JPH04285732A - Out-of-focus detecting method for optical head for optical disk - Google Patents

Abstract

PURPOSE:To obtain a servo signal and an information signal while the light quantity for an optical detector is scarcely adjusted and to obtain the stable servo signal and information signal even when the deviation, etc., of the optical detector occurs. CONSTITUTION:Plural laser beams with different wavelengths are emitted by a semiconductor laser 1 and coupled with light spots 12, 13 and 14 on a disk recording film surface 11, reflection light from the relevent surface 11 is split into a (p) polarized light spot and a (s) poralized light spot and separately received with photodetectors 25a to 27a and 25b to 27b into which an optical detector 19 is split and the out of focus is detected from the output of these photodetectors.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defocus detection method for an optical head for an optical disk.

0002

[Prior Art] A conventional optical head for an optical disk uses a photodetector to receive reflected light from the disk recording film surface, and the photodetector includes a plurality of optical elements in order to detect an information signal and a servo signal. It was set up.

[0003] A conventional defocus detection method for an optical head for an optical disc will be described below with reference to FIGS. 10 and 11.

The laser beam emitted from the semiconductor laser 28 becomes parallel light by a collimating lens 29, is beam-shaped by a beam shaping prism 30, and after passing through a beam splitter 31, the optical path is changed by a corner mirror (or galvano mirror) 32. Instead, the light is focused as a light spot on the disk recording film surface 34 by the focus lens 33.

The laser beam reflected by the disk recording film surface 34 is reflected by a beam splitter 31, changes its optical path by a corner mirror 35, and becomes converged light by a convex lens 36. This focused light is separated into a transmitted beam and a reflected beam by a polarizing beam splitter 37, the transmitted beam focused light is received by a photodetector 38a after the focus (or before the focus), and the reflected beam focused light is received before the focus (or after the focus). ) is received by the photodetector 38b.

When the laser beam narrowed down as a light spot is focused on the disk recording film surface 34, the beam diameters incident on both photodetectors 38a and 38b are equal, as shown in FIG. 11(1). However, when the disk recording film surface 34 shifts in the direction approaching the focus lens 33, the beam diameter of the transmitting side photodetector 38a becomes smaller and the beam diameter of the reflecting side photodetector 38b decreases, as shown in (2) in the figure. becomes larger. Conversely, the disk recording film surface 34 is the focus lens 3.
3, as shown in (3) in the same figure, the beam diameter of the transmission side photodetector 38a increases, and the beam diameter of the reflection side photodetector 38b decreases.

As described above, since the amount of light received by the photodetectors 38a and 38b changes depending on the direction and amount of defocus, defocus can be detected. For example, the amount of defocus can be determined by the following calculation.

[0008] Defocus amount = (a1+a2)-(b1+b2)

000
9]

However, in the conventional defocus detection method, the light-receiving surface of the light-receiving element that receives the reflected beam from the disk recording film surface is 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). Furthermore, since the size of this divided light-receiving surface is minute (about several tens of micrometers), the amount of light received changes greatly with a deviation of several micrometers in the incident laser beam. Therefore, 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 also difficult to automate the adjustment. Furthermore, even if it is fixed with adhesive or screws after adjustment, it is likely to shift slightly due to temperature changes or changes over time, and these shifts (including adjustments) will cause an offset in the detected servo signal, making servo operation unstable. This sometimes makes it impossible to accurately record and reproduce information signals.

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

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the prior art, to obtain a servo signal and an information signal without adjusting the amount of light received by a photodetector, and to prevent misalignment of the photodetector. It is an object of the present invention to provide a defocus detection method for an optical head for an optical disk, which can obtain stable servo signals and information signals even when the defocus occurs.

[0013]

Means for Solving the Problems In order to achieve the above object, the present invention emits a plurality of laser beams having different wavelengths from a semiconductor laser and combines them as a light spot on the surface of a disk recording film. The reflected light from the surface is p
It is characterized in that the light is separated into a polarized light spot and an s-polarized light spot, which are individually received by a plurality of divided light receiving elements of a photodetector, and a defocus is detected from the outputs of these light receiving elements.

That is, the present invention detects the total amount of light of a laser beam incident on a photodetector (the light-receiving surface of the light-receiving element that receives each laser beam is not divided) as a defocus detection method for an optical head for an optical disk. This makes it possible to achieve almost no adjustment of the amount of light received by the photodetector and stable detection of servo signals and information signals.

[0015]

[Operation] A plurality of laser beams of different wavelengths emitted from a semiconductor laser are combined as a light spot on the disk recording film surface, but the imaging position shifts back and forth depending on the wavelength. The laser beam reflected by the disk recording film surface is separated into a p-polarized light spot and an s-polarized light spot, which are individually received by a plurality of divided light receiving elements of a photodetector.

Since the servo signals for defocus and track misalignment are detected by the total light amount detection method, the alignment and adjustment of each light-receiving element with respect to the incident laser beam is dramatically improved and simplified.

[0017] Furthermore, even when the photodetector is misaligned, the servo signal is unlikely to be offset, and the servo signal can be detected stably, making it possible to stably record and reproduce 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.

In FIG. 1 showing the first embodiment, 1 is a semiconductor laser which is a light source, and this semiconductor laser has a plurality of laser chips 2, 3, 4 having different wavelengths on a flat mount 5 as shown in FIG. They are arranged so as to be aligned and parallel to the beam emission direction. In this case, the laser beam 2a emitted from the central laser chip 2 is used for recording and reproducing information signals and for tracking signal detection, and the laser beams 3a and 4a emitted from the laser chips 3 and 4 on both sides are used for defocus detection. used for purposes.

The laser beams 2a, 3a, 4a are collimated by a collimating lens 6, and are further collimated by a beam shaping prism 7.
After passing through a beam splitter 8, the optical path is changed by a corner mirror (or galvano mirror) 9, and the beam is focused onto a disk recording film surface 11 by a focus lens 10.

In this case, when the laser beam 2a focuses 12 on the disc recording film surface 11, the laser beam 3a focuses 13 in a direction closer to the focus lens 10 than the disc recording film surface 11, and the laser beam 4a focuses on the disc recording film surface 11. The focal point 14 is set in a direction farther from the focus lens 10 than the film surface 11 . The former reduces the chromatic aberration of the lens system by making the oscillation wavelength of the laser chip 3 shorter than the oscillation wavelength of the laser chip 2, and the latter by making the oscillation wavelength of the laser chip 4 longer than the oscillation wavelength of the laser chip 2. Laser beams 3a, 4
The focal points 13 and 14 of the laser beam 2a are set in front and behind the disk recording film surface 11 (front and rear with respect to the focusing direction) than the focal point 12 of the laser beam 2a.

The format of the disk recording film surface 11 is as shown in FIG. 3, where one frame 20 is a sector mark,
It mainly consists of a preformat section 21 such as an address mark, a data section 22, and a pit section 23 for detecting defocus. Pit 2 of defocus detection pit section 23
4 has a diameter of about 1 μm and a depth of about λ/4 (λ: laser wavelength), for example.

Next, the principle of defocus detection will be explained.
First, when the optical spot 12 for recording/reproducing information signals and detecting tracking signals is on the disc recording film surface 11, the optical spots 13 and 14 for defocus detection are on the disc recording film surface 1.
1, the images are formed with equal distances shifted forward and backward in the aperture direction. These light spots 12, 13,
14 are pits 24a, 2 of the defocus detection pit section 23.
4b and 24c, the optical spot 12 has the minimum diameter because it is a focused point on the disk recording film surface 11, as shown in (1) in FIG. Since the focus is shifted from the disk recording film surface 11, the diameter of the light spot becomes large. In this case, the light spots 13 and 14 have different defocus directions but the same amount of defocus, so the light spot diameters on the disk recording film surface 11 are the same.

On the other hand, when the disc recording film surface 11 shifts in the direction toward the focus lens 10, one of the light spots 13 approaches the disc recording film surface 11, as shown in (2) in the figure. Focus shift detection pit 24
The diameter of the light spot at point b becomes smaller, and conversely, the other light spot 14 moves away from the disk recording film surface 11.
The light spot diameter at the defocus detection pit 24c becomes larger.

Furthermore, if the disk recording film surface 11 is shifted in the direction away from the focus lens 10, (3) in the figure
As shown in , since one of the light spots 13 moves away from the disk recording film surface 11, the defocus detection pit 24b
The diameter of the light spot at the defocus detection pit 24c becomes larger, and the other light spot 14 approaches the disk recording film surface 11, so the diameter of the light spot at the defocus detection pit 24c becomes smaller.

Each light spot reflected by the defocus detection 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 becomes a Wollaston beam. The prism 17 separates the light into P polarized light 18a and S polarized light 18b,
The light is incident on the photodetector 19.

The photodetector 19 has six light receiving elements 25a to 27a to receive each laser beam as shown in FIG.
, 25b to 27b, and the light receiving surface of each light receiving element is not divided. The light receiving elements 25a and 25b are used for reproducing information signals and detecting tracking signals. The light spot 12 for reproducing the information signal and detecting the tracking signal is separated by the Wollaston prism 17 into a P-polarized light spot 12a and an S-polarized light spot 12b, which are received by light receiving elements 25a and 25b, respectively. Then, by taking the difference between the outputs of these light receiving elements 25a and 25b, an information signal can be obtained.

The tracking signal is sent to the current light receiving element 25a at regular time intervals using a known sample support method.
, 25b from the light receiving element 25a, 25b a certain time ago.
It is obtained by subtracting the sum of the outputs of 25b.

Detection of the defocus signal is carried out when the disc recording film surface 11 deviates in the direction approaching the focus lens 10 as shown in (2) of FIG. Since the diameter becomes smaller, the amount of reflected light decreases significantly, and the light receiving elements 27a, 27b
The amount of light incident on the area is greatly reduced. On the other hand, in the defocus detection pit 24c, the spot diameter of the optical spot 14 becomes large, so that 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 is shifted 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, 27b decreases little, and the light is incident on the light receiving elements 26a, 26b. The amount of light decreases significantly.

As described above, a defocus signal can be detected by subtracting the outputs of the light receiving elements 27a, 27b from the outputs of the light receiving elements 26a, 26b. Expressing this in a formula is as follows.

Defocus signal=(26a+26b)−(27a+27b
) Note that the defocus signal = 26a-27a (or 26b-2
7b) may also be used. In this case, the light receiving elements 26b, 27
b (or 26a, 27a) is unnecessary.

In the above embodiment, in order to shift the imaging position of the defocus detection optical spots 13 and 14 back and forth from the imaging position of the optical spot 12 for recording/reproducing information signals and for tracking signal detection, laser chip 2,
However, by shifting these laser chips 2, 3, and 4 back and forth in the laser beam emission direction as shown in FIG. 6, the imaging position can be significantly shifted back and forth.

FIG. 7 shows a second embodiment of the present invention, in which the same parts as in the first embodiment of FIG. 1 are given the same reference numerals. The laser beam 2a emitted from the semiconductor laser 1 becomes parallel light by the collimating lens 6, but the laser beam 3a tends to diverge and the laser beam 4a tends to converge. These laser beams are shaped by a beam shaping prism 7 and split into a plurality of beams (±1st order light, 0th order light) by a diffraction grating 20. The laser beams 2a, 3a, 4a transmitted through the beam splitter 8 have their optical paths changed by a corner mirror (or galvano mirror) 9, and are focused by a focus lens 10. At this time, the laser beams 1a, 3a, and 4a are split into a plurality of beams (±1st order light, 0th order light) by the diffraction grating 20. The diffraction grating 20 is adjusted by rotating the diffraction grating 20 so that the 0th-order light of each beam is centered between the track grooves 27 on the disk recording film surface 11, and the ±1st-order light of each beam is centered between the track grooves 21. .

The laser beam 2a hits the disk recording film surface 11.
The focal point 12a (0th order light) and the focal points 12b, 12c (±
When focusing the laser beam 3a (primary light), the laser beam 3a is focused at the focus 1 in the direction approaching the focus lens 10 from the disk recording film surface 11.
3a (0th order light) and 13b, 13c (±1st order light), the laser beam 4a focuses 14a (0th order light) and 14b, 14c (±1st order light) in the direction away from the disk recording film surface 11 toward the focus lens 10. It is set to connect the following light. The former reduces the chromatic aberration of the lens system by making the oscillation wavelength of the laser chip 3 shorter than the oscillation wavelength of the laser chip 2, and the latter by making the oscillation wavelength of the laser chip 4 longer than the oscillation wavelength of the laser chip 2. The focal points 13a to 13c, 1 of the laser beams 3a, 4a are
4a to 14c are focal points 12a to 12c of the laser beam 2a
It becomes more connected at the front and rear of the disk recording film surface 11 (front and rear with respect to the narrowing direction).

Next, the principle of defocus detection will be explained.
First, a light spot 12a for recording and reproducing information signals (0th order light)
and tracking signal detection optical spots 12b, 12
When c (±1st order light) is in focus at the disc recording film surface 11, the defocus detection light spots 13b, 13c and 14b, 14c (±1st order light) are directed from the disc recording film surface 11 in the aperture direction. The images are shifted forward and backward by equal distances. As shown in (1) of FIG. 8, these light spots 12a, 12b, and 12c are focused on the disk recording film surface 11, so the light spot diameter is the minimum, whereas the focus shift detection light spots 13b, 13c
Since the beams 14b and 14c (±1st-order beams) are focused off the disk recording film surface 11, the diameter of the optical spot becomes large. In this case, the light spots 13b, 13c and 14b, 1
4c have different defocus directions but the same amount of defocus, so the light spot diameters on the disk recording film surface 11 are the same.

On the other hand, when the disk recording film surface 11 is shifted in the direction approaching the focus lens 10, one of the light spots 13b and 13c is shifted as shown in (2) in the figure.
Since the light spots 14b and 14c approach the disc recording film surface 11, the diameter of the light spot becomes small, and conversely, the other light spots 14b and 14c move away from the disc recording film surface 11, so the diameter of the light spot becomes large.

Furthermore, if the disk recording film surface 11 is shifted in the direction away from the focus lens 10, (3) in the figure
As shown in , one of the optical spots 13b and 13c moves away from the disc recording film surface 11, so the optical spot diameter increases, and conversely, the other optical spot 14b and 14c approaches the disc recording film surface 11, so the optical spot diameter increases. becomes smaller.

Disk recording film surface 11 and track 21
The respective light spots 12a to 12c, 1 reflected by
3a to 13c, 14a to 14c are beam splitters 8
The light is reflected by the corner mirror 15, the light path is changed by the convex lens 16, and the light is focused by the Wollaston prism 17.
The light is separated into polarized light 18a and S-polarized light 18b, and enters a photodetector 19.

The photodetector 19 has 10 light receiving elements 22s to 26 to receive each laser beam as shown in FIG.
s, 22p to 26p, and each light receiving element is not divided. The light receiving elements 22p and 22s are for reproducing information signals. The light spot 12a for reproducing the information signal is converted into a P-polarized light spot 12p by the Wollaston prism 17.
and an S-polarized light spot 12s, which are received by light-receiving elements 22p and 22s, respectively. Then, by taking the difference between the outputs of these light receiving elements 22p and 22s, an information signal can be obtained.

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 which receive the reflected light from the track groove 21 of the light beam 12b, the light receiving elements 26s and 2 which receive the reflected light from the track groove 21 of the light beam 12c
It is obtained by subtracting the output of 6p.

The detection of the defocus signal is performed when the disc recording film surface 11 deviates in the direction approaching the focus lens 10 as shown in (2) of FIG.
3c becomes smaller, the amount of reflected light decreases significantly due to the diffraction of the track groove 21, and the light receiving element 23s
, 23p is greatly reduced. On the other hand, since the spot diameters of the optical spots 14b and 14c become larger, the influence of the diffraction of the track groove 21 is small, so that the amount of reflected light decreases little, and the amount of light received by the light receiving elements 24s and 24p decreases little.

When the disk recording film surface 11 is shifted 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 23s and 23p decreases little, and the light is incident on the light receiving elements 24s and 24p. The amount of light decreases significantly.

From the above, a defocus signal can be detected by subtracting the outputs of the light receiving elements 24S, 24P from the outputs of the light receiving elements 23S, 23P. Expressing this in a formula is as follows.

Defocus signal=(23s+23p)−(24s+24p
) Note that the defocus signal = 23s-24s (or 23p-2
4p).

[0046]

[Effects of the Invention] In summary, according to the present invention, since the servo signals for defocus and track misalignment are detected by the total light amount detection method, the alignment and adjustment of each light receiving element with respect to the incident laser beam is dramatically improved. It gets easier.

[0047] Furthermore, even when the photodetector is misaligned, the servo signal is hardly offset, and the servo signal can be detected stably, so that information signals can be recorded and reproduced stably.

[Brief explanation of the drawing]

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

FIG. 2 is a perspective view showing the structure of a semiconductor laser.

FIG. 3 is a diagram showing a format configuration of a disc recording film surface.

FIG. 4 is a diagram showing the principle of defocus detection.

FIG. 5 is a diagram showing the configuration of a photodetector.

FIG. 6 is a perspective view showing another structure of the semiconductor laser.

FIG. 7 is a configuration diagram of an optical head optical system showing a second embodiment of the present invention.

FIG. 8 is a diagram showing the principle of defocus detection.

FIG. 9 is a diagram showing the configuration of a light detector.

FIG. 10 is a configuration diagram of a conventional optical head optical system.

FIG. 11 is a diagram showing the principle of conventional defocus detection.

[Explanation of symbols]

1 Semiconductor laser 11 Disc recording film surface 12, 13, 14 Light spot 19 Photodetector

Claims (7)

[Claims] 1. A plurality of laser beams with different wavelengths are emitted from a semiconductor laser and combined as a light spot on the disk recording film surface, and the reflected light from the disk recording film surface is divided into a p-polarized light spot and an s-polarized light spot. 1. A defocus detection method for an optical head for an optical disk, characterized in that light is received individually by a plurality of light receiving elements of a photodetector, and defocus is detected from the outputs of these light receiving elements. 2. The defocus detection method for an optical head for an optical disk according to claim 1, wherein the semiconductor laser is composed of a plurality of laser chips having different oscillation wavelengths. 3. The defocus detection method for an optical head for an optical disk according to claim 1, wherein at least two of the imaging light spots are used for defocus detection. 4. The imaging position of the optical spot for detecting defocus is shifted back and forth in the aperture direction from the imaging position of the optical spot for recording/reproducing information signals and detecting tracking signals. The defocus detection method for an optical head for an optical disk according to claim 3. 5. The defocus detection method for an optical head for an optical disk according to claim 1, wherein the disk recording film surface has pits for detecting defocus. 6. A plurality of laser beams having different wavelengths are emitted from a semiconductor laser, these are split into a plurality of beams by a diffraction grating, and the beams are combined as a light spot on the disk recording film surface, thereby emitting light from the disk recording film surface. An optical disc characterized in that reflected light is separated into a p-polarized light spot and an s-polarized light spot, each of which is individually received by a plurality of divided light-receiving elements of a photodetector, and a defocus is detected from the outputs of these light-receiving elements. Defocus detection method for optical heads. 7. The defocus detection method for an optical head for an optical disk according to claim 6, wherein the disk recording film surface has a track groove for detecting defocus.