Design Study of Broadband and Ultrahigh-Resolution Imaging Spectrometer Using Snapshot Multimode Interference in Fiber Bundles

Round 1

Reviewer 1 Report

This paper presents an ultrahigh-resolution imaging spectrometer that consists of a micro-lens array, multiple fiber bundles, a microscope, and a two-dimensional array detector. The imaging spectrometer based on low-cost multimode interference in fiber bundle is interesting and will have a significant impact on the fiber sensor research community. Although, the manuscript needs to address the grammatical errors and the following concerns;

1. The literature needs to be further exploited with the latest fiber-based imaging spectrometer.
2. The MMI theory is not clear and needs to explain clearly with the self-imaging technique.
3. A comparison table is helpful with previous fiber sensor-based spectrometer papers.

Author Response

Dear reviewer,

Please see the attachment. Thank you so much!!

Best,

Jiangong Cui

Author Response File: Author Response.pdf

Reviewer 2 Report

In this manuscript, the authors proposed to use the modal interference pattern from a tapered multimode fiber array to perform spectral imaging. The authors conducted theoretical analysis and numerical simulation to prove the feasibility. Indeed, the interference pattern is highly sensitive to the wavelength which could provide better spectral resolution. However, the reviewer has a major concern about one assumption applied in the analysis. The authors used a random function to generate modal distribution but fix it during the following analysis. This is a very strong assumption for practical application. Practically, any change of the input light field will alter the excited modal distribution in the multimode fibers. Therefore, the modal distribution may change between the measurements. Without additional calibration, can the author’s reconstruction method still provide unique solutions for the spectrum between different modal distributions? The authors should properly address this concern, otherwise the reviewer doubts the practical feasibility of the proposed design.

Furthermore, the manuscript is poorly prepared and there are several textual and format errors. Some presentations need to be clarified as well.

1. The presentation in figure 1 (a) is confusing and needs to be improved. The “Fiber bundle” labels both the thick horizontal black line and thin perpendicular line. The “Detector array” seems to label different components in the top and bottom figure.
2. The definitions of FOV and r_c are missing.
3. It is better to label R₁ in Fig. 1.
4. In the text, it is D_fb. But in Fig. 1, it is D_FB. It is better to keep the label consistent.
5. In line 124, the wf does not have subscript.
6. It is unclear why the authors choose Gaussian beam for the analysis.
7. Why did the authors select graded-index MMF in the design? The authors did not provide any justification.
8. It is unclear what do the x-axis and y-axis refer to in the inset of Fig. 3 (a)
9. Table 1 has a format problem. The last column is missing.

Overall, the manuscript is not suitable for the publication in its current form.

Author Response

Dear reviewer,

Please see the attachment. Thank you so much!!

Best,

Jiangong Cui

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors described a spectrometer system with micro lens array, multiple fibers with tapers and a CCD array. The light collected by the micro lens array is couple to different multimode fibers and the light coming out of the tapered end is received by CCD. Demodulation of the interference signal resolve the components from each wavelengths. While the sensing principle is valid, I think that some revision is needed. First, Table 1 is cropped and Figure 1 is very confusing. From what I understand, the tapered side of the fibers are laid flat on the adhesive and the leaked out light are collect by the CCD above. Then why is there a microscope? I would also like to see an actual phot of the system. Second and most importantly, the author provided some simulation result. More experiment should be provided to validate the system. Supposed you have a image pattern in front of the micro lens array, what is the final image reconstructed from the CCD? Lastly, fiber tapers have differences between from each other which means each system needs to be calibrated separately. The fabrication and calibration is not a quick task. Therefore the practical use of the system is limited. In sum, the authors demonstrated the system in theory but manuscript lacks experiment details and data. 

Author Response

Dear reviewer,

Please see the attachment. Thank you so much!!

Best,

Jiangong Cui

Author Response File: Author Response.pdf

Reviewer 4 Report

Manuscript No:  ms photonics-1681799

 

Title:  Design Study of Broadband and Ultrahigh-Resolution Imaging Spectrometer Using Snapshot Multimode Interference in Fiber Bundles

 

Authors:  Fan Meng, Zefang Liu, Pengfei Wu, Weiwei Feng, and Jiangong Cui

 

1. Overview
2. In this manuscript the authors report on experimental work on Ultrahigh-Resolution Imaging Spectrometry.
3. The contents are expressed clearly; the manuscript is well organized and it is written in reasonable English.
4. The authors have acknowledged recent related research.
5. As long as my knowledge, the work presented is original.

 

1. Detailed analysis.

Abstract: Please organize the ideas in each paragraph. Be clear, objective. State briefly what you did, how did you do it, the quantitative results you and the novelty of your work.

1. Introduction: provides an interesting approach to the subject and there are up to date references. However a more extended revision could be provided for the sake of the average reader..
2. Optical layout for the CBURIS: it provides a clear and correct explanation of the optical structure.
3. Operating principles of the CBURIS:

- “which enables the field angle of the microlens to be subdivided into finer angular resolution (corresponds to spatial resolution),” – elaborate/quantify the special resolution

- which “optical adhesive” did you used?

- Figure 1 must be improved for clarity and quality (The detector array shape is not clear)

- Please Add an ACTUAL picture of the set up.

 

1. Overall assessment

In my opinion the work can be published after minor correction in the manuscript.

 

1. Review Criteria
2. Scope of Journal

Rating: Medium

2. Novelty and Impact

Rating: Medium

3. Technical Content

Rating: Medium

4. Presentation Quality

Rating: Medium

Author Response

Dear reviewer,

Please see the attachment. Thank you so much!!

Best,

Jiangong Cui

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Thanks for the author's detailed response. All the reviewer's previous comments have been properly addressed. This version is suitable for the publication.

Author Response

Dear reviewer,

Thank you for your time. Please see the attachment.

Best,

Jiangong Cui

Author Response File: Author Response.pdf

Reviewer 3 Report

This is a re-review of the manuscript. The main comment from the last round of the review was the lack of experiment data. The authors didn't provide any experiments data to resolve the concern. Additionally, I agree with another reviewer's comment that the modal distribution of the input light will greatly affect the interference pattern of the tapered fiber. Therefore, using single wavelength light for calibration is not sufficient as you can not simulate all modal excitation states. This would be obvious if the authors performed any actual experiment. In sum, the principle of this system is flawed and the authors don't have the data to back it up. 

Author Response

Dear reviewer,

Thank you for your time. Please see the attachment.

Best,

Jiangong Cui

Author Response File: Author Response.pdf