M. H. Yaacob

20 GHz spacing multi-wavelength generation of Brillouin-Raman fiber laser in a hybrid linear cavity

We demonstrate a tunable multi-wavelength Brillouin-Raman fiber laser with 20 GHz wavelength spacing. The setup is arranged in a linear cavity by employing 7.2 and 11 km dispersion compensating fibers (DCF) in addition to a 30 cm Bismuth-oxide erbium doped fiber. In this experiment, for the purpose of increasing the Stokes lines, it is necessary to optimize Raman pump power and Brillouin pump power together with its corresponding wavelengths. At the specific Brillouin pump wavelength, it is found that the longer length of 11 km DCF with optimized parameters results in larger number of Stokes combs and optical signal to noise ratios (OSNRs). In this case, a total of 195 Brillouin Stokes combs are produced across 28 nm bandwidth at Brillouin pump power of -2 dBm and Raman pump power of 1000 mW. In addition, all Brillouin Stokes signals exhibit an average OSNR of 26 dB.

Multi-wavelength Brillouin-Raman fiber laser utilizing enhanced nonlinear amplifying loop mirror design

We demonstrate a single-spacing, multi-wavelength Brillouin-Raman fiber laser utilizing an enhanced cavity of nonlinear amplifying loop mirror. In this structure, the optimization of multi-wavelength lasing is done with proper adjustments of coupling ratio and Brillouin pump power. When setting the Raman pump power to 300 mW, up to 28 channels with an average 17 dB optical signal-to-noise ratio are achieved. In this case, the Brillouin pump power is maintained at -2.6 dBm when the splitting ratio and Brillouin pump wavelength are fixed at 99/1 and 1555 nm, correspondingly. Our achievements present high numbers of Stokes channels with an acceptable optical signal-to-noise ratio at low pump power operation.

Room temperature ammonia sensing using tapered multimode fiber coated with polyaniline nanofibers

We demonstrate an ammonia sensor composed of a tapered multimode fiber coated with polyaniline nanofibers that operates at room temperature (26°C). The optical properties of the polyaniline layer changes when it is exposed to ammonia, leading to a change in the absorption of evanescent field. The fiber sensor was tested by exposing it to ammonia at different concentrations and the absorbance is measured using a spectrophotometer system. Measured response and recovery times are about 2.27 minutes and 9.73 minutes, respectively. The sensor sensitivity can be controlled by adjusting the tapered fiber diameter and the highest sensitivity is achieved when the diameter is reduced to 20 µm.

150-Channel Four Wave Mixing Based Multiwavelength Brillouin-Erbium Doped Fiber Laser

A wide band tunable multiwavelength Brillouin-erbium fiber laser (BEFL) is developed. In this structure, the laser is formed between a double pass amplification box and a highly nonlinear fiber (HNLF), which acts as a virtual mirror, results in removing the reflective physical mirror from one side of the laser structure. A large number of Stokes and anti-Stokes lines are generated through cascading stimulated Brillouin scattering and inducing four wave mixing process inside the HNLF. Due to optimizing Brillouin and erbium doped fiber (EDF) pump powers, the Rayleigh back scattering is efficiently suppressed, and the generated BEFL wavelengths are free from self lasing cavity modes over a wide tuning range. At EDF pump power and Brillouin pump power of 100 mW and 3 dBm, respectively, up to 150 Stokes lines with wavelength spacing of 0.076 nm, and a tuning range of 40 nm were achieved.

Dynamic response of tapered optical multimode fiber coated with carbon nanotubes for ethanol sensing application.

Ethanol is a highly combustible chemical universally designed for biomedical applications. In this paper, optical sensing performance of tapered multimode fiber tip coated with carbon nanotube (CNT) thin film towards aqueous ethanol with different concentrations is investigated. The tapered optical multimode fiber tip is coated with CNT using drop-casting technique and is annealed at 70 °C to enhance the binding of the nanomaterial to the silica fiber tip. The optical fiber tip and the CNT sensing layer are micro-characterized using FESEM and Raman spectroscopy techniques. When the developed sensor was exposed to different concentrations of ethanol (5% to 80%), the sensor reflectance reduced proportionally. The developed sensors showed high sensitivity, repeatability and fast responses (<55 s) towards ethanol.

Development of a Hydrogen Gas Sensor Using a Double Saw Resonator System at Room Temperature

A double SAW resonator system was developed as a novel method for gas sensing applications. The proposed system was investigated for hydrogen sensing. Commercial Surface Acoustic Wave (SAW) resonators with resonance frequencies of 433.92 MHz and 433.42 MHz were employed in the double SAW resonator system configuration. The advantages of using this configuration include its ability for remote measurements, and insensitivity to vibrations and other external disturbances. The sensitive layer is composed of functionalized multiwalled carbon nanotubes and polyaniline nanofibers which were deposited on pre-patterned platinum metal electrodes fabricated on a piezoelectric substrate. This was mounted into the DSAWR circuit and connected in parallel. The sensor response was measured as the difference between the resonance frequencies of the SAW resonators, which is a measure of the gas concentration. The sensor showed good response towards hydrogen with a minimum detection limit of 1%.

Performance comparison of OCDMA codes for quasi-distributed fiber vibration sensing

The performance of Khazani Syed (KS) code based fiber vibration measurement for distributed sensing has been investigated. The setup was aimed at implementing quasi distributed vibration sensing with less complexity and optimum performance against Multiple Access Interference. The three sensor points system were compared with existing Optical Orthogonal Code (OOC) and Modified Congruence Code (MQC) in terms of level of power received, supported fiber length and complexity in implementation. Slightly better received power and longer fiber length were demonstrated by the system employing MQC code but a wide gap to OOC code. However, since KS code is implemented with less number of components which tends to reduce the cost and complexity of the system which becomes obvious as the sensor points grow, KS code is recommended for the quasi distributed vibration sensing.

Sensitive and Specific Protein Sensing Using Single-Mode Tapered Fiber Immobilized With Biorecognition Molecules

We examine and demonstrate a biosensor using single-mode tapered fiber that has been immobilized with biorecognition molecules to sense targeted proteins. Interaction of evanescent waves with the external medium surrounding the tapered region produces an interferometric-patterned spectrum, which shifts correspondingly to any changes of refractive index (RI) in the external medium. The proposed setup managed to obtain an RI sensitivity and concentration sensitivity of 2526.8 nm/RIU and 20.368 nm/μM, respectively, which, to our knowledge, is highly sensitive when compared with previous studies. The dynamic performance, good specificity, and high sensitivity of the proposed method highlight an immensely beneficial choice for immunological diagnostics.

Reflectance Response of Optical Fiber Coated With Carbon Nanotubes for Aqueous Ethanol Sensing

Ethanol is a highly flammable chemical and is widely used for medical and industrial applications. In this paper, optical sensing performance of aqueous ethanol with different concentrations is investigated using multimode fiber coated with carbon nanotubes (CNT). The multimode optical fiber tip is coated with CNT via a drop-casting technique and is annealed at 70 °C to improve the binding of the nanomaterial to the silica fiber. The optical fiber tip and the CNT sensing layer are microcharacterized using field emission scanning electron microscopy, Raman spectroscopy, and X-ray diffraction techniques. The reflectance response of the developed fiber sensor is measured using a spectrophotometer in the optical wavelength range of 500-800 nm. Upon exposure to ethanol with concentration ranges of 5%-80%, the sensor reflectance reduced proportionally. The dynamic response decreased by 4% when the sensor is exposed to ethanol with concentration of 80% in distilled water. It is found that the sensor shows fast response and recovery as low as 38 and 49 s, respectively.

Room temperature ammonia sensor using side-polished optical fiber coated with graphene/polyaniline nanocomposite

We developed a highly sensitive side-polished plastic optical fiber coated with chemical synthesized graphene/polyaniline nanocomposite for ammonia gas sensing application. It was found that the optical sensor absorbance spectrum linearly increases with increasing ammonia concentrations. The experimental results revealed that the side-polished fiber sensor coated with graphene/polyaniline nanocomposite exhibited higher performance than the ones coated with only polyaniline. The proposed sensor demonstrated sensitivity, response and recovery times of 132.8 AU/%, 112 s, and 185 s, respectively, at room temperature. The superior sensing performance of the developed fiber sensor indicates its high efficiency for NH3 gas-sensing applications at room temperature.