High-speed optical signal processing and performance monitoring towards Tbit/s optical networks

Field: Engineering (Physical Sciences)

Optical fiber communication systems are characterized by their extremely high transmission capacity. With high-bandwidth and on-demand applications continuing to emerge, next-generation core optical networks will likely require significant improvements in reconfigurability and ultra-fast operations that are able to reduce the latency at nodes as well as to increase the available bandwidth, without affecting the traffic performance. Optical signal processing overcomes the electronic bandwidth limitations with the advantages in terms of transparency and scalability. For these reasons, much effort has been spent in the past years to design photonic circuits that are fully optically controlled and can be realized with integration technologies. ❧ On the other hand, high-performance optical networks are susceptible to various degrading effects that can change over time. Knowledge of the data channel degradation can be used to diagnose the network, repair the damage, drive a compensator/equalizer, and/or reroute traffic around a non-optimal link. Therefore, it is valuable to monitor the channels for many types of impairments, such as optical signal-to-noise ratio, chromatic dispersion, polarization mode dispersion, and fiber nonlinearity, which can change with temperature, plant maintenance, and path reconfiguration. ❧ To this end, the work presented in this dissertation is aimed at the realization of a few key optical signal processing subsystems for high-speed optical communication systems, as well as various approaches for optical performance monitoring. By exploiting nonlinear effects in highly nonlinear fiber and periodically poled lithium niobate waveguide, the key optical signal processing subsystems presented include an optical parametric delay line operating at a bit rate of 160-Gbit/s, a pseudo-random bit sequence multiplexer with tunable order and bit-rate up to 171.2-Gbit/s, an optical multiplexer of two quadrature phase-shift keying data channels from different wavelengths onto a single star 16-quadrature amplitude modulated signal, a 40-to-640-Gbit/s wavelength-division multiplexing to time-division multiplexing convertor, a 640-Gbit/s reconfigurable demultiplexer, optical add-drop multiplexers at up to 640-Gbit/s, multiple optical logic gates operating at 160-Gbit/s and 640-Gbit/s, and a wavelength convertor for optical orthogonal frequency-division multiplexed signal. All of the signal processing functions are performed directly in the optical domain, eliminating the potential needs for optical-electrical-optical conversions. ❧ The second part of this dissertation is focused on optical performance monitoring. A technique for monitoring the time misalignments of in-phase/quadrature data streams and pulse carver/data in a return-to-zero quadrature phase-shift keying transmitter is presented. A novel approach for optical performance monitoring is proposed by applying artificial neural networks (ANNs) to train receivers in optical networks to distinguish and recognize received eye diagrams, delay-tap plots or constellation diagrams associated with different degrading effects. We experimentally demonstrate the use of ANNs trained with parameters derived from asynchronous diagrams for monitoring a 100-Gbit/s quadrature phase-shift keying data signals. High correlation is obtained, showing the potential of ANNs for optical performance monitoring and analysis in optical networks.