JPH0210491B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical information recording and reproducing device such as an optical disk, and more particularly to an optical information recording and reproducing device equipped with an optical track tracking device that utilizes diffracted light from an information track. .

As an information track tracking device used in an optical information recording/reproducing device such as an optical disk, the depth of the track groove is (2n-1) with respect to the wavelength λ of the light source (for example, a He-Ne laser or a semiconductor laser).
When the optical beam deviates from λ/4 (n=1, 2, 3...), the tracking control signal is detected using the fact that when the optical beam deviates from the track, the edges of the track groove cause asymmetry in the diffracted light. Devices for tracking tracks are known. In this device, two photodetectors placed parallel to the track receive the diffracted light pattern from the track groove, and a tracking control signal is detected by taking the difference in the outputs of these two photodetectors. However, since the detector is located in the far-field region of the lens, when the light beam is swung for tracking control, the diffracted light pattern on the photodetector surface is also swung, and this sway is used as a deviation signal in the tracking control signal. It appears as.
This results in the disadvantage that track tracking cannot be performed normally.

Such a device is disclosed in Japanese Patent Application Laid-Open No. 49-60702 or Japanese Patent Application Laid-open No. 52-62037, and will be explained using FIGS. 1 to 3. FIG. 1 is a diagram showing the configuration of a conventional track tracking device using diffracted light. A light beam emitted from a laser 1 is turned into parallel light by a lens 2, passes through a prism 3 and a diaphragm lens 4, and is converged onto the surface of a disk 5 into a spot of about 1 μm in diameter. Information tracks 51 are arranged on the surface of the disk 5 in a concave and convex manner. This track 51 has an optical depth of (2n-1)λ/4 (n=1, 2...
...). When a light spot is located within a track, a diffracted light pattern containing track information is generated in the light reflected from the track. This reflected light passes through the diaphragm lens 4, the prism 3, and the condenser lens 6 again, and is received by two photodetectors 7a and 7b placed on either side of the track. Since the diffraction component of the reflected light changes depending on the positional relationship between the light spot and the track, the relative position of the light spot and the track can be detected by detecting the difference in output between both detectors. Photodetector 7
The two outputs from a and 7b are differentiated by a differential amplifier 8, and this output is led to a track control circuit 9, which finely moves the lens 4 by controlling an actuator 10 mounted around the aperture lens 4. track. However, when the aperture lens 4 begins to move for track tracking, the light beam also moves on the surface of the detector as the optical axis moves. That is, when moving the spot by a distance d on the disk surface, it is necessary to move the lens 4 by d, so the optical axis will move by d. Therefore, if the focal length of the converging lens 6 is f and the distance from the focal point of this lens 6 to the photodetector is l, the amount of movement of the light beam on the photodetector surface at this time is d・l/ It becomes f. For example, if d=0.2mm, f=50mm, and l=25mm, the amount of movement will be 0.1mm. Set the aperture of the aperture lens 4 to 5
If mm, the diameter of the light beam on the 7th surface of the photodetector is
Since it is 2.5 mm, it will move by 4% of the light beam diameter. As a guideline, the tracking control signal obtained differentially should contain 8
A deviation signal corresponding to % will be superimposed.
However, the magnitude of this deviation signal largely depends on the configuration of the optical system, the size of the photodetector, its position, etc. FIG. 2a is a diagram showing an example of a photodetector used in the apparatus shown in FIG. 1. The two photodetectors 7a, 7b are silicon cells with a receiving surface of 2.5×1.2 mm ² and are separated from each other by a distance of 0.1 mm. At this time, the relationship between the diffracted light pattern distribution (near the center) on the photodetector surface and the photodetector is as shown in FIG. 2b. In the figure, a curve _P1 shown by a solid line shows the diffracted light pattern distribution due to the left edge of the track, and a curve P _r shown by a dotted line shows the diffracted light pattern distribution due to the right edge of the track. In each pattern, P ₀ is a non-diffracted component that hardly changes depending on the positional relationship between the light spot and the track, that is, a zero-order light component;
_P1 is a diffraction component that changes depending on the positional relationship between the light spot and the track, that is, a first-order light component. Third
The figure shows the relationship between the track deviation signal and the amount of deflection of the beam (corresponding to the amount of deflection of the lens). In the figure, the straight line A indicated by the dotted line is the second
A case is shown in which the photodetector shown in FIG. Therefore, if the lens is moved by 0.1 (mm), a deviation signal of 0.3 μm will be generated, and the track tracking accuracy will be significantly degraded.
The reason for the deviation signal is thought to be that in the diffracted light pattern shown in Figure 2b, the movement of the zero-order light component _P0 in the center, which accounts for most of the power, appears as a deviation signal. It will be done.

The present invention has been made in view of the above points, and is an optical track tracking device equipped with an optical track tracking device that can reduce deviation signals caused by beam deflection on the photodetector surface and achieve more accurate track tracking. The purpose of the present invention is to provide an information recording and reproducing device that can be used to record and reproduce information.

In order to achieve this object, in the present invention, the photodetector that receives the diffracted light from the information track receives only the light component of the diffracted light excluding the zero-order light component that does not include the tracking signal component, It is also characterized by having at least two light receiving sections separated from each other.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 4a is a diagram showing an embodiment of a photodetector used in the optical tracking device of the present invention. In the figure, D ₁ and D ₂ indicate the light receiving portion, and B indicates the dark portion. The photodetector 7 has a size of 1.5 mm x 1.5 mm, and is separated into two light receiving parts D ₁ and D ₂ by a dark part B with a width of 0.5 mm provided in the center. Note that the track extends in the vertical direction of the drawing, and includes the light receiving portion D ₁ ,
D ₂ is arranged symmetrically with respect to the direction of the track so as to sandwich the track.

That is, the symmetry axis O of the light receiving sections _D1 and _D2 is arranged substantially parallel to the direction of the track. When this photodetector is used, the relationship between the diffracted light pattern distribution on the photodetector surface and the light receiving portions D ₁ and D ₂ is shown in FIG. 4b. As is clear from the figure, the first-order light component P ₁ of the diffracted light pattern is irradiated onto the light-receiving parts D ₁ and D ₂ , and the 0-order light component
P ₀ is irradiated onto the dark area B.

Therefore, the photodetector detects only the first-order light component and not the zero-order light component. The primary light component changes depending on the positional relationship between the light spot and the track, so if the output signals from the light receiving sections D ₁ and D ₂ are respectively S ₁ and S ₂ , (S ₁ - _{S 2} ) becomes the track control signal. . The relationship between the deviation signal and the amount of lens shake when using a photodetector with such a configuration is shown by the solid line (b) in FIG. As is clear from the figure, the deviation signal is significantly reduced compared to the conventional system which also detects the zero-order light component.

In this embodiment, the number of light receiving sections of the photodetector is two, but the number is not limited to two. for example,
As shown in FIG. 5a, two more light receiving sections D ₃ and D ₄ are provided in a direction perpendicular to the light receiving sections D ₁ and D ₂ . If a photodetector with such a configuration is used, the light receiving parts D ₃ and D ₄
The length of the information pit of the information track can be detected using the difference signal between the two, and the information signal can be detected.
98113). That is, the light receiving section
If the output signals S ₃ and S ₄ from D ₃ and D ₄ are respectively input to a differential amplifier and a difference signal (S ₃ −S ₄ ) is obtained, this signal becomes an information signal.

Further, as shown in FIGS. 5b and 5c, the photodetector can be circular in shape, with a circular dark area B provided in the center and only the peripheral area used as a light receiving part. Figure 5b is for two pieces, Figure 5c is for four pieces.
In the case shown in the figure, the light receiving sections D ₁ and D ₂ are for detecting tracking control signals, and the light receiving sections D ₃ and D ₄ are for detecting information signals.

In the drawing, the track extends in the vertical direction of the drawing, and the symmetry axis O of the light receiving portions _D1 and _D2 is arranged substantially parallel to the track direction. This also applies to FIGS. 6 and 7.

FIG. 6 is a diagram showing the configuration of another embodiment of the photodetector used in the present invention. As shown in FIG. 6, this photodetector 7 is the same as the detector shown in FIG.
_D5 is provided. According to such a configuration,
Information signals and tracking signals can be detected with a good S/N ratio using one photodetector. That is, since the 0th order light component changes greatly depending on the information signal, by receiving this 0th order light component at the light receiving section _D5 , the S/N of the information signal can be reduced using only this central light receiving section. It can be easily detected. A photodetector with such a configuration is effective when recording and reproducing using a recording medium provided with a guide track having a depth of λ/8. The tracking signal is obtained by inputting the output signals S ₁ and S ₂ from the light receiving sections D ₁ and D ₂ to a differential amplifier and taking the difference. Furthermore, when reproducing an information signal, the information signal can be obtained by inputting the output signal _S5 from the light receiving section _D5 to an amplifier. In addition, clock synchronization signals, address signals, etc. are further
If the light receiving section D5 is provided, these can also be detected using the light receiving section _D5 .

Furthermore, FIG. 7 shows still another embodiment of the photodetector used in the present invention. In this embodiment, a track control signal, an autofocus control signal, and an information signal can be detected with a good S/N ratio using this single photodetector. This detector 7 is the detector shown in FIG. 6, in which the peripheral light-receiving parts D ₁ and D ₂ are separated into two light-receiving parts D ₁₁ , D ₁₂ and D ₂₁ , D ₂₂ , respectively.
Furthermore, the central light receiving part D ₅ is divided into four light receiving parts D ₅₁ , D ₅₂ ,
It is separated into D ₅₃ and D ₅₄ . These eight light receiving parts D ₁₁ , D ₁₂ , D ₂₁ , D ₂₂ , D ₅₁ , D ₅₂ , D ₅₃ .D ₅₄
The signals from S ₁₁ , S ₁₂ , S ₂₁ , S ₂₂ , S ₅₁ ,
S ₅₂ , S ₅₃ , and S ₅₄ , and the method of detecting the track control signal, autofocus signal, and information signal will be explained using FIG. FIG. 8 is a diagram showing an embodiment of an optical information reproducing device equipped with an optical track tracking device of the present invention. The light beam emitted from the laser 1 becomes parallel light by the lens 2, changes its optical path by the prism 3, and passes through the diaphragm lens 4 onto the disk 5 surface.
It is converged into a spot shape of about 1 μmφ. The light beam reflected from the surface of the disk 5 passes through the diaphragm lens 4 and the prism 3 and enters the condenser lens 6 again. Further, the light passes through a cylindrical lens 11 arranged at a plane perpendicular to the optical axis and rotated by 45 degrees with respect to the track direction, and enters the eight-divided photodetector 7 shown in FIG. The photodetector 7 is arranged so that the axis O is parallel to the direction of the track. Eight outputs from the photodetector 7 are separated by a signal processing circuit 12 into a track control signal _ST , a natural focus signal _SA , and an information signal _SG . According to this configuration, the image of the track is rotated at 90° by the cylindrical lens 11.
Since the image is rotated and projected, the signal being transmitted from the light receiving sections arranged symmetrically in the direction perpendicular to the track becomes the signal for the track. Therefore, the track control signal S _T is detected from (S ₁₁ +S ₁₂ )−(S ₁₂ +S ₂₂ ) and is caused to move up and down (in the figure) inside the actuator 10 for track tracking through the servo circuit 121. Track control is performed by driving the first actuator 101. As described in detail in Japanese Patent Publication No. 53-37722 (Automatic Focusing System), the autofocus signal S _A is detected by a four-part photodetector that receives astigmatism of a light beam caused by a cylindrical lens. That is, in this example, (D ₁₁ +D ₅₁ ), (D ₁₂ +D ₅₂ ), (D ₂₁ +
D ₅₃ ) and (D ₂₂ + D ₅₄ ) are each considered as one light receiving section, then (D ₁₁ + D ₅₁ + D ₂₂ + D ₅₄ ) and (D ₁₂ + D ₅₂ +
The difference signal (D ₂₁ +D ₅₃ ) becomes the signal for automatic focusing. Therefore, in this example, (S ₁₁ +S ₅₁ +
S ₂₂ )−(S ₁₂ +S ₅₂ +S ₅₃ +S ₂₁ ) becomes the autofocus signal S _A. This signal S _A passes through the servo circuit 122 and moves the second actuator 102 (outside) left and right, thereby performing automatic focus control. To detect the information signal S _G , the length of the information pit is detected using difference signals from light receiving sections arranged symmetrically in a direction parallel to the track. Therefore, in this embodiment, (S ₁₁ +S ₁₂ )−(S ₂₁ +S ₂₂ ) becomes the information signal _SG .

In this embodiment, a case has been described in which the cylindrical lens is arranged at an angle of 45 degrees with respect to the direction of the track, but instead of tilting the cylindrical lens, the photodetector 7 may be arranged at an angle of 45 degrees.

As described above, according to the present invention, the deviation component of the track control signal due to beam deflection can be reduced without using electrical or mechanical auxiliary means, and more accurate track tracking can be achieved.

[Brief explanation of drawings]

Fig. 1 is a diagram illustrating a conventional track tracking device using diffracted light, Fig. 2a is a diagram showing details of the photodetector in the device shown in Fig. 1, and Fig. 2b is a diagram illustrating this photodetector. 3 is a diagram showing the relationship between the deviation signal and the deflection amount of the beam, and FIG. 4a is a diagram showing the photodetector used in the device of the present invention. b is a diagram showing the relationship between this photodetector and the diffracted light pattern distribution; FIGS. 5a, b, and c are diagrams each showing the shape of the photodetector used in the device of the present invention; FIGS. FIG. 8 is a diagram showing another shape of the photodetector used in the device of the present invention, and FIG. 8 is a diagram showing an embodiment of an optical information reproducing device equipped with the optical track tracking device of the present invention.

Claims (1)

[Claims] 1 a light source, an optical means for narrowing down the light beam from the light source and making it incident on a lens to irradiate a track provided on a predetermined recording surface as a convergence spot; The diffracted light beam reflected by the recording surface is passed through the aperture lens having the same aperture diameter as the aperture diameter for the incident light beam to the aperture lens, and the reflected diffracted light beam is The two separated light-receiving sections are arranged to receive the first-order light component included in the reflected and diffracted light, and the zero-order light component that does not include the tracking signal component of the reflected and diffracted light is received by the two separated light-receiving sections. a photodetector configured to be illuminated between;
Detection means for detecting a deviation between the convergence spot and the track based on the difference between the output signals of the two separated light receiving sections, the deviation occurring on the photodetector as the convergence spot moves. and a means for moving the convergence spot in accordance with the output of the detection means to reduce the deviation. Optical information recording and reproducing device with special features.