Microfiber-Knot-Resonator-Induced Energy Transferring From Vector Noise-Like Pulse to Scalar Soliton Rains in an Erbium-Doped Fiber Laser

We report on scalar soliton rains (SRs) shedding from vector square-wave noise-like pulse (NLP) by introducing a microfiber-knot-resonator (MKR) into an erbium-doped fiber (EDF) laser. The EDF laser has an ultralong cavity of ~3.07 km and a large anomalous cavity-dispersion, facilitating the formation of NLP. Once an MKR was further incorporated, comb-like filtering effect could be clearly observed on the emission spectrum. Apart from that, SRs shedding from the NLP were observed, which resulted from the MKR-induced energy transferring effect from the NLP to SRs. It was further found that the SRs existed only along a particular polarization direction, whereas the NLPs could be found in any pair of orthogonal polarization directions, despite some differences in pulse peak power. These suggest that the SRs possess scalar feature, whereas the co-circulating NLP is a package of vector pulses. Our results represent the first observation of MKR-induced pulse energy transferring effect and also the first observation of the co-existence of scalar and vector pulses in a single fiber system. Besides enriching the dynamics and interactions of optical pulses in fiber lasers, our results extend the applications of MKR to the area of pulse manipulations through spectral tailoring and local nonlinearity engineering.