Fig. 1. Calculated pulse shapes and the corresponding spectra. (a) Gaussian-shape pulse and the corresponding (b), (c) spectra; (d) sawtooth-shape pulse and the corresponding (e), (f) spectra; (g) square-shape pulse and the corresponding (h), (i) spectra; (j) distorted-square-shape pulse and the corresponding (k), (l) spectra.

Fig. 2. Experimental setup for spectral measurement of Gaussian-like and square-like pulses. EOIM, electro-optic intensity modulator; AFG, arbitrary function generator; SWG, square wave generator; SMF-PA, single-mode-fiber-based preamplifier; LD, laser diode; WDM, wavelength division multiplexer; PM YDF, polarization-maintained Yb-doped fiber; BPF, band pass filter; ISO: isolator; FPI, Fabry–Perot interferometer.

Fig. 3. Measured pulse shapes and the corresponding spectra. (a) Gaussian-like pulse and corresponding spectra at the (b) input and (c) output of the GDF; (d) square-like pulse and corresponding spectra at the (e) input and (f) output of the GDF.

Fig. 4. Experimental setup of the LMA fiber amplifier. LD, laser diode; FPI, Fabry–Perot interferometer; P1, P2, power meter; PM YDF, polarization-maintained Yb-doped fiber; CLS, cladding laser stripper; CO, collimator.

Fig. 5. Average backward propagating power of the Gaussian-like pulses as a function of the forward propagating output power.

Fig. 6. Measured pulse shape and the corresponding spectra of the Gaussian-like pulse. (a) Output pulse shape; (b) spectrum of the pulsed seed; (c) spectrum of the output pulses.

Fig. 7. Average backward propagating power of square-like pulses as functions of the (a) average forward propagating output and (b) peak power.

Fig. 8. Measured pulse shapes and the corresponding spectra of square-like pulses. (a) 8 ns pulse and (b), (c) corresponding spectra; (d) 7 ns pulse and (e), (f) corresponding spectra; (g) 6 ns pulse and (h), (i) corresponding spectra; (j) 5 ns pulse and (k), (l) corresponding spectra.

Fig. 9. Measured (a) spectra and (b) PER in the main amplifier for 5 ns pulses.