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Register a new userRevealing the behavior of soliton build-up in a mode-locked laser
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Real-time spectroscopy based on an emerging time-stretch technique can map the spectral information of optical waves into the time domain, opening several fascinating explorations of nonlinear dynamics in mode-locked lasers. However, the self-starting process of mode-locked lasers is quite sensitive to the environmental perturbation, which causes the transient behavior of laser to deviate from the true build-up process of solitons. Here, we optimize the laser system to improve its stability that suppresses the Q-switched lasing induced by the environmental perturbation. We therefore demonstrate the first observation of the entire build-up process of solitons in a mode-locked laser, revealing two possible ways to generate the temporal solitons. One way includes the dynamics of raised relaxation oscillation, quasi mode-locking stage, spectral beating behavior, and finally the stable single-soliton mode-locking. The other way contains, however, an extra transient bound-state stage before the final single-pulse mode-locking operation.
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Cross phase modulation (XPM) could induce soliton trapping in nonlinear medium, which has been employed to achieve vector soliton, optical switching and optical analog of gravity-like potentials. These results are generally within the definition in Hamilton system. Here, we report on the observation of a XPM-forced frequency-oscillating soliton (XFOS) whose wavelength exhibits redshift and blueshift periodically like dancing in a mode-locked fiber laser under moderate birefringence. XFOS consists of two orthogonally polarized components exhibiting simultaneous frequency oscillation driven by XPM and gain effect, which allows withstanding higher pulse energy. The pulse trapping is maintained by differentiating the frequency-shift rate. Numerical simulations agree very well with experimental results, revealing an idiosyncratic evolution dynamic for asymmetry pulses in nonlinear dissipative system and envisaging a technique to control pulse feature with preset pulse chirp. XFOS may exist generally in polarization-independent ultrafast lasers, which enriches soliton family and brings useful insights into nonlinear science and applications.
By means of the emerging Dispersive Fourier transformation technique, we captured the pulse-resolved spectral evolution dynamics of the double-soliton (DS) states in a single-walled carbon nanotube based Er-doped fiber laser from the initial fluctuations, monitoring the evolution process up to 10 seconds (corresponding to ~260 million roundtrips) discontinuously. Two distinctly different evolutionary types of DS states have been investigated in detail: splitting from one pulse and forming simultaneously. Relaxation oscillations, beating, transient bound state, spectral broadening and pulse interval dynamics have been observed in the evolution process of the DS operation. Our study will be helpful for the further research of mode-locking operation.
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Alexey Andrianov
, Arkady Kim (Institute of Applied Physics of then Russian Academy of Sciences
, Nizhny Novgorod
2019
We present the first direct observation of the bound state of multiple dissipative optical solitons in which bond length and bond strength can be individually controlled in a broad range in a regular manner. We have observed experimentally a new type of stable and extremely elastic soliton crystals that can be stretched and compressed many times conserving their structure by adjusting the bond properties in real time in a specially designed passively mode-locked fiber laser incorporating highly asymmetric tunable Mach-Zehnder interferometer. The temporal structure and dynamics of the generated soliton crystals have been studied using an asynchronous optical sampling system with picosecond resolution. We demonstrated that stable and robust soliton crystal can be formed by two types of primitive structures: single dissipative solitons, and(or) pairs of dissipative soliton and pulse with lower amplitude. Continuous stretching and compression of a soliton crystal with extraordinary high ratio of more than 30 has been demonstrated with a smallest recorded separation between pulses as low as 5 ps corresponding to an effective repetition frequency of 200 GHz. Collective pulse dynamics, including soliton crystal self-assembling, cracking and transformation of crystals comprising pulse pairs to the crystals of similar pulses has been observed experimentally.
We study experimentally and theoretically the interactions among ultrashort optical pulses in the soliton rain multiple-pulse dynamics of a fiber laser. The laser is mode-locked by a graphene saturable absorber fabricated using the mechanical transfer technique. Dissipative optical solitons aggregate into pulse bunches that exhibit complex behavior, which includes acceleration and bi-directional motion in the moving reference frame. The drift speed and direction depend on the bunch size and relative location in the cavity, punctuated by abrupt changes under bunch collisions. We model the main effects using the recently proposed noise-mediated pulse interaction mechanism, and obtain a good agreement with experiments. This highlights the major role of long-range Casimir-like interactions over dynamical pattern formations within ultrafast lasers.
By identifying the similarities between the coupled-wave equations and the parametrically driven nonlinear Schrodinger equation, we unveil the existence condition of the quadratic soliton mode-locked degenerate optical parametric oscillator in the previously unexplored parameter space of near-zero group velocity mismatch. We study the nature of the quadratic solitons and divide their dynamics into two distinctive branches depending on the system parameters. We find the nonlinear interaction between the resonant pump and signal results in phenomena that resemble the dispersive two-photon absorption and the dispersive Kerr effect. Origin of the quadratic soliton perturbation is identified and strategy to mitigate its detrimental effect is developed. Terahertz comb bandwidth and femtosecond pulse duration are attainable in an example periodically poled lithium niobate waveguide resonator in the short-wave infrared and an example orientation-patterned gallium arsenide free-space cavity in the long-wave infrared. The quadratic soliton mode-locking principle can be extended to other material platforms, making it a competitive ultrashort pulse and broadband comb source architecture at the mid-infrared.
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