Showing papers by "Harith Ahmad published in 2018"

Mach-Zehnder interferometric magnetic field sensor based on a photonic crystal fiber and magnetic fluid.

Abstract: A Mach–Zehnder interferometric magnetic field sensor based on a photonic crystal fiber (PCF) and magnetic fluid (MF) was designed and experimentally demonstrated. The sensing probe consists of a single-mode-(SM)-multimode-PCF-SM fiber structure through arc fusion splicing. It was then laser engrave notched with the femtosecond laser so that the PCF cladding was selectively infilled MF. A well-defined interference pattern was obtained on account of the tunable refractive index of the MF infilled PCF cladding. The transmission spectra of the proposed sensor under different magnetic field intensities have been measured and theoretically analyzed. The results show that the sensitivity of the proposed sensor can reach −0.13 dB/mT and 0.07334 nm/mT in the magnetic field intensity from 1 mT to 20 mT and 2 mT to 20 mT, respectively.

A Recent Progress of Steel Bar Corrosion Diagnostic Techniques in RC Structures

Abstract: Corrosion of steel bar is one of key factors undermining reinforced concrete (RC) structures in a harsh environment. This paper attempts to review the non-destructive procedures from the aspect of the corrosion measurement techniques, especially their advantages and limitations. Systematical classification of diagnostic methods is carried out to determine any probable corrosion issues before the structures become severe, and helps choose the suitable method according to different construction features. Furthermore, the three electrochemical factors method is introduced to inspire researchers to combine various techniques to improve corrosion evaluation accuracy. The recommendations for future work are summarized, in conclusion.

Application of graphene oxide based Microfiber-Knot resonator for relative humidity sensing

Abstract: A relative humidity (RH) sensor is proposed and demonstrated using a micro-knot resonator (MKR) enhanced with a layer graphene oxide (GO) coating. The MKR is fabricated by means of tapering a standard fiber, with the GO coating added by the drop-cast method. The proposed sensor is tested for an RH range of between 0% and 80% at 20% intervals, and the configurations with and without the GO coating achieve sensitivities of 0.0104 nm/% and 0.0095 nm/%, respectively. The MKR configuration without the GO coating has a linear response correlation coefficient of 0.9098 and a resolution of 0.1%, while the configuration with the GO coating has a linear response correlation coefficient of 0.9548 and a resolution of 0.096% which is better. The proposed sensor has multiple applications, especially in the area of climate and atmospheric measurement and monitoring.

Studies of Ag/TiO2 plasmonics structures integrated in side polished optical fiber used as humidity sensor

Abstract: In this report, we investigate the effects of Ag/TiO2 integrated in side polished optical fiber. Several layers of Ag thickness has been deposited on glass substrates using electron beam (e-beam) evaporation technique in order to determinate the influence of silver with combination of TiO2 on final properties of the sensor. Several thicknesses of Ag NPs were sets to 5 nm, 7 nm, 12 nm, and 16 nm. Another layer of metal oxide, specifically titanium oxide (TiO2) is introduced, covering the Ag layer to study the effect of metal oxides toward the performance of the device. The morphology of the samples was observed using a field-emission scanning electron microscope (FESEM), Raman UV–Vis spectroscopy and Raman photoluminescence (PL) spectroscopy. A CST Microwave used to observe the electric field distribution for all the samples to support the experimental findings. Based on the simulation analysis, two thicknesses of Ag layers (7 nm and 16 nm) were selected to be coated on a side polished optical fiber and tested as a humidity sensor. TiO2 layer was introduced to see the enhancement in the sensing measurements as a suitable material for trapping the photo generated electrons and avoiding charge recombination. From this observation, it can be conclusively shows that the sensitivity of the sensor is improved with integration of Ag NPs and TiO2. Based on the experimental results, the sensor of Ag/TiO2 with 7 nm of Ag layers shows the best characteristics in humidity sensing with good sensitivity and linearity of 0.9201% and 13.4 mW/% RH, respectively.

Chitosan capped nickel oxide nanoparticles as a saturable absorber in a tunable passively Q-switched erbium doped fiber laser

Abstract: Nickel oxide (NiO) nanoparticles successfully prepared from a nickel(II) chloride hexahydrate precursor are used to form a chitosan capped NiO nanoparticle thin film to serve as a saturable absorber (SA) for the generation of passively Q-switched pulses in an erbium doped fiber laser (EDFL). The NiO/chitosan SA based EDFL is able to generate stable pulsed outputs at a low threshold pump power of 104.90 mW with a central wavelength at 1562 nm. The highest pulse energy obtainable by the system is 15.30 nJ at a repetition rate of 42.66 kHz and a pulse duration of 2.02 μs. The laser has a spectral range of 58 nm from 1522 to 1580 nm, covering the C and L bands and even portions of the S band. This study experimentally demonstrates that the potential of the NiO/chitosan film as an SA material for Q-switching operations, combined with the biocompatibility, non-toxicity and high thermal resistance of Chitosan, holds great prospects for a broad range of applications.

Design of dispersion-engineered As2Se3 channel waveguide for mid-infrared region supercontinuum generation

Abstract: In recent years, low cost and scalable integrated optics compatible planar waveguides have emerged for an ultrabroadband supercontinuum generation between ultraviolet and mid-infrared region applications. A 20-mm-long integrated photonics compatible highly nonlinear As2Se3 channel waveguide, which exhibited wider as well as lower magnitude and nearly flat anomalous dispersion region, designed and modeled by employing GeAsSe glass for its upper and lower claddings. Using pump source at 6 μm with a pulse duration of 170-fs, an ultrabroadband long wavelength region supercontinuum broadening covering the wavelength from 3.5 μm to 15 μm could be predicted with the largest input peak power of 10 kW. Increasing the power further to 20 kW does not enhance the supercontinuum expansion noticeably beyond 15 μm. This numerical demonstration could be the longest supercontinuum generation by an on-chip integrated photonics compatible planar waveguide which can be used for a variety of mid-infrared region applications.

Design and modeling of dispersion-engineered all-chalcogenide triangular-core fiber for mid-infrared-region supercontinuum generation

Abstract: An ultrabroadband mid-infrared supercontinuum (SC) source has been designed and modeled using a 10-mm-long all-chalcogenide triangular-core fiber (TCF). The TCF structure can be fabricated from Ge11.5As24Se64.5 chalcogenide glass as a core and Ge11.5As24S64.5 chalcogenide glass for its cladding running along the length of the fiber instead of air holes. Assuming the pump operates at 4 μm, the TCF is optimized by varying its side length using both anomalous-dispersion and all-normal-dispersion SC generation. Mid-infrared-region SC spectral broadening spanning beyond 15 μm could be generated with a low peak power of 3 kW by the proposed TCF structure optimized with varying its side length between 7 and 8 μm in anomalous-dispersion pumping. On the other hand, the TCF side length has to be decreased to 5.5 μm and below to optimize it for pumping in all-normal-dispersion-region SC generation. A coherent flat-top SC evolution in the mid-infrared region of up to 7 μm could be observed by this design with the same pump peak power and pulse duration applied before. The ultrawide optical bandwidth obtained by the proposed TCF design can be an effective tool for mid-infrared-region applications such as optical coherence tomography, molecular fingerprint spectroscopy, and biomedical imaging.

Mixed Transition Metal Dichalcogenide as Saturable Absorber in Ytterbium, Praseodymium, and Erbium Fiber Laser

Abstract: In this paper, a Mo(1– x )W x S2 thin film saturable absorber (SA) is proposed and fabricated and its performance over a wavelength region of 1.0 to $1.5~\mu \text{m}$ investigated. The few layer MoWS2 is obtained by hydrothermal exfoliation and fabricated into thin film with a host polymer. The SA is tested in a ring laser cavity with different gain media consisting of Ytterbium, Praseodymium, and Erbium doped fibers for Q-switching operation at 1.0, 1.3, and $1.56~\mu \text{m}$ . In all cases, the SA performs admirably with the mixed transition metal composition of the MoWS2 thin film allowing the optical properties of the SA to be altered by changing the composition ratio and the number of layers. The proposed SA has high potential as a new optical material to cater the needs of many optoelectronics application.

Mechanically exfoliated In2Se3 as a saturable absorber for mode-locking a thulium-doped fluoride fiber laser operating in S-band

Abstract: The rise of 2D materials since the discovery of graphene has been exponential. Their mechanical, electrical and optical properties are exceptional, similar to their 3D counterparts. In this paper, an α−In2Se3 crystal is mechanically exfoliated and transferred directly onto a fiber ferrule to serve as a saturable absorber (SA). A thulium-doped fluoride fiber is used as a gain medium to generate mode-locked pulses together with the In2Se3-based SA. The SA has a modulation depth of 14.6% and a saturation intensity of 0.4 kW/cm2. The passively generated mode-locked pulses have a repetition rate of 6.93 MHz and a pulse width of 5.79 ps. The mode-locked pulses also have a signal-to-noise ratio of 65.4 dB and a time-bandwidth product of 0.36. The pulse energy and peak power are 0.179 nJ and 27.2 W, respectively.

Dual-Wavelength Thulium Fluoride Fiber Laser Based on SMF-TMSIF-SMF Interferometer as Potential Source for Microwave Generation in 100-GHz Region

Abstract: A dual-wavelength thulium-doped fluoride fiber (TDFF) laser is presented. The generation of the TDFF laser is achieved with the incorporation of a single mode-multimode-single mode (SMS) interferometer in the laser cavity. The simple SMS interferometer is fabricated using the combination of two-mode step index fiber and single-mode fiber. With this proposed design, as many as eight stable laser lines are experimentally demonstrated. Moreover, when a tunable bandpass filter is inserted in the laser cavity, a dual-wavelength TDFF laser can be achieved in a 1.5- $\mu \text{m}$ region. By heterodyning the dual-wavelength laser, simulation results suggest that the generated microwave signals can be tuned from 105.678 to 106.524 GHz with a constant step of ~0.14 GHz. The presented photonics-based microwave generation method could provide alternative solution for 5G signal sources in 100-GHz region.

Tunable Q-switched thulium-doped fiber laser (TDFL) in 2.0 µm region based on gallium selenide saturable absorber

Abstract: A tunable Q-switched thulium-doped fiber laser (TDFL) using a Gallium Selenide (GaSe) based saturable absorber (SA) is proposed and demonstrated for operation in the 2.0 µm region. The Q-switched TDFL operates from 1960.0 nm to 1998.0 nm, covering a wavelength range of 38.0 nm. The generated output pulses have a repetition rate from 14.9 kHz to 40.9 kHz and minimum pulse width of 4.9 µs at the maximum pump power of 126.6 mW, as well as a maximum pulse energy of 92.8 nJ. This is, to the author’s knowledge, the first successful combination of a TDF and a GaSe based SA to generate tunable Q-switched pulses in 2.0 µm region.

Graphene-PVA saturable absorber for generation of a wavelength-tunable passively Q-switched thulium-doped fiber laser in 2.0 µm

Abstract: Graphene, a 2D material, has been used for generation of pulse lasers due to the presence of its various fascinating optical properties compared to other materials. Hence in this paper, we report the first demonstration of a thulium doped fiber laser with a wavelength-tunable, passive Q-switched output using a graphene-polyvinyl-alcohol composite film for operation in the 2.0 µm region. The proposed laser has a wavelength-tunable output spanning from 1932.0 nm to 1946.0 nm, giving a total tuning range of 14.0 nm. The generated pulse has a maximum repetition rate and average output power of 36.29 kHz and 0.394 mW at the maximum pump power of 130.87 mW, as well as a pulse width of 6.8 µs at this pump power. The generated pulses have a stable output, having a signal-to-noise ratio of 31.75 dB, and the laser output is stable when tested over a period of 60 min. The proposed laser would have multiple applications for operation near the 2.0 micron region, especially for bio-medical applications and range-finding.

Tunable passively Q-switched erbium-doped fiber laser with Chitosan/MoS 2 saturable absorber

Abstract: Chitosan, an organic polymer derived from the outer skeletons of crustacean and in the cell wall of fungi is explored as polymer host to develop thin film saturable absorber (SA). As a polymer, Chitosan shows high thermal stability as well as significant transmission characteristics. The highly transparent polymer serves as a good host for SA materials, and a composite Chitosan/MoS2 thin film is demonstrated to successfully generate stable Q-switched lasing output at operating wavelength of 1561.5 nm. At maximum pump power of 280.5 mW, the generated pulse exhibits maximum pulse repetition rate and pulse energy of 79.4 kHz and 43.69 nJ respectively as well as minimum pulse width of 1.02 μs. The overall efficiency of the laser cavity with the Chitosan/MoS2 thin film SA is approximately 0.93%. These results reflect the outstanding performance of Chitosan/MoS2 SA as compared to other MoS2 SA prepared using mechanical exfoliation and optical deposition technique. Moreover, the Chitosan polymer is shown to be a highly potential host in the SA fabrication process due to its promising performance which is comparable to PVA.

Temperature-independent hygrometry using micromachined photonic crystal fiber.

Abstract: An in-fiber Mach–Zehnder interferometer (MZI) is proposed and experimentally demonstrated for relative humidity (RH) and temperature measurements. The MZI is formed by a grapefruit-shaped photonic crystal fiber (G-PCF) cascaded with a short section of multimode fiber that serves as a mode coupler. To enhance sensitivity to humidity, femtosecond laser micromachining was performed to remove a portion of cladding of the G-PCF to expose its core to the ambient medium. The output interference spectrum is fast Fourier transformed to produce a spatial frequency spectrum that describes the intensity composition of the cladding modes in the MZI. In our investigation, it was observed that the interference dip intensity has a sensitivity of −0.077 dB/% RH to the change of RH in the range of 25%–80% RH, whereas the dip wavelength has a temperature sensitivity of ∼3.3 pm/°C in the range of 25°C–70°C. In addition, the dip intensity was insensitive to temperature. These characteristics have provided convenience in eliminating temperature cross talk and achieving accurate humidity measurement.

Modeling of dispersion engineered chalcogenide rib waveguide for ultraflat mid-infrared supercontinuum generation in all-normal dispersion regime

Abstract: A rigorous numerical investigation has been carried out through dispersion engineering of chalcogenide rib waveguide for near-infrared to mid-infrared ultraflat broadband supercontinuum generation in all-normal group-velocity dispersion regime. We propose a novel design of a 1-cm-long air-clad rib waveguide which is made from $$\text {Ge}_{11.5}\text {As}_{24}\text {Se}_{64.5}$$ chalcogenide glass as the core with either silica or $$\text {Ge}_{11.5}\text {As}_{24}\text {S}_{64.5}$$ chalcogenide glass as a lower cladding separately. A broadband ultraflat supercontinuum spanning from 1300 to 1900 nm could be generated when pumped at 1.55 $$\upmu \text {m}$$ with a low input peak power of 100 W. Shifting the pump to 2 $$\upmu \text {m}$$ , the supercontinuum spectra extended in the mid-infrared region up to 3400 nm with a moderate-input peak power of 500 W. To achieve further extension in mid-infrared, we excite our optimized rib waveguide in both the anomalous and all-normal dispersion pumping regions at 3.1 $$\upmu \text {m}$$ with a largest input peak power of 3 kW. In the case of anomalous dispersion region pumping, numerical analysis shows that supercontinuum spectrum can be extended in the mid-infrared up to 10 $$\upmu \text {m}$$ , although this contains high spectral amplitude fluctuations over the entire bandwidth which limits the supercontinuum sources in the field of high precision measurement applications. On the other hand, by optimizing a rib waveguide geometry for pumping in all-normal dispersion region, we are able to generate a smooth and flat-top coherent supercontinuum spectrum with a moderate bandwidth spanning the wavelength range 2–5.5 $$\upmu \text {m}$$ with less than 5 dB spectral fluctuation over the entire output bandwidth. Our proposed design is highly suitable for making on-chip SC light sources for a variety of applications such as biomedical imaging, and environmental and industrial sensing in the mid-infrared region.

Molybdenum disulfide saturable absorber for eye-safe mode-locked fiber laser generation

Abstract: We demonstrated an all-fiber mode-locked Thulium–Holmium co-doped fiber laser (THDFL) based on molybdenum disulfide (MoS2) tape saturable absorber. The THDFL generates a mode-locked pulse in anomal...

Infrared photodetectors based on reduced graphene oxide nanoparticles and graphene oxide

Abstract: Two photodiode (PD) designs incorporating graphene oxide (GO) and reduced graphene oxide (rGO) are proposed and fabricated. Both PDs have 50 mm thick silver electrodes deposited on the active area, and another electrode consisting of either GO or rGO nanoparticles (NPs). The GO and rGO NPs are deposited onto the p-type silicon substrate by the drop casting method. Both fabricated PDs show good sensitivity and quick responses under 974 nm laser illumination at 150 mW. The photoresponsivity values and external quantum efficiency of both photodetectors are measured to be approximately 800 I¼Aw-1 and 0.12 for the GO based PD and 1.6 m Aw-1 and 0.20 for the rGO based PD. Both PDs also have response and recovery times of 114 I¼s and 276 I¼s as well as 11 I¼s and 678 I¼s for the GO and rGO based PDs respectively. The proposed PDs would have significant applications in many optoelectronic devices as well as nanoelectronics. © 2018 Astro Ltd.

Highly stable mode-locked fiber laser with graphene oxide-coated side-polished D-shaped fiber saturable absorber

Abstract: A highly stable mode-lock fiber laser with a thin film coating of graphene oxide (GO) nanoparticles on a D-shaped fiber is proposed and demonstrated. The GO-coated D-shaped fiber, which serves as the cavity's saturable absorber (SA), is fabricated by drop-casting GO nanoparticles on the smooth and consistently polished area of the D-shaped fiber made using a disk-polishing machine. Mode-locking is induced through the interaction of the evanescent field from the D-shaped fiber and GO nanoparticle layer. The cavity has a length of 12.5 m with a fundamental frequency of 16.5 MHz and operates in the anomalous dispersion regime. Stable soliton modelocking is obtained above a pump power of 76.6 mW, with a central lasing wavelength of 1555.7 nm and welldefined Kelly's sidebands. The generated pulses have a repetition rate of 16.5 MHz and pulse duration of 1.18 ps over a pump power range of 76.6 to 280.5 mW, with only minor fluctuations observed. A signal-to-noise ratio of 58.3 dB is computed, indicating a highly stable output. The proposed SA fabrication technique provides a simple, cost-effective, and consistent method of generating mode-locked pulses in fiber lasers. © 2018 Society of Photo-Optical Instrumentation Engineers (SPIE).

Multi-wavelength Praseodymium fiber laser using stimulated Brillouin scattering

Abstract: A multi-wavelength Brillouin Praseodymium fiber laser (MWBPFL) operating at 1300 nm region is demonstrated based on the hybrid scheme by utilizing Brillouin gain medium and Praseodymium-doped fluoride fiber as linear gain medium. A 15 µm air gap is incorporated into the cavity to allow the switching of Brillouin frequency spacing from double to single spacing. Under the Brillouin pump of 8 dBm and the 1020 nm pump power of 567.2 mW, 36 Stokes lines with a wavelength spacing of 0.16 nm and 24 Stokes lines with a wavelength spacing of 0.08 nm are achieved. The wavelength tunability of 8 nm is realized for both MWBPFLs by shifting the Brillouin pump wavelength. The MWBPFLs exhibit an excellent stability in the number of generated Stokes and power level over one-hour period.

Switchable 10, 20, and 30 GHz region photonics-based microwave generation using thulium-doped fluoride fiber laser

Abstract: In this work, switchable 10, 20, and 30 GHz region photonics-based microwave generation in a fiber laser cavity is proposed and demonstrated. The microwave generation is based on the beating of a dual-wavelength thuliumdoped fluoride fiber laser. With the aid of a micro-air gap in an adapter, single, double, and triple Brillouin spacing can be generated in a single fiber laser cavity without re-routing the cavity. The wavelength spacing of the dual wavelengths that are induced by the single, double, and triple Brillouin spacing are 0.084, 0.166, and 0.254 nm, respectively, at a center wavelength of 1490 nm. In addition, a numerical calculation is performed using MATLAB to prove the generation of microwave signals at 11.34, 22.44, and 34.3 GHz. With the advantage of switchability among the 10, 20, and 30 GHz regions, the proposed photonics-based microwave generation is promising for the advancement of 5G technologies.

Tunable passively Q -switched ytterbium-doped fiber laser with mechanically exfoliated GaSe saturable absorber

Abstract: A tunable passively Q-switched ytterbium-doped fiber laser using few-layer gallium selenide (GaSe) as a saturable absorber (SA) is demonstrated. The few-layer GaSe SA, which is fabricated by the mechanical exfoliation method, is able to generate a Q-switched fiber laser that has a maximum repetition rate of 92.6 kHz and a minimum pulsed width of 2.3 μs. The highest pulse energy exhibited by the generated pulse is 18.8 nJ with a signal to noise ratio of ∼40 dB. The tunability of the proposed laser covers from 1042 to 1082 nm, giving a tuning range of 40 nm.

Q-Switched Erbium-Doped Fiber Laser Using Cadmium Selenide Coated onto Side-Polished D-Shape Fiber as Saturable Absorber

Abstract: A stable Q-switched erbium doped fiber laser emitting at 1558nm is demonstrated using a cadmium selenide (CdSe) material coated onto a side-polished D-shape fiber as the saturable absorber (SA). By elevating the input pump power from the threshold of 91mW to the maximum available power of 136mW, a pulse train with a maximum repetition rate of 57.44 kHz, minimum pulse width of 3.76 μs, maximum average output power of 7.99mW, maximum pulse energy of 0.1391 μJ, and maximum peak power of 36.99mW are obtained. The signalto-noise ratio of the spectrum is measured to be around 75 dB. This CdSe based SA is simple, robust, and reliable, and thus suitable for making a portable pulse laser source.

Visible Wireless Communications Using Solitonic Carriers Generated by Microring Resonators (MRRs)

Abstract: Optical wireless communications (OWC) using soliton pulses in the visible range (600 nm) have been presented. Filtering the input Gaussian spectrum is performed via the microring resonators (MRRs), where the range of 499.25 THz to 500.05 THz frequency band could be generated. The MRRs are simulated using InGaAsP/InP semiconductor with InGaAsP core having refractive index of 3.31 surrounded by InP (n = 3.18). In this research, ten soliton pulses having FSR of 8 GHz were generated at the drop port within the range 499.61 to 499.69 THz frequency band. Here, the generated carriers from the MRRs are modulated with the optical transmitter output which is a laser with extinction ratio of 10 dB and linewidth of 10 MHz utilizing a Mach–Zehnder modulator as an intensity modulator based on an interferometric principle. The frequency and time domain of the transmitted ten soliton carriers through the transmission link are presented as well as the eye diagram.