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Mode locked fiber ring laser using graphene nanoparticles as saturable absorbers to compress the pulse width has been studied. An experimental method to demonstrate the generation of pulse train with 50 GHz repetition rate with an ultrashort pulse width has been demonstrated. This method uses a combination of rational harmonic mode-locking (RHML) and a saturable absorber in the fiber ring laser. The pulse width using saturable absorbers is shorter by about a factor of 2 compared to that without a saturable absorber. Pulse generation using fiber ring laser with a saturable absorber has been analyzed. The experimental results are in agreement with the results from the simulation.

A fiber ring-cavity laser based on InP/InGaAsP multi-quantum wells semiconductor optical amplifier is proposed and experimentally demonstrated. The laser uses InP/InGaAsP multi-quantum as well as the gain medium and fiber Bragg grating as the wavelength selector. It’s demonstrated that the center wavelength of the output amplified spontaneous emission spectrum for the InP/InGaAsP multiple-quantum wells appears blue shift when its injection current increases. A lasing at central wavelength of 1549.66 nm with the maximum output power of 1.524 mW is obtained with electro-optical efficiency of 1.1% at injection current of 220 mA and the fiber Bragg grating operating temperature of 23${}^{\circ }$C. The threshold injection current of the laser is 78 mA. When the operating temperature of fiber Bragg grating increases from 8${}^{\circ }$C to 28${}^{\circ }$C, the center wavelength of output laser increases from 1549.27 to 1549.59 nm. It shows that the laser has good temperature stability.

The effect of semiconductor saturable absorber mirror (SESAM) on continuous-wave multi-wavelength fiber ring-cavity laser with semiconductor optical amplifier (SOA) is experimentally demonstrated. The evolutionary process of multi-wavelength oscillation and the decrease of oscillating mode number caused by an SESAM are discussed. It’s found that the free oscillating mode number of the multi-wavelength fiber ring-cavity laser with SOA can be upto three, and the lasing wavelengths are 1573.8 nm, 1578.09 nm and 1582.37 nm, respectively. When a SESAM is inserted in the fiber ring-cavity, it narrows the amplified spontaneous emission (ASE) spectrum of the SOA, and the oscillating mode number of the multi-wavelength fiber ring-cavity lasers with SOA decreases to two, a stable dual-wavelength lasing at 1560.91 nm and 1564.12 nm is obtained.

The corrosion products formed on the internal surfaces of the primary system are the major factor that generates radioactive contaminants such as oxide films and cruds during decommissioning, causing radiation exposure to workers. Thus, decontamination of nuclear facility surfaces is crucial to ensure the safe completion of decommissioning work. This study applied laser decontamination, which enables precise work while minimizing the deformation of the material surface through the control of process parameters, and investigated the characteristics of the decontaminated area. Specimens coated with Ni-ferrite on an aluminum alloy (A6061) substrate were fabricated and used in this experiment. Laser decontamination was performed using a low-power Q’switching fiber laser while varying the laser beam overlap rate and number of scans. The results of laser decontamination differed by the process parameters and material characteristics. It is determined that high decontamination efficiency can be achieved if appropriate conditions are applied.

Q-switched fiber lasers are very attractive sources in many applications such as in military affairs, surgical operation, laser machining, laser marking, nonlinear frequency conversion, range finding, remote sensing and optical time domain reflectometer. Our goal is to improve the pulse energy of a Q-switched fiber laser. In this paper, certain feasible methods to improve the pulse energy are presented, with their theoretical basis clarified, which may be helpful for the design of kindred Q-switched fiber lasers.

Q-switched fiber lasers are very attractive sources in many applications such as military affairs, surgical operation, laser machining, laser marking, nonlinear frequency conversion, range finding, remote sensing and optical time domain reflectometer. To improve the peak power of Q-switched fiber laser is what we pursue, and to know the factors that influence the peak power is what we should make clear first. In this paper, certain essential factors that influence the peak power are presented, with their theoretical basis clarified, which may be helpful to the design of the kindred Q-switched fiber lasers.

The author has experimentally demonstrated a wavelength switching single cavity fiber ring laser incorporating a Mach–Zehnder interferometer with two optical wavelength thin film filters. By changing the radius of the fiber bending in one path, the wavelength gradually shifts from one wavelength to another or forms a dual-wavelength operation due to the laser gain competition depending on the path loss.

Presently in shipbuilding, transportation and aerospace industries, the potential to apply welding using laser and laser-arc hybrid heat sources is widely under research. This study has the purpose of comparing the weldability depending on the arc mode by varying the welding modes of arc heat sources in applying laser-arc hybrid welding to aluminum alloy and of implementing efficient hybrid welding while controlling heat input. In the experimental study, we found that hybrid welding using CMT mode produced deeper penetration and sounder bead surface than those characteristics produced during only laser welding, with less heat input compared to that required in pulsed arc mode.

Based on the extended scalar nonlinear Schrödinger equation, the influences of pumping schemes on the properties of dissipative soliton are investigated theoretically in passively mode-locked ytterbium-doped fiber laser with positive dispersion cavity. Results show that, under the conditions of the same initial total gain, the dissipative solitons obtained in the backward pumping fiber laser have the narrowest spectral width, shortest pulse duration and highest pulse peak power for the forward, backward and bidirectional pumping schemes, moreover, the linear fitting degree of pulse chirp is lowest. With the same gain saturation energy, the pulse energies of the dissipative solitons are equal for three pumping schemes, but the differences of output spectra and temporal waveforms increase as the gain saturation energy increases.

We demonstrate the generation of harmonic mode-locking (HML) in an erbium-doped fiber laser with a microfiber-based rhenium disulfide (ReS₂) saturable absorber (SA). Taking advantages of both saturable absorption and large third-order nonlinear effect of ReS₂, HML pulse with 318.5 MHz repetition rate can be obtained, corresponding to 168th harmonic of fundamental repetition frequency of 1.896 MHz. When the pump power is increased gradually, the pulse interval remains constant, while the output power increases linearly. At the pump power of 450 mW, the output power is $\sim$12 mW. The proposed high-repetition-rate pulse lasers would attract considerable attention due to its potential applications in soliton communications and frequency combs.

Passively Q-switched fiber laser (PQFL) has great potential applications in remote sensing, ranging, and optical communications. However, the PQFLs were seldom studied in view of both theory and experiment. This paper is dedicated to make up for this shortcoming. On the one hand, by describing the coupling rate equations of the PQFL system, the Q-switched pulse output with a modulation frequency of 17.61 kHz and a modulation period of 56.8 μs was obtained at 140 mW pump power. On the other hand, an erbium-doped PQFL whose performance is tunable by controlling the pump power and polarization state was constructed by using a single-walled carbon nanotube (SWCNT) as the saturable absorber (SA). The Q-switched pulse with a repetition rate of 17.61 kHz and a signal-to-noise ratio of 50.2 dB was output at a pump power of 140 mW. The theoretical simulation results were in good agreement with the experimental results. It was also verified from such two aspects that the repetition rate of the output pulse of PQFL was approximately proportional to the pump power. This research promotes the theory and design of PQFL.

We review recent results on periodic pulsations of the soliton parameters in a passively mode-locked fiber laser. Solitons change their shape, amplitude, width and velocity periodically in time. These pulsations are limit cycles of a dissipative nonlinear system in an infinite-dimensional phase space. Pulsation periods can vary from a few to hundreds of round trips. We present a continuous model of a laser as well as a model with parameter management. The results of the modeling are supported with experimental results obtained using a fiber laser.

Erbium-doped unidirectional fiber ring laser has been passively mode-locked with a novel ultra-fast semiconductor saturable absorber used in transmission. The structure is based on InGaAs/InP multiple quantum wells grown on an InP substrate. Different structures with recovery time down to picosecond have been tested. Relaxation time reduction have been obtained by iron doping. With such structures, detrimental regimes such as Q-switch and Q-switch/ModeLock regimes have been avoided. Solitonic and slightly stretched-pulse dispersion regimes have been tested. The laser delivers for both, completely self-starting picosecond pulses of 8 mW maximum average output power at a repetition rate around 25 MHz.

The effect of Brillouin backscattering on the stability of a high power continuously pumped fiber laser is theoretically analyzed in the general framework of two-coupled modes laser model. It is demonstrated that, depending on the cavity losses, different type of instabilities can arise. Low loss cavity favours stable continuous regime in a large range of pumping rates while high loss configuration permits the emergence of different self-pulsing instabilities.

In this paper, we demonstrated a novel multi-wavelength fiber laser system operating in the O-band (1310 nm) region. The proposed O-band multi-wavelength fiber laser uses a 1 × 24 Arrayed Waveguide Grating to generate eight output channels simultaneously with a span width of 14.05 nm. In addition to this, the tunability of a single wavelength output is also demonstrated using a 1 × 16 AWG together with an optical channel selector. A Semiconductor Optical Amplifier (SOA) operating at 1310 nm is used as the gain medium to provide the spontaneous and stimulated emissions required for the laser operation. The fiber laser has a tuning range of 1301.26 nm to 1311.18 nm with 9.92 nm span and channel spacing of 0.7 nm.

We have demonstrated numerically a passively mode-locked fiber laser based on nonlinear optical loop mirror with a semiconductor optical amplifier (SOA). Its operation principle is based on the creation of nonlinear phase shift difference between the counter propagating beams through the use of SOA and a half-wavelength plate (HWP) in the loop. This is a novel passively mode-locked fiber laser based on SOA.

We report on a wavelength-tunable large-normal-dispersion erbium-doped mode-locking fiber oscillator. By using a grating as spectral filter, the intra-cavity mode-locking spectrum can be tuned continuously. The laser produces 250fs pulses with average power of 130mW and a tunable center wavelength range from 1528nm to 1570nm.

We demonstrated an all-fiber mode-locked Thulium–Holmium co-doped fiber laser (THDFL) based on molybdenum disulfide (MoS₂) tape saturable absorber. The THDFL generates a mode-locked pulse in anomalous regime at 1,979nm using 5m long Thulium–Holmium co-doped (THDF) as a gain medium. Through mechanical exfoliation method, the MoS₂ was mechanically extracted from a commercial MoS₂ crystal by using a clear scotch tape. Through balanced twin-detector measurement, the obtained MoS₂ tape has a nonlinear absorption of 10% with 100MW/cm² saturation intensity. Under 775mW to 852mW pump power, a stable pulse train was obtained at 9.12MHz repetition rate with a signal-to-noise ratio (SNR) of 45dB. The maximum output power and pulse energy were measured about 20mW and 2.2nJ, respectively. With a 3-dB spectral bandwidth of 2.1nm, the minimum possible pulse width was determined as 1.97ps.

We propose and demonstrate a dispersion-independent erbium-doped mode-locked fiber laser by incorporating a chirped fiber Bragg grating (CFBG) into the laser cavity. Our experimental results show that the fiber laser has similar output characteristics, no matter which section of the CFBG is connected to the laser cavity through a circulator, i.e., opposite dispersion is introduced into the laser cavity. Dispersion independent feature is attributed to the relatively large nonlinearity of the laser cavity with certain bandwidth. This enriches the laser dynamics and provides a new idea for the design of new lasers.

We report an experimental observation of a singular soliton dynamics in a mode-locked erbium doped fiber laser. This is the first time, to our knowledge, that output intensity exhibits a cyclic transition from a single-pulse to a multi-pulse regime for a fixed value of both pumping power and polarization controllers orientation. Moreover, the pulse duration of the single- and multi-pulse regimes is the same, in contrast with what is usually observed.