Monolithically Integrated Michelson Interferometer Using an InGaAs/InAlAs Quantum Cascade Laser at λ = 4 µm

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper describes integrating interferometric functions on-chip with a single frequency MWIR laser.  The architecture is taken from an earlier near-infrared paper, but is adapted in some ways to be compatible with intersubband emission and detection.

While I do not think all of the arguments and extrapolations made by the author are completely correct, there is still some feasibility in the overall concept that may be of interest to other readers interested in MWIR photonic integrated circuits.  I support publication, but, as there is no experiment in this paper, it would be much stronger with some more rigorous modeling to define/ optimize waveguide and device geometries.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In this manuscript, the authors propose a new version of their previous Michelson interferometer (dating back to 1995 and 1996). Obviously, there appears a solid merit in this proposal that suggests its publication. Also, the manuscript is prepared well in general, with the following exception that raises questions that need addressing.

1- First of all, their previous work (almost 30 years ago) achieved a displacement resolution of 20 nm. So, achieving 500 nm 30 years later, even as a proposal not an implementation needs a clear justification for granting a publication.

2- The gain here is using the laser source with 5 times longer wavelength. But is this really a significant gain with the current technology? Even if it is, is it worth the coarser resolution?

3- As stated in lines 80&81, the five times longer laser wavelength will obviously result in a 5-times lower (coarser) measurement resolution, but the numbers simply don’t add up: 5 times 20 nm is 100 nm, not 500 nm, right? This simple point needs clarification.

4- Why is this proposal made almost 30 years after the original proposal? Has there been any recent and specific development that enabled this proposal at this time?

5- It is not clear enough how much of this proposal is physically implemented. The authors thank to the “former” Institute of Physics at the University of Neuchâtel for making the experimental equipment available. Related to the comment above, when was this exactly, and

6- The authors have explained some of the suitable applications, but I guess the readers would like to see if and how the present proposal can provide some advantages in other applications, including quantum metrology, and gravitational wave detection.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have answered all the comments and revised the manuscript well. I recommend the publication of the manuscript.