Design and Fabrication of Metasurfaces-Based Polarizing Beam Splitter with Tailored Deflection Angles for 940-nm Wavelength

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

The manuscript entitled “Design and fabrication of metasurfaces-based polarizing beam splitter with tailored deflection angles for 940-nm wavelength” by Peng et al. showed a metasurface-based polarization beam splitter. The authors have explained how the PBS was designed and showed its polarization splitting and efficiency performance through numerical simulations. They further fabricated a metasurface and the beam splitting phenomenon was successfully obtained experimentally. My comments are as below:

1.    More reference relating to metasurface-based PBS should be added and a clear comparison of these work and this work should be provided to show the novelty or salient feature of this work. It seems like the design method of PBS, especially the required phase profile for realizing PBS, is different from the previous methods.

2.    The authors claim that “the phase mismatch between phase imposed by unit cell and ideal phase profile is quite small.”. What does the ideal and the metasurface-imposed phase profiles look like? And how small is the mismatch? It is suggested to include the required phase profiles and the metasurface pattern in the manuscript. In addition, will the deviation of the phase profile significantly affect the polarization beam splitting performance?

3.    The results shown in Figs. 4 and 5 are directly obtained from the FDTD simulation software. The label of “theta” should be “θ”. It is suggested to export the data from FDTD and plot it using a more professional data processing software like Origin or MATLAB.

4.    Why do the deflection efficiencies nearly halved compared to the transmission efficiencies? From the simulation results, almost all light energy is preserved in the desired diffraction order. Besides, what causes the difference of the results relating to the s- and p-polarizations (asymmetric side lobe and diffraction angle difference)? In addition, the figure caption of Fig. 4 is not proper, it is better to use “(a) s-polarization and (b) p-polarization” rather than “(a) 14.94 degrees and (b) -15.12 degrees”.

5.    From my understanding, conventional metasurface can be designed as polarization beam splitter by spatially and intersectionally arranging the meta-atoms imparting positive and negative phase gradient for the orthogonal polarizations, and the splitted polarization light is equal in terms of the splitting power under various splitting angle. However, for the proposed method it seems the splitted polarization energy becomes more unequal at larger splitting angles. Therefore, it would be better to make a direct comparison of this method and the conventional one that seems to be simpler and more efficient?

6.    It seems the results in Fig. 10 come from an unpolarized light and beam splitting phenomenon was successfully obtained. However, the polarization states of the splitted beams are not confirmed. What would the results look like if only s- and p-polarization is incident?

 

7.    In addition, I found some grammar issues like “Additionally, we demonstrate experimental results for 500-um diameter metasurfaces with deflection angle of 15 degrees for the light consisting of s-polarized and p-polarized normal incident light are demonstrated.”, “there are some studies have used the optical …”, “we used interpolation method to expand our database to 100×100 nanopillars so that could fit the ideal phase profile”, “Subsequently, perform a soft bake step on a hotplane…”, etc. It is suggested to have the manuscript polished in terms of its English.

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper presents a study on metasurfaces-based polarizing beam splitter. The design, simulation, fabrication and experimental results are presented. This research contains some interesting points, but several critical points are not clearly presented. Thus, I consider this paper has to make some necessary revision before publication.

 

1. In abstract and conclusion, authors present this study could “solve the problems of traditional PBS such as bulky size and deflection angle limit.”

In this paper, the experimental results are only about 15 degrees defection, and simulation results are not bigger than 30 degrees. However, in many publications, the deflection degrees are much larger than this data. Such as in “Li, J., Liu, C., Wu, T. et al. Efficient Polarization Beam Splitter Based on All-Dielectric Metasurface in Visible Region. Nanoscale Res Lett 14, 34 (2019)”, the experimental results are 45 degrees defection at 583 nm. Authors should present a table to compare the performance with other publications.

2. The diameter of metasurface in this paper is 50-um, but the light spot focus on the metasurface is not presented. As the description in Line 129 Page 6, the fiber laser for 940-nm laser is with 500-um spot size. In my opinion, the size of metasurface is dependent on the light spot size. From the paper, it is difficult to see the design can sufficiently reduce the metasurface size. In line 71 page2, authors present “we designed the 50-um diameter metasurfaces with deflection angles same as 500-um diameter metasurface”. If without aperture, can the 50-um diameter metasurfaces deflect 500-um spot size light?

3. In figure 10, the measurement points are too few, 5 degree measurement is not enough, more measurement points must be added.

4. The digitals in figures is too small. The xspan and yspan are not defined in manuscript.

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

The paper has demonstrated the metasurface linear PBS with two deflection angles for 940-nm wavelength to solve the problems of traditional PBS such as bulky size and deflection angle limit.. In my opinion the topic is of interest for Photonics readership, but the paper needs a careful review before it can be accepted for publication. More in detail, the following issues should be addressed:

 

1.One main concern is the meaning/effectiveness of the proposed method. In this version,  the major contribution is using metasurfaces to realize the function of PBSs. However, is there any other methodologies can achieve the same purpose. Hence, what is the superiority of the proposed method?

2.As mentioned in Section 2.2, to simulate the phase delay caused by nanopillars, the authors designed the 50-um diameter metasurfaces with deflection angles same as 500-um diameter metasurface. Such performance was limited by the computer resources, which is not suitable for scientific research. It is suggested the authors to give the theoretical boundary.

3.The presentation of this manuscript should be greatly improved. Please carefully improve the writing. Also, check the figures. For example, the text in Figure 7 is hard to see.

Comments on the Quality of English Language

The terminology needs to be more precise.

Author Response

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Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript by Kuan-Cheng Peng, Guo-Dung Su, et al., presents a novel approach to designing polarizing beam splitters (PBS) using metasurfaces. This method aims to overcome the limitations of traditional PBS devices, such as bulkiness and restricted deflection angles. The authors propose a metasurface-based PBS for a 940-nm wavelength, demonstrating potential for smaller device sizes and adjustable deflection angles through detailed simulation and experimental results. The paper is well-structured, with a clear progression from the problem statement to the proposed solution, methods, results, and conclusions, presenting the contents as a coherent story. I recommend " Accept after minor revision". The revisions should address the detailed comments below to strengthen the manuscript.

1. Methodology and Data Presentation:

The methodology is robust, involving detailed simulations and experimental setups. However, there are specific areas needing improvement: 

A: Figure 3: The units for the x and y-axis should be in nanometers (nm), not micrometers (um). Additionally, the phase shift units need clarification—whether they are in pi or radians.

B: Experimental Methods: The manuscript omits a detailed explanation of critical fabrication steps mentioned in Figure 8, from step E-gun Evaporation to Wet-Etching. A section is needed to describe these processes adequately.

2. Results:

The results section showcases the alignment between simulations and experimental outcomes. However, the authors need to address the discrepancies in transmission efficiency between the calculations and experimental results. Considerations such as the Gaussian profile of the laser, and NIR optical alignment challenges due to the beam spot size relative to the beam splitter should be discussed, will fabrication of bigger PBS help?

3. Conclusions:

The conclusion claims to "solve the problems of traditional PBS such as bulky size and deflection angle limit" might be overstated. It would be more accurate to say that the manuscript expands the operational angle range, as the angle limitation still exists but is less restrictive than traditional designs.

Comments on the Quality of English Language

The paper requires thorough proofreading to correct several typographical and grammatical errors, like in lines 65 and 84. All abbreviations should be fully named at their first occurrence, e.g., FDTD (Finite Difference Time Domain).

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have properly responded to my previous comments and made significant manuscript revsions. I have no further issue.

Reviewer 2 Report

Comments and Suggestions for Authors

I would like to thank the authors for addressing my comments. The article is now improved and can be accepted for publication after minor revision.

Figure 7(a) is fuzzy, and I suggest using black or blue to instead red of the PBS pattern。