In this paper, using an inverse scattering approach, we describe how the selection of mode effective indices and thus phase velocities can be used to control group velocity in a waveguide. As such it is shown that differential group delay can be equalised or minimised over a wavelength of choice. A particular feature of the new designs is the development of rings and a peaked core which may spl...

We propose a device to compensate for group-velocity mismatch (GVM) effects that limit the efficiency-bandwidth product in nonlinear frequency-mixing devices. Integrated wavelength-dependent delay lines are introduced periodically in a waveguide containing a series of quasi-phase-matching (QPM) gratings. Appropriate choice of the time delays can compensate for GVM. We have demonstrated a two-st...

We investigate experimentally the role that the initial temporal profile of ultrashort laser pulses has on the self-focusing dynamics in the anomalous group-velocity dispersion (GVD) regime. We observe that pulse-splitting occurs for super-Gaussian pulses, but not for Gaussian pulses. The splitting does not occur for either pulse shape when the GVD is near-zero. These observations agree with pr...

We demonstrate that simultaneous phase- and group-velocity-matched cascaded parametric processes can be achieved in two-dimensional quadratic nonlinear photonic crystals by proper matching of noncollinear processes with front tilting of the fundamental pulse. We present examples of cascaded third- and fourth-harmonic generation in a poled LiNbO3 planar structure.

Dissipative numerical approximations to the linear advection equation are considered with respect to their behaviour in the limit of weak dissipation. The context is wave propagation under typical far-field conditions where grids are highly stretched and waves are underresolved. Three classes of schemes are analysed: explicit two-level (i) symmetric and (ii) upwind schemes of optimal accuracy a...

We report ultraslow group velocities of light in a solid. Light speeds as slow as 45 m/s were observed, corresponding to a group delay of 66 μs in a 3-mm thick crystal. Reduction of the group velocity is accomplished by using a sharp spectral feature in absorption and dispersion, produced by a Raman excited spin coherence in an optically dense Pr doped Y2SiO5 crystal. PACS numbers: 42.50.-p, 42...