High-Efficiency and Large-Angle Homo-Metagratings for the Near-Infrared Region

Round 1

Reviewer 1 Report

In this manuscript, W.-C. Tsai et al. proposed an interesting and simple forward design method aimed at enhancing the overall diffraction efficiency of Si and GaAs metagratings by optimizing the degree of freedom for phase. Their experimental results demonstrate a remarkable average efficiency of 51.3% at the wavelength of 1550 nm with Si meta-grating, and 52.4% at the wavelength of 940 nm with GaAs. The manuscript is well-written, and the results are convincing. Therefore, I would like to recommend its publication with some minor revisions.

1. Could the authors clarify why they chose a hexagonal lattice for the meta-structures instead of the conventional square lattice?

2. It would be beneficial if the authors specify whether the silicon is amorphous or crystalline.

3. Regarding the title, the term “short-wave” is commonly associated with radio frequencies, which may not be suitable for the infrared region. Please double check.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

-          The authors present an interesting design using high-index dielectric materials to create a beam-deflecting metasurface. The control of the constructed beam after phase manipulation, enabled by the design of the metasurface, is not described in detail here. It would be more impactful if the authors present more information on their design. It would have been beneficial if the authors discussed the impact of their design and geometry in optical modes and how the diffraction angle is linked to the geometry of their nanostructures. How does the mode in the pillars manipulates the incident beam and how the angle is changed with respect to the selected parameters. Why did the authors choose those reported heights for the fabricated nanostructure? What motivated that? How does the height, lattice constant and the arrangement of the metaatoms impact the phase? and subsequently, how does the control of the phase led to angles of diffraction that the authors measured?

-          The complete form of equation (2) considers the refractive index of the input and output environment, as well as the incident and transmitted angles. It is suggested that the authors consider presenting the full equation to justify their findings.

 -          The authors present the periodicity of their metasurface is calculated as number unit cells multiplied by the lattice constants; however, it was not clear what periodicity was used to obtain the deflection angles that were reported for the corresponding wavelength.

 -          Line 58, the sentence is incomplete.

 -          Line 132-133, the authors mentioned the fabrication process of Cr aperture, however, there was no information about why this Cr aperture was fabricated until the end of the first paragraph of page 5 (line 163-1165).

 -          It would be beneficial in the authors included information on the etching recipe as well. The metaatoms were nicely fabricated and some additional information on how they were made (possibly in the supplementary document) can help increasing the value of the work.

 -          The variable “U” was first presented in equation 2 which is in page 3 and was not introduced until page 6. The authors need to be consistent with introducing the variables they use in their report for better comprehension and clarity.

The language of the manuscript can be improved. The authors should consider to rearrange part of their manuscript for better consistency. I have given some examples in the submitted reports. For instance, line 58-59, is an incomplete sentence.  I suggest some modification in the how some of the scientific information are presented. For example, in "In atmospheric conditions, light at 1550 nm is weaker compared to 905 nm." is not clear what the authors mean by "weaker".

or in "If we emit light at a wavelength of 1550 nm, it will experience less interference from ambient light than at 905 nm.", I suggest the authors revise their sentence as I believe the authors do not "emit" light. 

or in "When considering humid weather conditions, the absorption of 1550 nm  light by water vapor is similar to that of 905 nm.", I believe the authors are referring the optical windows in which the water absorption is low, however the statement can be improved by choosing more scientific languages.

There are a few examples like in the text which I believe can be addressed and help improving the quality of the manuscript.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

In this paper, the authors proposed a design method for optimization the diffraction efficiency for metagratings. By choosing proper overall add-on phase, the diffraction efficiency can be improved. They also carried out experiments to verify their design. Generally speaking, this work is interesting and can be accepted for publication after following issues being well addressed.

1.     I noticed that the authors have recently published a paper focused on similar topic (10.1364/OE.496042), I suggest the authors discussing the differences between these two works.

2.     In fact, the diffraction efficiency is also dependent on the simulated size of the sample, especially when the simulated sample is not large enough. The authors may also need to discuss this issue.

3.     I suggest the authors defining the term “diffraction efficiency”.

4.     In fact, there are many works considering improving the efficiency of metasurface, for example, 10.1002/adma.202008157, 10.1002/adom.201901389 and 10.1021/acsphotonics.6b00740. The authors should show the advantages of their design.

5.     When considering metasurfaces, the following references may be helpful. 10.29026/oea.2023.220073, 10.1002/adfm.202311286 and 10.1016/j.matdes.2022.111264.

Minor editing of English language required.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

High-efficiency and large-angle homo-metagratings at shortwave infrared region - authors presented simulation results related with two type of metagratings made of Si and GaAs, as well as described experimental details of fabrication and characterization of designed gratings. The presented topic is interesting for photonic community and in my opinion could find potential application.

Bellow I listed my remarks and questions:

1. Why authors decided to investigate grating operating at 1550 made of Si and 940 nm made of GaAs? Both wavelengths are rather related with GaAs based photonics than Si

2. Line 162 - spin coater instead of pin coater

3. Why different SEM were used for investigations of Si and GaAs based structures? Line 135 vs 168

4. Line 248 -can authors explain this numbers of impedance matching (1.44) - how it was determined, what is physical background of this?

5. Line 261 - ... which is about 1.6 times that reported in the literature [17] - lower/higher?

6. why the diffraction angle is lower for GaAs when compared with Si?

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors have addressed all my concerns and this paper can be accepted for publication in its current form.

Reviewer 4 Report

I am really satisfied with authors explaination to my remarks. In my opinion apper is ready for publication in Photonics.