JP3790037B2 - Optical disk device and optical disk - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention uses an optical disk as a recording medium, and in particular, an optical disk in which pits corresponding to data bits are recorded in advance on a part or all of the optical disk, and an encoded data string composed of the pits is reproduced by an optical head. The present invention relates to an apparatus and an optical disk.
[0002]
[Prior art]
Conventionally, there is a land / groove recording method as a high-density method for a rewritable optical disk device (see, for example, Japanese Patent Publication No. 63-57859). This method is a method of recording, for example, phase change marks on both lands and grooves, and can achieve higher density than a method of recording marks on only one of the lands and grooves.
[0003]
By the way, in a rewritable optical disc apparatus, in the case of a hard format, address information other than rewritable data (user data, etc.) and control information such as a rotation control signal are generally recorded in advance in a header area as pits (pre-pits). ing. For convenience, an area in which rewritable data is recorded is referred to as a recording area.
[0004]
In the method of recording only on one of the land and the groove, the header area is provided only on the land or groove track. On the other hand, in the land / groove recording system, header areas are provided on both tracks. However, if a pit is provided for each track in the header area, when information is reproduced from the header area, crosstalk from the pits of adjacent tracks may occur, making it difficult to reproduce the information.
[0005]
In the land / groove recording system, a system has been proposed in which the prepit patterns in the header area are arranged with a fixed shift to the left and right with respect to the track center, and the prepit patterns are shared between the land and the groove. When this method is adopted, the track pitch of the prepits in the header area is twice that of the recording area, so that the influence of crosstalk from adjacent tracks is reduced. In this case, a reproduction method using a differential output signal (push-pull signal) obtained from the two-divided photodetector is effective. Further, the off-track amount of the light beam spot can be detected by comparing the reproduction signal amplitudes of the prepit trains wobbled to the left and right.
[0006]
[Problems to be solved by the invention]
In the optical disc apparatus, since information such as an address ID is recorded in the header area, a high quality reproduction signal is required. As characteristic parameters that characterize signal quality, the optical disc standard generally defines asymmetry and modulation degree of the reproduction signal in the header area. However, although it is estimated that the symmetry control in the eye pattern of the playback signal based on the push-pull signal depends on the cross-sectional shape and depth of the pit to be played back, a clear standard is prescribed. It has not been. If the symmetry control of the reproduction signal is poor, the jitter of the reproduction signal is deteriorated, which becomes an obstacle to accurate data reproduction.
[0007]
Accordingly, an object of the present invention is to adopt a reproduction method that uses a push-pull signal obtained from a two-divided detector, and to define the pit structure related to the symmetry control of the reproduction signal, thereby controlling the symmetry of the reproduction signal. It is an object of the present invention to provide an optical disc apparatus and an optical disc capable of realizing an accurate data reproduction operation in a header area.
[0008]
[Means for Solving the Problems]
The present invention is an optical disc apparatus in which marks corresponding to data bits are recorded on an optical disc by external means or internal means, and a predetermined data string is reproduced based on the arrangement of the marks in the track tangent direction on the optical disc. A rotating means for rotating the optical disk and a reproducing means for reproducing the mark, and the reproducing linear velocity of the optical disk by the rotating means when reproducing the mark recorded at the radial position r1 of the optical disk. Sr1 [m / s], a predetermined channel bit rate at the radial position r1 of the optical disk is f _T [b / s], and the mark records data corresponding to an n channel bit length, and the mark When the length in the track tangential direction is PL [m], the PL is
“0.55 ≦ (f _T · PL) / (n · Sr1) ≦ 1.50”
An optical disc apparatus is provided that is set so as to satisfy the following conditional expression.
[0009]
That is, the reproduction linear velocity when the optical disk is rotated during the reproduction operation is Sr1 [m / s], the predetermined channel bit rate at the reproduction linear velocity is f _T [b / s], and corresponds to the n channel bit length. When the length of the recorded pit in the track tangent direction is PL [m], PL is a condition of the following formula: 0.55 ≦ (f _T · PL) / (n · Sr1) ≦ 1.50
Set to satisfy.
[0010]
Here, the pit length PL to be set is the pit length in the track tangential direction at the depth pd / 2, where pd is the depth of the deepest part of the pit. In particular, the pit length PL in the case of the densest signal (for example, 3T signal in the case of the 8-16 modulation method adopted in DVD) is strictly set so as to satisfy the above formula based on the relationship with asymmetry. It is necessary to
[0011]
By recording such a pre-pit pattern with a pit length PL in the header area on the optical disc, a reproduction system based on the differential signal from the two-divided photodetector can obtain a reproduction signal with good asymmetry. it can. Therefore, as a result, information can be reliably reproduced from the header area.
[0012]
The present invention relates to a track tangential direction at a depth pd / 2 when the depth of the deepest portion is pd for a pit recorded at a radial position r1 of an optical disc with a length corresponding to a code length nT in a predetermined modulation method. Pit length is PLn [m], a predetermined reproduction frequency of the 2nT periodic signal at the radial position r1 is fnT [1 / s], and the reproduction linear velocity of the optical disk at the radial position r1 is Sr1 [m / s]. In this case, the condition of the following expression PL = 0.55 ≦ (2 · fnT · PLn) /Sr1≦1.50
Provided is an optical disc apparatus which is set so as to satisfy the above.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
First, an optical disk apparatus according to this embodiment will be described with reference to FIG.
The optical disk apparatus is a rewritable optical disk apparatus adopting a land / groove recording system, and uses an optical disk in which control information is recorded in a prepit pattern (prepit arrangement) in the header area as shown in FIG. Is assumed.
[0014]
The optical disc apparatus includes a spindle motor 11 that rotates the optical disc 10, a spindle motor drive circuit 12 that drives the spindle motor 11, an optical head 13, an LD driver (laser diode driver) 18, an amplifier 21, and a differential amplifier 25. A servo control circuit 22, a signal processing circuit 26, and a system controller 28. The recording surface 20 of the optical disc 10 is provided with a recording area and a header area as shown in FIG. As will be described later, pits having a structure as shown in FIG. 3 are recorded in the header area.
[0015]
The optical head 13 includes a semiconductor laser 14, a collimating lens 15, an objective lens 16, an actuator 17, a polarizing beam splitter 19, a ¼ wavelength (λ / 4) plate 29, and a condensing lens 23. And a photodetector 24. The semiconductor laser 14 is driven by an LD driver 18 to emit a laser beam. The collimating lens 15 converts the laser beam from the semiconductor laser 14 into parallel light.
[0016]
The parallel light passes through the polarization beam splitter 19 and the quarter wavelength plate 29 and enters the objective lens 16. The objective lens 16 converges the light beam on the recording surface 20 of the optical disc 10. Here, a deviation in the radial direction from the target track of the light beam converged on the recording surface 20 by an optical system / electric system (not shown) is used as a tracking error signal, and a deviation in the vertical direction from the recording surface is used as a focus error signal. To the amplifier 21. The error signal amplified by the amplifier 21 is input to the servo control circuit 22. The servo control circuit 22 generates a drive signal corresponding to each shift amount, drives and controls the actuator 17 to change the position of the objective lens 16, and controls the light beam spot to be irradiated to the target position. To do. Here, as shown in FIG. 2, the light beam spot is controlled to be positioned at the center of the land 32 and the groove 33 in the recording area of the optical disk. In the header area, the radial position of the light beam spot is held immediately before scanning the header area, and the light beam spot is shifted from the center of the prepit 31 by an amount corresponding to a half of the track pitch of the recording area. Controlled to scan.
[0017]
On the other hand, the light beam reflected from the optical disk 10 passes through the objective lens 16, passes through the quarter-wave plate 29, is reflected by the polarization beam splitter 19, and enters the condenser lens 23. Here, the light beam from the header region is condensed by the condensing lens 23 onto the two-divided photodetector 24. As shown in FIG. 4, the two-divided photodetector 24 has light-receiving regions 24a and 24b divided into two with a dividing line 24c parallel to the track tangential direction on the optical disc as a center. The two-divided photodetector 24 may be used exclusively for signal detection in the header area, or for tracking error signal detection or RF signal detection. The differential amplifier 25 outputs a difference signal (push-pull signal) from the output signals from the light receiving regions 24 a and 24 b to the signal processing circuit 26. The signal processing circuit 26 executes signal processing including predetermined demodulation processing, generates a reproduction signal corresponding to the control information recorded in the header area, and outputs it to the system controller 28.
[0018]
The main point of the present invention is that, as will be described later, the length in the track tangential direction (pit length PL) among the pit structural elements is set so that the asymmetry AS that defines the signal quality of the reproduction signal is good. (See FIG. 3).
[0019]
Here, as a method for quantitatively evaluating the signal quality of the reproduction signal, a method of measuring an asymmetry AS, which is an index representing the symmetry between the densest signal and the coarsest signal of the prepit train, is well known.
[0020]
FIG. 5 is a diagram showing the definition of the asymmetry AS of the reproduction signal waveform. As shown in FIG. 5, the asymmetry AS is the maximum level and the minimum level of the reproduction signal of the shortest code length signal (the most dense signal, for example, the 3T signal in the case of the 8-16 modulation system used for DVD) in a certain modulation system. Are Imin H and Imin L, respectively, and the maximum level and the minimum level of the reproduction signal of the longest code length signal (the coarsest signal, for example, 14T signal in the case of 8-16 modulation method used for DVD) are Imax H and Imax, respectively. When L, it is expressed by the following formula (1). “NT” is a time interval of n channel bits.
[0021]
AS = [(Imax H + Imax L) − (Imin H + Imin L)] / [2 (Imax H−Imax L)] (1)
Depending on the optical disc standard, other equations may be used to quantify the asymmetry, but they are essentially equivalent except for their polarity.
[0022]
As described above, as a factor for determining the signal quality of the reproduction signal, it is a condition for obtaining a high-quality reproduction signal that the asymmetry AS is in a predetermined specified range. Specifically, the specified range is a range of “−0.15 to 0.15” in the characteristic diagram shown in FIG. 6 in consideration of the margin of the physical characteristics of the optical disc and the manufacturing margin of the optical disc drive device. It is desirable that FIG. 6 is a characteristic diagram showing the relationship between the pit length PL and the asymmetry AS. That is, in the structure of the pre-pit 1 shown in FIG. 3, the pit length PL in the track tangential direction of the most dense signal is closely related to the asymmetry AS of the push-pull signal when the pre-pit 1 is reproduced by the optical head 13. The relationship is almost inversely proportional. In this case, the push-pull signal is, as described above, when the light beam spot 34 of the optical head 13 is irradiated to a position having a certain offset in the radial direction from the pit center, as shown in FIG. It is a difference signal of the two-divided photodetector 24 when the pit is reproduced.
[0023]
Here, FIG. 6 shows a repetitive signal as shown in FIG. 8 with a pit pitch PP of 1.23 μm in the optical system (optical head 13) having a reproduction wavelength of 685 nm and a numerical aperture of 0.6 of the objective lens 16. Asymmetry AS characteristics with respect to the pit length PL of the densest signal when the coarsest signal is a repetitive signal as shown in FIG. 8 with a pit pitch PP of 5.74 μm and the pit length of the coarsest signal is 2.87 μm. FIG.
[0024]
Furthermore, the characteristic curve 60A corresponds to the structure of the pit 1 having a rectangular cross-sectional shape as shown in FIG. Further, as shown in FIG. 3, the characteristic curve 60B corresponds to the structure of the pit 1 having a trapezoidal cross section and a wall surface angle θ of about 30 degrees in both the radial direction and the track tangential direction. The pit depth pd is 90 nm. Here, in this embodiment, the pit length PL is the length in the track tangent direction at the half-value “pd / 2” position with respect to the pit depth pd.
[0025]
In a pit having a rectangular cross-sectional shape as shown in FIG. 9, it is confirmed by the same calculation that the characteristic curve 60A hardly changes even if the depth pd is changed from 90 nm, although the result is not shown. Further, FIG. 7 shows respective characteristic curves 60B to 60E when the wall surface angle θ and the pit depth pd are changed with respect to the characteristic curve 60A when the cross-sectional shape of the pit is rectangular. Here, the characteristic curve 60B is obtained when the wall surface angle θ is about 30 degrees and the depth pd is 90 nm. Similarly, the characteristic curve 60C is when the wall surface angle θ is about 45 degrees and the depth pd is 70 nm, and the characteristic curve 60D is when the wall surface angle θ is about 30 degrees and the depth pd is 70 nm. Further, the characteristic curve 60E is obtained when the wall surface angle θ is about 30 degrees and the depth pd is 30 nm. From the characteristic curves 60A to 60E, if the wall surface angle θ is the same, the depth pd is shifted to the left on the graph. Further, if the depth pd is the same, the lower the wall surface angle θ, the more the left side of the graph is shifted with respect to the rectangular case. Therefore, in the pit structure as shown in FIG. 3, in the pit having the wall surface angle θ of 30 degrees or more (90 degrees or less) and the depth pd of 90 nm or less, the characteristic curve is from FIG. 6 to the characteristic curve 60A. It changes in the range shown by hatching.
[0026]
By the way, when forming pits on an optical disk, it is practical that the wall surface angle θ is about 30 degrees or more (90 degrees or less), and the difference signal amplitude is optically maximum at the depth (λ / 8). In consideration of the minimum value of (λ / 4), a pit with a depth pd set to 90 nm or less is realistic in this reproducing optical system. In the case of a cross-sectional shape close to a rectangle, it is conceivable that the pit depth is set in the vicinity of (3λ / 8) and (5λ / 8), and the depth pd is 90 nm or more. This is no different from the present discussion where the thickness is 90 nm or less. In this embodiment, therefore, a characteristic curve in the range indicated by hatching in FIG. 6 is assumed for a pit shape that can be actually considered, and a pit length PL corresponding to a good asymmetry AS is set. That is, the good asymmetry AS is preferably in the range of “−0.15 to 0.15” as described above. Therefore, as apparent from FIG. 6, it is necessary to control the pit length PL in the range of “0.380 μm to 0.880 μm”. FIG. 10 shows the pit length PL corresponding to the range of asymmetry AS “−0.15 to 0.15” for each of the characteristic curves 60A and 60B.
[0027]
In the relationship between the pit length PL in the track tangent direction of the pre-pit 1 and the asymmetry AS of the push-pull signal when reproduced by the optical head 13, the pit pitch PP as shown in FIG. 8 is 1.23 μm. When the reproduction linear velocity of the pit is S [m / s], the reproduction signal frequency f [1 / s] of this single period signal is expressed by the following equation (2).
[0028]
f = S / (1.23 × 10 ⁻⁶ ) [1 / s] (2)
Therefore, in this case, controlling the pit length PL in the range of “0.380 μm to 0.880 μm” corresponds to controlling as in the following conditional expression (3).
[0029]
0.618 ≦ (2 · f · PL) /S≦1.43 (3)
When the closest signal is a pit train having a pit pitch PP of 1.02 μm, the characteristic curves 60A and 60B of the pit length PL with respect to the asymmetry AS are as shown in FIG. In this case, it is clear from the drawing that the pit length PL corresponding to the range of “−0.15 to 0.15” of the asymmetry AS is “0.302 μm to 0.745 μm”. Therefore, by the same calculation as in the case where the pit pitch PP is 1.23 μm, this corresponds to controlling the pit length PL as in the following conditional expression (4).
[0030]
0.592 ≦ (2 · f · PL) /S≦1.46 (4)
This is because f = S / (1.02 × 10 ⁻⁶ ).
From the above-mentioned tendency, the above-described realistic pit shape (when the wall surface angle θ is about 30 degrees or more and 90 degrees or less and the depth pd is 90 nm or less, or when the wall surface angle is close to 90 degrees, the depth pd is 90 nm. In order to perform control so that the asymmetry AS is good, the 2nT periodic signal at the radial position r1 at which the pit is reproduced is reproduced. When the predetermined reproduction frequency is fnT [1 / s] and the linear velocity at the radial position r1 is Sr1 [m / s], the pit length PLn preferably satisfies the following conditional expression (5).
[0031]
0.55 ≦ (2 · fnT · PLn) /Sr1≦1.50 (5)
Here, instead of the conditional expression (5), a pit length PL that satisfies the following conditional expression (6) may be used. That is, when the channel bit rate at the reproduction linear velocity Sr1 [m / s] is f _T [b / s], the pit length PL of the pit recorded corresponding to the n channel bit length is expressed by the following equation (6). Set to satisfy.
[0032]
0.55 ≦ (f _T · PL) / (n · Sr1) ≦ 1.50 (6)
In the above example, the asymmetry AS is set in the range of “−0.15 to 0.15”, but this is limited to the range of “−0.10 to 0.10” depending on the allocation of the margin in the optical disc system. In some cases. In this _{case, (f T · PL) /} (n · Sr1) is set as follows. That is, from FIG. 6, the pit length PL is determined in the range of “0.445 μm to 0.827 μm”. Controlling the pit length PL within this range is equivalent to controlling the following conditional expression (7).
[0033]
0.724 ≦ (2 · f · PL) /S≦1.34 (7)
Further, when the closest signal is a pit row having a pit pitch PP of 1.02 μm, the pit length PL corresponding to the range of a good asymmetry AS is “0.354 μm to 0.698 μm”. 11 is clear. Therefore, by the same calculation as in the case where the pit pitch PP is 1.23 μm, this corresponds to controlling the pit length PL as in the following conditional expression (8).
[0034]
0.694 ≦ (2 · f · PL) /S≦1.37 (8)
From the above tendency, in order to control the asymmetry within the range of “−0.10 to 0.10” when the above-described realistic pit shape is assumed, the pit length PLn is expressed by the following conditional expression ( It is desirable to satisfy 10).
[0035]
0.65 ≦ (2 · fnT · PLn) /Sr1≦1.40 (9)
Here, instead of the conditional expression (9), a pit length PL that satisfies the following conditional expression (10) may be used.
[0036]
0.65 ≦ (f _T · PL) / (n · Sr1) ≦ 1.40 (10)
As described above, according to the present embodiment, in the pit structure of the pre-pit arrangement (arranged to the left and right with respect to the track center as shown in FIG. 2) recorded in the header area on the optical disc, When reproducing with a beam spot irradiated to a position having a certain offset, the conditional expression (5) or (6) or the expression (9) or (10) is satisfied particularly for each pit of the densest signal. By setting the pit length PL in such a manner, it becomes possible to obtain a good asymmetry AS push-pull signal by the two-divided photodetector. Therefore, a high-quality reproduction signal can be obtained in a reproduction system in which a push-pull signal is generated using a two-divided photodetector and data is reproduced based on the push-pull signal. Accordingly, when the land / groove recording method is adopted for the recording area and the prepit arrangement as shown in FIG. 2 is adopted for the header area, a high-quality reproduction signal can be obtained from the header area. Accordingly, the land / groove recording method can increase the recording density of data, and can realize a highly accurate reproducing operation that reliably reproduces various information from the pre-pit pattern in the head area.
[0037]
FIG. 12 and FIG. 13 show an optical disc in which tracks by lands / grooves are formed in a single spiral shape and a double spiral shape, that is, a single spiral format optical disc and a double spiral format optical disc, respectively. The single spiral format is a format in which the land track 32 and the groove track 33 are formed as one spiral track 41 from the start point P0 to the end point PE. The double spiral format is a format in which the land track 32 and the groove track 33 are formed as two parallel spiral tracks. In this case, two start points are P0G and P0L, and end points are PEG and PEL. There will be two.
[0038]
The optical disk 10 is a double-sided optical disk as shown in FIG. In other words, the optical disk is configured such that two recording layers 54 bonded to each other by an adhesive layer 55 are interposed between two transparent substrates 53. A center hole 50, a clamp area 51 around the center hole, and a reading surface 52 are provided on each surface of the optical disc. In the recording layer 54 of the optical disc 10, prepits 31, lands 32, and grooves 33 are formed as shown in FIG.
In the above embodiment, the pits are formed on the optical disc. However, various marks corresponding to the data bits may be formed on the optical disc.
[0039]
【The invention's effect】
As described above in detail, according to the present invention, in a rewritable optical disk apparatus employing a land / groove recording method, reproduction using a push-pull signal obtained from a two-divided photodetector, particularly for a pre-pit arrangement in a header area. When the method is applied, it is possible to set a pit structure capable of obtaining a good asymmetry AS push-pull signal. Accordingly, a high-quality reproduction signal can be obtained particularly when various kinds of information are reproduced from the pre-pit pattern in the header area, so that a reliable reproduction operation can be realized.
[Brief description of the drawings]
FIG. 1 is a block diagram of a main part of an optical disc apparatus related to an embodiment of the present invention. FIG. 2 is a diagram showing a pre-pit pattern recorded on the optical disc. FIG. 3 is related to an embodiment of the present invention. FIG. 4 is a diagram illustrating the planar structure of a two-divided detector used in an optical head. FIG. 5 is a diagram illustrating the definition of asymmetry of a reproduction signal waveform. FIG. 7 is a characteristic diagram showing the relationship between pit length and asymmetry related to the embodiment. FIG. 7 is a characteristic diagram showing the relationship between pit length and asymmetry related to the embodiment of the present invention. FIG. 9 is a diagram for explaining a pit row related to the form. FIG. 9 is a view showing a pit structure having a rectangular cross-sectional shape related to the embodiment of the present invention.
FIG. 10 is a characteristic diagram showing the relationship between pit length and asymmetry related to the embodiment of the present invention. FIG. 11 is a characteristic diagram showing the relationship between pit length and asymmetry related to the embodiment of the present invention. 12 is a plan view of a single spiral format optical disc as an optical recording medium to which the present invention is applied. FIG. 13 is a plan view of a double spiral format optical disc as an optical recording medium to which the present invention is applied. Figure [Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Optical disk 11 ... Spindle motor 12 ... Spindle motor drive circuit 13 ... Optical head 14 ... Semiconductor laser 15 ... Collimating lens 16 ... Objective lens 17 ... Actuator 18 ... LD driver 19 ... Polarizing beam splitter 21 ... Amplifier 22 ... Servo control circuit 23 ... Condensing lens 24 ... 2 split photodetector 25 ... Differential amplifier 26 ... Signal processing circuit 28 ... System controller

Claims (2)

An optical disc on which pits corresponding to bit data are formed;
Rotating means for rotating the optical disc;
Track tangent for detecting the pits by reflected light obtained by irradiating a light beam spot having a maximum light intensity peak at a position having a certain offset in the radial direction with respect to the center of the pits on the disk A two-part light detection means having a parting line parallel to the direction, and constituted by a reproduction means for reproducing data based on a difference signal of the output of the two-part light detection means;
The length PLn of each pit is set to a value satisfying the following formula,
0.65 ≦ (2 · fnT · PLn) /Sr1≦1.40
However, the length of each pit measured in the track tangential direction is a length corresponding to the code length nT in a predetermined modulation method, and the depth of the deepest portion of each pit recorded at the radial position r1 of the optical disc is pd. Is PLn [m] at a depth pd / 2, the predetermined reproduction frequency of the 2nT pitch signal at the radial position r1 is fnT [1 / s], and the reproduction linear velocity of the optical disk at the radial position r1 is An optical disk device, sr1. An optical disk having a large number of pits corresponding to bit data reproduced by a light beam spot emitted from a reproducing apparatus, wherein the light beam spot detects the pit on the optical disk rotated by a rotating means. It has the maximum light intensity at a position having a predetermined offset in the radial direction with respect to the center of each pit, and the length PLn of each pit is set to a value satisfying the following equation:
0.65 ≦ (2 · fnT · PLn) /Sr1≦1.40
However, the length of each pit measured in the track tangential direction is a length corresponding to the code length nT in a predetermined modulation method, and the depth of the deepest portion of each pit recorded at the radial position r1 of the optical disc is pd. Is PLn [m] at a depth pd / 2, the predetermined reproduction frequency of the 2nT pitch signal at the radial position r1 is fnT [1 / s], and the reproduction linear velocity of the optical disk at the radial position r1 is An optical disk, sr1.

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