M. A. Mahdi

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.

Preparation of silver nanoparticles in virgin coconut oil using laser ablation.

Laser ablation of a silver plate immersed in virgin coconut oil was carried out for fabrication of silver nanoparticles. A Nd:YAG laser at wavelengths of 1064 nm was used for ablation of the plate at different times. The virgin coconut oil allowed formation of nanoparticles with well-dispersed, uniform particle diameters that were stable for a reasonable length of time. The particle sizes and volume fraction of nanoparticles inside the solutions obtained at 15, 30, 45 min ablation times were 4.84, 5.18, 6.33 nm and 1.0 × 10−8, 1.6 × 10−8, 2.4 × 10−8, respectively. The presented method for preparation of silver nanoparticles in virgin coconut oil is environmentally friendly and may be considered a green method.

Seamless tuning range based-on available gain bandwidth in multiwavelength Brillouin fiber laser.

We experimentally demonstrate a simple widely tunable multiwavelength Brillouin/Erbium fiber laser that can be tuned over the entire C-band, thereby greatly improving the tuning range limitation faced by the previous Brillouin-erbium fiber laser architectures. Tuning range of 39 nm from 1527 nm to 1566 nm, which is only limited by the amplification bandwidth of the erbium gain was successfully achieved. At Brillouin pump wavelength of 1550 nm and 1480 nm laser pump and Brillouin pump powers of 130 mW and 2 mW respectively, all the generated output channels have peak power above 0 dBm, with the first output channel having a peak power of 8.52 dBm. The experimental set up that consists of only 4 optical components, is simple, devoid of the complex structure employed previously to enhance the tunability and feedback mechanism normally associated with multiwavelength Brillouin-erbium fiber laser sources. The generated output channels are stable, rigidly separated by 10 GHz (0.08 nm).

Effects of pump recycling technique on stimulated Brillouin scattering threshold: A theoretical model

We develop a theoretical model that can be used to predict stimulated Brillouin scattering (SBS) threshold in optical fibers that arises through the effect of Brillouin pump recycling technique. Obtained simulation results from our model are in close agreement with our experimental results. The developed model utilizes single mode optical fiber of different lengths as the Brillouin gain media. For 5-km long single mode fiber, the calculated threshold power for SBS is about 16 mW for conventional technique. This value is reduced to about 8 mW when the residual Brillouin pump is recycled at the end of the fiber. The decrement of SBS threshold is due to longer interaction lengths between Brillouin pump and Stokes wave.

Multi-wavelength Brillouin-Raman ring-cavity fiber laser with 22-GHz spacing

We experimentally demonstrate a multi-wave length Brillouin-Raman fiber laser configured in a ring-cavity resonator. Interactions between stimulated Brillouin scattering and Raman amplification in a dispersion compensating fiber, attributed to the generation of 16 output channels at injected Raman pump unit power of 650 mW and Brillouin pump power of 2.0 mW. The first output channel has a peak power of 14.8 mW. By discriminating the even-order Brillouin Stokes signals from circulating in the resonator, the generated output channels were found to have wavelength spacing of ∼22 GHz. The output channels were also found to have average optical signal-to-noise ratio value of 11.7 dB.

Optimization of Brillouin pump wavelength location on tunable multiwavelength BEFL

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.

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

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.

Characterization of phase noise in a single-mode fiber grating Fabry–Perot laser

A comprehensive study on the phase noise characteristics of a single-mode fiber grating Fabry–Perot (FGFP) laser was conducted numerically. Adding to previous studies, the effects of external optical feedback (OFB), external cavity length, temperature, injection current, cavity volume, nonlinear gain compression factor and fiber grating parameters on phase noise characteristics are presented. The temperature dependence (TD) of phase noise was calculated according to the TD of laser parameters and not by the well-known Parkove equation. The frequency spectra of FGFP laser phase noise were calculated by using a Fourier transform. Results show that the TD of the phase noise in FGFP lasers is smaller than that for distributed feedback lasers. The shortest external cavity length that provides the minimum phase noise is found to be around 3.1 cm. In addition, the relaxation oscillation frequency shifts towards more than 6 GHz, which provides larger flat frequency range. Furthermore, phase noise can be eliminated either by increasing the injection current or the OFB level.

Characterization of Turn-On Time Delay in a Fiber Grating Fabry–Perot Lasers

In this paper, turn-on time delay characteristics of a fiber grating Fabry-Perot (FGFP) laser are numerically investigated by considering all the carrier recombination rate (CRR) R(N) coefficients (nonradiative, Anr; radiative, B; and Auger coefficient, C). The results show that the turn-on time delay significantly reduces by increasing the injection current (Iinj) and/or the initial value of carrier density (Ni). Meanwhile, the turn-on time delay increases by increasing the CRR coefficients. However, its effect can be minimized by increasing Iinj and/or Ni. In addition, the turn-on time delay can be reduced by increasing the external optical feedback (OFB) level. Moreover, it is shown that the optimum external-cavity length (Lext) is 3.1 cm. Furthermore, an antireflection (AR) coating reflectivity value of 1 × 10-2 is sufficient for the laser to operate at good turn-on time delay and low fabrication complexity. The obtained results can provide an important idea for the practical fabrication of the FGFP laser used in the dense wavelength-division multiplexing (DWDM) systems and optical access networks.

Compact Brillouin Fiber Laser Based on Highly Nonlinear Fiber With 51 Double Spacing Channels

A compact multiwavelength Brillouin fiber laser (BFL) with 51 stable double Brillouin frequency shift channels is demonstrated at room temperature. It uses a ring cavity with a 3-dB coupler for separation of odd-ordered and even-ordered Brillouin Stokes (BS) channels using a highly nonlinear fiber (HNLF) as the Brillouin gain medium. Compared with the use of a standard single-mode fiber, the HNLF-based BFL produces higher output power and a higher count of Stokes lines. At the maximum Brillouin pump (BP) power of 16.7 dBm, 36 odd channels and 15 even channels are generated with a channel spacing of 0.15 nm. The output power of the even channels is observed to be always lower than that of the odd channels as they are generated from the previous odd BS.