Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This review paper focuses on the progress achieved in the domain of integrated laser sources on the silicon photonics platform. These on-chip lasers are categorized based on their gain media, encompassing V semiconductors, III-V semiconductors, two-dimensional materials, and colloidal quantum dots. The organization of this paper is well-structured, and its content is rich, making it suitable for acceptance; however, minor revisions are recommended.

 

Compared with heterogeneous integration, monolithic integration through direct epitaxial growth is more economically favorable. However, the large mismatch of lattice constants between the silicon and the III–V materials lead to high densities of crystalline defects which act as non-radiative recombination centers that grow with device operation, severely limiting the luminescence efficiency and the device lifetime. To improve the defect tolerance of the active region, replacing the quantum well structure with quantum dots greatly suppresses lateral diffusion and non-radiative growth of defects. Furthermore, compared with quantum well, another important aspect of quantum dot lasers is the small linewidth enhancement factor, which is beneficial to a reduced reflection sensitivity. The reflection insensitivity is of paramount importance for PIC applications wherein external reflections may quickly accumulate from different inner interfaces, therefore affecting the laser source. However, up to now, no integrated isolator has been demonstrated that provides strong isolation and negligible insertion loss. Overall, the isolator-free silicon-based quantum dot laser source eliminates the need for co-packaged/integrated optical isolators while still maintaining the required feedback tolerance, significantly reducing the packaging complexities and enhancing the integration density for future PICs.

 

I strongly recommend the author to incorporate the aforementioned points into the paper. Relevant literature references can be found in the following articles. Photonics Research, 7(11), 2019; Frontiers in Materials,8, 648049, 2021.

Comments on the Quality of English Language

Good.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper is well organized and reviews the state of art on-chip lasers in every aspect. It could be published on Photonics once the authors addressed the following concerns: 

1.  By using wafer bonding technology,  a turnkey soliton comb was achieved, and a Tb/s transmission on-chip system was demoed as well. It is suggested to discuss these two remarkable works （Shen, B., Chang, L., Liu, J. et al. Integrated turnkey soliton microcombs. Nature 582, 365–369 (2020; Rizzo, A., Novick, A., Gopal, V. et al. Massively scalable Kerr comb-driven silicon photonic link. Nat. Photon. 17, 781–790 (2023)).  in the manuscript.

2. Although quantum dots are one of the most promising materials for monolithic integration, people are still making improvements on quantum well on silicon technology. It would be good to include some recent progress about QW on Si.

3. Other than traditional III-V material systems such as GaAs and InP, it is suggested to cover some works about III-N on-chip laser. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Kindly see attached.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

NA

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The comments have been well addressed and I would recommend publication in Photonics.