Since Ovshinsky has published a switching phenomena through phase transition in chalcogenide compound, there have been a number of attempts to apply this phenomena to optical recording. And recently, re-writable phase change media such as CD-RW and PD are commercialized.
In this paper, a model of writing and erasing in phase change recording is reviewed and a method of determining complex refractive index is introduced, which is based upon the incident angle dependence of reflectivity and transmittance. Based upon these, a new multilayer structure has been provided, which has higher absoptivity for crystalline state than for amorphous one. Thus, phase change media of this structure shows improved characteristics of overwriting and cross-erase, which are high density technologies adoped in DVD-RAM.
On the other hand, solid immersion lens(SIL) is recently applied in optical recording to enhance the storage density of data. Since SIL has NA over 1.2 mostly, we can have the storage density over 4 times higher than the conventional objective lens with NA of 0.6 or less.
However, the focussed field formed by SIL is composed of waves with large spectrum of incident angles and polarization directions. Thus, in modeling the focused field, vector diffraction is required instead of scalar diffraction. In addition, the optical properties of layered structure, such as reflectivity(R), transmittance(T), and absorptance(A) should be calculated for the focused field incidence, instead of plane wave incidence.
TO meet these demand, a formu1ation to model the focused field inside a layered structure has been developed using Debye integral representation,and the formulae of R, T, and A have been developed.
Through the computer calculations based on this model, it has been first found that the size of the spot formed by SIL varies with layer thickness, and verified through the track cross signal of grooved substrate. The origin of spot size change has been found to be the variation of the amount of p-polarized wave, which is responsible for the z-components of fields.
Finally, a layered structure of phase change media has been designed and prepared by sputtering for the near-field recording using SIL. By measuring carrier-to-noise ratio, the feasibility of phase change recording using SIL is verified.
