Characteristics of Collimators Based on the Large-Mode-Area CMCF for Coupling Laser Beam

Round 1

Reviewer 1 Report

Fiber-coupled collimators are widely used in different devices, including integrated fiber-optics devices and fiber lasers. Therefore, any improvements in design of such collimators may be important. In this paper, the authors have demonstrated the possibility to improve tolerance to the angular misalignment for collimators by using large-mode-area fibers in them. However, this improvement is achieved at the cost of significant degradation of tolerance to other types of misalignments (such as Off-axis and Axial misaligments). Therefore, it is necessary to discuss which kind of applications can benefit from such partial improvement. It is necessary to justify the use of the proposed collimator design accounting for different types of its possible applications, including integrated fiber-optic devices [ https://doi.org/10.1364/OE.22.003557 ] and

fiber lasers [ https://doi.org/10.1070/QE2008v038n09ABEH013924

https://doi.org/10.1109/JLT.2019.2893291

] which employ fiber collimators.

Author Response

Original Manuscript ID: applsci-1457371   

Original Article Title: “Characteristics of Collimators based on the Large-mode-area CMCF for Coupling Laser Beam”

To: Applied Sciences Editor and Reviewer 1

Re: Response to Reviewer 1

Dear Editor,

Thank you for allowing a resubmission of our manuscript, with an opportunity to address the reviewers’ comments.

We are uploading (a) our point-by-point response to the comments (below) (response to reviewers), and (b) an updated manuscript which would be marked up using the “Track Changes” function indicating changes.

Best regards,

Xiao Liang et al.

Reviewer#1, Concern # 1: Fiber-coupled collimators are widely used in different devices, including integrated fiber-optics devices and fiber lasers. Therefore, any improvements in design of such collimators may be important. In this paper, the authors have demonstrated the possibility to improve tolerance to the angular misalignment for collimators by using large-mode-area fibers in them. However, this improvement is achieved at the cost of significant degradation of tolerance to other types of misalignments (such as Off-axis and Axial misalignments). Therefore, it is necessary to discuss which kind of applications can benefit from such partial improvement. It is necessary to justify the use of the proposed collimator design accounting for different types of its possible applications, including integrated fiber-optic devices [https://doi.org/10.1364/OE.22.003557] and fiber lasers [https://doi.org/10.1070/QE2008v038n09ABEH013924；https://doi.org/10.1109/JLT.2019.2893291] which employ fiber collimators.

Author response:  Thanks for your reminding. It is necessary to justify the use of the proposed collimator design accounting for more possible applications. We added more examples for the applications in the scene of movable connection. In addition, the advantage of this homemade collimator based on such partial improvement is explicated. Compared to fiber-to-fiber coupling, the fiber collimators allow a bigger gap between the fibers and makes the system less sensitive to axial and off-axis deviations, but makes more sensitive to an angular tilt misalignment. Therefore, the adjustable range in off-axis or axial would supply a loosely-coupled application for the alignment between two collimators, and the one in angular is so narrow that the collimator alignment would meet with some difficulty. There is an urgent need to improve the anti-deviation capability during fiber collimator coupling. Some related presentations would be added, and the changes are modified in the revision manuscript.

Author action: We updated the manuscript by making appropriate revision. The changes are modified as shown below with red marks.

(Page 1, Paragraph.2, Line 10)

“Fiber collimators have been widely used in various fields, especially for the scene of movable connection, such as spatial coupling of the laser [6-9], integrated fiber-optic devices [10] and so on.”

Reference

[8] Denisov, V.I.; Ivanenko, A.V.; Nyushkov, B.N.; Pivtsov, V.S. Femtosecond fibre laser with a hybrid linear-ring cavity. Quantum Electronics 2008, 38, 801-802.

[9] Nyushkov, B.; Kobtsev, S.; Antropov, A.; Kolker, D.; Pivtsov, V. Femtosecond 78-nm tunable Er:fibre Laser Based on Drop-shaped Resonator Topology. Journal of Lightwave Technology 2019, 1-1.

[10] Wan, Q.; Wan, Z.; Liu, H.; Liu, D. A two-in-one Faraday rotator mirror exempt of active optical alignment. Optics Express 2014, 22, 3557-3563, doi:10.1364/OE.22.003557.

(Page 1, Paragraph.3, Line 6)

“Compared to fiber-to-fiber coupling, the fiber collimators allow a bigger gap between the fibers and make the system less sensitive to axial and off-axis deviations [11].”

Reference

[11] Mi, L.; Yao, S.; Sun, C.; Bo, S.; Zhang, H. A single-channel fiber optic rotary joint on the basis Of TEC fiber collimators. In Proceedings of the International Conference on Optical Communications & Networks, 2011.

(Page 7, Paragraph.2, Line 3)

“As shown in Figure 4, 6 and 8, when the coupling loss between collimators is below 2 dB, the off-axis deviation could have a maximum 70 μm, the angular deviation could have a maximum 0.09°, and the axial deviation could have a maximum 5 cm. Obviously, the adjustable range in off-axis or axial would supply a loosely-coupled application for the alignment between two collimators, and the one in angular is so narrow that the collimator alignment would meet with some difficulty. From the above analysis, it could be seen that the coupling loss between collimators is comparatively more sensitive to angular deviation, and more tolerant to off-axis and axial deviation.”

Author Response File: Author Response.pdf

Reviewer 2 Report

The article could be interesting, unfortunately as a new type of collimator is presented, the design methodology is completely absent. In fact, the explanation given in paragraph 3.1. Design and fabrication of the large-mode-area CMCF, does not clarify at all how the device was designed. The collimator structure is presented in figure 9 without specifying how it was designed.

It should also be said that the misuse of the English language does not allow us to understand well the explanations given.

Other issues are:

When quoting with the surname, it does not matter to include the initial of the name unless there is a problem of ambiguity. In that case, a period is added after the initial of the name.

Even if the meaning of the abbreviation in the abstract has been explained, the definition must also be repeated the first time it is used in the text.

It is not clear where the x, y and z axes are located

Equation 3. Since a radial variable X is used, it is possible to provide Equation 3 in radial format?

Please cite the reference for the Equation 4

Lines 180-182 From the above analysis, it could be seen that the coupling loss between collimators is comparatively more sensitive to angular deviation, and more tolerant to off-axis and axial deviation. It seems to me that this sentence could be true only for fibers with ω=5mm. It can be noticed that for ω=9mm  the graph in figure 8, reporting “Coulping loss due to axial deviation”, has a maximum around 35, the graph in figure 5, reporting” Coulping loss due to off-axis deviation”, has a maximum around 16, while the graph in figure 6, reporting” Coulping loss due to angular deviation”, has a maximum around 1.5.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report