All-Monolithically Integrated Self-Scanning Addressable VCSEL Array for 3D Sensing

Round 1

Reviewer 1 Report

The authors describe their work on developing an integrated addressable high power VCSEL with several advantages. All of which is fine. What I struggled to understand was the starting context of time of flight systems. The authors describe how VCSELs can be used for ToF and describe some of the problems that Tof systems face. They do not however discuss how their technology overcomes any of those problems. They produce test pulses from their system that are 10nS in duration. Such pulses are too long to be useful for Tof - unless the rapid rise time is being used not the pulse length. Either way they need to explain this better. 

Author Response

Dear reviewers 

Thank you for your comment.

 I add comment “The pulse width can be shortened up to 2.5 ns with keeping rise time and fall time same for one-block and all-blocks emissions.” at the end of 3.Results.

That is correspond to measurement frequency of 200MHz.

100MHz measurement frequency or slow are mainly used for recent indirect ToF sensor. 

We explain problems in the manuscript.

As for measurement error due to flare noise or multi-pass noise, Addressable VCSEL is important to avoiding emission obstacles (in introduction).

As for distance measurement performance and large power consumption. There is “This result shows that the signal-to-noise (S/N) ratio is higher, measurement distance is longer, and power consumption and heat generation are lower when using the SS-VCSEL in comparison with those of the conventional multi-junction VCSEL.” in discussion

If you are talking about numerical result of those. I’d like to show those in different paper.

Best regards,

Takashi Kondo

Author Response File: Author Response.docx

Reviewer 2 Report

The authors should clearly write whether the epitaxial structure was fabricated by them or was it a commercial structure.

The authors should provide more details of the laser. What are the layers in the laser, what are their thicknesses and doping levels, how may periods in the DBRs are there, what is the length of the resonator, what active region was used etc. What are the diameters of the aperture and the mesa?

The analysis of the results would be much easier if the authors provided an LIV curve of a single emiter and its threshold current and voltage.

In figure 2 the oxide layer is shown on the n side. Is it really the case? If so, in what terms is it better than the usual p-side aperture?

Author Response

Dear Reviewer

The authors should clearly write whether the epitaxial structure was fabricated by them or was it a commercial structure.

I added “fabricated by us” on 56 line in the manuscript.

The authors should provide more details of the laser. What are the layers in the laser, what are their thicknesses and doping levels, how may periods in the DBRs are there, what is the length of the resonator, what active region was used etc. What are the diameters of the aperture and the mesa?

I wrote　“There are 22pairs p-Al0.15GaAs/Al0.9GaAs DBRs, 45pairs n-Al0.15GaAs/Al0.95GaAs DBRs and 3 InGaAs/AlGaAs quantum wells as an active layer.” on 57-58 line in the manuscript

The analysis of the results would be much easier if the authors provided an LIV curve of a single emiter and its threshold current and voltage.

Sorry we can’t add it.

In figure 2 the oxide layer is shown on the n side. Is it really the case? If so, in what terms is it better than the usual p-side aperture?

Thank you for your comment. I changed the figure.

Best regards,

Takashi Kondo

Author Response File: Author Response.docx

Reviewer 3 Report

In this manuscript, the authors studied the characteristics of the proposed self-scanning addressable VCSEL array, which has important application in the field of ToF.

The manuscript is well prepared. The method is scientific correct, and the results and discussion can strongly support the conclusion. In my option, the manuscript can be published on this journal.

For my opinion, in section 3 (Results), more explanations for the results are needed. For instance:

1. In Fig. 10, “Narrow spectrum widths of 0.6 and 0.27 nm were 120 achieved in the one-block and all-blocks emission modes, respectively.” What is the reason for the difference of the spectrum widths.

2. In Fig. 11, “The divergence angles corresponding to one-block and all-blocks emissions at 25 °C 127 were 18.9° and 13.5°, respectively.” What is the reason for the difference of the divergence angles.

3. In Fig. 12, “The rise times during all-blocks and one-block emissions 132 were 243 and 282 ps, respectively.” What is the reason for the difference of the rise times. And why there is overshot in Fig. 12(a).

Author Response

Dear reviewer 

Thank you for your comment.

1. In Fig. 10, “Narrow spectrum widths of 0.6 and 0.27 nm were 120 achieved in the one-block and all-blocks emission modes, respectively.” What is the reason for the difference of the spectrum widths.

I added “The spectrum width of one-block emission modes is wider than that of all-blocks emission modes due to the number of transverse modes with higher injected current density.” on 124-126 in the manuscript.

2. In Fig. 11, “The divergence angles corresponding to one-block and all-blocks emissions at 25 °C 127 were 18.9° and 13.5°, respectively.” What is the reason for the difference of the divergence angles.

I added “The divergence angles of one-block emission modes is wider than that of all-blocks emission modes due to the number of transverse modes with higher injected current density.” on 132-134 in the manuscript.

3. In Fig. 12, “The rise times during all-blocks and one-block emissions 132 were 243 and 282 ps, respectively.” What is the reason for the difference of the rise times. And why there is overshot in Fig. 12(a).

I think there is no difference. Just an error.

I added “The overshot in fig. 12(a) is a conventional relaxation oscillation of the lasing.” on 140 in the manuscript. 

Best regards,

Takashi Kondo

Author Response File: Author Response.docx