Digital Programmable Metasurface with Element-Independent Visible-Light Sensing

Round 1

Reviewer 1 Report

The refereed manuscript is devoted to study of the digital programmable metasurface with element-independent visible-light sensing. The authors state that “We fabricated the metasurface using standard printed circuit board (PCB) technology and measured the metasurface in far-fields. The measurement results show good agreement with the simulaitons, verifying our design.” The manuscript is interesting and with potential for publication. However, some issues have to be attended before the acceptance of the manuscript.

1- The discussion of the results suffers from the physics of the problem. The authors essentially limit themselves to describing the captions of the figures in an enlarged way or to illustrate what is observed in them without entering into justifying or giving arguments that support these results. 

2- It will be better understanding and interesting for reading the manuscript if some practical application (example) of the study is presented in the manuscript.

3- The references are not enough, especially in the “Principle and design” section.

Author Response

To Reviewer 1

Comments:

1. The discussion of the results suffers from the physics of the problem. The authors essentially limit themselves to describing the captions of the figures in an enlarged way or to illustrate what is observed in them without entering into justifying or giving arguments that support these results.

Our response:

       Thank you very much for your comment. In order to provide stronger theoretical support, we introduce the principle of coding metasurface and analyze the correctness of our results theoretically. The generalized Snell’s theorem is to arrange the units with different abrupt phases in a gradient or a specific phase distribution on a plane, which can realize the functions of anomalous deflection (negative reflection), anomalous reflection, and focusing of the incident electromagnetic waves. By applying this design idea to a 1-bit coding metasurface, two units with 180° phase difference are encoded as “0” and “1”, and these two units are arranged on a two-dimensional plane in a predetermined sequence, forming a metasurface with a regulatory function for electromagnetic waves. For example, when the coding sequence is “0101...”, the vertically incident electromagnetic waves will be divided into dual-beam, and when the coding becomes a checkerboard distribution, the radiation direction will form as four beams. Our proposed pattern A with the code “11100001111000” and pattern B with the code “11000001111100” both get dual-beams. The simulation results of pattern C with “11100001111000” chessboard coding are indeed four beams, that is our results are consistent with the theory, which proves the feasibility of our proposed light-sensing coding metasurface.

Supplemented sentences：

The generalized Snell’s theorem is to arrange the units with different abrupt phases in a gradient or a specific phase distribution on a plane, which can realize the functions of anomalous deflection (negative reflection), anomalous reflection, and focusing of the incident electromagnetic waves. By applying this design idea to a 1-bit coding metasurface, two units with 180° phase difference are encoded as “0” and “1”, and these two units are arranged on a two-dimensional plane in a predetermined sequence, forming a metasurface with a regulatory function for electromagnetic waves. For example, when the coding sequence is “0101...”, the vertically incident electromagnetic waves will be divided into dual-beam, and when the coding becomes a checkerboard distribution, the radiation direction will form as four beams. Our proposed pattern A with the code “11100001111000” and pattern B with the code “11000001111100” both get dual-beam. The simulation results of pattern C with “11100001111000” chessboard coding are indeed four beams, that is our results are consistent with the theory, which proves the feasibility of our proposed light-sensing coding metasurface.

2. It will be better understanding and interesting for reading the manuscript if some practical application (example) of the study is presented in the manuscript.

Our response:

Thank you very much for your comment. As we introduced the digital programmable metasurface is controlled by light frequency, allowing for independent unit tuning for adjusting the microwave phase, further expanding the degrees of freedom for metasurface sensing and manipulation. Firstly, this manner of regulation is valuable for the development of hybrid electron-photon devices for use in more advanced electronics and communication systems. The second, since digital programmable metasurface is an open platform, which can combine with customized control and computational programs and executive circuits to extend into the adaptive light-sensing metasurface, and establish software and hardware control or intelligent meta-devices with autonomous adaptive programmable functions for the next generation of wireless systems.

We have supplemented sentences as below,

Supplements sentences:

In addition, we use light frequency to control the microwave phase.

Moreover, the digital programmable metasurface also can be combined with customized control and computational programs and executive circuits to extend into the adaptive light-sensing metasurface and establish software and hardware control or intelligent meta-devices with autonomous adaptive programmable functions for the next generation of wireless systems.

Moreover, we have established a metasurface architecture for electromagnetic scattering field modulation from complex optics to microwave wavelengths, which enables a wide variety of light sensing for modulation., which is valuable for developing hybrid electronic-photonic devices for more advanced electronic and communication systems.

3. The references are not enough, especially in the “Principle and design” section.

Our response:

Thank you very much for your comment. We have supplemented more references in the “Principle and design” section.

Reviewer 2 Report

This paper presents a digital programable metasurface to achieve several electromagnetic wave manipulation

The authors should improve in order to show the innovations; in this way it will be possible to call attention of the readers 

Potential applications have to be more deeply described

Measured and simulated results are presented in fig 6; more comparisons are necessary to show the applications . Moreover the discussion has to be done more deeply presented

The state of art has to be better exposed in the introduction

The metasurface is composed of 16x16 units: this should be clarified to present its importance

The advantage of using the  digital programmable metasurface needs improvement : if the state of art is presented more properly perhaps it will be able  the attract the readers   and convince them to use it

Author Response

To reviewer 2

This paper presents a digital programable metasurface to achieve several electromagnetic wave manipulations. The authors should improve in order to show the innovations; in this way it will be possible to call attention of the readers.

1. Potential applications have to be more deeply described.

Our response:

Thank you very much for your comment. As we introduced the digital programmable metasurface is controlled by light frequency, allowing for independent unit tuning for adjusting the microwave phase, further expanding the degrees of freedom for metasurface sensing and manipulation. Firstly, this manner of regulation is valuable for the development of hybrid electron-photon devices for use in more advanced electronics and communication systems. The second, since digital programmable metasurface is an open platform, which can combine with customized control and computational programs and executive circuits to extend into the adaptive light-sensing metasurface, and establish software and hardware control or intelligent meta-devices with autonomous adaptive programmable functions for the next generation of wireless systems.

We have supplemented sentences as below,

Supplements sentences:

In addition, we use light frequency to control the microwave phase.

Moreover, the digital programmable metasurface also can be combined with customized control and computational programs and executive circuits to extend into the adaptive light-sensing metasurface and establish software and hardware control or intelligent meta-devices with autonomous adaptive programmable functions for the next generation of wireless systems.

Moreover, we have established a metasurface architecture for electromagnetic scattering field modulation from complex optics to microwave wavelengths, which enables a wide variety of light sensing for modulation., which is valuable for developing hybrid electronic-photonic devices for more advanced electronic and communication systems.

2. Measured and simulated results are presented in fig 6; more comparisons are necessary to show the applications. Moreover, the discussion has to be done more deeply present.

Our response:

Thank you very much for your comment. In the comparison between simulation results and measurement results, we selected 3 of the 4 simulation patterns for measuring. The measured results are highly consistent with the simulation results, which can well illustrate the feasibility of our point of view. In the discussion, we added the theoretical proof related to forming abnormal electromagnetic wave reflection beam angles and analyze the correctness of our results theoretically.

We have supplemented sentences as below,

Supplements sentences:

The generalized Snell’s Law is to arrange the units with different abrupt phases in a gradient or a specific phase distribution on a plane, which can realize the functions of anomalous deflection (negative reflection), anomalous reflection, and focusing of the incident electromagnetic waves. By applying this design idea to a 1-bit coding metasurface, two units with 180° phase difference are encoded as “0” and “1”, and these two units are arranged on a two-dimensional plane in a predetermined sequence, forming a metasurface with a regulatory function for electromagnetic waves. For example, when the coding sequence is “0101...”, the vertically incident electromagnetic waves will be divided into dual-beam, and when the coding becomes a checkerboard distribution, the radiation direction will form as four beams. Our proposed pattern A with the code “11100001111000” and pattern B with the code “11000001111100” both get dual-beams. The simulation results of pattern C with “11100001111000” chessboard coding are indeed 4 beams, that is our results are consistent with the theory, which proves the feasibility of our proposed light-sensing coding metasurface.

3. The state of art has to be better exposed in the introduction.

Our response:

Thank you very much for your comment. We have revised the introduction part. Please refer to the revised paper for details.

4. The metasurface is composed of 16x16 units: this should be clarified to present its importance.

Our response:

Thank you very much for your comment. In this research, we chose the metasurface which is composed of 16x16 units for experimental verification because it is sufficient for us to verify the electromagnetic functions of the metasurface. The size of the metasurface can be changed according to the specific application requirements.

5. The advantage of using the digital programmable metasurface needs improvement: if the state of art is presented more properly perhaps it will be able the attract the readers and convince them to use it.

Our response:

Thank you very much for your comment. The digital coding metasurface is simply connected to the digital expression by assigning the phase response of the meta-atom as “0” and “1”. Therefore, the traditional metasurface pattern structure is completely digitized into coding patterns, introducing different ideas of information science, simplifying the design process, and creating more functions. In addition, unlike the traditional metasurface, once it is processed, it can only achieve specific functions and cannot be adjusted, while the digital coding metasurface can realize functional reuse. Moreover, the digital metasurface can also introduce other regulation mechanisms for different requests, with more flexible and convenient characteristics.

Supplements sentences:

Unlike traditional metasurfaces, which perform specific functions only after the process is complete, digital coding metasurfaces allow functional reuse by reassigning the phase response of meta-atom to “0” and “1” based on numerical expressions. In addition, the digital metasurface can also introduce other regulating mechanisms according to different requests, making it more flexible and convenient.

Reviewer 3 Report

The work titled "Digital programmable metasurface with element-independent visible-light sensing" is interesting work but the authors have left out many important aspects in the manuscript. Following are the points which author can consider including for the improvement of the manuscript:

1. Please provide more information about the trichromatic color sensor. How you are using it in your work?

2. Which coding algorithms are used to design metasurfaces? Please explain with a flowchart.

3.  No information about the feedback link with FPGA is provided

4 Authors are basically controlling the RCS of the different metasurface patterns. How this work is related to visible light sensing.

5. Abstract and conclusion are incomplete in terms of the work done in the manuscript.

Author Response

To Reviewer 3

1. Please provide more information about the trichromatic color sensor. How you are using it in your work?

Our response:

Thank you very much for your comment. As we introduced in the paper, in the trichromatic sensor[1], the light-to-frequency converter reads an 8×8 array of photodiodes. Sixteen photodiodes have blue filters, 16 photodiodes have green filters, 16 photodiodes have red filters, and 16 photodiodes are clear with no filters. Four colors of photodiodes are connected to reduce the effect of uneven incident irradiance. By controlling the digital state of the enabling ports SH2 and SH3, the sensing target is converted to one of the colors of the enabling port and the result is output at a certain frequency. In this case, the purpose of color-sensing sensors is to sense the frequency of visible light.

In our work, the sensing modules are integrated into the fifth layer using PCB technology. And the modules are connected to PIN on the metasurface through the vias. By integrated trichromatic sensors on the metasurface, the color information in incident light can be detected, it can also be regarded as a light-coding input to guide the metasurface to perform corresponding functions. For example, we code the metasurface to perform three EM functions, such as dual-beam, four-beam, and RCS control, corresponding to blue, green, and red detection, respectively. As prototype proof, according to the theoretical knowledge of coding metasurface[2], four typical coding patterns are selected for simulation and measurement verification to prove the above ideas.

Supplements sentences:

In our work, the sensing modules are integrated into the fifth layer using PCB technology. And the modules are connected to PIN on the metasurface through the vias. By integrated trichromatic sensors on the metasurface, the color information in incident light can be detected, it can also be regarded as a light-coding input to guide the metasurface to perform corresponding functions. For example, we code the metasurface to perform three EM functions, such as dual-beam, four-beam, and RCS control, corresponding to blue, green, and red detection, respectively. As prototype proof, according to the theoretical knowledge of coding metasurface, four typical coding patterns are selected for simulation and measurement verification to prove the above ideas.

2. Which coding algorithms are used to design metasurfaces? Please explain with a flowchart.

Our response:

Thank you very much for your valuable comment. Since the algorithm mentioned here concerns the working principle of the proposed metasurface, for a clearer description, we describe the working principle in detail in the article. The algorithm links the process of Light-sensing metasurfaces from detection to sensory data, data comparison, and finally the formation of different voltage distribution patterns on the metasurface. Specifically, when the frequency information of the light is sensed by the trichromatic sensors and output to the high-speed ADC, the ADC determines whether the threshold is exceeded, and then the FPGA makes the threshold judgment and performs the coding pattern of the color corresponding to the current threshold on the metasurface. For instance, when the FPGA determines that the incident light is red, the metasurface performs the coding pattern of dual-beam, the incident light is green, the metasurface performs the coding pattern of four-beam, and the incident light is red, the metasurface performs the coding pattern of RCS.

In addition, in order to show more clearly how we proposed metasurface works, we have given a schematic illustration in the article, as shown in Fig. 1(b).

Supplements sentences:                                            

The algorithm links the process of Light-sensing metasurfaces from detection to sensory data, data comparison, and finally the formation of different voltage distribution patterns on the metasurface. Specifically, when the frequency information of the light is sensed by the trichromatic sensors and output to the high-speed ADC, the ADC determines whether the threshold is exceeded, and then the FPGA makes the threshold judgment and controls the PIN diode on the metasurface to perform the coding patterns of the color corresponding to the current threshold value. For instance, when the FPGA determines that the incident light is red, the metasurface performs the coding pattern of dual-beam, the incident light is green, the metasurface performs the coding pattern of four-beam, and the incident light is red, the metasurface performs the coding pattern of RCS.

In addition, in order to show more clearly how we proposed metasurface works, we have given a schematic illustration in the article, as shown in Fig. 1(b).

3. No information about the feedback link with FPGA is provided.

Our response:

Thank you very much for your comment. In this work, the role of the FPGA is to determine the corresponding color based on the value of the ADC output and control the PIN diode on the metasurface to form the coding pattern corresponding to the current color. In particular, when the trichromatic sensors sense the frequency information of light and output it to the high-speed ADC, the ADC determines whether the threshold value is exceeded. Then the FPGA makes the threshold judgment and controls the PIN diode on the metasurface to perform the coding patterns of the color corresponding to the current threshold value.

In order to show more clearly how we proposed metasurface works, we have given a schematic illustration in the article, as shown in Fig. 1(b).

Supplements sentences:

Specifically, when the trichromatic sensors sense the frequency information of light and output it to the high-speed ADC, the ADC determines whether the threshold value is exceeded. Then the FPGA makes the threshold judgment and controls the PIN diode on the metasurface to perform the coding patterns of the color corresponding to the current threshold value. For example, we have marked the implementation of electromagnetic functions such as dual-beam, four-beam, and RCS as detecting blue, green, and red respectively.

In addition, to show more clearly how we proposed metasurface works, we have given a schematic illustration in the article, as shown in Fig. 1(b).

4. Authors are basically controlling the RCS of the different metasurface patterns. How this work is related to visible light sensing.

Our response:

Thank you very much for your comment. We use a trichromatic sensor combined with FPGA and algorithm, aiming to build a metasurface architecture for modulating electromagnetic scattering fields from complex optical to microwave wavelengths, which can achieve a wide variety of light-sensing modulation. In addition, because it is controlled by an independent unit, it can achieve finer control according to demand.

Supplements sentences:

Moreover, we have established a metasurface architecture for electromagnetic scattering field modulation from complex optics to microwave wavelengths, which enables a wide variety of light sensing for modulation., which is valuable for developing hybrid electronic-photonic devices for more advanced electronic and communication systems.

5. Abstract and conclusion are incomplete in terms of the work done in the manuscript.

Our response:

Thank you very much for your comment. We have revised the abstract and the conclusion.

Supplements sentences:

Abstract: By integrating trichromatic color sensors, high-speed ADC, FPGA, and algorithm into the metasurface, we have achieved a wide variety of electromagnetic modulation, like dual-beam, four-beam, and RCS, and have realized the detection of incident light color.

Conclusion: In this work, we have achieved a wide range of electromagnetic modulations such as dual-beam, four-beam, and RCS, as well as color detection of incident light by integrating trichromatic color sensors, high-speed ADC, FPGA, and algorithms onto a metasurface.

[1]        TCS3200 TCS3210, PROGRAMMABLE COLOR LIGHT-TO-FREQUENCY CONVERTER, Texas Advanced Optoelectronic Solutions Inc, 2019.

[2]        T. J. Cui, M. Q. Qi, X. Wan, J. Zhao, and Q. Cheng, "Coding metamaterials, digital metamaterials and programmable metamaterials," (in English), Light: Science & Applications, vol. 3, no. 10, pp. e218-e218, Oct 2014, Art no. e218, doi: 10.1038/lsa.2014.99.

Round 2

Reviewer 1 Report

  The Authors have adequately addressed all of my comments.  I have no additional or further comments, and can recommend acceptance of the manuscript in its current form.

Reviewer 2 Report

The authors attended properly the suggestion

Based on this I recommend the approval

Reviewer 3 Report

Paper can be accepted in its present form.