Vector-resonance-multimode instability

The modulation and multimode instabilities are the main mechanisms which drive spontaneous spatial and temporal patterns formation in a vast number of nonlinear systems ranging from biology to the laser physics. Using Er-doped fiber laser as a test bed, here for the first time we demonstrate both experimentally and theoretically a new type of a low threshold vector resonance multimode instability which inherits features of multimode and modulation instabilities. The same as for the multimode instability, the large number of longitudinal modes can be excited without modes synchronization. To enable modulation instability, we modulate the state of polarization of the lasing signal with the period of the beat length by adjustment of the in-cavity birefringence and the state of polarization of the pump wave. As a result, we show regimes tunability from complex oscillatory to periodic with longitudinal modes synchronization in the case of the resonance matching between beat and cavity lengths. Apart from the interest in laser physics for unlocking tunability and stability of dynamic regimes, the proposed mechanism of the vector resonance multimode instability can be of fundamental interest for nonlinear dynamics of various distributed systems.