High-Nonlinearity in Glass Fibers and Cross-Phase Modulation - Optical Signal Processing by Silicon Photonics - page 65

conventional nonlinear fiber devices usually require either long length or high
power for a sufficient nonlinear phase shift in order to achieve the desired nonlin-
ear effects. The long length of fiber leads to the serious problems of pulse walk-
off, pulse broadening, and polarization fluctuation. It is also certain that one can
drastically reduce the required device length by introducing the HNL glasses due
to their high nonlinearities and thus can suppress the problems caused by the long
length. Moreover, the fabrication processes of HNL glasses are easier because of
their low melting temperatures and high glass stability. Also, they have wide trans-
mission range from near-infrared to far-infrared.
5.6.5 Disadvantages of High-Nonlinearity Glasses
However, the HNL glasses have extremely high losses and GVDs. This extremely
high-group velocity dispersion can cause the deleterious effects of high relative
group delay and rapid pulse walk-off between two pulses at different wavelengths,
despite the short device length, due to extremely high-group velocity difference. It
also can cause huge pulse broadening and high loss limits the performance of the
devices. These problems can be major limiting factors for response time, switch-
ing bandwidth, and maximum transmittable bit-rate.
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