Transmission characteristics are studied for parallel-plate waveguide coupler. It is shown that the stable light field distribution and mode pattern are determined by its own geometric and dielectric parameters, but have nothing to do with the categories of incident sources. It is also found that the coupling effect would generate between waveguides through evanescent field. The calculated results indicate that the field amplitudes in both waveguides are changing with the change of propagation distances, simultaneously the transmitted powers are changing periodically between the two waveguides along the direction of wave propagation. According to the field distributions, the optimum coupling length and coupling efficiency can be obtained. Our numerical simulation is based on the finite difference time domain method without using special mathematical knowledge.
The optical field distribution of TEo in the waveguide grating coupler is obtained by the vector two-dimensional finite difference time domain (FDTD) method. The calculated results indicate that the same optical field distribution and stable mode pattern can be obtainable through the different kinds of driving sources. It is found that the optical mode is determined by waveguide structure and dielectric parameters rather than the categories of incident light sources. These results are direct-viewing and accurate, and can be quickly obtained. According to the mode field distribution, the optimum coupling efficiency can be predicted. The results by this method agree very well with those of published papers by different algorithms, but the CPU-time and memory elements of computer used by FDTD are much less.
Transmission studies for quantum well (QW) structures composed by two-dimension photonic crystals are presented. The results indicate that, with the multiple QW structure, each resonant peak which appears in the single QW structure would split, and the splitting times increases in step with the increasing number of the wells. It is also found that the frequency spacing between adjacent splitting spectra can be finely tuned by adjusting the barrier widths properly, leading to great improvement of spectral efficiency. The physical explanation of the origin of the spectral splitting are provided. These results provide the prospects in super dense wavelength division multiplexing for optical communication and precise optical measurement for the purpose of maximization of channel density.
The wavelength conversion based on cascaded second-order nonlinearity by using pulsed pump waves is theoretically analyzed in a periodically poled lithium niobate waveguide. By numerical simulation, the evolution of pulses and the walk-off between pulses is discussed, and a distorted waveform of converted pulse is illustrated. A tunable and single-to-dual-channel wavelength converter is realized by pumping with picosecond pulses at a repetition rate of 40 GHz, and the waveform distortion of a converted pulse is demonstrated in our experiments.
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