E-mail Alert
RSS
| Citation: |
Imas JJ, Matías IR, Del Villar I, Ozcáriz A, Zamarreño CR et al. All-fiber ellipsometer for nanoscale dielectric coatings. Opto-Electron Adv 6, 230048 (2023). doi: 10.29026/oea.2023.230048
|
-
Abstract
Multiple mode resonance shifts in tilted fiber Bragg gratings (TFBGs) are used to simultaneously measure the thickness and the refractive index of TiO2 thin films formed by Atomic Layer Deposition (ALD) on optical fibers. This is achieved by comparing the experimental wavelength shifts of 8 TFBG resonances during the deposition process with simulated shifts from a range of thicknesses (T) and values of the real part of the refractive index (n). The minimization of an error function computed for each (n,T) pair then provides a solution for the thickness and refractive index of the deposited film and, a posteriori, to verify the deposition rate throughout the process from the time evolution of the wavelength shift data. Validations of the results were carried out with a conventional ellipsometer on flat witness samples deposited simultaneously with the fiber and with scanning electron measurements on cut pieces of the fiber itself. The final values obtained by the TFBG (n= 2.25, final thickness of 185 nm) were both within 4% of the validation measurements. This approach provides a method to measure the formation of nanoscale dielectric coatings on fibers in situ for applications that require precise thicknesses and refractive indices, such as the optical fiber sensor field. Furthermore, the TFBG can also be used as a process monitor for deposition on other substrates for deposition methods that produce uniform coatings on dissimilar shaped substrates, such as ALD.-
Keywords:
- tilted fiber Bragg grating (TFBG) /
- mode transition /
- ellipsometer
-
-
References
[1] Ohring M. Chapter 10 - Characterization of thin films and surfaces. In Ohring M. Materials Science of Thin Films 2nd ed (Academic Press, San Diego, 2002);http://doi.org/10.1016/B978-012524975-1/50013-6. [2] Podraza NJ, Jellison GE Jr. Ellipsometry. In Lindon JC, Tranter GE, Koppenaal DW. Encyclopedia of Spectroscopy and Spectrometry 3rd ed 482–489 (Academic Press, Oxford, 2017);http://doi.org/10.1016/B978-0-12-409547-2.10991-6. [3] Garcia-Caurel E, De Martino A, Gaston JP, Yan L. Application of spectroscopic ellipsometry and mueller ellipsometry to optical characterization. Appl Spectrosc 67, 1–21 (2013). doi: 10.1366/12-06883 [4] McCrackin FL, Passaglia E, Stromberg RR, Steinberg HL. Measurement of the thickness and refractive index of very thin films and the optical properties of surfaces by ellipsometry. J Res Natl Bur Stand A Phys Chem 67A, 363–377 (1963). [5] Wei JS, Westwood WD. A new method for determining thin‐film refractive index and thickness using guided optical waves. Appl Phys Lett 32, 819–821 (1978). doi: 10.1063/1.89928 [6] Ding TN, Garmire E. Measuring refractive index and thickness of thin films: a new technique. Appl Opt 22, 3177–3181 (1983). doi: 10.1364/AO.22.003177 [7] Kersten RT. A new method for measuring refractive index and thickness of liquid and deposited solid thin films. Opt Commun 13, 327–329 (1975). doi: 10.1016/0030-4018(75)90112-1 [8] Kirsch ST. Determining the refractive index and thickness of thin films from prism coupler measurements. Appl Opt 20, 2085–2089 (1981). doi: 10.1364/AO.20.002085 [9] Choi HJ, Lim HH, Moon HS, Eom TB, Ju JJ et al. Measurement of refractive index and thickness of transparent plate by dual-wavelength interference. Opt Express 18, 9429–9434 (2010). doi: 10.1364/OE.18.009429 [10] Jafarfard MR, Moon S, Tayebi B, Kim DY. Dual-wavelength diffraction phase microscopy for simultaneous measurement of refractive index and thickness. Opt Lett 39, 2908–2911 (2014). doi: 10.1364/OL.39.002908 [11] Kim S, Na J, Kim MJ, Lee BH. Simultaneous measurement of refractive index and thickness by combining low-coherence interferometry and confocal optics. Opt Express 16, 5516–5526 (2008). doi: 10.1364/OE.16.005516 [12] Cheng HC, Liu YC. Simultaneous measurement of group refractive index and thickness of optical samples using optical coherence tomography. Appl Opt 49, 790–797 (2010). doi: 10.1364/AO.49.000790 [13] De Bruijn HE, Kooyman RPH, Greve J. Determination of dielectric permittivity and thickness of a metal layer from a surface Plasmon resonance experiment. Appl Opt 29, 1974–1978 (1990). doi: 10.1364/AO.29.001974 [14] De Bruijn HE, Minor M, Kooyman RPH, Greve J. Thickness and dielectric constant determination of thin dielectric layers. Opt Commun 95, 183–188 (1993). doi: 10.1016/0030-4018(93)90659-S [15] Del Rosso T, Sánchez JEH, Dos Santos Carvalho R, Pandoli O, Cremona M. Accurate and simultaneous measurement of thickness and refractive index of thermally evaporated thin organic films by surface Plasmon resonance spectroscopy. Opt Express 22, 18914–18923 (2014). doi: 10.1364/OE.22.018914 [16] Salvi J, Barchiesi D. Measurement of thicknesses and optical properties of thin films from Surface Plasmon Resonance (SPR). Appl Phys A 115, 245–255 (2014). doi: 10.1007/s00339-013-8038-z [17] Rees ND, James SW, Tatam RP, Ashwell GJ. Optical fiber long-period gratings with Langmuir–Blodgett thin-film overlays. Opt Lett 27, 686–688 (2002). doi: 10.1364/OL.27.000686 [18] Cusano A, Iadicicco A, Pilla P, Contessa L, Campopiano S et al. Mode transition in high refractive index coated long period gratings. Opt Express 14, 19–34 (2006). doi: 10.1364/OPEX.14.000019 [19] Del Villar I, Matías IR, Arregui FJ, Lalanne P. Optimization of sensitivity in Long Period Fiber Gratings with overlay deposition. Opt Express 13, 56–69 (2005). doi: 10.1364/OPEX.13.000056 [20] Del Villar I, Achaerandio M, Matías IR, Arregui FJ. Deposition of overlays by electrostatic self-assembly in long-period fiber gratings. Opt Lett 30, 720–722 (2005). doi: 10.1364/OL.30.000720 [21] Pilla P, Trono C, Baldini F, Chiavaioli F, Giordano M et al. Giant sensitivity of long period gratings in transition mode near the dispersion turning point: an integrated design approach. Opt Lett 37, 4152–4154 (2012). doi: 10.1364/OL.37.004152 [22] Śmietana M, Koba M, Mikulic P, Bock WJ. Towards refractive index sensitivity of long-period gratings at level of tens of µm per refractive index unit: fiber cladding etching and Nano-coating deposition. Opt Express 24, 11897–11904 (2016). doi: 10.1364/OE.24.011897 [23] Cusano A, Iadicicco A, Pilla P, Contessa L, Campopiano S et al. Coated long-period fiber gratings as high-sensitivity optochemical sensors. J Lightwave Technol 24, 1776–1786 (2006). doi: 10.1109/JLT.2006.871128 [24] Esposito F, Sansone L, Srivastava A, Baldini F, Campopiano S et al. Long period grating in double cladding fiber coated with graphene oxide as high-performance optical platform for biosensing. Biosens Bioelectron 172, 112747 (2021). doi: 10.1016/j.bios.2020.112747 [25] Imas JJ, Albert J, Del Villar I, Ozcáriz A, Zamarreño CR et al. Mode transitions and thickness measurements during deposition of nanoscale TiO2 coatings on tilted fiber Bragg gratings. J Lightwave Technol 40, 6006–6012 (2022). doi: 10.1109/JLT.2022.3186596 [26] Imas JJ, Albert J, Del Villar I, Ozcáriz A, Zamarreño CR et al. Mode transition during deposition of nanoscale ITO coatings on tilted fiber Bragg gratings. In Bragg Gratings, Photosensitivity and Poling in Glass Waveguides and Materials 2022 BM3A. 5 (Optica Publishing Group, 2022); https://doi.org/10.1364/BGPPM.2022.BM3A.5. [27] Albert J, Shao LY, Caucheteur C. Tilted fiber Bragg grating sensors. Laser Photon Rev 7, 83–108 (2013). doi: 10.1002/lpor.201100039 [28] Lu YC, Huang WP, Lu YC, Jian SS. Full vector complex coupled mode theory for tilted fiber gratings. Opt Express 18, 713–726 (2010). doi: 10.1364/OE.18.000713 [29] Erdogan T. Cladding-mode resonances in short- and long-period fiber grating filters. J Opt Soc Am A 14, 1760–1773 (1997). doi: 10.1364/JOSAA.14.001760 [30] Malitson IH. Interspecimen comparison of the refractive index of fused silica. J Opt Soc Am 55, 1205–1209 (1965). doi: 10.1364/JOSA.55.001205 [31] Sarkar S, Gupta V, Kumar M, Schubert J, Probst PT et al. Hybridized guided-mode resonances via colloidal plasmonic self-assembled grating. ACS Appl Mater Interfaces 11, 13752–13760 (2019). doi: 10.1021/acsami.8b20535 [32] Kischkat J, Peters S, Gruska B, Semtsiv M, Chashnikova M et al. Mid-infrared optical properties of thin films of aluminum oxide, titanium dioxide, silicon dioxide, aluminum nitride, and silicon nitride. Appl Opt 51, 6789–6798 (2012). doi: 10.1364/AO.51.006789 [33] Del Villar I, Zamarreño CR, Hernaez M, Arregui FJ, Matias IR. Resonances in coated long period fiber gratings and cladding removed multimode optical fibers: a comparative study. Opt Express 18, 20183–20189 (2010). doi: 10.1364/OE.18.020183 [34] Del Villar I, Corres JM, Achaerandio M, Arregui FJ, Matias IR. Spectral evolution with incremental nanocoating of long period fiber gratings. Opt Express 14, 11972–11981 (2006). doi: 10.1364/OE.14.011972 [35] Del Villar I, Matias IR, Arregui FJ, Achaerandio M. Nanodeposition of materials with complex refractive index in long-period fiber gratings. J Lightwave Technol 23, 4192–4199 (2005). doi: 10.1109/JLT.2005.858246 -
Supplementary Information
Supplymentary video 
-
Access History
Figures(11)
Tables(2)
Article Metrics
Export File
Citation
Imas JJ, Matías IR, Del Villar I, Ozcáriz A, Zamarreño CR et al. All-fiber ellipsometer for nanoscale dielectric coatings. Opto-Electron Adv 6, 230048 (2023). doi: 10.29026/oea.2023.230048
Format
Content
DownLoad:
-
Figure 1.
Transmission spectrum of the S-polarized TFBG before starting the deposition. The 8 resonances that are employed in the method described in the results section are marked (in red for the resonances of modes with even azimuthal order, in green for resonances with odd azimuthal order).
-
Figure 2.
Schematic diagram of the setup employed in the deposition.
-
Figure 3.
(a) Experimental shift of the 8 TFBG resonances employed in the proposed method. Resonances S1 - S4 (top row) correspond to even azimuthal orders, and resonances S5 - S8 (bottom row) correspond to odd azimuthal orders. (b) Evolution of the spectrum in the 1515 - 1545 nm range during the deposition.
-
Figure 4.
Graphical representation of how to obtain the deposition rate that best fits the experimental with the simulated data for each n value. Here, the experimental wavelength shift of resonance S1 and the simulated data for n = 2.00 and n = 2.48 are used.
-
Figure 5.
Graphical explanation on how to calculate the time instant that minimizes the total error for the 8 resonances for a certain simulated (n, T) point. In this example, (n = 2.20, T = 100 nm), and the error is graphically shown for ti = 150 min.
-
Figure 6.
(a) Fitted (n, T, tfitted) points plotted in a thickness vs. time graph for n = 2.00, n = 2.20 , and n = 2.48. (b) Final thickness obtained for each n value with the proposed method.
-
Figure 7.
Mean wavelength error per resonance over all thicknesses (εglobal(n)) for each tested index value (n).
-
Figure 8.
(a) Simulated wavelength shift for S1 for n values between 2.00 and 2.48 (0.04 steps) and different thicknesses that vary depending on the n value. (b) Experimental wavelength shift of S1 during the deposition.
-
Figure 9.
Second iteration results. (a) Mean wavelength error per resonance (εglobal(n)) over all thicknesses for each tested index value (n). (b) Final thickness obtained for each n value with the proposed method. In both graphs the optimum solution is marked with a green star and (b) includes an inset that shows how the error in the n value of the solution is calculated.
-
Figure 10.
Dispersion curve for n measured by the ellipsometer on a thin film on a witness sample.
-
Figure 11.
FESEM images in which the thin film thickness is measured in the TFBG cross-section.
