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

Paulina Listewnik,Mikhael Bechelany,Matthieu Weber,Małgorzata Jędrzejewska-Szczerska,Przemysław Struk,Marzena Hirsch

doi:10.3390/nano9020306

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.

Highlights

Fiber-optic sensing devices present enormous potential, as they benefit from low-cost manufacturing, while maintaining high sensitivity and robustness
The presented microsphere shows a regular spherical shape and the diameter of the microsphere head was calculated by circle fitting and it is equal to ΦrZnO = 240.7 μm for the microsphere with the zinc oxide (ZnO) layer
The interferometric fiber-optic sensor with the incorporation of a microsphere coated with a thin film of ZnO by atomic layer deposition (ALD) at the tip of the optical fiber is reported for the first time

Summary

Introduction

Fiber-optic sensing devices present enormous potential, as they benefit from low-cost manufacturing, while maintaining high sensitivity and robustness. Nowadays, advanced fabrication techniques allow the incorporation of various nanomaterials for the tuning of sensing devices, including fiber-optic sensors [1–4]. Fiber-optic sensing devices can find application in many different fields of science such as chemistry (composition and content of various solutions) [1,2,5,6], biology [7–10] and physics [11–14]. Fiber-optics based sensors present a number of advantages, including high sensitivity, the ability to be used in demanding environments (narrow spaces, hazardous areas), as well as immunity to electromagnetic noise during operation [15,16]. The properties of fiber-optic sensors can be tuned by modifying their design with optical coatings.

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Conclusion