Actively mode-locked fibre ring laser based on in-fibre acousto-optic amplitude modulation

Recent advances in the development of all-fibre amplitude modulators have led to the implementation of a series of different actively mode-locked fibre lasers [1-4]. In-fibre acousto-optic modulation based on intermodal coupling induced my a standing flexural acoustic wave permits the implementation of broad bandwidth (1.5 nm), high modulation depth (0.72), low-insertion-loss (0.75 dB) all-fibre amplitude modulators that operate in the MHz frequency range. The experimental characterization of a laser with the configuration depicted in Fig. 1 (a) as a function of the radio frequency voltage that controls the modulator (see Fig. 1 (b)), the length of the Erbium doped fibre (EDF), and the optical bandwidth of the intracavity filter implemented with a fibre Bragg grating (FBG), has led to an improved performance: Optical pulses of 1.4 W peak power and 34 ps temporal width were obtained at 4.7 MHz repetition rate. These values represent a significant improvement within the framework of actively mode-locked all-fiber lasers. Our work suggests that further improvements can be produced following this research line.