Temperature Sensing of Stepped-Metal Coated Optical Fiber Bragg Grating with the Restructured Dual-Peak Resonance
Round 1
Reviewer 1 Report
(1) The paper presents an interesting analysis and experimental verification of using a metallically double-clad fiber Bragg grating for simultaneously sensing two physical parameters. The concept, theoretical analysis, and experimental verification are well done and the dialog is easy to follow. The figures are well presented and clear.
(2) In Sec. 3.1.1 and 3.1.2 and the accompanying figures, the use of the words “factual elongation” and “actual elongation” are confusing. Did you mean “fractional elongation”?
(3) The words “column” and “solution” are spelled incorrectly in Figure 2.
(4) The word “nickel” is spelled incorrectly in Figure 3d.
(5) What is the parameter λ0 (lambda sub zero) in Table 1?
Author Response
1. In Sec. 3.1.1 and 3.1.2 and the accompanying figures, the use of the words “factual elongation” and “actual elongation” are confusing. Did you mean “fractional elongation”?
Response 1: No, it doesn’t mean “fractional elongation”. The word “actual elongation” was a writing error.The words “actual elongation” in Fig. 7, Fig.8 and Fig.9 have been revised to “factual elongation”.
2. The words “column” and “solution” are spelled incorrectly in Figure 2.
Response 2:The words “clumn” and “soulution” in Figure 2 have been revised to “column” and “solution”.
3. The word “nickel” is spelled incorrectly in Figure 3d.
Response 3: The word “nickle” in Figure 3d has been revised to “nickel”.
4. What is the parameter λ0 (lambda sub zero) in Table 1?
Response 4: The parameter λ0 in Table 1 means the initial Bragg wavelength. λ0 in Table 1 has been revised to λB.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors propose a method for the development of stepped-metal coating on FBGs. This is an interesting work, nevertheless, some aspects to be highlight:
1. Experimental set-up and results: Include more experimental details (What was the fiber used? How were the FBGs inscribed? What was the FBGs’ length)?
2. The acronym OFBG is not defined in the text.
3. What temperature oven was used? Provide more details.
4. Why is the separation between the dual-peak resonance different (Figures 4a), 5a), 6a)? This is due to the different layers, but scientifically, can you explain this better?
5. What is the stability/physical integrity of these coatings in practical applications? These will provide measurements with accuracy? There will be hysteresis after some experiments?
Author Response
1. Experimental set-up and results: Include more experimental details (What was the fiber used? How were the FBGs inscribed? What was the FBGs’ length)?
Response 1: Three FBGs were inscribed into the single mode fiber SMF-128 by UV phase mask with a nominal resonance wavelength of 1541.325nm, 1539.502nm and 1547.835nm at 25℃. The length of the Bragg grating is 10mm.
Theses sentences have been revised in Sec.2.
2. The acronym OFBG is not defined in the text.
Response 2: The acronym OFBG means “Optical fiber Bragg grating ”, but it is not defined in the text. So, the words “OFBG” have been revised to ‘FBG” in Sec. 3.1.1 and in Fig. 1.
3. What temperature oven was used? Provide more details.
Response 3: We employed a temperature oven (DK-500, Shanghai,China) to control the electroless-plating temperature. Its temperature range is from room temperature to 100℃ and its temperature resolution is 0.5℃. And the optical spectrum analyzer (MS9740A, Anritsu,Japan) was used to record the FBGs’ data.
Theses sentences have been added into Sec.2.
4. Why is the separation between the dual-peak resonance different (Figures 4a), 5a), 6a)? This is due to the different layers, but scientifically, can you explain this better?
Response 4: We consider that the spectrum difference is caused by the factors related to the plating process, such as different tension arising from suspension of FBG. FBG is taped by hand, which will cause different tension that is difficult to control accurately.
5. What is the stability/physical integrity of these coatings in practical applications? These will provide measurements with accuracy? There will be hysteresis after some experiments?
Response 5: A metallically clad and double-clad FBG can be embedded into metal structures by soldering, ultrasonic welding and laser welding, shown in Fig.1. Attached please find the photos.
Generally, this kind of FBGs embedded in metal structures can work for two years or much more longer. There exists hysteresis and sensitivity drift after these FBGs have worked for a period of time. They need to be calibrated periodically.
Author Response File: Author Response.pdf
Reviewer 3 Report
My recommendation is to publish after clarification of a few points and an English review.
Points to be clarified:
Abstract- The abstract is difficult to understand at first reading and so could reduce visibility of the paper.
2.1. First layer of inner metal coating by electroless-plating- As is presented the composition of sensitizing and nucleation solutions, should be presented also details on the copper and nickel solutions and time.
Author Response
1. The abstract is difficult to understand at first reading and so could reduce visibility of the paper.
Response 1: In abstract, the sentence “The modeling and experimental analysis is categorized into: 1) Type A, in which the inner metal coating thermal expansion coefficient is bigger than the outer stepped-metal coating; 2) Type B, in which the inner coating thermal expansion coefficient is smaller than the outer stepped-metal coating; and 3) Type C, in which the inner coating thermal expansion coefficient equals to the outer stepped-metal coating.” is too long to understand at first reading. It has been revised to “According to the coefficients of linear thermal expansion of the coatings, the modeling and experimental analysis is categorized into three types: Type A, Type B and Type C.”
2. First layer of inner metal coating by electroless-plating- As is presented the composition of sensitizing and nucleation solutions, should be presented also details on the copper and nickel solutions and time.
Response 2: The electroless copper plating solution is mainly listed as the following: CuSO4•5H2O,10g/L; NaKC4H4O6•4H2O, 40g/L; NaOH,8g/L; Na2CO3,2g/L; NiCl2·6H2O,1g/L; HCHO(37%), 20ml/L. The electroless nickel plating solution is mainly listed as the following: NiSO4•6H2O,25g/L; NaH2PO2•H2O, 20g/L; H3BO3, 20g/L; C3H6O2,20ml/L.
These sentences have been added into Sec.2.1.
For Type A, it took about three hours to get the inner copper layer and thirteen hours to get the stepped-nickel layer. For Type B, it took about two hours to get the inner nickel layer and fourteen hours to get the stepped-copper layer. For Type C, it took about two hours to get the inner nickel layer and twelve hours to get the stepped-nickel layer.
These sentences have been added into Sec.2.2.
Author Response File: Author Response.pdf
