Numerical investigation of the performance of an SPR-based optical fiber sensor in an aqueous environment using finite-difference time domain

We investigate a surface plasmon resonance (SPR)-based optical fiber sensor using 2-D finite-difference time domain (FDTD) simulations. The optical sensor is designed by polishing a single-mode optical fiber by symmetrically removing a portion of its cladding forming two sensing regions. We analyze the effects of two physical parameters of the sensor in an aqueous medium, i.e. the thickness of the metal layer and the amount of residual cladding using numerical simulations. The results show that a good transmission dip can be obtained by optimizing these parameters. Thus, the sensor structure can be deployed as an optical biosensor in aqueous environments

Dynamic response of tapered optical fiber coated with graphene oxide for detecting aqueous ethanol

Typically, evanescent-field optical fiber sensors utilize tapered fiber structure to enhance the evanescent filed interaction with the sensing medium. A nanostructured sensing layer is applied to further enhance the sensitivity of the sensor. This paper investigates the use of tapered fiber sensor coated with graphene oxide (GO) nano-film. Optimization of the GO layer and the tapering parameters were performed and the sensing capability of the device is tested using different concentrations of ethanol. The sensor demonstrates fast response and recovery to aqueous ethanol when interrogated in the visible region using a spectrometer and light source which is 20 seconds and 30 seconds respectively

Fiber Bragg grating based surface plasmon resonance sensor utilizing FDTD for alcohol detection applications

A fiber Bragg grating (FBG) based surface plasmon resonance (SPR) sensor is investigated using 2-D finite difference time domain (FDTD) simulation. The sensitivity and accuracy of the sensor with and without gratings is observed as well as the effect of changing the grating distance on the resonant wavelength. The findings show that high sensitivity of above 500nm/RIU and a fourfold increase in signal to noise ratio (SNR) is obtained by introducing FBG to the basic fiber optic based SPR structure. Increasing the grating period results in a red shift in the resonant wavelength, thus enabling multiple sensor fabrication on a single fiber optic cable. Simulation of the FBG based SPR sensor to detect alcohol concentration from 0 to 100% in water is also demonstrated

Highly sensitive plastic optical fiber with palladium sensing layer for detection of hydrogen gas

This paper reports an optical sensor using plastic optical fiber for the detection of hydrogen gas. A thin layer of palladium is used as the sensing layer to enhance the performance of the optical fiber sensor. When interrogated with a broadband white light source and a spectrometer, significant changes were observed in the intensity spectrum and dynamic response of the sensor as the concentration of hydrogen in air changed. The sensor demonstrated high sensitivity towards concentrations of hydrogen between 0.5% to 2% in synthetic air with a high response and recovery time of 50s and 80s respectively

Tapered multimode fiber sensor for ethanol sensing application

Ethanol is a widely used chemical in the industry which can be volatile and flammable. However, the availability of optical sensors for ethanol is still in its maturing stage. In this project, a tapered multimode fiber optic sensor for detection of ethanol with different concentrations in water was developed. The working principle of the sensor is based on absorption spectroscopy in the visible wavelength ranges. The tapered multimode fiber was fabricated using Vytran glass processing workstation to achieve waist diameter and length of 40 μm and 20 mm, respectively. Upon exposure to ethanol concentrations of ranges 5% to 40%, the developed fiber sensor absorbance increases linearly. The sensor shows fast response and recovery as low as 14 s and 27 s, respectively

Investigation of the performance of an SPR-based optical fiber sensor using finite-difference time domain

Finite-difference time domain (FDTD) method was used to investigate the performance of surface plasmon resonance (SPR)-based optical fiber sensors. The results show that the performance of the fiber sensor can be optimized by choosing a proper combination of metal layer thickness of 40–60 nm and residual cladding thickness of 400–500 nm. Furthermore, the roughness effect of the gold surface layering the fiber sensor is significant in rough surfaces when sigma rms is greater than 5 nm or correlation length is lower than 100 nm

Acetone liquid sensing based on fiber optic Mach-Zehnder interferometer

Fiber based optical sensors have been widely used in many industries today to detect parameters such as temperature, pressure, vibrations, concentrations and many more. A Mach-Zehnder Interferometer (MZI) is well known for its compact structure and small size which are advantageous for sensing purposes. In this project, an MZI with a singlemode-multimode-singlemode-multimode (SMSM) structure is developed for measuring acetone concentration in reverse osmosis (RO) water. The MZI consists of two single mode fibers (SMF) and two multimode fibers (MMF) spliced together using an arc fusion splicer machine to produce a SMSM structure. The MZI generates a good, reflected interference spectrum where the dip wavelength is red-shifted with the increase of acetone concentration. The sensitivity of the fiber sensor is 1.5391 nm/M within the range of 0M until 4M of acetone concentration. Based on the result, the sensor has a linear response towards the changes of concentration of 94.38%. This preliminary result shows that the proposed sensor can be used to detect acetone concentration to avoid contaminated water that may be of potential concern for human health

Fiber Bragg grating sensor for detecting ageing transformer oil

In this paper, we report the investigation of monitoring the degradation of transformer oil in power transformer using fiber Bragg grating sensor (FBG). The findings show that aging transformer oil has a higher refractive index (RI) compared to fresh transformer oil. This is detected by a wavelength shift in the FBG sensor's spectral response. The outcome complies with the breakdown voltage test which is the standard test for testing transformer oil ageing. Finally, we show that the sensor is temperature independent

Reduced graphene oxide nano-composites layer on fiber optic tip sensor reflectance response for sensing of aqueous ethanol

In this study, the used of tapered optical fiber tip as sensors coated with reduced Graphene Oxide (rGO) is investigated. The resultant rGO nanocomposites coated on the tapered fiber sensor were characterized by X-ray Diffraction (XRD), Raman spectroscopy, and field emission scanning electron microscopy (FESEM). Optimization of the rGO layer and the tapering parameters are found and the sensing capability of the device is tested using different concentrations of ethanol in water. The nanocomposite layer improved the performance of the sensor by demonstrating high sensitivity to aqueous ethanol when interrogated in the visible region using a spectrometer in the optical wavelength range of 500–700 nm. The reflectance response of the rGO coated fiber tip reduced linearly, upon exposure to ethanol concentrations ranging between 20-80 %

Characterization of ZnO–TiO2-coated tapered fibres synthesized by a low-temperature hydrothermal method

We characterize ZnO-nanorod fibres doped with different concentrations of TiO2 powder which is introduced on the final stage of synthesis of ZnO nanorods, using a low-temperature hydrothermal method. Their surface morphology, size of particles, behaviour of crystallites and optical properties are investigated using techniques of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and an optical spectrometer. A presence of ZnO nanorods and a globular structure of TiO2 are confirmed by the SEM analysis. The EDS spectra and chemical-element mapping reveals a presence of Ti incorporated into a globular surface, along with Zn. The XRD analysis testifies that ZnO doped with TiO2 has a primary crystallite phase of ZnO. ZnO doped with 10 and 15 mM of TiO2 shows a stronger and more expressed peak corresponding to (002) and (011) planes, which implies improved crystallinity of ZnO–TiO2 system. Optical properties of ZnO–TiO2 are studied by measuring the intensity of halogen-source light transmitted through the fibres. The ZnO & 15 mM TiO2 fibre sample shows the lowest intensity of the transmitted light due to higher refractive index of a cladding layer coated under condition of high TiO2 concentration. The increased light leakage in such a fibre can improve sensitivity of a relevant sensor, especially a gas one