A Narrow-Linewidth Optical Parametric Oscillator Inserted with Fabry–Perot Etalon
Round 1
Reviewer 1 Report
The authors present the use of etalon composed of ultrathin silicon wafers in a pulsed nanosecond PPLN OPO. The fabrication and characterization of the silicon wafers are discussed, and the applications of these silicon wafers used in a pulsed nanosecond OPO in the air-gap etalon configuration is given. The effect of wavelength selection using the intracavity placed etalon is discussed along with power scaling. I would recommend this paper if the following problems are addressed.
1) The authors mentioned that the introduced wafers would bring significant loss in the cavity. However, no supporting data is given in the manuscript. The detailed comparison of the output power with and without the etalon should be supplemented.
2) Why do the authors choose silicon etalons since there are a lot of optional materials? Its performance compared with the other materials or methods should be given. It is helpful to illustrate the significance of this article.
3) There are many language problems in the text. I suggest the authors find a native English speaker or ask professional editing service for content revision.
Author Response
Please see the attachment
Author Response File: 
Author Response.doc
Reviewer 2 Report
In this manuscript, the author reports on line-narrowing of a nanosecond pulsed OPO by use of an intracavity etalon composed of two ultra-thin silicon wafers.
While the technical content of the paper does not contain any significant errors, the reported progress from the state of the art is too incremental to merit publication in Photonics. Indeed, since the first reported demonstration of a single-longitudinal-mode emission from an OPO by use of an intracavity etalon more than 50 years ago [21], many papers have reported on this approach in the literature. In particular, in [28] an OPO combining a PPLN crystal and a Fabry–Perot etalon already provided better performances with a much better conversion efficiency (12% without etalon and 8% with etalon instead of 6.6 % and 1.9% here, respectively) and single axial mode oscillation (< 500 MHz bandwidth while only a 0.03 nm bandwidth [or 4 GHz] is proved here). Moreover, in this previous paper, wavelength tuning was also demonstrated, which is not the case here. The only novelty here is to use etalon composed of two ultra-thin silicon wafers to improve the filtering performance, which is no sufficient since the reported performances are not striking (very low efficiency and limited linewidth-narrowing).
Moreover, the relevance of some the cited papers in the references list are questionable. Indeed, several papers concern CW or synchronously-pumped OPOs where line narrowing strategies are quite different than for nanosecond pulsed OPOs in transient regime as reported here. This is particularly the case about references [30-32] for which it is hard for me to understand why the authors chose them to motivate their work. Moreover, other efficient techniques to narrow the linewidth of pulsed OPOs are not considered in the introduction, including injection-seeded OPOs and dual-cavity doubly resonant OPOs.
I thus recommend to reject this manuscript.
Author Response
Please see the attachment
Author Response File: Author Response.doc
Reviewer 3 Report
The research presented by the author has a certain value and interest for the reader. There are no significant drawbacks to work, but there are several aspects that could improve the quality of work:
- more emphasis should be placed on the novelty of the results obtained, especially in quantitative comparison with existing approaches;
- weak analytical background, there is no description of mathematical models, approaches to modeling, etc.
- it would be necessary to estimate the magnitude of the compression of the spectral width of the emission line for the experimental setup.
Author Response
Please see the attachment
Author Response File: Author Response.doc
Round 2
Reviewer 1 Report
The authors have answered all the questions and made appropriate revisions to the manuscript. I think the manuscript can be accepted in the present form.
Reviewer 2 Report
The authors improved the presentation of the background and the context. However, my main concern about the lack of improvement from the state of the art is still the same.
