Multipulse Generation Research Articles

Flat-topped optical spectrum as a specific marker of multi-pulse grouping in a soliton fiber laser.

We report the experimental observation of a stable generation regime in a soliton fiber laser, characterized by a distinct flat-topped optical spectrum. Notably, in multi-pulse generation, this specific spectrum shape prevents the harmonic mode-locking state, instead connecting the solitons into bound complexes or tight chaotic bunches. Physically, this suggests that in the observed regime, long-range attractive forces dominate over the inter-pulse repulsion across the entire laser cavity. Our experimental findings align with numerical simulations, which demonstrate that the predominance of a long-range inter-pulse attraction is due to a complex interaction mechanism. This mechanism combines the generation of dispersive waves with dissipative forces arising from gain depletion and recovery.

Coherence evolution of multi-pulse pumped supercontinuum generation in all-normal dispersion fibers

We numerically calculate the coherence of supercontinuum (SC) spectrum generated in all-normal dispersion (ANDi) fibers by multiple picosecond pulses. We show that multi-pulse pumping significantly mitigates the phenomenon of coherence degradation and maintains high spectral coherence over a broader wavelength range compared to the single pumping. It is found that inter-pulse four-wave-mixing (FWM) and stimulated Raman scattering (SRS) significantly contribute to the superior coherence characteristics of the SC. We further discuss the impact of key parameters on the multi-pulse pumped SC. Results indicate that a large temporal interval between pulses reduces spectral broadening efficiency, while closely spaced pulses generate a significant number of incoherent photons, severely degrading spectral coherence. Introducing initial chirp effectively mitigates this coherence degradation. A slight increase in the dispersion parameter notably suppresses the spectral broadening efficiency of the multi-pulse generation. Pulse shape primarily affects the SC shape without significantly impacting the spectral broadening efficiency.

Manipulation of tunable soliton molecule generation in a fiber laser

On-demand soliton molecule (SM) generation is an advanced coherent multipulse technique in the field of nonlinear optics. Experimentally generating controllable SMs is a significant challenge. Here, we propose to manipulate the generation of tunable SMs in a mode-locked fiber laser based on the self-constructed cascaded compound filtering effect. The cascaded compound filter is achieved by incorporating nonlinear polarization rotation (NPR) filtering into two-stage Lyot filtering for performing a multiplication operation between these two filtering functions. Tunable SMs with flexible parameters of the internal soliton spacings from 4.64 to 6.47 ps, pulse numbers from 2 to 26 and some special phases of ∼ π and ∼ 0.5π are experimentally created on demand by adjusting the cascaded compound filtering profiles. The simulation of SM generation in a fiber laser is carried out to reproduce the transient processes of experimental observations, which reveals that cascaded compound filtering is beneficial for manipulating the generation of SMs. Our research provides a good platform for studying coherent multipulse generation in a dissipative nonlinear system and a novel method for manipulating tunable SM generation.

All-fiber wavelength-widely tunable multi-pulse gain-switched Tm3+-doped double-clad fiber laser

We report a wavelength-widely tunable multi-pulse gain-switched Tm3+-doped fiber laser. The laser has a continuous wavelength-tunable range of 105 nm in 2 μm band. The combination of Tm3+-doped double clad fiber and 793 nm pulsed pump source achieves large-energy pulse and multi-pulse operation. The single-pulse energy can reach 4.3 μJ and the multi-pulse energy can be 13.2 μJ. The effects of pump pulse energy, pulse repetition rate and pulse duration on multi-pulse generation are studied in detail. This easy-to-operate large-energy 2 μm pulsed fiber laser with adjustable pulse duration and repetition rate can provide a stable single-pulse or multi-pulse source in spectroscopy, medical surgery, material processing, etc.

Influence of Spectral Filtration on Pulse Dynamics in Ring-Cavity Mamyshev Oscillator

Here we present a numerical study of pulsing build-up dynamics inside the fiber Mamyshev Oscillator (MO). The main scope of the investigation is to describe the influence of the spectral separation between the filters on self-starting MO dynamics and transition from multipulse to single-pulse generation regimes. It was found that Floquet stability analysis provides a straightforward way to determine whether the system will be self-starting or if it has to be excited by external source and predicts the repetition rate of the pulse train. We showed that spectrally overlapped bandpass filters provide reliable multi-pulse generation due to Faraday instability. Adiabatic increase in the spectral separation between the filters decreases the number of pulses down to single-pulse regime, therefore providing a flexible way to generate adjustable number of mode-locked pulses on demand.

Nature of soliton interaction in fiber lasers with continuous external optical injection

It has been shown by numerical simulation that the nonlinear interaction between a laser soliton and an injected monochromatic cw results in their phase locking. As a consequence, the velocity of the soliton begins to depend on the amplitude and frequency of the injected radiation. It has been found that if the frequency of the external signal coincides with the frequency of the dispersive waves emitted by solitons in a laser cavity with lumped intracavity elements, a mechanism for controlling long-range soliton interaction occurs. This mechanism is related to the interference between the injected wave and the dispersive waves involved in the strong long-range interaction between solitons. We have demonstrated the mechanism of soliton-soliton repulsion and, as its consequence, the occurrence of harmonic passive mode locking (multipulse generation with an equidistant arrangement of identical solitons in the laser cavity).

Route to stabilized ultrabroadband microresonator-based frequency combs

We perform the first theoretical modeling of the full spectral-temporal dynamics of octave-spanning parametric microresonator comb generation through use of the Lugiato-Lefever model extended to include higher-order dispersion and self-steepening. We show that three distinct stages are necessary to achieve single-pulse modelocking and discuss the dispersion characteristics required for ultrabroadband, stabilized comb generation. Our simulations agree well with previous experimental demonstrations and predict many of the observed features, including multipulse generation, dispersive wave generation, modelocking, and comb stabilization.

Competition and coexistence of ultrashort pulses in passive mode-locked lasers under dissipative-soliton-resonance conditions

It has been shown by numerical simulation that the dissipative soliton resonance suppresses the appearance of new ultrashort pulses in the laser cavity that usually arise with increasing pumping. As a consequence, the energy of the pulses can reach an arbitrarily large value, which is determined by the corresponding pump power. The mechanism of the suppression is due to interaction between pulses through a saturable gain medium. The generation remains multistable: the number of pulses in steady-state operation depends on the initial conditions. In the case of multipulse generation, all pulses have identical durations, shapes, peak intensities, and chirps. The effect of maintaining single pulse operation with increasing pump power can be used to generate high-energy pulses.

利用脉冲循环产生高压多脉冲

利用脉冲循环产生高压多脉冲

A XeCl laser with a controlled radiation pulse shape

The pump parameters of a three-contour excitation system are studied in a gas-discharge excimer XeCl laser using a Ne—Xe—HCl mixture. A computation model is developed for finding the parameters of multi-contour excitation systems. A setup incorporating a three-contour system for excitation and automatic UV preionisation is designed, which provides multipulse generation of 65-ns, 26-mJ laser pulses at the laser efficiency of 1%. It is shown that generation of short radiation pulses of duration 7 ns and relatively long pulses of duration 65 ns in the multipulse generation regime is possible in the excitation system under study in Xe:HCl = 20:1 mixtures containing neon as buffer gas.

Stable multipulse generation from a self-mode-locked Ti:sapphire laser

Multipulses up to 6 pulses are generated from a self-mode-locked Ti:sapphire laser with slightly altered cavity configurations. Double and triple pulse operations are found to be very stable and last for several hours. It is noted that the pulse interval takes discrete values of ∼80 fs interval and its distribution is strongly dependent on the stability of the multipulse oscillation. The laser spectrum in multipulse operation shows a clear periodic modulation, indicating that pulse shaping is attained under the transform-limited condition. It is demonstrated that the application of the external pulse shaping technique to the present multipulse generation widely expands the pulse shaping capability.

Effect of gain switching frequency on ultrashort pulse generation from laser diodes

In this work, the effects of gain switching frequency on ultrashort pulse generation are investigated using a model based on the multi-mode rate equations. In addition to the commonly used laser diode parameters, the key parameters corresponding to the different laser diode materials and structures are included in the model. Effects of some laser diode parameters, and d.c. and RF drive conditions on the full width at half-maximum (FWHM) of gain switched pulses are investigated for the 1–15 GHz gain switching frequency range. Multi-pulse generation and the cut-off frequency of gain switching are also determined for this frequency range. It is found that the FWHM of pulses decrease as the RF current is increased, at a constant frequency. However, the FWHM of pulses either decrease or increase as the d.c. bias is increased, depending especially on the gain compression and gain peak. As the frequency is increased, pulse widths start to decrease or increase depending on the laser diode parameters. The FWHM of pulses for shorter cavity lasers are found to be almost insensitive to the frequency. Among the parameters affecting the multi-pulse generation and cut-off, gain compression, gain constant, and d.c. and RF current amplitudes are found to be the most effective. All calculations are also carried out using single-mode rate equations and results of multi-mode and single-mode solutions are compared.