JP3105637B2 - Optical information reader - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information reading apparatus, and more particularly to an information reading apparatus which is reduced in size and weight by using a hologram for a main part of an optical pickup.

[0002]

2. Description of the Related Art FIG. 9 is a diagram showing an arrangement of a hologram element and a photodetector in a conventional optical information reading apparatus. A hologram element 32 is provided on one surface of the substrate 31.
Is formed, and return light emitted from a light source (not shown) and reflected by an information recording medium (not shown) such as an optical disk passes through the hologram 32. The return light is split into zero-order light and ± first-order light by the action of the hologram 32, and the ± first-order lights are received by the photodetectors 33 and 34, respectively.

FIG. 10 shows a hologram element 32 shown in FIG.
3 is a diagram of the photodetectors 33 and 34 viewed from the direction of arrow C. FIG. The grating of the hologram 32 is formed in a direction indicated by an arrow D in FIG. 10 (a direction orthogonal to the paper surface in FIG. 9), and each of the photodetectors 33 and 34 is composed of six a, b, c, d, e, f Is divided into two areas. The hologram element 32 has a lens effect, and is configured such that the position of the image forming point of ± first-order light is shifted back and forth in the optical axis direction as shown in FIG. The photodetectors 33 and 34 are respectively disposed before and after respective image forming points of ± first-order light.
The focus error signal FE is

FE = (PD33c + PD33f + PD34a + PD34b + PD34d + PD34e) − (PD33a + PD33b + PD33d + PD33e + PD34c + PD34f), and the tracking error signal TE is obtained.

## EQU2 ## TE = (PD33b + PD33c + PD33d + PD34a + PD34f + PD34e)-(PD33a + PD33f + PD33e + PD34b + PD34c + PD34d).

The focus error signal FE is detected as follows. As shown in FIG. 11A, when the position of the objective lens 35 with respect to the information recording medium 36 is at the in-focus position, the first and second photodetectors 33 and 34 as shown in FIG. The focus error signal FE becomes 0 because the light spots formed thereon have the same size. FIG.
As shown in FIG. 1B, when the objective lens 35 is close to the information recording medium 36 (-defocus), the light emitted from the objective lens 35 becomes divergent light, and this divergent light enters the hologram element 32. Hologram element 32
The position of the image point of the light beam after transmitting the light beam is indicated by an arrow A in FIG.
Move in the direction indicated by. Therefore, the photodetectors 33, 3
The light beam spot formed on 4 is large on the photodetector 34 and small on the photodetector 33 as shown in FIG. 12B, and FE> 0. Conversely, when the objective lens 35 moves away from the information recording medium 36 as shown in FIG. 11C, the light emitted from the objective lens 35 becomes convergent light, and this convergent light enters the hologram element 32. ,
The position of the image point of the light beam moves in the direction indicated by arrow B in FIG. The light beam spots formed on the photodetectors 33 and 34 are large on the photodetector 33 and small on the photodetector 34 as shown in FIG. 12C, and FE <0.

[0005]

FIG. 12 (a) to FIG. 12 (c)
As shown in the figure, the direction of the diffraction pattern of the light beam spot formed on the photodetectors 33 and 34 due to the grooves of the information recording medium 36 is a dividing line orthogonal to the groove extending direction of the photodetectors 33 and 34. It is perpendicular to the extending direction of 37 and 38. That is, in order to form such a diffraction pattern, the extending direction of the groove formed in the information recording medium 36 is perpendicular to the extending direction of the dividing lines 37 and 38 of the photodetectors 33 and 34. It is necessary to dispose each element. If the groove of the information recording medium 36 is formed in parallel with the dividing lines 37 and 38 of the photodetectors 33 and 34, the diffraction pattern of the light spot is shown in FIG.
The diffraction patterns are rotated by 90 ° from the diffraction patterns shown in (a) to (c) (see FIG. 13). In this case, the light detector 33,
There is no particular problem as long as the center of the light spot coincides with the center of the light spot. However, if the track of the objective lens 35 is shifted or the adjustment of the photodetectors 33 and 34 is misaligned, the track offset is reduced. Leakage into the focus error signal causes malfunction.

For example, as shown in FIG.
Even if the spot sizes on the spots 3 and 34 are the same, the shaded area in FIG. 13 becomes a dark area, and the FE signal indicates minus, causing malfunction. Therefore, usually, as shown in FIGS. 12A to 12C, the direction of the diffraction pattern, that is, the extending direction of the groove of the information recording medium 36 and the extending of the dividing lines 37 and 38 of the photodetectors 33 and 34. Each element is arranged so that directions are orthogonal to each other.

As another example of the conventional optical information reading apparatus, there is an apparatus disclosed in Japanese Patent Application Laid-Open No. 63-20737, for example. FIG. 14 is a diagram showing the configuration of the device described in this publication. Laser diode 41 of light source
The divergent laser beam emitted from the first hologram 43 and 1 /
The light is focused on the optical disk 45 via the four-wavelength plate 44.
The reflected light from the disk 45 is condensed on the photodetector 46 by the second hologram element 42 via the 波長 wavelength plate 44 and the first hologram element 43. The polarization direction of the laser diode 41 is set parallel to a plane including the Y axis and the Z axis in FIG.
The output beam from 1 passes through the second hologram element 42 and is diffracted by the first hologram element 43. Furthermore,
The light is converted into circularly polarized light by the 板 wavelength plate 44 and enters the disk 45. After being reflected by the disk 45 and passing through the quarter-wave plate 44 again, the plane of polarization becomes linearly polarized light rotated by 90 ° around the optical axis from the plane of polarization on the outward path.
Since the plane of polarization of this linearly polarized light is rotated, it passes through the first hologram element 43 and passes through the second hologram element 4.
2 diffracted. As described above, in this information reading apparatus, two holograms are arranged so that their grating directions are orthogonal to each other to perform polarization separation. Therefore, the 波長 wavelength plate 44 is an essential component. The direction in which the division line of the photodetector 46 extends is parallel or perpendicular to the diffraction directions of the first and second hologram elements 42 and 43.

The first conventional example described with reference to FIGS. 9 to 13 has the following problems. In this device, a tracking error signal is detected by a push-pull method, and a photodetector 3 for detecting a tracking error is used.
The directions of the dividing lines 39 of 3 and 34 are as shown in FIG. In this case, if the wavelength of the light source fluctuates, the divergence angle of the ± first-order light diffracted by the hologram element 32 fluctuates. Therefore, as shown in FIG.
On 34, the light beam spot moves outward. Therefore, the tracking error signal is not 0 even though the track is not actually off-track, and if the tracking error is adjusted according to this signal, a track offset occurs to cause a malfunction.

Further, in the second conventional example shown in FIG. 14, as described above, since the quarter-wave plate 64 is an essential component, the number of parts increases. Further, as described above, since the direction of the dividing line of the photodetector 46 is provided in a direction parallel or orthogonal to the lattice direction of the first and second holograms 42, a wavelength variation occurs in the laser diode 41 of the light source. In this case, a malfunction may occur as in the first conventional example.

An object of the present invention is to provide an optical information reading apparatus which has a simple structure using a hologram element and does not cause a track offset and a focus offset even when the wavelength of a laser diode as a light source fluctuates. Things.

[0011]

In order to solve the above problems, an optical information reading apparatus according to the present invention comprises a light source, an objective lens, first and second hologram elements,
A plurality of photodetectors divided into at least two or more regions, wherein the first and second hologram elements are arranged such that their respective grid directions are non-parallel to each other, and after emitted information is the return light reflected by the recording medium is diffracted separated by the first and second holographic element, in an optical information reading device configured to be incident on the plurality of light detecting elements, Among the plurality of light detection elements, the division line of the light detection element that receives the light beam deflected by the diffraction of both the first and second hologram elements has a grid direction of the first hologram element and Both in the grid direction of the second hologram element
The first and second hologram elements in directions different from
Wavelength fluctuations determined based on the relationship between the lattice directions
Extending in the direction of movement of the beam spot at
The tracking error signal is detected based on the output of the detection element.
Configured to output the partial of the first light detecting element for receiving the deflected light beam by the diffraction only the hologram element
Secant is a direction perpendicular to the grating direction of the first holographic element, and extending groove provided in said information recording medium
Extending in the direction perpendicular to the direction in which
Detect focusing error signal based on force
It is characterized by having comprised .

[0012] Thus, in an optical information reading apparatus of the present invention, among the plurality of light detecting elements, the light detector for receiving the deflected light beam by diffraction of both the first and second holographic element The element sets the dividing line in a direction different from both the grid direction of the first hologram element and the grid direction of the second hologram element , and the first and second photo-elements.
Determined based on the relationship between the grid directions of the program elements
Extends in the moving direction of the beam spot during wavelength fluctuation
To detect the tracking error signal .
The photodetector, which receives the light beam deflected by the diffraction of only the hologram element, sets the dividing line in the direction orthogonal to the lattice direction of the first hologram element and in the information recording medium.
Extending in the direction perpendicular to the direction in which the grooves provided in the body extend
To detect the focusing error signal
Therefore, even when the wavelength of the light source fluctuates, no focus offset or track offset occurs.

[0013]

1 to 5 show the configuration of a first embodiment of the optical information reading apparatus of the present invention. FIG. 1 is a diagram showing the overall configuration of the device of the first embodiment. As shown in FIG. 1, a laser diode 9 as a light source, a beam splitter 6,
An objective lens 7, a substrate 1 on which a hologram is formed, a first hologram element 2 formed on one surface of the substrate 1, a second hologram element 3 formed on the other surface of the substrate 1,
Photodetectors 4 and 5 are provided.

FIG. 2 is a view showing the arrangement of the first and second hologram elements 2 and 3 and the photodetectors 4 and 5 in the apparatus of the first embodiment. After the one surface of the substrate 1 first hologram element 2, the lower surface is provided with a second holographic element 3, the return light from the information recording medium 8 is reflected by the beam splitter 6 It is separated by the first hologram element 2 and the zero-order light and the ± 1-order light. ± 1st order light among them enters the second hologram 3 formed on the other surface of the substrate 1. The second hologram 3 is a mere grating having no lens effect, and separates the incident ± 1st order light into 0th order light and ± 1st order light. FIG. 3 is a view of the hologram element 3 and the photodetector 4 shown in FIG. FIG. 4 is a view as seen from the direction of arrow F. Each photodetector 4 and 5 each of the three photodetector elements 4-1, which comprises a 4 -2,4-3,5-1,5-2,5-3, each light detecting element further plurality It is divided into light detection areas. As shown in FIG. 3, the 0th-order and ± 1st-order lights separated by the second hologram element 3 are respectively divided into first photodetector groups PD4-1, PD4-2, PD4-3 and second
To the photodetector groups PD5-1, PD5-2, and PD5-3. The grid direction of the first hologram element 2 and the grid direction of the second hologram element 3 are configured to be orthogonal to each other, so that the direction in which ± first-order light is expanded by the first hologram element 2 and the second hologram The spreading direction of the ± first-order light by the element 3 is made to be orthogonal. The first hologram element 2 has a lens effect, and the second hologram element 3 has no lens effect. The focusing error signal FE detects a light beam that is ± 1st-order light of the first hologram element 2 and 0th-order light of the second hologram element by the photodetectors PD4-2 and PD5-2. It can be obtained in a similar manner. Tracking error signal TE
Is ± 1 order light separated by the first hologram element 2,
In addition, as shown in FIG. 4, a photodetector PD is used by using a light beam that is the ± first-order light separated by the second hologram element.
4-1 and PD4-3, PD5-1 and PD5-3.

As described above, the laser diode 9 as the light source
When the wavelength variation occurs, the divergence angle of the ± primary light separated by the first hologram element 2 changes, and the light beam spot on each photodetector moves in the direction indicated by arrow G in FIG. Moving. These ± first-order lights are further reduced to 0 by the second hologram 3.
Are separated into the primary light and the ± first-order light.
The spread angle of the next light changes, and the light beam spot moves on each photodetector in the direction indicated by arrow H in FIG. However,
The 0-order light that forms an image on the photodetectors PD4-2 and PD5-2 does not move.

That is, according to the configuration of this embodiment, the light beams incident on the photodetectors PD4-2 and PD5-2 are:
± 1 order light diffracted by the first hologram element 2,
In addition, since the light is the zero-order light transmitted through the second hologram element 3, when the laser diode 9 fluctuates in wavelength, these beam spots move along the direction indicated by the arrow G in FIG. Become. However, the photodetector PD4-
2 and the dividing line of PD 5-2 extend in the same direction as the movement direction of these beam spots, so that no focus offset occurs. Further, since these dividing lines are provided so as to extend in a direction orthogonal to the extending direction of the groove provided in the information recording medium, crosstalk to a focus error due to off-track does not occur.

Furthermore, <br/> photodetector PD4-1 for tracking error signal detection, PD4-3 and PD5-1, PD
The light beam incident on 5-3 is the first hologram element 2
± 1 order light of the second hologram element 3
Since it is also the next light, when a wavelength variation occurs in the laser diode 9, the beam spot moves in a direction in which the effects of the first and second hologram elements 2 and 3 are added. In the case of this embodiment, as shown by the arrow I in FIG. 5, the moving direction by the first hologram element 2 (the direction shown by the arrow G) and the moving direction by the second hologram element 3 (the arrow H)
), That is, the beam spot moves in a diagonal direction shifted by 45 °.
As is apparent from FIG. 5, the photodetectors PD4-1, PD4-3 and PD5-1, PD5-1, PD4-1 for tracking error signal detection.
Since the division line 5-3 extends in the moving direction of these beam spots, that is, in the diagonal direction, even if the laser diode 9 has a wavelength variation, no track offset occurs.

In the apparatus of this embodiment, the focusing error signal FE is

FE = ｛(PD4−2a) + (PD4−2c) + (PD5−2b)｝ − ｛(PD5−2a) + (PD5−2c) + (PD4−2b) . The tracking error signal TE is

[Equation 4] TE ₁ = ｛(PD4-3a) + (PD4-1b)｝ − ｛(PD4-3b) + (PD4-1a)｝, TE ₂ = ｛(PD5-3a) + (PD5-1b) } - {(PD5-1a) + ( PD5-3b)} obtained by calculating the TE = TE ₁ + TE ₂ when.

FIG. 6 shows a second embodiment of the information reading apparatus of the present invention.
It is a figure showing composition of an example. This example differs from the first example in that the first hologram element 12 is provided on the emission end face of the beam splitter 16 and the second hologram element 13 is formed on the surface of the cover glass 11 of the photodetector. The same operation and effect as those of the first embodiment can be obtained.
In the second embodiment, since it is not necessary to provide a hologram substrate separately, it is possible to provide a more compact apparatus and to reduce the manufacturing cost.

FIG. 7 shows a third embodiment of the information reading apparatus according to the present invention.
FIG. 8 is a diagram showing the overall configuration of the embodiment, and FIG. 8 is a diagram showing the arrangement of the photodetectors of the third embodiment. In the third embodiment, six photodetectors PD24-1, PD24-2,
PD24-3 and PD25-1, PD25-2, PD2
5-3 is arranged as shown in FIG. A step portion 21a is provided on the surface of the semiconductor substrate 21, and the reflection mirror 26 is formed here by giving a 45 ° inclination to the step portion. A laser diode 29 is mounted on the semiconductor substrate 21 so as to face the reflection mirror 26 so that the photodetector and the laser diode are integrated. In the third embodiment, since a beam splitter is not required,
An even more compact device can be provided, and manufacturing costs can be reduced.

[0021]

As described above, according to the optical information reading apparatus of the present invention, a focus offset and a track offset do not occur even when the wavelength of the light source fluctuates.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a first embodiment of an optical information reading apparatus of the present invention.

FIG. 2 is a diagram showing an arrangement of a hologram element of the first embodiment of the optical information reading apparatus of the present invention.

FIG. 3 is a diagram showing an arrangement of a hologram element of the first embodiment of the optical information reading apparatus of the present invention.

FIG. 4 is a diagram showing an arrangement of a hologram element and a photodetector in a first embodiment of the optical information reading apparatus of the present invention.

FIG. 5 is a diagram showing an arrangement of a photodetector and a moving direction of a light beam spot in the first embodiment of the optical information reading apparatus of the present invention.

FIG. 6 is a diagram showing the overall configuration of a second embodiment of the optical information reading apparatus of the present invention.

FIG. 7 is a diagram showing an overall configuration of a third embodiment of the optical information reading apparatus of the present invention.

FIG. 8 is a diagram showing an arrangement of a photodetector of a third embodiment of the optical information reading apparatus of the present invention.

FIG. 9 is a diagram showing a configuration of a conventional optical information reading device.

10 is a diagram showing an arrangement of a hologram element and a photodetector of the conventional device shown in FIG.

FIG. 11 is a diagram for explaining a principle of detecting a focusing error of the conventional device shown in FIG. 9;

FIG. 12 is a diagram for explaining a principle of detecting a focusing error of the conventional device shown in FIG. 9;

13 is a diagram for explaining the principle of detecting a focusing error of the conventional device shown in FIG.

FIG. 14 is a diagram showing the overall configuration of another conventional optical information reading apparatus.

FIG. 15 is a diagram for explaining a principle of detecting a tracking error of a conventional device.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 first hologram element 3 second hologram element 4, 5 photodetector 6 beam splitter 7 optical disk 8 objective lens 9 laser diode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 7/09 G11B 7/095 G11B 7/135

Claims (1)

(57) [Claims] 1. A hologram element comprising: a light source; an objective lens; first and second hologram elements; and a plurality of light detection elements divided into at least two or more regions. but are arranged so that each grating directions are not parallel to each other, the diffracted return light reflected by the emitted information recording medium from said light source in said first and second holographic <br/> grams elements An optical information reading device configured to be incident on the plurality of light detection elements after being separated, wherein diffraction of both the first and second hologram elements among the plurality of light detection elements is performed. The dividing line of the photodetector that receives the light beam deflected by the first direction and the second direction is different from both the lattice direction of the first hologram element and the lattice direction of the second hologram element . Holo
Waves determined based on the relationship between lattice directions of Gram elements
Extend in the direction of movement of the beam spot during long fluctuations
Tracking error based on the output of the photodetector.
The dividing line of the photodetector configured to detect a signal and receiving the light beam deflected by diffraction of only the first hologram element is in a direction orthogonal to the lattice direction of the first hologram element , and Said
The direction perpendicular to the extending direction of the groove provided on the information recording medium
In the same direction based on the output of the photodetector.
An optical information reading device configured to detect a caching error signal .