Fig. 1. (a) GVD and refractive-index curves of Ge and GVD curve of ZBLAN fiber. Sellmeier equations of Ge and ZBLAN are used from Refs. 18 and 19. (b) Transmission curve of 2-cm-long antireflection-coated Ge rod measured using a Fourier-transform spectrometer.

Fig. 2. Schematic of the breathing-pulse mode-locked Er:ZBLAN fiber laser. LD, laser diode; DM, dichroic mirror; OC, output coupler with a transmission of 40%; ISO, optical isolator; λ/2, half-wave plate; λ/4, quarter-wave plate; and Ge, germanium rod.

Fig. 3. Soliton mode-locked Er:ZBLAN fiber laser: (a) pulse trains in nanosecond and millisecond time scales, respectively; (b) radiofrequency spectrum; (c) measured intensity autocorrelation trace; and (d) mode-locked pulse spectrum.

Fig. 4. Characteristics of the breathing-pulse mode-locked Er:ZBLAN fiber laser. Evolution of (a) pulse energy and duration, (b) autocorrelation trace, and (c) mode-locking spectrum with the Ge rod length. The net intracavity dispersions are −0.191, −0.158, −0.141, and −0.090ps2 for Ge rod lengths of 0, 2, 3, and 6 cm, respectively. Evolution of the (d) pulse energy and duration with the launched pump power in the soliton and breathing-pulse regimes. (e) Measured autocorrelation trace and (f) mode-locking spectrum for 9.3-nJ output pulses.

Fig. 5. Numerical simulation of a breathing-pulse MLFFL consisting of an NPR system, a Ge rod, an Er:ZBLAN fiber, and an OC. Evolution of (a) pulse duration, (b) spectrum, and (c) pulse energy along the cavity.