JPH0457231A - Optical head - Google Patents

Abstract

PURPOSE:To prevent a beam from leaking into another reproducing system by arranging a prism before a photodetector in an optical head to execute recording and reproducing by condensing the beams of various wavelengths to various positions. CONSTITUTION:A prism 14 is arranged between an image formation lens 8 and a bisected photodetector 15 so that a polarizing direction can be coincident with the direction of arranging a recording beam 11 and a reproducing beam 12 on an optical recording medium 1. Thus, the recording beam 11 and the reproducing beam 12 transmitted through the image formation lens 8 are dis persed in the dividing direction of the bisected photodetector 15 based on the difference of the wavelengths by the prism 14 and in this case, by arranging the bisected photodetector 15 so as to condense the dispersed recording beam 11 and reproducing beam 12 on respectively separate elements, a regenerative signal can be obtained without any influence of the recording beam 11. Thus, the regenerative signal can be obtained without the leakage of the other beam.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical head for an apparatus for optically recording or reproducing information.

(Prior Art) Conventionally, there have been optical recording and reproducing devices, such as optical disk devices, which improve data transfer speed by simultaneously recording and reproducing information.

FIG. 2 shows an example of a conventional optical head of this type of optical disk device. In the figure, 1 is an optical recording medium, 2 is a semiconductor laser for a recording beam, 3 is a semiconductor laser for a reproduction beam, and 4 is a semiconductor laser for a reproduction beam. is a photodetector, 5 is a dichromic mirror, 6 is a beam splitter, 7 is an objective lens, 8 is an imaging lens, 9,
10 is a collimator lens.

In the above configuration, the recording beam 11 emitted from the semiconductor laser 2 is focused onto the optical recording medium 1 through the collimator lens 9, the dichromic mirror 5, and the objective lens 7, and information is recorded.

Furthermore, the reproduction beam 12 emitted from the semiconductor laser 3 is focused on the optical recording medium 1 through the collimator lens 10, the beam splitter 6, the dichromic mirror 5, and the objective lens 7, and changes in reflectance are recorded on the medium 1. The beam is reflected after undergoing intensity modulation due to the beam intensity or rotation of the plane of polarization due to Kerr rotation.

The reflected reproduction beam 12 passes through an objective lens 7, a dichromic mirror 5, a beam splitter 6 and an imaging lens 8.
The light is focused on the photodetector 4 through the light, and the information is reproduced.

Here, the recording beam 11 and the reproduction beam 12 have different wavelengths, and the dichromic mirror 5 is set so that the transmittance for the wavelength of the reproduction beam 12 is sufficiently larger than the transmittance for the wavelength of the recording beam 11. Further, the positions of the semiconductor lasers 2 and 3 and the objective lens 7 and the angle of the dichromic mirror 5 are adjusted so that the recording beam 11 and the reproducing beam 12 are respectively focused on different positions on the optical recording medium 1.

(Problem to be Solved by the Invention) However, in the optical head, the recording beam 11 reflected by the optical recording medium 1 cannot be completely blocked by the dichromic mirror 5, and a part of it passes through the beam splitter 6 and the imaging lens 8. There was a problem in that the light leaked into the photodetector 4 and generated noise.

For example, if the recording beam wavelength in magneto-optical disk recording is 830 nm and the reproduction beam wavelength is 780 nm, the intensities of the recording beam and reproduction beam are set to about 10 mW and 1 mW, but when using an ISO standard recording medium, The intensity of the reproduced beam after reflection is about 1 to 5 μW. On the other hand, when the reflectance of the dichromic mirror is about 1%, the intensity due to the leakage of the reflected light of the recording beam is about several μW, which is about the same as that of the reproduction beam.

FIG. 3 shows the optical head of FIG. 2 in which an interference filter 13 is provided between the dichromic mirror 5 and the beam splitter 6 to transmit light with the wavelength of the reproduction beam 12 and reflect light with the wavelength of the recording beam 11. However, in reality, the reproduction beam 12
Since there is attenuation even for the wavelengths of , the intensity of the reproduced signal decreases, and the expensive interference filter increases the cost.

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the prior art, it is an object of the present invention to provide an optical head that does not require expensive parts and that does not cause beam leakage into other reproduction systems.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, as claim (1), at least two beams having different wavelengths are focused on different positions on an optical recording medium to record information. Or an optical head for reproducing, in which a prism is arranged in front of a photodetector, and as claimed in claim (2), a recording beam and a reproducing beam of different wavelengths are focused on different positions on an optical recording medium. , an optical head for simultaneously recording and reproducing information, in which a prism is arranged in front of a photodetector so that its polarization direction matches the arrangement direction of recording beams and reproduction beams on an optical recording medium; As item (3), we propose the optical head according to claim (2), wherein the polarization direction based on the rotation of the polarization plane of the reflected reproduction beam is orthogonal to the arrangement direction of the recording beam and reproduction beam on the optical recording medium. .

(Function) According to claim (1) of the present invention, the other beam reflected from the optical recording medium and leaking into the photodetector side of the - beam is transmitted to the prism arranged in front of the photodetector. Due to the wavelength dispersion of the two beams, the distance between the two beams is greatly expanded, and spatial separation becomes possible.

According to claim (2), the recording beam that is reflected from the optical recording medium and leaks into the photodetector side of the reproduction beam is converted into a reproduction beam due to wavelength dispersion of a prism placed in front of the photodetector. The distance between them is greatly increased, which allows for spatial separation.

In addition, according to claim (3), even in systems such as magneto-optical recording where the rotation of the polarization plane of the reproduced beam after reflection is detected as a change in the polarization direction, the wavelength separation of the prism allows the distance between the recording beam and the recording beam to be increased. will be greatly expanded.

(Embodiment) FIG. 1 shows a first embodiment of the optical head of the present invention, and in the figure, the same components as in FIG. 2 are denoted by the same symbols. In other words, 1 is an optical recording medium, 2 is a semiconductor laser for a recording beam, 3 is a semiconductor laser for a reproduction beam, 5 is a dichromic mirror, 6 is a beam splitter, 7 is an objective lens, 8 is an imaging lens, 9, 10 is a collimator lens, 1
1 is a recording beam, 12 is a reproduction beam, 14 is a prism,
15 is a two-split photodetector.

The prism 14 includes an imaging lens 8 and a two-split photodetector 15.
They are arranged so that the direction in which the thickness changes between them, that is, the polarization direction, coincides with the arrangement direction of the recording beam 11 and the reproducing beam 12 on the optical recording medium 1. Further, the two-split photodetector 15 is composed of a two-split photodiode, etc., and is arranged so that its splitting direction matches the polarization direction of the prism 14.

According to the above configuration, the recording beam 11 and the reproduction beam 12 that have passed through the imaging lens 8 are dispersed by the prism 14 in the dividing direction of the two-split photodetector 15 based on the difference in wavelength. , dispersed recording beam 11
If the two-split photodetector 15 is arranged so that the reproduction beam 12 and the reproduction beam 12 are respectively focused on different elements, the recording beam 11
It is possible to obtain a reproduced signal that is not affected by

Next, we will discuss the two-split photodetector 15 in the case where a prism is provided as described above and in the case where there is no prism as in the conventional case.
Let's take a specific example and compare the margins of placement.

For example, suppose that the spot interval of the recording beam 11 and the reproduction beam 12 on the optical recording medium 1 is 10 μm and the spot diameter is 1 μm, and the focal lengths of the objective lens 7 and the imaging lens 8 are 411 m and 20 m, respectively. If there is no prism, the interval between the spots focused on the two-split photodetector 15 is about 50 μm, and the spot diameter is about 5 μm. In this case, the allowance for the arrangement of the two-split photodetector 15 is (50-5)/2=22.5 (μm).

On the other hand, when a prism is provided as described above, its apex angle is 32.5°, and its deflection angle with respect to the recording beam 11 is 45.9°.
If the deflection angle with respect to the reproduction beam 12 is 46.5 degrees, the interval between the spots condensed on the two-split photodetector 15 is about 224 μm, and the spot diameter is about 17 μm. In this case, the allowance for the arrangement of the two-split photodetector 15 is (224-17)/2=103.5 (μm), which is about four times that in the case without the prism.

When a two-split photodiode is used as the two-split photodetector 15, the width of the split portion is 5 to 10 μm, so when there is no prism, the two-split photodetector 15 must be arranged with an accuracy of approximately ±5 μm. However, when there is a prism, it is sufficient to arrange it with an accuracy of approximately ±45 μm.

FIG. 4 shows a second embodiment of the optical head of the present invention, and here an example is shown in which it is applied to a magneto-optical disk device. In the figure, 21 is a magneto-optical disk, 22 is a semiconductor laser for a recording beam, 23 is a semiconductor laser for a reproduction beam, 24 is a dichromic mirror, 25, 26, 27 is a polarizing beam splitter, and 28 is a 1/4 wavelength Board, 29 is 1/
2-wavelength plate, 30 is a prism, 31 is a Wollaston prism, 32 is a 4-split photodetector for information reproduction, 33.34 is a photodetector for servo detection, 35 is an objective lens, 36 is an imaging lens, 37 .38 is a lens for servo detection, 39.
40 is a collimator lens.

The prism 30 includes an imaging lens 36 and a four-split photodetector 3.
2, so that the direction in which the thickness changes, that is, the polarization direction, coincides with the arrangement direction of the recording beam and reproduction beam on the magneto-optical disk 21. The Wollaston prism 31 is used to polarize the reproduction beam according to the rotational state of the polarization plane of the reproduction beam, that is, the direction of magnetization in the magneto-optical disk 21. The prism 3 as shown in FIG.
It is arranged so as to be orthogonal to the polarization direction due to zero. Further, the four-split photodetector 32 is composed of a four-split photodiode, etc., and is arranged so that its dividing direction coincides with the polarization direction of the prism 30 and Wollaston prism 31. Note that the photodetector 33 and lens 37 are for detecting a focus error signal by the astigmatism method,
Further, the photodetector 34 and the lens 38 are for detecting a tracking error signal by a push-pull method, and other methods such as the Foucault method or spot diameter comparison method may be used, and are not directly related to the present invention.

In the above configuration, the recording beam 41 emitted from the semiconductor laser 22 passes through the collimator lens 39, the polarizing beam splitter 25, the 1/4 wavelength plate 28, and the dichromic mirror 2.
4 and an objective lens 35 onto the magneto-optical disk 21, and information is recorded together with a separately applied magnetic field. Furthermore, the reproduction beam 42 emitted from the semiconductor laser 23 is transmitted through a collimator lens 40 and a polarizing beam splitter 2.
7°26, dichromic mirror 24 and objective lens 3
5, the light is focused on the magneto-optical disk 21, and is reflected after the plane of polarization is rotated by the magnetization direction of the disk 21. The reflected reproduction beam 42 passes through an objective lens 35, a dichromic mirror 24 and a polarizing beam splitter 26.
172 wavelength plate 29, where the plane of polarization is 4.
The light is rotated by 5 degrees and further polarized by the Wollaston prism 31 according to its polarization plane as described above. The polarized reproduction beam 42 enters the prism 30 through the imaging lens 36, where it receives polarized light corresponding to its wavelength and is focused onto two elements of the 4-split photodetector 32, where information is reproduced. It is done.

On the other hand, the recording beam 41 reflected by the magneto-optical disk 21
A part of the beam passes through the dichromic mirror 24, is polarized by the polarizing beam splitter 26, the 1/2 wavelength plate 29 and the Wollaston prism 31 in the same way as the reproduction beam 42, and is further polarized by the prism 30. However, since its wavelength is different from that of the reproduction beam 42, it will be focused on the other two elements of the 4-split photodetector 32.

Therefore, of the four-split photodetector 32, the reproduction beam 4
By differentially detecting the outputs of the two elements on which only the beam 2 is focused, information can be reproduced without the influence of leakage beams caused by the recording beam 41.

In the first and second embodiments, the leaked recording beam was focused on a two-split photodetector or a four-split photodetector, but
The recording beam may be focused on the outside of a normal photodetector and a two-split photodetector, respectively.
Alternatively, a light shielding plate may be provided in front of them to cut the recording beam.

In addition, in the explanation so far, we have described the case where one recording beam and one reproducing beam are used, but it is also possible to use two or more of either or both of these beams, or even use other beams. Applicable. Moreover, it is effective not only for magneto-optical recording but also for all optical recording using a light spot, such as optical recording using a phase change medium.

(Effects of the Invention) As explained above, according to claim (1) of the present invention, at least two beams with different wavelengths are focused on different positions on an optical recording medium to record or reproduce information. Because the prism is placed in front of the photodetector in the optical head,
The interval between at least two beams reflected from the optical recording medium can be greatly expanded by the wavelength dispersion of the prism, thereby making it possible to obtain a reproduced signal without leakage of other beams.

According to claim (2) of the present invention, in an optical head that simultaneously records and reproduces information by converging recording beams and reproduction beams with different wavelengths at different positions on an optical recording medium, a photodetector is used. Since a prism is placed in front of the optical recording medium so that its polarization direction matches the alignment direction of the recording beam and reproduction beam on the optical recording medium, the distance between the recording beam and reproduction beam reflected from the optical recording medium can be adjusted by the wavelength dispersion of the prism. It is possible to widen the beam greatly, thereby making it possible to obtain a reproduced signal without leakage of the recording beam.

Further, according to claim (3) of the present invention, since the polarization direction based on the rotation of the polarization plane of the reproduction beam after reflection is made orthogonal to the arrangement direction of the recording beam and reproduction beam on the optical recording medium, magneto-optical recording etc., it is possible to obtain a reproduced signal without recording beam leakage.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing a first embodiment of the optical head of the present invention, FIG. 2 is a configuration diagram showing an example of a conventional optical head, and FIG. 3 is a configuration diagram showing another example of the conventional optical head. 4 are block diagrams showing a second embodiment of the optical head of the present invention, and FIG. 5 is an explanatory diagram showing the essential parts of FIG. 4 as viewed from above. 1... Optical recording medium, 2.3, 22.23... Semiconductor laser, 5.24-... Dichroic mirror 11°41... Recording beam, 12.42... Reproduction beam,
14.30... Prism, 15... 2-split photodetector, 21... Magneto-optical disk, 29... 1/2 wavelength plate, 31... Wollaston prism, 32... 4-split Photodetector. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (3)

[Claims] (1) An optical head that records or reproduces information by focusing at least two beams with different wavelengths on different positions on an optical recording medium, characterized in that a prism is disposed in front of a photodetector. light head. (2) In an optical head that simultaneously records and reproduces information by focusing recording beams and reproduction beams with different wavelengths on different positions on an optical recording medium, a prism is placed in front of a photodetector so that its polarization direction is optically recorded. An optical head characterized in that the optical head is arranged so as to match the arrangement direction of a recording beam and a reproduction beam on a medium. (3) The optical head according to claim (2), wherein the polarization direction based on the rotation of the polarization plane of the reflected reproduction beam is perpendicular to the arrangement direction of the recording beam and reproduction beam on the optical recording medium.