Fine Focusing Onto an Optical Disk
Original Publication Date: 1987-Jul-01
Included in the Prior Art Database: 2005-Feb-01
When focusing a laser of an optical head onto a rotating grooved optical disk, the focusing lens is dithered up and down at a frequency much higher than that of the disk's rotation. The signal used to achieve this lens dither is compared to the dither component of the head's read signal. The phase relationship between these two signals is used to achieve proper focus. Fig. 1 shows the device. Fig. 2 shows two relative positions of the lens and the groove/land area of the disk, and the dithered read signal which results from the two relative positions. Once approximate focus has been achieved, and laser light 10 is tracking either groove 11 or land 12 on the surface of disk 13, more precise focusing is accomplished. The intensity of return beam signal 14 indicates the amount of light being reflected from the disk.