Soliton molecules in femtosecond fiber lasers: universal binding mechanism and direct electronic control

Abstract

Sequences of ultrashort pulses form the basis of extremely precise laser applications ranging from femtosecond spectroscopy, to material microprocessing, to biomedical imaging. Dynamic patterns of temporal solitons—termed “soliton molecules”—inside mode-locked cavities provide yet unexplored means for generating reconfigurable arrangements of ultrashort pulses. Here, we demonstrate the external control of solitonic bound states in widespread erbium-doped fiber lasers via direct electronic modulation of the semiconductor pump source. This straightforward approach allows for switching between discrete soliton doublet states of picosecond separations, employing and relying on laser-intrinsic soliton interactions. We analyze the externally induced dynamics based on real-time switching data acquired by time-stretch dispersive Fourier transform spectroscopy and identify a universal bound-state formation mechanism different from broadly considered models. Owing to the ease of implementation and its intrinsic tunability, our control scheme is readily applicable to various laser platforms enabling, e.g., rapid multipulse measurements and tailored nonlinear light–matter interactions.

Intracavity Raman scattering couples soliton molecules with terahertz phonons

“…3a : Two initially separated solitons (red) experience different laser gain due to transient gain depletion (blue). Whereas closely spaced pulses in modelocked lasers without Kerr-lensing typically separate further apart due to the dominant role of the gain gradient 18 , 28 , here, the high Kerr nonlinearity is accompanied by significant self-steepening. In line with experimental observations, the resultant intensity-dependent group velocity difference slows the first soliton and induces approaching relative motion.…”

“…Recently, real-time spectroscopy based on the time-stretch dispersive Fourier transform (TS-DFT) has enabled high throughput measurements in laser science and nonlinear optics, yielding consecutive single-shot spectra exceeding 100 million frames per second. Following observations in passive nonlinear systems 14 , 15 , the scheme has been applied to nonlinear behavior inside ultrafast laser oscillators, opening up views into the buildup of soliton mode-locking and complex multi-soliton interactions in real-time 10 , 16 – 18 . Moreover, temporal solitons are observed to form stable and meta-stable bound states—termed “soliton molecules”—with non-commensurate temporal separation distances, spanning from picoseconds down to few 10-femtoseconds.…”

Breathing Dissipative Soliton Molecule Switching in a Bidirectional Mode‐Locked Fiber Laser

“…Moreover, the recently reported soliton molecule switching with direct electronic control identified a universal bound‐state formation mechanism different from broadly considered models, wherein the soliton coupling mechanism is based on linear reflections. [ 46 ] However, the linear reflections will lead to the soliton molecule binding with only several specific pulse temporal separations that may not be applicable to the all‐optical switching of bidirectional BSM in our experiment. The consecutive 36 switching of doublet and 10 switching of triplet BSMs (Figure 4) with different temporal separation are dominated by gain relaxation through gain depletion and recovery mechanism rather than the linear reflections.…”

Superlocalization reveals long-range synchronization of vibrating soliton molecules

“…The specific oscillation pattern depends on the laser parameters, which determine the existence and the intrinsic properties of a multi-dimensional limit-cycle attractor for dissipative solitons [6]. The actual dynamics is also affected by laser noise [7] and other experimental perturbations [8][9][10]. Beyond their fundamental appeal, soliton molecules could be involved in multi-pulse patterns of practical interest, such as in harmonic modelocking or in optical data manipulation [11].…”

“…After numerical processing, DFT spectra yield the dynamics of relative timing and phase between temporally separated pulses. As a major limitation, the related observation windows T obs is limited to pulse separations typically below a hundred of picoseconds [8][9][10]12]. Such practical limitation is due to the finite spectral resolution, which is bound on one side by the speed of the detection electronics and on another side by the magnitude of the dispersive line used for pulse stretching.…”