Reducing the residual focus error signal in optical pickup head astigmatism displacement systems using the signal conditioning method.

Focusing error detection by the astigmatic method, an important measurement technique, is used widely due to its simple operation and low cost. However, the focus error signal (FES) is prone to noise with the control circuit and the signal conditioning method. To address this, an astigmatic detection system was constructed with a modified digital video disc (DVD) optical head. By designing a stable laser drive control circuit using a low-noise signal conditioning method, the developed system can reduce the FES of background noise. Additionally, by analyzing the data interpolation and approximation model, the corresponding defocus error signal is extracted. The exact optical design of the method has been verified through simulations. Moreover, an experiment is set up to verify the feasibility of the developed method. It is concluded that the method is effective to reduce the background noise 2 nm and the standard deviation 2.15 mV, with PZT working frequencies ranging from 300 Hz to 2 kHz.