Transverse mode instability (TMI) has become the major limitation for power scaling of fiber lasers with nearly diffraction-limited beam quality. Compared with a co-pumped fiber laser, a counter-pumped fiber laser reveals TMI threshold enhancement through a semi-analytical model calculation. We demonstrated a 2 kW high-power counter-pumped all-fiberized laser without observation of TMI. Compared with the co-pumped scheme, the TMI threshold is enhanced at least 50% in counter-pumped scheme, moreover, stimulated Raman scattering and four-wave mixing are suppressed simultaneously.

The time-delay signature (TDS) of chaos output in a 1550 nm vertical-cavity surface-emitting laser (VCSEL) subject to fiber Bragg grating (FBG) feedback is investigated experimentally. Autocorrelation function (ACF) and mutual information (MI) are used for quantitatively identifying the TDS of chaos. For various bias currents, the TDS evolution with the feedback strength is different, as the FBG provides wavelength-selective feedback. Furthermore, based on the TDS map of the FBG feedback VCSEL (FBGF-VCSEL) in the parameter space of feedback strength and bias current, the optimal TDS suppression regions, where the dominant polarization mode of FBGF-VCSEL locates at the edge of the main lobe of FBG reflection spectrum, have been determined. Finally, for comparative purpose, the TDS of chaos in mirror feedback VCSEL (MF-VCSEL) also has been presented, and the results show that an FBGF-VCSEL possesses better TDS suppression performance than an MF-VCSEL.(XDJK2016D060).

Polarization switching (PS) characteristics in a 1550 nm vertical-cavity surface-emitting laser (VCSEL) subject to circularly polarized optical injection (CPOI) are experimentally investigated. The results show that, under different biased current, a solitary 1550 nm VCSEL can oscillate at y polarization mode (y mode), two polarization components (PCs) coexistence or x polarization mode (x mode). The PS characteristics induced by CPOI for the VCSEL operating at y mode and x mode are analyzed and the evolutions of dynamical states with the injected power are discussed. Additionally, the mappings of nonlinear dynamical states are given in the parameters space of the injected power and frequency detuning.

An external-cavity semiconductor laser with nonlinear optical feedback to generate broadband chaos with time delay signature (TDS) suppression is investigated. The system is composed of three semiconductor lasers, one of which is regarded as the chaos generator, while the other two play a role of a built-in nonlinear modulator in the external cavity of the generator. The results show that by properly setting the feedback strength and time delay of the first semiconductor laser in the nonlinear modulator, the TDS embedded in the intensity and phase time-series of the chaos can be effectively concealed in a wide range of frequency detuning.

Femtosecond laser filamentation is generally initialized from unpredictable symmetry breaking caused by random noise, causing it to be barely controlled. However, it is always anticipated for stable and controllable filamentation. We present and demonstrate the idea that hybridly polarized vector fields with axial symmetry broken polarization, associated with a pair of orthogonally linearly polarized vortices carrying the opposite-handed orbital angular momenta, could achieve controllable and robust multiple filamentation. Here, our motivation is to unveil the underlying physics behind such controllable and robust multiple filamentation. The symmetry breaking should first be actively controllable and then be able to effectively inhibit random noise. Robust multiple filamentation is inseparable from the fact that the phases between the multiple filaments are always locked. In contrast, uncontrollable multiple filamentation is always accompanied with loss of phase, i.e., the multiple filaments become incoherent to each other. Our results may offer a suggestion for achieving controllable and robust multiple filamentation in other systems.and Equipment Development Project (2012YQ17004); Collaborative Innovation Center of Extreme Optics.

A ring of three unidirectionally coupled semiconductor lasers (RTUC-SLs) is used to generate broadband chaos with no pronounced time-delay (TD) signature. Using the autocorrelation function and permutation entropy as the TD measures, we demonstrate that under suitable coupling strength, the loss of the TD signature of the lasers in the RTUC-SL configuration is achieved both for the intensity and the phase. These findings should prove valuable for developing high-quality optical chaos for potential applications, such as chaos-based communications and random number generation.

Nonlinear dynamics in an optoelectronic delayed feedback semiconductor laser and its application in sensing are studied. We analyze the theories of stability and period of the laser. A route to quasi-periodic bifurcation or a stochastic state from stability is numerically analyzed by shifting the feedback level. The induced dynamics are found to be in one of four distributions (stable, periodic pulsed, period-three pulsed, and undamping oscillating). An external injection into the laser results in the process being more or less the opposite with the conventional optical injection cases. Based on this process or the dynamic regimes, we present a modeling of the incoherent detection sensor using the nonlinear period-one characteristic of the laser. The sensor discriminates the injection light variation as a sensing signal via detecting the behaviors from the period-one laser.