Marzena Hirsch

Application of Thin ZnO ALD Layers in Fiber-Optic Fabry-Pérot Sensing Interferometers

In this paper we investigated the response of a fiber-optic Fabry-Pérot sensing interferometer with thin ZnO layers deposited on the end faces of the optical fibers forming the cavity. Standard telecommunication single-mode optical fiber (SMF-28) segments were used with the thin ZnO layers deposited by Atomic Layer Deposition (ALD). Measurements were performed with the interferometer illuminated by two broadband sources operating at 1300 nm and 1550 nm. Reflected interference signal was acquired by an optical spectrum analyzer while the length of the air cavity was varied. Thickness of the ZnO layers used in the experiments was 50 nm, 100 nm, and 200 nm. Uncoated SMF-28 fiber was also used as a reference. Based on the results of measurements, the thickness of the ZnO layers and the length of the cavity were selected in order to achieve good visibility. Following, the interferometer was used to determine the refractive index of selected liquids.

Low-Coherence Interferometric Fiber-Optic Sensors with Potential Applications as Biosensors

Fiber-optic Fabry-Pérot interferometers (FPI) can be applied as optical sensors, and excellent measurement sensitivity can be obtained by fine-tuning the interferometer design. In this work, we evaluate the ability of selected dielectric thin films to optimize the reflectivity of the Fabry-Pérot cavity. The spectral reflectance and transmittance of dielectric films made of titanium dioxide (TiO2) and aluminum oxide (Al2O3) with thicknesses from 30 to 220 nm have been evaluated numerically and compared. TiO2 films were found to be the most promising candidates for the tuning of FPI reflectivity. In order to verify and illustrate the results of modelling, TiO2 films with the thickness of 80 nm have been deposited on the tip of a single-mode optical fiber by atomic layer deposition (ALD). The thickness, the structure, and the chemical properties of the films have been determined. The ability of the selected TiO2 films to modify the reflectivity of the Fabry-Pérot cavity, to provide protection of the fibers from aggressive environments, and to create multi-cavity interferometric sensors in FPI has then been studied. The presented sensor exhibits an ability to measure refractive index in the range close to that of silica glass fiber, where sensors without reflective films do not work, as was demonstrated by the measurement of the refractive index of benzene. This opens up the prospects of applying the investigated sensor in biosensing, which we confirmed by measuring the refractive index of hemoglobin and glucose.

Nanolayers in Fiber-Optic Biosensing

Abstract In this chapter, fiber-optic sensors based on nanolayers or thin films and their ability to perform biophotonic measurements is presented. In the last decade, fiber-optic sensors have gained popularity as biosensing devices. This has been made possible because of the design and the integration of new materials in fiber-optic technology. Nanolayers and thin films made from various materials such as nanodiamond (NCD), boron-doped nanodiamond (B-NCD), zinc oxide (ZnO), titanium dioxide (TiO2), and aluminum oxide (Al2O3) have been successfully applied in the construction of fiber-optic sensors. NCD and B-NCD have been synthesized by the chemical vapor deposition (CVD) methods, while oxide- and nitride-based thin films were designed using atomic layer deposition. These nanolayers and thin films have been widely used in fiber-optic sensor technology as a protective coating, reflective layers, and/or as a sensing medium.

Enhancement of fiber-optic low-coherence Fabry-Pérot interferometer with ZnO ALD films

In this paper investigation of the enhanced fiber-optic low coherence Fabry-Pérot interferometer with zinc oxide (ZnO) film deposited by atomic layer deposition (ALD) was presented. Model of the interferometer, which was constructed of single-mode optical fiber with applied ZnO ALD films, was built. The interferometer was also examined by means of experiment. Measurements were performed for both reflective and transmission modes, using wavelengths of 1300 nm and 1500 nm. The measurements with the air cavity showed the best performance in terms of a visibility of the interference signal can be achieved for small cavity lengths (~ 50μm) in both configurations. Combined with the enhancement of reflectance of the interferometer mirrors due to the ALD film, proposed construction could be successfully applied in refractive index (RI) sensor that can operate with improved visibility of the signal even in 1.3-1.5 RI range as well as with small volume samples, as shown by the modeling.

Optical properties of thin TiO2 film deposited on the fiber optic sensor head

The presented study was focused on investigation of the titanium dioxide (TiO2) thin film deposited on the fiber tip. The intention of this investigation was using TiO2 film in the construction of the optical fiber sensor head. In the demonstrated construction TiO2 thin layer was deposited on the tip of a commonly used telecommunication single mode optical fiber (SMF-28) by means of the Atomic Layer Deposition (ALD). Thickness of the fabricated film was 80 nm. The characterization of the optical properties focuses on the most significant factors for the application in the interferometric sensing devices, namely - spectral reflectance function and its thermal dependence. The measurements were performed using two broadband sources with central wavelengths of 1300 nm and 1550 nm. The examination of the sensitivity of reflectance spectra to the temperature changes were conducted for temperatures in the range from 25°C up to 150°C. Obtained results have showed that the investigated layer exhibited reflectance value 0.174 and 0.061 at 1300 nm and 1550 nm respectively. Moreover, while the variation of the measured signal intensity induced by temperature change is noticeable, no significant spectral shift is observed in the reflection function. Therefore the examined structure presents interesting choice for the use in the interferometric fiber optic sensors.

Stability of thin film diamond mirror for applications in interferometers under the short-time exposure on selected aggressive chemicals

In presented study a thin boron-doped diamond film was proposed for application in the interferometry as a highly durable optical mirror. The unique properties of the diamond films, like high chemical stability and hardness, allow them to be used even in the chemically aggressive environment, where the commonly used silver mirrors can be susceptible to damage. The investigated nanodiamond layer was fabricated by uPE CVD method on a glass plate and the boron concentration in the gas phase was 7500 ppm. The mirror made from this layer was exposed to several corrosive acids and then the optical properties and surface quality of the film was examined by optical microscopy. To further evaluate the performance of the proposed mirror, it was placed in a fiber optic Fabry-Pѐrot interferometer and the quality of the detected spectra was also analyzed. Performed measurements allow us to conclude that the thin film diamond mirror is well suited for the application in the optical interferometer and it ensures high resistance to the harsh environmental conditions.

Fiber optic low-coherence Fabry-Pérot interferometer with ZnO layers in transmission and reflective mode: comparative study

A construction of a low-coherence fiber-optic Fabry-Pérot interferometer using a thin ZnO layer as a reflective surfaces was proposed and examined. In the investigated setup, the ZnO layer of thickness 200 nm were deposited on the face of the standard telecommunication single-mode optical fiber (SMF-28). Measurements of interference signal were performed for the interferometer working in the transmission and reflective mode, as well. The measurements were performed for two wavelength (1300 nm and 1550 nm) for various length of the air cavity. The optimal parameters of the Fabry-Pérot cavity was chosen for achieving the best visibility of the interference signal in the both modes.

Spectral reflectance and transmission modeling of multi-cavity Fabry-Perot interferometer with ZnO thin films

In this paper spectral reflectance and transmission of a low-coherence fiber-optic Fabry-Pérot interferometer with thin ZnO layers is analyzed using a multi-cavity approach. In the investigated setup two standard single-mode optical fibers (SMF-28) with thin ZnO films deposited on their end-faces form an extrinsic Fabry-Pérot interferometer with air cavity. Calculations of the spectral response of the interferometer were performed for different thickness of the layers (50, 100, 150, 200 nm). Based on the obtained results, it can be concluded that the use of ZnO thin films improves the reflectance of the interferometer. Moreover, addition of another cavity can make it possible to perform sensing of two different quantities (e.g. temperature and refractive index). The optimal lengths of the Fabry-Pérot cavities were selected using the results of modelling for achieving the best performance in a sensing application.

Application of thin dielectric films in low coherence fiber-optic Fabry-Pérot sensing interferometers: comparative study

We examine the application of selected thin dielectric films, deposited by atomic layer deposition (ALD), in a low coherence fiber-optic Fabry-Pérot interferometer designed for sensing applications. Such films can be deposited on the end-face of a single mode optical fiber (SMF-28) in order to modify the reflectivity of the Fabry-Pérot cavity, to provide protection of the fibers from aggressive environments or to create a multi-cavity interferometric sensor. Spectral reflectance of films made from zinc oxide (ZnO), titanium dioxide (TiO2), aluminum oxide (Al2O3) and boron nitride (BN) was calculated for various thickness of the films and compared. The results show that the most promising materials for use in fiber-optic Fabry-Pérot interferometer are TiO2 and ZnO, although Al2O3 is also suitable for this application.