JPS6163945A - Photomagnetic disk device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of quality of the reproduction signal and to facilitate an easy high-speed access to tracks, by using a wavelength plate provided into a rotary optical axis to compensate the retardation which is caused by the 1st and 2nd reflection members set on a rotary member. CONSTITUTION:A wavelength plate 100 is set on the incident face of an optical conduction member 2 to offset the retardations caused on the reflection faces 2a and 2b of the member 2. The plate 100 has a fast phase axis Fast and a slow axis Slow which are orthogonal to each other. Thus the plate 100 is set on the incident face of the member 2 so that the light passing over the axis P (phase slower than the axis S by delta) of the faces 2a and 2b passes through the axis Fast of the plate 100 and that the light passing through the axis S passes through the axis Slow of the plate 100 respectively. When the phase difference between both axes Fast and Slow is set at 2delta for the plate 100, the retardation is completely eliminated. This avoids the deterioration of quality of the reproduction signal and facilitates an easy high-speed access to the tracks.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a magneto-optical disk device having a high-speed access function.

Conventional Structures and Problems Magneto-optical recording is a high-density, writable and erasable recording method that has attracted attention in recent years.

FIG. 1 shows a side view of a conventional magneto-optical disk device. In Fig. 1, 1 is an objective lens, 4 is a laser emission source 4
a, collimator lens 4b, spectroscopic element 4c, analyzer 4e
, a light-receiving lens 4d, and a light-receiving element 5. 10 is a rotating magneto-optical disk, and 2o is a traverse motor that moves the optical system main body 4 and the objective lens along the radial direction of the disk. Not limited to magneto-optical disks, optical disks generally record information in the size of several micrometers.
), the amount of surface runout and eccentricity (several tens of microns) is large, so the objective lens 1 must follow the fluctuations in the recording signal train (track) as the disk rotates. For this reason, in a typical optical disk device, the objective lens is connected to the body using a spring material or the like, and can be electromagnetically driven in the direction of deflection and eccentricity of the disk. However, since the configuration regarding these follow-up control systems is not directly related to the present application, details thereof will be omitted. Further, the external magnetic field applying device used for recording and erasing signals 4 on the magneto-optical disk 10 does not need to be explained, and will therefore be omitted.

The operation of the conventional magneto-optical disk device configured as described above will be explained.

The light emitted from the laser light source 4a is collimated by a collimator lens 4b, and then focused by an objective lens 1 onto a magneto-optical disk 1o. The original light is then reflected, passes through the objective lens 1 again, is changed direction by the spectroscopic element 4C, and reaches the light receiving element 6 through the analyzer 4e and the light receiving lens Adi.

On the magneto-optical disk 10, there are two
Value information is recorded. When linearly polarized light hits the surface and is reflected, the polarization angle changes in opposite directions depending on the polarity of the magnetic domain. This phenomenon is called the Kerr effect. The change in polarization angle due to the Kerr effect can be detected as a signal by using the analyzer 4e. This situation is shown in FIG. The analyzer 4e is an optical element made so that only light having a certain polarization angle (light vibrating in the direction of a straight line indicated by W in the figure) can pass through. Now, the analysis direction (W direction) of the analyzer 4e and the analyzer 4e
Suppose that the polarization direction of the incident light is at a certain angle (in general, the polarization direction of the incident light that is not affected by the Kerr effect is 0).
(W is set in the direction of 45°). When light (S, N) subjected to the Kerr effect enters in opposite directions, only the W-direction projected components of each will pass through the analyzer, so the difference in polarization angle will be converted into the strength of the light. Therefore, the light receiving element 5 can extract it as an electrical signal.

Since information can be recorded over almost the entire surface of a disk-shaped recording medium, there are many information sectors on the disk. By moving the disc device's most convenient location, you can quickly read out information written anywhere on the disk (accessible). ) in particular. However, in the case of an optical disk device, the optical head is heavy and has a precise and complicated structure, so it is not easy to move the optical head to the optical head at high speed. The general method for moving the optical head is shown in FIG. 1, in which the entire optical system including the light emitting source and light receiving element is moved by a traverse motor.

An optical disk device using a separate rotating optical pickup as an optical head with high access capability has already been proposed. Figure 3 shows a separate rotating optical camera.

1 shows a side view of a magneto-optical disk device using a backup. A partial cross-sectional view is used to clarify the structure. In FIG. 3, the optical system main body 4 is exactly the same as that in FIG. In FIG. 3, a rotating member 3 and a light-conducting member 2 having two reflecting surfaces 2a and 2bi mounted on the upper surface thereof and facing each other in parallel are provided between the objective lens 1 and the optical system main body 4. is a special enemy. Furthermore, the rotational axis of the rotational member 3 is the center of the objective lens 1, the photoconductive member 2,
Of the optical axes passing through the optical system main body 4, does it completely coincide with the one connecting the optical system main body 4 and the photoconductive member 2? It is a feature.

11 minutes configured like this! The operation of the u-rotation type magneto-optical disk will be briefly explained as follows.

That is, when performing track access, the optical system main body 4 is not moved, and the objective lens 1 and the light-conducting member 2 are moved to the rotating member 3.
rotate with the Objective lens 1 is magneto-optical disk 1
If the position of the center of rotation is determined for the entire magneto-optical disk 1Q so that it moves on an arc substantially along the direction of the zero half-sphere, the entire disk surface can be accessed. In particular, since the optical axis passing through the center of the objective lens 1 and the rotation axis of the rotation member 3 coincide, even if the objective lens 1 and the light-conducting member 2 are rotated, the light from the optical system body 4 remains unchanged. There is no deviation between the axis and the optical axis of the objective lens 1, so that the magneto-optical disk 10 and the optical system main body 4 can always exchange light beam information accurately.

The greatest feature of this separate rotary optical pickup is that it minimizes the weight of the movable mass during track access. Unlike the conventional example shown in FIG. 1, only the objective lens 1 and the light-conducting member 2 need to be moved during track access. As a result, it is possible to solve the problem regarding high-speed access capability, which has been the biggest drawback of optical disk devices.

However, there are major problems when applying this separate rotary optical pickup to a magneto-optical disk device. That is, since the reflective surfaces 2a and 2b of the photoconductive member 2 cause retardation of the incident light beam, there is a problem in that the quality of magneto-optical signal reproduction is degraded. This situation is shown in FIG.

Now, it is assumed that the photoconductive member 2 is rotated by an angle φ with respect to the polarization direction of the incident light (light emitted from the optical system main body 4) (FIG. 2a). Generally, when light is reflected by a reflective surface, a phase delay of the light wave occurs anisotropically.

Taking FIG. 4 as an example, between the p-axis, the intersection line of the reflecting surface 2b and the plane containing the incident and reflected rays, and the S-axis perpendicular thereto, the angle of incidence n is cos2-n's in2θ+n2θ. = nl / n2 n, . . . refractive index n2 inside the reflective surface, . . . generates a phase difference expressed by the refractive index outside the reflective surface. This is a phenomenon called reversion. If the anti-↓1j surface 2b is set at 45° with respect to the incident light, and the reflective surface 2b is a total reflection prism using glass with a refractive index of 1.5, θ=45°, n
+=1.6, "2="Th Substituting into equation (1), we obtain the value δ=38.6°. In the configuration shown in FIG. 2, the reflection 2a-
2bA: Soup 31Y-M, 21- and l? : Near 'r knee injury, I'-II 4 F-John will also occur 4δ, 154° in the above example.

The occurrence of such retardation in the optical system of a magneto-optical disk device greatly affects the quality of reproduced signals. Now, if the s and p axes are φ with respect to the polarization direction of the incident beam, there will be a phase difference between the S and P axis projection directions of the incident beam, so the ray 0 that has received the retardation will be elliptically polarized. Become. As mentioned above, signals in a magneto-optical disk device are read by detecting changes in the polarization angle caused by positive and negative magnetic poles, which are recorded signals on the magneto-optical disk.

Retab! The effects of the −7 controller on the magneto-optical reproduction signal are: ■deterioration of the f signal due to the retardation itself;■
There are two types of signal deterioration caused by the reproduction light beam being made into an oval due to retardation. This will be briefly explained below.

I will not explain in detail about ■, but the retardation δ
It is known that the amplitude of the reproduced signal is attenuated in proportion to cos δ. At δ-900, the reproduced signal is 1
Since the return knee by the photoconductive member 2 using the total reflection prism of 154° is 154°, the amplitude of the reproduced signal is reduced to 4°, that is, 9 (l).

■ is a problem specific to division 1 ([rotation + q+, I optical system, , the light ray O is rotated four times in the reciprocating optical path passing through the magneto-optical disk 10, and as a result, the light beam O returns to the optical system main body 4.
It was mentioned that the light may become elliptically polarized. What should be noted here is the degree to which ray 0 is an ellipse (ellipticity)
is the reflective surface 2a.

2b, that is, it changes depending on the rotation angle φ of the light-conducting member 2 with respect to the polarization direction of the incident beam. By rotating the photoconductive member 2, the S
This is clear from the fact that the axis and the P axis rotate, and as a result, the projection components to the s and p axes change (Figure 2, c). From FIG. 4, when φ=0°, the emitted light ray O returns as linearly polarized light (the light ray S due to the rotation of the light ray received on the surface of the disk).

(Ignore the 11'1 circularization that occurs when considering the P axis).

It is unfavorable for signal reproduction that the (11 yen rate) of the ray 0 depends on the rotation angle of the photoconductive member 2.The reason is explained below.The biggest problem with magneto-optical disk devices is the reproduction signal. I mentioned earlier that the magneto-optical device obtains a reproduced signal by detecting the difference in polarization angle due to the Kerr effect, but the Kerr rotation angle is about 1° at most. is very small.Therefore, the laser emission #, 4a
The signal-to-noise ratio of the reproduced signal is extremely degraded by the noise emitted by the receiver.A signal detection method using a differential canceller shown in FIG. 5 is often used as a countermeasure for improving the signal-to-noise ratio. As explained in Fig. 2, the magneto-optical reproduction signal is transmitted to the analyzer 4.
This can be obtained by detecting all the alternating current components of the light that has passed through zero. Now, assume that the component perpendicular to the W direction that did not pass through the analyzer 48 is reflected and received by another light receiving element. Figure 5 shows the outputs of the light receiving element 5a, into which the passing light enters, and the light receiving element 5b, into which the reflected light enters. They are in opposite phases to each other (Rsa + R5b
).

Therefore, if the balance between both outputs is properly set and the difference is taken, the noise component can be canceled and only the signal component can be extracted (Rout). However, when a separate rotary pickup is used, the photoconductive member 20 The ellipticity of light entering the analyzer 4e changes depending on the rotation angle φ. If the ellipticity changes, the ratio between the amount of light passing through the analyzer 4e and the amount of light reflected changes. In other words, the conditions for noise cancellation are completely different depending on the rotation angle of the photoconductive member 2, making noise cancellation extremely difficult.

The following is a summary of what I have said/20 below.

Separate rotary optical pickups are optical pickups that have few moving parts and can be easily accessed at high speeds, but when this system is introduced into magneto-optical disk drives, the quality of the reproduced signal deteriorates due to the retardation of the two rotating reflective surfaces. There was a problem with that.

Purpose of invention competition
R1-Task 1≠＼The object of the present invention is to realize a magneto-optical disk device which can obtain reproduction signal quality equivalent to that of the conventional device.

Structure of the Invention The present invention includes an objective lens on a rotating member, a first reflecting member, a second reflecting member set opposite to the first reflecting member, and an optical fast axis. The optical phase members having slow axes are arranged in a line along the optical axis, and the second reflecting member is provided on the rotation axis of the rotation member, and By optically aligning the optical system main body having the light emitting means and the light receiving means with the second reflecting member, it not only reduces the weight of the movable parts during track access, but also reduces the weight of the movable parts when accessing the track. To easily realize high-speed track access without deteriorating the quality of a reproduced signal by compensating for the retardation caused by the first and second reflecting members by providing an optical phase member in the rotating optical axis. The objective is to realize a magneto-optical disk device that can perform the following functions.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 6 shows a side view of the magneto-optical disk device in this embodiment. Note that a partial cross-sectional view is used to clarify the structure.

In FIG. 6, everything is the same as that shown in FIG. 3, except that a wavelength plate 100 is provided on the second photoconductive part. A wave plate is a linear retarder formed from a birefringent crystal, and has a fast axis and a slow axis that are orthogonal to each other.

The present embodiment configured in this manner will be described below.

It has already been mentioned that retardation occurs on the reflective surfaces 2a and 2b of the photoconductive member 2. In this embodiment, this retardation is canceled by providing a wave plate 100 gold light (5, J) on the incident surface of the J member 2. This situation is shown in FIG. (Fast)
It has a slow axis (Slow). Therefore, the reflective surface 2a
, 2b so that the light passing on the P axis (the phase of which is delayed by δ from the S axis) passes through the fast axis of the wave plate 100, and the light passing through the S axis passes through the slow axis. If the plate 100 is provided on the incident surface of the photoconductive member 2 and a wavelength plate is selected in which the phase lead of the fast axis with respect to the slow axis is exactly 26,
The retardation caused by the photoconductive member 2 is completely canceled by the wave plate 1Q○. As a result, it is possible to prevent the reproduced light from becoming 111 yen due to the rotation of the photoconductive member 2, and there is no deterioration in the quality of the reproduced signal due to the use of the separate rotation type pickup in the magneto-optical disk device.

As described above, according to this embodiment, it is possible to realize an excellent magneto-optical disk device that has a structure that can easily realize high-speed access, and that does not cause any quality deterioration of the reproduced signal. can.

Next, other embodiments of the present invention will be described with reference to the drawings.

FIG. 8 shows a second embodiment of the invention. In the previous embodiment, the wavelength plate 100 was provided on the incident surface of the light-conducting member 2 on the objective lens 1 side, but in this embodiment, it is provided on the rotating member 3 side. By doing so, the moment of inertia due to the wave plate 100 can be reduced, and the rotational load can be reduced.

FIG. 9 shows a third embodiment of the present invention. In this embodiment, in order to reduce the weight of the light-conducting member 2, a mirror surface is used as the reflecting means without using a total reflection prism. Even on a mirror surface, some retardation occurs, so a compensating wave plate 100 is necessary. Wave plate 100 can also be provided between two reflective surfaces 2a and 2b.

FIG. 310 shows a fourth embodiment of the present invention. In this embodiment, compensation of beam length is realized without using a wave plate. 2a in FIG.

2b are reflective surfaces facing each other in parallel. 2c.

2d are also reflective surfaces that face each other in parallel.

However, the reflective surface 2c and the reflective surface 2d respectively receive light 1qlILa + L with respect to the reflective surface 2a and reflective surface 2b.
c It is installed in a direction rotated 90 degrees to the center.

If it is made like this (14 structures), the S axis of the reflection 1 river 2a will be opposite to the S 1111 of the ↑ surface 2C, and will be directed towards I,
In the end, the retardation cancels out. The same can be said of the reflective surfaces 2b and 2d. With this method, retardation/g can be eliminated without using an expensive wave plate. Of course, the reflective surfaces 2a and 20, and the reflective surfaces 2b and 2d
The values of retardation caused by must be exactly the same.

Effects of the Invention As described above, according to the present invention, an objective lens, two reflecting surfaces, and an optical phase member for canceling the retardation caused by the reflecting surfaces are provided on the rotating member, and these members are attached to the rotating member. By adopting a structure in which the optical system body is optically coupled to the optical system body that has an external light emitting means and light receiving means, high-speed access can be easily achieved, and the quality of the reproduced signal does not deteriorate due to retardation of the reflective surface. Therefore, it is possible to realize a magneto-optical disk device, which has been a problem.

[Brief explanation of the drawing]

Fig. 1 is a side view of a conventional magneto-optical disk device, Fig. 2 is a diagram for explaining the principle of XS magnetic signal reproduction, and Fig. 3 is a side view of a magneto-optical disk device using a separate rotary optical pickup. 4 is a diagram showing the occurrence of retardation in a separate rotation type pickup, FIG. 6 is a diagram showing a measure against laser noise in a conventional magneto-optical disk device, and FIG. A side view of the magnetic disk device, FIG. 7 is an explanatory diagram showing the effects of the embodiment, and FIG.
9 and 10 are diagrams showing different embodiments of ponds, respectively. 1...Objective lens, 2a, 2b...Reflecting surface, 3...Rotating member, 4...Optical system main body,
100...wave plate, 2C, 2d...reflection surface. Name of agent: Patent attorney Nakao (late man) and 1 other person (Mio 2)
Figure 50w 5' Figure 3 Figure 4 Figure 7 Stone Figure 8? Figure 9

Claims (7)

[Claims] (1) An objective lens on a rotating member, a first reflecting member provided on the central axis of the objective lens, a second reflecting member set opposite to the first reflecting member, and an optical optical phase members having a fast axis and a slow axis are arranged in a line along the optical axis, and the second reflecting member is provided on the rotation axis of the rotation member, and the second reflection member is provided on the rotation axis of the rotation member. An optical system main body having a light emitting means and a light receiving means provided outside the rotating member;
What is claimed is: 1. A magneto-optical disk device comprising: optically coupled reflective members; (2) The magneto-optical disk device according to claim 1, wherein total reflection prisms are used as the first and second reflecting members. (3) A magneto-optical disk device according to claim 1, characterized in that a linear phase shifter made of a birefringent crystal is used as an optical phase member. (4) A magneto-optical disk device according to claim 2, wherein an optical phase member is provided on the incident surface of the first or second reflecting member. (5) A third reflecting member and a fourth reflecting member are provided in the optical path connecting the first reflecting member and the second reflecting member, and the third reflecting member is opposite to the first reflecting member. 9 points relative to the first reflecting member around the optical axis connecting the third reflecting member.
The fourth reflecting member is provided in a direction rotated by 0° with respect to the second reflecting member around the optical axis connecting the second reflecting member and the fourth reflecting member. A magneto-optical disk device according to claim 1. (6) The magneto-optical disk device according to claim 1, wherein the first reflecting member and the second reflecting member are provided parallel to each other. (7) The magneto-optical disk device according to claim 4, wherein the first and second reflecting members are installed parallel to each other, and the third and fourth reflecting members are installed parallel to each other. .