Adaptive Optoelectrical Filters for Improved Generation of Optical Single Sideband Signals With Different Pulse Shapes

The use of optoelectrical filters to generate optical single sideband (OSSB) signals from pure intensity-modulated optical double sideband (IM-ODSB) signals is investigated. Three realizations of OSSB signal generators based on phase modulating an IM-ODSB signal are presented and compared in terms of sideband suppression ratio (SSR). The three phase modulations are phase modulation proposed by Powers (PM-P), phase modulation proposed by Villard (PM-V), and an approximation to the PM-V (APM-V). Non-return-to-zero (NRZ) and RZ pulses are considered in evaluating the adaptive filters' performance. All the proposed realizations present null intensity distortion and wavelength-independent operation. Highest SSR is observed by the PM-P, as the PM-V and APM-V are based on mathematical approximations of the ideal generation process of the OSSB signal. Two different realizations are experimentally analyzed and compared: PM-V and APM-V. SSRs above 22 and 14 dB are experimentally obtained by considering the NRZ and RZ pulses, respectively, for the PM-V, whereas the APM-V presents lower SSR values as it is based on an approximation of the PM-V. Significant tolerance to group-velocity dispersion (GVD) is observed by the generated 10-Gb/s OSSB signals, as -factor penalties not exceeding 6 dB to the back-to-back situation are obtained for the accumulated GVD of 2720 ps/nm. A further increase in this value is achieved by considering an electrical dispersion compensation (EDC) after photodetection, allowing the reach of 8500 ps/nm of the accumulated GVD with a Q-factor penalty not exceeding 3 dB relative to the back-to-back situation. For both cases (with and without EDC), negligible Q-factor penalty differences are observed between the investigated phase modulations, and the simplest implementation (APM-V) can be used without significant degradation. Compared to the OSSB signals generated using detuned optical filters, higher tolerance to the accumulated GVD is observed by signals generated using the proposed optoelectrical filters when EDC is considered. This fact results from the reduction of phase preservation after photodetection is observed using the detuned optical filter technique due to optical carrier power suppression.