Arbitrary pulse shaping in Er-doped fiber amplifiers—Possibilities and limitations

• Temporal distortion of nanosecond pulses in 2-stage MOPA system is studied.
• The 1.45 kW peak power, all-fiber MOPA system operated at 1550 nm was developed.
• Pulse shaping method based on current modulation and analytical calculations.
• SBS was as a main limitations of the pulse shaping method.

A temporal deformation of nanosecond laser pulses occurring during an amplification process in a two-stage erbium-doped fiber amplifier operating in saturation is presented. We discuss distortion of rectangular laser pulses with duration ranging from 5 ns to 300 ns, generated at 20 kHz repetition rate. Calculations of a suitable peak power scaling factor for distorted pulses are presented. A simple compensation method of temporal pulse distortion, based on the direct current modulation with the use of arbitrary function generator (AFG), is also reported. An appropriate input pulse shape modification leads to obtaining an output amplified pulse with any desired shape. The main limitation of pulse shaping in a fiber amplifier seeded by a narrow linewidth laser diode turns out to be stimulated Brillouin scattering (SBS). However, the pulse shaping method can also improve the amplifier performance by increasing the power threshold of SBS. SBS phenomenon in the context of arbitrary pulse shaping have been also discussed.