A novel wavelength assignment method for a bidirectional two-fibre WDM network of star topology is proposed. It is shown that the minimal number of wavelengths required for an n-node star network is n (when n is odd) or n 1 (when n is even). A simple and explicit recursive formula, which completes wavelength assignment quickly with a time complexity of O(n2 log2(n)), is given. Simulation results show that the present method can give an optimal wavelength assignment much faster than conventional methods for a star network.

With a perfectly matched layer boundary treatment, a semivectorial finite-difference method is used to calculate the eigenmodes of a single-mode (SM) or multimode (MM) bent rib waveguide. A detailed analysis is given for the dependence of the bending losses (including the pure bending loss and the transition loss) on geometrical parameters of the bent rib waveguide such as the rib width, the rib height, and the bending radius. The characteristics of the higher-order modes are analyzed. It is shown that the bending loss of the fundamental mode can be reduced effectively by increasing the width and height of the rib. For an integrated device, undesired effects due to the higher-order modes of a MM bent waveguide can be removed by appropriate choice of the geometrical parameters. An appropriately designed MM bent waveguide is used to reduce effectively the bending loss of the fundamental mode, and a low-loss SM propagation in a MM bent waveguide is realized when the bending losses of the higher-order modes are large enough.

A novel directional coupler with a left-handed material (LHM) layer between two single-mode (SM) waveguides of usual material is introduced. The coupling system is analyzed with the supermode theory. It is shown that such an LHM layer of finite length can shorten significantly the coupling length for the two SMwaveguides. An LHM layer with two slowly tapered ends is used to avoid the reflection loss at the ends

The characteristics of an imaging system formed by a left-handed material (LHM) slab of finite length are studied, and the influence of the finite length of the slab on the image quality is a nalyzed. Unusual phenomena such as surface bright spots and negative energy stream at the image side are observed and explained as the cavity effects of surface plasmons excited by the vanescent components of the incident field. For a thin LHM slab, the cavity effects are found rather nsitive to the length of the slab; the bright spots on the bottom surface of the slab may stretch to the image plane and degrade the image quality.