Exclusive-OR Gate for RZ-DPSK Signals Using Four-Wave Mixing in a Highly Nonlinear Bismuth-Oxide Fiber

Ultrafast all-optical logic gates are important for use in future high-speed communication systems. In particular, the exclusive-OR (XOR) gate is a commonly used device in optical signal processing like data encoding and high-speed pattern generation. Recently, much attention has been focused on DPSK signal owing to its higher immunity to optical nonlinearity during fiber transmission. An XOR gate has been previously demonstrated for RZ-DPSK signal using four-wave mixing in a SOA (Chan et al., 2004). In this paper, we demonstrate an XOR operation in a 35-cm highly nonlinear bismuth-oxide fiber (Bi-NLF). Owing to the extremely large nonlinear coefficient of ~1100 (W.km)^-1 in the Bi-NLF, a very short fiber segment is sufficient to introduce significant four-wave mixing. The short fiber segment also minimizes the walk-off originated from group velocity mismatch, thus allowing a relatively wide-band (~12 nm) XOR operation. The passive, robust, and potentially low-cost fiber logic device offers another alternative to realize a compact XOR gate.