JPS63222357A - Magneto-optical head device - Google Patents

Abstract

PURPOSE:To miniaturize and simplify a device by dividing reflected light from a recording medium into five light beams and using one of them of signal detection and using four other light beam for error detection and deflecting them in different directions. CONSTITUTION:The reflected light from a disk 8 is separated by a beam splitter 29 and is made incident on a converging lens 30 with five-divided prism. The incident light is divided into a first light beam in the center part and the radial straight line part and second - fifth light beams in the peripheral part. The first beam passes a reflection mirror 31 with slit and is divided into two by a Rochon prism 20 and is made incident on a two-divided detector 22, and the output difference between two light receiving faces of the detector 22 is a reproduced signal. Second - fifth beams are reflected on the mirror 31, and each of light beams whose light beam areas diagonal are condensed on respec tive detecting parts of six-divided detected 25. A focusing error signal and a tracking error signal are obtained from outputs. Thus, the device is miniatur ized and simplified.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magneto-optical head device for recording, reproducing, or erasing information by converging a laser beam onto a disk-shaped magneto-optical recording medium. It is.

[Conventional technology]

In magneto-optical recording, a perpendicularly magnetized film is used as the recording medium, and information is recorded and erased by reversing the direction of magnetization of the recording medium using the heat of a laser beam and a bias magnetic field. Information is reproduced using a perpendicularly magnetized film. This is done by making use of the fact that linearly polarized light is incident on the magnetic Kerr effect, and the plane of polarization of the reflected light rotates in different directions depending on the direction of magnetization of the recording medium.

FIG. 5 shows an example of the configuration of a conventional magneto-optical head device. Light emitted from a semiconductor laser 1 is collimated by a collimating lens 2, circularized by a prism 3, and then sent to a predetermined position by beam splitters 4 and 5. The light is transmitted at a transmittance, reflected by a total reflection mirror 6, and focused onto a recording medium of a disk 8 by an objective lens 7. The incident light on the recording medium is P-polarized light, but the plane of polarization of the reflected light has been rotated due to the magnetic Kerr effect, and a part of the zero-reflected light having an S-polarized component is separated by the beam splitter 5 and divided into 1/2 The plane of polarization is rotated by 45 degrees by the wave plate 9 and enters the polarization beam splitter 10.

The transmitted light and the reflected light from the polarizing beam splitter 10 are received by a signal detector 13.14 through a converging lens 11.12, respectively. 1/2 wavelength plate 9 and polarizing beam splitter 1
0 corresponds to an analyzer, and a difference in the direction of rotation of the polarization plane of the reflected light from the recording medium is detected as a difference in the output from the signal detectors 13 and 14. On the other hand, a part of the reflected light from the recording medium is separated by the beam splitter 4 and enters the beam splitter 16 through the converging lens 15. Approximately half of the light transmitted through the beam splitter 16 is blocked by a knife 17, and then received by a focus error detector 18, which is used for focus error detection using the knife method. The reflected light from the beam splitter 16 is received by a track error detector 19 and used for track error detection using a push-pull method.

As an example of miniaturizing the magneto-optical head device by reducing the number of parts in the signal detection system and error detection system compared to the conventional example shown in FIG. There is one described in 94.

The optical system on the outward path, the configuration of which is shown in FIG. 6, is the same as that shown in FIG. A portion of the reflected light from the recording medium is separated by a beam splitter 5, passes through a Rochon prism 20 and a converging lens 21, and is received by a two-split photodetector 22. The details of this part are shown in Fig. 7.The light incident on the Rochon prism 20 is divided into two polarization direction components making an angle of +45° with respect to the P polarization plane, one of which travels straight and the other with the P polarization plane. The two light beams traveling in planes forming an angle of +45° or -45° pass through the converging lens 21 and are received by the two light receiving surfaces of the two-split photodetector 22, respectively. The Rochon prism 20 corresponds to an analyzer, and the difference in output from the two light receiving surfaces of the two-split photodetector 22 becomes a reproduction signal. On the other hand, in FIG. 6, a part of the reflected light from the recording medium is separated by a beam splitter 4.5, passes through a 4-split prism converging lens 23, is reflected by a total reflection mirror 24, and is received by a 6-split photodetector 25. Ru.

The details of this part are shown in FIG. 8, in which the beam splitter 5 and total reflection mirror 24 are omitted for simplicity. Furthermore, the positional relationship between the four-split prism 26 and the convergence range 27 is reversed from that in FIG. The four-split prism 26 is divided into regions 26a to 26d, and the transmitted light of each region is deflected in slightly different directions. In addition, regions 25a' and 25b in the 6-split photodetector 25 constitute a first 2-split photodetector, regions 25c and 25d constitute a second 2-split photodetector, and regions 25e and 25f respectively It constitutes an independent photodetector. Region 2 of 4-split prism 26
The transmitted light of 6a and 26b passes through the converging lens 27 and passes through the first and second two-split photodetector (2) of the 6-split photodetector 25.
The light is focused on the dividing lines 5a, 25b and 25c, 25d), respectively. Also, the area 26c of the 4-split prism 26
The transmitted light beams 26d and 26d are condensed through a converging lens 27 onto areas 25e and 25f of the six-divided photodetector 25, respectively.

FIG. 9 shows changes in the shape of the light beam on the light receiving surface of the six-divided photodetector 25 when the distance between the objective lens 7 and the disk 8 changes in FIG. 8.

The figure (b) shows when the recording medium of the disk 8 is at the focal point of the objective lens 7, and the figure (a) shows the case where the disk 8 is closer to the objective lens 7 than the figure (b), and the figure (c) This is the case where the disk 8 has moved away from the objective lens 7 as shown in FIG. The light beams 28a to 28d correspond to the light transmitted through the regions 26a to 26d of the four-split prism 26 in FIG. 8, respectively. As can be seen from FIG. 9, if the outputs from the photodetectors 25a to 25f of the 6-split photodetector 25 are Sa to Sf, respectively, (Sa + Sd) −
(Sl+ +Sc) is the focus error signal, Se
By using −9f as a track error signal, focus error detection and track error detection can be performed based on the principles of the Foucault method, Buch, and Spurr method, respectively.

[Problem that the invention seeks to solve]

In the configuration shown in FIG. 6, the number of parts is reduced compared to the configuration shown in FIG. 5, and the device is made smaller.

However, with such a configuration in which the signal detection system and error detection system are independent, it is difficult to further downsize and simplify the system. In order to shorten access time and reduce costs in magneto-optical disk file systems, magneto-optical head devices are required to be further downsized and simplified.

By the way, a recording medium in a magneto-optical disk is formed on a transparent substrate, and a light beam is incident on the recording medium through the substrate. Polycarbonate is considered a promising material for substrates due to its cost and reliability, but polycarbonate substrates have a large refractive index difference between the in-plane direction and the vertical direction due to residual stress during molding. There is. When a light beam passes through a substrate having such refractive index anisotropy,
At normal incidence, it is not affected by refractive index anisotropy, but
At oblique incidence, linearly polarized light becomes elliptically polarized due to the effect of refractive index anisotropy. The degree of elliptical polarization increases as the angle of incidence increases. In a magneto-optical head device, a convergent beam passes through the substrate, so the incident angle increases and the degree of elliptical polarization increases as the optical beam goes from the center to the periphery. Such elliptical polarization of linearly polarized light lowers the degree of modulation of the reproduced signal, leading to deterioration of the reproduced C/N. Therefore, it is necessary to suppress the deterioration of the reproduced C/N by devising the optical system, but such deterioration has not been done in the configuration shown in FIG.

The purpose of the present invention is to solve the above-mentioned conventional problems,
It is an object of the present invention to provide a magneto-optical head device that can be made small and simple, and can suppress deterioration of reproduction C/N when using a substrate having refractive index anisotropy.

[Means for solving problems]

The magneto-optical head device of the present invention includes a condensing optical system that focuses emitted light from a laser light source as a minute spot on a magneto-optical recording medium, and a part of the reflected light from the magneto-optical recording medium that passes through an analyzer. a first detection optical system that guides the reflected light from the magneto-optical recording medium to the first photodetector; and a second detection optical system that guides a portion of the reflected light from the magneto-optical recording medium to the second photodetector through a converging lens; and the second photodetector includes two two-split photodetectors and a second photodetector.
It is a 6-segment photodetector with two independent photodetectors,
A first light beam that includes, in the optical path of the reflected light from the magneto-optical recording medium, a central portion of the reflected light and portions adjacent to straight lines extending in four mutually orthogonal directions from the center toward the periphery, and a peripheral portion. radial 4 excluding the vicinity of the straight line from
The first light beam passes through the analyzer, and the first light beam passes through the analyzer. A pair of diagonal light beams among the second to fifth light beams guided to the first photodetector pass through the converging lens to two two-split photodetectors of the six-split photodetector. and the other set of diagonal light beams are respectively focused on two independent light detection sections of the six-segment photodetector through the converging lens. There is.

[Effect]

As mentioned earlier, in a magneto-optical head device, a convergent beam passes through the substrate, so the angle of incidence on the substrate increases as you go from the center of the light beam to the periphery, and the degree of elliptical polarization of the transmitted light increases. also becomes larger. However, the degree of elliptical polarization depends on the angle θ between the plane of incidence of the light incident on the substrate and the plane of polarization.
It also varies depending on.

Figure 4 shows the ellipticity of the light transmitted through the substrate [long axis of the ellipse].

When the lengths of the short axes are A and B, respectively, jan "'
This is an example of calculating the incident angle dependence of ``(B/A>] using θ as a parameter.From this figure, θ=O',
It can be seen that if the vicinity of the straight line extending in four directions of 90°, 180', and 270° is used for signal detection, deterioration of the reproduced C/N can be suppressed. Furthermore, if error detection is performed using the same method as the conventional example shown in FIG. 6 using four radial areas obtained by excluding the area near the straight line from the peripheral area of the light beam, the signal detection system and error detection Compared to the conventional example in which the systems are independent, the magneto-optical head device can be further downsized and simplified. To this end, the present invention uses an optical path splitting means that divides the reflected light from the recording medium into one optical beam for signal detection and four optical beams for error detection, and deflects each beam in different directions. It is being

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the magneto-optical head device of the present invention. The optical system on the outward path is almost the same as in FIG. 6, but the two beam splitters 4.5 are replaced by one beam splitter 29. A portion of the reflected light from the recording medium is separated by a beam splitter 29 and enters a five-split prism converging lens 30 .

FIG. 2(a) shows the divided shape of the five-split prism and the incident light beam 32. In this embodiment, the polarization direction of the light incident on the disk and the radial direction of the disk form an angle of 45 degrees. θ=0°, 90°, 180 mentioned earlier
The four directions of 270' and 270' correspond to the polarization direction of the disc incident light and the direction perpendicular thereto.The transmitted light of the region 30a of the 5-split prism is transmitted through the slit portion of the pinhole-equipped reflective mirror 31 in FIG. lotion prism 20
The light is separated into two parts and received by a two-split photodetector 22.

FIG. 2(b) shows the light receiving surface of the two-split photodetector 22 and the incident light beam. Two light receiving surfaces 22a.

The difference between the outputs from 22b becomes a reproduction signal. On the other hand, the light transmitted through the areas 30b to 30e of the five-split prism is reflected by a portion of the slit-equipped reflective mirror 31 in FIG. 1, and is received by the six-split photodetector 25.

FIG. 2(C) shows the light receiving surface of the six-divided photodetector 25 and the incident light beam. The transmitted light of the areas 30b and 30c of the 5-split prism is transmitted to the first . second 2
Split light detection section (25a, 25b and 25c, 25d)
The light is focused on the dividing lines of the areas 30d and 30, respectively.
The transmitted light e is focused on regions 25e and 25f, which serve as photodetecting sections of the 6-split photodetector 25, respectively. A focus error signal and a tracking error signal are obtained from the output of each photodetector in the same manner as in the conventional example shown in FIG.

FIG. 3 is a block diagram showing another embodiment of the magneto-optical head device of the present invention. All of the transmitted light from the five areas of the 5-split prism is reflected by the total reflection mirror 24, separated into two by the Rochon prism 20, and then sent to the 8-split photodetector 33.
The light is received by

FIG. 2(d) shows the light receiving surface of the eight-divided photodetector 33 and the incident light beam. Areas 33g and 33 as photodetecting parts
h corresponds to the light-receiving surfaces 22a and 22b in FIG.
) corresponds to regions 25a to 25f as photodetecting sections. Even if the light beam for focus error detection is separated into two by the Rochon prism 20, both are focused on the dividing line, so there is no problem in focus error detection.

In the embodiments shown in FIGS. 1 and 3, a five-split prism is used as the optical path dividing means. This is a combination of prisms whose incident and exit surfaces form five different angles, and can be made by bonding five glass prisms together or by integrally molding glass or plastic.

In the embodiment, it is further integrated with the converging lens, but it may be separate. Further, instead of the 5-split prism, a 5-split mirror that is a combination of mirrors forming five different angles can also be used. In these cases, the converging lens may be positioned before or after the 5-split prism or the 5-split mirror. Other optical path splitting means include separating the light beam for signal detection using a mirror with a slit as shown in Figure 1, and then splitting the light beam for error detection using a 4-split prism or a 4-split mirror as shown in Figure 6. There is a method of dividing the light beam into four parts. In these cases, the converging lens may be positioned in front of the slit mirror, between the slit mirror and the 4-split prism or the 4-split mirror, or after the 4-split prism or the 4-split mirror. Still another optical path dividing means is a method of using a 4-split mirror with slits, in which a portion of the mirror with slits is divided into four parts. In this case, the converging lens may be positioned on either the incident light side or the reflected light side of the 4-split mirror with slits. Furthermore, instead of the above-described split prisms and mirrors, a combination of transmissive or reflective hologram elements that diffract incident light in different directions may be used.

On the other hand, in the embodiments shown in FIGS. 1 and 3, differential detection is performed using a Rochon prism as an analyzer, but a polarizing beam splitter is used instead of the Rochon prism to separate transmitted light and reflected light. Differential detection in which light is received by separate photodetectors is also possible. It is also possible to perform single detection by using a Glan-Thompson prism or a polarizing beam splitter as an analyzer to receive only transmitted light.

Note that in the embodiments shown in FIGS. 1 and 3, the total reflection mirror 6.24 may be omitted.

〔Effect of the invention〕

As described above, the magneto-optical head device of the present invention can be made smaller and simpler than the conventional example, and can reduce the deterioration of reproduction C/N when using a substrate having refractive index anisotropy. It is possible to suppress the

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the magneto-optical head device of the present invention, FIG. 2 is an explanatory diagram showing the division shape of a five-split prism and the light receiving surface of a photodetector in the embodiment of the present invention, and FIG. The figure is a configuration diagram showing another embodiment of the magneto-optical head device of the present invention.
Fig. 4 is a characteristic diagram showing the incident angle dependence of the ellipticity of transmitted light through a general substrate, Figs. FIG. 8 is a perspective view showing details of the signal detection system in the conventional example; FIG. 9 is a perspective view showing details of the error detection system in the conventional example; FIG. 9 is the light beam on the light receiving surface of the 6-split photodetector in the conventional example. It is an explanatory view showing the shape of. 1... Semiconductor laser, 2... Collimator lens, 3
... Beam shaping prism, 4, 5... Beam splitter, 6... Total reflection mirror, 7... Objective lens, 8
...Disc, 9...1/2 wavelength plate, 10...Polarizing beam splitter, 11.12...Converging lens, 1
3.14... Signal detector, 15... Converging lens, 1
6... Beam splitter, 17... Naifetsuji,
18... Focus error detector, 19... Track error detector, 20... Lotion prism, 21
...Convergent lens, 22...2-split photodetector, 22a
, 22b... Light-receiving surface, 23... 4-split prism converging lens, 24... Total reflection mirror, 25... 6-split photodetector, 25a to 25f... Area as a photodetection section, 26... 4-split prism, 26a-26d... area, 27... converging lens, 28a-28 (1... light beam, 29... beam splitter, 30... 5-split prism co-converging Lens, 30a to 30e... area,
31...Reflection mirror with slit, 32...Light beam, 33...8-divided photodetector, 33a'''\~331]...Area as a photodetector. -
H, ; T soo 2nd 3rd Figure 0 10 20 . 30 Shadow 4 Figure 1 Dialogue

Claims (2)

[Claims] (1) A focusing optical system that focuses the light emitted from the laser light source as a minute spot on the magneto-optical recording medium, and a first photodetector that passes a part of the reflected light from the magneto-optical recording medium through an analyzer. A magneto-optical head device comprising: a first detection optical system that guides a portion of the reflected light from the magneto-optical recording medium to a second photodetector through a convergent lens; The second photodetector consists of two two-split photodetectors and two
It is a 6-segment photodetector with two independent photodetectors,
A first light beam that includes, in the optical path of the reflected light from the magneto-optical recording medium, a central portion of the reflected light and portions adjacent to straight lines extending in four mutually orthogonal directions from the center toward the periphery, and a peripheral portion. radial 4 excluding the vicinity of the straight line from
The first light beam passes through the analyzer, and the first light beam passes through the analyzer. A pair of diagonal light beams among the second to fifth light beams guided to the first photodetector pass through the converging lens to two two-split photodetectors of the six-split photodetector. The light beams are respectively focused on the dividing line, and the other set of diagonal light beams are respectively focused through the converging lens on two independent photodetecting parts of the six-divided photodetector. Magneto-optical head device. (2) The light according to claim (1), wherein the photodetecting portions of the first photodetector and the photodetector of the 6-split detector are formed on the same surface. magnetic head device.