OPTIMIZATION OF SPHERICAL ABERRATION TO DETERMINE CURRENT LAYER

A spherical aberration correction mechanism is optimised early in the start-up process by measuring responses for various settings of the spherical aberration correction device that are removed from the initial settings of the spherical aberration correction by small amounts and comparing these responses with those anticipated for various of the multiple layers on the optical media. Signal measurements and calibrations can be performed prior to attempting to read data from the disc or concurrently with reading data from the disc. Comparing the responses with ideal, typical or anticipated curves for the various layers can derive the address of the current layer and the desired layer can be immediately accessed. ® KIPO & WIPO 2008