All-optical logic gates have found a large variety of uses for signal processing applications. All-optical XOR-gates, for example, are useful in all-optical data comparison for packet address recognition, encryption/decryption, parity checking and generation of pseudorandom bit patterns. All-optical AND-gates had served as sampling gates in optical sampling oscilloscopes owing to their ultrafast operation compared to traditional electrical methods. All-optical NOT-gates can be used in rectifying inverted optical signal processing elements. Of the many different possible all-optical gate implementations, most are based on semiconductor optical amplifiers (SOA) as the nonlinear medium for nonlinear optical signal processing. Cross-gain modulation (XGM) and cross-phase modulation (XPM) in SOA have been widely explored for logic gate implementations using a single or multiple SOAs. Recent technique of using an SOA together with a detuned filter can provide picosecond response time despite a much longer, nanosecond-scale carrier recovery time. This may prove to be very desirable candidate for logic applications requiring XGM effects. However, this approach requires a very dedicated setting of SOA conditions and filter offset.

Alternatively, all-optical logic gates can be realized using a fiber-based optical parametric amplifier (OPA). In contrast to SOA-based approaches, the fiber-based OPA operation is possible to support data rate at 160 Gb/s or beyond without modification of the setup. This is due to femtosecond response time of fiber nonlinearity. The only limitation of the signal response is due to the dispersion induced phase mismatch among the interplaying signals. However, this limitation is relieved with the recent advancement of fiber fabrication techniques. The newly developed highly-nonlinear dispersion-shifted fibers (HNL-DSFs) reduce the required length needed in fiber-based nonlinear signal processors for reduced latency and improved phase matching in the interested wavelength range.

In the experiment conducted, the OPA was manifested by a single spool of HNL-DSF to construct all-optical XOR-, OR-, NOT-, and AND-gate. The bit-rate of the setup was 10 Gb/s, having input full-width at half-maximum (FWHM) pulsewidths of 4.6 ps. The FWHM pulsewidth was measured to be 5.1 ps at the output. This reveals a possibility of operating at 80 Gb/s and beyond.