Nonlinear Fiber Optics - 4 ed. Agrawal

8.4. Soliton Effects 309
Figure 8.21: Pulse spectra at the output of a 150-m-long fiber when 0.83-ps input pulses
are launched with the peak power of 530 W. The zero-dispersion wavelength of the fiber is
1.317 μm. (After Ref. [155]; c○1987 IEEE.)
30-ps input pulses at 1.54 μm were propagated through a 250-m-long fiber [151]. Figure
8.20 shows the observed pulse spectra for four input peak powers P 0 in the range
of 50 to 900 W. For P 0 = 80 W, a long tail toward the red side appears. This value of
P 0 corresponds to N = 30 in this experiment. A soliton of such a high order is compressed
by a factor of about 120 at a distance of 300 m, if we use z 0 = 27 km for the
soliton period (T 0 ≈ 17 ps). The spectral width of such a compressed pulse is close to
2 THz. The autocorrelation trace of the energy in the Stokes tail of the topmost spectrum
(downshifted 1.6 THz from the pump frequency) is also shown in Figure 8.20. It
corresponds to a pedestal-free Raman soliton of 200-fs width.
Intrapulse Raman scattering has attracted considerable attention as it provides a
convenient way of generating Raman solitons whose carrier wavelength can be tuned
by changing fiber length or input peak power [151]–[158]. In one experiment [155],
the use of a dye laser permitted tuning of the input wavelength over a range of 1.25 to
1.35 μm as 0.83-ps input pulses with a peak power of 530 W were propagated over a
150-m-long fiber. In this experiment, the input pulse could be launched in the normal
or the anomalous GVD regime of the fiber whose zero-dispersion wavelength was near
1.317 μm. Figure 8.21 shows the pulse spectra as the input wavelength λ p is varied
from 1.28 to 1.317 μm. No Stokes band was generated for λ p = 1.28 μm because
of the normal GVD of the fiber, although SPM-induced spectral broadening is clearly
seen. Two Stokes bands formed for λ p = 1.3 μm, even though the input wavelength
is below the zero-dispersion wavelength, because a substantial part of the pulse energy
appeared in the negative-GVD region after SPM-induced spectral broadening. For