JP2752178B2 - Optical storage - Google Patents

Description

The present invention relates to an optical storage device for recording and reproducing information using a rotating medium such as an optical disk, a magneto-optical disk, etc., and to minimize a DC offset of a tracking error even if a track position changes. In order to improve the tracking accuracy, the position setting of the two-part light receiving unit that detects the tracking error from the light reflected and diffracted by the track guide groove by the irradiation of the beam spot is set to the innermost circumference of the rotary recording medium. Positioning is set so as to be symmetrical with respect to the center of the center track located between the track and the outermost track.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical storage device for recording and reproducing information using a rotating medium such as an optical disk, a magneto-optical disk, and the like.

Attention has been paid to rewritable optical disk devices and magneto-optical disk devices as external storage devices of computer systems, and their practical use is being promoted.

In such an optical storage device, for example, a track pitch of 1.6 μm
The recording track is formed in a concentric or spiral state, and the spot light of the laser beam by the optical head must be accurately tracked (tracked) in order to accurately write or read on the track. .

Therefore, it is necessary to detect a tracking error as a deviation amount of the beam spot from the track center. For example, a push-pull method (far-field method) is known.

In the push-pull method, light reflected and diffracted by a track guide groove on an optical disc is received by a two-divided light-receiving unit disposed symmetrically with respect to the track center, and a tracking error is detected as an output difference between the two.

In the detection of the tracking error by the push-pull method, a DC offset that does not make the tracking error signal zero even when the beam spot is located at the center of the track occurs due to various factors. One of the causes of this DC offset is the positioning setting of the two-divided light receiving unit in a system in which two optical heads are mounted on a slider and moved in the radial direction of the disk to perform track access, and the track position changes. Even so, it is desirable to minimize the DC offset included in the tracking error in order to increase the tracking accuracy.

[Prior Art] FIG. 5 is a schematic configuration diagram of a conventional optical storage device, and a carriage driven by a voice coil motor 18 on an optical disk 10 rotated at a constant speed by a spindle motor 16.
20, two sets of optical heads 12-1 and 12-1,
12-2 is installed.

FIG. 7 shows the principle of detecting a tracking error by the push-pull method.

In FIG. 7, the optical disk 10 has a recording track 28 and a track guide groove 30 formed at a track pitch P = 1.6 μm on a disk substrate 26 covered with a protective film 24. When such a disk 12 is irradiated with a beam spot light having a track pitch P, the track guide groove 30 acts as a diffraction grating, and the zero-order diffracted light PTo
And the first-order diffracted light PT1. Therefore, the objective lens 32
Since the intensity distribution of the beam spot changes in the overlapping portion of the 0th-order diffracted light and the 1st-order diffracted light passing through due to the interference effect due to the track shift, the two-divided light-receiving portion 14 having the light-receiving portions C and D should be placed at this position. For example, the tracking error signal TES can be detected by taking the output difference between the light receiving units C and D by the differential amplifier 36.

By the way, the positioning of the two-part light receiving section 14 for tracking error detection must be set so that the light receiving sections C and D are symmetric with respect to the track center on the disk viewed through the head optical system. Absent.

Therefore, in the conventional two-bed system shown in FIGS. 5 and 6, the two-division light receiving section is symmetrical with respect to the track center with reference to the innermost track or outermost track in the recording area of the optical disk. Is set.

[Problems to be Solved by the Invention] However, in the positioning setting of the two-divided light receiving unit with reference to the innermost track or the outermost track in such a conventional apparatus, for example, as shown in FIG. Assuming that the heads 12-1 and 12-2 are positioned in accordance with the innermost track 36, the DC offset of the tracking error in the innermost track 36 is zero, but when the outermost track 38 is accessed, Increasing the curvature of the track causes rotation of the light receiving pattern of the reflected diffracted light, resulting in a problem that the DC offset increases.

Explaining in detail with reference to FIG. 9, FIG. 9A shows a state where the two-part light receiving unit is positioned and set so as to be symmetric with respect to the center of the track with respect to the innermost track. The dividing line Ld and the track center line Ls match. For this reason, the reflection diffraction patterns received by the light receiving sections C and D have the same semicircular shape, and the tracking error signal undergoes a one-cycle S-shaped change every time the track crosses as shown on the left, and reaches the innermost track. The DC offset when the tracking center is a trace can be 0V.

FIG. 9 (b) shows a light receiving pattern and a tracking error signal of the two-part light receiving unit when the center track located at the center between the inner and outer circumferences is accessed. The light receiving pattern rotates and becomes symmetrical with an increase in the track curvature. It does not become a pattern and causes a DC offset.

Further, FIG. 9 (c) shows a case where the maximum outer track is accessed. The light receiving pattern is further rotated to lose the symmetry, a DC offset twice as large as the center track is generated, and the tracking accuracy is reduced. .

This is the same when the positioning of the two-divided light receiving portion is set with reference to the outermost track, and the DC offset increases toward the inner track.

The present invention has been made in view of such conventional problems, and provides an optical storage device capable of improving tracking accuracy by minimizing a DC offset of a tracking error even when a track position changes. The purpose is to:

[Means for Solving the Problems] FIG. 1 is an explanatory view of the principle of the present invention.

First, the present invention has an optical head 12 that is movable in a straight line that is parallel to the radial direction of the rotary recording medium 10 and does not pass through the center of rotation. The light reflected and diffracted by the track guide groove is received by the light receiving unit 14 which is divided and arranged symmetrically with respect to the center of the track.
It is intended for an optical storage device for detecting an error.

In the present invention regarding such an optical storage device,
The positioning of the light receiving unit 14 is set so as to be symmetrical with respect to the track center of a substantially central track located between the innermost track and the outermost track of the rotary recording medium.

[Operation] According to the optical storage device of the present invention having such a configuration, since the reflection diffraction pattern is positioned and set to be the target in the light receiving unit with respect to the center track,
The DC offset of the tracking error signal caused by the rotation of the reflection diffraction pattern when accessing the innermost track and the outermost track can be suppressed to half of the conventional one, and the tracking accuracy can be improved by reducing the DC offset. it can.

[Embodiment] FIG. 2 is an embodiment configuration diagram showing one embodiment of an optical system of an optical head provided in the optical storage device of the present invention.

In FIG. 2, reference numeral 12-1 denotes an optical head. As shown in FIG. 3, for example, two optical heads 12-1 and 12-1 are mounted on a carriage 20 which is movable in a radial direction with respect to an optical disk 10 as a rotary recording medium. 12-2, so the optical head 12
-1 and 12-2 move on straight lines L1 and L2 which are parallel to the radial direction of the optical disk 10 and do not pass through the center 0.

Referring again to FIG. 2, the optical head 12-1 has an optical isolator 50 having a laser diode 42, a collimator lens 44, a polarizing beam splitter (PBS) 46 and a λ / 4 plate 48,
A head optical system including an objective lens 32 and a condenser lens 52 is provided.

More specifically, the laser diode 42 emits a laser beam as a light source, and the light beam from the laser diode 42 enters the collimator lens 44. The collimator lens 44 converts the divergent light from the laser diode 42 into a parallel beam because the beam radiated from the laser diode 42 has a far field pattern (FFP) that spreads largely in an elliptical shape. The light converted into a parallel beam by the collimator lens 44 is incident on the optical isolator 50, is narrowed down by the objective lens 32, and is irradiated on the optical disk 10 as a beam spot light having a size substantially equal to the track pitch P.

The light reflected on the optical disk 10 passes through the objective lens 32, enters the optical isolator 50, and is polarized by the polarization beam splitter 46.
Then, the beam spot image reflected in the right angle direction and condensed by the condenser lens 52 is formed on the light receiving surface of the two-part light receiving unit 14.

Here, the polarizing beam splitter 46 constituting the optical isolator 50 is formed of two prisms, and the inclined surface of the two prisms is coated with a polarizing film. The polarizing beam splitter 46 passes the electric vibration component of the light wave parallel to the left and right incident surfaces, that is, the P-polarized light as the electric field component, and reflects the S-polarized light having the electric field component perpendicular to the incident surface in the perpendicular direction. Has an action.

Further, the λ / 4 plate 48 provided on the objective lens 32 side of the polarizing beam splitter 46 has a function of converting vertical polarized light into circular polarized light and converting circular polarized light into vertical polarized light.

Therefore, since the incident beam from the collimator lens 44 is P-polarized light, it passes through the polarization beam splitter 46,
The light is converted into circularly polarized light by the λ / 4 plate 48 and is irradiated as a beam spot on the optical disk 10 by the objective lens 32. Further, since the reflected light from the optical disk 10 is circularly polarized light, it is converted to the original linearly polarized light by the λ / 4 plate 48 and further becomes S-polarized light. And is imaged on the two-divided light receiving unit 14 through the condenser lens 52.

As the two-division light receiving unit 14, a two-division photodiode (2D
-PD) is used, and the two-piece light receiving section 14 is fixed on a mounting base 54 as shown in the figure.
56 is attached and fixed behind the window 60 opened in the head housing 58. The mounting base 54 can be positioned and adjusted so that the light receiving surface of the two-piece light receiving unit 14 is orthogonal to the optical axis from the condenser lens 52, and is capable of adjusting the movement in the X and Y directions in the plane orthogonal to the optical axis. I have.

In this embodiment, since the tracking error detecting optical system and the focusing error detecting optical system are the same optical system in the present embodiment, the four divided light receiving units A, B, and C are actually used. , D (A and B, C and D are diagonal positions) are used, and the adder calculates the sum (A + D) and (B + C) of the adjacent light receiving sections to obtain substantially two.
The output of the divided light receiving unit can be used.

The four-division light receiving unit detects a focusing error based on the astigmatism method, and a focusing error signal is obtained as the difference between the sum (A + B) and (C + D) of the two diagonal light receiving units.

FIG. 3 is a plan view showing the head position with respect to the optical disk when the positioning of the two-divided light receiving unit 14 provided in the optical head in the optical recording and reading apparatus of the present invention shown in FIG. 2 is set.

In FIG. 3, a center track 40 located between the innermost track 36 and the outermost track 38 in the recording area of the optical disk 10 is first selected as a reference track for positioning and setting the two-divided light receiving unit 14. Of course, the center track 40 may be a track located between the two, and the track pitch is as small as 1.6 μm.
It is not always necessary to select a strict center track, but an arbitrary track within a predetermined range around the center track may be selected as the center track 40.

Thus, the optical heads 12-1 and 12-1 of the center track 40
In the state of irradiating the beam spot according to -2, the adjusting screw 56 of the mounting base 54 to which the two-part light receiving unit 14 shown in FIG. Positioning is set so that the light receiving units C and D are symmetric.

More specifically, the DC voltage of the tracking error signal TES obtained as the difference between the light receiving outputs of the light receiving sections C and D of the two-piece light receiving section 14, that is, the DC offset, becomes zero.
Adjust the position of 54.

FIG. 4 shows the center track 40 according to the present invention.
A reflection diffraction pattern from the track groove for the two-divided light receiving unit 14 when the positioning setting of the divided light receiving unit 14 is performed;
FIG. 4 is an explanatory diagram showing a detected tracking error signal TES.

That is, according to the present invention, as shown in FIG. 4 (b), the center line Ls of the center track is
Positioning is set so that Ld coincides, and in this state, the DC offset obtained in the trace state (tracking on state) after the head access (track jump) to the center track is 0 volt as shown.

FIG. 4 (a) shows a case where a head access (track jump) is made to the innermost track 36 after the positioning setting with respect to the center track 40, and the light receiving pattern of the reflected and diffracted light is reduced due to the reduced track curvature. Rotation causes the track center line Ls to deviate from the division line Ld, causing a DC offset of + ΔV.

Further, FIG. 4 (c) shows a case where the outermost track 38 is accessed (track jump) after the positioning is set by the center track 40, and the track curvature is increased, so that the outer circumference track 38 is rotated in the opposite direction to FIG. 4 (a). The light receiving pattern rotates, and the track center Ls is shifted with respect to the division line Ld. In this case, a DC offset of −ΔV occurs.

Here, the offset + ΔV at the innermost track in FIG. 4A and the offset −ΔV at the outermost track in FIG.
ΔV has substantially the same magnitude and opposite polarity, and the DC offset can be suppressed within a range of ± ΔV with respect to the center track where the DC offset is zero. On the other hand, when the conventional innermost track shown in FIG. 9 is used as a reference, the outermost track has a DC offset of 2 × ΔV, which is twice that of the present invention. The positioning setting of the two-divided light receiving unit can reduce the DC offset to half or less as compared with the conventional example.

It is a matter of course that an optical system for detecting a tracking error may be separately provided for the optical system for detecting a focusing error, and a dedicated two-division light receiving unit 14 may be used.

[Effects of the Invention] As described above, according to the present invention, it is possible to minimize a DC offset that varies depending on a track position due to a beam spot light from an optical head not moving on a radius on an optical disk. In addition, the tracking accuracy at the time of high-speed access can be greatly improved.

Further, when a tracking error is detected by using a four-divided light receiving section for detecting a focusing error, the accuracy of detecting the focusing error can be improved at the same time.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention; FIG. 2 is a diagram illustrating the configuration of an embodiment of the present invention; FIG. 3 is a diagram illustrating a positioning track of a two-part light receiving unit according to the present invention; FIG. 5 is a schematic diagram of a conventional device; FIG. 6 is a diagram of a conventional head mounted state; FIG. 7 is a diagram of the principle of tracking error detection by a push-pull method; FIG. FIG. 9 is an explanatory view of positioning based on a circumferential track; FIG. 9 is an explanatory view of a conventional light receiving pattern and offset. In the figure, 10: rotating recording medium (optical disk) 12-1, 12-2: optical head 14: split light receiving section 16: spindle motor 18: voice coil motor (VCM) 20: slider 24: protective film 26: disk substrate 28: recording track 30: track guide groove 32: objective lens 34: differential amplifier 36: innermost track 38: outermost track 40: center track 42: laser diode (LD) 44: collimator lens 46: polarizing beam splitter ( PBS) 48: λ / 4 plate 50: Optical isolator 52: Condensing lens 54: Mounting base 56: Adjustment screw 58: Head housing 60: Window

Claims (1)

(57) [Claims] An optical head (12) movable in a radial direction of a rotary recording medium (10) is provided, and a track guide groove of light emitted from the optical head (12) onto the rotary recording medium (10) is provided. In an optical storage device for receiving reflected light by a light receiving portion (14) divided symmetrically with respect to a track center and detecting a tracking error signal as an output difference of the light receiving portion, a beam of the optical head is provided. When the spot is positioned with respect to the center of a substantially center track located between the innermost track and the outermost track of the rotary recording medium, the offset of the tracking error signal is symmetrical between the inner offset and the outer offset. An optical storage device, wherein a dividing line of the light receiving section is arranged so as to coincide with a center line of a track such that: