Design and Simulation of Photonic Crystal Fiber for Liquid Sensing

Round 1

Reviewer 1 Report

In this manuscript, the authors present a numerical study about a micro-structured photonic crystal fiber for nano-liquids sensing.

 

For this manuscript, I have some concerns and I think this article could be published on “photonics” after major correction. Please see some of the major concerns below:

 

1. Micro-structured PCF has been studied by a lot of researcher such as “ Opt. 54, 8637-8643 (2015)” or “Optics Communications, 2018, 423: 140-144.”. So, what is the novelty of your proposed PCF design? And as mentioned in this manuscript, it is a simple structured PCF, are there any available technologies for fabrication?

 

2. The analyte of nanoliquid needs to be infiltrated through the PCF core, therefore how you achieve that in a real experiment?

 

3. The manuscript lacks discussion on sensing part. Although it is a design and simulation based manuscript, without the sufficient discussion on sensing, this manuscript is not completed. And the proposed sensor, can be used to detect only water, ethanol and benzene or it can be used to other liquid as well? Moreover, what is nanoliquid should be added into the manuscript, so does the difference between nanoliquid and normal liquid.

 

4. So based on eq.3, the relative sensitivity can be calculated. In order to know what the sensed material is, we need to know r (relative sensitivity) and n_eff (modal refractive index) while f (total power fraction), it assumes can be obtained from OSA. So, is that means even if we can perform the experiment, the refractive index of sensed analyte will still need to be defined by using simulation result (r and n_eff), instead of using the experiment result as validation result for comparison. Therefore, please give some discussion on this sensing part in detail.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The authors present a numerical simulation regarding a new structure design for a photonic crystal fiber (PCF) for liquid sensing. In general, the paper is well structured and written. Figures are clear and correctly complement the text. However, a few points must be addressed by the authors, resulting in the need of a major revision, as it will be explained next.

1. The authors mention “nanoliquid sensing”. What is the intended meaning of “nanoliquid”? Typically, nanoliquids, or more often, nanofluids, refers to liquids or fluids with nanoparticles within. But, in the proposed paper, that is not the case. Perhaps the use of just “liquid” is more appropriate?

2. There is a recurrent assessment of the degree of manufacture ease regarding the different types of PCF structure (in the introduction, regarding the state of the art, and the presented one, in different sections). In which sense the difficulty of fabrication is evaluated? This is particularly relevant since this and the majority of the works referenced are simulations without any practical implementation. This should be explained so the reader can evaluate it.

3. Regarding the design (section 3), what was the drive for this design? The authors mention specific values for the different relevant factors (pitch distance, holes’ diameters, etc,) but it is not clear why these values were chosen.

4. Still regarding section 3, what would be the impact of the dimensional tolerances in the manufacture process? Since the (alleged) ease of manufacture is a factor used to distinguish the proposed design from others, and in practice, there are always tolerances, a tolerance analysis is mandatory. In some cases, if the tolerances are too tight, the design can even impossible to be implemented.

5. The authors mention the use of a finite element method (FEM) software but are not clear with the data regarding its implementation like, for example, mesh characteristics, or computational computational means used. This information is important to a better understanding of how the simulations were implemented.

6. Equations 3 and 4 are associated to references 21 and 22 but these articles just mention exactly the same that it is mentioned in this paper. From them, there is no understanding of what the “origins” of these formulae were. If the relative sensitivity is a straightforward relation, equation 4 might require some information for its understanding. A reference that minimally explains why the power fraction takes this form should replace references 21 and 22 (which do not add nothing), or the authors can give a brief explanation.

7. From equations 3 and 4, it is clear that there should be similar spectral behaviours regarding relative sensitivity and power fraction. This is clearly evident in the plots of figures 5 and 6. Thus:

7.1. Including the fact that the authors of ref. 8 have not presented data from the power fraction as a drawback (lines 64-66) isn’t totally correct since they have presented the relative sensitivity spectral behaviour.

7.2. It seems that plots 5 and 6 could be merged in just one using two Y-axis.

8. A table resuming the main performances and characteristics between the different state of the art designs (presented in section 1) and the results of the authors work would help the reader to better compare between them.

9. In lines 44-45, what the authors mean by “(…) and this tends to result in the efficiency.”? Perhaps they mean “(…) and this tends to result in improved efficiency.”? Please clarify.

10. In line 138, it seems that “(…) PCF sensor is structure (…)” should be instead “(…) PCF sensor is a structure (…)” or “(…) PCF sensor is structured (…)”.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thank you for authors` reply and effort to my concerned questions.

Only one additional suggestion is proposed here:  The pros and cons of such designed PCF sensor for liquid sensing could be summarized in some lines and added after Table.2 in manuscript. Some points can be drawn from the previous reply letter.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The authors correctly addressed the issues presented in the first revision. The re-submitted version maintains the qualities of the first version and clearly solves its problems. Thus, I believe the paper can be accepted as it is.

Author Response

Thank you very much. We truly appreciated your time and knowledge in reviewing the paper.