Method and device for detecting thickness of optical disc

A device for detecting a thickness of an optical disc, the device comprising:

• a processing unit for issuing a focus control output signal;
• a motor driver electrically connected to the processing unit for issuing a focus motor output signal according to the focus control output signal;
• a focusing actuator electrically connected to the motor driver for generating a driving force according to the focus motor output signal;
• an objective lens connected to the focusing actuator and moved in response to the driving force;
• a photo sensor for receiving laser beam reflected from an optical disc in response to movement of the objective lens, thereby generating plural photo signals;
• and
• a pre-amplifier electrically connected to the photo sensor for receiving the photo signals, synthesizing the photo signals into a beam intensity signal and a focusing error signal, and transmitting the beam intensity signal and the focusing error signal to the processing unit,
• wherein a first time interval for a focus point of the laser beam to move from a first layer to a second layer of the optical disc is acquired by the processing unit according to the beam intensity signal or the focusing error signal, a second time interval between two peak values of an S curve of the focusing error signal is detected by the processing unit, and the thickness between the first layer and the second layer is calculated according to a known S-curve detection range, the first time interval and the second time interval.