Source: http://www.google.com/patents/US6339564?dq=mirroring+data+in+a+remote+data+storage+system
Timestamp: 2017-10-23 01:50:50
Document Index: 158483787

Matched Legal Cases: ['arts 25', 'art 25', 'art 25', 'arts 25', 'arts 216', 'arts 216', 'arts 35', 'art 35', 'art 35', 'art 35', 'art 35', 'art 35', 'art 35', 'art 35', 'art 35', 'arts 45', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45', 'art 45', 'arts 55', 'art 55', 'arts 37', 'arts 37', 'arts 37', 'arts 37', 'arts 37', 'arts 37', 'arts 37', 'art 35', 'art 35', 'art 35', 'art 35', 'art 35', 'arts 35', 'arts 35', 'arts 37', 'art 75', 'art 75', 'arts 75', 'arts 75', 'art 75', 'art 75', 'art 75', 'art 75', 'arts 75', 'arts 75', 'art 75', 'art 75', 'art 75', 'arts 75', 'art 75', 'art 75', 'arts 75', 'art 75', 'art 75', 'art 75', 'art 90', 'art 90', 'art 90', 'art 85', 'Application No. 7', 'arts 547', 'art 547', 'arts 547', 'art 547', 'arts 547', 'arts 547', 'arts 571', 'art 547', 'art 547', 'art 547', 'art 547', 'art 547', 'arts 135', 'art 135', 'arts 135', 'art 135', 'arts 135', 'arts 135', 'arts 35', 'Application No. 98111079', 'Application No. 98111085']

Patent US6339564 - Optical information recording/reproducing apparatus - Google Patents
An optical information recording/reproducing apparatus records information on and/or reproduces information from an optical recording medium based on a reflected light beam from the optical recording medium. The apparatus includes a light splitting part having a plurality of light splitting stages which...http://www.google.com/patents/US6339564?utm_source=gb-gplus-sharePatent US6339564 - Optical information recording/reproducing apparatus
Publication number US6339564 B2
Application number US 09/734,217
Also published as US6185166, US20010001264
Publication number 09734217, 734217, US 6339564 B2, US 6339564B2, US-B2-6339564, US6339564 B2, US6339564B2
Inventors Koichi Tezuka, Kyoko Miyabe, Satoshi Itami, Tohru Fujimaki, Kazushi Uno
Patent Citations (31), Non-Patent Citations (6), Referenced by (5), Classifications (48), Legal Events (5)
US 6339564 B2
1. An optical information recording/reproducing apparatus which records information on and/or reproduces information from an optical recording medium based on a reflected light beam from the optical recording medium, comprising:
a light splitting part having a plurality of light splitting stages which split the reflected light beam from the optical recording medium into a plurality of light beams;
a photodetector unit including n photodetectors which receive m light beams output from a final stage of said light splitting part, where m=6 and n=5, said n photodetectors of said photodetector unit including a plurality of photodetectors which are arranged to receive light beams used to detect a focal error and include two two-part photodetectors respectively having photodetector parts A and B and photodetector parts C and D, at least one photodetector which is arranged to receive a light beam used to detect a tracking error, and a plurality of photodetectors which are arranged to receive light beams used to detect optical information recorded on the optical recording medium; and
first calculating means for calculating a focal error signal FES based on outputs of the photodetector parts A, B, C and D by a formula FEC=(A+C)−(B+D), where the outputs of the photodetector parts A, B, C and D are designated by the same designations as the photodetector parts A, B, C and D.
2. The optical information recording/reproducing apparatus as claimed in claim 1, wherein:
said at least one photodetector which is arranged to receive the light beams used to detect the tracking error includes one two-part photodetector having photodetector parts E and F; and
second calculating means for calculating a tracking error signal TES based on outputs of the photodetector parts E and F by a formula TES=E−F, where the outputs of the photodetector parts E and F are designated by the same designations as the photodetector parts E and F.
3. The optical information recording/reproducing apparatus as claimed in claim 1, wherein:
said photodetectors which are arranged to receive the light beams used to detect the optical information include two photodetector parts G and H; and
second calculating means for calculating an optical signal MO based on outputs of the photodetector parts G and H by one of formulas MO=(A+B+H)−(C+D+G) and MO=(A+B+C+D)−(G+H), where the outputs of the photodetector parts G and H are designated by the same designations as the photodetector parts G and H.
4. The optical information recording/reproducing apparatus as claimed in claim 1, wherein:
said at least one photodetector which is arranged to receive the light beams used to detect the tracking error includes one two-part photodetector having photodetector parts E and F;
second calculating means for calculating an identification signal ID based on outputs of at least some of the photodetector parts A, B, C, D, E, F, G and H by one of formulas ID=A+B+C+D+G+H and ID=A+B+C+D+E+F+G+H, where the outputs of the photodetector parts E, F, G and H are designated by the same designations as the photodetector parts E, F, G and H.
5. An optical information recording/reproducing apparatus which records information on and/or reproduces information from an optical recording medium based on a reflected light beam from the optical recording medium, comprising:
a photodetector unit including n photodetectors which receive m light beams output from a final stage of said light splitting part, where m=6 and n=6, said n photodetectors of said photodetector unit including a plurality of photodetectors which are arranged to receive light beams used to detect a focal error and include two two-part photodetectors respectively having photodetector parts A and B and photodetector parts C and D, at least one photodetector which is arranged to receive a light beam used to detect a tracking error, and a plurality of photodetectors which are arranged to receive light beams used to detect optical information recorded on the optical recording medium; and
first calculating means for calculating a focal error signal FES based on outputs of the photodetector parts A, B, C and D by a formula FES=(A+C)−(B+D), where the outputs of the photodetector parts A, B, C and D are designated by the same designations as the photodetector parts A, B, C and D.
6. The optical information recording/reproducing apparatus as claimed in claim 5, wherein:
said at least one photodetector which is arranged to receive the light beams used to detect the tracking error includes two two-part photodetectors respectively having photodetector parts E1 and F1 and photodetector parts E2 and F2; and
second calculating means for calculating a tracking error signal TES based on outputs of the photodetector parts E1, F1, E2 and F2 by a formula TES=(E1+E2)−(F1+F2), where the outputs of the photodetector parts E1, F1, E2 and F2 are designated by the same designations as the photodetector parts E1, F1, E2 and F2.
7. The optical information recording/reproducing apparatus as claimed in claim 5, wherein:
said at least one photodetector which is arranged to receive the light beams used to detect the tracking error includes two two-part photodetectors respectively having photodetector parts E1 and F1 and photodetector parts E2 and F2;
second calculating means for calculating an optical signal MO based on outputs of at least some of the photodetector parts A, B, C, D, E1, F1, E2, F2, G and H by one of formulas MO=(E1+F1+G)−(E2+F2+H) and MO=(A+B+E2+F2+H)−(C+D +E1+F1+G), where the outputs of the photodetector parts E1, F1, E2, F2, G and H are designated by the same designations as the photodetector parts E1, F1, E2, F2, G and H.
8. The optical information recording/reproducing apparatus as claimed in claim 5, wherein:
said at least one photodetector which is arranged to receive the light beams used to detect the tracking error includes two two-part photodetectors having photodetector parts E1 and F1 and photodetector parts E2 and F2;
second calculating means for calculating an identification signal ID based on outputs of at least some of the photodetector parts A, B, C, D, E1, F1, E2, F2, G and H by one of formulas ID=E1+F1+G+E2+F2+H and ID=A+B+C+D+E1+E2+F1+F2+G+H, where the outputs of the photodetector parts E1, F1, E2, F2, G and H are designated by the same designations as the photodetector parts E1, F1, E2, F2, G and H.
9. An optical information recording/reproducing apparatus which records information on and/or reproduces information from an optical recording medium based on a reflected light beam from the optical recording medium, comprising:
a photodetector unit including n photodetectors which receive m light beams output from a final stage of said light splitting part, where m=10 and n=6, said n photodetectors of said photodetector unit including a plurality of photodetectors which are arranged to receive light beams used to detect a focal error and include two two-part photodetectors respectively having photodetector parts A and B and photodetector parts C and D, at least one photodetector which is arranged to receive a light beam used to detect a tracking error, and a plurality of photodetectors which are arranged to receive light beams used to detect optical information recorded on the optical recording medium; and
10. The optical information recording/reproducing apparatus as claimed in claim 9, wherein:
11. The optical information recording/reproducing apparatus as claimed in claim 9, wherein:
second calculating means for calculating an optical signal MO based on outputs of the photodetector parts E1, F1, E2 and F2 by a formula MO=(E1+F1)−(E2+F2), where the outputs of the photodetector parts E1, F1, E2 and F2 are designated by the same designations as the photodetector parts E1, F1, E2 and F2.
12. The optical information recording/reproducing apparatus as claimed in claim 9, wherein:
said at least one photodetector which is arranged to receive the light beams used to detect the tracking error includes two two-part photodetector having photodetector parts E1 and F1 and photodetector parts E2 and F2;
second calculating means for calculating an identification signal ID based on outputs of at least some of the photodetector parts A, B, C, D, E1, F1, E2, F2, G and H by one of formulas ID=E1+F1+G+E2+F3+H and ID=A+B+C+D+E1+E2+F1+F2+G+H, where the outputs of the photodetector parts E1, F1, E2, F2, G and H are designated by the same designations as the photodetector parts E1, F1, E2, F2, G and H.
This application is a division of prior application Ser. No. 08/993,703, filed Dec. 18, 1997, now U.S. Pat. No. 6,185,166, which is a Continuation-In-Part application of prior application Ser. No. 08/742,764, filed Nov. 1, 1996, now U.S. Pat. No. 5,793, 725, which is a division of prior application Ser. No. 08/513,578, filed Aug. 10, 1995, now U.S. Pat. No. 5,623,462, which is a File-Wrapper-Continuation of prior application Ser. No. 08/084,362, filed Jun. 30, 1993, now abandoned.
The servo signal detection system includes a condenser lens 212, a beam splitter 213, a 2-part photodetector 214, a composite prism 215 and a 4-part photodetector 216. The other of the two light beams output from the beam splitter 208 is input to the 2-part photodetector 214 via the condenser lens 212 and the beam splitter 213 on one hand, and is input to the 4-part photodetector 216 via the composite prism 215 on the other. The 2-part photodetector 214 forms a tracking error detection system in the servo signal detection system, and generates a tracking error signal by obtaining a difference between the outputs of the 2-part photodetector 214 according to the push-pull technique. The composite prism 215 and the 4part photodetector 216 form a focal error detection system in the servo signal detection system, and generates a focal error signal based on outputs of the 4-part photodetector 216 according to the Foucault technique. A focus servo operation controls the relative positional relationship of the objective lens 206 and the disk 207 based on the focal error signal, so that an in-focus position is located on the disk 207.
TES=A−B (1)
FES=(A−B)+(C−D) (2)
Another and more specific object of the present invention is to provide an optical information recording/reproducing apparatus which records information on and/or reproduces information from an optical recording medium and detects a focal error based on a reflected light beam from the optical recording medium, comprising a composite prism deflecting a part of the reflected light beam to at least two positions excluding a central part of the reflected light beam,.and photodetector means including a plurality of photodetectors for respectively detecting the deflected parts of the reflected light beam and outputting detection outputs, where the focal error is detected based on the detection outputs of the photodetector means. According to the optical information recording/reproducing apparatus of the present invention, it is possible to obtain an accurate focal error signal because the tolerable margin of the focal error detection system can be set large with respect to the unbalanced distribution of the quantity of the light beam irradiated on the optical recording medium, the mounting error of the composite prism, the photodetector and the like.
FIG. 4 is a perspective view showing an 10 example of the shapes of a composite prism and a 4part photodetector;
FIG. 17 is a diagram showing a fifth embodiment of the optical information recording/reproducing apparatus-according to the present invention;
The reflected light beam which is obtained via the beam splitters 204 and 208, the condenser lens 212 and the beam splitter 213 is input to the composite prism 25. Out of the reflected light beam which is input to the-composite prism 25, the light beams transmitted through the tapered parts 25 a and 25 b of the composite prism 25 form spots on the corresponding 2-part photodetectors 26 a and 26 b of the 4-part photodetector unit 26. Accordingly, by carrying out the operation of the formula (2) described above using the outputs of the 2-part photodetectors 26 a and 26 b, it is possible to obtain a focal error signal FES similarly to the conventional case.
In this embodiment, a light absorbing or blocking layer 25 cA is formed on the central part 25 c of a composite prism 25A which has a triangular prism shape so as to absorb or block the light beam which has the wavelength of the light emitted from the laser diode 201 shown in FIG. 1. This light absorbing or blocking layer 25 cA may be formed on the front surface or the rear surface of the composite prism 25A at the central part 25 c. In addition, this embodiment uses a 4-part photodetector 216A shown in FIG. 12.
In this case, the reflected light beam which is obtained via the beam splitters 204 and 208, the condenser lens 212 and the beam splitter 213 is input to the composite prism 25A. Out of the reflected light beam which is input to the composite prism 25A, the light beams transmitted through the tapered parts 25 a and 25 b of the composite prism 25A form spots on the corresponding detector parts 216 a, 216 b, 216 c and 216 d of the 4-part photodetector 216A. Accordingly, by carrying out the operation of the formula (2) described above using the outputs of the detector parts 216 a, 216 b, 216 c and 216 d, it is possible to obtain a focal error signal FES similarly to the conventional case
FIGS. 13(a) through 13(d) show simulation results describing the relationship of the focal position and the focal error signal FES in the prior art shown in FIG. 4. In FIGS. 13(a) through 13(d), a bold solid line indicates a case where a detector shift is 0, a solid line indicates a case-where the detector shift is +10 μm, a dotted line indicates a case where the detector shift is +20 μm, a bold dotted line indicates a case where the detector shift is −10 μm, and a bold and fine dotted line indicates a case where the detector shift is −20 μm. The “detector shift” refers to the shift of the division line E of the 4-part photodetector 216 in the y-direction in FIG. 4, and an upward shift in FIG. 4 is taken as a positive (+) shift and a downward shift in FIG. 4 is taken as a negative (−) shift.
On the other hand, FIGS. 14(a) through 14(d) show simulation results describing the relationship of the focal position and the focal error signal FES in 10 the first embodiment shown in FIG. 9 or the third embodiment shown in FIG. 11. In FIGS. 14(a) through 14(d), a bold solid line indicates a case where the detector shift is 0, a solid line indicates a case where the detector shift is +10 μm, a dotted line indicates a case where the detector shift is +20 μm, a bold dotted line indicates a case where the detector shift is −10 μm, and a bold and fine dotted line indicates a case where the detector shift is −20 μm.
FIGS. 18(a) and 18(b) show the composite prism 35 on an enlarged scale. FIG. 18(a) shows a perspective view of the composite prism 35, and FIG. 18(b) shows a plan view of the composite prism 35. As shown in FIGS. 18(a) and 18(b), the composite prism 35 includes tapered first and second parts 35 a and 35 b, and a third part 35 c which has a convex surface with a slight curvature. Hence, a reflected light beam 30 which is obtained via the beam splitter 208 is split into three light beams 30 a, 30 b and 30 c.
FIG. 19 is a perspective view, on an enlarged scale, showing an important part of FIG. 17. The photodetector unit 36 includes a first photodetector 36 a, a second photodetector 36 b, and a third photodetector 36 c. The first photodetector 36 a includes photodetectors 37 a and 37 b. The second photodetector 36 b includes photodetectors 37 c and 37 d. The third photodetector 36 c includes photodetectors 37 e and 37 f.
Out of the reflected light beam 30 which is refracted and condensed via the condenser lens 212, the light beam 30 a which is transmitted through the first part 35 a is deflected depending on the taper angle of the first part 35 a and is irradiated on the first photodetector 36 a of the photodetector unit 36, while the light beam 30 b which is transmitted through the second part 35 b is deflected depending on the taper angle of the second part 35 b and is irradiated on the second photodetector 36 b of the photodetector unit 36. In addition, the light beam 30 c which is transmitted through the third part 35 c is refracted depending on the curvature of the third part 35 c and is irradiated on the third photodetector 36 c of the photodetector unit 36. In other words, the light beams 30 a and 30 b are only subjected to the refraction function of the condenser lens 212, but the light beam 30 c is subjected to the refraction function of the condenser lens 212 and the third part 35 c itself. Therefore, image formation points 300 a and 300 b of the respective light beams 30 a and 30 b are different from an image formation point 300 c of the light beam 30 c. That is, distances L1 and L2 from the condenser lens 212 to the image formation points 300 a and 300 b of the respective light beams 30 a and 30 b are different from a distance L3 from the condenser lens 212 to the image formation point 300 c of the light beam 30 c.
In FIG. 19, the photodetector unit 36 is arranged on a plane which is perpendicular to the optical axis of the reflected light beam 30 and includes the image formation points 300 a and 300 b. Because of this arrangement, the first and second photodetectors 36 a and 36 b which are used to generate the focal error signal FES based on the Foucault technique are respectively provided at the positions of the image formation points 300 a and 300 b of the light beams 30 a and 30 b. On the other hand, the third photodetector 36 c which is used to generate the tracking error signal TES based on the push-pull technique is provided at a position deviated from the position of the image formation point 300 c of the light beam 30 c. Hence, it is possible to generate the focal error signal FES using the Foucault technique and to generate the tracking error signal TES using the push-pull technique by use of a simple optical system. The generation itself of the focal error signal FES and the tracking error signal TES may be made similarly to the prior art, and a description thereof will be omitted.
FIGS. 20(a) and 20(b) show the composite prism 45 on an enlarged scale. FIG. 20(a) shows a perspective view of the composite prism 45, and FIG. 20(b) shows a plan view of the composite prism 45. As shown in FIGS. 20(a) and 20(b), the composite prism 45 includes tapered first and second parts 45 a and 45 b, and a third part 45 c which has a concave surface with a slight curvature. Hence, a reflected light beam 30 which is obtained via the beam splitter 208 is split into three light beams 30 a, 30 b and 30 c.
FIG. 21 is a perspective view, on an enlarged scale, showing an important part of this embodiment. The photodetector unit 36 is the same as the photodetector unit 36 used in the fifth embodiment.
Out of the reflected light beam 30 which is refracted and condensed via the condenser lens 212, the light beam 30 a which is transmitted through the first part 45 a is deflected depending on the taper angle of the first part 45 a and is irradiated on the first photodetector 36 a of the photodetector unit 36, while the light beam 30 b which is transmitted through the second part 45 b is deflected depending on the taper angle of the second part 45 b and is irradiated on the second photodetector 36 b of the photodetector unit 36. In addition, the light beam 30 c which is transmitted through the third part 45 c is refracted depending on the curvature of the third part 45 c and is irradiated on the third photodetector 36 c of the photodetector unit 36. In other words, the light beams 30 a and 30 b are only subjected to the refraction function of the condenser lens 212, but the light beam 30 c is subjected to the refraction function of the condenser lens 212 and the third part 45 c itself. Therefore, image formation points 300 a and 300 b of the respective light beams 30 a and 30 b are different from an image formation point 300 c of the light beam 30 c. That is, distances L1 and L2 from the condenser lens 212 to the image formation points 300 a and 300 b of the respective light beams 30 a and 30 b are different from a distance L3 from the condenser lens 212 to the image formation point 300 c of the light beam 30 c.
In other words, the image formation point 300 c of the light beam 30 c is located between the composite prism 35 and the photodetector unit 36 in the fifth embodiment, but the image formation point 300 c of the light beam 30 c in this embodiment is located beyond the photodetector unit 36 in FIG. 21 along the traveling direction of the light beam.
FIGS. 22(a) and 22(b) show the composite prism 55 on an enlarged scale. FIG. 22(a) shows a perspective view of the composite prism 55, and FIG. 22(b) shows a plan view of the composite prism 55. As shown in FIGS. 22(a) and 22(b), the composite prism 55 includes tapered first and second parts 55 a and 55 b, and a flat third part 55 c which has not taper. Hence, a reflected light beam 30 which is obtained via the beam splitter 208 is split into three light beams 30 a, 30 b and 30 c.
FIG. 23 is a perspective view, on an enlarged scale, showing an important part of this embodiment. The photodetector unit 56 includes a first photodetector 56 a, a second photodetector 56 b, and a third photodetector 56 c. The first photodetector 56 a includes photodetectors 37 a and 37 b. The second photodetector 56 b includes photodetectors 37 c and 37 d. The third photodetector 56 c includes photodetectors 37 e and 37 f. The third photodetector 56 c is arranged on a plane different from a plane on which the first and second photodetectors 56 a and 56 b are arranged.
In this embodiment, an analyzer 208A shown in FIGS. 24 and 25 is used together with the composite prism 35 and the photodetector unit 36 shown in FIG. 17.
FIG. 26 shows a plan view of the photodetector unit 66. The focal error signal FES can be generated according to the Foucault technique based on outputs of the photodetectors 66 a, 66 b, 66 d, 66 e, 66 g and 66 h of the photodetector unit 66. The photodetectors 66 a, 66 d and 66 g receive the three light beams from the first part of the composite prism 35, while the photodetectors 66 b, 66 e and 66 h receive the three light beams from the second part of the composite prism 35. The image formation points of these six light beams match the positions of the photodetectors 66 a, 66 b, 66 d, 66 e, 66 g and 66 h. On the other hand, the tracking error signal TES can be generated according to the push-pull technique based on outputs of the photodetectors 66 c, 66 f and 66 i. The photodetectors 66 c, 66 f and 66 i receive the three light beams from the third part of the composite prism 35. The image formation points of these three light beams are deviated from the positions of the photodetectors 66 c, 66 f and 66 i.
As shown in FIG. 26, the photodetector 66 a includes photodetector parts 37 a and 37 b, the photodetector 66 b includes photodetector parts 37 c and 37 d, . . . , and the photodetector 66 i includes photodetector parts 37 q and 37 r. Accordingly, if the outputs of these photodetector parts 37 a through 37 i are denoted by the same reference numerals as these parts, the focal error signal FES using the Foucault technique can be generated based on any one of the following formulas (3a) through (3d) by calculation.
FES=[(37 a)+(37 g)+(37 m)+(37 d)+(37 j)+(37 p)]−[(37 b)+(37 h)+(37 n)+(37 c)+(37 i)+(37 o)] (3a)
FES=[(37 a)+(37 p)]−[(37 b)+(37 o)] (3b)
FES=[(37 m)+(37 d)]−[(37 n)+(37 c)] (3c)
FES=[(37 a)+(37 d)+(37 m)+(37p)]−[(37 b)+(37 c) +(37 n)+(37 o)] (3d)
The focal error signal FES obtained by the formula (3a) has a high signal-to-noise (S/N) ratio and is uneasily affected by external disturbances because all of the beams irradiated on the photodetector unit 66 is used and consequently a large amount of light is used to detect the focal error signal FES.
On the other hand, the focal error signal FES obtained by the formula (3b) or (3c) enables easy and simple adjustments since only two beams are used to detect the focal error signal FES and thus only two beams need to be irradiated on corresponding two photodetectors 66 a and 66 h or, 66 b and 66 g, of the photodetector unit 66 so that each beam irradiates a division line separating the two photodetector parts forming each of the photodetectors 66 a and 66 h or, 66 b and 66 g.
Furthermore, the focal error signal FES obtained by the formula (3d) can obtain, to a certain extent, the above described effects obtainable with respect to the focal error signals FES obtained by the formulas (3a) and (3b) or (3c). In addition, in the case of the focal error signal FES obtained by the formula (3d), the required adjustments are simpler compared to the case of the focal error signal FES obtained by the formula (3a). Moreover, the focal error signal FES obtained by the formula (3d) has a higher S/N ratio and is less affected by external disturbances as compared to the focal error signal FES obtained by the formulas (3b) or (3c).
The tracking error signal TES using the push-pull technique can be generated based on one of the following formulas (4a) and (4b) by calculation.
TES=[(37 e)+(37 k)+(37 q)]−[(37 f)+(371)+(37 r)] (4a)
TES=[(37 e)+(37 q)]−[(37 f)+(37 r)] (4b)
The tracking error signal TES obtained by the formula (4a) has a high S/N ratio and is uneasily affected by external disturbances because all of the beams irradiated on the photodetector unit 66 is used and consequently a large amount of light is used to detect the tracking error signal TES.
On the other hand, the tracking error signal TES obtained by the formula (4b) enables easy and simple adjustments since only two beams are used to detect the tracking error signal TES and thus only two beams need to be irradiated on corresponding two photodetectors 66 c and 66 i of the photodetector unit 66 so that each beam irradiates a division line separating the two photodetector parts forming each of the photodetectors 66 c and 66 i.
Furthermore, by the function of the analyzer 208A, a magneto-optic signal (information signal) MO which is recorded on the disk 207 can be reproduced based on one of the following formulas (5a) and (5b) by calculation.
The tracking error signal TES according to the above described formulas (4a) and (4b) can be generated by use of known adders and subtracter.
MO=[(37 a)+(37 b)+(37 e)+(37 f)+(37 c)+(37 d)]−[(37 m)+(37 n)+(37 q)+(37 r)+(37 o)+(37 p)] (5a)
MO=[(37 a)+(37 b)+(37 c)+(37 d)]−[(37 m)+(37 n) +(37 o)+(37 p)] (5b)
According to the magneto-optic signal MO obtained by the formula (5a), it is possible to obtain an average signal amplitude which is relatively large. On the other hand, according to the magneto-optic signal MO obtained by the formula (5b), it is possible to obtain a relatively high resolution.
The disk 207 is also recorded with positional information which indicates a track, sector and the like on the disk 207. This positional information is often referred to as an identification signal ID, and this identification signal ID can be recorded in the form of pits on the disk 207 as is well known. The identification signal ID can be reproduced based on the following formula (6) by calculation. In other words, the magneto-optic signal MO is reproduced by obtaining a difference between the outputs of the adders, while the identification signal ID is reproduced by obtaining a sum of the outputs of the adders.
ID=[(37 a)+(37 b)+(37 e)+(37 f)+(37 c)+(37 d]+[(37 m)+(37 n)+(37 q)+(37 r)+(37 o)+(37 p)] (6)
The identification signal ID according to the above described formula (6) can be generated by use of known adders.
FES=(A+C)−(B+D) (7)
The focal error signal FES according to the above described formula (7) can be generated by use of known adders and subtracter.
TES=E−F (8)
The tracking error signal TES according to the above described formula (8) can be generated by use of a known subtracter.
MO=G−H (9)
The magneto-optic signal MO according to the above described formula (9) can be generated by use of a known subtracter.
ID=G+H (10)
The identification signal ID according to the above described formula (10) can be generated by use of a known adder.
FIG. 31 shows a plan view of the photodetector unit 66B. As shown in FIG. 31, the photodetector unit 66B includes photodetectors 66 aa through 66 ii. The photodetector 66 aa includes photodetector parts 37 aa and 37 bb, the photodetector 66 bb includes photodetector parts 37 cc and 37 dd, . . . , and the photodetector 66 ii includes photodetector parts 37 qq and 37 rr.
The three light beams output from the third part 35B-3 of the composite prism 35B are respectively irradiated on the photodetectors 66 cc, 66 ff and 66 ii. The three light beams output from the fourth part 35B-4 of the composite prism 35B are respectively irradiated on the photodetectors 66 cc, 66 ff and 66 ii. Further, the three light beams output from the fifth part 35B-5 of the composite prism 35B are respectively irradiated on the photodetectors 66 cc, 66 ff and 66 ii. On the other hand, the three light beams output from the first part 35B-1 of the composite prism 35B are respectively irradiated on the photodetectors 66 aa, 66 dd and 66 gg. The three light beams output from the second part 35B-2 of the composite prism 35B are respectively irradiated on the photodetectors 66 bb, 66 ee and 66 hh.
The image formation points of the six light beams output from the-first and second parts 35B-1 and 35B-2 match the positions of the photodetectors 66 aa, 66 bb, 66 dd, 66 ee, 66 gg and 66 hh. On the other hand, the image formation points of the three light beams output from each of the third, fourth and fifth parts 35B-3, 35B-4 and 35B-5 are deviated from the positions of the photodetectors 66 cc, 66 ff and 66 ii.
If the outputs of the photodetector parts 37 aa through 37 ii of the photodetector unit 66B are denoted by the same reference numerals as these parts, the focal error signal FES using the Foucault technique, the tracking error signal TES using the push-pull technique and the identification signal ID can be obtained by calculations similarly to the eighth embodiment described above based on the formulas (3a) through (3d), (4a), (4b) and (6).
Furthermore, the magneto-optic signal MO recorded on the disk 207 can be reproduced based on one of the following formulas (11a) and (11b) by calculation.
MO=[(37 aa)+(37 bb)+(37 ee)+(37 ff)+(37 cc)+(37 dd)]−[(37 mm)+(37 nn)+(37 qq)+(37 rr)+(37 oo)+(37 pp)] (11a)
MO=[(37 ee)+(37 ff)]−[(37 qq+(37 rr)] (11b)
According to the magneto-optic signal MO obtained by the formula (11a), it is possible to obtain an average signal amplitude which is relatively large. On the other hand, according to the magneto-optic signal MO obtained by the formula (11b), it is possible to obtain a relatively high resolution. Moreover, the resolution obtainable according to the magneto-optic signal MO obtained by the formula (11b) is further improved compared to that obtainable according to the formula (5b). The reason for this further improved resolution of the magneto-optic signal MO using the composite prism 35B having the shape shown in FIG. 30 may be understood from the teachings of the Proceedings of Magneto-Optical Recording International Symposium '96, J. Magn. Soc. Jpn., Vol. 20, Supplement No. S1 (1996), pp. 233-238.
Accordingly, this embodiment uses a +1st order diffracted light 30-1 which is diffracted by the grating of the first part 75 a, a +1st order diffracted light 30-2 which is diffracted by the grating of the second part 75 b, and a 0th order diffracted light 30-3 which passes through the first and second parts 75 a and 75 b without being affected by the gratings thereof. In addition, the grating patterns of the first and second parts 75 a and 75 b are designed such that the +1st order diffracted light 30-1 which is emitted from the first part 75 a is refracted twice via the condenser lens 212 and the first part 75 a before being imaged at an image formation point 300 a, and the +1st order diffracted light 30-2 which is emitted from the second part 75 b is refracted twice via the condenser lens 212 and the second part 75 b before being imaged at an image formation point 300 b. On the other hand, since the 0th order diffracted light 30-3 passes through the holographic optical element 75 as it is without being affected by the grating patterns, the 0th order diffracted light 30-3 is refracted only by the condenser lens 212 and is imaged at an image formation point 300 c.
In FIG. 32, the photodetector unit 36 is arranged on a plane which is perpendicular to the optical axis of the reflected light beam and includes the image formation points 300 a and 300 b. Because of this arrangement, the first and second photodetectors 36 a and 36 b which are used to generate the focal error signal FES based on the Foucault technique are respectively provided at the positions of the image formation points 300 a and 300 b of the +1st-order diffracted lights 30-1 and 30-2. On the other hand, the third photodetector 36 c which is used to generate the tracking error signal TES based on the push-pull technique is provided at a position deviated from the position of the image formation point 300 c of the 0th order diffracted light 30-3. Hence, it is possible to generate the focal error signal FES using the Foucault technique and to generate the tracking error signal TES using the push-pull technique by use of a simple optical system. The generation itself of the focal error signal FES and the tracking error signal TES may be made similarly to the prior art, and a description thereof will be omitted.
As described above, the holographic optical element 75 includes the first and second parts 75 a and 75 b which are provided with independent patterns for deflecting, converging and diverging the light. More particularly, the patterns of the first and second parts 75 a and 75 b are respectively set so that the +1st order diffracted light 30-1 from the first part 75 a converges to a point P′ (−x, 0) and the +1st order diffracted light 30-2 from the second part 75 b converges to a point P(x, 0). Points P and P′ are located on a plane η which is a distance f away from the holographic optical element 75 along the optical axis. In other words, the function of the first part 75 a is to image the parallel incident light at a focal point O at a focal distance f, and to converge the light to the point P′ by deflecting the light by a distance x in the negative x-direction.
FIG. 35 shows a plan view of the holographic optical element 75. Since the patterns of the first and second parts 75 a and 75 b are in point symmetry with respect to the origin 0 in FIG. 35, the pattern of the first part 75 a, for example, is made up of concentric grooves or projections having a center at the point P′ (−x, 0). A radius ri of an ith concentric groove or projection can be obtained from the following formula (12), where λ denotes the wavelength of the light output from the light source.
ri={square root over ((2+L ·f·λ·i))} (12)
In addition, the cross sectional shape of the first part 75 a is determined so that the ratios of the 0th order diffracted light and the +1st order diffracted light with respect to the total quantity of light become predetermined values.
In FIG. 37, the patterns of the first and second parts 75 a and 75 b are set so that the +1st order diffracted light 30-1 from the first part 75 a converges to a point Q′ (−x, y), the −1st order diffracted light from the first part 75 a is projected in a semicircular shape about a point R′ (x, −y), the +1st order diffracted light 30-2 from the second part 75 b converges to a point Q(x, y), and the −1st order diffracted light is projected in a semicircular shape about a point R(−x, −y). The points Q, Q′, R and R′ are located on the plane η which is the distance f from the holographic optical element 75 along the optical axis.
The first emission surface 85 a and the third emission surface 85 c are inclined towards the same direction, and an inclination angle α1 of the first emission surface 85 a relative to a reference plane is smaller than an inclination angle α3 of the third emission surface 85 c. For example, the reference plane is the back surface of the composite prism 85, which is approximately perpendicular to the traveling direction of the incoming reflected light beam. On the other hand, the second emission surface 85 b and the fourth emission surface 85 d are inclined towards the same direction, and an inclination angle α2 of the second emission surface 85 b is smaller than an inclination angle α4 of the fourth emission surface 85 d.
In FIG. 40, the first light beam 87 a which is emitted from the first emission surface 85 a of the composite prism 85 is received by the light receiving parts A and D of the first photodetector 86 a. In addition, the second light beam 87 b which is emitted from the second emission surface 85 b of the composite prism 85 is received by the light receiving parts B and C of the first photodetector 86 a. Hence, a focal error signal FES is generated according to the Foucault technique based on the formula (2) described above. More particularly, the outputs of the light receiving parts A and C are added in an adder 321, the outputs of the light receiving parts B and D are added in an adder 322, and the outputs of these adders 321 and 322 are supplied to a differential amplifier 323 which outputs the focal error signal FES.
On the other hand, the third light beam 87 c which is emitted from-the third emission surface 85 c of the composite prism 85 is received by the light receiving part E of the second photodetector 86 b, and the fourth light beam 87 d which is emitted from the fourth emission surface 85 d of the composite prism 85 is received by the light receiving part F of the third photodetector 86 c. Hence, a tracking error signal TES is generated according to the push-pull technique based on the formula (1) described above. More particularly, the outputs of the light receiving parts E and F are supplied to a differential amplifier 331, and the tracking error signal TES is output from this differential amplifier 331.
Moreover, if the photodetector unit 86 is adjusted to detect a predetermined focal error signal FES, it is possible to employ a structure that would automatically receive the third light beam 87 c by the light receiving part E of the photodetector 86 b and receive the fourth light beam 87 d by the light receiving part F of the photodetector 86 c. Hence, there is an additional advantage in that no adjustment is required in this case for the detection of the tracking error signal TES.
On the other hand, the photodetector unit 86A includes a first photodetector 86Aa, a second photodetector 86Ab-1. a third photodetector 86Ab-2, a fourth photodetector 86Ac-1 and a fifth photodetector 86Ac-2 which are provided on a single plane as shown in FIG. 44. The first photodetector 86Aa includes four light receiving parts A through D for receiving the first and second light beams 91 a and 91 b. The second photodetector 86Ab-1 includes a light receiving part E1 for receiving the third light beam 91 c, and the third photodetector 86Ab-2 includes a light receiving part E2 for receiving the fourth light beam 91 d. The fourth photodetector 86Ac-1 includes a light receiving part F1 for receiving the fifth light beam 91 e, and the fifth photodetector 86Ac-2 includes a light receiving part F2 for receiving the sixth light beam 91 f.
Out of the reflected light beam 89 which is input to the integral part 90 via the condenser lens 212, a light component 89-1 which passes above the upper part of the Wollaston prism 92 in FIG. 43 and reaches the composite prism 85 directly is refracted. by the first emission surface 85 a and is emitted from the first emission surface 85 a as the first light beam 91 a. As shown in FIG. 44, this first light beam 91 a is received by the light-receiving parts A and D of the first photodetector 86Aa.
On the other hand, out of the reflected light beam 89 which is input to the integral part 90 via the condenser lens 212, a light component 89-2 which passes below the lower part of the Wollaston prism 92 in FIG. 43 and reaches the composite prism 85 directly is refracted by the second emission surface 85 b and is emitted from the second emission surface 85 b as the second light beam 91 b. As shown in FIG. 44, this second light beam 91 b is received by the light receiving parts B and C of the first photodetector 86Aa.
A focal error signal FES is generated according to the Foucault technique based on the formula (2) described above, similarly to the eleventh embodiment shown in FIG. 38.
Out of the reflected light beam 89 which is input to the integral part 90 via the condenser lens 212, a light component 89-3 which reaches the Wollaston prism 92 is split into a p-polarized light (wave) 95 and an s-polarized light (wave) 96. The p-polarized light 95 is, deflected by an angle β with respect to an extension line 97 of the light component 89-3 towards the first emission surface 85 a. On the other hand, the s-polarized light 96 is deflected by an angle β with respect to the extension line 97 towards the second emission surface 85 b.
The p-polarized light 95 and the s-polarized light 96 output from the Wollaston prism 92 is input to the composite prism 85. The angle β is small, and the p-polarized light 95 and the s-polarized light 96 propagate within the mountain part 85 e of the composite prism 85. The p-polarized light 95 and the s-polarized light 96 reach the third and fourth emission surfaces 85 c and 85 d and are refracted thereby, and are thereafter emitted from the third and fourth emission surfaces 85 c and 85 d.
In other words, in FIG. 44 the p-polarized light 95 is emitted from the third emission surface 85 c as the third light beam 91 c. This third light beam 91 c irradiates the light receiving part E1 of the second photodetector 86Ab-1. On the other hand, the s-polarized light 96 is emitted from the third emission surface 85 c as the fourth light beam 91 d. This fourth light beam 91 d irradiates the light receiving part E2 of the third photodetector 86Ab-2.
Similarly in FIG. 44, p-polarized light 95 is. emitted from the fourth emission surface 85 d as the fifth light beam 91 e. This fifth light beam 91 e irradiates the light receiving part F1 of the fourth photodetector 86Ac-1. On the other hand, the s-polarized light 96 is emitted from the fourth emission surface 85 e as the sixth light beam 91 f. This sixth light beam 91 f irradiates the light receiving part F2 of the fifth photodetector 86Ac-2.
In addition a magneto-optic signal (information signal) MO is obtained based on the outputs of the light receiving parts E1, E2, F1 and F2 of the second through fifth photodetectors 86Ab-1 through 86Ac-2. More particularly, the magneto-optic signal MO is obtained through adders 312 and 313, and the differential amplifier 311B shown in FIG. 44, by calculating MO (E1+F1)−(E2+F2).
Furthermore, an address signal ADR is. obtained based on the outputs of the light receiving parts E1, E2, F1 and F2 of the second through fifth. photodetectors 86Ab-1 through 86Ac-2. More particularly, the address- signal ADR is obtained through the adder 332, the adder 333, and the adder 311A shown in FIG. 44, by calculating ADR=(E1+E2)+(F1+F2).
By comparing FIG. 41 to FIG. 38, it may be seen that this twelfth embodiment shown in FIG. 41 does not have the optical path which extends horizontally from the beam splitter 208 in FIG. 38. For this reason, the space occupied by the optical system within the optical information recording/reproducing apparatus and the number of required parts are further reduced in this embodiment when compared to the eleventh embodiment. In other words, both the size and cost of the optical information recording/reproducing apparatus in this embodiment can further be reduced when compared to those of the eleventh embodiment.
According to the fifth embodiment of the optical information recording/reproducing apparatus described above in conjunction with FIGS. 24, 25 and 26, the reflected light beam from the disk 207 is split into nine light beams which are irradiated on. the photodetector unit 66. But the optical information recording/reproducing apparatus can be made to have a more simple construction which is more compact, if the focal error signal FES, the tracking error signal TES, the magneto-optic signal MO and the identification signal ID can be obtained based on detections of a smaller number of light beams at the photodetector unit. Hence, a description will now be given of further embodiments of the optical information recording/reproducing apparatus which can obtain the signals FES, TES, MO and ID based on a smaller number of light beams-without greatly deteriorating the signal qualities.
FIG. 45 shows a thirteenth embodiment of the optical information recording/reproducing apparatus according to the present invention. As shown in FIG. 45, a magneto-optic head unit of an optical information recording/reproducing apparatus is arranged under a magneto-optic disk 505. A laser beam emitted from a laser diode 501 which is used as a coherent light source is converted into a parallel-ray by a collimator lens 502, and is input to a beam splitter 503. The parallel ray transmitted through the beam splitter 503 is converged on a magnetic layer of the magneto-optic disk 505 by an objective lens 504. The converged laser beam is reflected by the magneto-optic disk 505, and is input again to the beam splitter 503. This time, the reflected light beam is reflected by the beam splitter 503 towards. a photodetector unit 509. More particularly, the reflected light beam is reflected by the beam splitter 503 and is input to a Wollaston prism 506 which is an analyzer.
FIGS. 47 through 49 respectively show plan views of the photodetector unit 509. FIG. 47 shows a state where the objective lens 504 and the magneto-optic disk 505 are close to each other. FIG. 48 shows a state where the laser beam is in focus on the magneto-optic disk 505 In addition, FIG. 49 shows a state where the objective lens 504 and the magneto-optic disk 505 are far away from each other. For the sake of convenience, FIGS. 47 through 49 show the photodetector unit 509 viewed from a back surface side of the photodetector unit 509.
As may be seen from FIGS. 47 through 49, the photodetector unit 509 is a light receiving element, and photodetectors of the photodetector unit 509 are arranged in three stages from the top to bottom in the vertical direction. An upper stage portion of the photodetector unit,509 has a photodetector including a photodetector part G for detecting a magneto-optic signal MO and an identification signal ID, and a 2-part photodetector including photodetector parts A and B for detecting a focal error signal FES. A middle stage portion of the photodetector unit 509 has a 2-part photodetector including photodetector parts E and F for detecting a tracking error signal TES. Further, a lower stage portion of the photodetector unit 509 has a 2-part photodetector including photodetector parts C and D for detecting the focal error signal FES, and a photodetector including a photodetector part H for detecting the magneto-optic signal MO and the identification signal ID.
FES=(A+C)−(B+D) (13)
The tracking error signal TES using the push-pull technique can be generated based on the following formula (14) by calculation using a known subtracter.
TES=E−F (14)
The magneto-optic signal MO can be reproduced based on the following formula (15) by calculation, using known adders and subtracter.
MO=(A+B+H)−(C+D+G) (15)
In addition, the identification signal ID can be reproduced based on the following formula (16a) or (16b) by calculation, using known adders.
ID=(A+B+H)+(C+D+G) (16a)
ID=A+B+C+D+E+F+H+G (16b)
When the identification signal ID is reproduced based on the formula (16a), the number of adders provided in the LSI is relatively small, thereby making it possible to improve the S/N ratio of the identification signal ID. On the other hand, the identification signal ID may become distorted depending on the shape and depth of the pits formed in the magneto-optic disk 505. Hence, when the identification signal ID is reproduced based on the formula (16b), it is possible to positively prevent the identification signal ID from becoming distorted because all of the diffracted light beams from the pits of the magneto-optic disk 505 are used to detect the identification signal ID.
According to this embodiment, a beam splitter means comprises a plurality of beam splitting stages for splitting the reflected light beam from the magneto-optic disk 505-into a plurality of light beams which are projected onto a single light receiving element. More particularly, the beam splitter means comprises the Wollaston prism 506 and the composite prism 507 in this embodiment, and the reflected light beam from the magneto-optic disk 505 is split into six light beams. The six split light beams are projected onto the single photodetector unit 509. As a result, the optical information recording/reproducing apparatus can be formed by a relatively small number of parts, and the arrangement of these relatively small number of parts can be simply adjusted with ease. Furthermore, the cost of the optical information recording/reproducing apparatus can be reduced due to the relatively small number of parts used. In addition, since the photodetector unit 509 is formed by only five photodetectors (eight photodetector parts A through H), it is possible to reduce the stray capacitance of the photodetectors and to reduce the noise generated by the adders and subtracter within the LSI which obtains the focal error signal FES, the-tracking error signal TES, the magneto-optic signal MO and the identification signal ID, as compared to the embodiment shown in FIGS. 25 and 26, for example. Consequently, the signal qualities of these signals FES, TES, MO and ID can be improved.
In addition, the magneto-optic signal MO and the identification signal ID are reproduced using also the outputs of the 2-part photodetectors (photodetector parts A, B, C and D) which detect the light beams for obtaining the focal error signal FES, in addition to using the outputs of the photodetectors (photodetector parts G and H) which detect the light beams for obtaining the magneto-optic signal and the identification signal ID. Thus, because of the small number of photodetector parts used to reproduce the magneto-optic signal MO and the identification signal ID, the SIN ratio of these signal MO and ID is improved. On the other hand, the required frequency bands of the magneto-optic signal MO and the identification signal ID are higher than those of the tracking error signal TES and the focal error signal FES which requires a frequency band lower than that of the tracking error signal TES. Further, when two or more kinds of signals are obtained based on the detection of the same light beam, the circuit construction of the circuit used to obtain these signals becomes simpler as the frequency bands of these signal become wider apart from each other. Therefore, by obtaining-the magneto-optic signal MO and the identification signal ID based on-the detection of the same light beam that is used to obtain the focal error signal FES, it is possible to simplify the circuit construction also from this point of view.
Furthermore, because the magneto-optic signal MO and the identification signal ID are reproduced using also the outputs of the 2-part photodetectors (photodetector parts A, B, C and D) which detect the light beams for obtaining the focal error signal FES in addition to using the outputs of the photodetectors (photodetector parts G and H) which detect the light beams for obtaining the magneto-optic signal and the identification signal ID, the resolution of the magneto-optic signal MO and the identification signal ID is improved. It is taught in a Japanese Laid-Open Patent Application No. 7-6379 that the resolution of the magneto-optic signal is improved when a central portion of the reflected light beam from a recording medium is masked and the magneto-optic signal is detected from a peripheral portion of the reflected light beam. In this embodiment, the light beam used to detect the focal error signal FES is the light beam transmitted through the tapered deflection surfaces 571 and 573 of the composite prism 507 as shown in FIG. 46. In other words, out of the reflected light beam from the magneto-optic disk 505, the light beam transmitted through the central deflection surface 572 of the composite prism 507 is not used, and only the light beam transmitted through the tapered deflection-surfaces 571 and 573 on both sides of the central deflection surface 572 of the composite prism 507 is used to detect the focal error signal FES. As a result, the resolution of the magneto-optic signal MO and the identification signal ID is improved by obtaining the magneto-optic signal MO and the identification signal ID using the light beam which is transmitted through the tapered. deflection surfaces 571 and 573 of the composite prism 507 and is used to detect the focal error signal FES.
Next, a description will be given of the light beam that is used to detect the focal error signal FES in this embodiment. FIGS. 50A through 50C are diagrams for explaining the shape of spots formed by the split light beams. FIG. 50A shows a plan view of the deflection surfaces 571, 572 and 573 of the composite prism 507, together with light beams “a” and “b” when the two polarized light beams are transmitted through the deflection surfaces 571, 572 and 573. FIGS. 50B and 50C respectively show plan views of the photodetector part G of the photodetector unit 509 on which the light beams “a” and “b” are projected, together with spots “aa” and “bb” of the light beams “a” and “b” irradiated on the photodetector part G and the photodetector parts A and B via the deflection surface 571. FIGS. 50B and 50C show the photodetector viewed from the back surface side of the photodetector unit 509.
The area of the light beam “b” transmitted through the deflection surface 571 is smaller than that of the light beam “a”, which means that the light beam “b” is deflected more. In this state, the length of the spot “bb” formed on the photodetector parts A and B along the major axis is longer than that of the spot “aa” formed on the photodetector part G. According to the Foucault technique, the longer the length of the spot along the major axis, the easier it is to perform the required adjustments of the arrangement of the optical elements and the photodetectors, and the-focal error signal FES is less affected by changes with time, temperature changes and the like. Hence, in this embodiment, the locations of the 2-part photodetector including the photodetector parts A and B and the 2-part photodetector including the photodetector parts C and D are determined so that out of the light beams transmitted through the deflection surfaces 571 and 573, the light beams which are deflected more are projected onto the 2-part photodetector including the photodetector parts A and B and the 2-part photodetector including the photodetector part C and D.
Next, a description will be given of the effects of the temperature on this embodiment. When the temperature of the optical information recording/reproducing apparatus rises, a housing which fixes the photodetector unit 509 undergoes a thermal expansion, thereby making the photodetectors of the photodetector unit 509 farther away from the composite prism 507. For similar reasons, the objective lens 504 become farther away from the magneto-optic disk 505. As a result, the reflected light beam from the magneto-optic disk 505 is once converged and thereafter spreads before being projected onto the photodetector unit 509. The spot formed on the 2-part photodetector including the photodetector parts A and B and the spot formed on the 2-part photodetector including the photodetector parts C and D are projected on the corresponding division lines of the 2-part photodetectors when the 2-part photodetectors are located at the focal positions of the light beams. However, if the 2-part photodetectors are located farther away from the focal positions of the light beams, the spots of the light beams are formed on the outer sides of the corresponding division lines of the 2-part photodetectors as shown in FIG. 49, and in this case, the spots of the light beams are only formed on the photodetector parts B. and D of the 2-part photodetectors.
When the temperature of the magneto-optic head rises; the separation angle of the light beams output from the Wollaston prism 506 also changes. FIG. 51 shows a plan view of the photodetector unit 509 at a high temperature, viewed from the back surface side of the photodetector unit 509. The Wollaston prism 506 is made of a birefringence material such as crystal and lithium-niobate, and the separation angle of the light beams changes depending on the temperature. For example, a description will be given of the Wollaston prism 506 having a separation angle which becomes narrow at high temperatures. As shown in FIG. 51, the spots of the light beams formed on the 2-part photodetectors located on the right and left move towards the inner side of the photodetector unit 509 due to the temperature characteristic of the Wollaston prism 506. In other words, the separation angle of the light beams output from the Wollaston prism 506 becomes narrow due to the temperature rise, and the spots of the light beams move toward the inner side of the photodetector unit 509 to become projected on the corresponding division lines of the 2-part photodetectors respectively including the photodetector parts A and B and the photodetector parts C and D.
On the other hand, in the case where the separation angle of the light beams output from the Wollaston prism 506 used or, a Rochon prism (not shown) which is use in place of the Wollaston prism 506, becomes wide at high temperatures and the 2-part photodetectors located on the right and left of the photodetector unit 509 are positioned farther away from the focal positions of the light beams, the light. beams used are such that the spots of the light beams are formed on the inner side of the corresponding division lines of the 2-part photodetectors. Hence, when the temperature rises and the 2-part photodetectors become farther away from the Wollaston prism 506, the separation angle of the light beams output from the Wollaston prism 506 becomes wide such that the spots of the light beams are projected on the corresponding division lines of the 2-part photodetectors of the photodetector unit 509. As a result, it is possible to carry out a stable automatic focusing operation based on an accurate focal error signal FES even when the temperature becomes high.
Next, a description will be given of a first modification of the thirteenth embodiment of the optical information recording/reproducing apparatus according to the present invention, by referring to FIG. 52. In this first modification of the thirteenth embodiment, the basic-construction of the optical information recording/reproducing apparatus is basically the same as that of the thirteenth embodiment shown in. FIGS. 45 and 46, but a photodetector unit 591 is used in place of the photodetector unit 509. FIG. 52 shows a plan view of the photodetector unit 591 used in this first modification of the thirteenth embodiment. In FIG. 52, those parts which are the same as those corresponding parts in FIGS. 46 and 47 are designated by the same reference characters, and a description thereof will be omitted.
FIG. 52 shows the photodetector unit 591 in a state where the laser beam is in focus on the magneto-optic disk 505, viewed from the back surface side of the photodetector unit 591. The light beams reaching the photodetector unit 591 via the Wollaston prism 506 and the composite prism 507 is obtained via the same optical path as that of the thirteenth embodiment. Photodetectors-of the photodetector unit 591 are arranged in three stages from the top to bottom in the vertical direction. An upper stage portion of the photodetector unit 591 has a photodetector including a photodetector part G for detecting a magneto-optic signal MO and an identification signal ID, and a 2-part photodetector including photodetector parts AA and BB for detecting a focal error signal FES. A middle stage portion of the photodetector unit 591 has a 2-part photodetector including photodetector parts E and F for detecting a tracking error signal TES. Further, a lower stage portion of the photodetector unit 591 has a 2-part photodetector including photodetector parts C and D for detecting the focal error signal FES, and a photodetector including a photodetector part H for detecting the magneto-optic signal MO and the identification signal ID.
This first modification of the thirteenth embodiment, the light beam which forms a spot having an oval shape which is longer along the major axis and the light beam which forms a spot having an oval shape which is shorter along the major axis on the photodetector unit 591 are used to obtain the focal error signal FES. In other words, one of the two light beams obtained by the separation made at the Wollaston prism 506 or Rochon prism is used to detect the focal error signal FES. As a result, the obtained focal error signal FES is less affected by the temperature characteristic of the Wollaston prism 506 or Rochon prism when compared with the thirteenth embodiment described above.
As described above, the separation angle of the two light beams output from the Wollaston prism 506 or Rochon prism changes with temperature. For example, the separation-angle of the two light beams output from the Wollaston prism 506 becomes narrow at high temperatures. Hence, if both the two light beams separated and output from the Wollaston prism 506 are used to detect the focal error signal FES, the focal error signal FES is greatly affected by the temperature. But if only one of the two light beams separated and output from the Wollaston prism 506 is used to detect the focal error signal FES as in the case of the first modification of the thirteenth embodiment, it is possible to detect the focal error signal FES without being affected by the temperature characteristic of the Wollaston prism 506 or Rochon prism.
FES=(AA+C)−(BB+D) (17)
TES=E−F (18)
MO=(AA+BB+C+D)−(G+H) (19)
ID=(AA+BB+C+D)+(G+H) (20a).
ID=AA+BB+C+D+E+F+G+H (20b)
When the identification signal ID is reproduced based on the formula (20a), the number of adders provided in the LSI is relatively small, thereby making it possible to improve the S/N ratio of the identification signal ID. On the other hand, the identification signal ID may become distorted depending on the shape and depth of the pits formed in the magneto-optic disk 505. Hence, when the identification signal ID is reproduced based on the formula (20b), it is possible to positively prevent the identification signal ID from becoming distorted because all of the diffracted light beams from the pits of the magneto-optic disk 505 are used to detect the identification signal ID.
FIG. 53 shows the photodetector unit 592 in a state where the laser beam is in focus on the magneto-optic disk 505, viewed from the back surface side of the photodetector unit 592. The light beams reaching the photodetector unit 592 via the Wollaston prism 506 and the composite prism 507 is obtained via the same optical path as that of the thirteenth embodiment. Photodetectors of the photodetector unit 592 are arranged in three stages from the top to bottom in the vertical direction. An upper stage portion of the photodetector unit 592 has a photodetector including a photodetector part G for detecting a magneto-optic signal MO and an identification signal ID, and a 2-part photodetector including photodetector parts A and B for detecting a focal error signal FES. A middle stage portion of the photodetector unit 592 has a 2-part photodetector including photodetector parts E1 and F1 and a 2-part photodetector including photodetector parts E2 and F2 for detecting a tracking error signal TES. Further, a lower stage portion of the photodetector unit 592 has a 2-part photodetector including photodetector parts C and D for detecting the focal error signal FES, and a photodetector including a photodetector part H for detecting the magneto-optic signal MO and the identification signal ID.
The 2-part photodetectors respectively including the photodetector parts E1 and F1 and the photodetector parts E2 and F2 receive the light beams output from the deflection surface 572 of the composite prism 507. If the outputs of the photodetector parts A through D, E1, E2, F1, F2, G and H of the photodetector-unit 592 are denoted by the same reference characters as these parts, the focal error signal FES according to the Foucault technique, the tracking error signal TES according to-the pushpull technique, the magneto-optic signal MO and the identification signal-ID can be obtained based on the following formulas (21a) through (24a) or (24a′) by calculation using known adders and subtracter.
FES=(A+C)−(B+D) (21a)
TES=(E1+E2)−(F1+F2) (22a)
MO=(E1+F1+G)−(E2+F2+H) (23a)
ID=(E1+F1+G)+(E2+F2+H) (24a)
ID=A+B+C+D+E1+E2+F1+F2+G+H (24a′)
When the identification signal ID is reproduced based on the formula (24a), the number of adders provided in the LSI is relatively small, thereby making it possible to improve the S/N ratio of the identification signal ID. On the other hand, the dentification signal ID may become distorted depending on the shape-and depth of the pits formed in the magneto-optic disk 505. Hence, when the identification signal ID is reproduced based on the formula (24a′), it is possible to positively prevent the identification signal ID from becoming distorted because all of the diffracted light beams from the pits of the magneto-optic disk 505 are used to detect the identification signal ID.
Alternatively, it is possible to reproduce the magneto-optic signal MO and the identification signal ID using the light beams which are used to detect both the tracking error signal TES and-the focal error signal FEB. In this case, the focal error signal FES according to the Foucault technique, the tracking error signal TES according to the push-pull technique, the magneto-optic signal MO and the identification signal ID can be obtained based on the following formulas (21b) through (24b) by calculation using known adders and subtracter.
FES=(A+C)−(B+D) (21b)
TES=(E1+E2)−(F1+F2) (22b)
MO=(A+B+E2+F2+H)−(C+D+E1+F1+G) (23b)
ID=(A+B+E2+F2+H)+(C+D+E1+F1+G) (24b)
When the identification signal ID is reproduced based on the formula (24b), the number of adders provided in the LSI is relatively small, thereby making it possible to improve the S/N ratio of the identification signal ID.
Next, a description will be given of a third modification of the thirteenth embodiment of the optical information recording/reproducing apparatus according to the present invention, by referring to F1GS. 54 through 56. In F1G. 54, those parts which are the same as those corresponding parts in F1G. 46 and 53 are designated by the same reference numerals, and a description thereof will be omitted.
In this third modification of the thirteenth embodiment, the analyzer 506 is used together with a composite prism 547 shown in F1G. 55 and the photodetector unit 592 shown in F1G. 54.
The reflected light beam from the magneto-optic disk 505 is split into two light beams by the analyzer 506, and each of the two light beams are further-split into five light beams by the composite prism 547, thereby resulting in ten (2×5=10) light beams being output from the composite prism 547. The ten light beams from the composite prism 547 are irradiated on corresponding ones of six photodetectors which form the photodetector unit 592.
F1G. 55 shows a perspective view of the composite prism 547. As shown in F1G. 55, the composite prism. 547 includes tapered first and second parts 547-1 and 547-2, a central third part 547-3 which has a convex surface with a slight curvature, and peripheral fourth and fifth parts 547-4 and 547-5 which have convex surfaces with a slight curvature matching that of the third part 547-3. In other words, the third, fourth and fifth parts 547-3, 547-4 and 547-5 are all parts of a single convex surface having a slight curvature. The first and second parts 547-1 and 547-2 function similarly to the first and second parts 571 and 573 of the composite prism 507.
F1G. 56 shows a plan view of the photodetector unit 592. As shown in F1G. 56, the photodetector unit 592 includes the photodetectors respectively including the photodetector parts G and H, and the 2-part photodetectors respectively including the photodetector parts A and B, C and D, E1 and F2, and E2 and F2.
The two light beams output from the third part 547-3 of the composite prism 547 are respectively irradiated on the 2-part photodetector including the photodetector parts. E1 and F1 and the 2-part photodetector including the photodetector parts E2 and F2. The two light beams output from the fourth part 547-4 of the composite prism 547 are respectively irradiated on the 2-part photodetector including the photodetector parts E1 and F1 and the 2-part photodetector including the photodetector parts E2 and F2. Further, the two light beams output from the fifth part 547-5 of the composite prism-547 are respectively irradiated on the 2-part photodetector including the photodetector parts E1 and F1 and the 2-part photodetector including the photodetector parts E2 and F2. On the other hand, the two light beams output from the first part 547-1 of the composite prism 547 are respectively irradiated on the photodetector including-the photodetector part G and the 2-part photodetector including the photodetector parts A and B. The two light beams output from the second part 547-2 of the composite prism 547 are respectively irradiated on the 2-part photodetector including the photodetectors C and D and the photodetector including the photodetector part H.
FES=(A+C)−(B+D) (25)
TES=(E1+E2)−(F1+F2) (26)
MO=(E1+F1)−(E2+F2) (27)
ID=(E1+F1)+(E2+F2) (28a)
ID=A+B+C+D+E1+E2+F1+F2+G+H (28b)
When the identification signal ID is reproduced based on the formula (28a), the number of adders provided in the LSI is relatively small, thereby making it possible to improve the S/N ratio of the identification signal ID. On the other hand, the identification signal ID may become distorted depending on the shape and depth of the pits formed in the magneto-optic disk 505. Hence, when the identification signal ID is reproduced based on the formula (28b), it is possible to positively prevent the identification signal ID from becoming distorted because all of the diffracted light beams from the pits of the magneto-optic disk 505 are used to detect the identification signal ID.
According to the magneto-optic signal MO obtained by the formula (27), it is possible to obtain a relatively high resolution. The reason for this further improved resolution of the magneto-optic signal MO using the composite prism 547 having the shape shown in F1G. 55 may be understood from the teachings of the Proceedings of Magneto-Optical Recording International Symposium '96, J. Magn. Soc. Jpn., Vol. 20, Supplement No. S1 (1996), pp. 233-238.
Next, a description will be given of a fourteenth embodiment of the optical information recording/reproducing apparatus according to the present invention, by referring to F1G. 57. F1G. 57 shows a perspective view of an important part of the fourteenth embodiment of the optical information recording/reproducing apparatus, that is, a signal detection system, on an enlarged scale. In F1G. 57, those parts which are-the same as those corresponding parts in F1G. 46 are designated by the same reference numerals, and a description thereof will be omitted.
F1G. 57 shows a state where the light beam output from the Wollaston prism 506 is projected on the photodetector unit 509. The reflected light beam input to the Wollaston prism 506 is separated into two polarized light beams and input to a composite prism 517. As shown in F1G. 57, the composite prism 517 is an optical element having three deflection surfaces 571, 572 a and 573 arranged side by side from the left to right. The deflection surfaces 571 and 573 on both sides of the composite prism 517 have tapered surfaces for deflecting the light beam in-upward and downward directions by mutually different angles. On the other hand, the deflection surface 572 a at the central part of the composite prism 517 has a concave shape having a curvature with respect to the optical axis, and directs the two split light beams towards the photodetector parts E and F of the 2-part photodetector forming the photodetector unit 509. Each of the two polarized light beams input to the composite prism 517 having the structure described above is spatially split into three by the three deflection surfaces 571, 572 a and 573, thereby. outputting a total of six light beams from the composite prism 517. The six light beams output from. the composite prism 517 are projected on the photodetector unit 509 via a condenser lens 508. For the sake of convenience, the illustration of the condenser lens 508 shown in F1G. 45 is omitted in F1G. 57.
Otherwise, the functions and effects of this embodiment are similar to those of the thirteenth embodiment described above, and the focal-error signal FES, the tracking error signal TES, the magneto-optic signal MO and the identification signal ID can be obtained based on the formulas described with reference to the thirteenth embodiment. Furthermore, this embodiment may employ the photodetector unit 591 or 592 of the first or second modification of the thirteenth embodiment described above, so as to obtain similar functions and effects as those of the first or second modification of the thirteenth embodiment.
Next, a description will be given of a fifteenth embodiment of the optical information recording/reproducing apparatus according to the present invention, by referring to F1G. 58. F1G. 58 shows a perspective view of an important part of the fifteenth embodiment of the optical information recording/reproducing apparatus, that is, a signal detection system, on an enlarged scale. In F1G. 58, those parts which are the same as those corresponding parts in F1G. 46 are designated by the same reference numerals, and a description thereof will be omitted.
F1G. 58 shows a state where the light beam output from the Wollaston prism 506 is projected on a photodetector unit 593. The reflected light beam input to the Wollaston prism 506 is separated into two polarized light beams and input to a composite prism 527. As shown in F1G. 58, the composite prism 527 is. an optical element having three deflection surfaces 571 b, 572 b and 573 b arranged side by side from the left to right. The deflection surfaces 571 b and 573 b on both sides of the composite prism 527 have tapered surfaces for deflecting the light beam in upward and downward directions by mutually different angles. On the other hand, the deflection surface 572 b at the central part of the composite prism 527 has a flat surface which is perpendicular to the optical axis, and directs the two split light beams towards the photodetector parts E and F of a 2-part photodetector forming the photodetector unit 593. Each of the two polarized light beams-input to the composite prism 527 having the structure described above is spatially split into three by the three deflection surfaces 571 b, 572 b and 573 b, thereby outputting a total of six light beams from the composite prism 527. The six light beams output from the composite prism 527 are projected on the photodetector unit 593 via a condenser lens 508. For the sake of convenience, the illustration of the condenser lens 508 shown in F1G. 45 is omitted in F1G. 58.
Next, a description will be given of a sixteenth embodiment of the optical information recording/reproducing apparatus according to the present invention, by referring to F1G. 59. F1G. 59 shows a perspective view of an important part of the sixteenth embodiment of the optical information recording/reproducing apparatus, that is, a signal detection system, on an enlarged scale. In F1G. 59, those parts which are the same as those corresponding parts in F1G. 46 are designated by the same reference numerals, and a description thereof will be omitted.
F1G. 59 shows a state where the light beam output from the Wollaston prism 506 is projected on a photodetector unit 593. The reflected light beam input to the Wollaston prism 506 is separated into two polarized light beams and input to a holographic optical element 537. As shown in F1G. 59, the holographic optical element 537 is an optical element having two diffraction surfaces 537 a and 537 b arranged side by side from to each other. The diffraction surfaces 537 a and 537 b of the holographic optical element 537 have gratings with sawtooth-shaped cross sections which are provided symmetrically about a center point of the holographic optical element 537.
The two polarized light beams input to the holographic optical element 537 are respectively separated mainly into ±1st and ±0th order diffracted light beams by the diffraction surfaces 527 a and 537 b, and a total of six light beams are projected onto the corresponding photodetectors of the photodetector unit 509 via a condenser lens 508. Actually, high order diffracted light beams of ±2nd order or greater are generated from the holographic optical element 537, but the light quantity of the high order diffracted light beams is small and negligible. For the sake of convenience, the illustration of the condenser lens 508 shown in F1G. 45 is omitted in F1G. 59.
F1GS. 60A through 60D respectively are circuit diagrams showing circuits for obtaining the focal error signal FES, the tracking error signal TES, the magneto-optic signal MO and the identification signal ID of the first modification of the eighth embodiment based on the formulas (7) through (10) described above.
F1G. 60A shows a circuit including adders 801 and 802 and a subtracter 803 which are connected as shown to generate the focal error-signal FES based on the outputs of the photodetector parts A through D.
F1G. 60B shows a circuit including a subtracter 804 to generate the tracking error signal TES based on the outputs of the photodetector parts E and F.
F1G. 60C shows a circuit including a subtracter 805 to reproduce the magneto-optic signal MO based on the outputs of the photodetector parts G and G.
F1G. 60D shows a circuit including an adder 806 to reproduce the identification signal ID based on the outputs of the photodetector parts G and H.
F1G. 61 is a perspective view showing a composite prism which may be used in place of the composite prisms 35B and 547 shown in F1GS. 30 and 55.
As shown in F1G. 61, a composite prism 135B includes tapered first and second parts 135B-1 and 135B-2, a central third part 135B-3 which has a concave surface with a slight curvature, and peripheral fourth and fifth parts 135B-4 and 135B-5 which have concave surfaces with a slight curvature matching that of the third part 135B-3. In other words, the third, fourth and fifth parts 135B-3, 135B-4 and 135B-5 are all parts of a single concave surface having a slight curvature. The first and second parts 135B-1 and 135B-2 function similarly to the first and second parts 35B-1 and.35B-2 of the composite prism 35B shown in F1G. 30. This composite prism 135B may be used in the optical system shown in F1GS. 29 and 54, for example, and substantially the same effects are obtainable as in the embodiments shown in F1GS. 29 and 54.
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JPH0373425A Title not available
JPH0750030A Title not available
JPH0935284A Title not available
JPH0997434A Title not available
JPH01144233A Title not available
JPH03157821A Title not available
JPH04349248A Title not available
JPH04372728A Title not available
JPH06251396A Title not available
JPS61260440A Title not available
JPS63127436A Title not available
JPS63275044A Title not available
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U.S. Classification 369/44.23, 369/112.28, G9B/7.134, G9B/11.029, G9B/7.07, G9B/7.115, G9B/7.089, 369/44.41, G9B/7.113, G9B/7.124, G9B/7.092, G9B/11.044, G9B/7.067, G9B/11.054, G9B/7.075, G9B/7.114
International Classification G11B7/135, G11B7/13, G11B7/09, G11B11/105
Cooperative Classification G11B7/1353, G11B7/131, G11B7/1356, G11B7/0901, G11B11/10576, G11B11/10543, G11B7/1381, G11B7/0903, G11B7/0943, G11B7/0912, G11B7/094, G11B7/0908, G11B7/1359, G11B7/0916, G11B11/10597
European Classification G11B7/1359, G11B7/1356, G11B7/1381, G11B7/1353, G11B7/131, G11B7/09A2, G11B7/09L, G11B11/105P1, G11B11/105D2B, G11B7/09B, G11B11/105G3, G11B7/09G, G11B7/09B6