Modulation Format Conversion in Future Optical Networks

Abstract

The signal generation and receiver schemes of different modulation formats such as on off keying (OOK) in either non‐return to zero (NRZ) or return to zero (RZ), correlative coding and phase‐shift keying (PSK) are described and numerically simulated. Their receiver sensitivities for back to back structure are numerically simulated at 40 Gb/s and compared. The results show how using balanced reception, DPSK has the benefit of approximately 3 dB. We demonstrate that duobinary modulation is characterized by a higher tolerance to the chromatic dispersion in comparison with NRZ. Conversion techniques between modulation formats are described. Different all optical format conversion based on the mentioned method are discussed. Finally, format conversion from RZ‐OOK to RZ‐DPSK based on HNLF nonlinearities is investigated in great detail and numerically simulated at 40 Gb/s. Some converter requirements such as powers, wavelengths, bandwidths, pulse widths and pulse shapes among other are studied. The results show that shorter pulse widths in control signal for the case of walk‐off presence provide worse conversion. Sensitivity of converted RZ‐DPSK is compared with a conventional 33RZ‐DPSK signal showing a penalty close to 4 dB. Finally, the effect of the control wavelength variation at the input of the converter is investigated when the probe signal corresponds with conventional 33%RZ, 50%RZ and 67%RZ duty cycle.