Magneto-optic Recording Materials

Abstract

With significant developments in laser and semiconductor industries, optical-storage technology has successfully emerged into the consumer marketplace and more recently into the computer-based data-storage marketplace as well. For computer-based data storage and other purposes, the first generation of the International Standards Organization (ISO) standard 5-1/4-in. magneto-optic (MO) drive (325 Mbytes × 2/double-sided) was introduced in 1988 and the 3.5-in. drive (128 Mbytes) in 1991. Since then progress has been remarkable in capacity and data-transfer rate as well as cost/performance ratio, and the so-called 2X (650 Mbytes × 2 per 5-in. double-sided disk) and 3X (1 Gbyte × 2 per 5-in. double-sided disk) drives are now in the marketplace. Also a remarkable product called the MiniDisc (2.5 in.), the first recordable optical system for both the consumer and the data market, utilizes data compression and direct overwrite schemes. The solution for increasing the capacity is by no means simple since the new technology must accommodate many factors. One of the key factors is backward compatibility. This feature is important to removable media because the customer expects new products to be compatible with their previous investments in data stored on older generation media. Another key factor is cost. The sales price ($/Mbyte) must be significantly lower than prior generations of optical-storage products and alternative storage systems (e.g., removable hard disks). To increase the capacity in optical-storage media, several solutions are possible: short-wavelength lasers, magnetically induced super resolution (MSR), pulse width modulation (PWM), volumetric recording, land/groove recording with crosstalk cancellation, partial-response channels, banding of data, and higher numerical aperture objective lenses.