1 - Magneto-Optical Data Recording: Introduction and Overview

Abstract

Magneto-optical (MO) storage is rewritable storage. Magneto-optical discs allow a customer to read, write, erase, and rewrite the same disc nearly infinite number of times. For a magneto-optical disk, the storage medium is a thin magnetic film or films deposited onto a transparent substrate. Data is recorded in a binary form as submicron-sized magnetic domains arranged serially in tracks on the disk. Readout takes place by reflecting light from the film, with the interaction between the light and the medium producing a change in the polarization of the light, the magneto-optical effect. The polarization change between alternating bits is converted to electrical signals and decoded in the magneto-optical head and drive electronics. Magneto-optical thin films have very large vertical anisotropy that means that they only support magnetization in a direction that is perpendicular to the plane of the thin film. Hence only two magnetization orientations can be recorded on the disk. Standard MO disk track pitches range from 1.6 to 1.15 micrometers per track (15,000-22,000 tracks per inch). MO heads and media are designed such that the signal-to-noise ratio from the reading of a narrow domain on an optical disk is comparable to the signal-to-noise ratio from a several-tunes-wider domain on an inductively read magnetic disk.