JPH0311007B2 - - 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, and particularly relates to an optical device that records information on a recording medium on a disk by irradiating light focused in the shape of a minute spot, and plays back the recorded information. The present invention relates to an optical information processing device that performs focus control so that the size of a spot light is always maintained at an optimum diameter for recording and reproducing operations.

Video disks such as VLP are well known as means for optically reproducing information recorded on a disk. For video discs, the diameter is approx.
Information is reproduced by irradiating a spot light focused to about 1 μm onto a pre-recorded information track while performing focus control, tracking control, etc. and tracking the track correctly. However, since the disc plate of a video disc is rotated at high speed during the 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 reliably perform focus control and tracking control of the spot light by following the positional changes of the disc plate, and the position detection mechanism of the disc plate and information track, as well as the spot light irradiation system. A drive control mechanism is required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a new and useful optical information processing device that is equipped with a focus position detection mechanism in a pickup device that can perform the above-mentioned focus control using 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 emitted from 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 this embodiment, the laser beam emitted from the semiconductor laser 1 first enters the collimator lens 3, is made into parallel light, and then enters the beam splitter 2, and then similarly passes through the λ/4 plate 4 and the objective. After passing through the lens 5, the light is focused on the disk 6. disk 6
The light beam reflected from the surface similarly passes through the objective lens 5 and the λ/4 plate 4, and is almost completely reflected by the beam splitter 2 and enters the coupling lens 7. The laser light transmitted through the coupling lens 7 is incident on the detector 8 with a predetermined beam diameter.

FIG. 3 is a configuration diagram mainly showing the shape of the light receiving surface of the detector 8 used in the above embodiment.

The light-receiving surface of this detector 8 is divided into two sets of divided detectors 8-a ₁ , 8-a ₂ and 8-b ₁ , each having a large light-receiving surface on both sides.
8-b ₂ and a pair of split detectors 8-c ₁ and 8-c ₂ each having a smaller light-receiving surface in the center than the detectors on both sides, and the split portions of each set of detectors are arranged in a straight line. They are placed close enough to each other. Detector 8 is the first
The detector is installed perpendicularly to the optical axis so that the center of the detector is on the optical axis of the collimating lens 3 in the figure, and on the optical axis of the coupling lens 7 in FIG.
The distance between the detector 8 and the detector 8 is determined by the size of the detector 8 and the collimating lens 3 or coupling lens 7.
The lens is set at a predetermined position determined by the focal length and aperture of the lens.

Next, the principle of detecting in-focus and out-of-focus states for performing focus control will be explained according to FIG. 4. In addition, in FIG. 4, for ease of understanding, the process from reflection from the optical disk 6 to incidence on the detector 8 is illustrated, and the objective lens 5 and collimating lens 3 or coupling lens 7 are combined into one objective lens 9.
It is substituted with A light spot 10 irradiated onto the detector at each position of the objective lens 9 and the disk 6
-a, 10-b, 10-c, and 10-d are also illustrated.

First, as shown in FIG. 4b, at the focus 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 detector 8 is set so that the output of the set of divided detectors 8-c and the sum of the outputs of the two sets of divided detectors 8-a and 8-b on both sides are equal to each other. As clearly shown in the same figure, the vertical length of the divided detector 8-c placed in the center is the same as that of the detector 8 in the focused state.
This substantially matches the diameter of the reflected light spot 10-c. Therefore, the difference between the output of one set of divided detectors 8-c in the center and the sum of the outputs of two sets of divided detectors 8-a and 8-b on both sides V _F ={V _(8-a) +V _{( 8-b)} }−V _(8-c) becomes zero. Here, V _(8-a) , V _(8-b) , and V _(8-c) represent output values from each set of divided detectors.

However, as shown in FIG. 4a, as the disk 6 deviates from the focused state and moves away from the objective lens 9, the light spot 10-a on the detector 8 becomes smaller, so that the two sets of divided detectors 8-a on both sides become smaller. ,8
The amount of light incident on -b decreases, while the amount of light incident on the central pair of divided detectors 8-c increases. Therefore, a differential output difference V _F = {V _{(8- a)} +V _(8-b) }-V _(8-c) ＜
0 appears.

Conversely, as shown in FIG. 4c, when the disk 6 deviates from the focused state and approaches the objective lens 6, the imaging position moves backward, and the light spot 10 on the detector 8
-c becomes larger. Therefore, the amount of light incident on the two sets of divided detectors 8-a and 8-b on both sides increases, and the amount of light incident on the one set of divided detectors 8-c in the center decreases. As a result, the output difference between the output of one set of divided detectors 8-c in the center and the sum of the outputs of two sets of divided detectors 8-a and 8-b on both sides has a sign opposite to that in the case of FIG. 4a. An output difference appears.

In this way, the central set of divided detectors 8-
output from c and two sets of divided detectors 8-a on both sides,
From the output difference V _F with the output from 8-b, signals with opposite signs are detected depending on the position of the disk 6 with the in-focus position of the disk 6 as the boundary.

However, if the disk 6 moves further away from the objective lens 9 than the position shown in FIG. .
Therefore, the output difference V F between the output from one set of divided detectors 8-c in the center and the outputs from two sets of divided detectors 8-a and 8-b on both sides is determined by the output difference V _F at the disk 6 position in Fig. 4a. As the distance from the objective lens 9 increases, the output difference V F becomes as shown in FIG. 4 d, and the same output difference V _F as the output difference V _F corresponding to the disk position shown in FIG. 4 b is obtained. Figure 5 shows the output difference obtained from the three sets of detectors when the disk 6 is brought into close contact with the objective lens 9 and the disk 6 is gradually separated from the objective lens 9.
FIG. 3 is a signal waveform diagram showing changes in _VF . a in the figure,
b, c, and d are signals corresponding to a, b, c, and d in FIG. 4, respectively. In this way, the disk 6 position where the differential output V _F = {V _(8-a) +V _(8-b) }-V _(8-c) of the three sets of detectors becomes zero is the case shown in Figure 4b. There are two positions, the focal position and the pseudo-focal position shown in Fig. 4d, but for example, by gradually separating the disk 6 from the objective lens 9, the position where the output difference V F changes from a positive sign to a negative sign is the position where the output difference V _F changes from a positive sign to a negative sign. A position that changes from a negative sign to a positive sign in a focused state becomes a quasi-focused state, and the two can be distinguished. Furthermore, if the disk 6 is brought close to the objective lens 9, it is clear that the above will be reversed, and the differential output V _F ′=V _(8-c) −{V _(8-a) +V _{(8 -b)} } The position of disk 6 can be detected in the same way.

As described above, by detecting changes in the differential output V _F of the three sets of detectors, it is possible to distinguish between the in-focus state and the out-of-focus state, and also to By detecting signals of opposite signs, the in-focus position and the pseudo-in-focus position can be identified. The differential output V _F is fed back to the drive mechanism of the optical system as a disk position detection signal, and the optical system is controlled and driven so that the condensing spot illuminates the six surfaces of the disk in a focused state.

Next, the principle of detecting the track position for tracking control will be explained with reference to FIG. FIG. 6 schematically shows the positional relationship between the pit 11 and the condensing spot 13 recorded as information on the track on the disk 6, and the corresponding incident light spot 10 and pit image 12 on the detector 8. .

First, as shown in FIG. 6b, when the center of the pit 11 and the center of the condensing spot 13 exactly match and the track is irradiated with light, a pit image is formed at the center of the incident light spot 10-b on the detector. 12 is formed. Therefore, the three divided detectors 8-a ₁ , 8- in the upper half are divided into upper and lower parts by the center line of the detector 8.
Since the output of the sum of b ₁ , 8-c ₁ and the sum of the outputs of the three divided detectors 8-a ₂ , 8-b ₂ , 8-c ₂ in the lower half are equal, Divided detector 8-a ₁ , 8-
The difference V _T between the output corresponding to the sum of b ₁ , 8-c ₁ and the output corresponding to the sum of the lower half divided detectors 8-a ₂ , 8-b ₂ , 8-c ₂ becomes zero.

Next, as shown in FIG. 6a, when the center of the pit 11 deviates from the center of the condensing spot 13 and moves downward in the figure, a pit image 12 is formed above the incident light spot 10-b on the detector. . Therefore, the three divided detectors 8-a ₁ in the upper half of the detector 8 in the figure
Since the output of the sum of 8-b ₁ and 8-c ₁ is smaller than the output of the sum of the three divided detectors 8-a ₂ , 8-b ₂ , and 8-c ₂ in the lower half, division detection in the upper half is performed. Vessel 8-a ₁ , 8-
The difference V _T between the output corresponding to the sum of b ₁ , 8-c ₁ and the output corresponding to the sum of the lower half divided detectors 8-a ₂ , 8-b ₂ , 8-c ₂ is generated as a differential output. do.

On the other hand, if the center of the pit 11 deviates from the center of the condensing spot 13 and moves upward in the figure, as shown in Fig. 6c, the result will be opposite to that of Fig. 6a, and the incident light spot on the detector will be A pit image 12 is formed below 10-b. Therefore, the three divided detectors 8-a ₁ , 8-b ₁ , 8-
The output of the sum of c ₁ is sent to the lower half of the three divided detectors 8-
Since the output is larger than the sum of a ₂ , 8-b ₂ , 8-c ₂ , the upper half divided detector 8-a ₁ , 8-b ₁ , 8-c ₁
The output corresponding to the sum of and the lower half divided detector 8-
The output difference V _T corresponding to the sum of a ₂ , 8-b ₂ , and 8-c ₂ appears as a differential output with a sign opposite to that in FIG. 6a.

That is, when the center of the pit 11 is located below the center of the condensing spot 13 as shown in FIG.
Figure 6b shows the case where it is located above as shown in Figure c.
As shown in _FIG .
The output corresponding to the sum of -b ₁ and 8-c ₁ and the output corresponding to the sum of divided detectors 8-a ₂ , 8- _b 2 and 8-c ₂ are inverted, so they are combined into the above two sets. By performing differential amplification of the corresponding sum outputs, signals with opposite signs corresponding to pit positions or track positions are detected.

FIG. 7 shows the sum signal, that is, the sum output of each divided detector, and the track error signal, that is, V _T ={V _(8-a1) + V _(8-b1) +
FIG. 2 is a waveform diagram showing an example of a signal of V _(8-c1) }−{V _(8-a2) +V _(8-b2) +V _(8-c2) }. Here, there are two positions where the track error signal becomes zero: when the sum signal becomes the minimum value, and when the sum signal becomes the maximum value, but when the sum signal becomes the maximum value, it is at the intermediate position between the pits. This is when the focused spot 13 is located at the center of the pit, and the sum signal becomes the minimum value when the focused spot 13 coincides with the center of the pit. Further, as shown in the track error signal, the above two cases can be distinguished from the manner in which the signal changes, that is, in the figure, the location where the signal changes from negative to positive is a matching track state.

The disk position detection signal and track position detection signal obtained in this way are fed back to the control coils in each drive system to move the light irradiation point of the optical system and perform focus control and tracking control. Even if the lens 6 vibrates, the focused spot can always be accurately illuminated on the track in a focused state, and stable information reproducing operation can be established.
Furthermore, as shown in Figure 6, in order to detect the track position, the difference between the output of the sum of the three divided detectors in the upper half of the figure and the sum of the output of the three divided detectors in the lower half of the figure is output. In addition to detecting the value, at least the output of the difference between the outputs of the upper and lower divided detectors, for example, the difference between the upper and lower divided detectors in the center as shown in Figure 8, or the output of the difference between the upper and lower divided detectors in the center as shown in Figure 9. The track position can be detected based on the same principle by detecting the differential output of the upper and lower divided detectors on both sides.

As detailed above, by using a detector system consisting of a plurality of divided detectors, it is possible to construct an optical system of a pickup device equipped with a focus control mechanism that allows focus control to be performed with a simple optical system. Thus, an optical information processing device capable of reliably reading information is obtained.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing embodiments of a pickup device having a disk position detection system according to the present invention, respectively. FIG. 3 is an explanatory diagram showing one embodiment of the detector used in the pickup apparatus 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 a waveform diagram showing an example of a disk position detection signal, that is, a focus error signal. FIG. 6 is an explanatory diagram illustrating the principle of the track error detection mechanism. FIG. 7 is a waveform diagram showing an example of a track position detection signal, that is, a track error signal. FIGS. 8 and 9 are explanatory diagrams of a detector showing another embodiment of the present invention. 1... Semiconductor laser element, 2... Polarizing beam splitter, 3... Collimating lens, 4... λ/
4 plates, 5... objective lens, 6... disk, 7...
...Coupling lens, 8...Detector, 9...Objective lens, 10-a, 10-b, 10-c, 10
-d...Incoming spot light, 11...Pit, 12
...Pitsuto statue, 13...Light condensing spot.

Claims (1)

[Scope of Claims] 1. In an optical information processing device that optically reproduces recorded information by irradiating a recording track on a disk surface with a minute spot light, in a normal state, the minute spot light is irradiated on the disk surface. An input optical system is arranged so as to be in a focused state, and three types of photodetectors are arranged in a horizontal row close to each other in the vicinity of an imaging position where the reflected light from the disk surface is imaged; In a focused state, the image of the reflected light extends across the three types of photodetectors, and the vertical length of the centrally located photodetector is equal to the diameter of the reflected light spot on the photodetector in the focused state. configuring the three types of photodetectors so that they substantially match and the vertical lengths of the photodetectors on both sides are sufficiently longer than the vertical length of the photodetector placed at the center; It is characterized by comprising a detection means for detecting an output difference between the detection output of the photodetector placed at the center and the sum of the detection outputs of the photodetectors on both sides as a focal position detection signal of the minute spot light. Optical information processing device.