Essential Guide to Computer Data Storage: From Floppy to DVD, The

Basics of MO Reading

Unlike traditional magnetic recording systems, which use currents induced in the magnetic heads by the changing magnetic fluxes on the disk surface to read the data, MO systems use polarized light to read the data from the disk. The changes in light polarization occur due to a presence of magnetic field on the surface of the disk (the Kerr effect). If a beam of the polarized light is shined onto the surface, the light polarization of the reflected beam will change slightly (typically less than 0.5°) if it is reflected from a magnetized surface (see Figure 5-3). If the magnetization is reversed, the change in polarization (the Kerr angle) is reversed too.

Figure 5-3. An illustration of the Kerr effect. E is the polarization ...