JPS6192461A - Optomagnetic disc device - Google Patents

Abstract

PURPOSE:To improve S/N of a reproducing signal, to attain light weight of a moving part and high-speed access by using a rod prism and applying a metallic film to the reflecting plane. CONSTITUTION:The metallic films 35, 36 are applied to full reflecting planes 14, 15 of the rod prism 13. In rotating the rod prism 13, the phase of P and S components on the full reflecting plane of the rod prism 13 is advanced respectively by phiP, phiS. In general, the reflecting factor is deteriorated at the reflection of the metallic surface, and the said phase difference (phiP-phiS) is known to be smaller than the full reflection, the phase difference on the full reflecting plane of the rod prism by the metallic surface reflection, not by the full reflection, is reduced by applying the metallic film to the full reflection plane of the rod prism and the reflecting light from the recording medium is minimized to be elliptic polarized light (as the elliptic rate of the elliptic polarized light is smaller, transmitted luminous amounts A'x, A'y of the analyzer are equal).

Description

[Detailed Description of the Invention] Industrial Application Field The present invention reads information by irradiating a minute spot of a light beam onto a recording medium and detecting reflected light whose polarization plane has been rotated by the magneto-optic effect. The present invention relates to magneto-optical disk devices.

Conventional Structure and Problems In recent years, optical disk devices such as optical file devices that are capable of optical recording and reproduction have begun to appear.

In general, disc devices that perform optical recording and playback are divided into two types: a linear system in which an optical head including an objective lens is moved linearly in a direction perpendicular to the track on the disc, and a swing arm system in which the optical head is rotated around a certain point. Broadly classified.

The present invention relates to this swing arm type magneto-optical disk device. FIG. 1 is a block diagram of a conventional improved swing arm type optical disk device. The optical disc 1 is rotated by a disc rotating means, such as a motor.

Reference numeral 2 denotes a rotation actuator which is rotation control means for simultaneously performing recording track access operation and track following operation, and M is its rotation center axis. Reference numeral 3 denotes a rotor that rotates together with the rotation actuator, to which a rod-shaped prism 4, which is a rod-shaped light guiding means, and parallel springs sa and sb are attached. An objective lens and a focus coil 8 are fixed to the tips of the parallel springs 5a and 5kl via a tip member 6. The focus coil 8 is inserted into a gap in a focus magnetic circuit (not shown). An optical system consisting of a semiconductor laser light source, a collimator lens, a spectroscopic prism, a mirror, a photodetector, etc. is fixed above the rotation center axis M, and the light emitted along the rotation center axis M is fixed. The beam is totally reflected at one end of the rod-shaped prism 4, passes through the inside of the rod-shaped prism, is totally reflected again at the opposite end, and is focused by the objective lens 7 and irradiated onto the surface of the optical disk 10.

Contrary to the above, the reflected light from the optical disk 1 passes through the inside of the rod-shaped prism and is returned to the optical system along the rotation center axis M again. In this way, the rod-shaped prism that guides the light beam has excellent rigidity because it is made of a single rod.Furthermore, since there are no special attachments other than the rod, it has low inertia and can be used for high-speed access operation. is very beneficial. Furthermore, by using a prism, efficient total reflection is performed on the reflecting surface, resulting in good light efficiency. It is also possible to use a hollow light pipe instead of a rod-shaped prism and fix a mirror at the tip, but this would require a thicker light pipe for rigidity, or it would be necessary to set the mirror mounting angle with high precision. , complicated installation may require jigs, resulting in large inertia. At these points, the bar prism is very submerged.

However, although the above-mentioned method using total reflection on a prism reflective surface is superior in terms of optical efficiency, it causes various problems in magneto-optical disk devices that read playback signals by detecting differences in polarization direction. .

These problems will be explained below.

FIG. 2 shows a magneto-optical reproducing optical system using the rod-shaped prism. The light emitted from the semiconductor laser 9 is turned into a parallel beam by the collimating lens 10. A polarizer 11 converts the light beam into linearly polarized light. A beam splitter 12 separates incident light and reflected light from the recording medium. The light that has become linearly polarized by the polarizer passes through the beam splitter and passes through the (shaped prism 13)
incident on . This incident light is reflected by the total reflection surfaces 14 and 15, turned into a minute spot by the focus lens 16, and hits the disk 17, which is a recording medium.

Corresponding to the magnetization direction of the recording medium, the polarization plane is reflected by θ or 100 rotations due to the Kerr effect. This reflected light passes through the focus lens again, undergoes two total reflections at the rod-shaped prism, is separated by the beam splitter 12, and is split into two directions by the half mirror 18. The divided light beams are each analyzed by an analyzer 19.20
The light is guided to photodetectors 21 and 22 and extracted as an electrical signal. Here, the reproduced signal is obtained by a differential detection method, and this detection method will be explained using FIG. 3. Third
Figure C9d shows analyzers 19 and 20 in Figure 2, respectively.
(7) In the diagram showing the transmission axis direction, 23 indicates the direction of the polarization plane of the light incident on the recording medium, and 24 and 26 are rotated by 10 and -θ depending on the direction of magnetization of the recording medium, respectively. This shows the direction of the polarization plane of reflected light.

Now, the transmission axis of the analyzer 19 in Fig. 2 is set to 2 in Fig. 3 a.
As shown in FIG. 6, the recording medium is arranged at an angle of -45° to the polarization plane of the light incident on the recording medium. One solution is to arrange the transmission axis of the analyzer 20 shown in FIG. 2 in a direction of +45° with respect to the polarization plane of the light incident on the recording medium, as shown in FIG. With this arrangement,
The electrical signals obtained by the photodetectors 21 and 22 in FIG. 2 are signals whose signal phases are shifted by 1800, as shown in FIG. 3 C9d. Further, recording media usually have uneven reflectance, dust, etc., and noise components due to these influences are detected in the same way by the detectors 21 and 22 regardless of whether an analyzer is used or not. For example, if there is uneven reflectance, the broken lines in Figure 3 c and d.

The signal waveform is wavy due to the noise component shown in .

In the magneto-optical system shown in FIG. 2, by taking the difference between the detection signals shown in FIG. The final reproduced signal is obtained as shown in Figure 3e,
Therefore, there is an effect of improving the S/N ratio of signal reproduction.

However, in the swing arm method using the rod-shaped prism, the DC components of the detection signals detected by the detectors 21 and 22 differ depending on the rotation of the rod-shaped prism, so the noise components that are in the same phase are not canceled out. , is detected as a noise component of the information signal, and S of the signal reproduction
/N ratio deteriorates. The aforementioned S/N deterioration will be explained below using FIG. 4, FIG. 5, and FIG. 6. The coordinates of the bar-shaped prism 28 are determined as shown in FIG. Total reflection surface 29.3
0 is cut at an angle of approximately -46°, 46° to the P axis. Linearly polarized light 33 is incident on this rod-shaped prism 31 along an optical axis 32 . This linearly polarized light is (p, s
) plane as shown in Figure 6a, A=Acos θcoswt = A, coswt
M5 = A sin θcosWt = person scoswt
It is expressed as (However, AP I's is the (P, S) a portion of the linearly polarized light 33, and θ is the angle between the linearly polarized light 33 and the P axis.) When this linearly polarized light 33 enters the total reflection surface 29 and is totally reflected, It is generally known that the phase of each component of linearly polarized light advances by OP, . . . gs.

Therefore, the totally reflected light is no longer linearly polarized light, but is expressed as: m', = A, cos (wt-, gP), 15 = A, cos (wt - me2b. It becomes elliptically polarized light expressed as .Yoshi zero Yome 2ヅ, ).If the material of the prism has a refractive index n = 1.5 and total reflection occurs at an incident angle of 45°, then lP';3T0.J258!; 74°.

Since this total reflection also occurs on the surface 30, the light incident on the medium 34 becomes: p = A, cos (wt-2g, ) A turtle = person, cos (wt-2g,). Assuming that we ignore the Kerr effect of )IP
, = As cos (wt-40,). (Fig. 6b) This elliptically polarized light is separated by a beam splitter 12, and is separated by a nof mirror 1.
It is divided into two directions by B. Each of the divided light beams passes through an analyzer 19.20, is guided to a photodetector 21.22, and is extracted as an electrical signal.However, as mentioned above, the reflected light from the recording medium is converted into elliptically polarized light by the rotation of the rod-shaped prism. Then, as shown in FIG. 6, the output of each photodetector will fluctuate. In Figure 6, the S-axis and P-axis are the coordinate axes of the rod-shaped prism, and the y-axis is the axis that indicates the polarization direction of the incident light incident on the rod-shaped prism. ), and the y-axis indicates the transmission optical axis of the analyzer 19.20. The linearly polarized light A that is now polarized parallel to the y-axis becomes elliptically polarized light 7 by total reflection four times as described above. Since the transmitted light of this elliptically polarized light r by the analyzer 19.20 is considered to be projected onto the y-axis and the y-axis, the output of the photodetector 21.22 is h'x,
Proportional to A/y. In FIG. 6, Ar<Aari<A'y, and A-<Ar. Therefore, the DC component of the detection signal of the elliptically polarized light due to the rotation of the rod-shaped prism is different between the photodetector 21 and the photodetector 22. Therefore, noise components detected in the same phase are not canceled out despite the differential system and are detected as noise components of the information signal, resulting in a worsening of the S/N ratio of signal reproduction.

In this way, a rotary actuator using a rod-shaped prism has excellent rigidity and is lightweight, making high-speed access easy, but when this method is introduced into a magneto-optical disk drive, there is a problem that the quality of the information signal deteriorates. was there.

OBJECTS OF THE INVENTION An object of the present invention is to realize a magneto-optical disk device that can easily realize high-speed access and can suppress deterioration in the quality of information signals.

Structure of the Invention The optical disk device according to the present invention includes a rotation control means for controlling the rotation of an objective lens in a direction across the track about the rotation center axis, and a light beam incident along the rotation center axis. A rod-shaped rod that guides the light reflected from the disk surface to the objective lens and returns it to the rotation center axis, and has one end fixed to the rotation control means side and the other end on the objective lens side free. It consists of a light guiding means, and a metal film is applied to the light reflecting surface of the rod-shaped light guiding means.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 7 shows a magneto-optical reproducing optical system in this embodiment.

In FIG. 7, everything is the same as that shown in FIG. 2, except that metal films 35 and 36 are applied to the total reflection surfaces 14 and 16 of the rod-shaped prism. The operation of this embodiment configured in this way will be described below.

As mentioned above, when the rod-shaped prism 13 rotates, the phases of the P component and the S component advance by a, ... as on the total reflection surface of the rod-shaped prism 13, but in general, in the reflection of a metal surface, the reflection It is known that the above-mentioned phase difference (*P-/s) is smaller than total internal reflection, although the rate is worse. In this example, a metal film is applied to the total reflection surface of the rod-shaped prism, so that total reflection is not achieved.
The metal surface reflection reduces the phase difference on the total reflection surface of the rod-shaped prism, and it is possible to suppress as much as possible the reflected light from the recording medium from becoming elliptically polarized light. (The smaller the ellipticity of elliptically polarized light, the more the amount of light transmitted by the analyzer A'.

It is clear from FIG. 6 that the values are equal. ) Here, it is possible to fix a metal surface mirror instead of the total reflection surface of the rod-shaped prism of this embodiment, but as mentioned above, this is not possible in this embodiment in terms of the rigidity and accuracy of mounting the metal surface mirror. It is better to apply a metal film to a bar-shaped prism. Furthermore, by selecting the type of metal, it is possible to reduce the reflectance on the reflective surface, thereby achieving a reflectance that is close to total reflection.

As described above, according to this embodiment, it is possible to realize an excellent magneto-optical disk device which has a structure that allows high-speed access to be easily realized, and which does not cause a deterioration in the quality of information signals. be able to. In the above embodiment, a trapezoidal prism is used as the rod-shaped light guiding means, but any parallel prism or similar shape that transmits laser light may be used. Furthermore, the metal film applied to the reflective surface can be appropriately selected depending on the wavelength of the laser beam.

Effects of the Invention As is clear from the above description, the present invention uses a rod-shaped prism and coats its reflective surface with a metal film, thereby improving the S/N ratio of the reproduced signal in a rotary actuator type magneto-optical disk reproducing device. The effect of this is that the weight of the movable parts can be reduced, and high-speed access can be realized.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway perspective view of a conventional improved swing arm type magneto-optical disk device, Fig. 2 is a configuration diagram of its magneto-optical reproducing optical system, and Fig. 3 shows the principle of reproducing a magneto-optical disk. Figure 4 is a perspective view of a rod-shaped prism for explanation purposes.
5 and 6 are diagrams for explaining problems when a bar-shaped prism is used for reproducing a magneto-optical disk, and FIG. 7 is a block diagram of a magneto-optical disk device according to an embodiment of the present invention. 13... Rod prism, 16... Objective lens, 17... Magneto-optical disk, 19, 2
0...Analyzer, 21.22...Photodetector, 35.36...Metal film. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 3 (cl,] (b)

Claims (1)

[Claims] an objective lens for condensing reflected light from a disk having concentric or spiral tracks; a rotation control means for controlling the rotation of the objective lens in a direction across the tracks around a rotation center axis; A light beam incident along the central axis is guided to the objective lens, and the reflected light from the disk surface, which is focused by the objective lens, is returned to the rotation center axis, and one end thereof is on the rotation control means side. What is claimed is: 1. A magneto-optical disk device comprising a rod-shaped light guiding means which is fixed to the lens and whose other end on the objective lens side is a free end, and a metal film is applied to a light reflecting surface of the rod-shaped light guiding means.