JPH01184644A - Magneto-optical head device - Google Patents

Abstract

PURPOSE:To simplify an optical path itself and to realize a compact and light magneto-optical head by constituting a photodetective means of a plate form photodetector small in a space occupying ratio and consisting reflected light detecting system of a single optical path. CONSTITUTION:A system for applying light projected from a semiconductor laser 1 to a magneto-optical disk 9 has the same constitution as an ordinary system and a reflected light divided by a beam splitter 6 is guided to the reflected light detecting system 11 formed only by the single optical path 10. Herein, the detecting system consists of the photodetective means 14 consisting of photodetective plates 12 and 13 as the photodetector, an astigmatic aberration system focusing error detecting means 17 consisting of a focusing lens 15 and a cylindrical lens 16 in which the generator of a cylindrical surface is inclined at 45 deg. to the surface of paper and a photodetector 18 constituted of four photodetective elements. In such a way, the photodetector 18 is used also as a tracking error detecting means, the four elements are combined symmetrically to three types centering the photodetector 18 to execute three types of the detections of the detection of recording information, the detection of the focusing error and the detection of the tracking error.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to the configuration of an optical system of an optical head of a magneto-optical recording device.

[Conventional technology]

In a magneto-optical disk as a magneto-optical recording medium, the magnetization directions of the information recording parts in the recording state or the erased state are opposite to each other. Therefore, while applying a magnetic field in the direction corresponding to the direction of magnetization in each state, The temperature of the information recording section is raised to near the Curie temperature by projecting light focused onto a minute spot, and the information recording section is magnetized in the direction of the magnetic field to record or erase information.

In addition, when reproducing information, the Kerr effect is used, in which when linearly polarized light is reflected by a magnetic material, the polarization direction of the reflected light rotates with respect to the polarization direction of the incident light, and the reflected light is passed through an analyzer. By doing this, the intensity signal of the light corresponding to the rotation direction of the polarization direction, that is, the magnetization direction of the information recording section is detected.

The reflected light detection system in the magneto-optical head device uses the reflected light received during information reproduction to detect the presence or absence of minute spots on the surface of the magneto-optical disk in all cases of recording, erasing, and reproduction.Focus error detection and,
It is necessary to provide a total of three functions: tracking error detection, which detects whether the minute spot deviates from the information track.

FIG. 4 is a configuration diagram of an optical system of a conventional magneto-optical head device. A semiconductor laser 1 serving as a light source projects linearly polarized light 2 whose polarization direction is perpendicular to the plane of the paper and is indicated by the symbol O, and is converted into a parallel light beam by a collimating lens 3. Since the projection light from the semiconductor laser 1 has different spread angles in the horizontal direction and the vertical direction, the cross section of the parallel light beam is elliptical. This parallel light beam is shaped by a beam shaping prism 4 into a parallel beam 5 having a circular cross section. This parallel beam 5 passes through a beam splitter 6 and a reflection mirror 7, and is focused by an objective lens 8 onto a microscopic slot 7) with a diameter of approximately 1-10 mm on a magnetic recording portion (not shown) of a magneto-optical disk 9 as a magneto-optical recording medium. and is projected.

The information track on which the magnetic recording section is provided is arranged in a direction parallel to the plane of the paper, and the direction of polarization of the projected light is approximately perpendicular to the direction of the information trunk. The projected light is reflected by a magnetic recording section (not shown), and this reflected light changes its polarization direction according to the direction of magnetization of the magnetic recording section, passes through the objective lens 81 and reflection mirror 7 again, and is sent to the beam splinter 6. The light is reflected and guided to the reflected light detection system 41.

In the reflected light detection system 41, the reflected light passes through a 172 wavelength plate 42.
After passing through the polarizing beam splinter 43, the beam is split into two optical paths 46 and 47 each having a photodetector 44 and 45, respectively.

In the optical path 46, the photodetector 44 is divided into two parts parallel to the plane of the drawing, and constitutes a push-pull type tracking error detection means. In this method, when a minute spot deviates from the information trunk, the diffracted light from the edge of the information trunk included in the reflected light is directed in a specific direction in a plane perpendicular to the optical path 46, that is, in a direction perpendicular to the information track, that is, perpendicular to the plane of the paper. Since this gives a variation in the light amount distribution, this is detected by the two-divided photodetector 44.

Further, the optical path 47 is provided with a condensing lens and a cylindrical lens 49, which constitute astigmatism type focus error detection means. As shown in Fig. 5, this method produces astigmatism with a cylindrical lens 49, and the state of convergence between light rays in a plane parallel to the plane of the paper shown by solid lines and light rays in a plane perpendicular to the paper plane shown by dotted lines. If there is no focus error, the projected image of the light on the photodetector 45 divided into four parts becomes a circle, otherwise it becomes an ellipse whose long axis is diagonal to each other,
Focus errors are detected by making use of variations in the light intensity distribution in two diagonal directions, which are specific directions in a plane perpendicular to the optical path. The outputs of the diagonal elements of the four-divided photodetector 45 are summed, and a focus error is detected based on the difference between these sums.

Further, the 172 wavelength plate 42 shown in FIG. 4 is arranged so that its optical axis makes an angle of 22.5 degrees with respect to the direction of polarization of the projected light, and rotates the same direction of polarized light as the projected light by 45 degrees. The polarizing beam splitter 43 is also an analysis means, and among the above-mentioned light split by the polarizing beam splitter 43, the light on the optical path 46 becomes a component whose polarization direction is parallel to the plane of the paper indicated by the symbol, and the light on the optical path 47 becomes a polarized component. The direction of is the component perpendicular to the plane of the paper, which is indicated by the symbol ○. The amount of light divided into components whose polarization directions are perpendicular to each other changes differentially as the polarization direction is rotated, as will be explained later in the section on embodiments of the invention. Information is detected by calculating the difference between the outputs of the detectors 44 and 45.

[Problem that the invention seeks to solve]

The magneto-optical recording device has an I-spray amount that is as small as possible, partly because the magneto-optical recording medium itself is a disc that is easy to handle.

On the other hand, in a reflected light detection system in which the optical path is composed of multiple systems, the space occupied by the optical path is large and the number of optical components including the photodetector is large, resulting in a complicated configuration.

In particular, the polarizing beam splitter, which serves both as an optical path splitting means and a light analysis means, has a shape of two right-angled prisms, has approximately the same vertical and horizontal dimensions, and occupies a relatively large space.

Configuring the reflected light detection system with multiple optical paths in this way not only occupies space in the optical path, but also increases the number of optical parts, which hinders the miniaturization of the head and also hinders weight reduction. become.

Furthermore, each optical component is expensive, and the greater the number of components, the more expensive the device and the more man-hours for assembly.

In addition, the present invention solves the above-mentioned problems that require adjustment for each optical path, which hinders the cost reduction of the device, and provides a compact, lightweight, and inexpensive magneto-optical recording head device with a simple configuration of the reflected light detection system. The purpose is to provide.

[Means for solving problems]

This invention comprises at least one pair of plate-shaped analyzers as an analysis means, detects information based on fluctuations given to the light intensity distribution in one direction in a plane perpendicular to the optical path, and uses focus error detection means and tracking The error detection means is also of a type that detects the variation of the light amount distribution in a specific direction in a plane perpendicular to the optical path, and the directions in which these variations are given are different, and the The reflected light detection system is configured to consist of a short single optical path so that the detection means detects these variations in the light amount distribution.

That is, the reflected light detection system is configured as follows.

Information is recorded by focusing linearly polarized light into a minute spot and projecting it onto an information track on a magneto-optical recording medium.

In a device for erasing and reproducing, a reflected light detection system for detecting reflected light from the magneto-optical recording medium is composed of at least one pair of plate-shaped analyzers, and the transmission axis of each of the pair of analyzers is is arranged so as to form an angle of 45 degrees with the direction of polarization of the linearly polarized light and to be orthogonal to each other;
a converging lens, a cylindrical lens whose generating line of the cylindrical surface is inclined at 45 degrees with respect to the direction of polarization of the linearly polarized light;
A photodetecting means consisting of several photodetecting element elements is provided on a single optical path.

(Function) Since the pair of analyzers constituting the analyzer is plate-shaped, their space occupancy is extremely small, and their respective transmission axes are perpendicular to each other, so that the polarization direction of the linearly polarized light projected onto the information track is They are arranged at an angle of 45 degrees, so when linearly polarized light whose polarization direction is rotated from the above direction is incident, the amount of transmitted light from each of the pair of analyzers increases on one side and decreases on the other. Therefore, variations are given to the light intensity distribution in the direction in which the analyzers form a pair, which is a specific direction in a plane perpendicular to the optical path.

The focusing lens and the cylindrical lens constitute an astigmatic focus error detection means, and the generatrix of the cylindrical surface of the cylindrical lens is
When the lens is tilted by 5 degrees, a focus error causes a variation in the light quantity distribution in a direction different from that produced by the analyzer in a plane perpendicular to the optical path.

The optical system of the light analysis means or the focus error detection means simultaneously constitutes a push-pull type tracking error detection means that detects tracking errors based on fluctuations in the light intensity distribution in a specific direction in a plane perpendicular to the optical path. The two means described above are arranged along the same optical path so that the specific directions in which the fluctuations in the light intensity distribution are given are different, and the above-mentioned method is obtained by respectively different combinations of the plurality of photodetecting element elements constituting the photodetecting means. Fluctuations in light intensity in each direction can be detected. This makes the optical path of the reflected light detection system single and short.

(Embodiment) Fig. 1 is a diagram showing the configuration of an optical system in an embodiment of the present invention. The reflected light divided by 6 is guided to the reflected light detection system 11 formed by only a single optical path 10. It consists of an analyzing means 14 in which analyzing plates 12 and 13 are coupled on the optical axis which is the center of the optical path 10, a focusing lens 15, and a cylindrical lens 16 whose generatrix of the cylindrical surface is inclined at 45 degrees with respect to the plane of the paper. The light passes through the astigmatism type focus error detection means 17, and then enters a photodetector 18 as a photodetection means composed of four photodetection element elements.As will be explained later, this photodetector 18 It also serves as a tracking error detection means, and also serves as a light detection means common to the light analysis means 14, focus error detection means 17, and tracking error detection means, and four detection element elements are arranged symmetrically around the center of the photodetector 18. The three types of detection are performed in combination in three ways: recording information detection, focus error detection, and tracking error detection.

FIG. 2 is a diagram showing the principle of the above three types of detection in the reflected light detection system 11.

FIG. 2 (1M) is a principle diagram schematically showing the configuration and function of the reflected light detection system 11, (bl is a diagram of the operating principle of the analyzing means 14, and (C1, ldl are the lights projected onto the photodetector 18. It is a state diagram of a light beam.

The direction of polarization of the light from the semiconductor laser 1 projected onto the information track is the direction indicated by the arrow at the left end of (al).

The analysis means 14 includes analysis plates 12 and 13 as a pair of analyzers.
are connected by edges parallel to the L direction, and this combined edge is arranged on the optical axis of the optical path 10.

The transmission axes of each analyzer plate are orthogonal to each other as shown by the arrows in the figure, and are each inclined at 45 degrees with respect to the L direction.

The linearly polarized light incident on the reflected light detection system 11 is detected by the analyzer 14.
The right half and left half of the beam, which is projected as a light beam with a circular cross section as shown in the figure, and which has passed through the analyzer 14, are two component lights whose polarization directions are in the direction of the transmission axes of the analyzers 12 and 13, respectively. Become. Here, the right half is the P component light 21. The left half will be referred to as S component light 22.

The above-mentioned light beam passes through a focus error detection means 17 composed of a focusing lens 15 and a cylindrical lens 16, and then enters a photodetector 18 as a light detection means. The photodetector 18 is composed of four photodetector elements A, B, C, and D separated by straight lines parallel and perpendicular to the L direction.

The focus error detection means 17 is based on the conventional astigmatism method shown in FIG.
The cylindrical surface is arranged with its generating line inclined at 45 degrees with respect to the L direction. Therefore, the optical path 10 seen from the direction of the white arrow parallel to the generatrix of the cylindrical surface of this cylindrical lens or its center plane 23 is the same as that shown in FIG. The light beam is once focused in a plane perpendicular to the central plane 23 and then diverged to the photodetector 18.
Therefore, the cross section of the light beam on the photodetector 18 is symmetrical about the cross section of the light beam incident on the cylindrical lens 16 and the center plane 23 of the cylindrical lens 16, and the boundary between the P component light 21 and the S component light 22 is symmetrical. rotates from the L direction to the horizontal direction.

Accordingly, the P component light 21 is transmitted to the upper half of the photodetector elements A and B, and the S component light 22 is transmitted to the lower half of the photodetector element C,
The light is received at D.

These P-component light 21 and S-component light 22 fluctuate in the vertical direction, which is one specific direction on the surface of the photodetector 18 perpendicular to the optical path 10, in reproducing information from a magneto-optical disk, as described below. do.

FIG. 2(b) shows how the amounts of the P component light 21 and the S component light 22 change due to the magnetization of the magnetic recording portion of the magneto-optical disk 9. FIG. Linearly polarized light is shown by an arrow, the direction of the arrow corresponds to the direction of polarization, and the length corresponds to the amount of light.

If the P and S axes are taken at 45 degrees to the right and left with respect to the L direction in FIG. This corresponds to the light amount of the S component light 22.

The direction of polarization of the light projected onto the magneto-optical disk 9 is (a)
This is shown by the arrow OA.On the other hand, the reflected light in the erased state where the magnetic recording section is initially magnetized is shown by the arrow OR where the rotation angle from the L direction is θ in the right direction. If there is, the reflected light from the recorded information is indicated by an arrow OC rotated by an angle θ from the L direction to the left.

In each case, the amount of reflected light does not change in OA - OB - QC, but the amount of P component light 21 changes from OPl to OPz with respect to the rotation of the polarization direction in 20 above.
As is clear from FIG. 8 that the amount of S component light 22 changes from OS to O38, this change is differential in opposite directions. This reverse change is also a differential change in the opposite direction. Therefore, by taking the difference between the P component light 21 and the S component light 22, it is possible to extract the sum of the respective fluctuation components.

On the other hand, a change in the amount of reflected light results in a change in the length of the arrow, and on the other hand, the P component light 21. Since both of the S component lights 22 exhibit fluctuations in the same direction, by taking the above-mentioned difference, this fluctuation is almost canceled out. This allows highly reliable information detection with an extremely good S/N ratio.

In the focus error detection means 17, the generatrix of the cylindrical lens 16 is inclined at 45 degrees in the L direction as described above.

Therefore, if a focus error occurs (C).

As shown in ld3, light is projected in an elliptical shape with major axes in the directions of photodetector elements A, C or B, D that are diagonal to each other in a specific direction, and the light intensity distribution in these directions varies. In order to give
Detected by 2&ll of B and D.

Further, the tracking error detection means in this embodiment also uses a push-pull method similar to the prior art. As already mentioned, in this method, variations in the light amount distribution are given in a direction perpendicular to the information track.

As explained in FIG. 1, the direction is the same as the polarization direction of the light projected onto the information trunk, that is, the L direction. However, due to the tilted cylindrical lens 16, variations in the light quantity distribution in the L direction are projected onto the photodetector 18 as variations in the light quantity distribution in the horizontal direction.
It is detected by two sets, D and B,C. Thus, in this embodiment, the light detection means 18 also serves as tracking error detection means.

The sum 1i+Im of the outputs of the photodetector elements A and B and the sum IC+In of the outputs C and D are respectively given as differential inputs of the differential amplifier 24, and the difference amplifier 24 is Ha −
zs) -Nc +Ie), which is expressed by the following equation +11, is given to reproduce the information.

■, Qing KI ((Ia +rm) (Ic +Ie)
)-...1llKI is a constant.

Further, the photodetector elements A, C and B, D are connected to a differential amplifier 25, respectively, and the photodetector elements A, D and B, C are connected to a differential amplifier 25, respectively.
is connected to the differential amplifier 26 and is expressed by the following equation (2), which is the error signal output I for focusing error, and the following equation (
3) provides an error signal output It for tracking error detection.

1F −Kz ((Is +Ic) (Is +
Ie) ) ---(211T -Ks ((Is
+Ic) (Ia +1++) ) −−=−+
31Kt and Ks are constants.

Since IF and I'T are differential outputs as described above, the fluctuation components are given as a sum, increasing the error detection sensitivity. A control system (not shown) receiving these outputs It, It is I
It operates so that t and It are always zero, so that a minute spot is always formed on the information trunk.

Comparing FIG. 1 showing this embodiment with FIG. 4 showing the prior art, we can see that the polarizing beam splinter 4 has a large space occupation ratio.
3 has been removed, and along with this, the 1/2 wavelength plate 42 is also no longer necessary. Furthermore, the two optical paths become one system, and therefore the photodetector 44 divided into two can also be omitted. 1/2 wavelength plate 42. Since the analyzer plates 12 and 13, which replace the polarizing beam splitter 43, are thin plates, the optical path length of the above-mentioned one system is shortened, and the magneto-optical head device can be significantly downsized.

FIG. 3 shows another embodiment of the invention. In this embodiment, an analysis type photodetector is constructed by stacking and integrating an analysis means 33 made up of two analysis plates 31 and 32 and a photodetector 34 made up of four photodetection elements. 35 constitutes the reflected light detection system 30.

In this configuration, the analyzer plates 31 and 32 are the detection element elements A and B in the upper half of the photodetector 34 and the photodetection element C in the lower half of the photodetector 34.
D, and the direction of their transmission axes is P projected onto the photodetector 18 of 1M+ in FIG.
The direction of polarization is the same as that of the component light 21 and the S component light 22. Therefore, the function of the photodetector 34 is exactly the same as the photodetector 18 of the first embodiment.

In this embodiment, the light analysis means 33 and the light detection means 34 are integrated as a light analysis type detector 35, so that the optical path of the reflected light detection system is further shortened and the apparatus can be made more compact.

In the above embodiment, the light projected onto the magneto-optical disk 9 was linearly polarized light whose direction of polarization was perpendicular to the information track for convenience of explanation, but the transmission axis of the analyzer plate was 45@ Therefore, the same effect can be obtained even with linearly polarized light whose polarization direction is parallel to the information track.

Furthermore, the number of analyzers is not limited to two, but multiple pairs of analyzers whose transmission axes are perpendicular to the direction of polarization of the projected linearly polarized light at 45° are used. A photodetector in which four or more photodetector elements are arranged corresponding to the positions of may be used, and the focus error detection means and tracking error detection means are not limited to the above embodiments. Any structure may be used as long as the light intensity distribution is varied in a plane perpendicular to the optical path, and the direction in which the light intensity distribution is varied by the light analysis means, focus error detection means, and tracking error detection means is different from each other. By configuring the reflected light detection system in this embodiment, the same effects as in the embodiment can be obtained.

〔Effect of the invention〕

According to this invention, the analyzing means is constructed of a plate-shaped analyzer that occupies a small space, and the reflected light detection system consists of a single optical path. Not only can the space-occupying and expensive polarizing beam splitter and photodetector for divided optical paths be omitted, but the optical path itself can be simplified and shortened, and the space occupied by the optical path can be reduced. The magneto-optical head device can be made significantly smaller and lighter.

Moreover, because the number of optical parts is reduced, the configuration of the optical path is simplified, making assembly and adjustment easier. This has the effect of significantly reducing the cost of the head device.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical system of an embodiment of a magneto-optical head device according to the present invention, FIG. 2 is a principle diagram schematically showing the configuration and function of a reflected light detection system in this embodiment, and FIG. FIG. 4 is a block diagram of an optical system of another embodiment of the invention, FIG. 4 is a block diagram of an optical system of an example of a magneto-optical head device according to the prior art, and FIG. 5 is a block diagram of an optical system of an astigmatic focus error detection means. FIG. 2: Optical path, 11: Reflected light detection system, 12.13, 31.3
2: Analyzer plate (analyzer), 14.337 Analyzer means, 15
: Focusing lens, 16: Cylindrical lens, 17: Focus error detection means, 18.34: Photodetector (light detection means,
tracking error detection means), A, B, C, D: photodetection element elements. (b) (a)
114Figure 7.9 15rIA

Claims (1)

[Scope of Claims] 1) In an apparatus for recording, erasing, and reproducing information by focusing linearly polarized light into a minute spot and projecting it onto an information track on a magneto-optical recording medium, A reflected light detection system for detecting reflected light is composed of at least one pair of plate-shaped analyzers, the transmission axes of each of the analyzers forming the pair forming an angle of 45 degrees with the direction of polarization of the linearly polarized light, and mutually arranged. It consists of an analysis means arranged orthogonally to each other, a focusing lens, a cylindrical lens whose generatrix of a cylindrical surface is inclined at 45 degrees with respect to the direction of polarization of the linearly polarized light, and at least four photodetector elements. What is claimed is: 1. A magneto-optical head device comprising: a light detection means on a single optical path; 2) A magneto-optical head device according to claim 1, characterized in that the light analysis means and the light detection means are stacked and integrated.