N. M. Ali

Axial contraction in etched optical fiber due to internal stress reduction

When an optical fiber is dipped in an etching solution, the internal stress profile in the fiber varies with the fiber diameter. We observed a physical contraction as much as 0.2% in the fiber axial dimension when the fiber was reduced from its original diameter to ~6 µm through analysis using high resolution microscope images of the grating period of an etched FBG at different fiber diameters. This axial contraction is related to the varying axial stress profile in the fiber when the fiber diameter is reduced. On top of that, the refractive index of fiber core increases with reducing fiber diameter due to stress-optic effect. The calculated index increment is as much as 1.8 × 10(-3) at the center of fiber core after the diameter is reduced down to ~6 µm. In comparison with the conventional model that assumes constant grating period and neglects the variation in stress-induced index change in fiber core, our proposed model indicates a discrepancy as much as 3nm in Bragg wavelength at a fiber diameter of ~6 µm.

Multi-wavelength Brillouin fiber laser using dual-cavity configuration

A simple technique for achieving multi-wavelength tunable multi-wavelength Brillouin fiber laser (BFL) based on dual-pass configuration is demonstrated. The BFL uses a piece of 10 km long non-zero dispersion shifted fiber (NZ-DSF) as a Brillouin gain medium to obtain odd-order Brillouin Stokes waves as an output with the line spacing of 0.16 nm (20 GHz) between each two consecutive waves by employing even-order Brillouin Stokes to improve output performance of the laser. With a BP of 15.3 dBm, at least 15 odd-order Brillouin Stokes and anti-Stokes lines are generated. The laser is room temperature stable, tunable over 50 nm wavelength range and has an optical signal to noise ratio of more than 30 dB at 1560 nm region. This Brillouin fiber laser can operate at any wavelength depending on the Brillouin pump (BP) wavelength used.

Multi-wavelength Q-switched erbium-doped fibre laser using saturable absorber based on carbon nanotube film

A stable passively Q-switched multi-wavelength erbium-doped fibre laser operating near 1533.5 nm is demonstrated using a saturable absorber based on single-walled carbon nanotube film, which is prepared using polyvinyl alcohol as a host polymer. The laser achieves a multi-wavelength oscillation regime as a result of nonlinear polarization rotation effect, which overcomes unstable mode competition in the ring cavity. It generates a stable multi-wavelength comb of seven lines, with the wavelength spacing of 0.10 nm at the pump power 64 mW. At the same pump power, the laser produces a stable pulse train with the repetition rate 13.1 kHz, the pulse width 7.2 µs and the pulse energy 21 nJ. A high performance of our Q- switched laser is achieved by optimizing the saturable absorber and the laser cavity.

Self-Starting Harmonic Mode-Locked Thulium-Doped Fiber Laser with Carbon Nanotubes Saturable Absorber

We report a ring cavity passively harmonic mode-locked thulium-doped fiber laser (TDFL) using a newly developed single-wall carbon nanotube-based saturable absorber. The TDFL generates the 25th harmonic mode-locked stretched pulse train with a high repetition rate of 213 MHz and a pulse duration of 710 fs. The laser operates at 1901.6 nm with an average power of 1.89 mW, which corresponds to the pulse energy of 0.008 nJ, at 1552 nm pump power of 719 mW. The peak-to-background ratio is measured to be 60 dB, which indicates the stability of the laser.

A Multi-Wavelength Brillouin Erbium Fiber Laser With Double Brillouin Frequency Spacing and Q-Switching Characteristics

A multiwavelength Brillouin Erbium fiber laser (MWBEFL) with double brillouin frequency spacing and Q-switching characteristics is demonstrated based on figure-of-eight configuration. The proposed MWBEFL uses a four-port circulator as a double-frequency shifter to isolate and circulate the odd-stokes signals through the Brillouin gain medium. Multiwavelength combs with 14 and 8 lasing lines and spacing of 0.16 nm are obtained by the use of 10-km long nonzero dispersion shifted fiber (NZDSF) and 2-km long dispersion compensating fiber (DCF), respectively. The Q-switched pulse trains are obtained in the proposed MWBEFL at 1480-nm pump power within 29 to 40 mW. It has repetition rates of 20.4 and 104.2 kHz with the corresponding pulse widths of 3.84 and 1.03 μs using the NZDSF and DCF, respectively, as the gain medium.

Q-switched Er-doped fiber laser with low pumping threshold using graphene saturable absorber

We propose a Q-switched Er-doped fiber laser (EDFL) with a threshold pumping power as low as 7.4 mW, and demonstrate using graphene polyvinyl alcohol (PVA) thin film as a passive saturable absorber (SA). The SA is fabricated from graphene flakes, which is synthesized by electrochemical exfoliation of graphite at room temperature in 1% sodium dodecyl sulfate aqueous solution. The flakes are mixed with PVA solution to produce a thin film, which is then sandwiched between two ferrules to form a SA and integrated in the EDFL ring cavity to generate a stable Q-switched pulse train. The pulse train operates at 1560 nm with a threshold pump power of 7.4 mW. At maximum 1480 nm pump power of 33.0 mW, the EDFL generates an optical pulse train with a repetition rate of 27.0 kHz and pulse width of 3.56 μs. The maximum pulse energy of 39.4 nJ is obtained at a pump power of 14.9 mW. This laser can be used as a simple and low-cost light source for metrology, environmental sensing, and biomedical diagnostics.

Multi-wavelength Brillouin fiber laser generation using dual-pass approach

A simple and compact multi-wavelength tunable Brillouin fiber laser (BFL) in conjunction with dual-pass approach is proposed and experimentally compared with the output of a conventional single ring cavity architecture. This BFL source is demonstrated using 10 km long non-zero dispersion shifted fiber (NZ-DSF) as a Brillouin gain medium. By single ring cavity configuration, odd-order Brillouin Stokes lines appear in the backward direction with the line spacing 0.16 nm (∼20 GHz) between each two consecutive waves. However, this single ring cavity in conjunction with dual-pass configuration is able to generate Brillouin Stokes lines with 0.08 nm spacing by providing bi-directional oscillations of Brillouin waves in both forward and backward directions. With a Brillouin pump power of 15.3 dBm, approximately up to 17 Brillouin Stokes lines are generated which is tunable over 40 nm tuning range.

Photonic crystal fiber-based multi-wavelength Brillouin fiber laser with dual-pass amplification configuration

A simple technique for achieving a stable, room temperature and multi-wavelength lasing with narrow linewidth is demonstrated using Brillouin fiber laser (BFL) with a 100-m-long photonic crystal fiber (PCF) in conjunction with a dual-pass configuration. A broadband fiber Bragg grating (FBG) operating in the C-band region is incorporated at the end side of the setup to allow a dual-pass operation. The proposed BFL can operate at any wavelength depending on the Brillouin pump wavelength and the FBGs reflection region used. With a Brillouin pump (BP) of 15.7 dBm, approximately 7 Stokes and 4 anti-Stokes lines are obtained with a line spacing of 0.08 nm.

Q-switched multi-wavelength Brillouin erbium fiber laser

In this paper, a demonstration of performance of a multi-wavelength Brillouin Erbium Fiber Laser (BEFL) with double Brillouin spacing (DBS) output comb and Q-switching characteristics featuring a figure-of-eight configuration is presented. It utilizes a four-port circulator to discriminate the odd and even order Stokes lines which allows, using 7 km long dispersion shifted fiber (DSF), the generation of a spectrum with DBS, multi-wavelength comb of nine lasing lines and a 0.16 nm spacing. The Q-switched pulse trains are obtained from the proposed BEFL configured with the DSF and pumped at 1480 nm and power ranging from 20 mW to 40 mW based on relaxation oscillation technique. It has the highest repetition rate of 609 kHz and the smallest pulse width of 0.73 μs at the pump power of 40 mW. The highest pulse energy of 6.15 nJ is obtained at pump power of 30 mW. The repetition rate and pulse width of the BEFL are reduced by replacing the DSF with 10 km long nonzero dispersion shifted fiber (NZ-DSF).

Investigation on stimulated Brillouin scattering characteristics in a highly doped Bismuth-based Erbium-doped fiber

Stimulated Brillouin scattering (SBS) characteristics in a 49 cm long highly doped Bismuth-based Erbium doped fiber (Bi-EDF) is investigated in the ring and linear cavity configurations. At Brillouin pump (BP) power of 6 dBm, the Brillouin laser peak power of the optimized ring Brillouin Erbium fiber laser (BEFL) is obtained at 23 dB higher than the peak power of the conventional linear cavity at an up shifted wavelength of 0.08 nm. This Bi-EDF ring cavity operates at nearly 1563 nm wavelength region, which is up-shifted by 0.08 nm from the Brillouin pump wavelength with the side mode suppression ratios (SMSR) of 29 and 23 dB in the forward and backward directions, respectively.