Xueming Liu’s research while affiliated with Nanjing University of Information Science and Technology and other places

Vector soliton originates from the soliton trapping dynamics via cross-phase modulation (XPM) which has been used to achieve supercontinuum, optical switching and optical analog of gravity-like potentials. Dual-state vector soliton (DSVS) is reported in mode-locked fiber laser under appropriate birefringence. Two vector soliton states emitted alternatively display double-peak and Lorentz-shaped spectral profile, respectively. The two orthogonally polarized components of the double-peak spectrum exhibit obvious redshift and blueshift, respectively, while the frequency shift for the other state is limited even with the reversed shift direction, which illustrates a unique vector soliton evolution dynamic. DSVS originates from the pulse trapping induced by XPM, as well as the periodical evolution and frequency shift induced by self-phase modulation under dispersion-managed condition. The vector period-doubling phenomenon will further enrich the understanding about soliton, and also guide the design of mode-locked laser.

Soliton molecules have been a striking research area, which is significant for the exploration of physical mechanism in various nonlinear systems, the analog to the molecule of matter, and the potential applications in multilevel encoding of optical communications. Here, we demonstrate a novel dichromatic soliton-molecular compound (SMC) that is a hybrid bound states of multiple pulses with two different frequencies connected by two different binding mechanisms. It exhibits unique temporal and spectral profiles that can be described as the bounded temporal and dichromatic soliton molecules. The vibrating SMCs are generated experimentally and numerically to demonstrate the intrinsic solution in the dissipative nonlinear system, which is characterized with the vibration both in time and frequency dimensions and dual-peak evolution trajectory induced by the time-frequency coupling. These results enrich the concept of soliton molecules and further promote the analogy to matter molecules.

In article number 2000216, Xueming Liu and co‐workers demonstrate novel optical nonlinear dynamics in a mode‐locked laser induced by the coupling interaction of two orthogonally polarized pulses via cross‐phase modulation (XPM). The XPM‐induced vector asymmetrical soliton displays period‐doubling spectral evolution with alternate redshift and blueshift, which is helpful to laser design and brings useful insights into the optical nonlinearity and chaos for solitons.

Cross phase modulation (XPM) can induce soliton trapping in nonlinear medium, which has been employed to achieve vector soliton, optical switching, and optical analog of gravity‐like potentials. Here, the first observation of a novel soliton operation is reported whose wavelength exhibits redshift and blueshift periodically in a mode‐locked fiber laser under appropriate birefringence and dispersion map. XPM dominates the dynamics by inducing and sustaining the vector asymmetrical soliton (VAS) with spectral period doubling, and exhibits a unique trajectory of pulse trapping. The XPM‐induced VAS is an idiosyncratic steady state featured with asymmetry in the model based on the coupled Ginzburg–Landau equation, which depicts the distinct pulse features in comparison with vector soliton, soliton molecule, and traditional period‐doubling evolutions. The two orthogonal polarized directions of mode‐locked fiber laser can be regarded as the XPM‐coupled dissipative resonators guiding the further study of the optical nonlinear dynamics and chaos for soliton, which is helpful to laser design and brings useful insights into nonlinear science and applications.

Creeping solitons, which belong to the class of pulsating solitons, can be meaningful for fundamental physics owing to their fruitful nonlinear dynamics. Their characteristics in mode-locked lasers have been studied theoretically, but it is difficult to experimentally observe evolution dynamics in real time. Here, we have experimentally observed the temporal and spectral evolution dynamics of creeping solitons in a passively mode-locked fiber laser by employing time-lens and dispersive Fourier transform technique. With the aid of Raman amplification, the measured recording length of the time lens in the asynchronous mode could be substantially improved. Temporal soliton snaking motion and spectral breathing dynamics are experimentally obtained, confirming intrinsic feature of pulsation dynamics. These results display how single-shot measurements can offer new insights into ultrafast transient dynamics in nonlinear optics.

Two-dimensional (2D) heterostructure materials have attracted increasing attention in ultrafast nonlinear optical applications due to their intriguing properties. Here, we fabricate a graphene/α-In2Se3 heterostructure by dropping α-In2Se3 dispersion onto the surface of few-layered graphene film and investigate its nonlinear optical responses. We show that the graphene/α-In2Se3 heterostructure has combined advantages of ultrafast relaxation (τ1 ∼ 78 fs, τ2 ∼ 14 ps) and a large effective nonlinear absorption coefficient (βeff ∼ −1.2 × 10⁴ cm/GW) with relatively large modulation depth. We have further integrated the heterostructure into an erbium-doped fiber laser for mode-locked pulse generation. These results indicate that graphene/α-In2Se3 heterostructures are a promising 2D material for ultrafast nonlinear optical applications.

Real-time measurement of ultrafast pulses together with high temporal resolution and long recording length is an urgent requirement of all optical communication systems and nonlinear science. Here, external motion dynamics of soliton pairs in mode-locking ultrafast fiber lasers can be single-shot characterized with long recording length, by using an asynchronous four-wave-mixing (FWM)-based temporal magnifier (AFTM) system. Recording length of more than one thousand roundtrips can be achieved through the AFTM system. Temporal propagation dynamics of soliton pairs with tunable separations are observed, revealing that soliton pairs with narrower separation display vibration-like dynamics, while the two solitons with wider separation remain relatively unchanged. We believe our results will provide a promising solution for real-time measurement of ultrafast pulse and can offer novel insights for ultrafast transient dynamics in nonlinear optics.