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In this work, we have demonstrated the generation of dissipative soliton from single to multi-pulsing phenomenon. The generation of ultrashort pulses was achieved with nickel-based metal organic framework (Ni-MOF) as saturable absorber in a ring cavity erbium-doped fiber laser. The SA was fabricated by spin-coating Ni-MOF/polydimethylsiloxane composite on a tapered fiber substrate, which had an insertion loss of 2.82 dB, a modulation depth of 4.61 %, and saturation intensity of 30.12 MW/cm2. A self-started DS mode-locked pulse was observed at 1559.89 nm central wavelength with 3-dB bandwidth of 19.72 nm at threshold pump power of 33.5 mW. Its pulse width of 7.89 ps was recorded at 7.94 MHz repetition rate. The nature of pulse splitting was observed up to three pulses which were separated with 2.62 ns time spacing with the increment of pump power until 134.2 mW. The generated multiple dissipative soliton pulses realized in the laser cavity through Ni-MOF saturable absorber were stable and invariant for 1-hour stability measurement.

Chlorine gas is a greenish-yellow gas that is one of the most utilized gases in numerous industrial fields. It has been categorized as a choking agent that can threaten human, animal, and environmental safety. Currently, development of highly sensitive, selective, and precise chlorine sensors receives much attention. This review focuses on several sensing techniques used for chlorine gas and free chlorine in water. The fundamental working principles, as well as the sensing mechanisms of chlorine detection covering spectrophotometric, electrochemical, and optical techniques, are described. A comparison of various sensing materials is also discussed. Finally, an overview of the future improvements needed of high-performance chlorine sensors was suggested.

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.

Gaseous pollutants such as hydrogen gas (H2) are emitted in daily human activities. They have been massively studied owing to their high explosivity and widespread usage in many domains. The current research is designed to analyse optical fiber-based H2 gas sensors by incorporating palladium/graphene oxide (Pd/GO) nanocomposite coating as sensing layers. The fabricated multimode silica fiber (MMF) sensors were used as a transducing platform. The tapering process is essential to improve the sensitivity to the environment through the interaction of the evanescent field over the area of the tapered surface area. Several characterization methods including FESEM, EDX, AFM, and XRD were adopted to examine the structure properties of the materials and achieve more understandable facts about their functional performance of the optical sensor. Characterisation results demonstrated structures with a higher surface for analyte gas reaction to the optical sensor performance. Results indicated an observed increment in the Pd/GO nanocomposite-based sensor responses subjected to the H2 concentrations increased from 0.125% to 2.00%. The achieved sensitivities were 33.22/vol% with a response time of 48 s and recovery time of 7 min. The developed optical fiber sensors achieved excellent selectivity and stability toward H2 gas upon exposure to other gases such as ammonia and methane.

We present a polyamidoamine-graphene oxide (PAMAM-GO) integrated microfiber sensor for the detection of Dengue virus II E protein (DENV II E protein). The microfiber was fabricated by heating a region of a single-mode optical fiber and pulling both ends at constant speed to achieve a diameter of 12 μm from 125 μm. The narrowing of the optical fiber diameter induced evanescent waves on the surface of the microfiber that interacted with the antibody/antigen complex adhered on the surface of the microfiber. The intensity of the interaction corresponds to the concentration of the antigen and can be quantified as a wavelength shift to the transmission spectrum. With the integration of PAMAM-GO, the sensor managed to achieve a sensitivity of 13.25 ± 0.2 nm/nM which is double the value achieved with a standard microfiber configuration. The overall performance of the sensor has potential towards improving dengue diagnostics today.

The functionalization of multi-walled carbon nanotubes (CNT) with amide group is reported as an alternative to enhance response time, recovery time and sensitivity of detecting acetone gas. We have fabricated an interdigitated transducer (IDT) deposited with amide-functionalized CNT. The elemental compositional analysis was characterized using Energy Dispersion X-ray spectroscopy and CHNOS elemental analyzer. The detection of acetone gas was performed in room temperature and digital multimeter was employed to record the changes of resistivity of IDT upon exposure of acetone. Results showed that amide functional group increases sensitivity, shortens the response time as well as recovery time of the sensor.

Certain organic liquids like ethanol in water are considered hazardous and have an enormous environmental impact since it is toxic and classified as class I flammable liquids. Remote sensing with complex sensors is a common technique for detecting and tracking spillages of hazardous spillages. Most of the applied remote sensing methods suffer from location and control issues that force the user to be at the exact sensing spot during operation. The present work introduces a simple and highly sensitive tapered multimode optical fiber (TMOF) sensor coated with carbon nanotubes (CNT) for flammable liquids remote sensing applications. The new proposed sensor ability to transfer signals to a remote data collection center of about 3 km from the sensor location was investigated. Ethanol was utilized as the index solution to be tested in the present work. The proposed sensor was attached to 3 km multimode silica optical fiber and characterized towards different concentrations of ethanol in de-ionized water at room temperature. Various characterization techniques have investigated the detailed structural properties of the sensing layer. The experimental results demonstrated that the proposed remote sensor exhibits rapid response with recovery times of 8.7 s and 18 s, respectively, and relative absorbance of 26% upon exposure to 100% ethanol. The sensor attains an overall sensitivity of 1.3/vol% towards low ethanol concentrations in water (0.01–0.5%). Besides, the optical sensor manifests outstanding repeatability when exposed to another cycle of ethanol with concentrations of 20% and 40% in de-ionized water. The proposed optical remote sensor's superior performance via low cost and simple techniques indicates its high efficiency for ethanol detection in various industrial applications.

Self-homodyne optical orthogonal frequency division multiplexing (OFDM) transmission system is a variant of self-coherent systems with a relaxed laser linewidth requirement as opposed to a full coherent system. The system is designed by transmitting a carrier together with the subcarriers, ensuring a strong phase-correlation between them at a receiver compared to the coherent system where only the subcarriers are transmitted. Despite the strong phase-correlation, the laser phase noise (PN) can still degrade the self-homodyne system performance due to the interaction of the PN with a chromatic dispersion (CD) induces a phase-modulation to intensity-modulation (PM-to-IM) conversion noise which cannot be canceled using a balanced-receiver. This imposes a high noise pedestal underneath each subcarrier, with the highest pedestal's peak imposed beneath the subcarriers that are farthest away from the carrier. This in turn produces a phase-decorrelation between the carrier and subcarriers which degrades the Q-factor between the lowest and highest subcarrier frequencies. In this work, the effect of the PM-to-IM conversion noise is reduced for the transmission of up to 174 Gb/s using a simple delay-line assigned to realign the phase-decorrelation of the subcarriers. With this technique, the subcarriers Q-degradation can be improved and the total transmission length can be tripled with Q-improvements of 5.4, 5.3, and 5-dB for 16-quadrature amplitude modulation (QAM) over 1360 km, 32- QAM over 800 km, and 64-QAM over 480 km, respectively, using 10-MHz LW with a 15-GHz total signal bandwidth. For 29 GHz signal bandwidth, the phase-walk-off of the high frequency subcarrier becomes more severe where the introduced delay can increase the transmission length by 2.5 times than without the delay, which increased the signal tolerance to the conversion noise.

The increased deployment of optical fiber sensors along with the development of internet of things has increased the demand for real-time in situ remote monitoring systems in the optical sensing industry. Etched-tapered single-mode optical fiber (ETSMF) sensors coated with polyaniline nanofiber/graphite nanofiber (PANI/GNF) nanocomposites have been developed for the real-time in situ remote monitoring of NH3. In this investigation, the sensors with a reel of SMF with 3 km length were integrated with Erbium-doped fiber amplifier (EDFA) with 15 dB gain. Modification performed on SMF significantly enhanced the interaction between the PANI/GNF sensing layer and the evanescent wave due to the light that propagates from the core layer. The response of the modified fiber sensor to NH3 with different concentrations over the C-band (1535–1565 nm) was investigated. The integration of EDFA into SMF sensors extended the remote monitoring distance. In the C band, the developed sensor showed the response, recovery time, and sensitivity of 59 s, 461 s, and 210, respectively. ETSMF sensors coated with nanocomposite of PANI/GNF exhibit successful remote-sensing performances.

Using the radiofrequency (RF) magnetron sputtering method, zinc oxide (ZnO) thin films were optimized for the optical hydrogen gas sensor at 27 °C. To generate optically controlled thin films, the following parameters have been optimized: argon/oxygen (Ar/O2), RF power, gas concentration and deposition time. As a result, ZnO thin films optimized at 4 % of O2, 150 W RF and 180 min gas concentration. This work focused on the effect of deposition parameters that included deposition time, RF power, argon/oxygen (Ar/O2) gas percentage, and annealing condition on thin-film thickness, surface roughness, crystal phase, phonon modes, and optical bandgap. From the physical characterization, we found that the formed product is crystalline in nature (powdered XRD) and Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy (ATR-FTIR) analysis provided the surface functionality and bonding, while the UV–vis spectroscopy for the optical properties. AFM images show that the surface roughness is varying from 18.9 to 89.83 nm. The gas sensing mechanism of the RF-sputtered ZnO thin film was based on the surface reaction between adsorbed oxygen and the H2 gas where more oxygen was chemisorbed in the form of O2−, O−, and O2- by ZnO thin film. The calculated molar absorptivity, e increased with the increase of RMS surface roughness whereby relatively high surface roughness is better to optically absorb H2 gas.

A novel H2 sensor using tapered optical fiber coated with Pd/ZnO nanostructures have been developed. The ZnO nanostructures was synthesized and deposited onto tapered optical fiber via chemical bath deposition (CBD) method. The ZnO was characterized by FESEM, XRD and EDX to confirm the material properties. It was discovered that the sensor is sensitive towards different concentrations of H2 in synthetic air at 180° C of operating temperature. By varying the deposition time of ZnO coating, different thickness of ZnO layer can be obtained. It was observed that with 280 nm thickness, the maximum absorbance response can be achieved. Further investigation with sensor sample of as-prepared and annealed was carried out to study its sensing performance towards H2. The absorbance response of 280 nm thickness of annealed Pd/ZnO has increased 64% as compared to as-prepared Pd/ZnO upon 1% H2 exposure in the synthetic air when measured in the visible to near infra-red optical wavelength. It can be concluded that the Pd/ZnO optical fiber sensor with thickness around 280 nm provided better sensitivity in sensing H2 at 180°C as compared to other thicknesses investigated.

Wide availability and diversity of dangerous microbes poses a considerable problem for health professionals and in the development of new healthcare products. Numerous studies have been conducted to develop membrane filters that have antibacterial properties to solve this problem. Without proper protective filter equipment, healthcare providers, essential workers, and the general public are exposed to the risk of infection. A combination of nanotechnology and biosorption is expected to offer a new and greener approach to improve the usefulness of polysaccharides as an advanced membrane filtration material. Nanocellulose is among the emerging materials of this century and several studies had proven its usefulness in filtering microbes. Its high specific surface area enables the adsorption of various microbial species, and its innate porosity can separate various molecules and retain microbial objects. Besides that, the presence of an abundant OH groups in nanocellulose allows its surface modification which can increase its filtration efficiency through the formation of affinity interactions toward microbes. In this review, an update of the most relevant uses of nanocellulose as a new class of membrane filters against microbes is outlined. Key advancements in surface modifications of nanocellulose to enhance its rejection mechanism is also critically discussed. To the best of our knowledge, this is the first review focusing on the development of nanocellulose as a membrane filter against microbes.

The exponential escalation of dengue cases has indeed become a global health crisis. This work elaborates on the development of a biofunctionalized tapered optical fiber (TOF) based sensor with the integration of polyamidoamine (PAMAM) dendrimer for the detection of dengue E protein. The dimension of the TOF generated an evanescent field that was sensitive to any changes in the external medium while the integration of PAMAM promoted more adhesion of bio-recognition molecules; anti-DENV II E protein antibodies; that were complementary to the targeted protein. This in return created more active sites for the absorption of DENV II E proteins onto the tapered region. The resolution and detection limit of the sensor are 19.53 nm/nM and 1 pM, respectively with Kd = 1.02 × 10−10 M.

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.

An etched tapered single mode optical fiber (SMF) coated with polyaniline (PANI) nanofibers is developed to detect ammonia (NH3) in low concentrations. The SMF is etched with hydrofluoric acid and subsequently tapered using a glass processing workstation. The etched tapered SMF is coated with PANI via spray-coating deposition. This SMF modification significantly enhances the interaction of the evanescent field of the light propagating in the core with the PANI-sensing layer. The modified fiber sensor response is investigated by exposing the sensor to different concentrations of NH3 over the C-band wavelengths of 1535–1565 nm. Integrating the modified optical fiber with the nanostructured PANI films produces highly sensitive optical sensor that operates at room temperature. The $50~\mu \text{m}$ etched tapered SMF coated with PANI produced response, recovery times, and sensitivity of 58 and 475 s, and 231.5%, respectively, in the C-band range. The limit of detection of the modified fiber sensor was 0.0025%, which is equal to 25 ppm. The developed sensor exhibits good repeatability, reversibility, and selectivity.

A prism-based surface plasmon resonance (SPR) sensor deposited with reduced graphene oxide/maghemite is presented for the detection of lead ions (Pb2+) in water. The SPR setup proposed followed the Kretschmann configuration with the installment of the nanocomposite integrated bilayer sensor chip onto the prism. For protection, the nanocomposite active layer was coated with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimidehydrochloride/N-hydroxysuccinimide. When the sensor was tested with different concentrations of Pb2+ in static water, the limit of detection was achieved at 0.001 ppm with a resonance angle shift of 0.184°. As an improvisation, a sample circulation design was adapted into the setup in order to increase the interaction rate between the sample and the sensing layer. This managed to improve the detection limit to 0.3 ppb.

Ammonia detection in ambient air is critical, given its implication on the environment and human health. In this work, an optical fiber tapered to a 20 µm diameter and coated with graphene oxide was developed for absorbance response monitoring of ammonia at visible (500–700 nm) and near-infrared wavelength regions (700–900 nm). The morphology, surface characteristics, and chemical composition of the graphene oxide samples were confirmed by a field emission scanning electron microscope, an atomic force microscope, X-ray diffraction, and an energy dispersion X-ray. The sensing performance of the graphene oxide-coated optical microfiber sensor towards ammonia at room temperature revealed better absorbance response at the near-infrared wavelength region compared to the visible region. The sensitivity, response and recovery times at the near-infrared wavelength region were 61.78 AU/%, 385 s, and 288 s, respectively. The sensitivity, response and recovery times at the visible wavelength region were 26.99 AU/%, 497 s, and 192 s, respectively. The selectivity of the sensor towards ammonia was affirmed with no response towards other gases.

This paper describes the application of a palladium (Pd)-coated tapered optical fiber in order to develop hydrogen (H2) sensor. A transducing channel was fabricated with multimode optical fiber (MMF) with cladding and core diameters of 125 µm and 62.5 µm respectively, to enhance the evanescent field of light propagation through the fiber. The multimode optical fiber was tapered from cladding diameter of 125 µm to waist diameter of 20 µm, waist-length of 10 mm, and down taper and up of 5 mm and coated with Pd using drop-casting technique. In order to establish the palladium’s properties, various characterization techniques were applied such as FESEM, EDX and XRD. The developed palladium sensor functioned reproducibly at a gas concentration of 0.125% to 1.00% H2 at room temperature in the synthetic air. In this case, the response and recovery times were 50 and 200 seconds, respectively. Furthermore, this study demonstrated that the production of a dependable, effective, and reproducible H2 sensor by applying a basic cost-effective method is possible.

Modified optical fiber sensors received increasing attention because of their superior properties over electrical sensors. These properties include their immunity towards electromagnetic interference and the ability to be deployed in corrosive and volatile environment. Several optical fiber platforms have been developed for chemical sensing applications based on modifying optical fiber cladding layer such as etched, tapered, D-shaped and etched-tapered. The modifications purpose is to extend the evanescent wave propagating out of the core physical dimensions. Thus, evanescent wave interaction with analyte is enhanced. Modified optical transducing platforms are integrated in gas sensing applications, such as ammonia. Modified optical fiber sensors coated with nanostructured thin films have been developed and gained popularity as practical devices towards gases with low concentrations. The development and characterization of the modified SMF sensing platforms including etched, tapered and etched-tapered platforms against ammonia will be presented in this chapter. These platforms were coated with PANI nanostructured thin film. The 50 μm etched-tapered SMF coated with PANI produced response, recovery times, and sensitivity of 58 s, 475 s, and 231.5%, respectively, in the C-band range. The limit of detection of the modified fiber sensor was 25 ppm. The developed sensors exhibit good repeatability, reversibility, and selectivity.

An optical fiber tip sensing probe coated with graphene is proposed for nitrate-sensing application. The sensor was coated with graphene using dip-casting method to detect nitrate at different concentrations ranging from 0 to 50 ppm. The graphene-coated fiber tip sensor was highly sensitive in detecting nitrate ion. When the concentration of the nitrate solution was dropped onto the sensing region, the reflected optical power decreased as the nitrate concentration increased. Without the graphene layer, the uncoated fiber tip sensor only had a sensitivity of 0.0076 dBm/ppm. However, the coated sensor's sensitivity was significantly enhanced to 0.0624 dBm/ppm, eight times higher than the uncoated fiber tip sensor, mainly due to the adsorption of nitrate on the graphene surface. This graphene-coated optical fiber tip sensor has a high potential to be used in nitrate-sensing applications.

The fabrication and characterization of a distributed magnetic field optical fiber sensor based on magnetostriction method is presented. A conventional single mode fiber (SMF) is coated with nickel-acrylate mixture, with volume ratio of 1:3. The coated SMF is characterized under scanning electron microscope (SEM) to observe the thickness and the morphology of the coating layer. The sensor response was measured by using the Rayleigh backscattering frequency shift method. The results show that the frequency shift is directly proportional to the applied magnetic field. At the magnetic field strength of 95 mT, the sensor response is −2 GHz of frequency shift. The sensitivity of the sensor is 0.09346 GHz/mT (below 10 mT) and 0.01008 GHz/mT (above 10 mT).

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.