Ultra-narrow-linewidth mode-locked lasers with wide wavelength tunability can be versatile light sources for a variety of newly emergent applications. However, it is very challenging to achieve the stable mode locking of substantially long, anomalously dispersive fiber laser cavities employing a narrowband spectral filter at the telecom band. Here, we show that a nearly dispersion-insensitive dissipative mode-locking regime can be accessed through a subtle counterbalance among significantly narrowband spectral filtering, sufficiently deep saturable absorption, and moderately strong in-fiber Kerr nonlinearity. This achieves ultra-narrow-linewidth (a few gigahertz) nearly transform-limited self-starting stable dissipative soliton generation at low repetition rates (a few megahertz) without cavity dispersion management over a broad tuning range of wavelengths covering the entire telecom C-band. This unique laser may have immediate application as an idealized pump source for high-efficiency nonlinear frequency conversion and nonclassical light generation in dispersion-engineered tightly light-confining microphotonic/nanophotonic systems.
A variety of nonequilibrium multi-pulse states can emerge in a mode-locked laser through the interactions between the quasi-continuous-wave background (qCWB) and optical pulses inside the laser cavity. However, they have been long regarded as unpredictable and hardly controllable due to the noise-like nature of the qCWB, and relevant previous studies thus lack a clear understanding of their underlying mechanisms. Here, we demonstrate that the qCWB landscape can be manipulated via optoacoustically mediated interactions between the qCWB and mode-locked pulses, which dramatically alters the behaviors of multi-pulse dynamics in unprecedented manners. In this process, impulsive qCWB modulations are created at well-defined temporal locations, which act as the point emitters and attractive potentials for drifting pulse bunches and soliton rains. Hence, we can transport a single pulse bunch from a certain temporal position to another on the qCWB, and also make the soliton rain created and collided exclusively at specific temporal locations, in sharp contrast to the conventional cases. Our study opens up new possibilities to control the nonequilibrium multi-pulse phenomena precisely in the time domain, which would not only help the observation and clear understanding of undiscovered features of multi-pulse dynamics but offer a practical means of advanced optical information processing.
Optical nanotapers fabricated by tapering optical fibers have attracted considerable interest as an ultimate platform for high-efficiency light-matter interactions. While previously demonstrated applications relied exclusively on the low-loss transmission of only the fundamental mode, the implementation of multimode tapers that adiabatically transmit several modes has remained very challenging, hindering their use in various emerging applications in multimode nonlinear optics and quantum optics. Here, we report the realization of multimode submicron tapers that permit the simultaneous adiabatic transmission of multiple higher-order modes including the LP02 mode, through introducing deep wet-etching of conventional fiber before fiber tapering. Furthermore, as a critical application, we demonstrate fundamental-to-fundamental all-fiber third-harmonic generation with high conversion efficiencies. Our work paves the way for ultrahigh-efficiency multimode nonlinear and quantum optics, facilitating nonclassical light generation in the multimode regime, multimode soliton interactions and photonic quantum gates, and manipulation of the evanescent-field-induced optical trapping potentials of atoms and nanoparticles.
We successfully fabricate silica nanofibers that permit adiabatic transmission of the higher-order spatial modes by tapering wet-etched optical fibers. Phase-matched intermodal third-harmonic generation in a 760-nm-thick nanofiber is demonstrated with an efficiency higher than 1.05*10-4.
Noise-like quasi-continuous-wave background (qCWB) in a mode-locked fiber laser mediates various multi-pulse dynamics via long-range inter-pulse interactions. This raises a possibility to control multi-pulse phenomena through manipulation of the qCWB, while it has been rarely studied yet. Here, we investigate the qCWB engineering by imposing optomechanically induced impulsive intensity modulations on the qCWB. The mode-locked pulses excite electrostrictively several transverse acoustic resonance modes inside the fiber cavity, which eventually leads to the formation of sharp qCWB modulations regularly spaced in the time domain. In particular, we experimentally demonstrate that the characteristics of the optomechanical qCWB modulations can be adjusted by controlling the in-fiber optomechanical interactions via changing the structure of the fiber core, cladding, and coating. Our observations are supported by directly measured forward stimulated Brillouin scattering spectra of the intracavity fibers.
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