High-Efficiency Characterization of Optical Vortices with Arbitrary State of Polarization Using Straight-Line and Parabolic-Line Polarization Gratings
, Tomoki Yayama 1, Kohei Noda 1,2, Tomoyuki Sasaki 1,2, Nobuhiro Kawatsuki 2,3 and Hiroshi Ono 1,2Round 1
Reviewer 1 Report
The paper entitled "High-efficiency characterization of optical vortices with arbitrary state of polarization using straight-line and parabolic-line polarization gratings" presents experimental as well as numerical results of the characterization of optical vortexes (OV) with arbitrary states of polarization. The authors demonstrate a novel optical setup based on the SPG and two PPGs, that is capable to determine topological charge of the OV. The paper is well-organized, the content is clear, and the graphics are clear and of high quality as well. The authors provide strong results and upon revision of several minor comments this article is recommended for publication in MDPI Journal of Applied science.
Let me address the following for further clarification or revision:
1. Line 18 the manuscript says "the number of dark lines correspond to the topological charge (TC) of the incident OV". By the number of dark lines we can study the magnitude of the TC, which in fact, can be either positive, or negative. Please revise this sentence.
2. Line 52: the abbreviation SLM is used for the first time, please provide full term
3. Line 94: manuscript says "but diffracts toward the -1st/+1st order mode direction", please check if the Figure 2(c) correspons to what's written in line 94. It seems that in Figure 2(c) the LCP light will diffract toward the -1st order mode direction, and the RCP light will diffract toward the +1st order mode direction.
4. Line 104 manuscript says "both OVs introduce a parabolic phase..." Did you mean "both PPGs introduce a parabolic phase"?
5. In the Section 4 (Conclusion) the phrase "our system" is repeated too many times. I recommend to replace it with various synonyms, for ex. "the proposed system", "the proposed setup", etc.
6. Line 17. In abstract the authors claim that the spot is converted with 100% efficiency, however the experimental results show the efficiency of 70%. Please indicate both the "ideal" case and the obtained efficiency in the abstract.
Author Response
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To Reviewer 1
Comment:
The paper entitled "High-efficiency characterization of optical vortices with arbitrary state of polarization using straight-line and parabolic-line polarization gratings" presents experimental as well as numerical results of the characterization of optical vortexes (OV) with arbitrary states of polarization. The authors demonstrate a novel optical setup based on the SPG and two PPGs, that is capable to determine topological charge of the OV. The paper is well-organized, the content is clear, and the graphics are clear and of high quality as well. The authors provide strong results and upon revision of several minor comments this article is recommended for publication in MDPI Journal of Applied science.
Let me address the following for further clarification or revision:
Response:
We appreciate reviewer’s careful and helpful comments. We revised manuscript according to the reviewer comments.
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Comment 1:
Line 18 the manuscript says "the number of dark lines correspond to the topological charge (TC) of the incident OV". By the number of dark lines we can study the magnitude of the TC, which in fact, can be either positive, or negative. Please revise this sentence.
Response 1:
Thank you for your indication. As you say, the number of dark lines correspond to the magnitude of TC. Also, the orientation of dark lines corresponds to the sign of TC. Hence, we revised statement “the number of dark lines correspond to the topological charge (TC) of the incident OV” to “the number of dark lines and its orientation respectively correspond to the magnitude and sign of topological charge (TC) of the incident OV”
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Comment 2:
Line 52: the abbreviation SLM is used for the first time, please provide full term
Response:
We added full term of SLM in line 54.
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Comment 3:
Line 94: manuscript says "but diffracts toward the -1st/+1st order mode direction", please check if the Figure 2(c) correspons to what's written in line 94. It seems that in Figure 2(c) the LCP light will diffract toward the -1st order mode direction, and the RCP light will diffract toward the +1st order mode direction.
Response:
Thank you for your indication. Figure 2(c) is correct. We mistook the description of line 94. Correct sentence is “but diffracts toward the +1st/-1st order mode direction”. We revised this sentence (see line 96).
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Comment 4:
Line 104 manuscript says "both OVs introduce a parabolic phase..." Did you mean "both PPGs introduce a parabolic phase"?
Response:
Thank you for your comment. We revised this sentence to “both PPGs introduce a parabolic phase”.
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Comment 5:
In the Section 4 (Conclusion) the phrase "our system" is repeated too many times. I recommend to replace it with various synonyms, for ex. "the proposed system", "the proposed setup", etc.
Response:
Thank you for your comment. We replaced and eliminated the phrase “our system” in Section 4.
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Comment 6:
Line 17. In abstract the authors claim that the spot is converted with 100% efficiency, however the experimental results show the efficiency of 70%. Please indicate both the "ideal" case and the obtained efficiency in the abstract.
Response:
Thank you for your comment. We added sentence “The experimentally obtained efficiency is 70.2%.” in abstract.
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We appreciate reviewer’s careful comment, and believe that the manuscript has been improved and hope it will be accepted for publication.
Reviewer 2 Report
In this manuscript, the authors proposed, implemented, and tested a new method to measure optical vortices (OVs) with any states of polarization based on straight-line and parabolic-line polarization gratings (SPGs and PPGs) in sequence. Topological charge numbers, signs, and polarization can be identified that agree well with theoretical calculations and simulations. I found the proposed method is very interesting and could be very useful for the community as OVs are get more and more popular for a variety of applications, and therefore, a high efficiency characterization technique is very welcome.
In general, the paper is well presented, and I would recommend the publication of the manuscript if the authors can address the following comments and questions:
1. Since the idea of using parabolic optical components to characterize OVs and polarization vortices (PVs) is very similar to the original demonstration of using a cylindrical lens, can the authors achieve the same characterizations by bulk optics that include waveplates, polarizers, and cylindrical lens? If so, what would be the main differences?
2. Can one implement SPGs and PPGs using, say, a few different SLMs?
3. Does the proposed method work for a broadband light source carrying OVs and/or PVs?
4. In Fig.2, the color bars are labeled -pi to -pi, instead of -pi to +pi? Are those typos?
Author Response
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To Reviewer 2
Comment:
In this manuscript, the authors proposed, implemented, and tested a new method to measure optical vortices (OVs) with any states of polarization based on straight-line and parabolic-line polarization gratings (SPGs and PPGs) in sequence. Topological charge numbers, signs, and polarization can be identified that agree well with theoretical calculations and simulations. I found the proposed method is very interesting and could be very useful for the community as OVs are get more and more popular for a variety of applications, and therefore, a high efficiency characterization technique is very welcome.
In general, the paper is well presented, and I would recommend the publication of the manuscript if the authors can address the following comments and questions:
Response:
We appreciate reviewer comments. We revised manuscript according with your comments as listed in bellow.
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Comment 1:
Since the idea of using parabolic optical components to characterize OVs and polarization vortices (PVs) is very similar to the original demonstration of using a cylindrical lens, can the authors achieve the same characterizations by bulk optics that include waveplates, polarizers, and cylindrical lens? If so, what would be the main differences?
Response 1:
Thank you for your comment. As you pointed out, we can also characterize the topological charge number and sign, and its polarization of incident OVs by using waveplates, polarizers, and cylindrical lens. However, we need some image measurements by changing the fast axis angle of waveplates. Compared with this approach, our system need only single image without any rotation of waveplate. Hence, the main difference between these two approaches is time cost for characterizing the OVs and PVs.
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Comment 2:
Can one implement SPGs and PPGs using, say, a few different SLMs?
Response 2:
As you pointed out, we can implement SPGs and PPGs using a few different SLMs and waveplates. However, an approach using SLMs brings increasing in size of an equipment.
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Comment 3:
Does the proposed method work for a broadband light source carrying OVs and/or PVs?
Response 3:
Our system also can work for a broadband light source carrying OVs and/or PVs. However, we need to compensate the spatial dispersion caused by the difference of diffraction angles depends on the wavelength. This can be achieved by adding additional two SPGs. We would demonstrate this approach in future work.
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Comment 4:
In Fig.2, the color bars are labeled -pi to -pi, instead of -pi to +pi? Are those typos?
Response 4:
Thank you for your comment. We revised Fig. 2 to correct label of color bars.
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We appreciate reviewer’s careful comment, and believe that the manuscript has been improved and hope it will be accepted for publication.
Reviewer 3 Report
The authors have proposed and demonstrated the characterization scheme for optical vortices with arbitrary input-SOP. The theoretical detail and the experimental results have been well discussed in the current manuscript. The concept is interesting for the application of optical vortices. I suggest to accept the manuscript to the publication in Applied Science after the minor revision on the following issues:
1. The simulation and experimental results are compared in both Fig. 5 and 6. The number of the dark line could be used to quantify the value of the topological charge. But we also observe the fading or twisting bright spots, especially at the edge of the experimental figures. That might be misleading to the identification on the number of dak lines. Any reason causes to the distortion in the experimental? Any approach to mitigate the impact?
2. How about the stability of the observed beam profile in the experiment? Is it stable for the different input SOP? Any impact on the diffraction process on SPG and PPG?
Author Response
===============
To Reviewer 3
Comment:
The authors have proposed and demonstrated the characterization scheme for optical vortices with arbitrary input-SOP. The theoretical detail and the experimental results have been well discussed in the current manuscript. The concept is interesting for the application of optical vortices. I suggest to accept the manuscript to the publication in Applied Science after the minor revision on the following issues:
Response:
We appreciate reviewer comments. We revised manuscript according with your comments as listed in bellow.
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Comment 1:
The simulation and experimental results are compared in both Fig. 5 and 6. The number of the dark line could be used to quantify the value of the topological charge. But we also observe the fading or twisting bright spots, especially at the edge of the experimental figures. That might be misleading to the identification on the number of dak lines. Any reason causes to the distortion in the experimental? Any approach to mitigate the impact?
Response 1:
Thank you for your comment. As you say, the experimentally obtained results has the fading and twisting bright spots at the edge. We consider that this distortion is caused by the initial amplitude distribution of OV before the incident on the proposed system. Due to the accuracy of our experimental setup for generating OV, measured OV does not have a doughnut shape amplitude distribution which is completely matched with the pure Laguerre Gaussian beam. By measuring the number of dark lines along the centerline perpendicular to the dark line orientation, we would mitigate this impact.
We added above description in the manuscript.
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Comment 2:
How about the stability of the observed beam profile in the experiment? Is it stable for the different input SOP? Any impact on the diffraction process on SPG and PPG?
Response 2:
Observed beam profile in the experiment is stable for environmental fluctuation. Since the SPG and PPG is made of polymer liquid crystal, its birefringence and alignment pattern is almost immune to the temperature and vibration within the room temperature. As a result, diffraction properties of the SPG and PPG are also stable.
We added this description in the manuscript.
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We appreciate reviewer’s careful comment, and believe that the manuscript has been improved and hope it will be accepted for publication.
