HIGH-DENSITY RECORDING CAPABILITY OF 5-LAYERED PHASE-CHANGE OPTICAL DISC

High-density recording capability of the five-layered phase-change dis c has been examined from the viewpoints of optical simulation and disc performance. The optical simulation showed that the temperature rise in the amorphous state balanced that in the crystal state for the case when the thickness of the lower protective layer was adjusted from 70 nm to 120 nm. Carrier-to-noise ratio (CNR), overwriting erase ratio a nd jitter were measured by the optical recording system using a laser diode with a wavelength of 636 nm and an objective lens of 0.6 numeric al aperture. Track-pitch was fixed at 0.6 mu m and bit length was vari ed at a linear velocity of 6 mis. CNR of 52 dB, overwriting erase rati o of more than 35 dB, and overwriting jitter of less than 10% were obt ained on both land and groove at a bit length of 0.34 mu m/bit.