Abstract
In this paper we propose the operation of an all-optical logical gate
based in a symmetric nonlinear directional coupler (NLDC) operating with
a pulse position modulation (PPM). The performance of a symmetric NLDC
realizing two-input AND/OR logical functions, which can be applied in
transmission and processing of signals in all-optical form in TDM
systems, is examined. This integrated symmetric NLDC logical gate
operates with two ultrashort soliton light pulses (2 ps), which are
modulated in agreement with the technique of pulse position modulation
(PPM). Initially, we evaluate the effect resulting of an increment in
the PPM coding parameter offset (8), for the temporal position of the
output pulse, considering the anomalous group-velocity dispersion (GVD),
nonlinear self phase modulation (SPM) and without loss propagation
regime of input pulses, in the cores I and 2 of the NLDC. In this
situation, we analyze the four possible situations for the two-input
logical gate, modulating the I and 2 input pulses through temporal
displacement and allowing a variation in the coding parameter offset. We
can conclude that is possible to get AND/OR logical operations for the
cores 1 or 2, without to insert PPM error, since a phase control (Delta
phi) exists applied in agreement with the logical level of the input
pulse in the core 1. Finally we define the truth table, considering the
adequate phase difference and coding parameter offset for the stable
operation of the AND/OR logical gate based in the symmetric NLDC. (C)
2007 Elsevier B.V. All rights reserved.
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