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. 2019 Feb 23;9(2):306.
doi: 10.3390/nano9020306.

Preparation and Characterization of Microsphere ZnO ALD Coating Dedicated for the Fiber-Optic Refractive Index Sensor

Paulina Listewnik  1 , Marzena Hirsch  2 , Przemysław Struk  3 , Matthieu Weber  4 , Mikhael Bechelany  5 , Małgorzata Jędrzejewska-Szczerska  6
Affiliations
Free PMC article

Preparation and Characterization of Microsphere ZnO ALD Coating Dedicated for the Fiber-Optic Refractive Index Sensor

Paulina Listewnik et al. Nanomaterials (Basel). .
Free PMC article

Abstract

We report the fabrication of a novel fiber-optic sensor device, based on the use of a microsphere conformally coated with a thin layer of zinc oxide (ZnO) by atomic layer deposition (ALD), and its use as a refractive index sensor. The microsphere was prepared on the tip of a single-mode optical fiber, on which a conformal ZnO thin film of 200 nm was deposited using an ALD process based on diethyl zinc (DEZ) and water at 100 °C. The modified fiber-optic microsphere was examined using scanning electron microscopy and Raman spectroscopy. Theoretical modeling has been carried out to assess the structure performance, and the performed experimental measurements carried out confirmed the enhanced sensing abilities when the microsphere was coated with a ZnO layer. The fabricated refractive index sensor was operating in a reflective mode of a Fabry⁻Pérot configuration, using a low coherent measurement system. The application of the ALD ZnO coating enabled for a better measurement of the refractive index of samples in the range of the refractive index allowed by the optical fiber. The proof-of-concept results presented in this work open prospects for the sensing community and will promote the use of fiber-optic sensing technologies.

Keywords: ZnO; atomic layer deposition; coating; fiber-optic sensors; microsphere; refractive index.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic model of the microsphere with 200 nm ZnO thin film deposited on the surface, where: din—internal diameter of the sphere, dex—external diameter of the sphere, L—cavity length, ni—refractive index.
Figure 2
Figure 2
Operating principle of Fabry–Pérot interferometer used for measurements.
Figure 3
Figure 3
SEM images of optical fiber microsphere: (a) the microsphere with 200 nm ZnO coating, (b) the microsphere without ZnO coating, (c) surface topography on the front side of the microsphere with 200 nm ZnO coating, (d) surface topography on the front side of the microsphere without ZnO coating.
Figure 4
Figure 4
Raman spectra of the ZnO layer deposited on microsphere.
Figure 5
Figure 5
Simulation results upon illumination of superluminescent diode (SLD)-like light source: Normalized reflected spectra (a) for uncoated microsphere and (b) with 200 nm ZnO coating and signal peak intensity in function of external refractive index (c) for uncoated sphere and (d) with ZnO film.
Figure 6
Figure 6
Measured response of the fiber-optic interferometer for a microsphere with ZnO layer.
Figure 7
Figure 7
Measured response of the fiber-optic interferometer for a microsphere with ZnO layer.
See this image and copyright information in PMC

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