Narrow Linewidth 510 nm Laser via Single-Pass Frequency-Tripling by Waveguide PPLNs

Round 1

Reviewer 1 Report (Previous Reviewer 1)

The manuscript has improved much and can be published.

"can reduce" is correct in page8 line249...

Author Response

Thank you very much for taking the time to review this manuscript. And thanks for your positive comments on our work. The details are presnted in the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report (Previous Reviewer 3)

The authors claims that the novelty of their results compared to that in ref [9] is that the central wavelength and linewidth in [9] were 514 nm and <10 kHz; and in the presented paper 510 nm, and 5kHz. This difference is very small and does not affect amplification and frequency conversion processes. So, for me, there is no novelty in this paper. What if tomorrow another group will make a laser with 512 nm and 7 kHz, but based on the same principle, does it mean that it also should be published? 

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report (New Reviewer)

The authors develop the technology and the operating principles of a 510 nm green laser to be used for Cs atoms. The overall quality of the paper is good. All methods of frequency generation with very narrow linewidth are clearly developed as well as the measurement of laser characteristics like: spectrum of emission, narrow linewidth, frequency fluctuations, temperature and RIN...Experimental results agree with the objectives, 5kHz linewidth, 200 mW output power; the laser structure and obtained performances are well suited for applications. I recommend publication of the revised form of the paper. 

Author Response

Thank you very much for your careful check and positive comments. 

Round 2

Reviewer 2 Report (Previous Reviewer 3)

ok

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The authors studied experimentally a 510nm laser based on single-pass second-harmonic generation (SHG) and sum-frequency generation (SFG) via waveguide PPLN seeded with a common C-band laser (1530 nm). The main issue is the temperature-dependence of such a lasing system which makes it inappropriate for many applications. The authors do not mention that if they kept the PPLN temperature constant, how much would the output power drop. How do they propose to solve this problem? What about using chirped gratings at least by a citation: 10.1109/JLT.2007.909862 Thus, mentioning the limitations is a must.

The manuscript is clear however, it looks like a letter. To publish the manuscript, the reviewer thinks that the following points should be clarified after a major revision:

1- The frequency conversion part is very weak and overwhelmed. A modification for much coherency is necessary. The frequency conversion results should be fully described.

2- The experiment results including output spectra for the measurement have not been presented nor described. They MUST be presented before and after Brillouin fiber loop and after PPLNs.

3- The cut, dimensions of the PPLN waveguides and poling width as well as many other details (eg., on HNLF) have not been mentioned.

4- Figures have no legends (eg. Fig. 4) or wrong one (6b).

5- What is beta-separation?

6- The coupler in Figure 1 is misleading on the Stokes output. Circular or circulator?!

7- A review on the English grammar is inevitable, as so many errors are present (e.g., ‘The linewidth of the laser obtain by SBS…, ‘And then the linewidth of the output 510 nm light are also tested’ and so on).

A review on the English grammar is inevitable, as so many errors are present (e.g., ‘The linewidth of the laser obtain by SBS…, ‘And then the linewidth of the output 510 nm light are also tested’ and so on).

Author Response

We would like to thank you for your careful reading, helpful comments, and constructive suggestions, which has significantly improved the presentation of our manuscript. Please see the attachment for more details about the replys. Thank you a lot.

Author Response File: Author Response.pdf

Reviewer 2 Report

Authors reported a narrow-linewidth 510nm laser based on single-pass SHG and SFG via waveguide PPLN seeded with a common C-band laser (1530 nm). The final linewidth measured by delayed self-heterodyne method reaches a narrow linewidth of 4.8 kHz. Quite careful experiments were presented. This work is interesting and impressive. Overall, the article is generally well written and suitable for publication in Photonics, but before that some minor corrections need to be addressed.

1.      "3.2 conversion Efficiency" should be "3.2 Conversion Efficiency";

2.      For the horizontal text of Figure 6. (a) and (b), “pump power” should be “Pump power”;

3.      How about the long time stability of the laser system.

Overall, the English writting of this article is good.

Author Response

Thank you so much for your careful check, helpful comments, which has significantly improved the presentation of our manuscript. And the reply to each comment is attached as follow:Thank you so much for your careful check, helpful comments, which has significantly improved the presentation of our manuscript. And the reply to each comment is attached in the attachment. 

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript is devoted to the development of 510 nm laser for the study of Cesium Rydberg atoms. Authors demonstrated a laser via SHG and SFG of single-frequency light source. The approach is not new and was demonstrated in reference [9] with even higher output power and conversion efficiency. The light coupling to PPLNs is slightly different in the manuscript compared to [9], but it is only minor technical improvement. So, the novelty of the manuscript is not clear, and I would recommend to reject the paper for this reason.  Couple more comments:

1.      1. Can authors compare their approach to that from Ref [8]? YDFAs near 1 micron can provide higher power than EDFAs, thus increasing the nonlinear conversion efficiency and output power of 510 nm laser. Also, in [8] only one nonlinear process (SHG) is used instead of two processes in the manuscript (SHG and SFG). The current manuscript has lower output bandwidth (4.8 kHz vs 40 kHz in [8]), but the bandwidth is defined by a linewidth of the seed laser, and narrow-linewidth seed lasers near 1 micron are currently available. Are there any other advantages of the proposed approach? This discussion would improve the overall quality of the paper.

2.        2. The manuscript lacks technical details of the experiment. What was the power and linewidth of the ECDL? What was the power of the first amplifier and the Brillouin-based narrow-linewidth laser? What were the parameters and loss of PPLN waveguides?

English is ok. Few spelling errors should be fixed.

Author Response

Thanks for your comments. The replys to your comments are listed in the attachment. Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

The paper entitled "Narrow linewidth 510nm laser via single-pass frequency-tripling by waveguide PPLNs" presents an experimental method to generate narrow linewidth green lasing through cascaded second-order nonlinear processes in PPLN waveguides. The experiments are well conducted, and the results show that an ultra narrow bandwidth is achieved. I can recommend this work to be accepted, after the minor comments are well addressed. To make the results more convincing, the SHG and SFG performances, e.g. phase-matching wavelength, bandwidth, normalized efficiency, of each PPLN are supposed to be given, as the linewidth can be affected by the nonuniform poling. 

Author Response

    We thank the reviewer for reading our paper carefully and giving the above positive comments.

    We add Figure 8 showing the normalized power via different temperature. As you can see the FWHM bandwidth temperature for SHG is 8.85 ℃, and for SFG is 2.00 ℃. And the SHG and SFG PPLNs are all design for the frequency-tripling of 1530 nm. And the supplier information and the polarization condition has been added in subsection 2. Please see the attachment for the details. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

It is not a wise way to remove part of the reviewer’s comments. In fact, every question must be answered and the limitation must be clarified. The authors have fully ignored this part of my comments and left it unanswered:

“The main issue is the temperature-dependence of such a lasing system which makes it inappropriate for many applications. The authors do not mention that if they kept the PPLN temperature constant, how much would the output power drop. How do they propose to solve this problem? What about using chirped gratings at least by a citation: 10.1109/JLT.2007.909862 Thus, mentioning the limitations is a must.”

The authors do not answer that if they did not keep the PPLN temperature constant, how much would the output power drop, eg. percent per degree Celsius. The uniform PPLN has a narrow BW and is temperature-dependent. This limitation MUST be clarified in the conclusion and mentioning the solution for the future work, eg., using chirped grating with broad BW, including citation of a paper, eg. 10.1109/JLT.2007.909862 is a MUST.

A review on the English is necessary! “Stokes” not “stocks”!

A review on the English is necessary!

Author Response

see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors added more technical details and discussion about SHG of 1 um lasers as was asked. However, they did not addressed the main concern from  the original review: what is novelty of the manuscript? Except few technical differences, the same result in a similar scheme was achieved in ref [9]. So, novelty of the paper is still not clear.

Author Response

see the attachment

Author Response File: Author Response.pdf