JPS62223842A - Optical magnetic disk device - Google Patents

Abstract

PURPOSE:To easily access at a high speed by providing an objective lens and two reflecting surfaces constituted of a multi-layer film on a turning member, and coupling optically these members to an optical type main body having a light emitting means and a photodetecting means provided outside a turning member. CONSTITUTION:Two reflecting surfaces of a photoconducting member 2 are composed of reflecting members 30a and 30b (first and second reflecting members) formed by a multi-layer film and a supporting member 30 to hold the position relation of both. The incident angle of a light beam to respective reflecting members is always 45 deg. regardless of the turning angle of a turning member 3. Consequently, the reflecting member with large incident angle dependence can be used as the reflecting member. Further, since the incident light itself is a single color coherent light emitted from a laser light emitting source 4a, even the reflecting member with large wavelength dependence can be used as the reflecting member.

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.

BACKGROUND OF THE INVENTION Magneto-optical recording is a high-density, writable and erasable recording method that has attracted attention in recent years.

FIG. 6 shows a side view of a conventional magneto-optical disk device. In Fig. 6, ■ is an objective lens, and 4 is a laser emission source 4.
a, collimator lens 4b, spectroscopic element 4C1 analyzer 4e
, a light-receiving lens 4d, and a light-receiving element 5. 10 is a rotating magneto-optical disk, and 20 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 store recorded information in a size of several micrometers).
Since the amount of surface wobbling and eccentricity (several tens of microns) is larger than that of the disk, 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 housing by a spring material or the like, and can be electromagnetically driven in the direction of surface runout and eccentricity of the disk.

However, since the present application does not directly discuss the configuration of these follow-up control systems, details thereof will be omitted. Further, the external magnetic field applying device used for recording and erasing signals 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 the collimator lens 4b and then focused onto the magneto-optical disk 10 by the objective lens 1. The light is then reflected, passes through the objective lens 1 again, is changed direction by the spectroscopic element 4c, passes through the analyzer 4e and the light receiving lens 4d, and reaches the light receiving element 5.

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 degrees). When lights (S, N) with Kerr effects in opposite directions are incident, 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. The biggest advantage of disk drives is that by moving the head in the radial direction of the disk at high speed, information written anywhere on the disk can be quickly read (
accessible). However, in the case of an optical disk device, the optical head is heavy, precise, and has a complicated structure, so it is not easy to move the optical head at high speed. FIG. 6 shows a general method for moving the optical head, 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. FIG. 3 shows a side view of a magneto-optical disk device using a separate rotation type optical pickup. 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, there is a rotating member 3 between the objective lens 1 and the optical system main body 4, and two reflective surfaces 2a and 2b mounted on the upper surface thereof at an angle of 45° to the optical axis and facing each other in parallel. It is characterized in that a photoconductive member 2 is provided. Furthermore, the rotational axis of the rotating member 3 is completely aligned with the optical axis that connects the optical system body 4 and the optical system body 2, which passes through the center of the objective lens 1, the photoconductive member 2, and the optical system body 4. It is characterized by the presence of

The operation of the separate rotation type magneto-optical disk constructed as described above 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 l
If the position of the rotation center is determined with respect to the magneto-optical disk 10 so that it moves on an arc substantially along the radial direction of O, 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 amplifier is that it minimizes the weight of the movable mass during track access.

Unlike the conventional example shown in FIG. 6, 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 rotation type optical pickup to a magneto-optical disk device. That is, since the reflective surfaces 2a and 2b of the photoconductive member 2 cause retardation to the incident light beam, there is a problem in that the quality of the magneto-optical reproduction signal 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 body 4) (Fig. 4a). Generally, when light is reflected by a reflective surface, a phase delay of the light wave occurs anisotropically.

Taking FIG. 4 as an example, the intersection of the reflecting surface 2b and the plane containing the incident and reflected rays! Between the P axis and the S axis perpendicular to it,
. . . Incident angle n=n, /nz nl . . . Refractive index n2 inside the reflecting surface. A phase difference expressed by the refractive index outside the reflecting surface is generated. This is a phenomenon called retardation. If the reflective surface 2b is set at 45° with respect to the incident light, and the reflective surface 2b is a total reflection prism made of glass with a refractive index of 1.5, θ=45°, n+-1,
5. Substitute n2=1 into equation (1) to obtain a value of δ=38.6°. In the configuration shown in Figure 2, the reflection 2a
, 2b exists on the round trip optical path, so the retardation is also 4
δ, which in the above example would be 154°.

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 tilted by φ with respect to the polarization direction of the incident ray I, a phase difference will occur in the S and P axis projection directions of the incident ray, so the retardated ray 0 becomes elliptically polarized light. . 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.

There are two effects that retardation has on the magneto-optical reproduction signal: (1) signal deterioration due to retardation itself, and (2) signal deterioration due to ellipticalization of the reproduction beam due to retardation. This will be briefly explained in the following sections.

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. No reproduced signal can be obtained when δ=90°. Since the retardation due to the photoconductive member 2 using the total reflection prism was 154°, the amplitude of the reproduced signal is reduced to cos 154°, or 90%.

(2) is a problem specific to separate rotary optical pickups.

In FIG. 4, a linearly polarized light beam I emitted from the optical system main body 4 passes through the photoconductive member 2, the objective lens 1, and the magneto-optical disk 1.
It has already been mentioned that the light ray O that returns to the optical system main body 4 may become elliptically polarized light as a result of a four-turn tardion occurring in the reciprocating optical path passing through the optical system body 4. What should be noted here is that the degree to which the ray O is elliptical (ellipticity) is the reflection surface 2
a.

2b, that is, it changes depending on the rotation angle φ with respect to the polarization direction of the light beam I incident on the photoconductive member 20. 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 (Fig. 4, c). From FIG. 4, when φ=O゛ (ignoring the polarization due to Kerr rotation received on the disk surface), the emitted light ′! tIAo returns as linearly polarized light.

It is not preferable for signal reproduction that the ellipticity of the light ray O depends on the rotation angle of the photoconductive member 2. The reason is explained below. The most important problem with magneto-optical disk devices is the S/N ratio of the reproduced signal. As mentioned earlier, the magneto-optical disk device obtains a reproduction signal by detecting the difference in polarization angle due to the Kerr effect, but the Kerr rotation angle is very small, at most about 1°. Therefore, the S/N of the reproduced signal is extremely degraded due to noise etc. emitted by the laser light source 4a.

The fifth method is often used as a measure to improve S/N.
This is a signal detection method using the differential canceller shown in the figure.

As explained in FIG. 2, the magneto-optical reproduction signal is transmitted to the analyzer 4e.
It can be obtained by detecting the alternating current component of the light that has passed through the . Now, assume that the component perpendicular to the W direction that did not pass through the analyzer 4e is reflected and received by another light receiving element. Figure 5 shows the outputs of the light-receiving element 5a on which the passing light enters and the output of the light-receiving element 5b on which the reflected light enters.The DC component and noise component of the laser light are in phase with the pixel elements, and the out-of-phase component due to Kerr rotation is They are in opposite phases to each other (R5,.

R98). Therefore, by appropriately setting the balance between the two outputs and taking the difference, the noise component can be canceled and only the signal sentence can be extracted (Rout).

However, when a separate rotary type pivot amplifier is used, the ellipticity of light entering the analyzer 4e changes depending on the rotation angle φ of the photoconductive member 2. 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 problem that the invention seeks to solve A summary of what has been said above is as follows.

Separate rotating optical pickups are optical pickups that have few moving parts and can be easily accessed at high speed. However, if this method is introduced into a magneto-optical disk drive, the quality of the reproduced signal will deteriorate due to the retardation of the two rotating reflective surfaces. There was a problem with deterioration.

In view of the above-mentioned problems, the present invention provides a magneto-optical disk device in which high-speed access can be easily realized, and the quality of the reproduced signal can be equivalent to that of the conventional device.

Means for Solving the Problems In order to solve the above problems, the present invention provides a first reflecting member and a second reflecting member in which the retardation generated by them becomes almost zero at an appropriate incident angle and wavelength. It was constructed from a multilayer film designed as follows.

With this configuration, not only the weight of the movable part during track access is reduced, but also the retardation caused by the first and second reflective members is eliminated, and high-speed track access is easily realized without deteriorating the quality of the reproduced signal. I can do it.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 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. 1, the two reflective surfaces of the photoconductive member 2 are formed by reflective members 30a and 30b (first and second reflective members) formed of multilayer films, and a supporting member 30c that maintains the positional relationship between them. It is composed of All others are 3rd
It is the same as shown in the figure.

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

A reflective member as shown in this embodiment is generally called a multilayer mirror. A multilayer mirror is an optical element that reflects light by utilizing multiple reflections in thin films or mutual interference between adjacent films. Unlike metal mirrors or total reflection mirrors, multilayer mirrors have a strong dependence of reflectance on wavelength and angle of incidence; however, on the other hand, the number of constituent films and the refractive index and thickness of each film must be appropriately selected. By this, desired reflectance or various optical constants can be realized.

In the usage like this embodiment, the reflective members 30a and 30
b does not necessarily have to be a metal mirror or a total reflection mirror. The angle of incidence of the light beam on each reflecting member is always constant regardless of the rotation angle of the rotating member 3.

In this example, the angle of incidence is always 45°. Therefore, even a material having a large incidence angle dependence can be used as a reflecting member. Furthermore, the incident light itself is Ray Lin - light source 4a
It is monochromatic coherent light emitted by Therefore, even materials with high wavelength dependence can be used as reflective members.

The advantage of using a multilayer mirror as a reflective member is that retardation at an appropriate incident angle or wavelength can be reduced to almost zero by selecting the structure of the multilayer film and the thickness of each film. For example, both the reflecting members 30a and 30b can be made of multilayer films with retardation close to zero. 2. For example, by generating equal amounts of retardation (δ, -) in the orthogonal directions in each of the reflecting members 30a and 30b, mutual retardation is canceled (δ, -δ, ,), and as a result, the retardation generated in both can also be set to zero.

As a result, deterioration of the magneto-optical reproduction signal is eliminated. That is, it is possible to prevent the reproduced light from becoming oval 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 a separate rotation type pickup in the magneto-optical disk device.

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

Effects of the Invention As described above, according to the present invention, an objective lens and two reflective surfaces made of multilayer films are provided on a rotating member, and these members are provided outside the rotating member. A magneto-optical disk device that can easily achieve high-speed access by optically coupling an optical system body having a light-emitting means and a light-receiving means, and does not cause deterioration in the quality of reproduced signals due to retardation of a reflective surface. can be realized.

[Brief explanation of drawings]

FIG. 1 is a side view of a magneto-optical disk device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of the principle of magneto-optical signal reproduction, and FIG. 3 is a magneto-optical disk device using a separate rotary optical pickup. 4 is a schematic diagram showing the occurrence of retardation in a separate rotary pickup, FIG. 5 is a block diagram showing measures to improve the C/N in a magneto-optical disk device, and FIG. 6 is a conventional magneto-optical disk drive. FIG. 3 is a side view of the disk device. 1...Objective lens, 2a, 2b...Reflecting surface, 3...Rotating member, 4...Optical system body, 30a, 30b... ...Reflective member. Name of agent Patent attorney Toshio Nakao 1st person 1st attempt 2nd figure

Claims (4)

[Claims] (1) An objective lens is mounted on a rotary member, a first reflecting member provided on the central axis of the objective lens, and a second reflecting member set opposite to the first reflecting member. An optical system having a light emitting means and a light receiving means provided outside the rotary member, the second reflecting member being arranged in a line along the axis and on the rotation axis of the rotary member. The main body and the second reflective member are optically coupled, and the first reflective member and the second reflective member are each made of a multilayer film, and the above-mentioned A magneto-optical disk device characterized in that the multilayer film is formed so that retardation occurring in both the first reflecting member and the second reflecting member becomes almost zero at an appropriate incident angle or an appropriate wavelength. (2) A multilayer film is formed so that retardation occurring in both the first reflective member and the second reflective member is almost zero for monochromatic light with an incident angle of 45°. The magneto-optical disk device according to item (1). (3) A magneto-optical disk device according to claim (1), characterized in that the first reflecting member and the second reflecting member are provided parallel to each other. (4) A first reflective member and a second reflective member are provided parallel to each other, and the reflective surfaces of the first reflective member and the second reflective member are approximately 45°
Claim No. 3 (3) is characterized in that it is provided at an angle of
) The magneto-optical disk device described in item 2.