JPH034976B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to magneto-optic heads.

In recent years, information recorded in perpendicularly magnetized films has been
A method of optical reproduction using laser light such as a laser, Ar laser, or semiconductor laser, that is,
Research and development of magneto-optical reproduction methods is actively underway.

When this method is used in devices such as magnetic disks, magnetic drums, and magnetic tapes, the distance between the tip of the condensing lens, which is the reproducing head, and the recording element is about 1 mm, compared to the conventional reproducing method using a magnetic head. This has great advantages in that the influence of dust is small and there is no need to worry about head crushing.

Generally, optical memory devices capable of high-density recording have a bit size of about 1 μm, so it is necessary to focus the laser beam narrowly. This point is also the same in the magneto-optical reproduction method, and therefore a servo system is required to prevent the laser beam from deviating from the bit. FIG. 1 is an explanatory diagram of the configuration of a conventional magneto-optical head section. The beam emitted from laser 1 is passed through condensing lens 2 and polarizer 3.
The beam passes through the diffraction grating 4 into three beams, passes through a convex lens 5 , a reflecting mirror 6 , a half mirror 7 , and a condensing lens 8 and is combined onto a recording medium 9 . The reflected light from the recording medium 9 passes through the half mirror 7
one passes through an analyzer 11 and enters a light receiver 12, and the other passes through an analyzer 13 and a cylindrical lens 14 and enters light receivers 15, 16, and 17. The photoreceiver 16 has a four-division element, and thereby obtains a focus error signal. Also, a track error signal is obtained by the photodetectors 15 and 17. Further, information signals are extracted by the light receiver 12 and the light receiver 16. 18 is an amplifier for information signals, 19 is an amplifier for track error signals, and 20 is an amplifier for focus error signals.

The above-mentioned magneto-optical device uses the Kerr effect to extract information signals, but since the signal obtained by the Kerr effect is generally small, the amount of light after passing through the analyzer 13 is very small, so the accuracy is higher than this. It is often quite difficult to extract focus error signals and track error signals. On the other hand, when the above-mentioned conventional structure is used, another drawback is that the head has a large number of parts.

The present invention has been made in view of the above conventional points, and uses a polarizing beam splitter in the analyzer of a magneto-optical head to increase the amount of light output for extracting focus error signals and track error signals. , and to simplify the head structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a magneto-optical head according to the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram of one embodiment of the magneto-optical head according to the present invention. In this figure, the same parts as in FIG. 1 are designated by the same reference numerals. The beam emitted from the laser 1 passes through a condensing lens 2 , a half mirror 7 , and a condensing lens 8 and is projected onto a recording medium 9 made of a perpendicularly magnetized film. pass through. By this polarizing beam splitter 21, the information signal component of the light whose polarization plane has been rotated by the Kerr effect in the recording medium 9 enters the light receiver (second light receiver) 12, and the other light passes through the cylindrical lens 14. The light enters the four-part light receiver (first light receiver) 16. The information signal is basically taken out from the photoreceiver 12, and the focus error signal and the track error signal are taken out from the quadrant photoreceiver 16.
taken out.

Next, the function of the polarizing beam splitter 21 will be explained using the vector diagram shown in FIG. The laser beam enters as polarized light and is reflected by the recording medium, resulting in emitted light with a rotated plane of polarization due to the Kerr effect.
At this time, if the magnetization direction in the recording medium is reversed, the Kerr rotation direction is reversed, and the rotation direction of this polarization plane becomes information. In FIG. 3, the reflected light may be polarized light _S1 with the Kerr rotation angle rotated by α due to the difference in the magnetization direction of the recording medium, or polarized light _S2 with the Kerr rotation rotated by one α. S polarizing beam splitter
If set in the direction, S ₁ ' and S _{2 '} , which are S direction components of S ₁ and S ₂ , are obtained in the light receiver 12. Therefore, a signal waveform as shown in the waveform diagram of FIG. 4 is obtained as an optical output. On the other hand, as the P direction component of S ₁ and S ₂
S ₁ '' and S ₂ '' are obtained, and these S ₁ '' and S ₂ '' are detected by the 4-split photoreceiver 16, thereby obtaining focus error and track error signals. As shown in Figure 3, S ₁ '' and S ₂ '' have higher intensities than S ₁ ' and S ₂ ', and therefore focus error and track error signals with good S/N ratio can be obtained. be. If the intensity of the signal from the photoreceiver 16 is adjusted by an attenuator 22 as shown in FIG. Other noise components such as changes in laser light intensity can be removed, and the S/N ratio of the information signal can be improved. or,
A track error signal amplifier 19 and a focus error signal amplifier 20 amplify the output of the four-split photodetector 16. Incidentally, these constitute the error signal generating means.

As explained above, according to the present invention, by using a polarizing beam splitter in the analyzer of a magneto-optical head, the number of parts in the head can be greatly reduced, thereby making the head smaller and lighter. It becomes possible to force them. If a semiconductor laser is used as the laser, it becomes possible to further reduce the size and weight.
Furthermore, since the optical intensity for the focus error signal and the track error signal can be increased, the S/N ratio can be improved and the accuracy of the servo system can be improved.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the configuration of a conventional magneto-optical head.
FIG. 2 is an explanatory diagram of the configuration of the magneto-optical head of the present invention;
FIG. 3 shows a vector diagram, and FIG. 4 shows a signal waveform diagram. In the figure, 1: laser, 2: condensing lens, 7: half mirror, 8: condensing lens, 9: recording medium, 10: light receiver, 14: cylindrical lens, 16: light receiver, 18: information signal increaser. 19: Track error signal amplifier, 20: Focus error signal amplifier, 21: Polarizing beam splitter.

Claims (1)

[Scope of Claims] 1. A magneto-optical head that reproduces information recorded on a recording medium of a perpendicularly magnetized film using the Kerr effect, which includes a polarized beam splitter into which a beam whose polarization plane has been rotated after being reflected by the recording medium is incident. a first light receiver that receives the first light via the polarizing beam splitter; and an error signal generator that generates a focus error signal and a track error signal based on the output of the first light receiver. means; a second light receiver for receiving the second light via the polarizing beam splitter; and generating an information signal by the output of the second light receiver; and information signal generation means for removing noise components by differential outputs of the first light receiver and the first light receiver, the light intensity of the first light receiver being higher than that of the second light receiver. A magneto-optical head, characterized in that the orientation of the polarizing beam splitter is set so that the polarizing beam splitter becomes stronger.