JPS63306554A - Head for magneto-optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain a magneto-optical head having simple constitution in its optical system to be easily produced and having simple structure in its photodetector to be easily adjusted by using a composite polarizing prism obtained by sticking reflecting plane prisms having unparallel angles to a plane. CONSTITUTION:In order to detect a magneto-optical signal, reflected light from a disk is rotated by 45 deg. through a 1/2 wavelength plate 7 and separated into two polarized components (P and S polarized components) which are rectangular to each other by using the composite polarizing prism obtained by sticking the reflecting plane prisms 9 having unparallel angles to one face. Consequently, a normal plane triangular prism can be used for a reflecting plane prism 8, its production can be extremely simplified, the structure of the photodetector 15 can be simplified and its adjustment can be made easy.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a magneto-optical disk head, and in particular to a compact optical head suitable for recording and reproducing information on a magneto-optical disk preformatted using a sample servo method. This relates to the optical structure of the head.

[Conventional technology]

Magneto-optical disk heads have more complex optical systems than other optical heads, and therefore pose problems in miniaturization, assembly, and adjustment. Various structures have been proposed in the past, such as one proposed by the Japan Society of Applied Physics (Spring 1986, 2P-H-12, Heads for Small Magneto-Optical Disks, p. 112).

A linearly polarized minute light spot is formed by an objective lens via a collimator lens and a half prism on a magneto-optical disk on which a pre-group (groove depth 1/8 wavelength), which is well known for data recording optical disks, is formed. When a magneto-optical medium is magnetized, the reflected light of the laser beam irradiated thereon rotates by a small angle due to the Kerr effect. By optically detecting the rotation angle of linearly polarized light due to the Kerr effect, it is possible to detect a magneto-optical signal.

For optical discs, it is necessary to detect a bush-pull tracking signal, which is the amount of deviation of the center of the optical spot from the center of the pregroove on the disc, and a focus deviation of the optical spot from the disc surface. The linearly polarized reflected light, which has undergone slight polarization rotation, from the magneto-optical signal detection disk is rotated by 45° using a single wavelength plate, and is made incident on a polarizing prism. The P-polarized light component is reflected by the polarizing prism, passes through a projection lens, and forms an image on a photodetector. On the other hand, the S-polarized component passes through the beam splitter.

61%! ! As shown in Figure 2, the S-polarized light component is reflected in two directions different from the reflection direction of the P-polarized light on the composite prism surface consisting of a reflective cylindrical lens and a reflective mirror fitted to the polarizing prism, and the S-polarized light component is reflected in two directions different from the P-polarized light. Image point (light reflected from a cylindrical surface).

The light reflected by the plane mirror forms an image.

Furthermore, by using the bush-pull differential tracking signal from the S-polarized light reflected by the cylindrical surface of the composite surface, and by using the Knifezi method from the other S-polarized reflected light reflected by the plane mirror of the composite surface. Detect autofocus signal. The knife method detects out-of-focus by inserting a knife-like object into the light beam. Further, the structure is such that a magneto-optical signal is detected from the difference signal between the sum of the two S-polarized signals and the reflected light using a P-polarized polarizing prism. In this example, a focus signal and a tracking signal are obtained by attaching a composite prism consisting of a reflective plane and a reflective cylindrical surface to a polarizing prism. This is shown in detail in FIG.

[Problem that the invention seeks to solve]

However, since the composite surfaces (flat and cylindrical surfaces) have different shapes, it is very difficult to process them, and the boundary line between the cylindrical surface and the flat surface must be processed to avoid polishing. effect is lost, and the accuracy of the focus signal deteriorates. It is conceivable to mold objects with such compound curved surfaces into plastic, but in order to achieve the performance of a polarizing prism, it is necessary to use a high-quality polished glass material such as BK7, and plastic molding is difficult. The photodetector is composed of three photodetectors as shown in Fig. 7, and the photodetector is - It is difficult to adjust the photodetector because it must be adjusted while further rotating in the Y axis.

Furthermore, since the bush-pull tracking signal from the pre-group of the disk is obtained from a small light spot focused on the photodetector surface, it is difficult to detect the bush-pull signal, so a cylindrical lens is used to magnify it in one direction to detect the differential signal. However, there are problems such as offsets occurring due to axial movement of the objective lens.

The purpose of the present invention is to solve the following problems in the conventional example: (1) Since a composite reflective surface (cylindrical surface, flat surface) is used, it is difficult to process it.

(2) The configuration of the composite photodetector (op polarization detector, S polarization differential tracking signal detector, and S polarization focus signal detector) is complicated and adjustment is difficult.

■ A cylindrical lens is used to magnify the bush-pull tracking signal to one side and detect it on the lens imaging plane, but this causes offset and prevents accurate tracking.

The object of the present invention is to solve these problems and provide a magneto-optical head whose optical system has a simple configuration and is easy to manufacture, and whose photodetector structure and adjustment are easy.

[Means for solving problems]

In the present invention, in order to detect magneto-optical signals, a composite polarizing prism in which reflective plane prisms having angles that are not parallel to the D plane are bonded together is used.
It is characterized by separating into S-polarized light component).

[Effect]

In the present invention, the one-reflectance surface prism can be a normal planar triangular prism, and its manufacture becomes very simple. Furthermore, the structure of the photodetector is simple and its adjustment becomes easy.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of an optical head according to the present invention, and FIG. 2 is a block diagram showing details of an optical prism used in the present invention.

In FIG. 1, the laser 1 emits a collet lens 2. prism 39 reflecting mirror 4 and objective lens 5 with tracking and focus actuator
A minute light spot is formed on the disk 6 through the. Track 60 on disk 6 is sample servo formatted.

The sample servo format is as shown in Figure 3.
There are many segments consisting of servo area 60-1 and data area 63-1 in one track, for example, about 100.
0 pieces are provided. Furthermore, the servo area-60-1 has tracking marks 61-1 wobbled left and right.
and a focus area-62-1 consisting of a mirror surface.

In the sample servo disk format 60, the tracking error signal is detected from the wobble mark 61-1. When the light spot is reflected from the disk 6, the reflected light becomes linearly polarized light in the magneto-optical medium in which the incident linearly polarized light angle is rotated by several degrees due to the Kerr effect. The reflected light is turned into parallel light again by the objective lens, and mirror 4. The linearly polarized light reflected by the prism 3 is rotated by 45' through the prism 7, and is separated by the polarizing prism 8 into approximately equal P-polarized light and S-polarized light components, as shown in FIG. This is to detect the magneto-optical signal based on the difference between P-polarized light and S-polarized light, remove noise, and double the signal amount.

Now, in FIG. 2, the linearly polarized light 11 rotated by 45' becomes a reflected light 12 at the beam splitter, and the P polarized light component becomes reflected light 12, while the S polarized light component 13 is transmitted. The S-polarized light component 13 that has passed through the beam splitter 8 is incident on a reflective plane prism 9, and both surfaces of the prism 9, which correspond to the reflective surface 10, are not parallel but are tilted by several degrees. The thickness is arbitrary.

The normal to the reflective surface 10 of the reflective plane prism 9 and the incident S-polarized light 1
3 is the incident angle formed by θ. shall be.

Here θ. is reflected when the incident S-polarized light is completely parallel, that is, ■ θ. = sin-'-...■ This is called the critical angle. For example, if the wavelength of the laser is λ”83
0 nm, and the glass material of the 1 reflectance surface prism 9 is BK7.
Then, N=1.5097...■, and θ,=41.48 degrees...■.

That is, the angle of inclination of the reflective surface 10 is approximately Δθ=45
−〇.

=45-41.48 α3.52 degrees...■. The angle between the S-polarized light 13' reflected by the reflecting surface 10 and the P-polarized reflected light 12 is δ = 90-2 0° = 7.03 degrees...■ In other words, the angle between the P-polarized light 12 and the reflected S-polarized light 13' is The corner is
Approximately δQ is 117 degrees.

This S-polarized light 13 has a critical angle θ. Let it enter nearby.

In the case of parallel reflected light, the critical angle is θC, and when the objective lens is out of focus with the disk surface, the S polarized light 13 becomes the critical angle θ.
The light is incident on the prism surface 10 at a divergence and convergence angle slightly deviated from C, and a focus signal is detected using the change in reflectance at that time.

When this method is used, the prism 10 only needs to be a triangular prism having an approximately inclination Δθ and fitted onto the polarizing prism 8.

Now, the slope δ of 1 reflected Pm light 12 and reflected S polarized light 13' is
Since it is approximately several degrees, in order to separate these two beams,
A condensing lens 14 is used. Now, if the focal length of the condensing lens 14 is f, then the deviation between the image points of the two lights on the photodetector 15 installed approximately on the focus plane is Δx=fsin δ...■.

Now, if Δx = 2 vI■ ...■, then f = 16.3■■ ...■.

In the photodetector 15, the imaged P polarized light 12 and S polarized light 1
3', a lens 14 with f=16 mm is used to separate two photodetecting elements 15-1. It is sufficient to use a photodetector 15 shown in FIG. 4, which is a single-chip version of '15-2.

In FIG. 1, 15-1 detects P-polarized light, from which an electric signal 16-1 is obtained.

The detection element 15-2 detects S-polarized light, which is 1
It is made up of two divided elements 5-2' and 15-2', and two signals 16-2' and 16-21 are obtained from each of them.

The focus signal is obtained as an unbalance due to defocus of the S-polarized light, that is, a difference signal of 16-2' and 16-21.

The magneto-optical signal is obtained by the difference between the P-polarized light component and the S-polarized light component. Since the tracking signal uses a wobbling method, it is possible to select from 1, for example, P polarized light 12 and S polarized light + (16-2')) to 1 in the servo area of the preformat track.
It can be easily detected by extracting the output signal from the pair of wobbling marks.

Another deformed prism according to the present invention is shown in FIG.
In FIG. 5, surface 10' of prism 9.

10' are planes each having an angle of polarization.

The reflective surface 10' is coated with a reflective coating, and the surface 10' is not coated with a reflective coating. In this case, an autofocus signal is obtained from the reflected light 13' by the Knifezi method. Here, since the surface 10' is not coated with a reflective coating, half of one reflected light beam 11 is lost, and there is a possibility that the S/N will decrease when obtaining a magneto-optical signal. In order to prevent this, it is also possible to apply a reflective coating to the surface 10' and use the reflected light 13' for magneto-optical reproduction as a plane having a different angle from that of the surface 10'.

〔Effect of the invention〕

According to the present invention, an optical head for recording and reproducing data on a magneto-optical disk uses a prism having a complex compound curved surface that is a combination of two surfaces, an inclined plane and an inclined cylindrical surface, as shown in FIG. As shown in FIG. 7, the photodetector also consisted of three elements that required complicated adjustment. However, according to the present invention, the prism can be made into an ordinary planar triangular prism as shown in FIG. 2 or FIG. 5, and its manufacture becomes very simple.

Furthermore, the structure of the photodetector according to the present invention is characterized in that the structure and its adjustment are very easy, as shown in FIG.

[Brief explanation of drawings]

1 is a block diagram showing an example of a magneto-optical head according to the present invention, FIG. 2 is a diagram showing an example of a triangular plane prism used in the present invention, and FIG. 3 is a diagram showing an example of a sample servo format. , FIG. 4 shows a photodetector used in the present invention and
FIG. 5 is a diagram showing another example of the triangular plane prism used in the present invention, FIG. 6 is a diagram showing a conventional compound curved prism, and FIG. FIG. 3 is a diagram showing a photodetector structure. 1...Laser, 2...Collimator lens, 3...
Half prism, 4...Reflecting mirror, 5...Objective lens. 6...Disk, 7°...172 wavelength plate, 8...
Beam splitter-19...triangular prism, 10...
・Reflecting surface, 11...Reflected light, 12...P polarized light, 13
, 13'... S polarized light, 14... Condensing lens, 15.
15-1.15-2.15-2', 15-2'...
Photodetector, 16-1.16-2', 16-2'...
electoronic signals. /rilν C? L no
(Mushi 4th Eye Evening Prisoner

Claims (1)

[Claims] 1. In a magneto-optical disk, in order to detect the magneto-optical signal, the reflected light from the disk is rotated by 45 degrees with a 1/2 wavelength plate, and then a composite polarizing prism is used, in which a reflective plane prism with a non-parallel angle is attached to one surface. 1. A head for a magneto-optical recording/reproducing device, which separates light into mutually orthogonal polarized components.