The objective of the proposed research is to investigate new and more efficient techniques in numerical evaluation and experimental measurement of phase jitter impact on more general communication systems including dispersion management, filtering, and spectral inversion schemes. There has recently been a renewed effort to develop coherent optical communication systems. In particular, differential phase-shift keying (DPSK), which does not require a local oscillator to perform decoding, has focused the attention and is perceived to be the promising candidate for future optical communication systems updates. This motivates us to exploit DPSK in wavelength-division multiplexed systems. First, modulation formats based on phase show an increased robustness to nonlinear impairments such as cross-phase modulation (XPM) and nonlinear polarization rotation, primarily because the time-dependence of optical power is deterministic and periodic. Second, coherent formats allow a higher spectral efficiency since both in-phase and quadrature dimensions of the signal space are available to encode information. Optical phase is also used in intensity-modulated direct detection systems as an extra degree of freedom, for example to provide better resistance to intrachannel four-wave mixing (FWM), or to increase spectral efficiency in duobinary modulation. Finally, phase modulation outperforms its intensity counterpart in terms of sensitivity since a 3 dB improvement can be achieved when balanced detection is used. Nevertheless, DPSK-based formats show a different behavior to noise accumulated along the propagation. Noise-induced power fluctuations are converted into phase fluctuations by the Kerr effect and become a penalty source which limits the transmission system reach. In this context, there have been intense research activities for evaluating phase uncertainties but the previous studies assume an analytically determined pulse shape and a constant-dispersion optical link which is far from reflecting the actual and future structures of transmission lines.

This thesis describes research on acoustically excited bluff body flow-fields, motivated by the problem of combustion instabilities in devices utilizing these types of flame-holders. Vortices/convective-structures play a dominant role in perturbing the flame during these combustion instabilities. This thesis addresses a number of issues related to the origin, evolution and the interaction of these structures with the flame. The first part of this thesis reviews the fluid mechanics of non-reacting and reacting bluff body flows. The second part describes the spatio/temporal characteristics of bluff-body flames responding to excitation. The key processes controlling the flame response have been identified as 1) the anchoring of the flame at the bluff body, 2) the excitation of flame-front wrinkles by the oscillating velocity field and 3) flame propagation normal to itself at the local flame speed. The first two processes control the growth of the flame response and the last process controls the decay. The third part of this thesis describes the effect of acoustic excitation on the velocity field of reacting bluff body flows. Acoustic disturbances excite the Kelvin-Helmholtz (KH) instability of the reacting shear layer. This leads to a spatially decaying vorticity field downstream of the bluff body in the shear layers. The length over which the decay occurs was shown to scale with the length of the recirculation zone of the bluff body, i.e. the length over which the velocity profile transitions from shear layer to wake. The flame influences this decay process in two ways. Gas expansion across the flame reduces the extent of shear by reducing the magnitude of negative velocities within the recirculation zone. This combined with the higher product diffusivity reduces the length of the recirculation zone, thereby further augmenting the decay of the vorticity fluctuations. Lastly, these results also revealed phase jitter - a cycle-to-cycle variation in the position of the rolled-up vortices. Close to the bluff-body, phase jitter is very low but increases monotonically in the downstream direction. This leads to significant differences between instantaneous and ensemble averaged flow fields and, in particular, the decay rate of the vorticity in the downstream direction.