On-Chip Supercontinuum Generation Pumped by Short Wavelength Fiber Lasers

Round 1

Reviewer 1 Report

The manuscript titled "On-chip supercontinuum generation pumped by short wavelength fiber laser," which provides a valuable synthesis of the current state of research in this area. The paper is well-structured and covers a range of materials and methods for supercontinuum generation. However, there are opportunities to enhance the technical depth and clarity of the presentation. Here are my specific suggestions for revision:

1.While the manuscript mentions various materials, it lacks a detailed discussion on how the material's refractive index and dispersion profile are engineered to achieve specific supercontinuum spectra. Please provide a more nuanced analysis of the relationship between material properties and the resulting SC spectra, including examples of how dispersion engineering has been used to tailor the spectral broadening.

2.The paper briefly touches on the use of pump sources but does not delve into the impact of pump source harmonics on supercontinuum generation. Could you elaborate on how different pump wavelengths and pulse durations influence the SC generation process, and discuss any observed frequency-dependent effects?

3. The manuscript should address the technical challenges associated with fabricating waveguides for supercontinuum generation, such as controlling waveguide dimensions at the nanoscale and minimizing waveguide losses. Please provide specific examples of fabrication techniques and their impact on SC performance.

4. The paper would benefit from a more quantitative analysis of the nonlinear effects involved in supercontinuum generation, such as self-phase modulation and four-wave mixing. Please include calculations or simulations that demonstrate the relative contributions of these effects to the observed SC spectra.

5. While the manuscript reviews theoretical and simulated results, there is a need for a stronger emphasis on experimental validation. Please provide more detailed descriptions of experimental setups, measurement techniques, and a comparison of experimental results with theoretical predictions.

6. The manuscript should discuss the limitations to spectral broadening in supercontinuum generation, such as material absorption and scattering losses. Please clarify the current limits to spectral broadening and discuss potential strategies to overcome these challenges.

7. The paper would be strengthened by a more explicit discussion of the practical applications and implications of the research. How do the findings impact the development of on-chip photonic devices, and what potential technologies could benefit from the advancements in supercontinuum generation?

The English writing quality is generally good. The text is clear, well-structured, and uses appropriate technical terminology consistent with the field of photonics.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The review is very good and timely and can be published.

However, I would recommend revision of some sentences, for example

Authors say:” The brightness of the SC as a light source is several orders of the

magnitude of the synchrotron”

This is not clear. I assume they mean: The brightness of the SC as a light source is several orders of

magnitude lower than the brightness of a synchrotron.

This sentence can be acceptable, particularly to encourage readers to follow reading the review, because they claim, and it is true, that would be much cheaper than a synchrotron.

Other sentences as “While E-beam lithography is a solution that can produce high-quality waveguides, it is challenging to etch hard oxide materials like Ta2O5, physical etching like ion-milling is possible but the fabrication process for the individual materials should be further optimized.” Are difficult to read because they are far too long. Use a point instead of a comma in the middle, for example.  

I miss some scheme of the different lasers. Authos provide a lot of reprinted spectra, and this is perfect and well suited for the objective of the paper, but they miss some schemes on the SC generation. This will increase the readability of the paper. 

English is formally correct, but some sentences are misleading. As the ones indicated above. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Supercontinuum(SC) generation in various nonlinear media is an interesting topic that has attracted much interests recently. Especially, on-chip SC generation represents a tendency in the development of compact light source with small volume, and is finding practical applications in various fields as mentioned in the paper. Therefore the present paper is a timely summary covering several mainstream materials that are used in nonlinear optics. Moreover, in the end, the authors point out the possible issues that are limiting the spanning of  the SC spectra into the mid-infrared, especially the absorption of OH impurities at 2.9 um that is intrinsic in the materials but seldomly emphasized in the previous literatures. The paper can be published in Photonics after appropriate modifications. Below are some simple comments and questions about this work:

(1)    Subtitle 2. Si, SiN and SiO_{2 .} SiO2 has a low refractive index of 1.45 at 1.5 um and thus is used as cladding layer in the waveguides in most cases as mentioned in the paper.  It is arguable to include SiO2 in the subtitle since SC comes from the core layer with much high refractive index.

(2)     The missing part of the red shadow in Fig.5 is unclear and further explanation is needed.

(3)    The last sentence in the third paragraph  from the bottom in “Subtitle 9. Opportunities and challenging”  should be  ”but this has not been solved or has never been emphasized in the literature”. 

(4)    In the second paragraph  from the bottom in “Subtitle 9. Opportunities and challenging” . it is confusing  that ” this further amplifies the importance of high quality with low optical loss for achieving SC source down to the UV region”, is it “high quality waveguide”? 

The english should be improved.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf