Relative Humidity Measurement Based on a Tapered, PVA-Coated Fiber Optics Multimode Interference Sensor

Round 1

Reviewer 1 Report

The manuscript presents a relative humidity (RH) sensor based on a no-core fiber (NCF)  spliced between two standard single-mode fibers (SMFs) where the NCF segment is coated with polyvinyl alcohol (PVA). The authors compare the sensitivity of two configurations, 1) non-tapered and 2) tapered NCF segments. The authors also show that the sensitivity of this RH sensor is significantly high compared to most sensitive fiber optics humidity sensors reported in the literature.

However, my first concern about this work is that this work lacks novelty in light of the references [10, 18] cited by the authors in this manuscript. In Zebian, H.Y.; Taher, H.J. "Relative humidity sensor based on no-core multimode interferometer coated with Al2O3-PVA composite films," Optical Fiber Technology 2020, 54, 102110, (which is ref [10] in the present manuscript), Zebian et al. demonstrated that the RH sensitivity enhances when the NCF diameter is reduced in an SMF-NCF-SMF structure.   In Zhao, Y.; Zhao, J.; Zhao, Q. "Review of no-core optical fiber sensor and applications, " Sensors and Actuators A: Physical 2020, 313, 112160, (which is ref [18]), Figure 7. shows simulated diagrams of tapered NCF in an SMF-NCF-SMF structure and the transmission spectra and wavelength shift with taper diameters of 125μm and 13μm. 

My second concern about this work is the limited sensing range of the sensor. I fail to see any explanation behind this device's significantly small sensing range. Table 1 in the manuscript shows that many of the prior MMI-based RH sensors have a better sensing range than the one presented in this manuscript. 

The authors should explain why the tapered NCF device has even reduced sensing range compared to the non-tapered NCF. In this regard, more experiments are needed with different tapering geometries. 

In section 2.2, the authors mentioned, "The resulting NCFs had a visible thin transparent layer of PVA coating the entire NCF and extending into both the SMFs of each sensor."  What is meant by "visible thin"? Was the coating thickness measured? How does the coating thickness impact the sensitivity or the sensing range?

The work shows inadequate experimental results to conclude how the PVA coating thickness and different tapering geometries impact the sensitivity and the sensing range.

Therefore, to improve the quality of the paper, I recommend conducting additional experiments to establish what the authors envision in this work; in their words (Conclusions), "the combination of better materials and different taper geometries could lead to optimal performance, in terms of both the sensitivity and the dynamic range, for specific applications."  

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The work submitted by Abraham A. Quiñones-Flores et al. provides a study regarding relative humidity (RH) using optical sensing, mainly by analyzing the changes on the RH based on a PVA-coated fiber optics multimode interference.

 

As the authors correctly mentioned, this is not a novel approach or using novel techniques, although the presented work still fits the journal's scope.

 

The work is presented compactly and objectively, providing a good reading experience. The data is also well presented, and it is clear to interpret. However, the scientific soundness can be drastically improved.

 

 

Regarding the presented data, there are some minor improvements to be made, such as:

1) The authors need to present the complete data regarding the repeatability and reproducibility tests;

2) The experimental error associated with the RH must also be presented in the current and future figures. The experimental error associated with the wavelength is not necessary to be represented in the graphs, but it must be mentioned in their caption.

 

The major drawback of this work, which is the most worrying part, is related to the technique's novelty, the material used, and the RH range. For example, in 2021, Syuhada, Aneez, et al. published a paper entitled "Single-mode modified tapered fiber structure functionalized with GO-PVA composite layer for relative humidity sensing." in Photonic Sensors. If one compares the mentioned paper with the manuscript presented by the authors can state at least the following:

a) The RH range of the presented manuscript is much lower than Syuhada, Aneez, et al.;

b) Syuhada, Aneez, et al. have made a scientific discussion with a more considerable deepness than the presented manuscript;

c) The sensing material, PVA, was also combined with graphene oxide.

 

3) Regarding the mentioned paper, I wish the following questions to be addressed by the authors:

3-1) I could not find the previously cited article in the references. Why the authors missed such a recent publication in which the title (and content!) is close to theirs?

3-2) The authors must use this study in their comparison table (Table 1);

3-3) The author must discuss in detail the advantages/disadvantages of their work compared with the work published by Syuhada, Aneez, et al. once the RH range of the latter is broader.

3-4) Comparing the two studies, the authors must elaborate on which one will be more effective in becoming a future commercial RH sensor.

 

As I have mentioned before, the work submitted by Abraham A. Quiñones-Flores et al. is well-written and presented, but the response to comment #3 will be crucial for my final decision regarding the acceptance of the manuscript for publishing.

Minor editing of English language required.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

A relative humidity (RH) fiber optic sensor is demonstrated based on the multimode interference (MMI) phenomenon utilizing a no-core fiber (NCF) coated with polyvinyl alcohol (PVA).However,can you explained what is the impact of different length MMI on the measurement result?Can you give more data information?For example, the influence of ambient temperature on the test.How the parameters of PVA affect the measurement results.

Quality of English Language is good.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have addressed the comments and concerns satisfactorily.

Reviewer 2 Report

Undoubtedly, this work has many similarities compared to other published studies. Still, it is well known that many fields of science use the same optical techniques to characterize different types of materials, some very similar to those already published. Such a fact can not be a rejection factor.

In this particular situation, besides adding more references, the authors made a thorough comparison with other similar works in their revised version of the manuscript. Moreover, they emphasize and justify why their work should be published, i.e., they have better explained to the reader the construction novelty of their sensor, which used a standard coating and commercial-grade optical fibers.

Therefore, despite its low range, the constructing insight and the proper testing of a potential commercial RH persuaded me to accept their revised work.

Minor editing of English language required