Sin Jin Tan

Performance Comparison of Mode-Locked Erbium-Doped Fiber Laser with Nonlinear Polarization Rotation and Saturable Absorber Approaches

A mode-locked erbium-doped fiber laser (EDFL) is demonstrated using a highly concentrated erbium-doped fiber (EDF) as the gain medium in a ring configuration with and without a saturable absorber (SA). Without the SA, the proposed laser generates soliton pulses with a repetition rate of 12 MHz, pulse width of 1.11 ps and energy pulse of 1.6 pJ. By incorporating SA in the ring cavity, the optical output of the laser changes from soliton to stretched pulses due to the slight change in the group velocity dispersion. With the SA, a cleaner pulse is obtained with a repetition rate of 11.3 MHz, a pulse width of 0.58 ps and a pulse energy of 2.3 pJ.

Nonlinear Polarization Rotation-Based Mode-Locked Erbium-Doped Fiber Laser with Three Switchable Operation States

A simple mode-locked erbium-doped fiber laser (EDFL) with three switchable operation states is proposed and demonstrated based on nonlinear polarization rotation. The EDFL generates a stable square pulse at a third harmonic pulse repetition rate of 87 kHz as the 1480 nm pump power increases from the threshold of 17.5 mW to 34.3 mW. The square pulse duration increases from 105 ns to 245 ns as the pump power increases within this region. The pulse operation switches to the second operation state as the pump power is varied from 48.2 mW to 116.7 mW. The laser operates at a fundamental repetition rate of 29 kHz with a fixed pulse width of 8.5 μs within the pump power region. At a pump power of 116.7 mW, the average output power is 3.84 mW, which corresponds to the pulse energy of 131.5 nJ. When the pump power continues to increase, the pulse train experiences unstable oscillation before it reaches the third stable operation state within a pump power region of 138.9 mW to 145.0 mW. Within this region, the EDFL produces a fixed pulse width of 2.8 μs and a harmonic pulse repetition rate of 58 kHz.

Multi-wavelength Q-switched Erbium-doped fiber laser with photonic crystal fiber and multi-walled carbon nanotubes

A simple multi-wavelength passively Q-switched Erbium-doped fiber laser (EDFL) is demonstrated using low-cost multi-walled carbon nanotubes (MWCNTs)-based saturable absorber, which is prepared using polyvinyl alcohol as a host polymer. The multi-wavelength operation is achieved based on non-linear polarization rotation effect by incorporating 50 m long photonic crystal fiber in the ring cavity. The EDFL produces a stable multi-wavelength comb spectrum for more than 14 lines with a fixed spacing of 0.48 nm. The laser also demonstrates a stable pulse train with the repetition rate increasing from 14.9 to 25.4 kHz as the pump power increases from the threshold power of 69.0 mW to the maximum pump power of 133.8 mW. The minimum pulse width of 4.4 μs was obtained at the maximum pump power of 133.8 mW while the highest energy of 0.74 nJ was obtained at the pump power of 69.0 mW.

A Q-switched multi-wavelength Brillouin erbium fiber laser with a single-walled carbon nanotube saturable absorber

A Q-switched multi-wavelength Brillouin erbium fiber laser (MWBEFL) is demonstrated using a single-walled carbon nanotube–polyethylene oxide (SWCNT–PEO) saturable absorber (SA). The SA is fabricated by cutting off a small part of the developed SWCNT–PEO film and sandwiching it in between two FC/PC (fiber connector/physical contact) fiber connectors. Multi-wavelength combs with ten lasing lines and spacing of 0.158 nm are obtained by the use of 2 km long dispersion compensating fiber as the Brillouin gain medium and a four-port circulator to isolate and circulate the odd-order Stokes signals. Q-switched pulse trains with a repetition rate of 105.2 kHz and a pulse width of 0.996 μs are obtained in the proposed MWBEFL at a 1480 nm pump power of 120 mW and a Brillouin pump power of 5.4 dBm.

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.

Multi-wavelength fiber laser based on nonlinear polarization rotation in semiconductor optical amplifier and photonic crystal fiber

A nonlinear polarisation rotation (NPR) based multi-wavelength laser source is demonstrated using a semiconductor optical amplifier (SOA) and photonic crystal fiber (PCF). The SOA acts as not only the gain medium but also the phase retarder for multi-wavelength oscillation in conjunction with an isolator. The incorporation of PCF improves the NPR effect and thus assists in the multiwavelength generation. The wavelength spacing reduces from 4.82 to 2.76 nm as the PCF length increases from 50 to 100 m. With a 100 m long PCF, the proposed laser produces at least 42 lasing wavelengths with optical signal to noise ratio of more than 10 dB.

Q-Switching Pulse Generation with Thulium-Doped Fiber Saturable Absorber

A simple Q-switched erbium-doped fiber laser (EDFL) is proposed and demonstrated by using a 2-m-long thulium-doped fiber (TDF) as a passive saturable absorber (SA). The EDFL generates a Q-switching pulse operating at 1557.6 nm at a threshold pump power as low as 20.0 mW. The Q-switching operation is maintained before disappearance when the pump power is above 33.7 mW. This is due to the fact that the TDF SA could not fully recover in time after a pulse and less gain population is excited before the next pulsing. With the SA, the laser produces a stable pulse train with repetition rate ranging from 3.9 to 12.7 kHz and the pulse width reduces from 20.6 to 7.4 μs while varying the 1480 nm pump power from 20 mW to 33.7 mW. The maximum pulse energy of 22.8 nJ is obtained at a pump power of 20.0 mW. The laser is perspective for technology processes and medicine.

Effect of doped fiber length on the stretch pulses of a mode-locked erbium-doped fiber laser

A passively self-starting mode-locked fiber ring laser is demonstrated using a highly concentrated Erbium doped fiber (EDF) with a saturable absorber. The effect of EDF length on the performance of the laser is investigated. Stable stretched pulses are obtained at wavelength region of 1560nm with a repetition rate ranging from 10.1 to 12.1 MHz and a pulse width stretching from 0.52 to 0.75 ps as the EDF length is reduced from 4.5 to 1.5 m. The repetition rate goes higher as the cavity length decreases when a shorter EDF is used but the pulse width reduces as the EDF length increases since the total group velocity dispersion (GVD) in the cavity is close to zero. The article is published in the original.

Investigation of Q-Switching Characteristics in Single- and Double-Spacing Multi-Wavelength Brillouin Erbium Fiber Laser

A multi-wavelength Brillouin erbium fiber laser (BEFL) with a Q-switching characteristic is demonstrated using a piece of non-zero dispersion shifted fiber (NZ-DSF) as a Brillouin gain medium (BGM) in conjunction with relaxation oscillation technique. The performance of the multi-wavelength short pulse generation is investigated for two different BEFL configurations for single and double Brillouin spacing outputs. The Q-switched BEFL generates a pulse train with repetition rates of 10.36 and 20.41 kHz whose corresponding pulse widths are 13.21 and 3.84 μs for the single and double Brillouin spacing outputs, respectively. The self-starting pulses are obtained within a low 1480-nm pump power region at a slightly higher power than the lasing threshold power. This pulse laser based on stimulated Brillouin scattering (SBS) is fairly stable at room temperature.

Dual-cavity dual-output multi-wavelength fiber laser based on nonlinear polarization rotation effect

We demonstrate a multi-wavelength fiber laser based on nonlinear polarization rotation (NPR) in dual-cavity configuration with two output ports. The laser employs a piece of erbium doped fiber (EDF) and semiconductor optical amplifier (SOA) as the gain medium in a separate cavity. By incorporating PCF in the dual cavity the non-linear polarization rotation (NPR) effect is enhanced and thus higher output and more oscillating lasing can be achieved. The laser produces three strong lines with a spacing of 2.40 nm and side mode suppression ratio (SMSR) of more than 10 dB at 1535 nm region. Another output produces 8 lines of optical comb with a spacing of 0.54 at 1570 nm region.