Active breathing pulses induced by the periodic loss in a passive mode-locked laser

The breather is an important emerging topic in nonlinear optics. In fiber lasers, the breather is generally achieved by tuning the loss of the laser system to search for the proper Hopf-bifurcation route. Here, we propose a simple and reliable method to generate breathing pulses, i.e., to introduce a controlled periodic transmittance, i.e., a periodic loss, within the laser that drives the mode-locked pulses to produce a synchronous periodic evolution. Therefore, we name this type of pulse as active breathing pulses. Experimental results show that the characteristic parameters of the active breathing pulses, e.g., the breathing ratio and breathing frequency, can be accurately controlled by the modulation depth and modulation frequency of the periodic transmittance introduced by the electro-optical modulator (EOM). Numerical simulations can reproduce the experimental phenomena. Our work not only gives a new, to the best of our knowledge, approach to modulate the characteristics of the breather but is also promising for the discovery of novel Hopf-bifurcation phenomena and soliton patterns in a periodically varying system.