JPH0981943A - Information recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tracking detecting device capable of highly precise detection regardless of being large or small in track pitch. SOLUTION: The surface of a disk 7 on which a pit 8 is formed, is irradiated with a slender slit-like beam 5 and the obtained image of the pit passes through an aperture (field diaphragm) 14 located on a conjugate position with the disk. By detecting the passed light quantity, tracking detection is performed. A transmission part (B) for originally detecting a signal and two transmission parts (A, C) for tracking detection are provided in the aperture. Two transmission parts A and C are shifted by (+a, -a) from the optical center (the center of an objective lens), respectively, by detecting the intensity deference (difference of light quantity) of the pit images passing through two transmission parts, a tracking error is detected and tracking servo is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording / reproducing apparatus equipped with a tracking error detection system for an optical pickup, such as a CD (compact disc) or a VD (video disc).

[0002]

2. Description of the Related Art A disk player irradiates a pit on a track of a rotating disk with a spot of a laser beam narrowed down to a size of about 1 μm, which is close to a diffraction limit, while rotating an optical disk, and detects the reflected light. The information on the optical disc is read out.

In this type of disc player, there is a limit to the operating precision and the precision of mechanical production of the disc, and when the disc is rotated, various fluctuations cannot occur in the disc. Therefore, in order to read the correct information from the pits of the tracks, it is necessary to detect such fluctuations and control the light spot to follow the tracks of the rotating disk.

Here, particular attention is paid to fluctuations in the radial direction of the disk. In this regard, a tracking servo mechanism that tracks a light spot on the pit of the track is adopted. In this tracking control, the shift of the light spot with respect to the track is detected, and the mirror or lens of the optical system is moved to cause the light spot to track the pit of the track. In order to read the correct information from the track pits, it is necessary to perform tracking control with an accuracy of ± 0.1 μm or less from the center of the tracks or pits on the disc, and it is necessary to detect tracking errors with an accuracy corresponding to that. is there.

A three-spot method is known as a tracking error detection method in conventional VD (video disk) and CD (compact disk). This system uses a diffraction grating 21 as shown in FIG. 4 (a), and particularly the laser beam light 22 is divided into three beams by this diffraction grating 21, and the three beams are divided into three beams as shown in FIG. 4 (b). The beam is directed toward the row of pits 24 on the track of the disc 23. Here, the + first-order beam spot S ₊₁ and the −1st-order beam spot S _−1, which are respectively located at both ends of the zero-order beam spot S ₀ , are slightly in the tracking direction (radial direction of the disc). Move it so that it is illuminated. Here, the zero-order beam spot S ₀ located at the center is used for original signal detection, and the + first-order beam spot S ₊₁ and the −1st-order beam spot S ₋₁ located at both ends are displaced from each other. Is detected.

The reflected light quantities of the two beam spots S ₊₁ and S _-1 at the both ends are detected by the respective photosensors, and outputs corresponding to the reflected light quantities of the two beam spots S ₊₁ and S _-1 are produced. If they are balanced, the central recording / reproducing beam spot S ₀ is in the state of tracking the center of the pit, and the output depending on the reflected light amount of the two beam spots S ₊₁ and S _-1 at both ends thereof is different. If there is a tracking error, the tracking error is detected by the differential signal from the two sensors, and the light spot is tracked to the center of the track by moving the mirror or lens of the optical system of the pickup. I will let you.

[0007]

However, in the tracking and tracking method, the laser beam light is divided into three beams by using the diffraction grating, and the + first-order beams respectively positioned at both ends of the zero-order beam spot S _0. Spot S _{+ 1} ,
Since the reflected light amount of the −1st-order beam spot S ₋₁ is detected, there are the following problems.

That is, the above method requires a diffraction grating for splitting the laser beam light, and the diffraction grating needs to be arranged inside the optical system, which complicates the optical system. Further, there is a drawback that the utilization rate of the laser output is not good.

Further, there are the following problems. That is,
As shown in FIG. 4A, a condenser lens for focusing each beam and irradiating the beam on the disc is arranged between the disc and the diffraction grating. Therefore, the diameter d of the spot on the disc surface is determined by the disc 23 and the diffraction grating 21.
Assuming that the focal lengths of the condenser lenses L ₁ , L ₂ and L ₃ arranged between are f ₁ , f ₂ and f _3, they are given by the following equation.

D = f ₁ × f ₃ × λ / 3.14 × f ₂ × 1 (1) where λ is the wavelength of the light and l is the dimension of the illumination beam light on the diffraction grating 21.

For example, wavelength λ = 0.633 μm, f ₁ =
4 mm, f ₂ = 24 mm, f ₃ = 4 mm, and l = 100
If it is μm, then d = 1.3 μm. In this tracking and tracking method, the size relationship between the spot diameter d and the track pitch is extremely important for detecting tracking errors. That is, if the spot diameter "d" is not smaller than the track pitch " _pt ", the pits of the adjacent track will be read. However, since p _t is 1.6 μm in the current CD,
If d ≦ p _t is satisfied and is within this range,
It has been said that tracking servo is possible.

Recently, however, there has been a strong demand for a large capacity for storing a large amount of information such as images. In order to cope with the large capacity without increasing the size of the disk, the track pitch and the There is a growing need for smaller pit pitches.

However, when the pit pitch and the track pitch reach a value of 0.725 μm, it is quite difficult for the current optical system to further narrow down the laser light spot. Generally speaking, in order to focus light on a small spot, its wavelength should be small and the numerical aperture NA of the lens system should be large. However, it seems that we are at the limit because we cannot choose the wavelength so freely. On the other hand, in order to increase the numerical aperture NA, the optical system becomes extremely precise and complicated, and it becomes unrealistic in terms of cost. Moreover, from the viewpoint of the depth of focus and the like, increasing the numerical aperture NA of the lens system makes the optical system unstable, and there is a limit to increasing the numerical aperture NA.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to cope with a finer track pitch than ever, regardless of the size of the track pitch. An object is to provide an information recording / reproducing apparatus capable of realizing error detection.

[0015]

SUMMARY OF THE INVENTION In order to detect the above-mentioned problem, that is, a tracking error that can deal with a minute track pitch, the present invention is essentially provided on a disk surface on which pits are formed. The beam on the long and narrow slit is illuminated, and the pit image obtained at that time detects the amount of light passing through the aperture (field stop) installed at the conjugate position with the disk surface, thereby performing tracking detection. I do.

Further, the aperture is provided with a transparent portion (B) for original signal detection and two transparent portions (A, C) for tracking detection. The two transmission parts A and C of the aperture (field stop) are each shifted by (+ a, −a) with respect to the optical center (objective lens center), and the intensity of the pit image passing through these two transmission parts. By detecting the difference (light amount difference), tracking error detection and tracking servo are performed.

According to these, it is not always necessary to use a diffraction grating, and there is no special limitation on the type of light source.
High degree of freedom in design. Further, with the above configuration, it is possible to realize tracking error detection that can cope with a particularly minute track pitch.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a tracking error detection system. FIG. 1 (a)
Inside, 1 is a light source that emits an irradiation beam. This light source 1
For example, a semiconductor laser is used in the above, but other light sources such as a laser light source, a light emitting diode (LED), and a white light lamp can be used, or a divergent light source may be used.

The light emitted from the light source 1 passes through an entrance aperture 2 composed of a field diaphragm, is focused into a predetermined shape, and becomes an incident beam 5 focused by two sets of condenser lenses 3 and 4 of an incident optical system. . The incident beam 5 is reflected by the beam splitter 6 toward the optical disk 7 side and is irradiated onto the recording surface of the optical disk 7.

The entrance aperture 2 is installed at a position conjugate with the recording surface of the optical disk 7. In addition, the aperture through which the entrance aperture 2 penetrates has an elongated slit shape such as a long hole or an elongated ellipse, or a strip shape. Then, as shown in FIG. 1B, the irradiation is set in the form of a long and narrow slit along the track direction t of the optical disc 7. In FIG. 1B, a slit-shaped irradiation spot S is irradiated over a plurality of pits 8 on the track. Further, the length of the irradiation spot S here is the 3 degree or more sized to capture pit component in one track, its width is set to be smaller than the track pitch p _t.

On the other hand, the beam splitter 6 irradiates the optical disc 7 with the beam 5, and transmits the light reflected from the surface of the disc 7 without returning it to the light source 1 side. Therefore, it is also possible to use a polarization beam splitter for this.

The light reflected by the disk 7 and transmitted through the beam splitter 6 becomes a beam 13 focused by the two sets of condenser lenses 11 and 12 of the detection optical system 10 and is not conjugate with the spot irradiation surface of the optical disk 7. A screen on the surface of the optical disk 7 illuminated by the irradiation spot S is imaged on the aperture 14 for tracking error detection, which is installed at the relevant position. That is, the tracking error detecting aperture 14 is a field stop which is in a conjugate positional relationship with the light source 1, and forms a so-called screen for displaying an image on the surface of the optical disc 7 irradiated with the irradiation spot S.

Further, as shown in FIG. 1C, the tracking error detecting aperture 14 is provided with three light transmitting portions A, B and C corresponding to the irradiation portion of the irradiation spot S. It consists of a mask member. The openings of the light transmitting portions A, B, C may be holes that are mechanically opened in an opaque plate-shaped mask member, or the light transmitting portions A, B, C.
It is also possible to form only the part as a transparent part.

The light transmitting portion B located at the center is the original light transmitting portion for signal detection, and the two light transmitting portions A and C located at both ends thereof are the light transmitting portions for tracking detection. . Further, the light transmitting portion B located at the center is formed as a long strip-shaped opening along the radial direction of the corresponding optical disk 7, and is the light transmitting portion A at both ends.
The portion and the portion C are each formed in a rectangular opening.

Here, the point to be noted is that the parts A and C are
In the tracking direction Y (corresponding to the radial direction of the disk) with respect to the center of the central portion B (usually the optical center and often the center of the objective lens) (+ a, −
That is, they are arranged in a point-symmetrical positional relationship that is shifted by a).

As shown in FIG. 2, a signal detection sensor 15b for detecting the image intensity of the light transmitted through the portion B is provided on the back side of the central portion B which is a light transmitting portion for original signal detection. ing. On the other hand, tracking error detection sensors 15a and 15c for individually detecting the image intensity of the light transmitted through the A section and the C section are provided on the back sides of the A section and the C section, respectively. Corresponding to, is provided in close proximity.

The image of the irradiation portion of the irradiation spot S is shown in FIG.
The image is formed as shown by. That is, when the position of the track is at the original center position, the image is shown by the dotted line, and when a tracking error occurs, for example, an image deviated from the center is displayed as shown by the solid line or the two-dot chain line depending on the direction of the error. Be done. Therefore, each detection sensor 15a, 1
The image intensities can be detected by 5c, and the outputs at this time are defined as I _A and I _B. The difference between the output detected by the differential amplifier 16 takes out the difference signal △ I = I _A -I _B, can be than this obtaining a tracking error signal S.

Specifically, the intensities (light amounts) I _A and I _B of the respective pit images p when passing through the portions A and C change as shown in FIG. Also, △ I = I _A -I _C changes as shown in FIG dashed. I _A and I _C are received by the two-divided sensor and converted into electric signals S _A and S _C , respectively, and ΔS = S _A
By measuring the -S _C, the tracking error signal S is obtained, thereby performing tracking servo.

As described above, if the image intensity of the pit image of the irradiation portion of the irradiation spot S imaged on the tracking error detection aperture 14 is detected, the tracking error of the tracking error is detected unlike the method of detecting the light amount of the reflected light. The detection accuracy can be improved.

The ratio of the dimension of the spot irradiation portion of the disk 7 and the portion of the irradiation surface of the tracking error detecting aperture 14 which is in a conjugate relationship therewith, that is, the magnification, can be arbitrarily set by the detection optical system 10. Yes, especially if the magnification is increased, the tracking error detection aperture 14 and the tracking error detection sensors 15b, 15
The detection accuracy of c can easily be increased considerably.

At least the light source 1, the entrance aperture 2, the condenser lenses 3 and 4, of the tracking error detection system,
Beam splitter 6, condenser lenses 11, 1 of detection optical system
2, tracking error detection aperture 14, signal detection sensor 15a, tracking error detection sensor 15
b, 15c, etc. are incorporated in an optical head (not shown).

The present invention is not limited to the above-mentioned embodiment, but various modifications can be considered within the scope of the gist of the invention. For example, the shape of the irradiation spot formed on the recording surface of the optical disc formed by the entrance aperture is not limited to a continuous elongated slit shape or a strip shape, but may be a substantially elongated slit shape or a strip shape. Well, that is, if there is an aperture corresponding to each opening portion in the tracking error detecting aperture, the irradiation area of the irradiation spot may be intermittent.

[0033]

As can be seen from the above description,
According to the present invention, it is possible to simplify the optical system and realize highly accurate tracking error detection regardless of the size of the track pitch.

[Brief description of drawings]

FIG. 1A is an explanatory diagram of a schematic configuration of a tracking error detection system according to an embodiment of the present invention, and FIG. 1B is an explanatory diagram showing a state of a relationship between a pit row and an irradiation spot on a track of an optical disc. FIG. 6C is an explanatory diagram of the form of the tracking error detection aperture.

FIG. 2 is an explanatory diagram of a circuit configuration of a tracking error signal detection system of the same embodiment.

FIG. 3 is an explanatory diagram of sensor output in the tracking error signal detection system of the same embodiment.

FIG. 4 is a diagram for explaining a conventional tracking detection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source, 2 ... Incident aperture, 3, 4 ... Condensing lens, 5 ... Incident beam, 6 ... Beam splitter, 7 ... Optical disk, 8 ... Pit 10 ... Detection optical system, 11, 12 ... Condensing lens, 13 ... beam, 14 ... tracking error detection aperture, 15b ... signal detection sensor 15a, 15c ... tracking error detection sensor, A, B, C ... light transmitting portion, S ... irradiation spot.

Claims (3)

[Claims] 1. A disc in which pits are formed is irradiated with a beam having a substantially elongated slit shape in the track direction of the pits, and an image of the pits obtained at that time is conjugate with the disc surface. An information recording / reproducing apparatus characterized by performing tracking servo detection and tracking servo of an optical pickup by passing through an aperture of an aperture arranged at a position and detecting the amount of transmitted light. 2. The aperture is provided with a transmission part (B) for signal detection and a plurality of transmission parts (A, C) for tracking detection.
An information recording / reproducing apparatus according to claim 1. 3. A plurality of transparent portions (A, C) of the aperture.
Are each shifted with respect to the optical center (objective lens center), and tracking error detection and tracking servo are performed by detecting the intensity difference of the pit images passing through the plurality of transmission portions (A, C). The information recording / reproducing apparatus according to claim 1, wherein: