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This study successfully developed a semiconductor metal oxide-based ammonia gas sensor that was powered by an Ultraviolet–Visible-near-IR optical light source. However, optical fibre gas sensors using single metal oxide nanomaterial are limited. To address this situation, a h-MoO3 nanorod was grown on a tapered region of optical fibre glass using a simple chemical bath deposition to form a unique sensing element. An additional annealing treatment was then performed to modify the oxidation state of h-MoO3. The property changes of the samples were characterised using different techniques, such as FESEM, TEM, XRD, XPS, TGA and UV–Vis. Overall, the annealing treatment improved the sensitivity performance, response and recovery time of the sensor towards NH3. h-MoO3 that was annealed at 150 °C in air showed stable room temperature absorbance responses of 0.05, 0.18, 0.22, 0.28 and 0.35, a fast response time of 210 s towards 500 ppm of NH3 and strong stability and repeatability. The optical NH3 gas-sensing behaviour was significantly correlated with the non-stoichiometric Mo5+ content. The chemisorbed oxygen species and physiosorbed NH3 altered the refractive index and its absorption coefficient on the nanorod, which manipulated the optical signal and acts as a sensing mechanism. These results verify that a chemical bath deposition growth of the h-MoO3 nanorod exhibits a promising optical sensing characteristic, which paves a path for emerging gas-sensing technology.

The present work discusses the ammonia (NH3) sensing behavior of etched-tapered single mode fiber (SMF) sensors coated with polyaniline (PANI)/graphite nanofiber (GNF) nanocomposite at room temperature. SMF was etched with hydrofluoric acid and subsequently tapered in a glass processing workstation. The PANI/GNF ratio in the nanocomposite polymer film is 2:1. The etched–tapered SMF is spray-coated with PANI/GNF nanocomposite. By varying the waist SMF diameter, a comprehensive investigation of the optical response of PANI/GNF nanocomposite-coated SMF and etched–tapered SMF sensors at room temperature is performed. The scanning electron microscopy of PANI/GNF nanocomposites showed a high surface-area sensing layer due to formation of porous structures with 1-2 μm dimension. SMF modification significantly increases the interaction of the evanescent field of light that propagates in the core with the PANI/GNF sensing layer. The integration of modified SMF with the PANI/GNF nanocomposite films yields a highly sensitive optical sensor that can be operated at room temperature (26 °C) in the visible wavelength range. The 50-μm etched and then 15-μm tapered SMF coated with PANI/GNF nanocomposite exhibits response time and sensitivity of 58 s and 300, respectively. Moreover, increased surface area in sensitive regions allows the sensor to detect as low as 0.00142% NH3, which is equal to 14.2 ppm. The etched–tapered SMF sensors coated with PANI/GNF nanocomposite exhibits stronger performance toward NH3 in terms of response time and sensitivity as compared with pristine PANI-coated sensors.

The work presented in this paper is related to detection of ammonia gas in room temperature using modified carbon nanofibers (CNFs). CNFs is functionalized with carboxyl group and labeled as CNFs-Carboxylic. CNFs-Carboxylic is then further reacted with octadecanol producing decorated ester functional group and labeled as CNFs-Ester. Interdigitated transducers (IDT) were used as substrates for placement of materials and the samples were deposited via drop cast method. The IDT was placed in a customized chamber equipped with inlet/outlet gas and electrical fed through. The resistance changes due to interaction between resistance and ammonia gas was recorded by digital multimeter that connected to computer. Result showed that IDT with CNFs-Ester provides an extra active area for interaction between analyte gas and CNFs thus improved their response and increased their sensitivity.

Optical fibers coated with polyaniline (PANI) nanostructures were used to sense ammonia gas (NH3) concentration. The PANI nanostructures were synthesized using the oxidative polymerization process in a solution containing poly(methyl vinyl ether-alt-maleic acid) (PMVEA). The PANI nanostructures were in situ deposited on silica optical fibers by immersing the fibers in the solution during the polymerization process for specific durations. The morphology and the thickness of the PANI nanostructure coatings were characterized using Scanning Electron Microscopy (SEM). Raman and Fourier Transform Infra-red (FTIR) spectra confirmed that the PANI nanostructures were in the emeraldine salt (ES) state. The sensors were exposed to various concentrations of NH3 gas at room temperature. The sensor with a coating thickness of 639 nm shows the highest response with a cumulative absorbance response of 2.2 towards 1% NH3 in synthetic air. The response and recovery times are 2.82 min and 11.52 min, respectively.

In this study, surface plasmon resonance based on Kretschmann configuration is employed as an alternative method to detect adulteration of pure honey. The adulterated honey was prepared by diluting three types of sugar adulterants (fructose, glucose and sucrose) into pure honey. The concentration of each adulterant is tested from 2% until 10% adulteration with 0% adulteration represents the reference for pure honey. All the resonance angles of adulterated honey demonstrated similar behavior by shifting to smaller angle than pure honey. The measured sensitivities are 0.1266°/%, 0.1065°/%, and 0.0988°/% for fructose, glucose and sucrose adulterants, respectively. The shift of resonance angle as a function of adulterants concentration in pure honey was plotted with linear regression greater than 0.95 for all samples. The outcome has disclosed a real-time, rapid and non-destructive sensor to be promoted as well-developed honey sensor.

The surge of Dengue cases around the globe has intensified the demand for a reliable diagnostic method. The work demonstrates, to the best of our knowledge, the first label-free optical based sensor for detection of Dengue II E proteins. This was achieved by utilizing tapered optical fiber that has been functionalized with complementary recombinant antibodies. The fundamental concept of the sensor relies on the interaction between strong evanescent waves resulting from the dimensional change of the fiber and immune complex formed on the surface of the fiber when the virus is present. Sensitivity and detection limit values obtained with the sensor setup are 5.02 nm/nM and 1 pM, respectively, with a standard deviation value of no more than ±0.4. The compact and rapid sensor is a viable alternative for label-free and quantitative assessment of the infection, which may assist in providing better clinical management and understanding of the disease.

Two dimensional tungsten trioxide (WO3) films made of nanosheets were prepared using high temperature anodization of tungsten (W) thin films. The W thin films were deposited by R.F. magnetron sputtering onto quartz substrates and then anodized at 50 °C in an aqueous solution containing 1.5 M HNO3. The structural and morphological properties of the prepared films were fully characterized prior to employing them for hydrogen gas sensing application. The hydrogen gas sensing performance of WO3 thin films was investigated at different temperatures through the measurement of conductance changes upon gas exposure. Hydrogen gas exposure resulted in the intercalation and subsequent reduction of WO3 sheets, changing the charge carrier concentration and hence the conductivity of the films. The fabricated sensors were found to exhibit excellent sensitivity and repeatability when they were exposed to hydrogen gas while using air as the carrier gas. The effects of different operating temperatures on the sensitivity of the devices were studied in the range of 20–250 °C. The dynamic response of the 2D WO3 nanosheets based sensors at different operating temperatures are presented and discussed.

Multiwavelength output generation based on cascaded four-wave mixing in a distributed Raman amplifier is demonstrated experimentally. The technique consists of launching a probe signal and Fabry-Perot pump source in a co-propagating setup into a 2 km length of highly nonlinear fiber. In this configuration, the Fabry-Perot laser diode plays two roles; as a Raman pump and as a source for multiple wavelengths generation. The output of multiple wavelengths with 27.8 GHz spacing centered around the probe signal is generated over 43 nm operation bandwidth. Besides, the bandwidth of the multiwavelength spectrum is also investigated at different wavelength ranges.

A novel hydrogen (H2) sensor was developed using optical fiber coated with manganese dioxide (MnO2) nanostructures. Optical multimode fiber (MMF) of 125 μm in diameter as the transducing platform was tapered to 20 μm to enhance the evanescent field of the light propagates in the fiber core. The tapered fiber was coated with MnO2 nanograins synthesised via chemical bath deposition (CBD) process. Catalytic Palladium (Pd) was sputtered onto the MnO2 layer to improve the H2 detection. The sensing layer was characterized through Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray (EDX), X-ray Diffraction (XRD) and Raman Spectroscopy to verify the properties of MnO2. Two sets of sensors consist of as-prepared MnO2 and 200 °C annealed MnO2 were tested towards H2 gas. The tapered optical fiber coated with Pd/MnO2 nanograins was found to be sensitive towards H2 with different concentrations in synthetic air at 240 °C operating temperature. The annealed sensor showed higher response and sensitivity as compared to the as-prepared sensors when measured in the visible to near infra-red optical wavelength range. The absorbance response of the annealed Pd/MnO2 on fiber has increased to 65% as compared to 20% for the as-prepared Pd/MnO2 upon exposure to 1% H2 in synthetic air.

A single mode fiber Bragg grating (FBG) is used to generate Surface Plasmon Resonance (SPR). The uniform gratings of the FBG are used to scatter light from the fiber optic core into the cladding thus enabling the interaction between the light and a thin gold film in order to generate SPR. Applying this technique, the cladding around the FBG is left intact, making this sensor very robust and easy to handle. A thin film of graphene oxide (GO) is deposited over a 45 nm gold film to enhance the sensitivity of the SPR sensor. The gold coated sensor demonstrated high sensitivity of approximately 200 nm/RIU when tested with different concentrations of ethanol in an aqueous medium. A 2.5 times improvement in sensitivity is observed with the GO enhancement compared to the gold coated sensor.

In this work, we fabricate and characterize a surface plasmon resonance sensor based on etched plastic optical fibers. The etching method used ensures the geometrical circular symmetry of the optical fiber. The sensor was tested by immersion in sensing solutions of different refractive indices and the transmittance is measured using a spectrometer system. The sensor performance in terms of sensitivity and detection accuracy can be controlled by adjusting the design parameters such as gold thickness, residual fiber thickness, and sensing length. We realized a sensitive, cost-effective, and robust sensor suitable for aqueous media sensing by reducing the overall fiber thickness up to 964 μm with a sensing length of 10 mm coated with a thin gold film of around 55 nm. The demonstrated sensor exhibits a sensitivity of 1600 nm/RIU and a full width at half maximum of around 154 nm.

We demonstrate the enhancement of surface plasmon resonance (SPR) technique by implementing a multi-metallic layers of Au–Ag–Au nanostructure in the chitosan-graphene oxide (CS-GO) SPR sensor for lead(II) ion detection. The performance of the sensor is analyzed via SPR measurements, from which the sensitivity, signal-to-noise ratio and repeatability are determined. The nanostructure layers are characterized using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). We showed that the proposed structure has increased the shift in the SPR angle up to 3.5° within the range of 0.1–1 ppm due to the enhanced evanescent field at the sensing layer-analyte interface. This sensor also exhibits great repeatability which benefits from the stable multi-metallic nanostructure. The SNR value of 0.92 for 5 ppm lead(II) ion solution and reasonable linearity range up to that concentration shows that the tri-metallic CS-GO SPR sensor gives a good response towards the lead(II) ion solution. The CS-GO SPR sensor is also sensitive to at least a 10−5 change in the refractive index. The results prove that our proposed tri-metallic CS-GO SPR sensor demonstrates a strong performance and reliability for lead(II) ion detection in accordance with the standardized lead safety level for wastewater.

In this work, we fabricate and characterize an SPR sensor based on unmasked short tapered multimode fiber. The entire taper region is coated with gold without masking offering a simpler approach towards the sensor fabrication. The sensor was tested by immersion in sensing solutions of different refractive indices and the transmittance is measured using a spectrometer system. The sensor performance in terms of sensitivity, detection accuracy, and robustness can be controlled by adjusting the taper physical parameters such as waist diameter, waist length, and transition length. We realize a compact, sensitive, cost-effective and robust SPR sensor suitable for aqueous media sensing by reducing the waist diameter up to 25–45 μm with a total taper length of 3–5 mm coated with a thin gold film of around 55 nm. The demonstrated sensor exhibits a sensitivity of 1600–2000 nm/RIU and a full width at half maximum (FWHM) of 140–220 nm.

The sensing of ammonia leakage at room temperature has potential applications in many areas such as industry. A sensitive etched-tapered fiber Bragg grating (FBG) based ammonia sensor is developed and investigated towards different concentrations of ammonia. The investigations are performed at room temperature. FBGs are etched with 50 µm diameter and tapered with 15 and 30 µm waist diameters. These FBGs are coated with polyaniline/graphite nanofibers (PANI/GNF) nanostructures as a sensing layer using spray method. The developed FBG sensors are based on Bragg wavelength shift on exposure to different ammonia concentrations due to change in refractive index of the sensing layers as interact with ammonia molecules. FBG sensors proved a linear Bragg wavelength shift with ammonia concentrations. The developed sensors exhibited linear, stable response, high sensitivity and good repeatability. Furthermore, FBGs sensors proved strong response towards NH3 by exhibiting high Bragg wavelength shift. This is because of porous structures of PANI\GNF nanostructures which improves the capability to adsorb additional NH3 molecules. This is in turn eventually enhances the interaction between NH3 and PANI\GNF nanocomposites. PANI\GNF coated FBG sensor with 15 µm waist diameter shows the highest sensitivity and good selectivity towards NH3.

The optical NH3 gas sensing performance of polyaniline (PANI) and poly(3,4-ethylenedioxythiophene (PEDOT) in the form of bilayers and copolymers was analysed in this study. The order of the bilayers and the presence of acid dopant on the fabrication of the sensing platform produced different absorbance responses upon exposure to NH3 gas. The limit of detection of the bilayer (PANI(aq.)/PEDOT(aq.)) was 7.86 ppm which is under the threshold limit value of NH3, with response and recovery times of 2.33 min and 46.8 s, respectively. The gasochromic behaviour of PANI and PEDOT during the adsorption of NH3 gas was closely related to the changes in the oxidation state which have simultaneously altered the colour intensity of the respective sensing layer.

In this paper, a D-shaped optical fiber is presented in terms of sensor application using FiberBench rotating wave plate. The designed sensor was adopted to detect plumbum ions in aqueous medium using surface plasmon resonance (SPR). The fiber-based SPR sensor was designed using a bilayer sensor chip. The polished area of the D-shaped optical fiber was coated by reduced graphene-based maghemite nanocomposite+1-ethyl-3-(3-dimethylaminopropyl)-carbodiimidehydrochloride/N-hydroxysuccinimide as a sensing layer. The transmission response curves were investigated according to the wavelength and intensity shifts at different concentrations. By incorporating the sensing layer, Pb2+ can be easily detected by wavelength and intensity interrogation methods. The sensor exhibited a recognizable intensity shift at 0.3 ppb Pb ion concentration. The limit of detection due to wavelength shift was 1 ppm. The sensitivity of the Pb ion concentration was 0.116 nm/ppm, and the accuracy was 19.1×10−4. FiberBench rotating wave plate was used to control the depth and the width of the transmission curve using SPR. The outcome of the developed sensor revealed a high accuracy, high sensitivity, and real-time sensor in a static water environment.

In this work, the optical sensing performance of three different types of conducting polymers, polyaniline (PANI), poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy) towards ammonia (NH3) gas has been evaluated. The sensing analyses of the respective conducting polymers were measured in the optimised wavelength ranges that manifest absorbance response upon exposure to NH3 gas. Based on the dynamic response where the respective conducting polymers were exposed to NH3 gas within the concentration range of 0.0625 % to 1 %, PEDOT exhibited the highest sensitivity (9.03/%) towards NH3 gas comparing to PANI and PPy with the detection limit of 2.73 ppm, which is in agreement with their respective conductivity trends.

This work investigates the use of fiber Bragg grating (FBG) for monitoring of pressure in a full composite lightweight epoxy sleeve strengthening system for offshore oil and gas pipeline. An FBG incorporated within the polyethylene sleeve served as an indicator of increasing pressure and displacement inside the pipeline. The wavelength shift of the FBG increased linearly with the increment of pressure and displacement, producing measured sensitivity of up to 0.8831 nm/kN and 0.902 nm/mm, respectively. The effect of temperature on the embedded sensor was also analyzed and it was found that the temperature sensitivity of the sensor below 55 °C was only 9.04 pm/°C. The excellent pressure sensitivity and its minimal susceptibility to temperature further accentuate the potential of fiber-based sensor as an effective and accurate alternative for pipeline integrity monitoring.

A silver nanoparticle-incorporated reduced graphene oxide (Ag/rGO) nanocomposite-based tapered optical fiber sensor was successfully fabricated for the sensing of ethanol in an aqueous medium. The sensor probe was fabricated by using a drop-casting technique to coat Ag/rGO on a multimode tapered optical fiber, and the dynamic response was investigated under an exposed condition for ethanol in an aqueous medium. The operating principle of the sensor device was based on the spectral intensity interrogation technique in the visible region. The visible region spectral intensity was found to vary linearly with the ethanol content in the range of 1–100%. The high sensitivity, rapid response, and good stability of the Ag/rGO nanocomposite-based optical fiber sensor make it a potential candidate for monitoring environmental pollution and the safety requirements of industry and daily life.

The paper presents a refractive index sensor based on surface plasmon resonance (SPR) in etched plastic optical fibers (POF). The etching approach adopted here ensures the geometrical circular symmetry of the optical fiber. The influence of design parameters namely, residual fiber thickness and sensing length on the sensitivity of the proposed sensor was investigated. A lower value of residual fiber thickness and shorter sensing length result in greater sensitivity of the sensor. The proposed sensor provides numerous advantages such as simplicity in design, low cost of fabrication, higher mechanical strength, and ease of handling compared to other SPR structures.

A multiplexing technique for fiber vibration sensors is experimentally investigated using Khazani Syed (KS) code in SAC/OCDMA with direct decoding. The system is proposed to implement vibration sensor multiplexing which can eliminate the Multiple Access Interference (MAI) at low cost and complexity. The results show the proposed system having better SNR, less complex, and low cost when compared with complementary decoding, and higher power level when compared with simplified WDM. A frequency range of 0 to 400 Hz measured shows its suitability for quasi-distributed sensing in bridges, pipelines, transformers, and industrial machine that exhibit low vibrations within this range.

In this work, optical sensing performance of tapered multimode fiber tip coated with graphene oxide (GO) nanostructured thin film towards aqueous ethanol with different concentrations is investigated. The tapering process of the optical fiber is done by a glass processing machine. The multimode optical fiber tip is dip-coated with GO and annealed at 70 °C to enhance the binding of the nanomaterials to the silica fiber. FESEM, Raman microscopy and XRD analyses are performed to micro-characterize the GO thin films. The morphology of the GO is observed to be in sheets forms. The reflectance response of the GO coated fiber tip is compared with the uncoated tip. The measurements are taken using a spectrophotometer in the optical wavelength range of 550–720 nm. The reflectance response of the GO coated fiber tip reduced proportionally, upon exposure to ethanol with concentration range of 5–80%. The dynamic response of the developed sensor showed strong reversibility and repeatability when it is exposed to ethanol with concentrations of 5%, 20% and 40% in distilled water. At room temperature, the sensor shows fast response and recovery as low as 19 and 25 s, respectively.

Intensity modulated fiber vibrations sensing using Khazani Syed (KS) and Modified Quadratic Congruence Code (MQC) code for quasi distributed vibration measurement have been evaluated. The systems employed Spectral Direct (SD) Decoding for Spectral Amplitude Coding-Optical Code Division Multiple Access (SAC-OCDMA). SAC-OCDMA is adopted because of its enormous impact in dealing with Multiple Access Interference (MAI). The setup was carried out for three sensor points in three consecutive measurements. The performance of the sensing system with the KS and MQC codes were compared at the same weight and number of code sequence. It was observed that the applied vibration frequencies were obtained at the receivers and the signal employing MQC are received at slightly better power than KS code. However, KS code setup employed less number of components and therefore, reduce the cost and complexity of achieving quasi-distributed vibration sensing.

Optical sensors based on surface plasmon resonance (SPR) are utilized for detecting toxic heavy metals in solutions. To improve the sensitivity of SPR sensors, nanostructured thin films with active layers can be synthesized. In this study, the response to Pb (II) was measured and compared for SPR sensors incorporating gold–chitosan–graphene oxide (Au/CS/GO) nanostructured thin films and Au/CS films. The characterization of Au/CS/GO using FESEM analysis revealed a film composed of nanosheets with wrinkled, rough surfaces. The results from XRD analysis confirmed the successful incorporation of GO in the prepared films. Additionally, AFM analysis determined that the Au/CS/GO films had a root mean square (rms) roughness of 28.38 nm and were considerably rougher than the Au/CS films. Upon exposure to a 5 ppm Pb (II) ion solution, the Au/CS/GO films exhibited higher SPR sensitivity, as much as 1.11200 ppm−1, than Au/CS films, 0.77600 ppm−1. This enhancement of the SPR response was attributed to strong covalent bonding between CS and GO in these films. These results indicated that the Au/CS/GO films show potential for the detection of heavy metal pollution in environmental applications.

A novel hydrogen (H2) sensor was developed using acid-etched optical fiber coated with zinc oxide (ZnO) nanorods. The sensing performance was done by comparing the acid-etched fiber coated with ZnO nanorods with and without decorated Palladium (Pd). The conventional optical single-mode fiber (SMF) with a diameter of 125 μm has been modified as a transducing platform by etching it to 11 μm diameter using hydrofluoric acid (HF) to enhance the evanescent field of the light propagates in the fiber core. The etched fiber was coated with ZnO nanorods via hydrothermal process by using seeding and growth solution method. The sensing layer was characterized through Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX) and X-Ray Diffraction (XRD) to verify the properties of ZnO. Catalyst Palladium (Pd) was sputtered onto the ZnO nanorods to improve H2 detection. The developed sensor operating temperature was found to be 150 °C that produces 6.36 dBm increase in response towards the 1% concentration of H2 in synthetic air. It was then tested with different concentration of H2. The sensor decorated with Pd has better performance in sensing compared to non-decorated Pd based on the output power versus time. The sensor best response and recovery times is 6 and 5 min respectively, for acid-etched optical fiber coated with ZnO nanorods decorated with Pd for 0.75% of H2 concentrations at 150 °C. The results indicate the optical fiber sensor might improve the performance towards H2 as oppose to the conventional electrical sensor.

A simple technique to fabricate nanostructured WO3 thin films onto conductomeric transducers has been employed for ethanol sensing application. Initially, pure tungsten (W) thin films were deposited onto the substrate employing RF sputterer and followed by an etching process. Three types of etching agent were used: nitric (HNO3), sulphuric (H2SO4), and phosphoric (H3PO4) acid. It was found that the surface morphology and crystallinity of the WO3 films were heavily dependant to the etchants employed during the fabrication process. The developed sensors were tested towards ethanol vapor of different concentrations (10–200 ppm) at temperatures between room and 450 °C. The sensors showed stable and reproducible response at optimum operating temperatures. High sensor response towards vaporized ethanol as well as fast τres and τrec was observed during the “adsorption” and “desorption” interval. The recorded maximum response for these devices when exposed towards 100 ppm ethanol was measured to be 8 (Ro = 4.6 kΩ), 5.8 (Ro = 22.5 GΩ), and 5 (Ro = 0.29 MΩ) for HNO3, H3PO4, and H2SO4, respectively. The optimum operating temperatures were determined to be 400, 300–380, and 360 °C for the sensors developed using HNO3, H3PO4, and H2SO4, respectively.

An efficient multiwavelength Brillouin–Erbium fiber laser (BEFL) was developed by improving the feedback mechanism of Brillouin Stokes lines. The BEFL performance in terms of threshold power and wavelengths count was improved by using a new structure of double pass amplification cavity. The new structure utilized the variable optical coupler (VOA) not only as the input and output ports but also to form a fiber loop mirror that reduces the number of optical components, thus, only three optical components were needed. By optimizing the Brillouin and 1480 nm pump power, up to 41 channels and 26 channels were obtained using 0.6 km and 0.3 km long of standard single mode fiber (SSMF), respectively.

In this work, the optical H2-sensing properties of Pd/tungsten trioxide (WO3) nanorods prepared by rf magnetron sputtering with glancing-angle deposition (GLAD) technique are investigated. From grazing-incidence X-ray diffraction and field emission scanning electron microscopic characterizations, annealed WO3 structure deposited on a quartz substrate at glancing angle of 85° exhibited polycrystalline monoclinic crystal structure with uniform partially isolated columnar nanorod morphology. The nanorods have the average length, diameter and rod separation of around 400 nm, 50 nm and 20 nm, respectively. The developed sensors show remarkable gasochromic absorbance response when exposed to H2. Cumulative absorbance in 650–1000 nm wavelength range is increased by approximately 51% toward H2 with 0.1% concentration in synthetic air, which is more than an order of magnitude higher than that of WO3 dense film prepared by conventional sputtering method. Moreover, WO3 nanorod based sensor is much more promising for practical use due to its much faster response. Therefore, the developed Pd/WO3 nanorod based optical sensors are highly potential for low H2 concentration sensing with highly sensitivity, fast and stable responses and low operating temperature.

Nanostructured gold/tungsten trioxide (Au/WO3) thin films based gasochromic sensors have been developed and investigated towards hydrogen (H2) at low concentrations. Using a novel wet chemical method, atomically precise gold (Au) nanoclusters were deposited onto tungsten trioxide (WO3) films supported on a quartz substrate. The Au/WO3 based sensors exhibited change in gasochromic properties upon exposure to H2 in the visible-NIR (800–1000 nm) range. The total absorbance in this range increased by approximately 2.5%, when exposed to H2 gas (0.06%) balanced in synthetic air at an operating temperature of 200 °C. The micro-structural properties of the films were studied via energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). EDX analysis of the Au/WO3 films on quartz substrates shows the presence of strong tungsten (W) and oxygen (O) peaks, which indicates that the films are mainly consisted of WO3. TEM investigation showed that the synthesised Au nanoparticles have average diameters of 2–5 nm after deposition. SEM investigations revealed agglomeration of the Au phosphine [Au9(PPh3)8(NO3)3] clusters to form nanoparticles on top of WO3 layer. At optimum operating temperature (200 °C), fast response (

The gasochromic response of WO3 nanostructured films coated with a catalytic Pt or Pd layer on different transparent substrates upon exposure to H2 gas was investigated. WO3 nanostructured films with 500 nm thickness were coated with a 25 A thick Pt or Pd layer. The films were prepared on quartz, glass, indium-doped tin oxide (ITO) and fluorine-doped tin oxide (FTO) conductive glass. The nanostructured WO3 was deposited by RF magnetron sputtering, and the Pt or Pd layer was deposited by DC sputtering. Characterization of the film revealed that the WO3 was deposited as nanoscale grains of varied size depending on the substrate. WO3 grains on quartz and glass were 30–40 nm in size. WO3 grain sizes on ITO and FTO were 40–60 nm and 300–500 nm, respectively. The WO3 films were observed to show strong gasochromic response, with absorbance changes measured in the Vis-NIR (500–1100 nm) range. The cumulative absorbance response towards H2 is the highest and more stable for Pd/WO3 films on quartz, glass and ITO, compared to the FTO substrate. The gasochromic effect was also stronger in Pd/WO3 films compared to Pt/WO3 films.

For the first time, we have integrated nano-platelet Pd/WO3 films, which are formed using an acid etching method, with optical fibers to develop a hydrogen gas (H2) sensors. The tungsten films were firstly RF sputtered on top of optical fiber tips, and subsequently etched in 1.5 M nitric acid to produce tungstite films. After annealing at 300 and 480 °C, these films were coated with approximately 25 A thick Pd layers. The films were characterized using SEM, GADDS, EDX, and both Raman and UV–vis–NIR spectroscopy. H2 testing measurements were conducted when the sensors were interacting with 0.06–1% H2 in synthetic air at an optimum temperature of 100 °C. It was found that the highly crystalline nano-platelet Pd/WO3 film based optical fiber H2 sensors show large reflectance responses in the NIR wavelength of 6% and 12% in the presence of 0.06% and 1% H2, respectively.

Absorbance response of tungsten trioxide (WO3) nanorod thin films coated with palladium (Pd) towards hydrogen (H2) was investigated. WO3 nanorods were deposited onto quartz substrates via pulsed laser deposition (PLD) technique. Highly homogeneous arrays of nanorods in the sizes of 30 - 80 nm were observed. Subsequently, 25 A Pd was deposited onto films via dc sputtering. The Pd/WO3 nanorod thin films exhibited excellent gasochromic response when measured in the visible-NIR range (400 – 1000 nm). As low as 0.06% H2 concentration was clearly sensed. A significant reversible absorbance change and fast recovery (

Gas sensing performance of optical fibers coated with nano-platelet tungsten trioxide (WO 3 ) films and catalytic palladium (Pd) layers were investigated for low concentration hydrogen gas (H 2 ). Nano-platelet WO 3 film was formed on the tip of the multimode optical fiber via acid treatment of RF sputtered tungsten (W). After annealing, Pd layer of 25 A was sputtered as a catalyst. It was found that the optical fiber gas sensor based on the Pd/nano-platelet WO 3 film shows a remarkable reflectance response towards very low H 2 concentration (0.06%) in synthetic air balance.

Optical gas sensing performance of nanoporous TiO2 films coated with catalytic Pd layer was investigated for low concentration H2 sensing. Nanoporous TiO2 films were obtained from anodization of DC sputtered titanium (Ti). The Ti films were deposited onto quartz and subsequently anodized at room temperature and annealed at 800°C. Highly homogeneous arrays of nanopores having diameters in the range of 15-25nm were observed. It was found that the Pd/TiO2 nanoporous films show remarkable optical absorbance response towards H2 as low as 0.06%. The optimum operating temperature of the nanoporous films for H2 sensing was found to be very low (60°C).

The gasochromic response of WO3 nanotextured thin films coated with a 2.5 nm catalytic Pt layer upon exposure to hydrogen (H2) gas was investigated. The Pt/WO3 thin films exhibited gasochromic characteristics, when measured in the visible-NIR (400–900 nm) range. The total absorbance in this range increased approximately 15% when exposed to 0.06% H2 gas in synthetic air. Similarly, a 60% increase was measured to an exposure of 1% H2 gas in synthetic air. However, this response was reduced by approximately 40% when exposed to the same concentration of H2 gas in air with humidity of 6%. These measurements were conducted over a range of temperatures with extensive analysis preformed at both room temperature and 100 °C to ascertain the suitability of the films for low power applications. Despite having a comparatively slow recovery time at room temperature, it was observed that these films were highly sensitive, providing stable and repeatable responses towards low concentrations of H2 at 100 °C. Films typically had rapid response and recovery, in the range of few seconds. WO3 thin films were characterized via Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). XRD confirmed the presence of WO3 crystallites with a preferential miller index orientation of (2 0 0), and SEM investigations revealed that the WO3 compact thin films were comprised of nanotextured grains.

A new technique of fiber-break detecting and monitoring in optical communication network systems is proposed and experimentally demonstrated. The subsystem, namely fiber-break monitoring system is designed to be simpler, significantly less expensive and yet gives an appropriate measurement to the distance break in place of the optical time domain reflectometer. This new approach has a bright prospect to be utilized in existing optical communication network systems. The proposed technique gives a minimal insertion loss of 1.7 dB and measurement accuracy of 0.285 km.