Autofocusing effect due to wavelength change of diode lasers in an optical pickup.

A novel autofocusing effect in an optical pickup using a diode laser has been discovered. This effect occurs when a diode laser beam is focused on a disk surface through a focusing lens with chromatic aberration, and a certain amount of the reflected light from the disk is fed back to the diode laser. The wavelength of the diode laser changes with the movement of the disk to keep the amount of optical feedback to the diode laser at a maximum. As a result, focusing of the laser beam onto the disk may be automatically controlled without any lens actuators.