Ultrahigh Q-Guided Resonance Sensor Empowered by Near Merging Bound States in the Continuum

Round 1

Reviewer 1 Report

An all-dielectric metasurface has been designed, simulated, and optimized. The Q factor evolution versus the asymmetric degree of structure for different modes has been investigated systematically.  The paper is pepared well and the contents are interesting, which can be accepted for publication with minor revisions. 

1. Rigorous coupled wave analysis (RCWA) was used s to calculate the Q factor from the spectral responses and finite element method (FEM) was used to calculate the corresponding electric field distributions. Why did the authors choose two different methods?  FEM can also be used to calculate the Q factror.  Similarly, RCWA can also be used to check the field distributions.  

2. The details of the numerical methods should be provided. 

3. Comparisons with other reports should be made on the sensitivity of the potential sensor.  

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

In this paper, the authors report a design guideline of ultra-high-Q guided resonances based on merging BIC. The simulation studies are systematic and convincing, which offers a practical pathway of experimentally realizing robust high-Q resonances on the silicon-nitride-on-silica platform and the resulting ultra-sensitive surface detections. I believe further technical details and analyses should be included to make this technique easy for readers to appreciate. Therefore, before I can recommend this paper for acceptance, there are several points that require some revision. 

1) Why is the wavelength range of ~ 950-970 nm chosen for studies of high-Q resonances? Are there any limits in pushing the operation wavelength (or the sensing window) to the visible range?

2) On page 2, the authors should elaborate more on the details of Q extraction using rigorous coupled wave analysis (RCWA), or add proper references.

3) For Figure 4, what limits the extraction of ultra-high values in Regions B&C here? Is this due to the spectral resolution of the simulation configuration?

4) As the authors mentioned about the surface sensitivity calculation in Figure 8. However, I do not see any calculated values of sensitivity here. The authors should quantify it using a definition (say, resonance shift divided by the coated molecular layer thickness, in the unit of nm/nm). Besides, I do not see any discussions on the counterpart of plasmonic array-based structures shown in the right panel of Figure 8. Would it be good or bad in terms of sensitivity?

5) In the theoretical studies of surface sensing, the thickness of the coated molecular layer is not given. It will be much better to comply with a practical biosensing model, e.g., a monolayer of bovine serum albumin, so that the results can be easily benchmarked with other work.

6) More references on the topics of silicon-based on-chip sensors and metasurface sensors should be included, as they are highly related to the studied sensing application in this manuscript. The followings are some of those that I would suggest:

doi.org/10.1002/admt.201901138

doi.org/10.1002/anie.201901443

 

The followings are some minor issues.

1) It would be better to label the period p in Figure 1.

2) It would be also better to label the materials in different segments in the cross-sectional view in Figure 6-7.

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

In this manuscript, high-Q all-dielectric BIC was investigated with 

 

regard to the manufacturing error as well as the sensing property. 

 

Both the symmetry-protected BIC and accidental BIC are studied. The 

 

research field of BIC is currently an interesting topic, and this 

 

manuscript may be considered for the publication in the Photonics. 

 

My comments are as follows. 

1, What will happen if the material losses are taken into account?

2, It is better to introduce something before mentioning "GMR" and 

 

"solution".

3, The captions could be described in more detail. For instance, 

 

the information of wavelength and colorbar can be provided.

4, In line 177, "nonlinear coefficients" should be changed to 

 

"asymmetry parameter"?

5, In addition, the title may need to be revised, because the 

 

influence of manufacturing error is just be mentioned in the text, 

 

which is not specially discussed in the manuscript.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 4 Report

 

The authors have designed a dielectric metasurface composed of a nanocube with an asymmetric square hole, supporting triple resonant modes under normal incidence. They simulated and optimized the parameters of the system in order to generate Bound States in the Continuum.

 The subject is interesting; however, I have some remarks that should be considered in the revised version. The following are my critical comments: 

·        First of all, the basics theories and equations for the system and simulations are missing. These should be included in the manuscript.

• The authors should properly introduce the BIC in a separate section.  
• The high Q-factor is realized by several systems this should be mentioned. In particular physical applications should be discussed ( references such as Appl. Math. Inf. Sci 3 (2), 185-196 (2009)) and references therein are helpful  
• The limitations of the proposed method should be discussed.
• Applications of the results should be extensively discussed.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 4 Report

The revised version is ok. I accept it