JP2002197688A - Optical pickup device and differential push-pull type tracking control method for optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the constitution of an optical pickup 10 which implements differential push-pull type tracking control when commonly used for both of an ordinary type CD and so-called DDCD(double density CD) varying in track pitches. SOLUTION: The multibeam type optical pickup which forms >=4 pieces of sub-light spots from a piece of light emitting section 14 is adopted as the optical pickup 10. The spacing L in the R direction (=disk radial direction) of the light spot M of zero order and the light spot 1 of third order in the ordinary type CD 34a is so set as to be half the track pitch of the ordinary type CD 34a. The light spots of ± third order and ± second order are respectively utilized in the manner described above, by which the differential push-pull type tracking control of the ordinary type CD 34a and the DDCD 34b can be implemented without a hindrance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device used for reproduction and recording processing on an optical disk such as a CD (compact disk) and a differential push-pull tracking control method for the optical pickup device. .

[0002]

2. Description of the Related Art In a CD-R or CD-RW, a track type having a track pitch of 1.6 μm and a track type having a track pitch of 1.1 μm are used.
DCD (Double Density CD: Double Density C)
D). When reading and writing data to CD,
Tracking control is required for the upper light spot.

[0003]

SUMMARY OF THE INVENTION Normal type CD and DDC
In the conventional reproducing apparatus in which both the D and the D can be reproduced, it is necessary to prepare an array of light sources or diffraction gratings individually for the differential push-pull tracking control of the normal type CD and the DDCD, and the configuration of the optical pickup device is complicated. Had been transformed.

An object of the present invention is to provide an optical pickup device and an optical pickup device which can cope with a differential push-pull type tracking control method in reproducing and / or recording an optical disk having various track pitches and which can simplify the configuration. An object of the present invention is to provide a differential push-pull tracking control method.

[0005]

According to the optical pickup device of the first invention, the light from the light source (12) is passed through the optical element for light diffraction (18) to generate diffracted light, and the diffracted light is generated. The diffracted light from the 0th to the ith order (i is a natural number of 2 or more; the sign of the order is ignored) of the light is passed through the light spot forming optical element (30), and the diffracted light in the radial direction of the optical disc (34). A light spot corresponding to each order of diffracted light is generated in a different region, and a light spot corresponding to the first order or higher order diffracted light of the same order is symmetrically positioned with respect to a light spot corresponding to the zero order diffracted light. And the light spot corresponding to the diffracted light of the smaller order is closer to the light spot corresponding to the zero-order diffracted light. In the optical pickup device, it is assumed that the track pitches of the first and second types of optical discs are different from each other, P1 and P2, respectively, and the pitch of the light spots in the radial direction of the optical disc in the optical spot row on the optical disc. Is s, and P1 is approximately 2 · l ·
s (where l is a natural number less than or equal to i), and
P2 is set so that P2 is substantially equal to 2 · m · s (where m is a natural number less than 1), and in the reproduction and / or recording of the first type optical disc, 0th order and 1st are set. A tracking error signal for differential push-pull tracking control is detected based on the reflected light from the next light spot, and the 0th and mth light spots are reproduced and / or recorded on the second type of optical disc. A tracking error signal for differential push-pull tracking control is detected on the basis of the reflected light from the camera.

In the first aspect, the optical disk is, for example, a CD, MD, or DVD. CDs include CD-Rs and CD-RWs in addition to read-only CDs. The light spot forming optical element (30) includes not only a lens but also a Fresnel body having a uniform thickness in a plane direction. The zero-order diffracted light is actually light that has passed through the optical element for light diffraction (18) without being diffracted, that is, non-diffracted light. To Further, in this specification, each light spot will be appropriately referred to by an order corresponding to the order of the diffracted light that generates it. That is, for example, the primary light spot refers to a light spot generated on the optical disk by the primary diffracted light.

The optical element for light diffraction (18) comprises, for example, a diffraction grating or a hologram. s is the pitch of the light spot array on the optical disk in the radial direction of the optical disk, that is, not the pitch of the light spot array in the column direction.
In most optical pickup devices, the light spot array extends obliquely with respect to the radial direction of the optical disk. P1, P2
Both need not be strictly P1 = 2 · l · s and P2 = 2 · m · s, ie, one or both of P1 and P2 are P1 = 2 · l · s or P2 = 2 · m · s It does not have to be. In a typical optical pickup device, s is about 0.27
μm. If | P1-1s | is within ± 5% of P1 and | P2-ms | is within ± 5% of P2, P1 is approximately equal to 2 · ls. , P2 is approximately equal to 2 · m · s, so that a trouble-free differential push-pull tracking control can be performed.

Thus, the distance between the 0th-order light spot and the 1st-order light spot in the radial direction of the optical disk is set to approximately １ ／ of the track pitch of the first type of optical disk, and the 0th-order light spot and the mth-order light spot. The distance in the radial direction of the optical disk from the light spot can also be made approximately の of the track pitch of the second type of optical disk, and a common light beam for the first and second types of optical disks having different track pitches. A spot array, that is, a common optical diffraction optical element (1
By utilizing 8), the differential push-pull tracking control method can be implemented without any trouble.
As a result, it is possible to simplify the configuration of the optical pickup device by omitting the replacement and switching of the optical diffraction optical element (18) and the provision of a plurality of optical diffraction optical elements (18).

According to the optical pickup device of the second invention, in the optical pickup device of the first invention, 1 is 2
In the above case, the optical element for light diffraction is such that the light spot on the optical disk corresponding to the 1st and mth order diffracted light has a larger light amount than the light spot on the optical disk corresponding to the 1st order diffracted light. The pattern of (18) is set.

It is preferable that the light spot on the optical disk corresponding to the 1st and mth order diffracted light has a larger light intensity than the light spot on the optical disk corresponding to the 1st order diffracted light.
The light spot on the optical disk corresponding to the next-order diffracted light is twice or more the light amount as compared with the light spot on the optical disk corresponding to the first-order diffracted light.

The light quantity distribution of the light spots of each order can be arbitrarily changed by, for example, selecting the dimensions of the specifications of the diffraction pattern of the optical diffraction optical element (18). The decrease in the light quantity of the primary light spot can be used to increase the light quantity of the l-th and m-th light spots, thereby securing a light spot of a predetermined light quantity for differential push-pull tracking control. Increase of the output of the light source (14) can be avoided.

For example, an optical disc of the first type is a CD having a normal track pitch, and an optical disc of the second type is a so-called DDCD (DoD) having a track pitch.
double Density CD).
When the first and second types of optical discs are a CD and a DDCD, respectively, whose track pitch is a normal standard, s, l, and m are, for example, s = 1.6 μm / (2 ·
l), l = 3, m = 2 are set.

The track pitches of the conventional CD and DDCD are 1.6 μm and 1.1 μm, respectively. On the other hand, therefore, P1 / 2 and P2 / 2 are 0.8 μm, respectively.
0.55 μm. s = 1.6 μm / (2 · l), that is, s = track pitch of normal CD / (2 · l)
Further, by setting l = 3 and m = 2, the distance in the CD radial direction between the 0th-order light spot and the 3rd-order light spot becomes 3 s, which is exactly 1 track pitch of the normal type CD. / 2, and the distance in the CD radial direction between the zero-order light spot and the second-order light spot is 2 s,
Strictly speaking, exactly 1/2 of the track pitch of a normal CD
0.02 μm difference from the normal CD
The ratio of the difference to just ト ラ ッ ク of the track pitch is within a small range of 5% or less, and can be approximately と す る of the track pitch of DDCD. Thus,
The DDCD differential push-pull tracking control method can be implemented without any problem using the secondary light spot.

According to the differential push-pull tracking control method for an optical pickup device of the third invention, the light from the light source (12) is converted to the optical element for light diffraction (1).
8) to generate diffracted light, and diffracted light from the 0th order to the ith order (i is a natural number of 2 or more; the sign of the order is ignored) out of the diffracted light. (3
0) to generate a light spot corresponding to each order of diffracted light at different positions in the radial direction of the optical disc (34). The light spot corresponding to the first order or higher order diffracted light is the 0th order. The light spot corresponding to the diffracted light of the smaller order has a symmetrical positional relationship with respect to the light spot corresponding to the diffracted light, and the light spot corresponding to the diffracted light of the smaller order is located closer to the light spot corresponding to the zero-order diffracted light. In the differential push-pull tracking control method for the optical pickup device, it is assumed that the track pitches of the first and second types of optical disks are different from each other, P1 and P2, and the radius of the optical disk in the light spot array on the optical disk. The pitch of the light spot in the direction is s, P1 is almost equal to 2 · l · s (where 1 is a natural number equal to or less than i), and P2 is 2
S is set so as to be substantially equal to m · s (where m is a natural number less than 1), and in the reproduction and / or recording of the first type of optical disc, the 0th and 1st order A tracking error signal for differential push-pull tracking control is detected based on the reflected light from the light spot, and in the reproduction and / or recording of the second type of optical disc, the reflection from the 0th and mth order light spot is performed. A tracking error signal for differential push-pull tracking control is detected based on the light.

According to the differential push-pull tracking control method for an optical pickup device of the fourth invention, in the differential push-pull tracking control method for an optical pickup device of the third invention,
When 1 is 2 or more, the light diffraction on the optical disc corresponding to the 1st and mth order diffracted light is larger than the light spot on the optical disc corresponding to the 1st order diffracted light. The pattern of the optical element for use (18) is set.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an optical pickup device 1
0 is a schematic configuration diagram. The R direction and the T direction of the CD 34 indicate the radial direction of the CD 34 (the R direction and the anti-R direction correspond to the outer circumferential direction and the inner circumferential direction of the CD 34, respectively) and the tangential direction of the information track of the CD 34, respectively. The R direction and T direction of each optical element indicate the moving direction of each optical element when the light spot is displaced in the R direction and T direction of the CD 34, respectively. Further, the R ′ direction on the photodiode light receiving surface 68,
The T 'direction indicates a direction corresponding to the R direction and the anti-T direction of the CD 34, respectively, and the R' direction and T 'direction of the beam splitter 24 and the focusing lens 50 correspond to the R' direction and the T 'direction of the photodiode light receiving surface 68, respectively. The direction in which the beam splitter 24 and the focus adjustment lens 50 move when the light spot of the reflected light is displaced in the 'direction.

The semiconductor laser 12 has a light emitting section 14 at the center of the optical axis 32 from the semiconductor laser 12 to the CD 34. The diffraction grating plate 18 has a diffraction grating surface 20 on the surface on the semiconductor laser 12 side. The laser light emitted from the light emitting section 14 is diffracted by the diffraction grating surface 20 of the diffraction grating plate 18, one on the optical axis 32 and two on each side, that is, a total of five undiffracted lights ( (Light on the optical axis) and diffracted light. The five lights travel straight through the beam splitter 24, change their directions by 90 ° at the mirror 26, sequentially pass through the collimator lens 28 and the objective lens 30,
In the CD 34, light spots M, E, F, G, H, I, and J are generated in a line substantially in the T direction. The arrangement of the light spots M, E, F, G, H, I, and J is symmetrical with respect to the central light spot M, that is, the light spot M on the optical axis 32 and the light spot E. F and the light spots G and H are in a symmetrical relationship.

The optical axis 66 is the optical axis of the reflected light of the light spots M, E, F, G, H, I, and J starting from the light spot M. From the light spot M to the beam splitter 24,
It overlaps with the optical axis 32. That is, the reflected light of CD34 is
In order, the light passes through the objective lens 30, the collimator lens 28, and the mirror 26, enters the beam splitter 24, is turned 90 ° in the beam splitter 24, and travels toward the focusing lens 50. Photodiode light receiving surface 68 is a line of photodetectors 52M, 52E, 52F, 52G, 52H, 5H, which are arranged in a line at right angles to optical axis 66 and at a predetermined interval.
2I, 52J is defined as a plane including all light receiving surfaces. The reflected light emitted from the beam splitter 24 toward the focusing lens 50 passes through the focusing lens 50,
Each photodiode 52M, 52E, 52F, 52G,
The light is incident on 52H, 52I, and 52J.

Incidentally, a total of seven light spots M, E, F,
When G, H, I, and J are generated at each track portion of the CD 34 and data is simultaneously read from a total of seven tracks, the photodiodes 52M, E, F, G, H, I,
J is necessary, but if the optical pickup device 10 is used exclusively for the differential push-pull tracking control method, the photodiodes 52E, F
Is unnecessary.

The light spot M is generated from the zero-order diffracted light generated in the diffraction grating plate 18, that is, it is a non-diffracted light. I do. Light spots E and F are diffraction grating plates 1
8, the light spots G and H are generated from the second-order diffracted light generated in the diffraction grating plate 18.

FIG. 2 shows a conventional CD34a or DDCD34.
4B shows the relationship between the track pitch and the light spot in FIG. For convenience of explanation, FIG.
In contrast, the illustration of the light spot inside the R direction is omitted, and the reason that the primary light spot E is not used for the differential push-pull tracking control, and as described in FIG. Due to the reason that the light quantity ratio is lower than the secondary and tertiary light spots,
Illustration is omitted. In the entire light spot array, the light spot on the inside in the R direction with respect to the light spot M is located at a point symmetrical position with respect to the light spot on the outside in the R direction. The track 70 is a track of the normal type CD 34a, and the track 71 is a DDC.
D34b, and the tracks 70 and 71 in the figure
Indicate the positions only by their center lines without representing the width. The interval between the tracks 70 in the CD radial direction, that is, the above-described R direction is 1.6 μm, while the interval between the tracks 71 in the R direction is 1.1 μm. In FIG. 2, the lower scale is a track 70 illuminated by the zero-order light spot M, which is a reference track 70, and a reference track 7.
The absolute value of the distance in the ± R direction with respect to the center line of 0 is the unit μ
Indicated by m. The distance between adjacent light spots in the light spot row is set such that the distance L in the R direction between the 0th-order light spot M and the center of the + 3rd-order light spot I is の of the track pitch of 34a, that is, 0.8 μm. Is set. The setting can be performed without any trouble by adjusting the R-direction positions of the beam splitter 24, the mirror 26, and the collimator lens 28 of the optical pickup device 10. L =
By setting it to 0.8 μm, the distance s in the R direction between adjacent light spots in the light spot row is s = L / 3 = 0.26
66 μm, and the scale of the vertical line in FIG.
Are shown in numerical values up to the second decimal place. Accordingly, the position of the light spot G in the R direction becomes 0.53 μm. On the other hand, the pitch of the track 71 in the DDCD 34b is 1.1 μm, and 1.1 μm / 2 =
0.55 μm, and the position of the light spot G in the R direction is
Although it is shifted by 0.02 μm with respect to 0.55 μm, this shift is about 3.8% with respect to 0.55 μm,
That is, the error is within 5%, and the light spot M is almost half the pitch of the track 71 in the DDCD 34b.
Assuming that the light spot G exists at a position distant from the camera, it can be determined that there is no problem in performing the differential push-pull tracking control method described later.

FIG. 3 shows an example of two diffraction patterns for one pitch on the diffraction grating surface 20 of the diffraction grating plate 18. In the diffraction pattern of (a) and the diffraction pattern of (b), the groove 74 and the land 75 are reversed.
In the diffraction pattern shown in FIG.
4, the lands 75, the grooves 74, and the lands 75 are arranged. In the diffraction pattern of FIG. 3B, the lands 75, the grooves 74, the lands 75, and the grooves 74 are arranged from one end to the other end. Pt is the dimension of one pitch of the diffraction pattern, and Pa, Pb, Pc, and Pd are the R-direction lengths of each groove 74 or each land 75 from one end to the other end. Normal type C
For the differential push-pull tracking control of the D34a and the DDCD34b, the light quantity of the ± 1st order light spot is reduced, and the amount of the decrease is ± 2nd order and ± 2nd order.
It is desirable to increase the light quantity of the tertiary light spot. According to this purpose, the results of calculating each dimension with commercially available simulation software are as follows. In the simulation, the focal length of the objective lens 30 is 3 mm, the interval between the light spots is 0.01 mm, the wavelength of the laser light is 0.78 μm, and the objective lens 30 is disposed on the diffraction grating plate 18 in the collimated light beam. That is, the diffraction grating plate 18 is carried not between the vicinity of the light emitting unit 14 but between the collimator lens 28 and the objective lens 30. The diffraction grating plate 18 is provided with a collimator lens 28 and an objective lens 30.
In this case, even if the magnification of the lens system is changed, the pitch of the light spot on the CD 34 does not change. When the diffraction grating plate 18 is arranged near the light emitting unit 14, the dimensions of the diffraction pattern calculated by the simulation in the collimated light beam are scaled according to the distance between the light emitting unit 14 and the diffraction grating plate 18. If you bring it down, you can easily convert it. The basic pitch Pt of the scaled-down diffraction pattern must be at least 10 times the wavelength of the laser beam. As a result of the simulation, Pt = 0.234 mm, Pa = 37.87 μm, P
b = 107.29 μm, Pc = 39.61 μm, Pd =
When the depth of the groove 74 with respect to the land 75 is 0.334 μm and the light quantity of the 0-order light spot is 10, the light quantity of each primary light spot is 0.5, and the light quantity of each secondary light spot is 0.5. The light amount of each light spot was 1.0, and the light amount of each tertiary light spot was 1.0.

FIG. 4 shows a tracking error signal detection circuit for differential push-pull tracking control. For details of the tracking error signal detection circuit, see, for example, FIG. 8 of Japanese Patent Publication No. 4-34212. In FIG. 4, the tracking error signal detection circuit for differential push-pull type tracking control of the normal type CD 34a and the tracking error signal detection circuit for the DDCD 34b are collectively described. Normal type CD34a or DDC
The two tracking error signal detection circuits are switched and used in accordance with D34b. 52m
Is divided into two light amount detecting portions 80a and 80b, 52g and 52i are divided into two light amount detecting portions 81a and 81b, and 52h and 52j are two light amount detecting portions 82a and 8b.
2b. The reflected light spot 84 is a light spot generated by the reflected light from the light spot m on the photodiode 52m, and the reflected light spot 85 is formed by the reflected light from the light spot g or the light spot i on the photodiode 52g or 52i. Is a light spot generated at
The reflected light spot 86 is a light spot generated by the reflected light from the light spot h and the light spot j on the photodiode 52h or 52j. In the figure, the reflected light spot 8
4,85,86 exist on the dividing line, but CD3
During the reproduction of 4, the reflected light spots 84, 85, 86 move in the R ′ direction (R ′ is shown in FIG. 1 and corresponds to the horizontal direction in FIG. 4). The outputs of the light amount detection portions 80a and 80b are respectively input to the non-inverting input terminal and the inverting terminal of the differential amplifier 88, and the output of the differential amplifier 88 is set to Te1.
Generate The outputs of the light amount detecting portions 81a and 81b are input to the non-inverting input terminal and the inverting terminal of the differential amplifier 89, respectively, and generate Te2 on the output side of the differential amplifier 89. The outputs of the light amount detection portions 82a and 82b are input to the non-inverting input terminal and the inverting terminal of the differential amplifier 90, respectively, and generate Te3 on the output side of the differential amplifier 90. Te
3 is amplified by the variable amplifier 91 with a predetermined gain.
After the output of the variable amplifier 91 and Te2 are added,
The signal is amplified by the variable amplifier 92 with a predetermined gain. Te1
The outputs of the variable amplifier 92 and the differential amplifier 93 are
Of the differential amplifier 93, and generates Te3 at the output side of the differential amplifier 93. As is well known, if the gains of the variable amplifier 91 and the variable amplifier 92 are appropriately selected, the tracking error Te from which the DC fluctuation has been removed can be extracted from the output terminal 94.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical pickup device.

FIG. 2 is a diagram showing a relationship between a track pitch and a light spot in DDCD.

FIG. 3 is a diagram showing two diffraction pattern examples for one pitch on a diffraction grating surface of a diffraction grating plate.

FIG. 4 is a tracking error signal detection circuit for differential push-pull tracking control.

[Explanation of symbols]

 Reference Signs List 10 optical pickup device 14 light emitting section 18 diffraction grating plate (optical element for optical diffraction) 20 diffraction grating surface 30 objective lens (optical spot forming optical element) 34 CD (optical disk) 34a normal type CD 34b DDCD

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Soto Goto 1-14-6 Dogenzaka, Shibuya-ku, Tokyo F-term in Kenwood Corporation (reference) 5D118 AA26 CA13 CA23 CB06 CD03 CF03 CF17 CG05 CG24 CG33 DA33 DA35

Claims (4)

[Claims] 1. A light from a light source (12) is passed through an optical element for light diffraction (18) to generate diffracted light, and of the diffracted light from the 0th to the ith order (i is a natural number of 2 or more). (The sign of the order is ignored.) Through the light spot forming optical element (30) to generate light spots corresponding to the diffracted light of each order at different portions in the radial direction of the optical disc (34). The light spot corresponding to the first-order or higher order diffracted light has a symmetrical positional relationship with respect to the light spot corresponding to the zero-order diffracted light, and the light spot corresponding to the diffracted light having the smaller order has the following: In an optical pickup device located near an optical spot corresponding to the zero-order diffracted light, the track pitch of the first and second types of optical discs is:
Suppose that P1 and P2 are different from each other, and that the pitch of the light spot in the radial direction of the optical disk in the optical spot train on the optical disk is s. P1 is approximately 2 · l · s (where 1 is i or less). Natural number.), And P2 is 2 · m · s (where m
Is a natural number less than l. ), So that
s is set, and in the reproduction and / or recording of the first type optical disc, 0 is set.
A tracking error signal for differential push-pull tracking control is detected based on the reflected light from the first and first order light spots.
An optical pickup device for detecting a tracking error signal for differential push-pull tracking control based on reflected light from the next and m-th light spots. 2. When 1 is 2 or more, the light spot on the optical disk corresponding to the 1st and mth order diffracted light has a larger light amount than the light spot on the optical disk corresponding to the 1st order diffracted light. The optical pickup device according to claim 1, wherein the pattern of the optical element for light diffraction (18) is set as described above. 3. A light from a light source (12) is passed through an optical element for light diffraction (18) to generate diffracted light, and among the diffracted light, a zero-order to an i-th order (i is a natural number of 2 or more). (The sign of the order is ignored.) Through the light spot forming optical element (30) to generate light spots corresponding to the diffracted light of each order at different portions in the radial direction of the optical disc (34). The light spot corresponding to the first-order or higher order diffracted light has a symmetrical positional relationship with respect to the light spot corresponding to the zero-order diffracted light, and the light spot corresponding to the diffracted light having the smaller order has the following: In a differential push-pull tracking control method for an optical pickup device located near an optical spot corresponding to a zero-order diffracted light, the track pitch of the first and second types of optical discs is:
Suppose that P1 and P2 are different from each other, and that the pitch of the light spot in the radial direction of the optical disk in the optical spot train on the optical disk is s. P1 is approximately 2 · l · s (where 1 is i or less). Natural number.), And P2 is 2 · m · s (where m
Is a natural number less than l. ), So that
s is set, and in the reproduction and / or recording of the first type optical disc, 0 is set.
A tracking error signal for differential push-pull tracking control is detected based on the reflected light from the first and first order light spots.
A differential push-pull tracking control method for an optical pickup device, wherein a tracking error signal for differential push-pull tracking control is detected based on reflected light from the next and m-th light spots. 4. When 1 is 2 or more, the light spot on the optical disk corresponding to the 1st and mth order diffracted light has a larger light amount than the light spot on the optical disk corresponding to the 1st order diffracted light. 6. The differential push-pull tracking control method for an optical pickup device according to claim 5, wherein the pattern of the optical element for light diffraction (18) is set as described above.