Preparation, Characterization, and Electrical Conductivity Investigation of Multi-walled Carbon Nanotube-filled Composite Nanofibres

There is a growing interest in carbon nanofibre materials especially for applications that require high surface area, excellent chemical inertness, and good electrical conductivity. However, in certain applications a much higher electric conductivity is required before one can take the full advantage of the nanofibre network. Therefore, incorporating superconductive materials such carbon nanotubes is thought to be a feasible approach to enhance the electrical properties of the carbon nanofibres. The objectives of this study were to prepare and characterize multi-walled carbon nanotube-filled composite nanofibres. Carbon nanofibres were produced via electrospinning technique using precursor solutions of polyacrylonitrile in dimethylformamide loaded with different amount of multi-walled carbon nanotubes (MWCNT). The electrospun fibre samples were then pyrolyzed in a nitrogen-filled laboratory tube furnace. Characterization process was performed using scanning electron microscope (SEM), transmission electron microscope (TEM), and four-point probe method. It was found that the incorporation of MWCNT into the carbon nanofibre structures could significantly increase the electric properties of the nanofibres. The composite nanofibres with 0.1 wt.% of MWCNT loading has the highest electrical conductivity of 155.90 S/cm compared to just 10.71 S/cm of the pure carbon nanofibres. However, the electrical conductivity of the composite fibres reduced drastically when higher weight percentages of MWCNT were used. This was caused by agglomeration of MWCNT causing premature percolation, and broken fibre network as evidenced by SEM and TEM examinations. The results obtained from this study may facilitate improvements in the development of superconductive high surface area materials for electronic applications

Highly stable and tunable narrow-spacing dual-wavelength ytterbium-doped fiber using a microfiber Mach–Zehnder interferometer

We describe a successful demonstration of highly stable and narrowly spaced dual-wavelength output via an ytterbium-doped fiber laser. A microfiber-based Mach-Zehnder interferometer and a tunable bandpass filter were both placed into the laser ring cavity for the purpose of ensuring a stable and narrowly spaced dual-wavelength output. Experimental results comprised three sets of dual-wavelength lasing output with wavelength spacing of 0.06, 0.09, and 0.22 nm, respectively, and side-mode suppression ratio of ∼50 dBm. A subsequent stability test provided evidence that maximum power and wavelength fluctuation were less than 0.8 dB and 0.01 nm, respectively, and thus, the obtained output was considered to be highly stable in dual-wavelength operation. The proposed system offers advantages of flexibility in dual-wavelength laser generation in addition to excellent reliability

Q-switched ytterbium-doped fiber laser with zinc oxide based saturable absorber

A Q-switched ytterbium doped fiber laser (YDFL) with a ZnO saturable absorber (SA) is used to demonstrate the generation of pulses in the 1 micron region. The system has a Q-switching threshold of approximately 115.2 mW, and can generate pulses with a 3.0 µs full-width at half maximum as well as a peak-to-pedestal ratio of 53.0 dB. No spectral modulations are observed, indicating a highly stable system. The pulse output of the proposed system has repetition rates and pulse widths of approximately 50 kHz and 1.6 µs, as well as an average output power of 0.14 mW and a pulse energy of 2.8 nJ at its highest pump power of 196 mW. This is the first time, to the authors' knowledge, that a ZnO based SA has been used to generate pulses in the 1 micron region with a YDFL

Generation of stable and narrow spacing dual-wavelength ytterbium-doped fiber laser using a photonic crystal fiber

We demonstrate the design and operation of novel narrow spacing and stable dual-wavelength fiber laser (DWFL). A 70-cm ytterbium-doped fiber has been chosen as the gain medium in a ring cavity arrangement. Our design includes a short length photonic crystal fiber, acting as a dual-wavelength stabilizer based on its birefringence coefficient and nonlinear behavior and tunable band pass filter (TBPF) to achieve narrow spacing spectrum lasing. Our laser output is considered to be highly stable, with power fluctuation less than 0.8 dB over a period of 15 min. The flexibility and tunability of TBPF, together with polarization controller enable the spacing tuning of the DWFL from 0.03 nm up to 0.07 nm for 1040 nm region, and 0.10 nm up to 0.40 nm for 1060 nm region. The tunable wavelength spacing shows the flexibility of the DWFL in addition to stable and reliable properties of fiber laser in 1-m region

Generation of an ultra-stable dual-wavelength ytterbium-doped fiber laser using a photonic crystal fiber

This paper describes the demonstration of a simple ytterbium-doped fiber (YDF) laser that utilized a short length of photonic crystal fiber (PCF) in a ring cavity and adjustments to the polarization state of an incorporated polarization controller (PC) to achieve a stable dual-wavelength output. The dual-wavelength lasing operation exploited the Mach-Zehnder interferometer effect, and the laser output consistently achieved high power stability with a 0.8 dB fluctuation over a period of 30 min. This proposed setup has the capability for adjustable spacing of two lasing wavelengths from a minimum of 0.40 nm to a maximum of 3.40 nm, allowing for flexibility in dual-wavelength laser generation in addition to stable and reliable system features

The generation of passive dual wavelengths Q-switched YDFL by MoSe2film

A simple ytterbium doped fiber laser (YDFL) setup was used to generate Q-switching pulses by using a D-shaped polished fiber as a wavelength selective filter. The gain medium used in the cavity was ytterbium doped fiber with length 70 cm. By utilizing a MoSe2 film as saturable absorber into the cavity, a stable dual wavelength was produced at 1036.69 and 1039.22 nm. The wavelength separation of the output spectrum was 2.53 nm. We found a maximum pulse energy of 0.99 nJ and shortest pulse width of 1.2 μs. We have determined consistent dual-wavelength Q-switching pulses for the 1-micron region

Tunable single wavelength erbium-doped fiber ring laser based on in-line Mach-Zehnder strain

A tunable single-wavelength of an erbium-doped fiber ring laser is proposed and demonstrated. The laser integrates a tapered in-line Mach-Zehnder interferometer (IMZI) in its ring loop as an intracavity filter. The light spectrum is adjusted by changing an axial strain of the interferometer in a 60 μm range. As a result, a total tuning range of 6.19 nm that covers the wavelength from 1552.94 nm to 1559.13 nm is observed, and the sensitivity of 103.5 pm/μm is recorded. This high sensitivity lasing behavior is useful for high selectivity and fine tuning for narrow wavelength applications

Switchable multiwavelength ytterbium-doped fiber laser using a non-adiabatic microfiber interferometer

In this paper, we have successfully demonstrated a stable dual, triple and quad-wavelength generation of ytterbium-doped fiber by incorporating a non-adiabatic microfiber interferometer (N-MI) into the laser ring cavity. Three sets of dual-wavelength, two sets of triple-wavelength and one set of quad-wavelength with the same wavelength spacing of 4.24 nm for all sets of multiwavelengths over the range of 1035 nm to 1050 nm are obtained by means of a nonlinear polarization rotation mechanism. The side-mode suppression ratio (SMSR) is ∼53 dBm while the wavelength fluctuation and maximum power are 0.01 nm and less than 0.6 dB, respectively. Such features offer flexibility in multiwavelength generation and a stable output, with addition to a reliable system at an ambient temperature

Titanium dioxide-based Q-switched dual wavelength in the 1 micron region

In this work a passively Q-switched dual-wavelength ytterbium-doped fiber laser using a titanium dioxide-based saturable absorber is proposed and proven. The system also utilizes a side-polished fiber in a ring cavity configuration to obtain the desired pulse train. A stable dual-wavelength pulse output is obtained at 1034.7 and 1039.0 nm, with a maximum pulse energy of 2.0 nJ, and a shortest pulse width of 3.2 μs. The generated pulse train is stable, and has a pulse repetition rate from 31.2 to 64.5 kHz