US Patent 7646691 Optical disk face discriminating system and optical disk drive

An S-curve discriminating portion discriminates that a recording face of an optical disk is opposed to a pickup when a normal S-curve appears in a waveform of a focus error signal Fe that appears when an objective lens fluctuates vertically, while discriminates that a label face is opposed when the waveform of the focus error signal is distorted and two S-curves with large and small magnitudes appear. A signal indicating this discriminated result is supplied to a control portion for controlling respective portions of an optical disk drive.