M. H. Abu Bakar

Single mode tapered fiber-optic interferometer based refractive index sensor and its application to protein sensing.

We demonstrate refractive index sensors based on single mode tapered fiber and its application as a biosensor. We utilize this tapered fiber optic biosensor, operating at 1550 nm, for the detection of protein (gelatin) concentration in water. The sensor is based on the spectroscopy of mode coupling based on core modes-fiber cladding modes excited by the fundamental core mode of an optical fiber when it transitions into tapered regions from untapered regions. The changes are determined from the wavelength shift of the transmission spectrum. The proposed fiber sensor has sensitivity of refractive index around 1500 nm/RIU and for protein concentration detection, its highest sensitivity is 2.42141 nm/%W/V.

Spectral variations of the output spectrum in a random distributed feedback Raman fiber laser

We report an ultra-long Raman laser that implemented a variable pumping scheme in backward and forward configurations. Rayleigh backscattering effects were realized in the 51 km fiber length that functioned as a virtual mirror at one fiber end. With the employment of a fiber Bragg grating that has a peak reflection wavelength at 1553.3 nm, spectral broadening effects were observed. These occurred as the pump power level was diverted more to the forward direction. Owing to this fact, a maximum width of 0.9 nm was measured at 100% forward pumping. The obtained results show that the efficient exploitation of four-wave mixing interactions as well as strong Rayleigh backscattering are beneficial to influence the lasing performances. Both of these nonlinear responses can be adjusted by varying pumping distributions along the fiber longitudinal dimension.

Photonic Crystal Fiber in Photonic Crystal Fiber for Residual Dispersion Compensation Over

A photonic crystal fiber in photonic crystal fiber (PCF-in-PCF) architecture is numerically investigated for residual dispersion compensation in optical transmission link. The optimized structure shows a flattened and high average dispersion of -457.4 ps/nm/km in the wavelength range of 1360 nm to 1690 nm. The sensitivity of the fiber dispersion properties to a ±2% variation in the optimum parameters is studied for practical conditions. Additionally, the effect of variation in the structure parameters on effective mode area is simulated to understand its relationship to light confinement.

{\rm E} + {\rm S} + {\rm C} + {\rm L} + {\rm U}

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.

Wavelength Bands

An L-band remotely-pumped erbium-doped fiber amplifier incorporating a secondary pumping scheme utilizing stimulated Raman Scattering (SRS) was demonstrated. 1423 nm Raman laser was employed to generate SRS which became the secondary pump source. The amplifier displayed excellent gain of up to 27.3 dB at 1570 nm for −30 dBm input. Noise figures were also kept to a minimum, with the highest figure measured at 11 dB which was influenced by imperfection of the C/L coupler utilized in this architecture. Overall transmission performance was measured as well and demonstrated an encouraging outcome with gain as high as 24 dB while the noise figure was maintained at about 11 dB. The L-band signal amplification was also contributed by the stimulated Raman scattering along the transmission fiber. The outcome of this study emphasized the feasibility of secondary pumping scheme using SRS in L-band gain enhancement.

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

Optimization of Brillouin pump (BP) wavelength location on tunable multiwavelength Brillouin-erbium fiber laser (BEFL) with BP pre-amplified technique is experimentally investigated. The tunable multiwavelength BEFL is achieved by utilization a tunable band-pass filter in a laser cavity. The optimum BP power and BP wavelength location within the filter bandwidth is determined in order to obtain the maximum stable output channels. Optimum distance of launching the BP wavelength is found at 0.80 nm shorter from the center wavelength of the filter bandwidth. 15 stable output channels are achieved from the tunable fiber laser system within the optimum range of BP power which is found to be between 5.2 to 5.7 dBm.

Utilization of stimulated Raman Scattering as secondary pump on hybrid remotely-pump l-band Raman/erbium-doped fiber amplifier

An all-fiber comb filter using a tapered-erbium-doped fiber in a Mach-Zehnder interferometer structure is presented. The free spectral range, extinction ratio, bandwidth, and interference pattern of the comb filter can be shaped by controlling the taper waist length and the length of up and down taper transition regions. By varying the taper waist length from 5 to 25 mm, the free spectral range changes from 14.7 to 1.0 nm, and the linewidth varies from 3.3 to 0.3 nm, respectively. We demonstrate a tunable dual-wavelength laser by using the tapered-erbium-doped fiber as a gain medium as well as a wavelength-selective element. The laser can be tuned at a resolution of 0.2 nm with a side-mode suppression ratio of up to 46.88 dB and a linewidth of 0.09 nm.

Optimization of Brillouin pump wavelength location on tunable multiwavelength BEFL

The work presented in this paper details the changes in continuous-wave laser characteristics that were affected by the orientation of pumping separation. The Raman laser was constructed in forward and backward pumping schemes with respect to the 1553.3-nm fiber Bragg grating location. The laser cavity was formed by the induction of Rayleigh backscattering effects in the 51-km fiber length that served as a virtual mirror. From the results obtained, it can be concluded that low threshold operation around 788 mW was satisfied at a coupling ratio of 0 (forward pumping scheme). Moreover, the best output power attainment of 220 mW was realized when 60% of pump powers were delivered via a backward pumping scheme. Thus, the success of this research provides a basis to further understand the principle of backscattered wave interactions along the fiber longitudinal structure.

Tapered-EDF-Based Mach–Zehnder Interferometer for Dual-Wavelength Fiber Laser

Erbium-doped fiber amplifier with flat gain over 30 nm bandwidth is demonstrated using flexible selective band methods. The band optical amplifier was designed to cater 44 wavelength division multiplexing channels which were separated into bands of 4 nm. Without using any gain flattening filter, the gain of optical amplifier was maintained at 19 dB with a maximum gain variation of less than 1.6 dB even though the input signal power was varied from −19 to −6 dBm. The amplifier was able to maintain 1 dB gain flatness with 83% chance for any selective bands of 4 nm within the wavelength range from 1530 to 1565 nm. This feature is very attractive to support band optical networks.

Laser Parameter Variations in a Rayleigh Scattering-Based Raman Fiber Laser With Single Fiber Bragg Grating Reflector

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.