JPH02187929A - Optical head - Google Patents

Abstract

PURPOSE:To focus an optical system of an optical head by a simple and small- sized constitution by separating and focusing a laser beam from a storage medium to a first and a second laser beams by using a first and a second laser beams whose wavelength is different. CONSTITUTION:A first and a second laser beams whose wavelength is different from semiconductor lasers 5, 15 of an optical head are synthesized by a dichroic lens 11, passes through a beam splitter 13, etc. and irradiates an optical disk 1. A reflected laser beam from the disk 1 generated thereby transmits through the beam splitter 13 and separated and focused to a first and a second laser beams by a dichroic prism 23 and detected by photodetectors 27A, 27B, respectively, and detection outputs are compared. A distance from detection lenses 25A, 25B of the detectors 27A, 27B, respectively is set to a prescribed value in advance, and when a first and a second lasers are focused on the disk 1, spot images by a first and a second laser beams whose wave length is different and whose dispersion power is different become the same size. By such simple and small-sized constitution which requires no special optical system, focusing of an optical system of the optical head is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical head that emits a laser beam to an information storage medium in order to store or read information on the information storage medium.

<Prior Art> Optical disks, for example, are widely used as media for storing large amounts of information. In recent years, various types of optical discs have been proposed, including not only a reproduction-only type that only reproduces information, but also a write-once type that allows additional storage, and a rewritable type that allows information to be repeatedly stored and erased. Tracks are formed on such optical discs, and many minute bits for storing data information are formed on these tracks. In order to store or reproduce data information based on these minute bits, a spot-shaped laser beam is irradiated from an optical head.

Incidentally, an optical disk may cause surface wobbling as it rotates, and even when this wobbling occurs, it is necessary to focus the spot-shaped laser beam to accurately irradiate the laser beam onto the track. ing.

FIG. 7 is a configuration diagram showing a conventional optical head and its peripheral equipment.
3 is placed. Laser light 107 emitted from semiconductor laser 105 is converted into parallel light by collimator lens 109 and then directed to beam splitter 113 . The laser beam transmitted through this beam splitter 113 is transmitted through the objective lens 1.
The light that is irradiated onto the optical disc 101 via the optical disc 101 and further reflected from the optical disc 101 is transmitted through the objective lens ] 21
to the beam splitter 113 via.

The laser beam reflected by this beam splitter 113 is 1/
The light is applied to a beam splitter 123 via a two-wavelength plate 114 and lenses 120 and 122.

A portion of the light separated by the beam splitter 123 is detected by a detector 127, and a tracking signal, that is, an error signal in the radial direction of the optical disc 101 is extracted from an operational amplifier 129.

In addition, the other part of the laser beam separated by the beam splitter 123 passes through the cylindrical lens 126 to the detector 1.
Given to 31. Based on the detection information from this detector 131, a focus error signal is generated from the optical disc 1.
An error signal related to the distance between the signal plane of 01 and the objective lens 121 of the optical head 103 is extracted.

(Problem to be Solved by the Invention) However, in the conventional example shown in FIG. 7, the cylindrical lens 126 is used when focusing the laser beam on the detector 131, so that the cross section is adjusted to be circular in the focused state. Therefore, such optical adjustment required a lot of effort.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical head that can reduce costs and miniaturize the device with a simple configuration (without using a special optical system such as a cylindrical lens). purpose.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, an optical head provided by the present invention includes a first light emitting source that generates a first laser beam, and a first light emitting source that generates a first laser beam. a second light emitting source that generates a second laser light having a different wavelength from the first laser light emitted from the source; and first and second laser light emitted from the first and second light emitting sources. an optical means for guiding a laser beam to an information storage medium, a separation means for separating a first laser beam and a second laser beam from the information storage medium, and a first laser beam separated by the separation means. a first optical means for focusing the first laser beam; a first detection means for detecting the beam diameter of the first laser beam focused by the first optical means; and a second laser beam separated by the N1 means. a second optical means for converging light and having a dispersion power for different wavelengths different from that of the first optical means; and a second optical means for detecting a beam diameter of a second laser beam focused by the second optical means. and means for detecting the position of the optical means with respect to the information storage medium by comparing the detection results detected by the first and second detection means.

(Function) The present invention guides a first laser beam and a second laser beam having a different wavelength from the first laser beam to an information storage medium by optical means. Next, the first laser beam reflected from this information storage medium is separated by a separating means, and the separated first laser beam is focused toward a first detecting means using a first optical means. and detect the diameter of the luminous flux. Further, the second laser beam is focused onto a second detection means using a second optical means having a dispersion power for different wavelengths different from that of the first optical means, and the diameter of the beam is detected. Further, the optical means can detect the detection result obtained from the first laser beam and the second laser beam by both the first detection means and the second detection means, for example, by comparing the luminous flux diameter. It is possible to accurately detect the position of the information storage medium with respect to the information storage medium.

(Embodiment) An embodiment of the present invention will be described in detail below with reference to the drawings.

First, the configuration will be explained with reference to FIG.

The optical disc 1 has a recording layer 1a in which information is stored, and a disc substrate 1b made of a transparent material such as glass or polycarbonate. Further, in the storage layer 1a formed on the disk cloud plate 1b, tracks as guide grooves are formed at intervals of 1.6 μm, and a large number of bits as data information are formed on these tracks. .

An optical head 3 is arranged below the optical disc 1. This optical head 3 has a semiconductor laser 5. The semiconductor laser 5 is a first laser beam 7 for emitting a first laser beam 7.
The wavelength λ1 of this laser beam 7 is, for example, 8
It is set to 30/In. The collimator lens 9 converts the incident laser beam 7 into parallel light and outputs it to the dichroic prism 11 .

Further, the optical head 3 has a semiconductor laser 15. The semiconductor laser 15 is a second light source for emitting a second laser beam 17, and the wavelength λ2 of this laser beam 17 is set to, for example, 650/I11. The collimator lens 19 converts the incident laser beam 17 into parallel light and outputs it to the dichroic prism 11 .

The dichroic prism 11 combines the laser beam 7 incident from the collimator lens 9 and the laser beam 17 incident from the collimator lens 19, and outputs the combined laser beam to the beam splitter 13.

The beam splitter 13 outputs the combined laser light to the objective lens 21. The objective lens 21 converges the incident laser light and irradiates the storage layer 1a of the optical disc 1 with a beam of laser light.

The laser beam focused by the objective lens 21 reflects the storage H1a of the optical disk 1 and returns to the objective lens 21.
and is applied to the beam splitter 13. Beam splitter 13 outputs the reflected light from storage layer 1a to dichroic prism 23.

The dichroic prism 23 separates the laser beam with the wavelength λ1 and the laser beam with the wavelength λ2 included in the reflected light incident from the optical disk 1, outputs the laser beam blind to the wavelength λ to the detection lens 25A, and outputs the laser beam with the wavelength λ2. The light is output to the detection lens 25B.

The detection lens 25A, which is the first optical means, passes the laser beam LA of wavelength λ1 to the photodetector 2, which is the first detection means.
Focus towards 7A. Similarly, the detection lens 25B, which is the second optical means, focuses the laser beam LB having the wavelength λ2 toward the photodetector 27B, which is the second detection means. The detection lens 25Δ and the detection lens 25B are each made of the same material, and are formed to have a large optical property of dispersing light for each wavelength (hereinafter referred to as dispersion ability). Further, when the first and second laser beams are properly focused and irradiated onto the storage layer 1a of the optical disc 1, the photodetector 27A
The photodetectors 27A and 27B are arranged at positions such that the diameters of the light beams of both the photodetectors 27A and 27B are equal.

Next, the operation will be explained with reference to FIG.

Figure 2 shows the photodetector 2 passing through the detection lens 25A.
Laser light LA focused toward 7△ and detection lens 25
The laser beam LB passing through B and converging toward the photodetector 27B is schematically shown on the same optical axis.

As shown in FIG. 2, the laser beam LA is transmitted to the detection lens 25A
and when the laser beam LB passes through the detection lens 25B, the detection lens 25A and the detection lens 2
It has the same optical characteristics as 5B. However, since the dispersion power is large, so-called chromatic aberration occurs due to a difference in refractive index due to a difference in wavelength between the laser light LA and the laser light 1B. That is, the laser beam LA having a good wavelength is imaged at a position farther from the detection lens 25A than the laser beam LB. Therefore, if the photodetector 27A127B is placed at a distance La from the detection lenses 25A and 25B, that is, at a position Pa near the imaging point of the laser beam LB, the laser beam will be emitted as shown in FIGS. L.A.
The focusing diameter GA is larger than the focusing diameter GB due to the laser beam LB. Also, the distance from the detection lenses 25A and 25B is 1!
When the photodetector 27A127B is placed at a position tLb (1-a<Lb), that is, at a position pb intermediate between the imaging points of both the laser beams LA and 18, as shown in FIG.
) and (D), the focusing diameter G by the laser beam LA
A and the focused diameter GB of the laser beam LB have the same size. Furthermore, the distance Lc from the detection lenses 25A and 25B
When the photodetectors 27A and 27B are placed at positions pc that are separated by (Lc > Lb), that is, near the imaging point of the laser beam LA, as shown in FIGS. 3(E) and 3(F).
As shown in , the focusing diameter GA of the laser beam mA is smaller than the focusing diameter LB of the laser beam LB.

From the above, the photodetector 27A is placed at a distance MLm from the detection lens 25A, and the photodetector 27B is placed at a distance 1b from the detection lens 25B. As a result, if the first and second laser beams are properly focused on the recording layer 1a of the optical disc 1, that is, the objective lens 2
1 is in the focused position with respect to the optical disc 1, each photodetector area of the photodetector 27A, 27B has a light beam having the same radius as shown in FIGS. 3(C) and 3(D). diameter, i.e. beam spot GA, G
B is formed. To explain in more detail, the radar light, that is, the light beams LA and 1B with different wavelengths are detected by the detection lens 25A.
and 25B, the light beams are separated into light beams LA and LB of each wavelength, and their focal positions are shifted.

Therefore, a relatively short wavelength light beam LB that has been once focused and diverged again is irradiated onto the photodetection area 27BB of the photodetector 27B, and a relatively short wavelength light beam LB that is being focused is irradiated onto the other photodetection area 27AA. A light beam with a long wavelength is irradiated. In other words, the detection surfaces of the photodetectors 27A and 27B, that is, the installation positions of the respective detection areas 27AA and 278B, are located at intermediate positions between the focal point of the light beam LA and the focal point of the light beam LB. It is preset perpendicular to the optical path of the beam.

By arranging the photodetectors 27A and 27B at such positions, the shape of the piece spot of the light beam irradiated when out of focus is changed as follows. optical disc 1
When the position of the objective lens 21 with respect to the optical disk moves away from the in-focus position, the light beam emitted from the optical disk is focused slightly more than when it is in focus. Therefore, the photodetectors 27A, 27
Images as shown in FIGS. 3(E) and 3(F) are formed at B. That is, a circular beam spot GA with a smaller diameter than when focused is focused on the photodetection area 27AA, and a circular beam spot GA with a larger diameter than when focused is focused on the other photodetection area 27B1°2782. Beam spot QB is focused.

On the other hand, when the objective lens 21 is closer to the optical disc 1 than the in-focus position, the light beam emitted from the optical disc becomes slightly more divergent than when it is in focus. Therefore, images as shown in FIGS. 3(Δ) and 3(B) are formed on the photodetectors 27A and 27B. 1, that is, the photodetection area 27
A circular beam spot GA with a larger diameter than when focused is focused on AA, and circular beam spots 1 to GB with a smaller diameter than when focused are focused on the other photodetection area 278B.
is focused.

In this invention, a shift in the focus state can be detected by detecting changes in the shape of the beam spot during in-focus and out-of-focus states as described above. FIG. 8 shows a photodetector 17 according to an embodiment of the present invention capable of detecting a shift in focus state, a tracking state, and an information reproduction signal.

In FIG. 8, the photodetectors 27A and 27B are schematically connected to a photodetection area 27A to be irradiated with the first light beam LA.
Δ and a photodetection area 278B to be irradiated with the second light beam LB, each preferably having the same structure. Each photodetection area 27AA, 278B is separated into four areas by a non-detection area, and two approximately semicircular areas formed in the center of the separated areas are used to detect the light beam. . To be more specific, each of the detectors 27A and 27B is separated by a circular division 1132 as a non-detection area formed with a specific radius approximately at the center thereof, and at approximately the center thereof in the lateral direction (Yh direction). It is further separated vertically by an extending dividing line 35. The diameter of the circular dividing line 32 is preset to match the diameter of the beam spot formed during focusing described above.

Furthermore, the dividing line 35 is set in advance to be parallel to the direction in which the shadow of the group diffracted and projected from the optical disc 1 is projected (Y direction). Note that the photodetector 27A,
Among the separated areas of 27B, the photodetection area 27A1.27 is provided within the circular dividing line 32 at the center thereof.
By processing signals from the light beams irradiated onto A2 and 2781.27B2, servo signals and information reproduction signals for controlling the focus state and tracking state of the light beams are generated. Changes in the shape of the beam spot when the light beam irradiated to the photodetector described above is focused and unfocused are shown in FIGS. 8(A) to 8(F).

When the objective lens 21 is positioned at the in-focus position with respect to the optical disc 1, there is a
) and (D) are formed. That is, a beam spot GA having approximately the same cross-sectional diameter as the circular dividing line 32 is formed on the detection areas 27A1 and 27A2 of the photodetector. Also photo detection area 2781.278
A beam spot GB having approximately the same cross-sectional diameter as the circular dividing line 32 is formed on the circular dividing line 32 . In other words, if the detection outputs of the photodetection areas 27Δ1.27A2.27B1.27B2 are respectively represented by ■ to ■, then the force-twisting error signal (F , E signal) is zero, that is, F-E (Forcing error signal) - ((■+■)-(■+■)) =
It is irradiated to satisfy the condition of O.

When the detection signal of the light beam at the time of focusing is set as above, when the objective lens 21 moves away from the in-focus position with respect to the optical disc, the photodetector 17A.

An image as shown in FIGS. 8(E) and 8(F) is formed on 17B. In other words, on the photodetection #4 area 27AA, there is a circular beam spot G with a smaller diameter than when focused.
A is formed, and a circular beam spot GB having a larger diameter than when focused is formed on the other photodetection area 27BB. When a light beam having a cross-sectional shape larger than the diameter of the circular dividing line 32 is irradiated, a portion of the light beam is irradiated onto a non-detection area outside the circular dividing line 32. Therefore, the light beam L irradiated onto the photodetection area 27A1.27A2
A and the light beam LB irradiated onto the photodetection area 27B1.2782 has F-E (focusing error signal).
There is a relationship of =((■+■)-(■+■))>0.

On the other hand, when the objective lens 21 approaches the optical disc closer than the in-focus position, the image shown in FIG. 8 (A
) and (8) are formed. That is, a circular beam spot GA with a larger diameter than when focused is formed on the photodetection area 27AA, and a circular beam spot GB with a smaller diameter than when focused is formed on the other photodetector 1tA278B. It is formed. When a light beam having a cross-sectional shape larger than the diameter of the circular dividing line 32 is irradiated, a portion of the light beam is irradiated onto a non-detection area outside the circular dividing line 32. Therefore, the photodetection area 27A1.
The light beam LA irradiated to 27A2 and the photodetection area 27
B1.27The light beam LB irradiated to B2 has F-E.
(Forcing error signal) = ((■ + ■) - (■
10 ■)) There is a relationship of 0. Figure 8 (A) to Figure 8 (
According to the photodetector having the structure described in F), a focus shift is detected as well as a tracking shift.

4 to 6 show the light detection g of the photodetector 17 that can be used in the multi-beam optical head focus detection method of the present invention.
AI11! A number of examples are shown showing the shape of.

In FIGS. 4 to 6, elements designated by the same reference numerals have the same function.

For example, the photodetection area 27AA (278B) shown in FIG.
>, the detection region inside the circular dividing line 45 as a non-detecting region is further separated by a circular division $147. Therefore, focus detection is possible by determining, for example, the case where the light beam is irradiated on the area sandwiched between the circular dividing line 45 and the circular dividing line 47 as the in-focus state. That is, when the light beam is incident outside the circular dividing line 45 or when the area between the circular dividing line 45 and the circular dividing line 47 is not irradiated with the light beam, the objective lens 21 is driven. The focal position of the light beam is controlled with respect to the optical disc 1 by feeding back to the circuit. The structure of the photodetection area described in FIGS. 5 and 6 is also detected in a similar manner. Alternatively, the photodetection regions of the photodetection member shown in FIG. 4(A) are simply separated by a circular dividing line 45 determined to match the diameter of the beam spot at the time of focusing. Therefore, by providing this detection pattern for each light beam and feeding back the difference signal between the intensities of the light beams detected within each circular dividing line 45 to the driving circuit of the objective lens 21, the focal position of the light beam can be adjusted to the optical disk. 1. Furthermore, the fifth
The light beams irradiated onto the detection areas shown in Figures (A) and 6(A) are processed in a manner similar to that of Figure 4(A).

As described above, since the embodiment shown in FIG. 1 eliminates the need for special optical elements such as cylindrical lenses, it is possible to greatly simplify the optical adjustment work in the assembly process of the optical head.

[Effects of the Invention] As explained above, according to the present invention, when the first laser beam and the second laser beam reflected from the optical disk are focused on the first detection means and the second detection means, , causing chromatic aberration due to the difference in wavelength between the first laser beam and the second laser beam, and when the first and second laser beams are properly focused on the optical disk, the first detection means and Since the first and second detection means are arranged at positions where the diameters of the light fluxes of both the light beams and the second detection means are, for example, equal, it is possible to have a simple configuration without using a special optical system. Therefore, it is possible to reduce costs and downsize the device.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment according to the present invention, and FIG.
Figures 3 and 4 are explanatory diagrams showing the shape of the light beam in the photodetector. Figure 5 is an explanatory diagram when the shape of the image in the photodetector is square. Figure 6 is an explanatory diagram showing the shape of the image in the photodetector. An explanatory diagram when the shape of the elephant in the photodetector is rectangular, FIG. 7 is a configuration diagram of a conventional example, and FIG. 8 is an explanatory diagram of a photodetector according to the present invention. 5.15...Semiconductor laser 7...First laser beam 17...Second laser beam 25A, 25B...Detection lenses 27A, 27B...Photodetector (photodetector) FIG. Figure 3 (A) Figure 3 (C) Figure 3 (E) Figure 3 (B) Figure 3 (D) Figure 3 (F) Figure (A) Figure 5 (A) Figure 6 ( A) Figure 4 (B) Figure 5 (B) Figure 6 (B)

Claims (1)

[Scope of Claims] A first light emitting source that generates a first laser beam, and a second laser beam that generates a second laser beam that has a different wavelength from the first laser beam generated from the first light source. 2 light emitting sources; and first and second light emitting sources emitted from the first and second light emitting sources.
an optical means for guiding a laser beam to an information storage medium; a separation means for separating a first laser beam and a second laser beam from the information storage medium; and a first laser beam separated by the separation means. a first optical means for focusing the first laser beam; a first detection means for detecting the beam diameter of the first laser beam focused by the first optical means; and a second laser beam separated by the separation means. a second optical means having a dispersion power for different wavelengths different from that of the first optical means, and a second optical means for detecting a beam diameter of a second laser beam focused by the second optical means. An optical system comprising: a detection means; and means for detecting the position of the optical means with respect to the information storage medium by comparing the detection results detected by the first and second detection means. head.