A Stabilized Single-Longitudinal-Mode and Wide Wavelength Tunability Erbium Laser

Round 1

Reviewer 1 Report

In this paper, a quad-ring EDF laser with selectable CW output and stabilized SLM oscillation is exhibited. The simple quad-ring architecture was designed to generate the mode-filter influence based on the Vernier effect for MLM suppression. Besides, a C-band erbium-based gain medium is exploited and the tunable scope can be extended from C- to part of L-bands, which is of great significance. Here are the comments for this work:

1. Fig. 3 exhibits the five selected wavelength spectra of 1519.0, 1533.0, 1548.0, 1562.0 and 1576.0 nm in the EDF quad-ring laser, respectively.When measuring the output spectrum of different wavelengths, is the pump power used by the laser the same? If yes, please give the pump power value of the laser and the optical signal-to-noise ratio corresponding to each wavelength; If not, please give the corresponding pump power value and output optical signal-to-noise ratio of lasers with different wavelengths.
2. TBF is the key device of tunable laser. Please give the filter bandwidth, tuning range and other parameters of the filter.
3. Can you explain in detail how the laser realizes single longitudinal mode and whether the key device to realize single longitudinal mode is quad-ring structure or band-pass filter?

Author Response

Dear Editor,

 

Re: (photonics-1725623) Manuscript entitled “A Stabilized Single-Longitudinal-Mode and Wide Wavelength Tunability Erbium Laser,”

 

Please find attached the revised manuscript entitled “A Stabilized Single-Longitudinal-Mode and Wide Wavelength Tunability Erbium Laser”. We wish to resubmit the manuscript for consideration for publication in Photonics.

 

We truly appreciate all the constructive comments and suggestions from the editor and reviewer. We have adopted all the suggestions in our revised manuscript. We have carefully revised the manuscript and we have indicated the changes using underlined text in the following.

 

Reviewer #1:

In this paper, a quad-ring EDF laser with selectable CW output and stabilized SLM oscillation is exhibited. The simple quad-ring architecture was designed to generate the mode-filter influence based on the Vernier effect for MLM suppression. Besides, a C-band erbium-based gain medium is exploited and the tunable scope can be extended from C- to part of L-bands, which is of great significance. Here are the comments for this work:

 

1. 3 exhibits the five selected wavelength spectra of 1519.0, 1533.0, 1548.0, 1562.0 and 1576.0 nm in the EDF quad-ring laser, respectively. When measuring the output spectrum of different wavelengths, is the pump power used by the laser the same? If yes, please give the pump power value of the laser and the optical signal-to-noise ratio corresponding to each wavelength; If not, please give the corresponding pump power value and output optical signal-to-noise ratio of lasers with different wavelengths.

[Response] We appreciate the reviewer’s insightful and helpful comment to improve our manuscript. In the demonstration, since the C-band EDFA is a commercial product, we have no way of knowing the actual pumping power of 980 nm LD. However, we have included the related optical parameter of EDFA in the revision as below. The corresponding statements are exhibited as below.

 

In page 3:

Once the TBF is adjusted continuously in the presented laser cavity, the generated wavelength can be tuned from 1519.0 to 1584.0 nm. So, Fig. 3 exhibits the five selected wavelength spectra of 1519.0, 1533.0, 1548.0, 1562.0 and 1576.0 nm in the EDF quad-ring laser, when the pumping power of C-band EDFA is fixed, respectively.

 

In page 4:

Fig. 5 exhibits the observed optical signal to noise ratio (OSNR) versus the output wavelengths of 1519.0 to 1584.0 nm, when the pumping power is fixed. The entire obtained OSNRs are between 50.4 and 64.8 dB.

 

2. TBF is the key device of tunable laser. Please give the filter bandwidth, tuning range and other parameters of the filter.

[Response] We would like to thank the reviewer’s useful comment. We have added the description in the revision as follows.

 

In page 3:

Here, the 3 dB bandwidth and insertion loss of the TBF used are 0.4 nm and 6 dB in the achievable bandwidth of 1520 to 1610 nm.

 

3. Can you explain in detail how the laser realizes single longitudinal mode and whether the key device to realize single longitudinal mode is quad-ring structure or band-pass filter?

[Response] We would like to thank the reviewer providing constructive comments. To explain this phenomenon, we have stated the description and added the new figure 3 in the revision. Thanks a lot.

 

In page 3:

 

Figure 3. The schematic of SLM oscillation based on the Vernier effect under the proposed fiber structure of Ring 1 to Ring 4.

 

In page 3:

As displayed in Fig. 3, the multiple longitudinal modes could be reduced excellently due to the use of the quad-ring structure, which is used in the EDF laser to serve as the mode filter and to facilitate the SLM output, when the TBF is applied for wavelength selection randomly. Therefore, the proposed quad-ring scheme can suppress the dense MLM and make it easier for SLM selection.

 

 

Should you have any questions regarding the manuscript, you may contact me by email ([email protected]).

Yours sincerely,

 

Chien-Hung Yeh

Professor (Chair)

Department of Photonics

Feng Chia University

Taichung 40724, TWIAWN

Author Response File: Author Response.docx

Reviewer 2 Report

The authors designed and experimentally demonstrated a quad-ring EDF laser with selectable CW output and stabilized single-longitudinal-mode (SLM) oscillation. In their experiments, a C-band erbium-based gain medium is applied, both the tunable scope and linewidth of the laser are fine, which are interesting to me. I think this manuscript is worth of being published in Photonics provided that the authors address the following questions.

1. The Vernier effect is the main principle of this work, it would be better to add more details about the Vernier effect in quad-ring scheme.
2. Some important optical properties of the erbium-based gain medium are not provided, such as geometrical specifications, operating wavelength, absorption and gain. These factors are necessary for EDF laser system and should be provided.
3. In the manuscript, the authors state a self-homodyne technique is applied to confirm the SLM behavior, but the principle of this technique is not well explained, it is appropriate to explain or add references.
4. The authors claim that this is a stabilized SLM laser, but the measuring time is only 40 minutes, which is not enough. The stability of lasers should be measured in days or weeks.
5. Some errors: 1) Ref. 16 wasn`t cited in the manuscript. 2) The name of vertical coordinate in Fig. 4 should be OSNR, not “ONSR”.

Once the above concerns are fully addressed, the manuscript could be accepted for publication in this journal.

Author Response

Dear Editor,

 

Re: (photonics-1725623) Manuscript entitled “A Stabilized Single-Longitudinal-Mode and Wide Wavelength Tunability Erbium Laser,”

 

Please find attached the revised manuscript entitled “A Stabilized Single-Longitudinal-Mode and Wide Wavelength Tunability Erbium Laser”. We wish to resubmit the manuscript for consideration for publication in Photonics.

 

We truly appreciate all the constructive comments and suggestions from the editor and reviewer. We have adopted all the suggestions in our revised manuscript. We have carefully revised the manuscript and we have indicated the changes using underlined text in the following.

 

 

Reviewer #2:

The authors designed and experimentally demonstrated a quad-ring EDF laser with selectable CW output and stabilized single-longitudinal-mode (SLM) oscillation. In their experiments, a C-band erbium-based gain medium is applied, both the tunable scope and linewidth of the laser are fine, which are interesting to me. I think this manuscript is worth of being published in Photonics provided that the authors address the following questions.

 

1. The Vernier effect is the main principle of this work, it would be better to add more details about the Vernier effect in quad-ring scheme.

[Response] We would like to thank the reviewer providing constructive comments. To explain this phenomenon, we have stated the description and added the new figure 3 in the revision. Thanks a lot.

 

In page 3:

Here, in order to cause different FSRs for the mode-filter effect, the lengths of Ring 1 to Ring 4 of 26, 25, 23 and 27 m are used, respectively. The corresponding four FSRs of 7.86 (FSR 1), 8.17 (FSR 2), 8.88 (FSR 3) and 7.57 MHz (FSR 4) can be attained in the demonstrated EDF laser. As displayed in Fig. 3, the multiple longitudinal modes could be reduced excellently due to the use of the quad-ring structure, which is used in the EDF laser to serve as the mode filter and to facilitate the SLM output, when the TBF is applied for wavelength selection randomly. Therefore, the proposed quad-ring scheme can suppress the dense MLM and make it easier for SLM selection.

 

 

Figure 3. The schematic of SLM oscillation based on the Vernier effect under the proposed fiber structure of Ring 1 to Ring 4.

 

2. Some important optical properties of the erbium-based gain medium are not provided, such as geometrical specifications, operating wavelength, absorption and gain. These factors are necessary for EDF laser system and should be provided.

[Response] We highly appreciate the reviewer’s insightful comment on our revised manuscript. We have included the related parameters of the commercial EDFA in the revision.

 

In page 2:

Here, the commercial EDFA module (GIP, Taiwan), having the saturable output power of 13 dBm in the obtainable C-band gain range of 1528 to 1562 nm, is applied in the ring cavity as the gain medium. The input power range of EDFA is -30 to -10 dBm with the corresponding gain and noise figure of 30 and 5.5 dB over the operation bandwidth, respectively.

 

3. In the manuscript, the authors state a self-homodyne technique is applied to confirm the SLM behavior, but the principle of this technique is not well explained, it is appropriate to explain or add references.

[Response] We highly appreciate the reviewer’s useful suggestion on our revised manuscript. We have stated the description and added the related references in the revision as below.

 

In page 4:

Then, we will confirm the SLM behavior of the demonstrated quad-ring EDF laser design. A self-homodyne technique is applied for measurement. The optical setup is consisted of two CPR₂, a PC and a length of 50 km fiber, respectively, by the MZI architecture [9, 10]. Hence, each lasing wavelength can be verified by the beat signal from the MZI for SLM observation.

 

4. The authors claim that this is a stabilized SLM laser, but the measuring time is only 40 minutes, which is not enough. The stability of lasers should be measured in days or weeks.

[Response] We would like to thank the reviewer’s suggestion. In fact, to measure the output stability measured in days or weeks is more difficult to implement. Moreover, in the previous related studies [5, 7, 9, 17], the interval of 10 to 60 minutes was used as the main measurement time. Thus, the 40-minute measurement we use is a typical observed time to verify the output stability of EDF laser. We hope that the reviewer can understand the actual situation. Thanks a lot.

 

5. Some errors: 1) Ref. 16 wasn`t cited in the manuscript. 2) The name of vertical coordinate in Fig. 4 should be OSNR, not “ONSR”.

[Response] Thanks the reviewer to point out the mistake. We have modified according to the reviewer’s suggestion in the revision.

 

In page 1:

1) In the introduction part:

Therefore, to achieve a broad tunability in EDF lasers, using the high concentration EDFs [9, 15] and hybrid optical amplifiers [16, 17] have also been demonstrated.

 

In page 4:

2) We have corrected the error of Fig. 5.

 

Figure 5. Measured OSNR of each wavelength in the tuning range of 1519.0 to1584.0 nm.

 

Once the above concerns are fully addressed, the manuscript could be accepted for publication in this journal.

 

 

Should you have any questions regarding the manuscript, you may contact me by email ([email protected]).

Yours sincerely,

 

Chien-Hung Yeh

Professor (Chair)

Department of Photonics

Feng Chia University

Taichung 40724, TWIAWN

Author Response File: Author Response.docx

Reviewer 3 Report

In the manuscript 'A Stabilized Single-Longitudinal-Mode and Wide Wavelength Tunability Erbium Laser, ' the authors Chen et al reported their research on the tunable Erbium laser. The reported tunable range in wavelength was from 1519.0 to 1584.0 nm. The manuscript can be accepted as the publication in Photonics only after the following questions are answered.

1. In the authors' opinion, why different ring shape will affect the tunability of the laser? Please add some explanation in the manuscript.
2. The authors have claimed in the introduction that the high concentration contributes to the tunability, while they did not mention the relative information of the EDFs they just applied in the system, please add this information.

Author Response

Dear Editor,

 

Re: (photonics-1725623) Manuscript entitled “A Stabilized Single-Longitudinal-Mode and Wide Wavelength Tunability Erbium Laser,”

 

Please find attached the revised manuscript entitled “A Stabilized Single-Longitudinal-Mode and Wide Wavelength Tunability Erbium Laser”. We wish to resubmit the manuscript for consideration for publication in Photonics.

 

We truly appreciate all the constructive comments and suggestions from the editor and reviewer. We have adopted all the suggestions in our revised manuscript. We have carefully revised the manuscript and we have indicated the changes using underlined text in the following.

 

Reviewer #3:

In the manuscript “A Stabilized Single-Longitudinal-Mode and Wide Wavelength Tunability Erbium Laser,” the authors Chen et al reported their research on the tunable Erbium laser. The reported tunable range in wavelength was from 1519.0 to 1584.0 nm. The manuscript can be accepted as the publication in Photonics only after the following questions are answered.

 

1. In the authors' opinion, why different ring shape will affect the tunability of the laser? Please add some explanation in the manuscript.

[Response] We would like to thank the reviewer providing constructive comments. We have included the explanation in the revision.

 

In page 4:

As mentioned above, the original reachable gain of EDFA is between 1528 and 1562 nm. However, the achieved tunability of the presented quad-ring based EDF laser can be extended from 1519.0 to 1584.0 nm. This means that the quad-ring scheme also can suppress and increase the gain-medium range. Therefore, the proposed EDF laser results in a smaller output power over the obtainable tuning bandwidth, as seen in Fig. 4.

 

2. The authors have claimed in the introduction that the high concentration contributes to the tunability, while they did not mention the relative information of the EDFs they just applied in the system, please add this information.

[Response] We appreciate the reviewer’s helpful comments to improve our manuscript. In this paper, we only apply the commercial C-band EDFA acting as the gain-medium in our proposed quad-ring based EDF laser configuration. To avoid the confusion, we have added the related description in the revision.

 

In page 2:

Here, the commercial EDFA module (GIP, Taiwan), having the saturable output power of 13 dBm in the obtainable C-band gain range of 1528 to 1562 nm, is applied in the ring cavity as the gain medium. The input power range of EDFA is -30 to -10 dBm with the corresponding gain and noise figure of 30 and 5.5 dB over the operation bandwidth, respectively.

 

In page 4:

As mentioned above, the original reachable gain of EDFA is between 1528 and 1562 nm. However, the achieved tunability of the presented quad-ring based EDF laser can be extended from 1519.0 to 1584.0 nm. This means that the quad-ring scheme also can suppress and increase the gain-medium range. Therefore, the proposed EDF laser results in a smaller output power over the obtainable tuning bandwidth, as seen in Fig. 4.

 

 

Should you have any questions regarding the manuscript, you may contact me by email ([email protected]).

Yours sincerely,

 

Chien-Hung Yeh

Professor (Chair)

Department of Photonics

Feng Chia University

Taichung 40724, TWIAWN

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

can be accepted.