Abstract
Differential phase-shift keying (DPSK) signals are promising candidate for
the long-haul transmission systems. However, the development of the
all-optical signal processing techniques for the DPSK signals is still in
its infancy, especially the all-optical logic operations. In this work, a
general scheme for reconfigurable logic gates for multi-input DPSK signals
with integration possibility is proposed. Benefiting from the optical logic
minterms developed by two kinds of optical devices, i.e., optical delay
interferometers and semiconductor optical amplifiers (SOAs), target logic
functions can be realized by combining specific minterms together. The
scheme is reconfigured by changing the phase control of the delay
interferometers or the input wavelengths. The latter approach was adopted in
the experimental trials. Although the outputs of the scheme are on–off keying (OOK) signals, the data
format is compatible with all-optical decision circuits where OOK format is
preferred. Two- and three-input experiments are carried out at 20 Gbit/s
with nonreturn-to-zero DPSK signals. Various logic operations are
demonstrated, including full sets of two- and three-input minterms, AND, NOR, XOR, and XNOR logic operations where the AND and NOR logic are derived simultaneously
and the XOR and XNOR logic are convertible. The optical
SNR as well as the $Q$-factor of the two- and three-input results are measured and
compared. It shows that the input powers to the SOAs are critical in
achieving good extinction ratio and the $Q$-factor of logic results degrades when several minterms are
combined. The recovery time of the SOAs need to be optimized as well.
Finally, the scaling issues of the scheme are discussed.
© 2009 IEEE
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