Optical recording and/or reproducing apparatus

Claim 1

An optical recording and/or reproducing apparatus comprising an optical arrangement including light beam generating means (10) for producing a light beam (L), light beam dividing means (22) for dividing the light beam (L) from the light beam generating means (10) into a main light beam (Lm) and at least two auxiliary light beams (Lp,Ln), photosensing means (14), and optical path forming means for causing the main light beam (Lm) and two auxiliary light beams (Lp,Ln) obtained from the light beam dividing means (22) to impinge upon a disc-shaped record medium (D) and for guiding the main light beam (Lm') and two auxiliary light beams (Lp',Ln') emanating from the disc-shaped record medium (D) to the photosensing means (14), and a signal generating circuit block (40) operative to produce signals based on detection outputs obtained from the photosensing means (14), wherein the optical path forming means is so constituted that two auxiliary light spots (Qp,Qn) are formed on the disc-shaped record medium (D) by two auxiliary light beams (Lp,Ln), respectively, in such a manner that one of the auxiliary light beam spots (Qp,Qn) is distant substantially a distance corresponding to a quarter of a track pitch (Tp) from a main light beam spot (Qm) formed on the disc-shaped record medium (D) by the main light beam (Lm) toward an outer peripheral portion of the disc-shaped record medium (D) along a radial direction of the disc-shaped record medium (D) and the other of the auxiliary light beam spots (Qp,Qn) is distant substantially the distance corresponding to a quarter of the track pitch (Tp) from the main light beam spot (Qm) toward a central portion of the disc-shaped record medium (D) along the radial direction of the disc-shaped record medium (D); the photosensing means (14) is provided with a first photodetecting element (60) divided substantially into two parts for detecting the main light beam (Lm') from the disc-shaped record medium (D), a second photodetecting element (62) divided substantially into two parts for detecting one of two auxiliary light beams (Lp',Ln') from the disc-shaped record medium (D) and a third photodetecting element (64) divided substantially into two parts for detecting the other of two auxiliary light beams (Lp',Ln') from the disc-shaped record medium (D); and the signal generating circuit block (40) is constituted to obtain a first difference signal (Sm) between detection output signals obtained respectively from the two parts of the first photodetecting element(60), a second difference signal (Sp) between detection output signals obtained respectively from the two parts of the second photodetecting element (62) and a third difference signal (Sn) between detection output signals obtained respectively from the two parts of the third photodetecting element (64), and then to produce a tracking error signal (St) based on a ratio of a difference between the first difference signal (Sm) and the sum of the second and third difference signals (Sp,Sn) in relation to a difference between the second and third differences signals (Sp,Sn).