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We propose an all-optical modulation format conversion scheme from non-return-to-zero on-off-keying (NRZ-OOK) to return-to-zero (RZ) multiple-level phase-shift-keying (PSK) based on nonlinearity in optical fiber. The proposed conversion scheme is numerically investigated and experimentally demonstrated. We experimentally demonstrate error-free operation of NRZ-OOK/RZ- binary PSK conversion at 10.7 Gb/s. The operation of the NRZ-OOK/RZ-quadrature PSK conversion is shown by eye opening after balanced receiving at a symbol rate of 10.7 Gsymbol/s. In addition, we demonstrate the feasibility of the modulation format conversion from NRZ-OOK to RZ-8-levels PSK by numerical simulation.

A novel all-optical modulation format conversion from non-return-to-zero on-off-keying (NRZ-OOK) to return-to-zero quadrature-phase-shift-keying (RZ-QPSK) is proposed and experimentally demonstrated. The proposed format conversion scheme is based on parallel Mach-Zehnder interferometric (MZI) OOK/binary-PSK (BPSK) converters, consisting of integrated semiconductor optical amplifiers (SOAs). We experimentally demonstrate that in both decoded channels of the converted RZ-QPSK signal bit error rate (BER) curves show almost the same receiver sensitivity at a symbol-rate of 10.7 Gsymbol/s. In addition, a reasonable dispersion tolerance of the converted signal up to +295 ps/nm is observed. The numerical simulation based upon carrier rate equation verifies the experimental results.

Eigenvalue communication is a promising technology that can overcome capacity limitations caused by the Kerr nonlinearity in optical fibers. In this letter, we propose an artificial neural network-based demodulation method for optical eigenvalue-modulated signals using on-off encoding. The proposed method has a power margin improvement of 9.2 dB at the bit error rate of 3.8 × 10 −3 compared with the conventional inverse scattering transform-based demodulation method in numerical simulations.

Optical eigenvalue communication is a promising technique for overcoming the Kerr nonlinear limit in optical communication systems. The optical eigenvalue associated with the nonlinear Schrödinger equation remains invariant during fiber-based nonlinear dispersive transmission. However, practical applications involving use of such systems are limited by the occurrence of fiber loss and amplified noise that induce eigenvalue distortion. Thus, several time-domain neural-network-based approaches have been proposed and demonstrated to enhance receiver sensitivity toward eigenvalue-modulated signals. However, despite the substantial improvement in power margin realized using time-domain neural-network-based demodulators compared to their conventional counterparts, these devices require rigorous training for each transmission distance owing to changes in time-domain pulses during transmission. This paper presents a method for demodulation of eigenvalue-modulated signals using an eigenvalue-domain neural network and demonstrates its utility through simulation and experimental results. Simulation results obtained in this study reveal that the proposed demodulator demonstrates superior generalization performance compared to its time-domain counterpart with regard to the transmission distance. Moreover, experimental results demonstrate successful demodulation over distances from zero to 3,000 km without training for each distance.