An optically-pumped mode-locked fiber ring laser for optical clock recovery of
multiple wavelength division multiplexed optical signals actively mode-locks a
plurality of outputs of the laser as a plurality of recovered clocks for a plurality
of the multiple wavelength division multiplexed optical signals. The laser cavity
has a cavity length corresponding to an integer multiple of bit periods of at least
one of the multiplexed optical signals for receiving a pre-amplified version of
the plurality of wavelength division multiplexed optical signals to provide gain
modulation through a phase-insensitive parametric amplification and recirculating
a proportion of the output from the laser cavity back through the laser cavity
for spatially mode-locking the output of the laser cavity as a recovered clock
whereby the recovered optical clock each having a periodic train of optical pulses
with a repetition rate corresponding to the clock rate of the corresponding multiplexed
optical signal is generated by mode-locking of the optically-pumped laser produced
by a spatial modulation of the phase-insensitive parametric gain produced by the
pulsed nature of the wavelength division multiplexed optical signals. A nonlinear
gain medium disposed in the cavity has a sufficiently large dispersion at all of
the wavelengths corresponding to the multiple wavelength multiplexed optical signals
for minimizing four-wave mixing crosstalk among the multiple wavelength multiplexed
optical signals, among the recovered clocks, and between the plurality of multiple
wavelength multiplexed optical signals and the recovered clocks. The gain medium
is pumped by the plurality of pre-amplified multiplexed optical signals to provide
efficient gain modulation through the phase-insensitive parametric amplification
at a plurality of narrow wavelength bands, each of the plurality of narrow wavelength
bands immediately adjacent to a wavelength of a corresponding optical signal and
each of the plurality of narrow wavelength bands including a corresponding recovered
optical clock wavelength, and each of the corresponding optical signals copropagating
in the laser cavity through the nonlinear gain medium with the recovered optical
clocks. A parametric optical amplifier or a Raman amplifier having an inhomogenously
broadened gain amplifies the plurality of recovered clocks for compensating a portion
of the cavity loss at all wavelengths of the plurality of recovered clocks. A wavelength
selector passes the light at the plurality of wavelengths of the recovered clocks
for recirculation in the laser cavity and preventing the light from the multiple
wavelength division multiplexed optical signals and a plurality of idler waves
generated by four wave mixing between the multiple wavelength division multiplexed
optical signals and recovered optical clocks from recirculating in the laser cavity.