  Hawking radiation has been regarded as a more general phenomenon than in
gravitational physics, in particular in laboratory analogs of the event
horizon. Here we consider the fiber-optical analog of the event horizon, where
intense light pulses in fibers establish horizons for probe light. Then, we
calculate the Hawking spectrum in an experimentally realizable system. We found
that the Hawking radiation is peaked around group-velocity horizons in which
the speed of the pulse matches the group velocity of the probe light. The
radiation nearly vanishes at the phase horizon where the speed of the pulse
matches the phase velocity of light.
