JPH04121838A - Optical head - Google Patents

Abstract

PURPOSE:To prevent the leaking of a beam into other reproducing systems by disposing a light shielding plate at the conjugated imaging point of other beams exclusive of the beam which is formed before a photodetector and is to be detected or near this point. CONSTITUTION:The light shielding plate 14 is disposed at the conjugated imaging point of the recording beam before the photodetector 4 or the position which is near this point and where the conjugated image of the reproducing beam 12 is not shielded. The recording beam 11 transmitted through an imaging lens 8 is shielded by the light shielding plate 14 and is prevented from arriving at the photodetector 4 according to this constitution. On the other hand, the reproducing beam 12 arrives at the photodetector 4 without losses and, therefore, the reproduced signal having no influence by the recording beam 11 is obtd.

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. 5 is a photodetector, 5 is a dichroic 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 dichroic 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 dichroic mirror 5, and the objective lens 7. It is reflected after undergoing intensity modulation or rotation of the plane of polarization due to Kerr rotation.

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

Here, the recording beam 11 and the reproduction beam 12 have different wavelengths, and the dichroic mirror 5 is set so that its 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 dichroic 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 dichroic mirror 5, and a part of the beam passes through the beam splitter 6 and the imaging lens 8. There was a problem that the noise leaked into the detector 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 dichroic 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 that in the optical head of FIG. 2, an interference filter 13 is provided between the dichroic 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 light shielding plate is arranged at or near the conjugate imaging point of a beam other than the beam to be detected formed in front of the photodetector; )
In an optical head that records or reproduces information by condensing at least two beams with different wavelengths at different positions on an optical recording medium, the conjugate imaging point of the beam other than the beam to be detected and An optical head in which a photodetector is disposed at a position other than the vicinity thereof, and as claim (3),
In 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, a photodetector consisting of an element divided into at least two parts is used, and each We propose an optical head in which each element of a photodetector is placed at the conjugate focal point of the beam.

(Function) According to claim (1) of the present invention, other beams reflected from the optical recording medium and leaking into the photodetector side of the negative beam are removed by a light shield placed in front of the photodetector. It is blocked by the plate, which eliminates its influence.

Further, according to claim (2), the other beam reflected from the optical recording medium and leaking to the photodetector side of the negative beam is imaged at a position other than the photodetector, thereby causing the influence of is removed.

Further, according to claim (3), the other beam reflected from the optical recording medium and leaking into the photodetector side of the - beam is different from the element corresponding to the - beam of the photodetector. It is imaged onto another element, thereby eliminating its influence.

(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. That is, 1 is an optical recording medium, 2 is a semiconductor laser for recording beam, 3 is a semiconductor laser for reproduction beam, 4 is a photodetector, 5 is a dichroic mirror, 6 is a beam splitter, 7 is an objective lens, and 8 is a focusing lens. Image lens, 9 and 10 are collimator lenses, 11 is a recording beam, 12 is a reproduction beam, 1
4 is a light shielding plate.

The light shielding plate 14 is placed at or near the conjugate image formation point of the recording beam 11 in front of the photodetector 4, and at a position where it does not shield the conjugate image of the reproduction beam 12.

According to the above configuration, the recording beam 11 transmitted through the imaging lens 8 is blocked by the light shielding plate 14 and does not reach the photodetector 4, while the reproduction beam 12 reaches the photodetector 4 without loss. A reproduced signal that is not affected by the recording beam 11 can be obtained.

FIG. 4 shows a second embodiment of the optical head of the present invention, in which the same components as those in FIG. 2 are denoted by the same symbols. That is, 1 is an optical recording medium, 2 is a semiconductor laser for recording beam, 3 is a semiconductor laser for reproduction beam, 4° is a photodetector, 5 is a dichroic mirror, 6 is a beam splitter, 7 is an objective lens, and 8 is a An imaging lens, 9.10 is a collimator lens, 11 is a recording beam, and 12 is a reproduction beam.

Here, the photodetector 4' is arranged at a position excluding the conjugate image formation point of the recording beam 11 and its vicinity, and at a position where it can receive the conjugate image of the reproduction beam 12.

According to the above configuration, the recording beam 11 that has passed through the imaging lens 8 is imaged and does not reach a position away from the photodetector 4', while the reproduction beam 12 reaches the photodetector 4'' without loss. Therefore, a reproduced signal that is not affected by the recording beam 11 can be obtained.

FIG. 5 shows a third 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 recording beam (wavelength 830 nm), 23 is a semiconductor laser for reproduction beam (wavelength 780 nm), 24 is a dichroic mirror 25, 26, 27 is a polarizing beam splitter ( However, the p-polarized light transmittance is 100% and 5, respectively.
0-80%, 80-95%, S polarized light reflectance is all 10
It is 0%. ), 28 is a wavelength plate, 29 is a 1/2 wavelength plate, 30 is a Wollaston prism, 31 is a 4-split photodetector for information reproduction, 32.33 is a photodetector for servo detection, and 34 is a collector. Optical lens, 35.36 is a servo detection lens (combination of condensing lens and cylindrical lens), 37.3
8 is a collimator lens, 39 is a recording beam, and 40 is a reproduction beam.

The Wollaston prism 30 is for polarizing the reproduction beam 40 according to the rotational state of the polarization plane of the reproduction beam 40, that is, the direction of magnetization in the magneto-optical disk 21.
The polarization direction thereof is arranged to be perpendicular to the direction in which the recording beam 39 and the reproduction beam 40 are arranged by the dichroic mirror 24, etc., as shown in FIG. 6, which shows the main part of FIG. 5 viewed from above. The 4-split photodetector 31 is composed of a 4-split photodiode or the like, and is arranged so that its dividing direction coincides with the arrangement direction of the recording beam 39 and the reproducing beam 40 and the polarization direction of the Wollaston prism 30. FIG. 7 shows the above relationship in detail, showing a reproduction beam 40a formed by polarization by the Wollaston prism 30.

40b is an element 311.4 of the four elements of the 4-split photodetector 31. 312 , recording beams 39 a and 39 b formed in the same manner are transmitted to elements 313 . 314, respectively.

Note that the photodetector 32 and lens 35 are for detecting a focus error signal by the astigmatism method, and the photodetector 33 and lens 36 are for detecting a tracking error signal by the push-pull method. Other methods such as the Foucault method or the spot diameter comparison method may also be used, and are not directly related to the present invention.

In the above configuration, the recording beam 39 emitted from the semiconductor laser 22 is focused onto the magneto-optical disk 21 through the collimator lens 37, the polarizing beam splitter 25, the 1/4 wavelength plate 28, and the dichroic mirror 24, and is condensed together with a separately applied magnetic field. Record information. Furthermore, the reproduction beam 40 emitted from the semiconductor laser 23 is focused onto the magneto-optical disk 21 through the collimator lens 38, the polarizing beam splitter 27, 26, and the dichroic mirror 24, and undergoes rotation of the plane of polarization due to the magnetization direction of the disk 21. reflected. The reflected reproduction beam 40 passes through the dichroic mirror 24 and the polarizing beam splitter 2.
6, enters the 1/2 wavelength plate 29, where the plane of polarization is rotated by 456, is further polarized by the Wollaston prism 30 according to the plane of polarization as described above, and passes through the imaging lens 34 to the 4-split photodetector 31. The light is focused on two elements, and the information is reproduced.

On the other hand, the recording beam 39 reflected by the magneto-optical disk 21
A part of the beam passes through the dichroic mirror 24 and is polarized according to its polarization plane by the polarizing beam splitter 26, 1/2 wavelength plate 29 and Wollaston prism 30 in the same way as the reproduction beam 40, but as mentioned above, it is divided into four parts. The light will be focused on the other two elements of the photodetector 31.

Therefore, among the four-split photodetector 31, the reproduction beam 4
By differentially detecting the outputs of the two elements on which only 0 is focused, information can be reproduced without the influence of leakage beams caused by the recording beam 39.

In the above embodiment, the leaked recording beam was focused on the four-split photodetector, but the recording beam may be focused on the outside of the two-split photodetector, or the recording beam may be focused on the outside of the two-split photodetector. A light shielding plate may be provided in front to cut the recording beam. However, when a two-split photodiode is used as a two-split photodetector, noise is generated due to leakage current when the recording beam spot is imaged on an unobtrusive area around the light-receiving surface of the photodiode. On the other hand, if a 4-split photodiode is used as in the above embodiment, the leakage current from the recording beam to the reproduction beam element can be made smaller than in the case of the 2-split photodiode, resulting in better reproduction with less noise. I get a signal.

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. In the optical head, a light shielding plate is placed at or near the conjugate imaging point of the beam other than the beam to be detected formed in front of the photodetector, so that at least two beams reflected from the optical recording medium Of these, the undetected beams can be blocked by a light shielding plate, 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 records or reproduces information by condensing at least two beams with different wavelengths onto different positions on an optical recording medium,
Since the photodetector is placed at a position excluding the conjugate imaging point of the beam other than the beam to be detected and its vicinity, it is possible to photodetect the beam that is not detected among at least two beams reflected from the optical recording medium. The beam can be imaged at a position other than the beam, thereby making it possible to obtain a reproduced signal without leakage of other beams.

Further, according to claim (3) of the present invention, in an optical head for recording or reproducing information by focusing at least two beams having different wavelengths on different positions on an optical recording medium,
A photodetector consisting of an element divided into at least two parts is used, and each element of the photodetector is placed at the conjugate imaging point of each beam, so that at least two of the beams reflected from the optical recording medium are The beam that is not detected can be imaged on an element different from the element corresponding to the beam to be detected of the photodetector, thereby making it possible to obtain a reproduced signal without leakage of other beams.

[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 is a block diagram showing a second embodiment of the optical head of the present invention, FIG. 5 is a block diagram showing a third embodiment of the optical head of the present invention, and FIG. 6 is a block diagram showing a third embodiment of the optical head of the present invention. Explanatory diagram showing the main parts viewed from above, No. 7
The figure is a diagram showing in detail the relationship between the four-split photodetector and each beam. l... Optical recording medium, 2, 3, 22.23... Semiconductor laser, 4.4' 31... Photodetector, 5.24
... Dichroic mirror 11.39... Recording beam, 12°40... Reproduction beam, 14... Light shielding plate, 21... Magneto-optical disk, 31... Four-division photodetector. patent

Claims (3)

[Claims] (1) In 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, any beam other than the beam to be detected that is formed in front of the photodetector An optical head characterized in that a light shielding plate is disposed at or near a conjugate imaging point of another beam. (2) In an optical head that records or reproduces information by condensing at least two beams with different wavelengths onto different positions on an optical recording medium, the conjugate imaging point of a beam other than the beam to be detected. An optical head characterized in that a photodetector is arranged at a position excluding the area and the vicinity thereof. (3) In 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, a photodetector consisting of an element divided into at least two parts is used. Also, an optical head characterized in that each element of a photodetector is arranged at a conjugate imaging point of each beam.