JPH04301227A - Out-of-focus detecting system for optical head for optical disk - Google Patents

Abstract

PURPOSE:To obtain a servo signal and an information signal by scarcely necessitating adjusting the received light quantity of a photo detector. CONSTITUTION:Plural pieces of the semiconductor lasers 2, 3, 4 of the same wavelength are arranged in parallel as being shifted back and forth in the emitting direction of a laser beam, and one light spot 2a, at least, among the light spots which plural laser beams image-form on the recording film surface of a disk is made for the use for recording and reproducing the information signal and detecting a tracking signal, and the light spots 3a, 4a other than it are used for detecting out-of-focus, and the focusing positions of the light spots 3a, 4a are shifted upward and downward from the focusing position of the light spot 2a so that the relation of the size of the diameter of the spot is turned opposite for an upper part and a lower part to the vertical displacement of the recording film surface 11 of the disk. The light spots 3a, 4a can be shifted right and left on the recording film surface of the disk as well so that they are positioned at the track grooves 42 of the disk recording film surface 11.

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 an optical disk, and particularly to a defocus detection method.

0002

[Prior Art] In a conventional optical head for an optical disc, a photodetector receives reflected light from the disc recording film surface and detects an information signal and a servo signal.The photodetector has a divided light receiving surface. A plurality of light receiving elements were provided.

Hereinafter, a conventional defocus detection method for an optical head for an optical disk will be explained with reference to FIGS. 9 and 10.

The laser beam emitted from the semiconductor laser 28 is collimated by a collimating lens 29, formed into a beam by a beam shaping prism 30, transmitted through a beam splitter 31, and has its optical path changed by a corner mirror 32 (or galvano mirror). The light is focused on the disk recording film surface 34 by the focus lens 33 as a light spot. The laser beam reflected by the disk recording film surface 34 is reflected by the beam splitter 31, changes its optical path by the corner mirror 35, and becomes focused light by the convex lens 36. This focused light is separated into a transmitted beam and a reflected beam by a polarizing beam splitter 37, and these are transmitted to a transmitted beam photodetector 38(a) provided after (or before the focal point) of the focused transmitted beam, and a reflected beam. The light is received by a reflected beam photodetector 38(b) provided before (or after) the focal point of the converged beam. In this case, the light receiving element of the photodetector 38(a) is divided into light receiving surfaces a1 to a4, and the light receiving element of the photodetector 38(b) is divided into light receiving surfaces b1 to b4.

When the focused beam is focused on the disk recording film surface 34, the beam diameters incident on the photodetectors 38(a) and 38(b) are equal, as shown in FIG. 10(1). However, when the disk recording film surface 34 shifts in the direction approaching the focus lens 33, the diameter of the light beam of the transmission side photodetector 38(a) becomes smaller, as shown in FIG. ) becomes larger. Conversely, when the disk recording film surface 34 shifts away from the focus lens 33, the diameter of the light beam of the transmission side photodetector 38(a) increases, as shown in FIG. The diameter of the luminous flux in b) becomes smaller.

As described above, the amount of light received by the transmission-side photodetector 38(a) and the transmission-side photodetector 38(b) changes depending on the direction and amount of defocus, so defocus can be detected. . For example, the amount of defocus can be determined by the following calculation.

[0007] Defocus amount = (a1+a2)-(b1+b2)

000
8]

As described above, in the conventional defocus detection method, the light receiving element that receives the reflected beam from the disk recording film surface has a light receiving surface divided into a plurality of parts. Therefore, adjustment must be made so that the laser beam is correctly incident on each divided light-receiving surface (for example, the amount of light received by each divided light-receiving element is equal). Moreover, since the shape of this divided optical surface is minute (about several tens of micrometers), the amount of received light changes greatly with a deviation of several micrometers in the incident laser beam. For this reason, adjustment is extremely difficult and takes a long time.

Furthermore, since the light-receiving surface is divided into a plurality of parts, adjustment in at least two axes (up and down, left and right) is required, and it is difficult to automate the adjustment.

Furthermore, even if it is fixed by adhesive or screws after adjustment, it tends to shift slightly due to temperature changes, changes over time, etc. This deviation (including adjustment deviation) causes an offset in the detected servo signal, making the servo operation unstable. For this reason, it has sometimes become impossible to accurately record and reproduce information signals.

Furthermore, since the light-receiving surface is divided into a plurality of parts, the tracking signal tends to leak into the defocus signal, making the servo operation unstable.

An object of the invention is to eliminate the drawbacks of the prior art described above, to obtain a servo signal and an information signal without adjusting the amount of light received by a photodetector, and to avoid misalignment of the photodetector. Another object of the present invention is to provide a new defocus detection method for an optical head for an optical disk, which can obtain stable servo signals and information signals.

[0013]

[Means for Solving the Problems] In order to achieve the above object, the defocus detection method of the present invention focuses laser beams from a plurality of semiconductor lasers as a light spot on the disk recording film surface. In an optical head for an optical disk device, which obtains an information signal and a servo signal by individually receiving each reflected light from a surface with a light receiving element of a photodetector, multiple semiconductor lasers with the same wavelength are moved back and forth in the laser beam emission direction. At least one of the light spots, which are arranged parallel to each other and shifted from each other, is focused on the disk recording film surface, and at least one is used for recording and reproducing information signals and detecting tracking signals, and the other light spots are is used for defocus detection, and the focal position of this defocus detection light spot is shifted in the vertical direction with respect to the focal position of the information signal recording, reproduction, and tracking signal detection light spot.

As a specific configuration, the optical spot for detecting defocus is composed of a plurality of optical spots whose focal points are shifted upward and downward from the focal position of the optical spot for recording and reproducing the information signal and detecting the tracking signal. Claim 2). In this case, the optical spot for defocus detection can be imaged at the position of the defocus detection pit provided on the disk recording film surface (claim 3).

In another specific configuration, the optical spot for detecting defocus is formed to the left and right (in the disk radial direction) from the imaging position of the optical spot for recording, reproducing and tracking signals of the information signal. It consists of a plurality of light spots whose positions are shifted (claim 4). In this case, the optical spot for detecting defocus may be located at a track groove on the surface of the disk recording film (claim 5).

[0016]

[Operation] Laser beams are emitted from a plurality of semiconductor lasers arranged to be shifted back and forth in the emission direction, and are imaged on the disk recording film surface. Of these light spots,
At least one is used for recording and reproducing information signals and detecting tracking signals, and has a minimum spot diameter at the focused position. The other light spots are used for defocus detection. The focal position of this optical spot for defocus detection is vertically shifted from the focal position of the optical spot for recording, reproducing information signals and detecting tracking signals. An image is formed on the disk recording film surface with a spot diameter different from that of the light spot.

Therefore, when the disk recording film surface shifts in the vertical direction, the focal shift detection light spot diameter changes greatly on the disk recording film surface. When there are two optical spots for defocus detection above and below the disk recording film surface,
They change in opposite magnitude relationships. Therefore, since the amount of reflected light changes significantly, defocus detection can be performed without using a separate light-receiving element in the photodetector, that is, by using the total light amount detection method, thereby reducing the amount of light received by the photodetector. It is possible to achieve almost no adjustment and stable detection of servo signals and information signals.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a diagram showing the configuration of an optical head optical system for an optical disk according to the present invention. A semiconductor laser light source 1 includes laser chips 2, 3, and 4 having the same wavelength on a flat mount 5.
They are arranged so as to be shifted back and forth and parallel to the beam emission direction, and are hybridized in the same package (see FIG. 2). Here, the laser beam 2a
are used for recording and reproducing information signals and detecting tracking signals, and laser beams 3a and 4a are used for detecting defocus.

The laser beams 2a, 3a, 4a are collimated by a collimating lens 6, and are further collimated by a beam shaping prism 7.
The laser beams 2a, 3a, 4a that have been beam-shaped and transmitted through the beam splitter 8 change their optical paths with a corner mirror (or galvanometer mirror) 9, and then pass through a focus lens 10.
The area is narrowed down to the disk recording film surface 11.

The laser beam 2a hits the disk recording film surface 11.
When the focus 12 is set at , the laser beam 3a sets the focus 13 in a direction closer to the focus lens 10 than the disk recording film surface 11. This is because the laser chip 3 is shifted backward from the laser chip 2 with respect to the laser beam emission direction, so the focal point 13 of the laser beam 3a is shifted in the direction toward the focus lens 10. On the other hand, the laser beam 4a focuses 14 in a direction farther from the focus lens 10 than the disk recording film surface 11. This is because the laser chip 4 is shifted forward from the laser chip 2 with respect to the laser beam emission direction.
This is because the focal point 14 of a is shifted in the direction away from the focus lens 10.

Next, FIG. 5 shows the format structure of the disk recording film surface. 1 frame 20 is preformatted (
It consists of a sector mark, address mark, etc.) section 21, a data section 22, and a focus shift detection pit section 23. The shape of the defocus detection pit 24 is, for example, a size (diameter) of 1
The pit depth is approximately λ/4 (λ: laser wavelength).

Next, the principle of defocus detection will be explained using FIG. 3.

When the optical spots for recording and reproducing information signals and for detecting tracking signals are located on the disk recording film surface 11, the optical spots 13 and 14 for defocus detection are shifted from the disk recording film surface 11 by equal distances up and down, respectively. image is formed. These light spots 12, 13, 14 correspond to pits 24a, 24b, 2 of the defocus detection pit section 23.
In the section 4c, as shown in FIG. 3(1), the optical spot 12 is a focused point on the disk recording film surface 11, so the optical spot diameter is the smallest, whereas the optical spots 13 and 14 for defocus detection are Since the light is focused off the disk recording film surface 11, the diameter of the light spot is large. Here, since the optical spots 13 and 14 have different defocus directions but the same amount of defocus, the optical spot diameters of the optical spots 13 and 14 on the disk recording film surface 11 are equal.

On the other hand, if the disk recording film surface 11 is shifted in the direction approaching the focus lens 10,
), since the disk recording film surface 11 approaches the optical spot 13 of the laser beam 3a, the optical spot diameter 13 becomes smaller at the defocus detection pit 24b. Conversely, since the light spot 14 of the laser beam 4a moves away from the disk recording film surface 11, the focus shift detection pit 24
At c, the optical spot diameter 14 becomes large.

Furthermore, if the disk recording film surface 11 is shifted in the direction away from the focus lens 10, as shown in FIG. 3(3).
As shown in FIG. 3, since the light spot 13 of the laser beam 3a moves away from the disk recording film surface 11, the light spot diameter 13 becomes larger at the defocus detection pit 24b. Conversely, since the optical spot 14 of the laser beam 4a approaches the disk recording film surface 11, the optical spot diameter 14 becomes smaller at the defocus detection pit 24c.

Each of the light spots reflected by the defocus detecting pit portion 23 on the disk recording film surface 11 is reflected by the beam splitter 8, changes its optical path by the corner mirror 15, becomes converged light by the convex lens 16, and reaches the wollast. The prism 17 separates the light into P-polarized light 18a and S-polarized light 18b, and the light is incident on a photodetector 19.

FIG. 4 shows the configuration of the photodetector 19. In order to receive each laser beam individually, it is composed of six light receiving elements, and each of these light receiving elements (25a to 27a
, 25b to 27b) are not divided. The light receiving elements 25a and 25b are used for reproducing information signals and detecting tracking signals. The optical spot 12 for reproducing the information signal and detecting the tracking signal is formed by a Wollaston prism 17.
The light is separated into a P polarized light spot 12p and an S polarized light spot 12s, and the light is received by light receiving elements 25a and 25b, respectively. From this, an information signal can be obtained by taking the difference between the output of the light receiving element 25a and the output of the light receiving element 25b.

The tracking signal is obtained by subtracting the sum of the outputs of the light receiving elements 25a and 25b from the current sum of the outputs of the light receiving elements 25a and 25b at fixed time intervals using a known sample servo method. It will be done.

As shown in FIG. 3, the detection of the defocus signal is performed when the disk recording film surface 11 deviates in the direction approaching the focus lens 10, the light spot diameter 13 becomes smaller at the defocus detection pit 24b, so that it is reflected. The decrease in the amount of light is large, and the amount of light incident on the light receiving elements 27a and 27b is greatly reduced. On the other hand, since the optical spot diameter 14 becomes large at the defocus detection pit 24c, the amount of reflected light decreases little, and the amount of light incident on the light receiving elements 26a, 26b decreases little. When the disk recording film surface 11 shifts in the direction away from the focus lens 10, the situation is completely opposite to the above, and the amount of light incident on the light receiving elements 27a and 27b decreases little.
The amount of light incident on the light receiving elements 27a, 27b is greatly reduced.

As described above, a defocus signal can be detected by subtracting the outputs of the light receiving elements 27a and 27b from the outputs of the light receiving elements 26a and 26b.

[0032] Expressed as an equation, it is as follows.

Defocus signal=(26a+26b)−(27a+27b
) However, the present invention is not limited to this, and the defocus signal = (26a) - (
27a) or defocus signal = (26b) - (27b)
It's good as well. At this time, the light receiving element 26b, the light receiving element 2
7b (or the light receiving element 26a, the light receiving element 27a) is unnecessary.

According to the above configuration, since the servo (focal deviation, track deviation) signal can be detected by the total light amount detection method (the light receiving element that receives each light beam is not divided),
The alignment and adjustment of each photodetector with respect to the incident laser beam is dramatically improved and simplified. In addition, offsets are less likely to occur in the servo signal due to positional deviation of the photodetector, and the servo signal can be detected stably, so information signals can be recorded and reproduced stably.

Next, another embodiment will be explained.

The optical head optical system for an optical disk shown in FIG. 6 differs from the structure shown in FIG. 1 in that a diffraction grating 40 is provided between the beam shaping prism 7 and the beam splitter 8. As in the case of FIG. 1, the semiconductor laser light source 1 has laser chips 2, 3, and 4 having the same wavelength on a flat mount 5, which are shifted back and forth with respect to the beam emission direction, and are arranged parallel to each other. (See Figure 2). Here, the laser beam 2a is used for recording and reproducing information signals and detecting tracking signals, and the laser beams 3a and 4a are used for detecting defocus.

The laser beam 2a is turned into parallel light by the collimating lens 6, but the laser beam 3a is on the verge of divergence, and the laser beam 4a is on the verge of convergence. Each laser beam is beam-shaped by a beam-shaping prism 7, and a diffraction grating 21
The beam is divided into multiple beams (±1st order light, 0th order light). Each laser beam 2a, 3a transmitted through the beam splitter 8
, 4a changes the optical path with a corner mirror (or galvano mirror) 9, and focuses on the disc recording film surface 1 with a focus lens 10.
Narrowed down to 1. At this time, the laser beams 2a, 3a,
4a is a plurality of (±1st order light, 0th order light) by the diffraction grating 40
It is divided into two beams. In addition, the 0th order light (12
a, 13a, 14a) are adjusted by rotating the diffraction grating 40 so that they are centered between the track grooves 41 on the disk recording film surface 11, and the ±1st-order beams of each beam are centered between the track grooves 42 (see Fig. (see 7).

The laser beam 2a hits the disk recording film surface 11.
The focal point 12a (0th order light) and the focal points 12b, 12c (±1
When focusing the laser beam 3a, the laser beam 3a moves toward the focus lens 10 from the disk recording film surface 11 at the focal point 13.
a (0th order light), and 13b, 13c (±1st order light) are connected. This is because the laser chip 3 is shifted backward from the laser chip 2 with respect to the laser beam emission direction, so the focal point 13 of the laser beam 3a is shifted in the direction toward the focus lens 10.

On the other hand, the laser beam 4a (0th order light)
focuses 14a, 14b, and 14c (±1st-order light) in a direction farther from the focus lens 10 than the disk recording film surface 11. This converts laser chip 4 to laser chip 2.
Since it is shifted forward with respect to the laser beam emission direction, the focal points 14a, 14b, 14 of the laser beam 4a
This is because c (±first-order light) is shifted in the direction away from the focus lens 10.

Next, the principle of defocus detection will be explained using FIG. 7.

Optical spot 12a for recording and reproducing information signals
(0th order light), and tracking signal detection optical spot 1
When the beams 2b and 12c (±1st order beams) are in focus on the disk recording film surface 11, the optical spots 13b and 13 for detecting defocus are detected.
c (±1st-order light) and 14b, 14c (±1st-order light) are imaged vertically shifted by the same distance from the disk recording film surface 11, respectively. As shown in FIG. 7(1), the optical spots 12a, 12b, 12c are focused on the disk recording film surface 11, so the optical spot diameter is the minimum, whereas the optical spots 13b, 13c for defocus detection ( The light beams 14b and 14c (±1st order light) are focused at a position shifted from the disk recording film surface 11, so their light spot diameters are large. Here, the light spots 13b, 13c (±
1st order light) and 14b, 14c (±1st order light) have different defocus directions but the same amount of defocus, so light spots 13b, 13c and 14b are formed on the disk recording film surface 11.
, 14c have the same light spot diameter.

On the other hand, if the disk recording film surface 11 is shifted in the direction approaching the focus lens 10,
), the light spot 13b of the laser beam 3a,
Since the disk recording film surface 11 approaches 13c, the optical spot diameter 13 becomes smaller. Conversely, since the optical spots 14b and 14c of the laser beam 4a move away from the disk recording film surface 11, the optical spot diameter increases.

Furthermore, if the disk recording film surface 11 is shifted in the direction away from the focus lens 10, as shown in FIG. 7(3).
As shown in FIG.
Since the light beam 3c moves away from the disk recording film surface 11, the diameter of the light spot becomes large. Conversely, since the optical spots 14b and 14c of the laser beam 4a approach from the disk recording film surface 11, the optical spot diameter becomes small.

Disc recording film surface 11 and track board 2
Each light spot reflected by 1 (12a to 12c
, 13a to 13c, 14a to 14c) are reflected by the beam splitter 8, change the optical path by the corner mirror 15,
The convex lens 16 converges the light, and the Wollaston prism 1
7, the light is separated into P polarized light 18a and S polarized light 18b and sent to the photodetector 1.
9.

FIG. 8 shows the shape of the photodetector 19. In order to receive each laser beam, it is composed of 10 light receiving elements, and each light receiving element (2
2sa to 26s, 22p to 26p) are not divided. The light receiving elements 22p and 22s are for reproducing information signals. A light spot 12a for reproducing information signals is divided into a P polarization spot 12p and an S polarization spot 12 by a Wolast prism 17.
The light is separated into light receiving elements 22p and 22s, respectively. From this, an information signal can be obtained by taking the difference between the output of the light receiving elements 22p and 22s.

The tracking signal can be obtained using a known three-beam tracking method. For example, from the output of the light receiving elements 25s and 25p that receive the reflected light from the track groove 42 of the light beam 12b, the light receiving element 26s receives the reflected light from the track groove 42 of the light beam 12c.
, 26p.

As shown in FIG. 7, the detection of the defocus signal is performed when the disc recording film surface 11 deviates in the direction approaching the focus lens 10 (see FIG. 7 (2)).
Since the diameters of the light spots 3b and 13c become smaller, the amount of reflected light decreases significantly due to the diffraction of the track grooves 42. Therefore, the amount of light incident on the light receiving elements 23s and 23p into which the laser beam of the optical spot 13b (or 13c) is incident is greatly reduced. On the other hand, the light spots 14b,
Since the optical spot diameter of 14c becomes large, the track groove 2
The influence of the diffraction of 1 is reduced, and the amount of reflected light decreases less. Therefore, the amount of light received by the light receiving elements 24s and 24p, on which the laser beam of the light spot 14b (or 14c) is incident, decreases little.

Furthermore, when the disk recording film surface 11 shifts in the direction away from the focus lens 10 (see FIG. 7(3)
) is completely opposite to the above, and the light receiving elements 23s and 23p
There is little decrease in the amount of light incident on the light receiving elements 24s, 24.
The amount of light incident on p is greatly reduced.

As described above, the output of the light receiving element 23s, 23p
A defocus signal can be detected by subtracting the outputs of the light receiving elements 24s and 24p from the output.

Expressed as an equation, it is as follows.

Defocus signal=(23s+23p)−(24s+24p
) However, one of the calculations, for example, defocus signal =
It may be detected by (23s)-(24s).

In this embodiment, the light spots 13b, 13c
Any one light spot, also the light spot 14b, 1
Defocus detection was performed using any one of the light spots 4c, but all the light spots 13b, 13c, 14b, 1
It is also possible to perform defocus detection using 4c. At this time, it is necessary to increase the number of light receiving elements in the photodetector in accordance with the number of laser beams used.

[0053]

As described above, according to the present invention, servo signals such as defocus and track misalignment are detected by a photodetector using a light-receiving element whose light-receiving surface is not divided, that is, by a total light amount detection method. This makes it possible to dramatically improve the ease of alignment and adjustment of each light-receiving element with respect to the incident laser beam. In addition, the servo signal is less likely to be offset due to positional deviation of the photodetector, and the servo signal can be detected stably, so that information signals can be recorded and reproduced stably.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an optical system of an optical head showing an embodiment of the present invention.

[Figure 2] Diagram showing the arrangement relationship of laser chips

[Fig. 3] A diagram showing the principle of defocus detection in the embodiment of Fig. 1.

[Fig. 4] Configuration diagram of a photodetector in the embodiment of Fig. 1

[Figure 5
】Disk format configuration diagram

FIG. 6 is a configuration diagram of an optical system of an optical head showing another embodiment of the present invention.

[Fig. 7] A diagram showing the principle of defocus detection in the embodiment of Fig. 6.

FIG. 8 is a configuration diagram of a photodetector in the embodiment of FIG. 6.

[Figure 9
] Configuration diagram of the optical system of a conventional optical head

[Figure 10] Diagram showing the principle of conventional defocus detection

[Explanation of symbols]

1 Hybrid semiconductor laser light sources 2, 3, 4 Semiconductor laser 2a Laser beams 3a, 4a for recording and reproducing information signals and detecting tracking signals Laser beam 10 for detecting defocus
Focus lens 11 Disc recording film surface 12 Light spot 13 of laser beam 2a Light spot 14 of laser beam 3a Light spot 17 of laser beam 4a Wollaston prism 19 Photodetector 23 Focus shift detection pits 24a, 24b, 24c Focus shift Detection pit 25
a, 26a, 27a Photodetector 25b, 26b, 27b Photodetector 40 Diffraction grating 42 Track groove

Claims (5)

[Claims] Claim 1: Laser beams from a plurality of semiconductor lasers are imaged as optical spots on the disk recording film surface, and the reflected lights from the disk recording film surface are individually received by light receiving elements of a photodetector. In an optical head for an optical disk device that obtains information signals and servo signals, a plurality of semiconductor lasers with the same wavelength are arranged parallel to each other while being shifted back and forth in the laser beam emission direction. At least one of the optical spots to be imaged is used for recording and reproducing information signals and detecting tracking signals, and the other optical spots are used for defocus detection, and the focal position of this optical spot for defocus detection is set as described above. A defocus detection method for an optical head for an optical disk, characterized in that the focal position of a light spot for recording and reproducing information signals and detecting tracking signals is shifted in the vertical direction. 2. The optical spot for detecting defocus is comprised of a plurality of optical spots whose focus is shifted above and below the focal position of the optical spot for recording and reproducing information signals and detecting tracking signals. 2. The defocus detection method for an optical head for an optical disk according to claim 1. 3. The optical head for an optical disc according to claim 1, wherein the optical spot for detecting defocus is located at a pit portion for detecting defocus provided on the surface of the disc recording film. defocus detection method. 4. The optical spot for detecting defocus is formed from a plurality of optical spots whose imaging position is shifted in the disk radial direction from the imaging position of the optical spot for recording and reproducing the information signal and detecting the tracking signal. 2. The defocus detection method for an optical head for an optical disk according to claim 1. 5. The defocus detection method for an optical head for an optical disk according to claim 4, wherein the optical spot for detecting defocus is located at a track groove on the surface of the disk recording film.