  We propose to achieve a multi-color nonreciprocal optical amplifier, a
crucial device in optical communication and information processing, by spinning
an active resonator. We show that in such a device, due to the interplay of the
Sagnac effect and the optical gain, nonreciprocal signal {amplification} can be
realized, accompanied by a giant enhancement of optical group delay from
$0.3\;\mathrm{ms}$ to $35\;\mathrm{ms}$ in a chosen direction, which is
otherwise unattainable in a passive device. Also, coherent amplification of
higher-order optical sidebands and a slow-to-fast light switch can be achieved
by tuning both the pump power and the spinning velocity. Our work provides a
unique and accessible way, well-compatible with other existing techniques, to
realize multi-color nonreciprocal optical amplifiers for more flexible control
of optical fields.
