The self-phase modulation (SPM)-based reshaping
stage is shown in the right dashed box in Fig. 1. The
pulse reshaper is based on SPM-induced spectral
broadening in an HNLF followed by offset filtering[10].
The frequency chirp generated by the SPM effect has a
much smaller effect on the pulse pedestal and background
compared with the rising and trailing pulse
edges; after the offset filtering the pedestal or background
section is suppressed greatly. At the same time,
the reshaper compresses the pulse by temporal carving
of one of the pulse edges through spectral filtering the
SPM-induced frequency chirp components on the corresponding
edge[11]. This HNLF has a length of 1 km, a
dispersion slope of 0.018 ps/(nmgkm), a zero dispersion
wavelength of 1555 nm, and a nonlinear coefficient
of 8.4 W1
gkm1
. The BPF has a 3-dB bandwidth
of 2.5 nm. After amplification by the EDFA the
pulse train is launched to the HNLF for spectral broadening.
The center wavelength of the BPF has around 8
nm offset from the carrier in the short wavelength direction
for slicing part of the SPM-broadened spectrum