Novel all-optical switching and processing techniques for optical networking
In this thesis, the possibility of processing optical time-division multiplexing (OTDM) signals in both the temporal and spectral domains is investigated. The technique relies on the conversion of high-speed OTDM signals into a mixed time and wavelength division multiplexing (TDM-WDM) format. Depending on the specific network function, it may be advantageous to process the signal in one rather than the other domain. For example, channel add/drop multiplexing can be performed directly by passive filtering in the spectral domain. An investigation into the switching of the linearly-chirped pulses in a nonlinear optical loop mirror (NOLM) revealed that the product of the control-pulse duration and the chirprate of the linearly-chirped pulse should be above a minimum value to ensure a one-to-one relation between the temporal and spectral waveforms after the switching. Below this minimum value, severe spectral distortion of the mixed TDM-WDM signal was observed. The physics behind this distortion is unveiled and shown to be related to the interference between the spectral content in the switched pulse and the unavoidable residual components of the linearly-chirped pulse transmitted through the NOLM switch. These effects were identified in experiments which aimed at compressing/expanding waveforms at 40Gb/s by control of the group delay of the converted TDM-WDM signal in a dispersive medium. Apart from the packet compression/expansion experiments, demultiplexing and channel add/drop multiplexing of 40-Gb/s OTDM signals were also experimentally demonstrated. The technological challenges of implementing this technique at higher repetition rates are discussed.