All-optical nonlinear signal processing devices and their applications within fibre-optic communication systems

Abstract

This thesis is concerned with research into the development of a range of all-optical fibre based nonlinear devices for optical communication applications. The research can he divided into two main themes. The first concerns the use nf superstructured fibre Bragg grating technology together with fibre based nonlinear devices to improve the overall system performance in both OCDMA and OTDM systems. The second theme area concerns the use of highly nonlinear holey fibre within a range of nonlinear signal processing devices and an analysis of the performance of these devices from a system context. A range of nonlinear devices based on a holey fibre is demonstrated. Holey fibre has a nonlinearity around 10-100 times greater than conventional fibre. The use of a short (8.7 m), highly nonlinear holey fibre based optical switch is presented and shown to provide enhanced code recognition quality in a SSFBG based OCDMA system. The use of a short (75 m), highly nonlinear holey fibre to obtain strong L+-band Raman amplification and SRS based signal modulation is also demonstrated. The use of HF within Brillouin based devices is next considered. Both stimulated and spontaneous Brillouin scattering effects are investigated. The observed high SBS lasing threshold is found to be mainly due to reduction in the effective gain coefficient caused by structural non-uniformity along the HF length. A 5.8 m length of HF is then used to achieve tuneable WDM wavelength conversion based on XPM and it is experimentally demonstrated that HF with normal GVD should be used for this sort of device in order to eliminate the coherence degradation related intensity noise observed in experiments employing anomalously dispersive HF. Finally, a FWM based wavelength converter using a 15 m, highly nonlinear HF with a high SBS threshold is presented. The high SBS threshold is achieved by applying structural variation to the HF along its length during the fabrication process.

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