Dissipative Soliton Regime Research Articles

Switching and coexistence of stretched pulse and dissipative soliton in a hybrid mode-locked fiber laser

We experimentally demonstrate a thulium–holmium co-doped hybrid mode-locked fiber laser, which can operate in two modes. One is the switch between stretched pulse and dissipative soliton, the other is the dual-wavelength mode-locking corresponding to the coexistence of stretched pulse and dissipative soliton. The optical spectra of the stable dual-wavelength mode-locking pulses centers at 1905 nm and 1946 nm respectively, and the corresponding pulse widths are 5.9 ps and 823 fs. In addition, the central wavelength is in the tunable range of 27 nm when the laser operates on a dissipative soliton regime.

Three states of operation in the net-normal figure-nine fiber laser at 1560 nm

We report an experimental investigation of figure-nine-based Er-doped all-polarization-maintaining fiber laser operating in dissipative soliton regime within the net cavity dispersion ranging from +0.023 ps2 to +0.254 ps2. By changing the width of the spectral filter used inside the resonator, we observed three different states of operation that were dependent on the pumping power and the net cavity dispersion values. Indicated differences in the pulses generated from the two ports can be explained by the interferential work nature of the saturable absorber and the direction-dependent dispersion maps causing two distinct evolutions of pulse profiles. Our findings establish that, depending on the state of the operation, pulses at the reject port can offer at least comparable performance to those at the output port in net-normal mode-locked laser operating at 1.55 μm spectral range. A stability analysis has confirmed the steadiness of generated pulses over time. We examined the tunability of the laser in terms of spectral filter central wavelength and dispersion and their impact on laser operation. To our knowledge, observation of such behavior was not yet reported, and our work contributes to understanding the mechanisms of dissipative soliton generation in the 1.55 μm spectral region.

Studying the Operation of an All-PM Yb-Doped Fiber Laser Oscillator at Negative and Positive Net Cavity Dispersion

Chirped fiber Bragg gratings in Yb-doped fiber lasers allow tuning the net cavity dispersion, thus enabling access to pulse dynamics beyond the typical all-normal-dispersion dissipative soliton regime. This Letter demonstrates an ultrafast dispersion-managed all-polarization-maintaining fiber oscillator mode-locked with a nonlinear optical loop mirror. Using a chirped fiber Bragg grating inside the oscillator, it can work at net cavity dispersion in the range from -0.098 ps$^2$ up to +0.067 ps$^2$ and above at the wavelength of 1 $\mathrm{\mu}$m. Depending on the configuration, the system can deliver stable pulses with energies up to 2.3 nJ and pulse durations as short as 98 fs.

Investigation into the impact of the recovery time of a saturable absorber for stable dissipative soliton generation in Yb-doped fiber lasers.

In this study, we conduct a numerical evaluation of the impact of the recovery time of a saturable absorber (SA) on the output performance of an Yb-doped fiber laser operating in the dissipative soliton regime. Particularly, we evaluate the output pulse characteristics, such as the pulse width, spectral bandwidth, pulse peak power, and pulse energy depending on the change in recovery time. Applying a too-slow SA recovery time above a certain critical value is shown to make the output pulse unstable and broken. Furthermore, we demonstrate that there is an optimum recovery time range for stable dissipative soliton pulse generation, depending on the cavity dispersion and modulation depth of the SA. Further, we perform an additional numerical simulation of the pulse compression to demonstrate the relationship between the output dechirped pulse width and SA recovery time. The optimum approach for the generation of the shortest dechirped pulses in the dissipative soliton regime will be to construct a fiber laser cavity with a small normal cavity group velocity dispersion and use an SA with an appropriate recovery time.

Wave plate-dependent lasing regimes transitions in an all-normal-dispersion fiber laser mode-locked by nonlinear polarization rotation

We address the transitions between three different working regimes of an all-normal-dispersion pulsed fiber laser, mode-locked by nonlinear polarization rotation (NPR). In particular, we investigate numerically the dynamics and study in details the transitions induced by solely rotating the cavity wave plates. We analyze the phemomenon by putting forward a model for all-normal-dispersion NPR-moded-locked fiber laser, based on the coupled Ginzburg-Landau equations and Jones matrix. Numerical results show that depending on the values of the cavity parameters, the transitions between the dissipative soliton regime and amplifier similariton one, or the transition between the dissipative soliton regime and the splitting pulse one may be realized by simply rotating the cavity wave plates. We found that the transitions are intrinsically related to the NPR mode-locking mechanism by explicitly evaluating the polarization states across the pulse at different locations of the cavity. Our numerical results are in very good agreement with experimental results reported in the relevant literature, and provide evidence that besides gain saturation and spectral filtering, the orientations of wave plates may be exploited as a suitable degree of freedom to obtain the desired pulse regimes in all-normal-dispersion fiber lasers.

Energy Scaling of an Ultrafast All-PM-Fiber Laser Oscillator

In this article we demonstrate the first, to the best of our knowledge, all-fiber self-starting laser oscillator consisting entirely of polarization-maintaining large mode area (PLMA) fibers mode-locked with nonlinear optical loop mirror (NOLM). The system works in a Raman-free dissipative soliton regime and operates at a central wavelength of 1030 nm. It delivers stable ultrashort pulses of high energy of 12 nJ at a 7.56 MHz repetition rate which can be compressed down to the Fourier transform limit of ~250 fs. Higher energies were limited by the formation of multiple pulses in the cavity.

Development and numerical simulation of spherical microresonators based on SiO2 – GeO2 germanosilicate glasses for generation of optical frequency combs

We propose and theoretically investigate the possibility of using spherical, whispering gallery mode microresonators based on germanosilicate glasses with different GeO2 contents for generating optical frequency combs in the dissipative soliton regime under pumping at a wavelength of 1.55 or 2 μm. The dispersion and nonlinearity of microspheres of different radii are calculated and analysed, and their optimal characteristics and the expected parameters of the output radiation are determined. It is shown that the spectral widths of optical frequency combs formed in 0.8SiO2 – 0.2GeO2 and GeO2 glass microspheres pumped at λ = 1.55 and 2 μm can be ∼200 and ∼300 nm, respectively. In these cases, in addition to the dissipative soliton with a duration of ∼100 fs, the generation of dispersive waves is also observed.

All-fiber dissipative soliton Raman laser based on phosphosilicate fiber.

We propose and demonstrate an all-fiber, synchronously pumped Raman laser based on phosphosilicate fiber (P-doped fiber) for deep tissue multiphoton imaging. The laser operates in a dissipative soliton regime and produces 2.2 ps chirped pulses (compressible to 317 fs) with energy up to 9.2 nJ, 0.3 W average power and at 1240 nm center wavelength. We have also found a new cross-polarization Raman lasing operation that offers access to an important wavelength near 930 nm for calcium imaging.

Compressibility of Dissipative Solitons in Mode-Locked All-Normal-Dispersion Fiber Lasers

We numerically investigated the compressibility of dissipative soliton pulses in an all-normal-dispersion fiber laser which was mode-locked with a nonlinear optical loop mirror. A transition state within the area between the traditional dissipative soliton regime and dissipative soliton resonance regime was revealed to have much higher dechirped peak power and shorter dechirped pulse duration than its vicinity. This phenomenon is reported for the first time to the best of our knowledge. The peak power and pulse width of the dechirped pulse were calculated using the linear compression method. The dynamics and the distribution of the transition state were systematically analyzed in laser parameter spaces. The nonlinear frequency chirp was mainly induced by self-phase modulation and the pulse formation mechanism, which influenced the linear compressibility of the dissipative. We demonstrated that there were optimal filter bandwidth values corresponding to the best pulse compressibility under different laser parameters. The simulation results indicate that dechirped pulses with a pulse peak power of 0.5–1 MW, a pulse duration of the 100-fs level, and a pulse energy of ∼100 nJ can be obtained using the optimal parameters.

Generation of stretched pulses and dissipative solitons at 2 μm from an all-fiber mode-locked laser using carbon nanotube saturable absorbers.

We demonstrate for the first time, to the best of our knowledge, a thulium-doped, all-fiber, mode-locked laser using a carbon nanotube saturable absorber, operating in the dissipative-soliton regime and the stretched-pulse-soliton regime. The net dispersion of the laser cavity is adjusted by inserting different lengths of normal dispersion fiber, resulting in different mode-locking regimes. These results could serve as a foundation for the optimization of mode-locked fiber-laser cavity design at the 2μm wavelength region.

Multicolour nonlinearly bound chirped dissipative solitons.

The dissipative soliton regime is one of the most advanced ways to generate high-energy femtosecond pulses in mode-locked lasers. On the other hand, the stimulated Raman scattering in a fibre laser may convert the excess energy out of the coherent dissipative soliton to a noisy Raman pulse, thus limiting its energy. Here we demonstrate that intracavity feedback provided by re-injection of a Raman pulse into the laser cavity leads to formation of a coherent Raman dissipative soliton. Together, a dissipative soliton and a Raman dissipative soliton (of the first and second orders) form a two (three)-colour stable complex with higher total energy and broader spectrum than those of the dissipative soliton alone. Numerous applications can benefit from this approach, including frequency comb spectroscopy, transmission lines, seeding femtosecond parametric amplifiers, enhancement cavities and multiphoton fluorescence microscopy.

Nonlinear absorption of SWNT film and its effects to the operation state of pulsed fiber laser.

We study a single-wall carbon nanotube (SWNT) Polyvinyl alcohol (PVA) composite as a saturable absorber (SA) for pulse generation in Yb-doped fiber lasers. The saturable absorption and optical limiting (OL) characteristics of the SWNT device are investigated. By combing these two nonlinear effects, we find out for the first time, to the best of our knowledge, that mode-locking can be obtained in the dissipative soliton regime at low pumping followed by Q-switching at high pumping, which is quite different from conventional pulse dynamic evolutions. The Q-switched state operating at higher pump powers is due to the OL effect. The inverted operating fiber laser can be applied in various potential applications such as versatile material processing, optical communication and radar system etc.

Sub-80-fs pulses from an all-fiber-integrated dissipative-soliton laser at 1 µm

We report on a passively mode-locked femtosecond fiber oscillator using only fiber-based components without intracavity dispersion compensation. The all-normal dispersion fiber laser operates in the dissipative-soliton regime and utilizes a spectral filter for pulse shaping. The 3.8 ps long pulses with pulse energies of 3.6 nJ can be dechirped with a grating compressor to 76 fs. The output spectrum reveals a full width at half maximum of 39.7 nm and a center wavelength of 1032 nm. The repetition rate is 71 MHz. The influence of pulse energy variation is discussed.