Patent ID: 6377520
Filing Date: 2002-04-23
Classification: G11B

Abstract:
A focus/tracking method for use on an optical drive to control the focus/tracking of a pickup head, comprising the steps of:(1) generating a laser beam; (2) focusing the laser beam on an optical disc; (3) splitting a returning light from the optical disc in half along a line into a first half part and a second half part, wherein a first multi-element photodetector is formed with three parallel light-sensitive elements oriented perpendicular to the line dividing the light returning from the disc into the first half part and the second half part, each of which is capable of generating an opto-electrical signal whose magnitude is proportional to the intensity of the returning light from the optical disc spotted thereon, the three opto-electrical signals generated respectively by said three light-sensitive elements of said first multi-element photodetector being designated by A, B, and C; and a second multi-element photo detector is formed with three parallel light-sensitive elements oriented perpendicular to the line which divides the light returning from the disc into first and second half parts, each of which is capable of generating an opto-electrical signal whose magnitude is proportional to the intensity of the returning light from the optical disc spotted thereon, the three opto-electrical signals generated respectively by said three light-sensitive elements of said second multi-element photodetector being designated by A*, B*, and C*; (4) guiding the first half part of the returning light to a first optical axis while guiding the second half part of the returning light to a second optical axis; (5) at a fixed position on said first optical axis, detecting the first half part of the returning light to thereby generating a first set of opto-electrical signals; (6) at a fixed position on said second optical axis, detecting the second half part of the returning light to thereby generating a second set of opto-electrical signals; and (7) from said first and second set of opto-electrical signals, obtaining a focus error signal and a tracking error signal, said focus error signal being used for feedback control of the focusing of the laser beam until the laser beam is focused precisely on the optical disc, and said tracking error signal being used for feedback control of the tracking of the laser beam until the laser beam is spotted on the target data track, using a plurality of laser sources, each capable of generating a laser beam of a unique wavelength, and which are connected via optical fibers in a coaxial position, allowing each laser beam having a unique wavelength to be emitted along a same optical axis in a same direction, and wherein said optical fibers are linked to an optical coupler which allows a selected one of the laser beams having a unique wavelength to be guided to a source fiber which emits the selected laser beam along the same optical axis in the same direction.