JPH073698B2 - Optical pickup - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical pickup, and more specifically, to record information by condensing a light beam on an information track surface of an optical disk, or to collect a light beam on the optical disk. The present invention relates to an optical pickup for reproducing light by detecting light modulated by pits on an information track surface.

(Prior Art) In recent years, optical discs such as CDs (compact discs), optical video discs, optical document file discs, and optical still image discs in DAD (digital audio discs) have appeared,
These optical disks have been widely used as large-capacity information recording / reproducing media.

Such an optical disc is a CD (compact disc)
For example, a spiral information track is formed on the optical disk surface, and this information track is formed by a pit string corresponding to a digital signal obtained by converting an analog audio signal into a PCM.

The reading of this pit row is performed by focusing the light beam from the laser light source on the pit row by the objective lens while rotating the optical disc, and detecting the reflected light modulated by the pit row at this time. .

One of the features of such an optical disc is that the recording density of information is very high, and therefore the width of the information track, in other words, the width of the pit is very narrow (for example, 0.4 μm). The track pitch is also very narrow (eg 167 μm).

As described above, in order to accurately read pit information from an information track having a very narrow width and pitch, the objective lens should always be in focus with respect to the information track of the optical disc, and the light on the information track should be focused. It is necessary to set the spot diameter of the beam to a predetermined value.

Therefore, such an optical pickup has a device for detecting the defocus of the objective lens with respect to the information track surface, and focusing control for displacing the objective lens in the optical axis direction is performed based on the output signal of this device.

As such an apparatus for detecting defocus, as disclosed in, for example, Japanese Patent Laid-Open No. 59-90238, a knife edge portion is provided in the optical path of the reflected light from the information track surface of the optical disc. There is a device in which the reflected light passing through the knife edge is received by a photodetector, and the in-focus state is detected based on the movement of the spot on the photodetector.

However, in such a conventional device, the optical pickup becomes large in size, and a part of the reflected light from the information track is covered by the knife edge. For this reason, the utilization efficiency of the output light of the light source decreases, the S / N ratio of the photodetector deteriorates, and accurate detection may not be possible unless the output of the light source is increased. Will be changed.

Further, a semiconductor laser is generally used as a light source, and the divergence angle of the output beam of this laser has an elliptical shape. For this reason, it is necessary to use a shaping prism for converting the light of the semiconductor laser into a circular beam in the recording optical pickup in which it is necessary to position the accurate circular beam on the information track. Even in such a case, the same problem as described above occurs.

On the other hand, Japanese Patent Application Laid-Open No. 57-30810 describes an apparatus for performing focusing detection by disposing a wedge made of a small prism between a light source and an objective lens.
However, the configuration of the prior art has a drawback that an accurate focus detection error signal cannot be detected because the light spot for focus detection on the recording medium does not match the light spot for information reading.

Further, Japanese Patent Application Laid-Open No. 59-33636 describes a technique in which an information signal and a focus error signal are obtained by using a diffraction grating. However, in the prior art, a light beam for reading information out of the light beams directed to the recording medium is described. However, the diameter of the light spot on the recording medium cannot be reduced, and as a result, high density information cannot be read.

(Object) It is an object of the present invention to provide an optical pickup equipped with a compact and highly accurate focus detection device which solves the above-mentioned drawbacks.

(Outline) The optical pickup of the present invention is an optical pickup in which light emitted from a light source is converged on a recording medium by an objective lens and reflected light thereof is received by a photodetector. An optical lens for focus detection of an aperture smaller than the aperture diameter of the objective lens is disposed on the surface of the objective lens on the light source side in the optical path between the objective lens and the aperture diameter of the objective lens. The light flux from the light source is incident over the entire area, the converged light emitted from the objective lens is incident on the recording medium, and the light flux reflected by the recording medium and passing through the optical lens is used for focus detection. It is characterized in that the light is incident on the photodetector. Further, the optical pickup of the present invention is an optical pickup in which light emitted from a light source is converged on a recording medium by an objective lens and the reflected light is received by a photodetector, wherein the light source and the objective lens are combined. An optical lens for focus detection having an aperture diameter smaller than the aperture diameter of the objective lens is arranged on the surface of the objective lens on the light source side in the optical path between the objective lens and the entire aperture diameter of the objective lens. Of the light flux from the light source and the convergent light emitted from the objective lens to the recording medium, and the reflected light flux from the recording medium that has passed through the optical lens is used for focus detection. A lens holder incorporating an optical system that is made incident on the photodetector is driven in the tracking direction and the focusing direction by electromagnetic drive means. It is characterized by having done.

(Example) Hereinafter, the Example of this invention is described using drawing. First, one embodiment will be described with reference to FIGS. 1 to 5.

In FIGS. 1 and 2 showing the optical system and the signal processing system of the present embodiment, a light beam P from the light source 1 is collimated in front of a semiconductor laser light source (hereinafter abbreviated as “light source”) 1. The collimator lens 2 for converting the collimator lens 2 is arranged, and the shaping prism 54 having an inclined surface at a predetermined angle with respect to the central optical axis of the collimator lens 2 is arranged.
The shaping prism 54 converts the elliptical divergence angle of the light emitted from the light source 1 into a circular divergence angle,
The polarization beam splitter 3 is provided in front of the shaping prism 54.
Are arranged.

The polarization plane 3a of the polarization beam splitter 3 transmits the light linearly polarized in the direction perpendicular to the paper surface and reflects the light linearly polarized in the direction horizontal to the paper surface. A 1/4 corrugated plate 4 for converting linearly polarized light into circularly polarized light or changing circularly polarized light into linearly polarized light is arranged. An objective lens 5 is arranged in front of the quarter-wave plate 4, and a focusing coil 6 described later is attached to the objective lens 5. These are arranged to separate the round-trip optical paths by rotating the polarization angles of the incident light and the reflected light by 90 degrees.

At the focal length position of the objective lens 5, an information track surface 7a of an optical disk 7 which is rotationally driven by a motor (not shown) is arranged.

On the surface of the objective lens 5 on the light source side, a microlens 55, which is an optical lens for focus detection of an aperture smaller than the aperture diameter of the objective lens, is formed on the information track surface 7a.
Glued to focus the reflected light beam from. A cylindrical lens is provided on the upper surface of the eccentric beam splitter 3 at a position corresponding to the microlens 55.
56 are closely attached. A photodetector 80 is arranged on the side surface of the polarization beam splitter 3 at a predetermined distance.
This photo detector 80 has tracking error signal Tr and information signal
First light receiving element 81 and second light receiving element for generating RF
82 is formed, and at the position where the reflected light beam Q passing through the cylindrical lens 56 is reflected by the polarization plane 3a, the third to sixth light receiving elements 83 to 86 for producing the focusing error signal F ₀ are reflected light. It is formed so as to receive the 0th order light of the beam Q.

Each of the light receiving elements 81 to 86 of the photodetector 80 has a first light receiving element 81 and a second light receiving element 82, which are obtained by dividing a square light receiving area into two, as shown in FIG. Placed in
Third to sixth light receiving elements 83 to 86 are obtained by radially dividing a circular light receiving area into four.

The output terminals of the light receiving elements 83, 85 of the third and fifth pairs are connected to the respective non-inverting input terminals of the summing amplifier circuit 87, and the light receiving elements 84, 86 of the fourth and sixth pairs are connected. Each output terminal is connected to each non-inverting input terminal of the summing amplifier circuit 88. The output terminal of the summing amplifier circuit 87 is connected to the inverting input terminal of the error amplifier circuit 89, and the non-inverting input terminal of the circuit 89 is connected to the output terminal of the summing amplifier circuit 88. Focusing error signal F ₀ at 89 output
The output terminals of the summing amplifier circuits 87 and 88 are connected to the summing amplifier circuit 90.
Are connected to their respective non-inverting inputs. The output end of the addition amplification circuit 90 and the output end of the second light receiving element 82 are connected to the respective non-inverting input ends of the addition amplification circuit 91. The output terminal of the first light receiving element 81 is connected to the non-inverting input terminal of the error amplifying circuit 92, and the inverting input terminal of the circuit 92 is connected to the output terminal of the summing amplifying circuit 91. Tracking error signal Tr at the output of circuit 92
Is obtained.

Further, the output terminal of the first light receiving element 81 and the output terminal of the summing amplifier circuit 91 are connected to the respective non-inverting input terminals of the summing amplifier circuit 93, and an information signal is output from the output terminal of the circuit 93. RF can be obtained.

In the present embodiment configured as described above, the reflected light beam Q from the information track surface 7a is focused by the microlens 55, passes through the cylindrical lens 56, and is polarized by the polarization plane 3a.
And is incident on the third to sixth light receiving elements 83 to 86. At this time, at the time of just focusing, the reflected light beam Q is focused on the cylindrical lens 56 by the objective lens 5 and the microlens 55, so that it is reflected by the polarization plane 3a and is incident on the third to sixth light receiving elements 83 to 86. The spot shape is a circular spot as shown in FIG.

On the other hand, in the front pinning state and the rear pinning state, as shown in FIG. 4 or 5, the spot shape on the third to sixth light receiving elements 83 to 6 is a vertically long ellipse or a horizontally long ellipse. Therefore, the addition output of the third and fifth light receiving elements 83 and 85 of the pair, that is, the output of the addition amplification circuit 87, and the addition output of the fourth and sixth light receiving elements 84 and 86 of the pair, that is, the addition amplification Circuit 88
The focusing error signal F ₀ is obtained by finding the difference with the output of the error amplification circuit 89. This focusing error signal F ₀ is ₀ at just focus,
At the time of defocusing, an output having a polarity depending on the deviation direction of the front pin and the rear pin is obtained. Therefore, when a current corresponding to the signal F ₀ is passed through the focusing coil 6, the just focus state is always maintained.

In order to perform focusing drive and tracking drive in the optical system of the above-described embodiment, for example, the optical system 200 is housed in a holder 201 as shown in FIG. 6, and both ends of this holder 201 are provided with optical axes of the objective lens 5. It is supported by two-dimensional springs 202 and 203 that are biased in the direction orthogonal to the direction and the optical axis direction. As shown in FIG. 7, the two-dimensional spring 202 (203) has a cylindrical boss portion 202b at the center of a disc-shaped leaf spring 202a (203a) that is integrally formed with radial spring portions and is biased in the focusing direction. (203b) is provided, and this boss 202b (203b
b) A pair of leaf springs 202c, 20 biased in the tracking direction
2c (203c, 203c) are provided facing each other, and the leaf springs 202c, 202c (203c, (203c) are fixed to the holder 201 by using an adhesive or the like.

On the other hand, as a control mechanism for controlling the movement of the holder 201 in the focusing direction and the tracking direction, tracking magnetic motors 204 and 205 are provided on the peripheral surface of the holder 201 in the illustrated example.
Are arranged to face each other, and a focusing magnetic motor 206 is arranged on the bottom surface. Since all of the magnetic motors 204-206 have the same mechanism,
The reference numeral 204 will be taken up and described, and the same portions will be denoted by the same reference numerals after the numbers, and description of the other magnetic motors 205 and 206 will be omitted.
In the illustrated example, a disk-shaped magnet 204b is fitted into one end of a yoke 204a formed in a cylindrical shape, a hole 204c is formed at the center of this magnet 204b, and a cylindrical center ball 20 is formed therein.
4d is fixed to form a magnetic circuit. The tracking coil 204f is inserted into the magnetic gap 204e of this magnetic circuit to form the magnetic motor 204.

When the optical disk 7 causes surface wobbling for some reason, this pickup responds to the focusing error signal by the focusing coil 2 of the magnetic motor 206 for focusing.
A current is applied to 04f, and the focusing coil 204f is driven up and down according to Fleming's law to adjust the focus state of the objective lens 5. On the other hand, when the center of the optical disk 7 is deviated to cause eccentricity, a current is applied to the tracking coils 204f and 205f of the tracking magnetic motors 204 and 205 in accordance with the tracking error signal, and the tracking coils 204f,
205f can be moved in the left-right direction so that the focus of the lens 5 can follow the pit pattern of the information track surface 7a of the optical disk 7.

The shaping prism in each of the above embodiments may be provided as needed, and a mask having a circular opening may be used in the optical pickup for recording. Further, as a matter of course, when the light beam emitted from the light source has a circular divergence angle, it is not necessary to use the shaping prism.

(Effect of the Invention) In the optical pickup of the present invention, an optical lens for focus detection having an aperture smaller than the aperture diameter of the objective lens is arranged in the optical path between the light source and the objective lens to cover the entire aperture diameter of the objective lens. Focused light is emitted to the recording medium by using it, and a focus error signal is obtained by the light flux emitted from the optical lens, so that a sufficiently small light spot can be emitted to the recording medium surface, and as a result, high-density reading is possible. In addition, there is an advantage that the device can be downsized. Further, since a focus error signal is obtained by using a part of the reflected light of the light spot irradiated on the medium surface, it is possible to detect the focus at the read light spot position, and as a result, it is possible to read highly accurate information. is there.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system in an optical pickup showing an embodiment of the present invention, FIG. 2 is a signal processing circuit connected to a photodetector in the optical system of FIG. 1, and FIG. 5 is a front view for explaining the operation of the photodetector, FIG. 6 is a front view of a drive mechanism for performing the focusing operation and the tracking operation of the optical system of FIG. 1, and FIG. The figure is a perspective view of a leaf spring in the drive mechanism shown in FIG. 1 ... Semiconductor laser light source 2 ... Collimator lens 3 ... Polarization beam splitter 4 ... 1/4 wavelength plate 5 ... Objective lens 7 ... Optical disk 8 ... Photodetector 55 ... Microlens

Claims (2)

[Claims] 1. An optical pickup in which light emitted from a light source is converged on a recording medium by an objective lens and reflected light thereof is received by a photodetector, and an optical path between the light source and the objective lens is provided. In addition, an optical lens for focus detection having an aperture diameter smaller than the aperture diameter of the objective lens is arranged on the surface of the objective lens on the light source side, and the entire aperture diameter of the objective lens is covered. Light beam from the light source is made incident, and convergent light emitted from the objective lens is made incident on the recording medium. Further, of the reflected light beams from the recording medium, the light beam passing through the optical lens is used for focus detection. The optical pickup is characterized in that it is made incident on the photodetector of. 2. An optical pickup in which light emitted from a light source is converged on a recording medium by an objective lens and reflected light thereof is received by a photodetector, and an optical path between the light source and the objective lens. In addition, an optical lens for focus detection having an aperture diameter smaller than the aperture diameter of the objective lens is arranged on the surface of the objective lens on the light source side, and the entire aperture diameter of the objective lens is covered. Light beam from the light source is made incident, and convergent light emitted from the objective lens is made incident on the recording medium. Further, of the reflected light beams from the recording medium, the light beam passing through the optical lens is used for focus detection. The lens holder incorporating the optical system that is made incident on the photodetector is driven in the tracking direction and the focusing direction by the electromagnetic drive means. Characteristic optical pickup.