JPH11134661A - Optical head and optical recording/reproducing device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a displacement direction or a displacement amount of an objective lens without providing an exclusive detector on an objective lens drive means. SOLUTION: A diffraction grating 4 provided with an axial slide type actuator 10 and providing a cross-shaped division line between an objective lens 6 and a photodetector is arranged. The diffraction grating 4 quadrisects reflected luminous flux from an optical disk, and diffracted light diffraction separated in respective areas are led between respective independent light receiving surfaces on the photodetector by a detection lens. A direction of a boundary between the light receiving surfaces 9a, 9b or between the light receiving surfaces 9c, 9d is set up nearly vertically to the displacement direction of a light spot on the photodetector associated with tracking operation, and by detecting differences between respective light receiving surface outputs, the displacement direction or the displacement amount of the objective lens 6 is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for recording / reproducing information on / from an optical disk and an optical recording / reproducing apparatus using the optical head, in particular, without providing an objective lens driving means with a dedicated detector. The present invention also relates to an optical head capable of detecting a displacement direction or a displacement amount of an objective lens, and an optical recording / reproducing apparatus using the optical head.

[0002]

2. Description of the Related Art An optical recording / reproducing apparatus is an information recording / reproducing apparatus characterized by non-contact, large-capacity, high-speed access, and low-cost media. Alternatively, it is used as an external storage device of a computer. As the use of optical recording / reproducing devices has been required to be increased in speed with the expansion of use, it has become essential to feed back the direction or amount of displacement of the objective lens to a tracking control system.

As an effective means for detecting the direction or amount of displacement of the objective lens, there are disclosed many configurations in which the objective lens driving means is provided with a dedicated detector. For example, JP
According to Japanese Patent Application Laid-Open No. H-256232, a pin for detecting a lens displacement moves with the rotation of a movable holder on which an objective lens is mounted.
There is disclosed an effective configuration in which light from the ED is partially shielded by a pin and its shadow is projected by a two-part photodiode, and as a result, the direction or amount of displacement of the objective lens can be detected.

[0004]

By the way, in a configuration having a dedicated detector as a means for detecting the displacement direction or displacement amount of the objective lens as in the above invention, a light emitting element such as an LED and a light receiving element such as a photodiode are used. You need an element. As a result, there are many wirings to the objective lens driving means, and there is a problem that miniaturization and low cost are difficult.

Accordingly, the present invention provides a small and simple optical head capable of detecting the direction or amount of displacement of an objective lens without having a dedicated detector in the objective lens driving means, and an optical head using the same. To provide a dynamic recording and reproducing device.

[0006]

In order to solve the above-mentioned problems, according to the present invention, the direction of the boundary of each light receiving surface of the two-part focus error signal detection area is set on the photodetector accompanying the tracking following operation by the actuator. An optical head and an optical recording / reproducing apparatus were constructed using a photodetector set so as to be substantially perpendicular to the light spot displacement direction or a tangent to the displacement direction.

That is, a laser light source, an objective lens,
The photodetector, a diffraction grating divided into four crosses by a substantially cross-shaped dividing line in an optical path between the objective lens and the photodetector, and the objective lens and the diffraction grating integrated with each other. An optical head having a shaft sliding type actuator that drives
A two-part focus error signal detection area of the light detection surface is formed with respect to the displacement direction of each light spot on the photodetector or the tangent line in the displacement direction due to the tracking following operation of the shaft sliding type actuator. The direction of the boundary between the light receiving surfaces is substantially vertical. As a focus error signal detection method in the two-divided focus error signal detection area,
The knife edge method is used.

[0008] With this configuration, the spot on the two-part focus error signal detection area is displaced by the tracking operation. Alternatively, it becomes possible to obtain an objective lens displacement detection signal for detecting the displacement amount.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of an optical head according to an embodiment of the present invention and an optical recording / reproducing apparatus using the optical head will be described below with reference to the drawings.

FIG. 1 is a schematic front view of an optical head according to an embodiment of the present invention and an optical recording / reproducing apparatus using the optical head. An optical head 50 for recording and reproducing information on and from the optical disk 7 shown in FIG. 1, a laser drive 51 for driving the optical head, and light reflected from the optical disk 7 received by the photodetector 9 and converted into an electric signal. , Each signal generation circuit 52
To generate signals such as a focus error signal, a displacement detection signal of the objective lens, a tracking error signal, and an information recording signal. The generated signals are transmitted to the system control circuit 5
3 is supplied.

The system control circuit 53 drives the actuator 10 through an actuator drive circuit 54 based on each error signal, thereby displacing the objective lens 6, the quarter-wave plate 5 and the diffraction grating 4 together to perform focus control. And perform tracking control.

Next, the optical head 50 for recording and reproducing information.
Will be described. The laser light source 1 is arranged so that the emitted light beam enters the polarization beam splitter 3 as P-polarized light. The light beam emitted from the laser light source 1 is converted into a parallel light beam by the collimator lens 2, passes through the polarization beam splitter 3, and reaches the diffraction grating 4.

The diffraction grating 4 is divided into four crosses by a cross-shaped dividing line, and grating grooves are provided in each of the divided regions so that the diffraction directions of the light beams are different from each other. Further, the diffraction grating 4 is formed of a material having optical anisotropy. The forward light beam emitted from the laser light source 1 and traveling toward the optical disk 7 is hardly diffracted, and the light having linear polarization orthogonal to the polarization direction of the forward light is It is designed to diffract.

The outgoing luminous flux transmitted through the diffraction grating 4 further passes through the quarter-wave plate 5 and reaches the objective lens 6. The forward light beam incident on the objective lens 6 is condensed on an information recording track of the optical disk 7 with a predetermined amount of aberration or less. Then, the light beam reflected by the optical disk 7 passes through the objective lens 6 again and is guided to the １ ／ wavelength plate 5 and further to the diffraction grating 4. At this time, since the return light beam is transmitted and reciprocated through the quarter-wave plate 5, it becomes linearly polarized light whose polarization direction is orthogonal to the forward light beam, and is thus diffracted by the diffraction grating 4.

The ± 1st-order diffracted light of the return light beam diffracted in each region of the diffraction grating 4 is incident on the polarization beam splitter 3 as S-polarized light, is reflected by the beam splitter surface, passes through the detection lens 8, and passes through eight detection lenses. The light enters a predetermined light receiving surface of the detector 9 having an independent light receiving surface.

The objective lens 6 is composed of the diffraction gratings 4 and 1 /
Together with the four-wavelength plate 5, it is fixed to the shaft-sliding type actuator 10, and is driven integrally.

FIG. 2 is a schematic perspective view showing an example of the arrangement of the light receiving surface of the photodetector 9 and the positional relationship with the diffraction grating 4.

As shown in FIG. 2, for example, the photodetector 9 has eight strip-shaped light receiving surfaces 9a, 9b, 9c and 9d, and four rectangular light receiving surfaces 9e and 9 having a larger detection area.
f, 9g and 9h. Four strip-shaped light receiving surfaces are 9
Reference numerals a, 9b, 9c, and 9d denote light receiving surfaces for detecting a focus error signal by a so-called knife edge method, and two light receiving surfaces 9a and 9b and 9c and 9d which are respectively arranged in parallel.
Each combination forms a total of two light receiving areas. The rectangular light receiving surfaces 9e, 9f, 9g, 9h are for detecting a tracking error signal by the push-pull method or the DPD method and a recording information signal of the optical disk 7. The two light receiving areas for detecting the focus error signal and the four light receiving surfaces for detecting the tracking error signal are arranged on the circumference centered on the detector projection point of the central optical axis. However, they are not necessarily arranged on the same circumference depending on the difference in the grating pitch of each region of the diffraction grating 4.

The two sets of light receiving areas for detecting the focus error signal are set in consideration of the fact that the spot is displaced by the tracking operation as described later to detect the displacement direction or displacement amount of the objective lens. Are arranged such that the boundary line between the two light receiving surfaces constituting the light spot is substantially perpendicular to the displacement direction of each light spot or a tangent to the displacement direction.

The objective lens and 1 /
The return light beam having passed through the four-wavelength plate (not shown) travels from the top to the bottom of the figure (indicated by an arrow in the figure) and enters the diffraction grating 4. After being divided into approximately 1/4 discs in each of the divided regions of the diffraction grating 4 and diffracted in different directions, for example, of the ± 1st-order diffracted light generated in the region 4a, the + 1st-order light is the light receiving surfaces 9a and 9b. And the minus first order light enters the light receiving surface 9e. The +1 order light incident on the light receiving surfaces 9a and 9b is focused on the boundary between the light receiving surfaces 9a and 9b when the spot on the optical disk is focused on the recording track of the disk, and the spot on the optical disk is moved to the positive or negative side. When defocus occurs, a 1/4 disc-shaped spot is projected on the light receiving surface 9a or 9b side. Therefore, by detecting a difference signal between the light intensity signals detected on the respective light receiving surfaces 9a and 9b, a focus error signal based on a so-called knife edge method becomes possible. Similarly, the luminous fluxes divided and diffracted in the other regions are also arranged such that the + 1st-order light enters the light-receiving region for detecting the focus error signal and the -1st-order light enters the light-receiving surface for detecting the tracking error signal. . Therefore,
A focus error signal can be obtained from a difference signal between the light intensity signals in the light receiving areas for detecting each focus error signal.

Next, the displacement of the light spot on the detector 9 due to the displacement of the objective lens 6 during the tracking control will be described with reference to FIG.
This will be described with reference to FIG. 3A and 3B are schematic diagrams showing the movement of the actuator and the movement of the light spot on the photodetector according to the present embodiment. FIG. 3A shows a neutral state with no objective lens displacement, and FIG. This shows a state where the objective lens is displaced by the driving of the actuator at times.

In this embodiment, since the actuator 10 is a shaft-sliding type actuator, the movement of the objective lens 6 during tracking control is not parallel movement in the radial direction of the disk, but is centered on the rotation axis of the actuator 10 from the rotation axis. This is a rotational movement having a radius up to the optical axis of the objective lens.
Further, since the diffraction grating 4 and the quarter-wave plate 5 are fixed to the actuator 10 together with the objective lens 6 and are driven integrally, the diffraction grating 4 and the quarter-wave plate 5 are rotationally displaced together with the objective lens 6. Accordingly, the grating direction of each region of the diffraction grating 4 also rotates, and the diffraction direction is rotationally displaced around the optical axis. As a result, for example, FIG.
, The light spots 100a, 100b, 100c, 100 arranged at predetermined nominal positions, respectively.
d, 101a, and 101b are also displaced, and the light spots 100c, 100d, 101e, and 101 as shown in FIG.
f, 101g, and 101h. That is, the light spot on the detector 9 is also rotationally displaced about the projection point at the center of the optical axis. That is, by detecting the differential signal of the sum of the light intensity signals detected by the four rectangular light receiving surfaces 9a and 9c of the photodetector 9 and the sum of the light intensity signals detected by the light receiving surfaces 9b and 9d, It is possible to detect the displacement direction or displacement amount of the objective lens that is displaced by the tracking operation.

FIG. 4 is a schematic block diagram showing a mechanism for outputting a focus error signal, a displacement signal of an output objective lens, and a tracking error signal from a light intensity signal detected on each light receiving surface of the photodetector 9.

The light spot 100a is located in a light receiving area including the light receiving surfaces 9a and 9b, and the light spot 100b is located in the light receiving surface 9c and 9b.
Each light is incident on a light receiving region composed of 9d. Then, the sum of the detection signals from the light receiving surfaces 9a and 9d and the sum of the detection signals from the light receiving surfaces 9b and 9c are input to the operational amplifier 200, and the difference signal is detected to detect the focus error signal by the knife edge method. ing.

On the other hand, the sum of the light intensity signals detected by the light receiving surfaces 9a and 9c and the sum of the light intensity signals detected by the light receiving surfaces 9b and 9d are input to the operational amplifier 201, and the difference signal is detected. This makes it possible to detect the displacement direction or displacement amount of the objective lens that is displaced by the tracking operation.

The output signals from the light receiving surfaces 9e, 9f, 9g and 9h correspond to the light intensity modulation signals of the respective divided areas when the reflected light beam from the optical disk 7 is divided into four crosses. I have. Therefore, the output signal from each of the light receiving surfaces is input to a predetermined phase difference detection circuit 203 via a predetermined signal delay circuit 202 and is subjected to a predetermined calculation to detect a tracking error signal by the so-called DPD method.

For example, the sum signal of the output signals from the light receiving surfaces 9e and 9f and the sum signal of the output signals from the light receiving surfaces 9g and 9h are obtained when the reflected light beam from the optical disk 7 is divided into two in the radial direction of the disk. Since the signal corresponds to a light intensity modulation signal obtained in each divided region, if a difference signal between these signals is detected by the operational amplifier 204, a tracking error signal by a so-called push-pull method can be detected.

By performing a predetermined operation on the output signal of each light receiving surface of the detector 9 in this manner, the focus error signal and the displacement direction or displacement of the objective lens displaced by the tracking operation are further different from each other in the detection method. Two types of tracking error signals can be obtained at the same time, and a tracking error signal suitable for each of the optical disk 7 can be selected depending on whether the optical disk 7 is a recordable type or a read-only type.

Further, the information signal recorded on the disk is provided with light receiving surfaces 9a, 9b, 9 for tracking error signals.
Each output signal from c and 9d can be obtained by inputting it to the operational amplifier 205 and detecting the sum signal.
Alternatively, it may be detected from the sum signal of the output signals from all the light receiving areas.

The present invention is not limited to the above configuration.

[0031]

As described above, by adopting the above configuration, a compact and simple optical system capable of detecting the direction or amount of displacement of the objective lens without having a dedicated detector in the objective lens driving means. A head and an optical recording / reproducing apparatus using the same can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical head and an optical recording / reproducing apparatus using the optical head according to an embodiment of the present invention.

FIG. 2 is a schematic perspective view showing an arrangement of a light receiving surface of a photodetector and a positional relationship with a diffraction grating in an embodiment of the present invention.

FIG. 3 is a schematic diagram showing the movement of the actuator and the movement of the light spot on the photodetector according to the embodiment of the present invention.

FIG. 4 is a block diagram showing another example of a signal generator of a schematic shape and a focus error signal, a displacement signal of an output objective lens, and a tracking error signal of a detector light receiving unit in the embodiment of the present invention.

[Explanation of symbols]

1 ... laser light source, 2 ... collimator lens, 3 ...
..Polarizing beam splitter, 4 ... diffraction grating, 5 ...
· 1/4 wavelength plate, 6 ··· objective lens, 7 ··· optical disk, 8 ··· detection lens, 9 ··· photodetector, 10 ·
..Actuator, 50 ... optical head, 51 ...
Laser drive, 52 ... Signal generation circuit, 53 ... System control circuit, 54 ... Actuator drive circuit.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Kuniichi Onishi, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Multimedia Systems Development Division of Hitachi, Ltd. (72) Inventor Tohru Sasaki Yoshida, Totsuka-ku, Yokohama-shi, Kanagawa 292, Machi-cho, Hitachi, Ltd.Video and Media Division (72) Inventor Yukio Fukui 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture, Hitachi, Ltd.Video and Media Division of Hitachi, Ltd. 292 Yoshida-cho, Ward, Tokyo Hitachi, Ltd. Video Information Media Division (72) Inventor Hironori Saito 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa, Japan Hitachi Video Information Media Division

Claims (3)

[Claims] 1. A laser light source, an objective lens for condensing a light beam emitted from the laser light source on an information recording surface of an optical disk, a photodetector having a plurality of independent detection areas, and the objective lens A diffraction grating arranged in an optical path between the photodetector and divided into four regions each having a different diffraction direction by a substantially cross-shaped division line, and a driving unit for integrally driving the objective lens and the diffraction grating The objective lens and the diffraction grating are displaced on an arc of a predetermined radius in a plane substantially parallel to the information recording surface of the optical disk by the driving means, and a signal within the photodetector is provided. The direction of the boundary line between the detection surfaces in the detection area is substantially perpendicular to the displacement direction of each light spot irradiated on the photodetector surface due to the operation of the driving means or a tangent to the displacement direction. Vessel optical head or optical recording and reproducing apparatus according to claim border region using the displacement direction or displacement amount detection of the objective lens. 2. A boundary line of the photodetector, which is substantially perpendicular to a displacement direction or a tangent line of the displacement direction of each light spot irradiated on the photodetector surface due to the operation of the driving means of the objective lens. 2. The optical head or optical recording / reproducing apparatus according to claim 1, wherein the area is used for detecting a displacement direction or a displacement amount of the objective lens and detecting a focus error signal. 3. The apparatus according to claim 1, wherein said focus error signal detecting means of said photodetector is of a knife edge type.
An optical head or an optical recording / reproducing device according to claim 1.