1:

-Regarding the introduction:

The introduction is divided into three parts, part #1 deals with the application of the femtosecond laser (fs) in different fields to emphasize the importance of its development. The references [1-9] show these applications. To generate fs laser pulse, it is necessary to broaden the spectrum of an ordinary mode locked laser and to temporally compress the broaden spectrum. In this context, part #2, references [10-14], deals with different mechanisms for spectral broadening. References [15-22] in part #3 deal with different temporally compression methods.

-Regarding the technology development route of the new model:

a- For broadening

Most of the publications deal with internal methods for spectral broadening mode locked laser pulses. Since these methods depend on nonlinear behavior, only intense mode locked laser has been considered.

The current model is based on external broadening of low power mode locked laser rather than intense one.

b-For Compression

Most publications deal with either multi-stage compressor or compressor with movable elements to generate fs laser at a particular location.

In the current model:

1-The model is based on one-stage compressor that allows fs laser pulse to be generated at any desired location without compressor elements movement.

2-The compression is based on computer-controlled phases change such that at a desired location spectral constructive superposition is initiated.

Point 2. What are the original ideas? This paper should describe its own orginal ideas and make clear their advantages or differences from the past technology. It should be better to give more details and emphasis on them.

-The original ideas are based on

1-Generating fs laser pulse from low power mode locked laser with any temporal half width.

2- Constructing a compressor that allows fs laser to be generated at any desired location without compressor elements movement.

- The advantage of the current model compared with the past technologies are:

1- Applying low power mode locked laser in broadening process rather than intense one.

2- One-stage compressor is considered in the current model.

3- Generation of fs laser pulse at any desired location without compressor elements movement.

Point 3. The authors should try to improve in general the clarity of the presentation and the quality of the English. For example in "1.1 Aim of the work", the whole paragragh contains only one sentence which is too complex to understand. For example in "4. conclusion", there're some errors in grammar.

• Regarding the aim of the work, it is rewritten in the revised manuscript considering your comment.
• Regarding the clarity of presentation and quality of English, the manuscript has been sent to English Editing Services centre to improve the quality of English.
• The grammar’s errors and spelling error- mistakes have been corrected.

4.It should be better that the method may be verified in experiments if possible.

Unfortunately, the experimental verification is not possible due to financial difficulties.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

1. Since there is a laser pulse compression from 90fs to 30fs, there could have been a chirping of the laser pulse due to compression/stretching. Was this taken into consideration? 

2. How was the second-order non-linear electric field strength considered to be almost on the same order of magnitude as the first order (E) of the electric field, especially when the value of E was near 100V/mm?

Author Response

Dear Editor and Reviewers,

We would like to thank you and the reviewers for their fruitful review, and constructive suggestions and comments to improve the quality of the manuscript. Based on the suggestions and comments of the reviewers, we have modified the manuscript, and submitting it for consideration of publication in Photonics Journal. The point-to-point responses to the reviewers’ comments are listed below.

 

Point 1. Since there is a laser pulse compression from 90 fs to 30 fs, there could have been a chirping of the laser pulse due to compression/stretching. Was this taken into consideration?

 

Response 1

Regarding the chirping of the laser pulse due to compression, it is taken into consideration by the author according to his sentence” a grating pair produces a quadratic phase shift on the spectrum with a sign opposite to the chirp”

 

Point 2. How was the second-order non-linear electric field strength considered to be almost on the same order of magnitude as the first order (E) of the electric field, especially when the value of E was near 100 V/m.

 

Response 2

Regarding the magnitude of the electric field, in the current manuscript only Kerr’s effect has been considered to let n₂E² to be in the order of n_o which is necessary in equation (17). While E=100 V/mm is considered only in equation (20) to let  to be a fraction of 2π to account for constructive super-positioning of the spectral components at a desired location. By taking E instead of E², the slab length will be multiplied by 100 and thus the compressor length will be 100 x 20 cm=20m approximately.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

If possible, check the sentences and cut them shorter for reading

Author Response

Dear Editor and Reviewers,

We would like to thank you and the reviewers for their fruitful review, and constructive suggestions and comments to improve the quality of the manuscript. Based on the suggestions and comments of the reviewers, we have modified the manuscript, and submitting it for consideration of publication in Photonics Journal. The point-to-point responses to the reviewers’ comments are listed below. We are sorry for late reply.

For reviewer #1

Moderate English changes required

• Regarding the improvement of the quality of English. It has been done throughout the manuscript especially in the highlighted sections.

Check the sentences and cut them shorter for reading

• The sentences are shorted to be easy for reading.

Author Response File: Author Response.docx

Reviewer 2 Report

This paper has proposed a model for generating femtosecond laser pulses. Pulses of moderate temporal half width come from a low power mode locked laser. Their phase are modulated and their spectrum are boardened by  EDFA with a circular capacitor having an electric field of suitable intensity and frequency. Finally, the pulses are compressed to femtosecond pulsewidth by a four-prism compressor with a slab subjected to a DC electric field. This paper has shown the numerical simulation results.
1.In the introduction, the references have been listed but their relationship with the femtosecond laser generator model has not been shown clear. The technology development route of the new model is not clear.
2.The authors should try to improve in general the clarity of the presentation and the quality of the English.
3.It should be better that the method may be verified in experiments if possible.

Author Response

Dear Editor and Reviewers,

We would like to thank you and the reviewers for their fruitful review, and constructive suggestions and comments to improve the quality of the manuscript. Based on the suggestions and comments of the reviewers, we have modified the manuscript, and submitting it for consideration of publication in Photonics Journal. The point-to-point responses to the reviewers’ comments are listed below. We are sorry for late reply.

For reviewer #2

Extensive editing of English language and style required

• Regarding the improvement of the quality of English. It has been done throughout the manuscript especially in the highlighted sections.

This paper has proposed a model for generating femtosecond laser pulses. Pulses of moderate temporal half width come from a low power mode locked laser. Their phase are modulated and their spectrum are boardened by  EDFA with a circular capacitor having an electric field of suitable intensity and frequency. Finally, the pulses are compressed to femtosecond pulsewidth by a four-prism compressor with a slab subjected to a DC electric field. This paper has shown the numerical simulation results.

1. In the introduction, the references have been listed but their relationship with the femtosecond laser generator model has not been shown clear. The technology development route of the new model is not clear.

1- Besides the cited references, four references [23-26] related to the current work are added.

-Regarding the technology development route of the new model:

The study of previous publications showed that most of them are based on internal nonlinear effects for generating femtosecond laser. The presented work in contrary is devoted to apply external effects for generating femtosecond laser based on external phase-modulation for spectral broadening the laser pulse and external variation of the spectral optical path lengths to temporary compress the pulse. (See introduction and aim of the work). By this means it is possible to generate femtosecond laser from low power mode-locked laser.

 

2- The authors should try to improve in general the clarity of the presentation and the quality of the English.

2-   Besides, the corrections of the MDIP center, some corrections are made to improve the clarity of the presentation of English. (Highlighted).

3- It should be better that the method may be verified in experiments if possible.

3-   Unfortunately, the experimental verification of the presented model is not possible due to financial difficulties.

Author Response File: Author Response.docx