In the past eight years, the C/N value of Magneto-optic (MO) disks increased 5 db/per year and is now 60 db at 1 MHz. This advancement was achieved not only by the optical head improvement but also by the material design.
The C/N value depends on the several factors such as disk structure (on groove → on land, Trilayer → Quadrilayer), material (TC, θk, domain structure…).
In the present MO-disk, minimum bit length is 0.75 μm and track pitch is 1.6 μm. The bit density, thus obtained 8 × 10 bit/cm, is one order higher than the conventional magnetic hard disk. Data transfer rate of MO-disk, however, is 1 MB/s and is several times lower than that of hard disk.
In the coming 10 years, the bit density of MO-disk must be improved 10 times or more to the present density, as hard disks will realize in the past 10 years. Data transfer rate also must be improved from 1 MB/s or more than 3 MB/s in the near future.
These themes, however, seem possible to realize using following technologies: One is improvement of laser diode (λ = 800 → 600 →. 400 nm, multi-beam) and the other is improvement of MO material (large θk at shorter λ and lower TC).
From thus obtained results, we can estimate more than 20 times higher density and data rate in the coming 20 years.
Other important themes such as media life, high sensitivity, and overwrite technology are discussed.