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REVIEW 4 major objections 5 minor 22 references

Multifunctional Portable Optical Measuring Instrument Based on Y-Fiber Optics

T0 review · 4 major / 5 minor · reviewed 2026-08-11 · deepseek-v4-flash

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Pith's one-line read The paper tries to show that one compact, low-cost Y-fiber instrument can combine grating spectroscopy, concentration monitoring, and film-thickness measurement, with a claimed 340-1050 nm range, 1 nm resolution, and ±1.25 μm thickness…

desk verdict A real 3D-printed three-in-one optical instrument whose quantitative claims—1 nm resolution, circular concentration verification, and unsupported ±1.25 µm film-thickness accuracy—are not backed by the data. read the letter →

arxiv 2412.07531 v1 pith:4LVFLZI5 submitted 2024-12-10 physics.optics

Juntao He , Yikai Dang , Haoqi Wang , Shaohua Wang , Yingke Li , Ruiyun Ma , Yingyuan Li , Peilin Gao
show 2 more authors
Jianguo Cao Yong Pan
This is my paper · ORCID
classification physics.optics
keywords portableopticalmeasuringinstrumentY-typefibergratingspectrometerCCDimagesensorsolutionconcentrationmonitoringfilmthicknessmeasurementinterference
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper reports the construction of a single portable optical instrument built around a bifurcated 'Y' optical fiber, a grating and CCD camera, and a multi-color LED light source. The instrument is intended to perform three measurement tasks with one optical path: spectrum detection by grating diffraction, solution concentration from absorbance, and thin-film thickness from interference fringes. The authors' central claim is that the device reaches a usable wavelength range of about 340-1050 nm with 1 nm resolution and measures micron-scale film thickness to about ±1.25 μm. A sympathetic reader would care because the combination of these three functions in a low-cost, non-contact, battery-capable device would make routine optical measurement feasible outside a specialized laboratory.

What carries the argument

The carrying component is the Y-shaped optical fiber: one branch carries excitation light from the LED source toward the sample, and the other collects the returned light into a CCD grating spectrometer, so all three measurements share the same alignment. Around it, the design uses the grating equation $d\sin\theta = m\lambda$ for spectral dispersion, the absorbance law $A = \lg(I_0/I_1) = Kbc$ for concentration, and the interference-peak formula $d = \lambda_1\lambda_2/[2n(\lambda_1-\lambda_2)]$ for film thickness, where the two wavelengths are successive interference maxima and $n$ is the film refractive index. The instrument combines these with switchable LED colors for calibration and a 3D-printed black enclosure that separates the source chamber from the spectral chamber.

What would settle it

Measure a PET film whose thickness is already known independently—say 12.00 μm by a calibrated contact gauge—with this instrument; if the reported mean lies outside 10.75-13.25 μm, the claimed ±1.25 μm accuracy is contradicted.

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Extended reading notes

Core claim

The central claim, stated on the paper's own terms, is that an assembled instrument—using a 600-line transmission grating in a slit-grating-CCD layout, a Y-shaped fiber to route light, and a remote-controlled 16-color LED source—can deliver the spectral, concentration, and thickness functions in one package. Spectral detection is demonstrated by comparing natural-light spectra with a high-precision research spectrometer, with the observed working range given as about 340-1050 nm and resolution as 1 nm. Concentration monitoring is demonstrated with potassium permanganate solutions: absorbance at the green peak follows a fitted linear relation $A = 3.7718c + 0.04504$ and allows concentration readback below about 0.2 g/L. Film thickness is demonstrated on a PET protective film whose measured thickness falls near 11.5-11.8 μm, with standard deviations decreasing as more interference peaks are averaged, supporting the reported accuracy of ±1.25 μm.

Load-bearing premise

The film-thickness reading assumes a known refractive index for the PET film and assumes that the peaks selected from the spectrum are successive interference orders from the same film at normal incidence, and the paper never states the refractive index value it used.

Editorial extensions

If this is right

  • A single field instrument could measure emission spectra, solution concentration, and film thickness without contact, which would reduce the need to carry separate spectrometers and mechanical thickness gauges.
  • The reported 1 nm resolution and 340-1050 nm range would cover near-UV, visible, and near-IR absorption features, including the green absorption peak used for permanganate concentration.
  • If the ±1.25 μm thickness claim holds, the device is accurate enough to check 10-20 μm protective films in building-materials inspection.
  • Because the LED source is remotely switchable among colors, the same hardware can be recalibrated for different absorption bands without changing optics.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The thickness formula as used assumes a refractive index value for PET that the paper never states; a fair test of the accuracy claim would require revealing that value, since every computed thickness scales with it.
  • The same Y-fiber architecture could likely be extended to reflectance or fluorescence measurements by swapping the source color and adding a filter, functions the paper does not demonstrate.
  • The concentration calibration saturates at high concentrations where transmitted light vanishes; mapping that saturation boundary would give the instrument a stated dynamic range, which the paper leaves implicit.
  • A direct comparison of the instrument's wavelength scale against known atomic emission lines would turn the '1 nm resolution' claim into a testable calibration statement.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

4 major / 5 minor

Summary. The paper reports the construction of a portable optical instrument in which a CCD-based spectrometer is combined with a Y-shaped fiber-optic path, multi-color LED sources, and a 3D-printed enclosure. The authors claim three capabilities: spectral detection over roughly 340-1050 nm with 1 nm resolution, solution concentration measurement by absorbance, and film-thickness measurement with ±1.25 μm accuracy. Each function is demonstrated with a small set of experiments: a qualitative comparison of natural-light spectra, absorbance measurements on potassium permanganate solutions, and interference-peak analysis of a PET film. The central quantitative claims in the abstract and conclusion are much stronger than what the verification sections actually establish.

Significance. The work has value as a low-cost, student-built demonstration of an integrated optical instrument: the hardware is clearly described, the design is reproducible from the text, and the qualitative demonstrations show that the device can acquire spectra and produce interference-like fringes. However, the paper's advertised quantitative performance—1 nm spectral resolution, concentration-measurement capability, and ±1.25 μm film-thickness accuracy—is not supported by the evidence presented. Since those numbers are the main contribution claimed in the abstract and conclusion, the significance of the paper in its current form is limited to a proof-of-concept rather than a validated measurement instrument.

major comments (4)
  1. [§4.1] The claim that the spectrometer has an observable range of 340-1050 nm and a resolution of 1 nm is not supported by the experiment described. The validation is a qualitative visual comparison of natural-light spectra obtained with a reference spectrometer and the built device; no atomic line source, wavelength calibration standard, line-width measurement, or Rayleigh-criterion test is reported. A resolution of 1 nm is a quantitative statement that requires a calibrated determination, and the natural-light comparison cannot establish it.
  2. [§4.2, Eq. (4-2) and Eq. (4-4)] Equation (4-4), c = 0.2651 lg(40/I1) - 0.012, is obtained by algebraically inverting the fitted calibration line A = 3.7718c + 0.04504 together with A = lg(40/I1). The 'verification' in Table 2 then uses remeasured intensities from the same eight calibration samples and inserts them into this inverse formula. The agreement therefore reduces to identity and does not validate the method for unknown samples. An independent test on freshly prepared solutions with independently known concentrations, or a leave-one-out cross-validation, is required before the concentration-measurement function can be claimed.
  3. [§4.2, Table 1] The concentration values in Table 1 are internally inconsistent. A 0.4 g/L potassium permanganate solution is stated to correspond to 63.2136 mol/L, which is physically impossible for a dilute aqueous solution; the same discrepancy propagates through all listed mol/L entries. If the molar masses or the solution preparation are misreported, the entire absorbance-concentration calibration, including Eq. (4-2) and Eq. (4-4), is called into question.
  4. [§4.3, Eq. (4-6), Table 3, Table 4] The film-thickness claim of ±1.25 μm accuracy in the abstract and Section 5 is not established. Equation (4-6), d = λ1λ2/[2n(λ1-λ2)], requires knowledge of the film refractive index n and assumes that the two selected interference extrema are consecutive orders at normal incidence. The paper never states n for the PET film, never demonstrates that peaks 2, 4, 6, 8, and 10 are consecutive-order maxima, and does not account for the factor of two if every-other maxima were chosen. Moreover, no independent thickness reference (profilometer, calibrated film standard, or known sample) is used, so the computed thickness range of 11.5-11.8 μm cannot be validated. Table 4 further labels relative uncertainties in units of μm, which is dimensionally incorrect and obscures what uncertainty is being reported.
minor comments (5)
  1. [§4.2] There is an isolated Chinese character '根' at the beginning of a paragraph, and the sentence listing prepared solution concentrations contains garbled wording ('0.5g/L, At 0.025g/L') that makes the sample set ambiguous.
  2. [§4.2] The text states that 'some groups' have low transmitted intensity and attributes this to probe distance or angle, but no quantitative account of measurement repeatability or a systematic uncertainty budget is provided for the concentration measurement.
  3. [§4.3, Eq. (4-5)] In Eq. (4-5) the interference term is written as 2√(I1/I2) cos(...), which should presumably read 2√(I1 I2) cos(...); as written, the expression is dimensionally inconsistent.
  4. [Table 4] The 'Relative uncertainty' column is given in μm although the numerical values are percentages; this should be corrected (e.g., relative uncertainty as a percentage, and the absolute uncertainty in μm).
  5. [General] The English is frequently non-idiomatic and contains numerous spacing and punctuation errors (for example, 'Matratio', inconsistent use of commas, and irregular capitalization). A careful language edit would improve readability.

Circularity Check

1 steps flagged · score 6.0 of 10

The concentration-monitoring 'verification' reduces by construction: Eq. (4-4) is the algebraic inverse of the calibration line fit to the same samples used in Table 2, so it is a consistency check, not an independent prediction.

  1. fitted input called prediction [Section 4.2, Eqs. (4-2) and (4-4), Table 2]
    "The expression of the linear relationship between concentration and absorbance after fitting is: A = 3.7718c + 0.04504 (4-2) ... The relative transmitted light intensity and concentration relationship is deduced: c = 0.2651 lg(40/I1) - 0.012 (4-4) ... When the relative incident light is adjusted as the reference (40), the solutions of groups 1 to 8 were remeasured to verify the feasibility of the fitting relationship."

    Equation (4-4) is not derived from Lambert-Beer's law independently; it is the exact algebraic inverse of the empirical calibration line Eq. (4-2) after substituting A = lg(40/I1). Using the same groups 1 to 8 that generated the fit and plugging their remeasured intensities into the inverse of the fitted line necessarily returns concentrations close to the calibration values. The 'verification' therefore reduces to checking that the inverse of the fitted line reproduces the fit inputs; it cannot independently validate the concentration measurement.

full rationale

The one clearly circular step is in the solution-concentration section: Eq. (4-4) is obtained by solving the fitted calibration line Eq. (4-2) for c, and Table 2 then 'verifies' this relation by remeasuring the same eight calibration solutions. This is a fitted-input-called-prediction pattern: the quantitative agreement is forced by construction. The other advertised capabilities do not show this same reduction. The spectrometer range/resolution claim rests on qualitative spectral comparison rather than calibrated line sources, and the film-thickness claim depends on stated but unverified assumptions about refractive index and fringe order; these are serious correctness/evidence gaps but not circularity in the derivation itself. Since the central claim of the paper is the multifunctional instrument and the concentration monitoring is one of its three demonstrated functions, the paper is partially circular (score 6), though not wholly so.

Assumptions & free parameters 3 free parameters · 5 assumptions · 0 invented entities

The central claims rest on standard textbook optics plus several unquantified domain assumptions: CCD response is treated as a linear intensity measure, Beer-Lambert linearity is assumed after excluding high concentrations, the PET refractive index is silently required by Eq. (4-6), and the natural-light comparison is treated as a calibration. The only explicit fitted parameters are the absorbance-concentration line and the arbitrary 40 reference intensity; the refractive index n is an unstated input.

free parameters (3)
  • absorbance-concentration calibration slope and intercept = A = 3.7718 c + 0.04504 (c in g/L)
    Linear coefficients fitted to the calibration solutions in Table 1 and used to derive Eq. (4-4) and all concentration estimates.
  • relative incident light intensity reference = I0 = 40 (arbitrary units)
    Absorbance is defined as lg(40/I1); the arbitrary 40 scaling enters the concentration equation, and any offset changes the inferred concentration.
  • PET film refractive index n = not stated
    Eq. (4-6) divides by n, but no value or source for n is given, so the film thickness numbers cannot be reproduced independently.
assumptions (5)
  • standard math Grating equation d sin θ = m λ and Rayleigh criterion Λ = mN describe the spectrometer geometry.
    Used in Section 2 to select a 600-line grating; standard textbook relations, not questioned here.
  • domain assumption The CCD signal is proportional to incident light intensity with a stable, known response over 340-1050 nm.
    Relative intensities I0 and I1 are taken directly as CCD counts; no flat-field correction, stray-light rejection, or detector nonlinearity analysis is described.
  • domain assumption Lambert-Beer law A = Kbc holds linearly over the concentration range used after excluding high concentrations.
    Used in Section 4.2 to fit A versus c and then invert; the paper itself restricts the valid range to below 0.2 g/L, making the linearity assumption post hoc.
  • domain assumption Adjacent interference extrema in the reflected spectrum obey d = λ1λ2 / (2n(λ1-λ2)) with known, dispersionless n.
    Eq. (4-6) is asserted without derivation and requires normal incidence, a uniform film, correct fringe-order assignment, and a known refractive index.
  • domain assumption Comparison of natural-light spectra with an unnamed commercial spectrometer is sufficient calibration for wavelength range and resolution.
    Used in Section 4.1 to claim 340-1050 nm range and 1 nm resolution; no line-source calibration or quantitative metric is provided.

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Cite this review

Pith. "Pith review of Multifunctional Portable Optical Measuring Instrument Based on Y-Fiber Optics." pith.science (2026). https://pith.science/paper/4LVFLZI5

@misc{pith2026241207531,
  author       = {Pith},
  title        = {Pith review of: Multifunctional Portable Optical Measuring Instrument Based on Y-Fiber Optics},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/4LVFLZI5}},
  note         = {Machine review of arXiv:2412.07531}
}
read the original abstract

Based on grating diffraction principle, optical fiber transmission principle and optical interference principle, a multi-functional portable optical measuring instrument is constructed in this paper. The optical measurement visualization spectrometer based on CCD photoelectric image sensor is designed and assembled. The "Y" optical signal transmission fiber optical path suitable for multi-function measurement is improved and designed. The multi-function optical measurement system is built by combining with remote controlled multi-color LED lights. The spectral analysis, solution concentration monitoring and film thickness measurement are realized. The experimental results show that the observable wavelength range of the spectrometer is about 340-1050nm and the resolution is 1nm. The solution concentration can be obtained by measuring absorbance with optical fiber spectrometer. The film thickness measuring instrument can accurately measure the thickness of the micron film, and the measurement accuracy can reach 1.25 {\mu}m. It is proved that the instrument integrates multiple functions, has high measurement accuracy and wide range, and realizes non-contact measurement.

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Reference graph

Works this paper leans on

22 extracted references · 22 canonical work pages

  1. [1]

    Mouroulis P,Green R O.Review of high fidelity imaging spectrometer design for remote sensing [J].Optical Engineering,2018,57(4):040901

    work page 2018

  2. [2]

    When a forward voltage is added to both ends of the LED chip, electrons will flow from the cathode to the anode, and holes will flow from the anode to the cathode

    Detection principle The LED (Light Emitting Diode) chip is a semiconduc tor device that converts electricity into light energy. When a forward voltage is added to both ends of the LED chip, electrons will flow from the cathode to the anode, and holes will flow from the anode to the cathode. As the current flows through the sem iconductor, the electrons an...

    work page

  3. [3]

    The cover plate is used as the experimental base for the sample placement

    Instrument design The enclosure was generated using 3D printing, Is 174 mm long, Is about 174 mm wide, At 50 mm high, Small and portable; The whole appearance is black, Can prevent the influence of external natural light on the internal instruments, See Figure 2A; The material of the shell is PLA (polylactic acid), The material has the advantage that it b...

    work page

  4. [4]

    J.Opt.Soc.Am.,1962,52(7):768-773

    M.V .R.K.Murty.Use of convergent and divergentilluminati on with plane gratings[J]. J.Opt.Soc.Am.,1962,52(7):768-773

    work page 1962

  5. [5]

    Conclusion In this paper, a multi -functional portable optical measuring i nstrument is designed based on "Y" type optical fiber. Compared with the shortcomings of traditional optical measuring instrument, such as single function, large volume and complex operation, the multi -functional portable optical measuring instrument is a portable, simple operatio...

    work page

  6. [6]

    Lumb D H,Bautz M W,Burrows D N,et al.Recent developments for the AXAF CCD imaging spectrometer [C]//EUV ,X-Ray, and Gamma-Ray Instrumentation for Astronomy IV ,International Society for Optics and Photonics, 2006: 265-271

    work page 2006

  7. [7]

    Kudenov M W,Dereniak E L.Compact real-time birefringent imaging spectrometer[J].Optics Express,2012,20(16):17973 17986

    work page 2012

  8. [8]

    Aathur B. Shafer. Optimization of the Czerny -Turner Spectrometer [J]. J.Opt.Soc.Am., 1963,54(7):

    work page 1963

Show all 22 references
  1. [9]

    Murphy L.Dalton ,Jr.Astigmatism compensation in the Czerny -Turner spectrometer [J].Appl.Opt.,1966,5(7):1121-1123

    1966

  2. [10]

    Pavlycheva N K.Sov.J.Opt.Technol.1979,46(7):394

    1979

  3. [11]

    Hutley M C.Diffraction Gratings.Academic Press,1980

    1980

  4. [12]

    ZHOU Qian,ZENG L-i jiang,LI L-i feng.Spectroscopy and Spectral Analysis,2008,28(7):1673

    2008

  5. [13]

    Li Q C,Jiang Y J.Principle of spectroscopic instruments[M].Beijing:Machinery Industry Press, 1989:3-1 5

    1989

  6. [14]

    Ju H ,Wu Y H.The development status of micro -spectrometer[J].Optics And Precision Engineering,2001,9(4):372-376

    2001

  7. [15]

    Korablev O,Montmessin F,Trokhimovsky A ,et al.Compact echelle spectrometer for oc cultation sounding of the Martian atmosphere :design and performance [J].Applied Optics,2013,52(5):1054-65

    2013

  8. [16]

    Tousey R,Purcell J D,Garrett D L,et al.An echelle spectrograph for middle ultraviolet sola r spectroscopy from rockets[J].Applied Optics,1967,6(3):365

    1967

  9. [17]

    Guo H,Xiao G,Mrad N,et al.Echelle Diffractive Grating Based Wavelength Interrog ator for Potential Aerospace Applications[J].Journal of Lightwave Technology,2013,3 1(13):2099-105

    2013

  10. [18]

    Kane R,Siegmund O H,Beasley M,et al.The opto -mechanical design of the Colorado High-resolution Echelle Stellar Spectrograph(CHESS)[J].Proceedings of SPIE -The Inter national Society for Optical Engineering,201 1,8 145:8 1450P-P-8

  11. [19]

    Liu X L,Liu X,Li W,et al.Optical System D esign of Space -Based Filament LiDAR Spectr ometer[J].Chinese Journal of Lasers,2023.50(7),0708012

    2023

  12. [20]

    Liu Y Q,Jiang C,Liu Z Y ,et al.Long -Period Fiber Gratings[J].Laser&Optoelectronics Pr ogress,2023.60(9),0900001

    2023

  13. [21]

    Sun Y C,Huang C,Xia G,et al.Accurate wavelength calibration method for compact CCD spectrometer[J].Journal ofthe Optical Society ofAmerica A:2017.34(4):498-505. Page 18

    2017

  14. [22]

    Ballester P,Rosa R M P Ballester,Rosa M R.Modeling echelle spectrographs[J].Astronomy and Astrophysics:1997,126:563-571

    1997

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