System capable of retrieving information from an optical memory

Claim 2

A photoelectrical system for retrieving infor­mation from an optical memory (l), characterized by comprising: means (ll) for emitting a first and a second light beam (La, Lb); lens means (l2, l8) for converging first and second light beams (La, Lb) onto said optical memory (l), said first and second light beams (La, Lb) being reflected from said optical memory (l); photodetector means (l4) having photosensitive regions (l6A, l6B, l7A, l7B) responsive to said trans­ferred first and second light beams (Lal, La2, Lbl, Lb2) for converting the first light beam (Lal, La2, La3) and the second light beam (Lbl, Lb2, Lb3) into photoelectri­cal signals; and means (22, 23, 75, 80, 83, 88, 89, 44, 90) for processing the photoelectric signals from the photosen­sitive regions (l6A, l6B, l7A, l7B) to eliminate the effect of the signal due to the second light beam and to generate a control signal.

Claim 4

A system according to claim 2, characterized by further comprising means (80, 89-l) for keeping the objective lens (l) in the focused state by moving the objective lens (l) along the optical axis thereof in response to the focusing error signal.

Claim 5

The system according to claim 3, characterized by further comprising means (l9) for deflecting the first and second light beams in accordance with a change of state of the objective lens (l), located between the objective lens (l) and the photodetector means (l4), wherein the first light beam (La) is directed to a boundary line between the photosensitive regions (l6A, l6B) when the objective lens (l8) is in the focused state, and the first beam (La) is directed to one of the photosensitive regions (l6A, l6B) when the objective lens (l8) is in the defocused state.

Claim 6

The system according to claim 3, characterized by further comprising first and second energizing signal generating means (89-l, 89-2, 87, 88) adapted to supply a first energizing signal to the beam emitting means (ll) so that only the first light beam (La) is emitted from the emitting means (ll) and to supply the first and second energizing signals to the emitting means (ll) so that the first and second light beams (La, Lb) are emitted from the emitting means (ll).

Claim 7

The system according to claim 5, characterized in that said first signal generating means (80) includes means (75) adapted to be supplied with photoelectric signals delivered from the photosensitive regions (l6A, l6B, l7A, l7B), while the first energizing signal is being generated, whereby a difference signal indicative of the difference between the photoelectric signals from respective photosensitive regions (l6A, l6B, l7A, l7B) is generated as a focusing signal; switching means (32-l) connected between the photosensitive regions (l6A, l6B, l7A, l7B) and the difference signal generat­ing means (23) for disconnecting the photosensitive regions (l6A, l6B, l7A, l7B) from the difference signal generating means (23) when the second light beam is emitted; and signal holding means (37-l, 37-2) for hold­ing the levels of the photoelectric signals supplied to the difference signal generating means (23).

Claim 8

The system according to claim 3, characterized in that said photodetector means (l4) includes first, second, third, and fourth photosensitive regions (l6A, l6B, l7A, l7B) on which at least part of the first and second light beams is incident, signals from the first and second photosensitive regions (l6A, l6B, l7A, l7B) being supplied to the processing means (80, 90); and said processing means (80, 90) includes means (25, 26, 40, 58) for generating a correction signal responsive to photoelectric signals from the third and fourth photo­sensitive regions (l7A, l7B) equivalent to the signal generated from the second light beam incident on one of the first and second photosensitive regions (l6A, l6B, l7A, l7B), the intensity of the second light beam (Lb) varying with changes of reflection factor for each por­tion of the optical memory (l), means (24) for adding the correction signal to a photoelectric signal from the other of the first and second photosensitive regions (l6A, l6B, l7A, l7B), and means (23) for generating, as a focusing-error signal, a difference signal indicative of the difference between the photoelectric signal to which the correction signal is added and photoelectric signal supplied from the one of the first and second photosen­sitive regions (l6A, l6B).

Claim 9

The system according to claim 7, characterized in that said correction signal generating means (25, 40, 26, 58) includes means (25) for adding the photoelectric signals from the third and fourth photosensitive regions (l7A, l7B) and delivering a summation signal, and means (25, 26, 40) for converting the summation signal into the correction signal.

Claim 10

The system according to claim 7, characterized by further comprising means (5l, 52, 53, 54, 55, 56, 57, 58) for monitoring the first and second light beams (La, Lb) from the light beam generating means (ll) and generating respective monitor signals, wherein said correction signal generating means (25, 26, 40, 58) generates the correction signal in response to the monitor signals and the photoelectric signals from the third and fourth photoelectric signals (l7A, l7B).

Claim 11

l0. The system according to claim 9, characterized in that said monitor signal generating means (5l, 52, 53, 54, 55, 56, 57, 58) includes detecting means (52, 53) for detecting and converting the first and second light beams into said first and second monitor signals, respectively, adding means (56) for adding the first and second monitor signals and delivering a summation signal, and means (57) for dividing the second monitor signal by the summation signal and delivering a division signal.

Claim 13

A photoelectric system for retrieving in­formation from an optical memory, characterized by comprising: means (ll) for emitting first and second laser beams (La, Lb); optical means (l2, l8) for converging first and second laser beams onto a surface of said optical memory (l), said laser beams being reflected from said optical memory (l); photodetector means (l4) having photosensitive regions (l6A, l6B, l7A, l7B) responsive to said re­flected first and second laser beams (Lal, Lbl) for con­verting the first laser beam (Lal, Lbl) and the second laser beam (Lbl) into photoelectric signals; means (22, 23, 75, 80, 83, 88, 89, 44, 90) for processing the photoelectric signals from the photosen­sitive regions to eliminate the effect of the signal due to the second laser beam (Lbl) and to generate a control signal responsive only to the first laser beam (Lal); and means (8l) responsive to said control signal for moving said optical means (l8) for focusing said first laser beam on the optical memory (l).

Claim 14

A photoelectric system for retrieving in­formation from an optical memory, characterized by comprising: means (ll) for emitting first and second laser beams (La, Lb); optical means (l2, l8) for converging first and second laser beams onto a surface of said optical memory (l), said laser beams being reflected from said optical memory (l); photodetector means (l4) having photosensitive regions (l6A, l6B, l7A, l7B) responsive to said re­flected first and second laser beams (Lal, Lbl) for con­verting the first laser beam (Lal, Lbl) and the second laser beam (Lbl) into photoelectric signals; means (22, 23, 75, 80, 83, 88, 89, 44, 90) for processing the photoelectric signals from the photosen­sitive regions to eliminate the effect of the signal due to the second laser beam (Lbl) and to generate a control signal responsive only to the first laser beam (Lal); and means (8l) responsive to said control signal for moving said optical means (l8) for focusing said first laser beam on the optical memory (l).

Claim 19

A photoelectric system for retrieving infor­mation from an optical memory (l) comprising: a semiconductor laser (ll) for emitting a first and a second light beam (La, Lb); an objective lens (l8) for converging the first and second light beams (La, Lb) onto said optical memory (l), said first and second light beams (La, Lb) being reflected from said optical memory (l); photodetector means (l4) having at least four photosensitive regions (l6A, l6B, l7A, l7B) responsive to said reflected first and second light beams (Lal, Lbl) for converting the first and second light beams (Lal, Lbl) into photoelectric signals; and a correction circuit for processing the photo­electric signals (22) from the photosensitive regions (l6A, l6B, l7A, l7B) to generate a control signal which includes gain controller means (26) for developing a correction signal to eliminate the effect of the photo­electric signal caused by the second light beam (Lbl).

Claim 20

A photoelectric system for retrieving infor­mation from an optical memory (l) comprising: a semiconductor laser (ll) for emitting a first and a second light beam (La, Lb); an objective lens (l8) for converging the first and second light beams (La, Lb) onto said optical memory (l), said first and second light beams (La, Lb) being reflected from said optical memory (l); photodetector means (l4) having at least four photosensitive regions (l6A, l6B, l7A, l7B) responsive to said reflected first and second light beams (Lal, Lbl) for converting the first and second light beams (Lal, Lbl) into photoelectric signals; and a correction circuit for processing the photo­electric signals (22) from the photosensitive regions (l6A, l6B, l7A, l7B) to generate a control signal which includes gain controller means (26) for developing a correction signal to eliminate the effect of the photo­electric signal caused by the second light beam (Lbl).