Fig. 1. Schematic of the spatiotemporally mode-locked soliton Er:ZBLAN fiber laser. LD, laser diode; L₁, spherical lens; L₂ and L₃, aspherical ZnSe lenses; M, dichroic mirror; OC, output coupler; HWP, half-wave plate; QWP, quarter-wave plate; ISO, isolator. Inset: the enlargement of the fiber facet obtained by a scanning electron microscope, showing a 30-μm fiber core diameter.

Fig. 2. (a) The output beam pattern recorded in continuous-wave operation. (b)–(d) The output beam patterns recorded in spatiotemporal mode-locking operation at different pump powers. (e) The measured M² factors of the output beam at pump power of 4.40 W in the spatiotemporal mode-locking operation.

Fig. 3. (a) Recorded mode-locked pulse trains in the 200 ns and 1 ms time scales. (b) Sampled pulse trains at different spatial positions. (c) Intensities of sampled pulse trains versus spatial positions.

Fig. 4. (a) Measured radio-frequency (RF) spectrum of the mode-locked pulses. Inset: RF spectrum with 500 MHz span. (b) Measured autocorrelation trace of the mode-locked pulses (black dots) with a sech² fit (blue solid line). (c) Optical spectrum of mode-locked pulses. These results were measured under the average output power of 1.09 W.

Fig. 5. The output average power and pulse energy versus pump power for the spatiotemporally mode-locked soliton fiber laser. The recorded data are the corresponding pulse duration and peak power.