The present paper deals with the frequency-dependent finite difference time domain ((FD)2TD) method analysis of the light-beam diffraction from a land/groove recording phase-change (PC) disk model with a metal (Al or Au) reflective layer in order to improve the conventional analysis for PC optical disk models with a perfectly conducting reflective layer. The diffracted fields are numerically calculated for both recorded and non-recorded states of the recording layer, and the comparison of the detected signal characteristics between two states is discussed. The crosstalk between the recording marks on lands and grooves are evaluated and the optimum groove depth is examined for Al,Au and perfectly conducting layer models.

Various kinds of optical near-field apertures have been proposed for higher throughput and smaller spot size. However, few studies have mentioned the readout characteristics of the recorded marks on an optical disk illuminated by a near field optical light. In this paper, we have investigated the scattering light by a two-dimensional recorded mark on a phase change disk with Finite-Difference Time-Domain (FDTD) simulations. Instead of using Recursive Convolution (RC) and Piecewise Linear Recursive Convolution (PLRC) scheme, we integrated the motion equation of free electron into conventional FDTD method to solve the electromagnetic field in the metallic materials. The validity of the proposed method is illustrated by comparing its results with those from the analytic exact solution. We analyzed the distributions of optical near-field around a two-dimensional metallic nano-aperture, and then calculated the far-field scattering pattern from a two-dimensional recorded mark on a phase change disk while it was illuminated by an optical near-field though a nanoaperture. The sum signal by a condenser lens was calculated from far-field pattern, and its relationships with the width of recorded mark and the thickness of each layer in the phase change disk were illustrated. The cross-talk between the recorded marks was also discussed.

This paper implements some new techniques to analyze the light beam scattering from a magneto-optical (MO) disk using the three-dimensional finite-difference time-domain (FDTD) method. The anisotropic FDTD update equations are implemented to calculate the propagation of a coherent monochromatic light in the MO material. An anisotropic absorbing boundary condition based on Berenger's perfectly matched layer (PML) concept is also developed. The Gaussian incident light beam is introduced into FDTD computation region exactly by using equivalent electric and magnetic currents. The scattering pattern of light beam from the MO disk is computed and in part compared with that obtained by using the boundary element method. The scattering patterns by the circular recording bit of different radius are calculated to indicate the optimum radius of the recording bit.

The present paper describes the finite difference time domain (FDTD) analysis of the light-beam diffraction from two- and three-dimensional (2-D and 3-D) magneto-optical (MO) disk structures. First, we show that the proposed new FDTD formulation is valid for MO disk medium and can avoid the divergence of fields encountered during the conventional FDTD calculations. Second, as the application of the present method to more complicated models, the main- and cross-polarized diffracted fields are numerically calculated for 2-D and 3-D four-layered MO disk models. The phase differences between two kinds of polarized components are shown. The results obtained here indicate that the proposed FDTD formulation can be applied to more complicated MO disk structures.

The present paper deals with the scattering of a H-polarized Gaussian beam from a conducting cylinder with an irregular surface by using the perturbation technique. The correlation function and the variance of the far-zone scattered field are derived under the first-order perturbation and several numerical examples are shown.

The present paper deals with the frequency-dependent finite difference time domain ((FD)2TD) method analysis of the light-beam scattering from a land/groove recording magneto-optical (MO) disk model with an Al reflective layer (ALRL) in order to improve the conventional analysis for MO disk models under the assumption of perfectly conducting reflective layer (PCRL). Numerical examples of main- and cross-polarized scattered fields and the phase difference between them are presented. We show the comparison of the scattering characteristics between ALRL and PCRL, and also examine the dependence of the cross talk of the readout signal due to adjacent recorded marks on both the recorded mark size and the depth of grooves.

In order to realize a higher density version of the conventional optical disk, shorter wavelength laser and narrower track pitch have been put to practical use. However, using narrow track pitch can cause the increase of the crosstalk from the adjacent tracks. Moreover, the use of narrow pitch and short wavelength can also give rise to the increase of deterioration of the detected signal characteristics due to the microscopic roughness of disk surface. In this paper, in order to estimate the effect of surface roughness theoretically, we try to analyze the light-beam scattering and detected signal characteristics of a blue laser optical disk model with random rough surfaces by the Finite Difference Time Domain (FDTD) method.

In this paper, the electromagnetic scattering from a cylinder with a computer-generated random rough surface is analyzed by a numerical simulation method. The validity of the proposed numerical method is confirmed by comparing the present numerical results with those calculated by the perturbation method to second order and its Pade approximation. It is shown that the present proposed method can be applied to the case where the surface roughness becomes relatively large.