Abstract
640 Gb/s all-optical ON–OFF keying signal regeneration based on nonlinearities in
a periodically poled lithium niobate (PPLN) waveguide is demonstrated and characterized.
The data are transferred from the distorted original optical time division multiplexing
(OTDM) signal onto a high quality and locally generated 640 GHz clock by pump depletion
simultaneously operating a wavelength conversion. The thresholding behavior and the
saturation effect of pump depletion in the PPLN waveguide for low and high pump power
values, respectively, allow for a noise compression on the wavelength-converted replica
of the original signal. The use of a stable clock with a shorter pulsewidth also allows
for a sort of sampling of the original OTDM frame in the bit time center, resulting in a
pulse reshaping that eliminates all noise contributions on the pulse tails. This
operation produces a reduction of the original time jitter of the signal. The sampling
operation also results in a compression of the new OTDM frame pulses compensating for
the residual chromatic dispersion effects. After having characterized the transfer
function of the proposed regeneration scheme, we evaluate its effectiveness as a
function of optical signal-to-noise ratio (OSNR), pulse broadening, and time jitter of
the input signal. Regeneration performance is measured in terms of bit error rate (BER)
and power penalty @BER = 10<sup>-9</sup>. Error-free operation can be recovered and
maintained over an input signal OSNR range of 8 dB. This results in a BER improvement up
to several orders of magnitude, obtained when the input OSNR is reduced by 20 dB with
respect to the baseline. The time jitter of input signals with original jitter values
from 100 to 300 fs has been reduced of nearly one order of magnitude to values lower
than 40 fs. We also demonstrate that a pulse broadening up to 20% of the original
pulsewidth can be compensated. Finally, wavelength tunability of the regenerator input
and output signal can be, in principle, guaranteed over the whole C-band and
beyond.
© 2012 IEEE
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