Abstract

Optical data storage using short wavelengths (blue light) can reduce the spot area size and increase the data density by a factor of 4. A blue wavelength semiconductor laser with the necessary output power for writing information onto optical disks is not available. To increase the data transfer rates requires higher laser power because the switching of the magnetization during the writing process occurs in a proportionately shorter time period. Therefore, it is necessary to increase the efficiency of energy absorption by optical recording media so that the power requirement for writing can be reduced. However, a certain amount of reflectance is needed during reading since the reflected signal must be large enough to be detected. Applying conventional thin film coating techniques to optical data storage, we start from current available coating materials (e.g., TiO₂ or ZnS) and search for an optimal multi-layer structure. The optimally designed recording medium shows different optical properties at reading and writing wavelengths. The critical design points are low reflectance at writing wavelength (λ_w), optimal value of figure of merit at reading wavelength (λ_r), and small difference between λ_r and λ_w, which results in a small wavelength tuning in a second harmonic generation system. Our computer simulations show that an appropriate multilayer coating design can not only reduce the power requirement of an optical recording system but also enhance the signal-to-noise ratio.

© 1992 Optical Society of America