Simulation, Analysis And Design Of Diffraction Grating Devices

Diffraction grating based devices are exerting a great impact on various fields in today's information era. In Optics Communications, integrated diffraction grating devices based on the planar lightwave circuit (PLC) technology are one of the most important solutions for the wavelength division multiplexing (WDM) technology. Meanwhile, from the compact disk (CD) to today's digital versatile disk (DVD) and the coming blue-ray disk (BD), optical disks, which are based on two-dimensional metallic gratings, are perhaps one of the most successful and hopeful media for high-capacity and high-density information storage. The above two types of diffraction grating based devices are studied, which much emphasis on simulation, numerical analysis and optimal design.Two popular numerical simulation methods for diffractive optics, namely, the rigorous coupled-wave analysis (RCWA) and the finite difference time domain (FDTD), are summarized. In specific, the formulation of the RCWA for 2-D and 3-D metallic gratings and the formulation of the FDTD method for dispersive media are presented.A novel hybrid diffraction method, which is based on the Kirchhoff-Huygens diffraction formula and the RCWA, is proposed to simulate the working of a planar integrated diffraction grating. The hybrid method can simulate accurately both the imaging and polarization-dependent diffraction characteristics of a concave grating. To meet the growing need for flattened passband in a practical WDMsystem, three design methods, namely, the tapered output waveguide structure with air-slots, the three-focal-point method and the analytical method of spatial phase modulation, are introduced to achieve a passband-flattened diffraction grating device. The polarization-dependent diffraction characteristics of the metallic echelle and the total internal reflection (TIR) types of diffraction gratings are studied, and optimal design method based on the hybrid diffraction method is presented.A three-dimensional hybrid vectorial method, which is based on the FDTD algorithm and the vectorial diffraction formulation, is introduced to analyze the read out of an optical disk. With the modeling versatility in disk geometry and material, the 3-D hybrid method can simulate accurately the readout of an optical disk with direct investigations on the 3-D full-wave near-field distribution, the far-field pattern and the readout signal. The readout of a DVD ROM disk and of a BD ROM disk is simulated. The dependence of the readout data signal of a blue-ray ROM disk on the geometry of its information layer (the slope angle of the pits, in particular) is analyzed. Furthermore, the polarization-dependent diffraction characteristics of an ultra-density optical disk (i.e. a two dimensional periodic metallic grating) are studied, with specific emphasis on the polarization effect on major signals.