Spectral shaped PAM4 signal based on nonlinear differential coding for AOWC system with Self-pumping structure

Abstract

Spectral shaped 4-level pulse amplitude modulation (PAM4) signal based on nonlinear different coding (NLDC) is proposed in an all-optical wavelength conversion (AOWC) system with self-pumping structure. Laser-driven Mach-Zehnder modulator generates multiple spectra and forms self-pumping structure by selecting signal and pump light, which can ignore the laser phase conversion noise. However, uniform PAM4 signal is severely distorted by nonlinear effects of the practical bandwidth-limited and power-limited AOWC systems. In order to effectively reduce nonlinear interference and fully evaluate the performance of the AOWC systems with self-pumping structure, the PAM4 signal based on NLDC is proposed and demonstrated in two AOWC systems based on parallel pump and vertical pump structures. Compared with the uniform PAM4 signal, the bit error rate (BER) of converted light with NLDC can be reduced by two orders of magnitude, two pump structures can reach 3.496 × 10−5 and 2.85 × 10−4, respectively. The two structures can obtain bandwidth tolerance gains of 3.45 GHz and 3.7 GHz, respectively. When the bandwidth is 18 GHz, this scheme can obtain more than 10Gbit/s data rate gain. In addition, NLDC can make PAM4 signal insensitive to the injection current of semiconductor optical amplifier, which proves that the proposed scheme has high tolerance to the nonlinear effect and is suitable for high-capacity AOWC system.