JPS6149728B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical device that records information on a recording medium on a disk by irradiating light focused in the form of a minute spot, and reproduces the recorded information. The focus is controlled so that the size of the spot light is always kept at the optimum diameter for recording and reproducing operations, and the minute spot light is always accurately irradiated onto the track where information is recorded on the disk during recording and reproducing operations. The present invention relates to an optical device that performs tracking control.

Video disks such as VLP are well known as means for optically reproducing information recorded on a disk. For video discs, the diameter is approximately 1
Information is reproduced by irradiating a spot light focused on the order of micrometers onto a pre-recorded information track while performing controls such as focus control and tracking control, and tracking the track correctly.
However, since the disk plate of a video disk is rotated at high speed during a reading operation, the position of the spot light irradiation point constantly changes due to surface runout during rotation or external vibration. Therefore, in order to read information accurately, it is necessary to follow the positional fluctuations of the disk plate and reliably perform focus control and tracking control of the spot light. A drive control mechanism for the irradiation system is required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a new and useful optical device that is equipped with a focus detection mechanism and a tracking detection mechanism in a pickup device that can perform the above-mentioned focus control and tracking control with a simple optical system. .

Hereinafter, the present invention will be explained in detail according to embodiments with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a pickup device using the present invention.

Since the laser light emitted from the semiconductor laser 1 is set so that its polarization plane is parallel to the plane of the paper, when it enters the beam splitter 2 which has a polarizing film, the beam splitter will be split due to the characteristics of the polarizing film. The light almost completely passes through the twine 2 and enters the collimating lens 3. The light beam made parallel by the collimator lens 3 is converted into circularly polarized light by passing through the λ/4 plate 4, and then enters the objective lens 5. The light beam exiting the objective lens 5 is condensed to form a minute light spot on the surface of the disk 6 placed at the focal point of the objective lens 5. The light beam reflected from the surface of the disk 6 becomes circularly polarized light in the opposite direction to the incident light beam and enters the objective lens 5 again, and in a focused state becomes a parallel light beam and enters the λ/4 plate 4. The direction of linear polarization of the light beam exiting the λ/4 plate 4 is changed by 90 degrees with respect to the light beam at the time of incidence, and after passing through the collimating lens 3 again, it enters the beam splitter 2 having a polarizing film. It is almost completely reflected by the beam and enters the detector 8.

FIG. 2 is a block diagram showing another embodiment of a pickup device using the present invention.

In the case of this embodiment, the laser beam emitted from the semiconductor laser 1 is first incident on the collimating lens 3, and after being made parallel to the speed of light, it is incident on the beam splitter 2, and then, as in FIG. After passing through the objective lens 5, the light is focused on the disk 6. The light beam reflected from the disk 6 surface passes through the objective lens 5 and the λ/4 plate 4 as in FIG. It is incident. The laser light that has passed through the coupling lens 7 is incident on the detector 8 with a predetermined beam diameter.

FIG. 3 is a configuration diagram showing the arrangement of the light receiving surface of the detector 8 used in the above embodiment. The light-receiving surface of this detector 8 consists of a pair of divided detectors 8-a and 8-b with large light-receiving surfaces on both sides and a pair of divided detectors 8-c and 8-d with a small light-receiving surface in the center. The detectors are arranged so that the boundary direction of each divided detector is the same. The detector 8 is installed vertically so that the center of the detector coincides with the optical axis of the collimating lens 3 in FIG. 1 and the optical axis of the coupling lens 7 in FIG. The distance from the coupling lens 7 to the detector 8 is such that the size of the detector 8 is set at a predetermined position determined by the focal length and aperture of the collimator lens 3 or the coupling lens 7.

Next, the principle of detecting in-focus and out-of-focus states for performing focus control will be explained with reference to FIG. In order to facilitate understanding, FIG. 4 shows the process from when the light is reflected from the disk 6 to when it enters the detector 8. I am using it as a substitute. In addition, objective lens 9 and disk 6
The shape of the light spot 10 irradiated onto the detector at each position is also illustrated.

First, as shown in FIG. 4b, at the focused position, the light beam reflected from the disk 6 is irradiated onto the detector 8 in the shape of a light spot 10-b, and at this time, the two central divided detectors 8-c, The detector 8 is installed so that the sum of the outputs of the detector 8-d and the sum of the outputs of the two divided detectors 8-a and 8-b on both sides are equal to each other. Therefore, the sum Vc+Vd of the outputs of the two central divided detectors 8-c and 8-d and the two divided detectors 8-a on both sides.
The difference V _F between the sum Va + Vb of the outputs of 8-b and 8-b is V _F =
(Va+Vb)-(Vc+Vd)=O. However, the disk 6 is out of focus, and the objective lens 9
The light spot 10 on the detector 8 as it moves away from
-a becomes smaller, so the amount of light incident on the two divided detectors 8-a and 8-b on both sides becomes smaller,
On the other hand, the amount of light incident on the two central divided detectors 8-c and 8-d increases. Therefore, the sum Vc+Vd of the outputs of the two central divided detectors 8-c and 8-d and the sum of the outputs of the two divided detectors 8-a and 8-b on both sides.
An output difference V _F (kiO) appears between Va+Vb.

On the other hand, when the disk 6 deviates from the focused state and approaches the objective lens 6 as shown in FIG. becomes larger. Therefore, the amount of light incident on the two divided detectors 8-a and 8-b on both sides increases, and the amount of light incident on the two divided detectors 8-c and 8-b in the center increases.
The amount of light incident on -d decreases. Therefore, the central 2
Sum of the outputs of the divided detectors 8-c and 8-d Vc+
An output difference V _F having the opposite sign to that in the case of FIG. 4a appears between Vd and the sum Va+Vb of the outputs of the two divided detectors 8-a and 8-b on both sides.

In this way, the central two divided detectors 8-
From the output difference V _F between the outputs from c and 8-d and the outputs from the two divided detectors 8-a and 8-b on both sides,
A signal with a code corresponding to the position of the disk 6 is detected starting from the in-focus position. Next, Figure 4a
The disk 6 is further away from the objective lens 9 than the position shown in
When the laser beam moves further away, the laser beam forms an image in front of the detector 8 and then irradiates each light receiving surface.
The light spot above gradually becomes larger. Therefore, the sum Vc+Vd of the outputs from the two central divided detectors 8-c and 8-d and the two divided detectors 8- on both sides
Output difference V _F from the sum Va + Vb of outputs from a and 8-b
As the position of the disk 6 moves further away from the objective lens 9, an output difference V _F having the same sign as the output difference V _F obtained via the disk positions shown in FIGS. 4b to 4c is obtained.

FIG. 5 is an explanatory diagram showing changes in the output difference V _F between the two sets of detectors when the disk 6 is brought into close contact with the objective lens 9 and successively moved away from the objective lens 9. In the figure, Pa, Pb, and Pc are shown in Figure 4 a, b, respectively.
Corresponds to position c.

In this way, the output difference between the two sets of detectors J _F = (Va +
The disk position where Vb) - (Vc + Vd) becomes atmosphere is the 4th disk position.
There are two positions, the in-focus position and the quasi-in-focus position shown in Figure b, but the position where the output difference V _F changes from a positive sign to a negative sign by moving the disk 6 away from the objective lens 9 one after another is the in-focus position. In this state, a position where the sign changes from a negative sign to a positive sign becomes a quasi-focused state and can be distinguished. Also, the disk 6 is connected to the objective lens 9.
It is clear that the situation is opposite to the _above case when approaching
It is clear that the above case is similarly reversed when obtaining +Vd). In this way, by looking at the changes in the output difference V _F between the two sets of detectors, it is possible to distinguish between the in-focus state and the pseudo-in-focus state.

Note that even if the detector 8 is placed behind the imaging point in the in-focus state as shown in FIG. A code signal is detected, and it is also possible to distinguish between a focused position and a pseudo-focused position.

Next, the principle of detecting the track position for tracking control will be explained according to FIGS. 6a, b, and c. FIG. 6 shows the positional relationship between the pit 11 on the track and the condensed spot light 13, and the corresponding incident light spot 10-b on the detector 8,
A schematic diagram of a pit image 12 is shown.

First, as shown in FIG. 6b, when the track is irradiated with light so that the center of the pit 11 and the center of the spot light coincide, a pit image 12 is formed at the center of the incident light spot 10-b on the detector. Therefore, the two divided detectors 8 in the upper half of the detector 8 in the figure
Output Va + Vc of the sum of -a and 8-c and output Vb + Vd of the sum of the two lower half divided detectors 8-b and 8-d
are equal, and the difference between the output corresponding to the sum of divided detectors 8-a and 8-c and the output corresponding to the sum of divided detectors 8-b and 8-d is V _T = (Va + Vc) - (Vb +
Vd) becomes atmosphere.

Next, as shown in FIG. 6a, when the center of the pit 11 deviates from the center of the spot light 13 and moves upward in the figure, the incident light spot 10-
A pit image 12 is formed above b, and the amount of light is reduced in the pit image 12 portion. Therefore, the output Va+Vc of the sum of the two divided detectors 8-a and 8-c in the upper half of the detector 8 in the figure is the output Va+Vc of the sum of the two divided detectors 8-b and 8-d in the lower half. The output is smaller than the output Vb + Vd and corresponds to the sum of the divided detectors 8-a and 8-c in the figure.
A difference _VT appears between Va+Vc and the output Vb+Vd corresponding to the sum of the divided detectors 8-b and 8-d.

On the other hand, if the center of the pit 11 deviates from the center of the spot light 13 and moves downward in the figure as shown in FIG. 6c, the result is opposite to that of FIG. Pit statue 12 below
I can do it. For this reason, 2 in the upper half of the detector 8 in the figure
Output Va+ of the sum of divided detectors 8-a and 8-c
Vc is the two divided detectors 8-b and 8-d in the lower half.
The output Va corresponding to the sum of the divided detectors 8-a and 8-c in the figure is larger than the sum output Vb + Vd.
A difference _VT appears between +Vc and the output Vb+Vd corresponding to the sum of the divided detectors 8-b and 8-d.

That is, there is a case where the center of the pit 11 is located above the center of the spot light 13 as shown in FIG.
Figure 6b shows the case where it is located downward as shown in Figure c.
When the center of the pit 11 and the center of the spot light 13 coincide as shown in FIG.
- output Va + Vc corresponding to the sum of c and divided detector 8
Since the output Vb+Vd corresponding to the sum of -b and 8-d is inverted, it corresponds to the output Va+Vc corresponding to the sum of divided detectors 8-a and 8-c and the sum of divided detectors 8-b and 8-d. By differentially amplifying the outputs Vb+Vd, signals with opposite signs corresponding to the pit position, that is, the track position, are detected.

FIG. 7 is an explanatory diagram showing an example of the track position detection signal, and shows changes in the sum signal and the difference signal V _T with respect to track deviation. Pb′ in the figure is the 6th
This is the signal corresponding to the position in Figure b.

The disk position detection signal and track position detection signal obtained in this way are fed back to each control coil to perform focus control and tracking control, so that the spot light is always accurately irradiated on the track in a focused state. This allows stable information reproduction operation to be established.

In order to detect the track position, the output of the sum of the two divided detectors 8-a and 8-c in the upper half and the output of the sum of the two divided detectors 8-b and 8-d in the lower half are used. In addition to detecting the difference output _V The track position can also be detected based on the same principle by detecting the difference between the output of the divided detector 8-d and the output of the divided detector 8-d.

As detailed above, by using a detector system consisting of a photodetector divided into at least three parts, a focus control mechanism and a tracking control mechanism are provided that can perform focus control and tracking control with a simple optical system. Thus, an optical device can be obtained which can configure a pick-up optical system that can read information reliably.

[Brief explanation of the drawing]

FIGS. 1 and 2 are block diagrams showing one embodiment of a pickup device having a disk position detection system according to the present invention. FIG. 3 is an explanatory diagram showing one embodiment of the detector shown in FIGS. 1 and 2. FIG. FIG. 4 is an explanatory diagram illustrating the principle of the focus error detection mechanism. FIG. 5 is an explanatory diagram showing one embodiment of the disk position detection signal. FIG. 6 is an explanatory diagram illustrating the principle of the track error detection mechanism. FIG. 7 is an explanatory diagram showing one embodiment of the track position detection signal. 1...Semiconductor laser element, 2...Game splitter, 3...Collimating lens, 4...λ/4
Plate, 5... Objective lens, 6... Disk, 7...
Coupling lens, 8...Detector, 9...Objective lens, 10-a to 10-d...Incoming spot light, 11...Pit, 12...Pit image, 13...
...Light focus spot.

Claims (1)

[Claims] 1. In an optical information processing device that performs optical recording and reproduction of information by irradiating a recording track on a disk surface with a minute spot light, the disk surface is at the focal position of the minute spot light and the reflected light is reflected from the disk surface. is divided into at least three parts in front of or behind the image forming position on the detection optical system and arranged close to each other in a row, and the light receiving area of the detectors on both sides is sufficiently larger than the light receiving area of the central part. The detectors are arranged so that the dimensions of the detectors in the center in the array direction and the vertical direction are shorter than the detectors on both sides.
The output difference between the two detectors on both sides and the center detector is used as the focal position detection signal, and the output difference between the two detectors on both sides or the center detector is divided into two and the output difference between one pair of detectors or both sides is calculated. The output difference between the outputs of the two sets of the two divided center detectors on the same side as each detector is used as a track position detection signal, and the focus is controlled based on the focus position detection signal and the track position detection signal. and tracking control.