JPH0743826B2 - Disc player - Google Patents

Description

The present invention relates to a disk reproducing device for optically reproducing a disk formed with two independent signal tracks.

FIG. 1 shows an arrangement for making a double track disk master having two parallel signal tracks. In the figure, reference numeral 1 denotes a laser device, and a recording laser beam from the laser device is separated into two by passing through a beam splitter 2, one of which is supplied to an optical modulator 4 and the other. One is the optical modulator 5 via the mirror 3.
Is supplied to. Modulation signals are supplied to these optical modulators 4 and 5 from terminals 6 and 7, respectively. Two laser beams of S-polarized light and P-polarized light are generated at the outputs of the optical modulators 4 and 5, and one of them is supplied to the polarization beam splitter 9 after the optical path is changed through the mirror 8.
Along with the others, the light is projected onto the master 12 via the mirror 10 and the objective lens 11. The master 12 is formed by coating a surface of a glass disk with a photosensitive layer, and is rotated by a rotation driving unit 13 at a constant angular velocity or a constant linear velocity. By the two laser beams separated in the radial direction of the master 12 by the above-described optical system of the recording laser beam, as shown by the solid line and the broken line in FIG. Two parallel signal tracks T _A and T _B are formed simultaneously.

If the two modulation signals that are recorded are band-divided wideband signals such as digital video signals and high-resolution video signals, or those that are divided into two channels and have a lower transmission rate, the disk rotation speed is increased. It is possible to record a wide band signal without performing the above operation. Also,
Different information signals may be recorded in each track.

Using the master 12 formed as described above, a disk having two signal tracks is manufactured. When reproducing such a disk, the conventional reproduction optical system has
Since only the signal track of a book can be read, in order to reproduce complete information from two independent signal tracks T _A and T _B , these tracks must be read alternately and combined in memory. As described above, it is not preferable to alternately read the tracks because there are problems such as an adverse effect due to a transitional state when the tracks are transferred and complication of reproduction signal processing such as memory control. In addition, using two separately formed laser beams and reproducing each signal track by each of these laser beams requires two complicated reproducing optical systems, which increases the scale of the reproducing apparatus. However, there arises a problem that the cost increases.

The present invention has been made in view of the above points, and an object of the present invention is to realize a disk reproducing apparatus having one independent reproducing optical system having two independent spots capable of simultaneously reproducing signals from two signal tracks.

An embodiment of the present invention will be described below. Fig. 3A
4 is an enlarged view of the signal surface of the disk in this embodiment, in which the signal tracks T _A and T _B have geometric pattern pits corresponding to the recorded information signal. As an example, the track width of each of the signal tracks T _A and T _B is set to 0.5 μ corresponding to the spot diameter of the recording laser beam, and the interval between the two is set to 1.0 to 1.4 μ, for example 1.2 μ.

In FIG. 4, 14 indicates a disk, and this disk 14
Is rotated by the rotation drive unit 15. When the information recorded on the disk 14 is a video signal, the disk 14 is rotated at a constant angular velocity, and when the information is an audio PCM signal, the disk 14 is rotated at a constant linear velocity. Also, 16
Indicates a laser device. A gas laser such as helium / neon or a semiconductor laser can be used.
The P-polarized laser beam from the laser device 16 is passed through the phase diffraction grating 17 and separated into three spots of 0th order light and ± 1st order diffracted light.

In FIG. 3A, as indicated by the circle in the shaded area,
The spots B ₁ and B _{2 of the first-} order diffracted light and the spot B ₃ of the 0th-order light are applied to the signal surface of the disk 14. In this case, the distance in the radial direction of the disk 14 between the spots B ₁ and B _{2 of} the ± 1st order diffracted light is made to coincide with the distance between the signal tracks T _A and T _B , for example 1.2 μ, and when the tracking state is correct ,
As shown in FIG. 3A, the spots B ₁ and B ₂ scan the centers of the signal tracks T _A and T _B , respectively. Further, the spot B ₃ of the 0th-order light is positioned on the land existing between the signal tracks T _A and T _B. The width of this land, e.g. 0, to detect tracking errors.
It is preferable that the diameters of the spots B ₁ , B ₂ and B ₃ are slightly larger than 7 μ. Further, in FIG. 3B, 24 and 25 indicate the intensities of the ± first-order diffracted light, and 26 indicates the intensity of the zero-order light. As is clear from FIG. 3B, the intensity of the ± first-order diffracted light is larger than that of the zero-order light, for example, about three times. In this way, the relationship between the intensities of the ± 1st-order diffracted light and the 0th-order light can be realized by designing the phase diffraction grating 17. Further, by rotating the phase diffraction grating 17, as described above, the distance between the spots B ₁ and B ₂ is set to the signal track T _A and
Made equal to the interval of T _B.

The laser light from the phase diffraction grating 17 is reflected by the lens 18 and the polarized beam splitter 19. Then, the light enters the signal surface of the disk 14 through the galvano mirror 21 and the objective lens 22 in order. The angle of the galvano mirror 21 is changed by the tracking error signal, and the tracking is made correct. Also, the objective lens
The reference numeral 22 is adapted to be vertically displaceable, and is moved up and down by a focus error signal so that the read laser beam is focused on the signal surface of the disk 14 (bottom of the pit).

The laser light reflected on the signal surface of the disk 14 is transferred to the objective lens 22 and the galvano mirror 21. It is given to the polarized beam splitter 19 via and.

By passing the laser light twice in a round trip, the P-polarized light is changed to the S-polarized light, and thus the laser light reflected by the disk 14 is reflected by the polarized beam splitter 19,
It is supplied to the detector through the cylindrical lens 23. The detector is, as shown in FIG. 5A, photo diodes 27E and 27F to which the laser beams of spots B ₁ and B ₂ are given,
It has four photodiodes 27A, 27B, 27C and 27D to which the laser beam of spot B ₃ is given. The photodiodes 27A to 27D are arranged so as to divide a square into four equal parts. Photodiode 27E described above
The reproduction output of the signal track T _A is obtained at the output of, and the reproduction output of the signal track T _B is obtained at the output of the photodiode 27F.

Further, a focus error signal is generated by the astigmatism method using the cylindrical lens 23. That is, when the focus is correct, a circular spot is incident on the center of each of the photo diodes 27A to 27D, and when the focus shifts, this becomes an elliptical spot, and the inclination of the major axis of the ellipse varies depending on the direction of the shift. Will be things. When the output signals of the photodiodes 27A to 27D are S _A , S _B , S _C , and S _D , a focus error signal is formed by the calculation of (S _A + S _C ) − (S _B + S _D ). .

Photodiodes 27A to 27D are also available for tracking error detection.
Is done using the output of. As shown in FIG. 5B, when the 0th-order light spot B ₃ is located in the center between the signal tracks T _A and T _B in the correct tracking state, the outputs of the photodiodes 27A and 27B on one side are output. And the outputs of the photo diodes 27C and 27D on the other side have the same magnitude.
In contrast, as shown in FIG. 5 C, and when the Supotsuto B ₃ is positioned offset from the center between the signal tracks T _A and T _B, the output of the photodiode 27A~27D each side is not equal. Therefore, the tracking error signal can be formed by the calculation of (S _A + S _B ) − (S _C + S _D ). In this case, different information is recorded on adjacent tracks, and there is no regular relationship between the pit patterns between these tracks, but the tracking error signal is due to peak value detection corresponding to each pit. Instead, it is based on the averaged signal, so that tracking error detection can be performed. Such a detection method is called a push-pull method.

As can be understood from the above description of the embodiment, according to the present invention, unlike the case where two independent laser beams are used, the structure of the reproducing optical system is almost complicated as compared with the conventional one. Of course, two signal tracks can be reproduced at the same time. Therefore, when one channel signal is recorded as two signal tracks due to band division or the like as in the above-described embodiment, the read laser beam is alternately switched to the two signal tracks. There is no need to irradiate and synthesize by memory. When a normal video disk is reproduced according to the present invention, two images shifted by one frame can be reproduced at the same time, and special reproduction can be performed. Further, as described above, the intensity of the 0th-order light used for detecting the tracking error and the focus error is made lower than the intensity of the ± 1st-order diffracted light used for the reproduction of the track signal, so that the S / N reproduction is good. The track signal can be obtained.

[Brief description of drawings]

FIGS. 1 and 2 are block diagrams showing the configuration of a disk during recording according to an embodiment of the present invention and a schematic diagram showing a part of a signal track, and FIG. 3 shows a disk according to an embodiment of the present invention. A signal line, a spot of laser light, and a schematic diagram used to explain the intensity of this spot. FIG. 4 is a block diagram of a reproducing optical system according to an embodiment of the present invention. FIG. 5 is a detector according to an embodiment of the present invention. 3 is a schematic diagram used to explain the configuration of FIG. 1 and detection of a tracking error.

Claims (1)

[Claims] 1. A disc reproducing apparatus for optically reproducing a disc in which a recording signal is recorded as two independent signal tracks of a geometric pattern, and a diffraction grating for forming 0th-order light and two 1st-order diffracted lights. And setting the intensity of the two first-order diffracted lights to be greater than the intensity of the zero-order light, irradiating the two first-order diffracted lights to each of the two independent signal tracks, and The land between two adjacent independent signal tracks is irradiated, and the 0th-order light from the disk and two 1's are irradiated.
An optical system for guiding the second-order diffracted light to the detector means through the cylindrical lens, and first and second light-receiving elements for respectively receiving the two first-order diffracted lights from the disk and generating respective reproduction signals. , A detector means having a four-division light receiving element for receiving the 0th order light from the disk and generating a tracking error signal and a focus error signal, and simultaneously reproducing the two independent signal tracks. A disk reproducing device characterized by the above.