Low-Cost High-Speed Fiber-Coupled Interferometer for Precise Surface Profilometry

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this work the authors have creatively used a combination of x-coupler and fiber optic coupler to fabricate an interferometer capable of rapidly scanning the surface profile of a component, which has a definite effect on reducing the cost and increasing the sampling rate, and the whole work is novel. Therefore, I recommend this paper for publication with modifications.

Here is what I still don't fully understand from the article

1. What is the principle of the physical structure of the x-coupler? What role does it play for signal generation in this work?

2. How is z_m acquired by the observed fringes in this work?

3. What is the structure of the mechanism used for space scanning? How does it ensure the accuracy of control of its own spatial position during scanning.

4. What is the quantization noise of the ADC in the measurement? Is he the reason for the stepped data in Figure 7b?

5. Why is the data flat at both ends in Figure 5?

Comments on the Quality of English Language

1.Too many keywords

2. In page 8, line 254 and in page 10, line 290, the word “measurments” is misspelled.

3. The width of figure 2 seems too big.

Author Response

Please see the attached pdf document.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This work is dedicated to solve the problem that fiber optic interferometers may be disturbed by any kind of movement or vibration. The author proposed to embed both fiber-optic interferometer arms into wax to achieve this purpose. Although I don't think this is an important innovation, it seems from the manuscript that it plays an important role in improving measurement accuracy and scan velocities. The author has demonstrated the accuracy and speed advantages of the designed sensor through extensive and reliable experiments.

Further improvement is recommended. Specific suggestions are as follows:

1.     How is the impact of vibration or other factors specifically reduced by the special design proposed in this manuscript?  More specific analysis should be added.

2.     A chirp standard and a sinusoidal standard are used as the measured object. But the manuscript did not provide their profile standard values, either in figure 4, figure 5, or figure 6. The comparison error of measurement results between the standard values and the values measured by the designed sensor is also an important evaluation indicator.

3.     How does the reflectivity or roughness of the measured surface affect measurement accuracy? Suggest adding necessary analysis.

Author Response

Please see the attached pdf document.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This is in principle a nice paper some nicely written, both in terms of language and also how it guides the reader through the paper. There are however some areas that are overlooked in this paper and should be improved by including some additional material.

A major concern I have is on nonlinearity performance, which I would consider the most critical error sources that is not discussed at all in a paper on metrological dimensional measurements. For example, 1nm nonlinearity over micrometer height values equates to uncertainties on the order of 0.1%, which is quite high. Also, for spatial frequncy measurements they might introduce harmonic signal components that are not really there in reality. For a paper on interferometry, I would always expect to see a Lissajous figure or some other way of quantifying the nonlinearity error. Here, the authers must include some additional discussion and plots (for example Lissajous figure) in a major revision, however this should not be too difficult for the authors since they probably already have the necessary data.

Some other points that the authors should improve.
- Equation 1: Here the visibility V is missing in the equation.
- Sec. 2.2 Please discuss what laser was used (Type, Linewidth or Coherence Length)
- A question I have is regarding the Piezo amplitude. Is it controlled so that an exact number of fringes fit into the windows? Please elaborate, at least briefly even though details are found in the references.
- Section 3.1 discussed some AFM measurements, why are they not shown in a figure so the reader can judge.
- Details of the Grin lens used (manufacturer, Pitch, approx. spacing between fiber and lens) should be given, especially since it is desribed as better than previous setups.
- In plot 6b, an additional residual plot to show the differences between the four scan speed would be very useful.
- In Fig. 7 logarithmnic spectra would be more useful
- Can the authors briefly discuss polarisation senitivity in the fiber cables (external to the sensor unit). I would expect some signal fluctuations when the cable is distrubed.
- In the conclusions it is claimed that fiber optic sensors have a problem with vibration in the reference arm. This is strictly only true for fiber interferometers with a separate reference arm. Fiber interferometer in a fabry-perot (see https://doi.org/10.1515/teme-2024-0011) setup don't normally have this problem. Please therefore adapt this sentence.
- In the introduction, please also expand the horizon a bit by discussion commercially available fabry-perot fiber interferomters and include appropriate references such as https://doi.org/10.1515/teme-2024-0011 and some of the references included therein
- The conclusions should also discuss achievable uncertainties (see nonlinearities) in one or two sentences.

Author Response

Please see the attached pdf document.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

No other comments.

Author Response

Thank you for reviewing our manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have improved the paper and responded to most of my queries.

Author Response

Thank you for reviewing our manuscript.