JP3003160B2 - Composite beam splitter element and optical head for magneto-optical disk using the same - Google Patents

Description

Detailed Description of the Invention [Table of Contents] Overview page 6 Industrial application field page 7 Conventional technology (Fig. 12) page 8 Conventional technology (Fig. 13) page 12 Problems to be solved by the invention page 13 Means for Solving the Problems Page 14 Function page 17 Example page 17 Configuration of Composite Element (FIG. 1) Page 18 Explanation of Preparation Procedure of Composite Element (FIG. 2) Page 20 Configuration of Optical Head (FIG. 3) 21 Page 1 First Embodiment (FIG. 4) Page 23 Description of Magneto-Optical Signal Detection System (FIG. 5) Page 25 Description of First Photodetector (FIG. 6) Page 28 Second Embodiment (7 (Fig.) Page 30 Third embodiment (Fig. 8) Page 30 Fourth embodiment (Fig. 9) Page 31 Fifth embodiment (Fig. 10) Page 31 Sixth embodiment (Fig. 11) Page 31 Effects of the Invention Page 32 Brief Description of the Drawings Page 33 [Overview] The present invention relates to a magneto-optical disk drive, and particularly relates to a miniaturized optical head for a magneto-optical disk, and relates to a high light use efficiency and a polarization state. The purpose of the present invention is to provide a composite beam splitter element capable of simplifying and simplifying an optical element while maintaining the same, and to provide a miniaturized optical head using the element and an optical head for a magneto-optical disk that is hermetically sealed. Between a semiconductor laser serving as a light source and a collimating lens that receives a divergent light beam emitted from the semiconductor laser and converts it into parallel light, a multilayer film splitter is provided on one of the front and back surfaces of a transparent parallel flat substrate. The surface of the multilayer beam splitter of the composite beam splitter element in which the hologram beam splitter is integrally formed on the other surface is provided at a position where the divergent light beam is reflected and relayed to the collimating lens. An objective lens for condensing the converted parallel light on a magneto-optical disc is provided, and reflected by the magneto-optical disc to reverse the forward optical system. The first-order diffracted light obtained by separating the return light transmitted through the multilayer beam splitter and the parallel plane substrate by the hologram beam splitter is used for a magneto-optical signal detection system, and the zero-order transmitted light is used for a servo signal detection system. Constitute.

[Industrial applications]

The present invention relates to a magneto-optical disk drive, and more particularly to a miniaturized optical head for a magneto-optical disk.

2. Description of the Related Art Magneto-optical disk devices have attracted attention as external storage devices for computers because they can rewrite very large amounts of information, and have become widespread in the field of small computers. In order to use this magneto-optical disk device in a wider field, there is a demand for a smaller and thinner device size and improved cost performance (high-speed access, high-speed transfer, and low cost).

A smaller and lighter optical head is indispensable for reducing the size and thickness of the device and improving the cost performance.
Because the miniaturization of the optical head reduces the occupied space (including the access range) of the optical head in the device,
Promote miniaturization of equipment. Further, the reduction in the weight of the optical head is to reduce energy for moving the optical head and to enable high-speed access (movement).

[Conventional technology]

FIG. 12 shows a basic configuration diagram of a conventional optical head for a magneto-optical disk.

The optical head for a magneto-optical disk utilizes the polarization characteristic of light called the Kerr effect to read out information recorded on a medium. Therefore, unlike optical heads for other optical disk devices, the phase characteristics of the constituent optical components (polarization plane) Is especially important. The components are shown below.

1 is a semiconductor laser serving as a light source, 2 is a collimating lens that converts a divergent laser beam having an elliptical pattern emitted from the light source into a parallel laser beam, and 3 is a converter that converts an elliptical parallel laser beam into a circular parallel laser beam. A beam shaping (circularity correction) prism 4 that transmits or reflects incident parallel light at a certain ratio depending on the polarization plane, and separates the optical paths of the transmitted light and the reflected light while maintaining the polarization state; Reference numeral 5 denotes an objective lens for condensing the laser beam transmitted through the polarizing beam splitter 4 on a medium surface of a magneto-optical disk 6 to be described later to near a diffraction limit, and 6 denotes a magneto-optical recording medium for recording and holding information as a magnetization direction. The magneto-optical disk 7 detects the amount of parallel laser light emitted from the beam shaping prism 3 and guided to another optical path by reflection at the polarization beam splitter 4. That the photodetector, 8 auto power controller for controlling the semiconductor laser 1 of the power based on the value detected by the light detector 7 to a predetermined value (Auto P
power controller (hereinafter abbreviated as an APC circuit 8), 9 is reflected by the magneto-optical disk 6, returns to the polarization beam splitter 4 via the objective lens 5, and receives a focus error signal and a track from the separated light guided to another optical path by reflection. This signal detection system detects a light spot control signal (hereinafter, collectively referred to as a servo signal) such as an error signal, a magneto-optical signal, and an ID (preformat) signal.

There are various types of signal detection systems 9. In this example, the focus error signal is detected by the astigmatism method, the track error signal is detected by the push-pull method, and the magneto-optical signal is detected by the 1/1/3 method.
A method using a two-wavelength plate and a polarizing beam splitter, and a method using the total amount of light incident on the signal detection system 9 are used for ID signal detection. Since the principle of detecting each signal has no direct relation to the present invention, a detailed description is omitted.

Next, components 10 to 19 of the signal detection system 9 will be described. Reference numeral 10 denotes a plane of polarization of the light incident on the signal detection system 9 of about 45.
1/2 A rotating half-wave plate, 11 is a polarizing beam splitter that separates by the polarization state of incident light to detect a magneto-optical signal,
12 is a condensing lens that condenses each light separated by the polarizing beam splitter 11 so that it can be efficiently detected.
Is a cylindrical lens for detecting a focus error signal (astigmatism method); 14 is a split light detection for detecting a focus error signal, a track error signal, a magneto-optical signal, and a part of an ID signal by light transmitted through the polarizing beam splitter 11; Detector (only the photodetector is shown in plan view), 15 is a photodetector that detects a part of the magneto-optical signal and the ID signal by the reflected light of the polarization beam splitter 11, and 16 is the difference between the outputs of the split photodetector 14. A servo signal generation circuit created from a combination of signals,
It comprises a focus error signal generation circuit 16a and a track error signal generation circuit 16b. 18 is a quadrant photodetector 1
A magneto-optical signal generation circuit for generating a magneto-optical signal from the output signals of the photo detector 4 and the photo detector 15, 19 is a quadrant photo detector 14 and a photo detector
An ID signal generation circuit that generates an ID signal from each of the 15 output signals.

The electronic circuits of the APC circuit 8 and the signal generation circuits 16, 18, and 19 are not included in the optical head, and may be provided separately from the optical head.

In the above description, the optical system existing in the optical path from the semiconductor laser 1 as the light source to the magneto-optical disk 6 is called the outward optical system, and the optical system existing in the optical path of the light reflected by the magneto-optical disk 6 is defined as the return optical system. It is called a system.

FIG. 13 shows a basic configuration diagram of a conventional read-only optical disk optical head. In the figure, the optical head is provided with a semiconductor laser 20 as a light source, an objective lens 21 for condensing light emitted from the semiconductor laser 20 on a read-only medium 22, and between the semiconductor laser 20 and the objective lens 21. A beam splitter 23 for branching the optical path, and a split photodetector 24 for detecting the signal light branched by the beam splitter 23 with the reflected light from the read-only medium 23.

In such a configuration of the optical head for a read-only optical disk device, neither magneto-optical recording (erasing) nor reproduction is possible, and information on the magneto-optical disk cannot be rewritten or read. That is, since the magneto-optical recording (erasing) operation of heating to a temperature higher than the Curie point temperature of the read-only medium 22 is not required, the irradiation light power to the read-only medium 22 may be small, and the optical system with extremely reduced light efficiency may be used. It has become. Further, since there is no need to consider the polarization state of the light beam, which is indispensable for reproducing the magneto-optical signal, it is possible to construct a very simple circuit having no polarization maintaining function and no polarization separation function.

[Problems to be solved by the invention]

2. Description of the Related Art A conventional optical head for a magneto-optical disk drive is composed of many optical components sharing functions. The large number of parts leads to an increase in man-hours for parts management, assembling and adjustment and an increase in installation space.
In particular, the increase in size is a factor that hinders a reduction in the access time of the optical head. As a means for reducing the size of the optical head, it is conceivable to reduce the size of an optical system similar to the example shown in FIG. However, although this method can achieve a reduction in size and weight, it poses a problem in terms of price. In general, when the dimensions are reduced without lowering the precision of the optical component, the processing conditions become severe and the production price increases.

In addition, among the optical head components, the photoelectric conversion function element such as each photodetector is provided with an inert gas or dry nitrogen for each element in order to enhance its environmental resistance and to guarantee its function for a long time. Airtight sealing or solid sealing with a resin mold has been implemented, but these sealing portions are disadvantages that hinder miniaturization of the optical head.

Furthermore, the circuit components and the size required for the optical head also pose a problem, and there is a method of directly mounting the IC bare chip inside the optical head for the purpose of miniaturization. Hermetic sealing is essential.

The present invention has been created in view of the above-mentioned conventional disadvantages,
Provide composite beam splitter element capable of compounding and simplifying components while maintaining high light use efficiency and polarization state, miniaturized optical head using the element, and hermetically sealed magneto-optical disk The purpose is to provide an optical head.

[Means for solving the problem]

FIG. 1 is a structural view of a composite beam splitter element of the present invention, FIG. 3 is a structural view of an optical head for a magneto-optical disk using the composite beam splitter element, and FIGS.
FIG. 11 to FIG. 11 show first to sixth embodiments of the present invention, respectively. In the present invention, the light-use efficiency and the polarization state are made as simple as the conventional read-only optical head, and as means for reducing the number of components of the optical head in order to realize an optical head for magneto-optical recording and reproduction. While simplifying and simplifying components.

First, the multifunction of the lens system is attempted. In a read-only optical head for an optical disk, in the return optical system, reflected light (return light) from the optical disk is converged by an objective lens,
A servo signal and a magneto-optical signal are detected by using the convergent light. However, in order to use this method for an optical head for a magneto-optical disk, a collimating lens 2 having a similar function in an outward optical system is used. An optical head for a magneto-optical disk is constituted by also forming convergent light in the return optical system.

Next, the magneto-optical signal detection system and the servo signal detection system are constituted by flat optical elements which are simple in shape and easy to mount. Combining the beam splitter function to provide the function of switching between the forward path and the return path and the signal light separation function for signal detection, a multilayer film splitter 27 and a hologram beam splitter 28 are provided on each surface of one transparent parallel flat substrate 26, respectively. The formed composite beam splitter element 25 is used. In addition, the hologram beam splitter 28 uses the first-order diffracted light j, which has been corrected and separated for aberration accompanying transmission through the parallel plane substrate 26, for detecting a magneto-optical signal,
The polarization separation for the detection is constituted by a birefringent crystal plate 31 having a parallel plate shape. Further, the zero-order transmitted light k transmitted through the hologram beam splitter 28 is used for detecting a servo signal, and is converged and detected while correcting aberration through an optical parallel plate 33.

The optical head configured as described above further includes a wavelength plate 35 for facilitating the adjustment of the polarization direction of the outgoing light f of the semiconductor laser 1 or a third light detection used for power control of the outgoing light of the semiconductor laser 1. It is also possible to add a vessel 36 and the like, and it is possible to reduce the size by the combined and combined effects, and to integrate the airtight casing 37 into an airtight seal such as an inert gas.

(Operation)

Since the collimator lens 2 is also used as a condenser lens of the return optical system, the collimator lens 2
An optical path separation system, a magneto-optical signal detection system, and a servo signal detection system are provided in the space of the optical path leading to, thereby making it possible to dramatically reduce the size of the optical head for a magneto-optical disk. This uses a divergent and convergent light beam, so the light beam diameter becomes smaller,
This is because the size of the optical component used is reduced. Since the composite beam splitter element 25, the birefringent crystal plate 31, and the optical parallel flat plate 33 for aberration correction are all formed of parallel flat plates,
Polishing that requires high-precision angle setting like conventional optical system prisms is not required, making it easy to manufacture while maintaining accuracy even if the component size is reduced, and gas tightly sealed in the sealed housing 37 integrally. By doing so, downsizing is further promoted, and there is an effect that the access time can be reduced.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition,
To facilitate understanding of the description of the configuration and operation, the same portions are denoted by the same reference numerals throughout the drawings, and redundant description will be omitted.

FIG. 1 shows a configuration diagram of a composite beam splitter element of the present invention. In the figure, reference numeral 25 denotes a composite beam splitter element, which is a parallel plane substrate transparent to the wavelength of light to be used.
26, two opposing surfaces of the parallel plane substrate 26, that is, a multilayer film splitter 27 formed on one of the front and back surfaces,
The hologram beam splitter 28 formed on the other surface has a three-layer structure. This composite beam splitter element
Reference numeral 25 denotes an S-polarized light component having a reflectance of 60 to 70% with respect to incident light f (e.g., light emitted from a semiconductor laser) obliquely incident on the surface of the multilayer beam splitter 27, and P-polarized light of the incident light. It is preferable to form the component so as to have almost 100% transmittance for the components. The reflected light g and the transmitted light m are generated at the above ratios in accordance with the polarization state of the incident light f.

The reflected light g is applied to the magneto-optical disk via an objective lens (not shown), and the light wave (return light) h reflected by the magneto-optical disk is corresponding to the polarization state of the multi-layer beam splitter 27 and the parallel plane substrate. 26, the P-polarized light component passes through almost 100%, and the S-polarized light component passes through 40 to 30%, and becomes incident light i which reaches the hologram beam splitter 28.

The incident light i to the Holgram beam splitter 28 is
The light is separated into the first-order diffracted light j and the zero-order transmitted light k according to the polarization state, but has an aberration as a result of being transmitted obliquely through the parallel plane substrate 26. Therefore, the hologram beam splitter 28 corrects the aberration and corrects it in anticipation of the aberration added by an optical system (not shown) that the primary diffracted light j should transmit after diffraction (wavefront conversion function, substantially Distribution). Similarly, the zero-order transmitted light k, which is transmitted without being diffracted by the hologram beam splitter 28, also has an aberration associated with transmission through the parallel plane substrate 26, which can be corrected by an optical system described later.

The composite beam splitter element 25 configured as described above
Is the polarization beam splitter 4 of the conventional configuration shown in FIG.
And a half-wave plate 10 and a polarizing beam splitter 11, which have most of the combined functions, and are combined and simplified. The first-order diffracted light j is transmitted to the magneto-optical signal detection system by the zero- The next transmitted light k can be used for the servo signal detection system.

FIG. 2 is a diagram showing an example of a procedure for producing the composite beam splitter element of the present invention. The hologram can be made of either a surface irregularity type or a volume type, but in consideration of mass productivity, a method of duplicating the surface irregularity by stamping is preferable.
As a procedure for integrally forming the same flat plate together with the multilayer film, first, in the procedure, a multilayer film beam splitter 27 passes through a transparent parallel plane substrate 26 (for example, a general optical glass BK / 7 with a thickness of 0.5 m) through a multilayer film splitter 27. Titanium dioxide TiO ₂ and silicon dioxide SiO ₂ etc. are alternately deposited in multiple layers to obtain a ratio (approximately 100% for P-polarized light component: 40 to 30% for S-polarized light component) I do. In the procedure, a protective film 27a is formed with a photoresist or the like so as not to be damaged in a subsequent process. In the procedure, a hologram pattern of a lattice fringe distribution designed using a computer to correct the above-mentioned aberration (including an accrued portion) set in advance is formed on the surface opposite to the multilayer film beam splitter 27 by a photopolymer method or the like. Then, the protective film 27a is removed in the procedure to form a composite beam splitter.

FIG. 3 is a configuration diagram of an optical head for a magneto-optical disk using the composite beam splitter element of the present invention. In the figure, a semiconductor laser 1 serving as a light source and the semiconductor laser 1
The surface of the multilayer beam splitter 27 is set at a position between the collimating lens 2 that receives the divergent light beam emitted from the lens and converts the divergent light beam into parallel light and reflects and relays the divergent light beam to the collimating lens 2. Composite beam splitter element
25 are provided.

From this arrangement, the S-polarized light component contained in the divergent light beam is
After being reflected by 60 to 70% and converted into parallel light by the collimating lens 2, a light spot is formed on the surface of the magneto-optical disk 6 via the objective lens 5, and the light is reflected by the magneto-optical disk 6. The reflected light containing the polarization component due to the Kerr rotation travels backward in the forward optical system and returns to the surface of the multilayer beam splitter 27, and the multilayer beam splitter 27 corresponds to the polarization state of the returned light.
Then, the light passes through the parallel plane substrate 26 obliquely and reaches the surface of the hologram beam splitter 28. Here, the first-order diffracted light j and the zero-order transmitted light k are polarized and separated according to the polarization state of the returned light.

In the process of obtaining the first-order diffracted light j and the zero-order transmitted light k, the divergent outgoing light emitted from the semiconductor laser 1 using the composite beam splitter element 25 and the convergent light converged by the collimating lens 2 are used as they are. As a result, there is an advantage that the collimator lens 2 can be used also as a condensing lens of the return optical system, the light beam diameter is reduced, and the size of an optical component to be used can be reduced.

The return light containing the polarization component due to the Kerr rotation has its Kerr rotation component increased by transmission through the multilayer film beam splitter 27 (having polarization dependency), and the polarization direction of the incident light i is the main diffraction of the hologram beam splitter 28. An angle is formed with respect to a direction perpendicular to a plane (defined by a plane formed by the incident light i and the first-order diffracted light j). Therefore, the returning light has an S component and a P component with respect to the hologram beam splitter 8. The hologram beam splitter 28 generates a first-order diffracted light j with an appropriate efficiency for both S and P polarization components,
This is incident on the magneto-optical signal detection system 29. Zero-order transmitted light k that is transmitted without being diffracted by the hologram beam splitter 28
Can enter the servo signal detection system 30 and detect each signal. Since each of the signal detection systems uses the convergent light as it is, there is an advantage that the light beam diameter is reduced and the size of the optical component to be used can be reduced.

FIG. 4 shows a first embodiment of the present invention. In the figure,
A magneto-optical signal detection system 29 includes a parallel plate-shaped birefringent crystal plate 31 that receives and transmits the first-order diffracted light j, and the birefringent crystal plate 31.
And a first photodetector 32 for receiving and detecting the transmitted light transmitted through the optical parallel plate 33. The servo signal detection system 30 includes an optical parallel plate 33 for receiving and transmitting the zero-order transmitted light k and light transmitted through the optical parallel plate 33. And a second photodetector 34 for detecting.

For example, when a uniaxial crystal such as calcite or rutile is arranged so that its optical axis (crystal axis) is at an angle of about 45 ° with respect to the traveling direction of an incident light beam, the polarization plane (polarization component including the optical axis) The traveling direction is different in the crystal between the extraordinary light component) and the polarized light component (ordinary light component) having the polarization plane orthogonal to the extraordinary light component, and the position of the condensing point is shifted. The birefringent crystal plate 31 is used for the purpose of performing polarization separation utilizing this phenomenon, and is formed in a parallel plate shape in order to reduce the size of mounting in the optical head.

The optical parallel plate 33 that receives and transmits the zero-order transmitted light k has a function of removing coma caused by an oblique optical parallel plate placed in the optical path of the incident convergent light. It can be constituted by an optical system in which a flat plate is inserted at an angle opposite to that of the composite beam splitter element 25, and accurate detection can be performed if aberration is corrected and used. As a material of the optical parallel plate 33, for example, BK7, which is general optical glass, may be used. At the time of this aberration correction, the astigmatism is left, and the second photodetector 34 is constituted by a split photodetector and used for focus detection. The tracking error signal can be detected by the fish pull method.

FIG. 5 is a perspective view of a magneto-optical signal detection system according to the present invention.
In the figure, the detection of the magneto-optical signal utilizes the first-order diffracted light j separated by the hologram beam splitter 28. More specifically, the polarization direction of the incident light i is adjusted by the main diffraction surface (incident light) of the hologram beam splitter 28. An angle θ is formed with respect to a direction perpendicular to a plane formed by the light i and the first-order diffracted light j), and an X, Y coordinate system (X-axis is a hologram lattice fringe) taken on the hologram beam splitter 28. (Parallel direction), there is a component in the X direction (S-polarized component) and a component in the Y direction (P-polarized component). The P component is generated by the Kerr rotation. The hologram is formed so that the diffraction efficiency of the hologram for S-polarized light is 50 to 80%, and the efficiency for P-polarized light is equal to or higher than that for S-polarized light.

It is known that when linearly polarized light of the first-order diffracted light j is incident on the birefringent crystal plate 31, ordinary light and extraordinary light are separated. That is, by causing the convergent signal light from the magneto-optical disk to enter the birefringent crystal plate 31, the signal light can be separated into two orthogonal polarization components and spatially separated.

A Z-axis is provided for the X-axis and the Y-axis formed on the surface of the hologram beam splitter 28, and is separated by the hologram beam splitter 28 based on the incident light i incident on the coordinate origin in a plane including the Z-axis and the Y-axis. The birefringent crystal plate 31 having the origin of the coordinates x and y in the direction of travel of the first-order diffracted light j and the first
Are sequentially arranged. X, Y axis and x, y
It is assumed that the axes are set in parallel. The direction of the optical axis (crystal axis) of the birefringent crystal constituting the birefringent crystal plate 31 is set so as to form 45 ° with x ′ and y ′ in the plane pqrs. The birefringent crystal plate 31 is set such that its x 'axis forms 45 ° with the X-axis of the X- and Y-systems on the hologram plane. In this figure, the parallel plate shown as a rectangular parallelepiped is shown as being fixed by being rotated by 45 °, but this is for easy understanding of the description, and the actual shape may be cut out into a shape that is easy to mount.

The polarization direction of the signal light in the plane of the hologram beam splitter 28 forms an angle θ with the X axis. The occurrence of θ is caused by the Kerr rotation received during reflection on the magneto-optical disk surface, but it is transmitted through the multilayer beam splitter (with polarization dependence).
Has been lengthened. The component of the signal light incident on the birefringent crystal plate 31 in the y ′ direction (ordinary light; polarized light perpendicular to the plane including the crystal axis) passes through the birefringent crystal plate 31 according to the ordinary law of refraction, and the first light The light reaches the detector 32 (the origin of the coordinates x and y in this figure).

However, the polarization component of the signal light in the x 'direction (the extraordinary light; polarized light parallel to the plane including the crystal axis) generates a propagation component in the x' direction and is separated from the ordinary light. The light diffracted toward the birefringent crystal plate 31 by the hologram beam splitter 28 is convergent light, and as a result, connects two light spots on the surface of the first photodetector 32. The two light spots are received by different photodetectors (divided photodetectors), and a magneto-optical signal can be obtained by extracting a difference signal between the detected values.

The generation direction of the angle θ changes depending on the recording state (magnetization direction) of the magneto-optical disk, and the differential output of the first photodetector 32 fluctuates between positive and negative. The separation distance d between the two light spots on the surface of the first photodetector 32 is equal to the thickness t of the birefringent crystal plate 31.
Is proportional to When rutile is used as the material of the birefringent crystal plate 31, the relationship of d = 0.1t holds. A spot separation of about 200 μm is possible with a birefringent crystal plate 31 having a thickness of 2 mm, and a value sufficient for this purpose can be obtained. In this figure, the birefringent crystal plate 31 and the first photodetector 32 are shown separated from each other, but it is preferable to adopt an adhesive structure when mounting.

This polarization separation optical system can use a combination of a conventional half-wave plate and a polarization beam splitter, but has a disadvantage that it becomes complicated.

FIG. 6 is an explanatory diagram of a first photodetector used in the present invention, which will be described with reference to FIG. 1, FIG. 3 to FIG. The oscillation wavelength of a semiconductor laser not only varies individually, but also varies depending on a drive current, a resonator temperature, and the like. When wavelength changes, hologram beam splitter
Because the direction of diffraction of the light by 28 changes, the first photodetector
The light spot formed on the spot 32 moves, and the spot diameter (the spot in the figure is a schematic diagram) also changes as shown in FIG. The distance between the surface of the hologram beam splitter 28 and the first photodetector 32 is about 4 mm, the beam diameter on the hologram beam splitter 28 is about 1 mm, and the composite beam splitter element 25 of the present invention is returned to the central optical axis of the return light h. 45 for
゜ The tilt is set, and conditions are set such that the first-order diffracted light j by the hologram beam splitter 28 is emitted almost perpendicularly to the surface of the hologram beam splitter 28, the center wavelength of the semiconductor laser 1 is 790 nm, and the wavelength variation is ± 20 nm. Was assumed.
The spot shapes indicated by I to V in the figure are 770, 780, and 79, respectively.
It corresponds to the wavelength of 0,800,810nm. When the wavelength is 770,810 nm, the spot diameter has a maximum size of 40 μm in the x direction. The change in position is approximately
35 μm (moves in the positive direction of the y-axis when the wavelength increases).
Even if the beam diameter and position change as described above occur, the first
If the photodetector 32 is provided as shown, a magneto-optical signal can be detected stably. The separation distance between the two spots is about 150 μm, and the size of each photodetector is about 200 μm
× 100 μm and the distance between the photodetectors can be 10 μm or more, but this separation distance can be sufficiently realized as described above.

FIG. 7 is a view showing a second embodiment of the present invention. The difference from FIG. 4 is that a wavelength plate 35 (for example, 1) for controlling the polarization plane of laser light emitted from a semiconductor laser 1 serving as a light source. / 2
(Wave plate). The effect of the wavelength plate 35 is that a general semiconductor laser has a polarization component in a light beam with a small radiation angle, but has a role to make S-polarized light incident on the plane of incidence on the composite beam splitter element 25 by the half-wave plate. Let
This has the effect of facilitating the design of the beam splitter.

FIG. 8 is a view showing a third embodiment of the present invention. The difference from FIG. 4 is that laser light emitted from a semiconductor laser 1 serving as a light source is transmitted through a composite beam splitter element 25 first. The point is that a third photodetector 36 for detecting light is provided. Since the output of the third photodetector 36 does not include the return light component from the magneto-optical disk 6, it can be used as a power control signal for the laser output value of the semiconductor laser 1.

FIG. 9 is a view showing a fourth embodiment of the present invention. The difference from FIG. 4 is that the wave plate 35 of FIG. 7 and the third photodetector 36 of FIG. An example in which both are provided is shown. As a result, the adjustment of the mounting position of the semiconductor laser 1 is simplified, and a signal for controlling the power of the semiconductor laser 1 can be obtained in the same housing, which has the effect of increasing the function of the optical head.

FIG. 10 shows that the components other than the magneto-optical disk 6 and the objective lens 5 of the optical head shown in FIG. 9 are incorporated in the same closed casing 37 with at least the collimating lens 2 as a window as shown in FIG. The size is reduced by hermetically sealing with active gas or dry nitrogen, and it is of course possible to omit the wave plate 35 or the third photodetector 36 depending on the application.

FIG. 11 shows the components shown in FIG.
Heat sink 38 and APC circuit as shown in the conventional example
8, with the servo signal generation circuit 16 and the magneto-optical signal generation circuit 18
An electronic circuit 39 including an ID composed of the ID signal generation circuit 19, a light signal generation circuit 39a, and a connection terminal 39b for connecting the inside and the outside of the closed casing 37 and the like is added. Instead of hermetic sealing, the whole is hermetically sealed in an hermetic housing 37 to reduce the size.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, a laser light source, an optical path separation optical system, and a signal detection system are arranged in a space restricted by the focal length of a collimator lens, thereby making it possible to provide an optical system for a magneto-optical disk. The head is dramatically reduced in size and weight. As a result, while promoting the miniaturization of the device,
For example, it is easy to perform tracking by moving only the objective lens, and it is possible to greatly reduce the size of the space occupied by the movable part and to perform high-speed access. In addition, when miniaturizing the used optical components, the lens uses a small molded product, and the remaining optical components use flat components, so that there is an effect that the cost can be reduced while maintaining the processing accuracy. .

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a composite beam splitter element of the present invention, FIG. 2 is a view showing an example of a procedure for producing the composite beam splitter element of the present invention, and FIG. 3 is light using the composite beam splitter element of the present invention. FIG. 4 is a configuration diagram of an optical head for a magnetic disk, FIG. 4 is a first embodiment of the present invention, FIG. 5 is a perspective view of a magneto-optical signal detection system of the present invention, and FIG. 6 is a first light used in the present invention. FIG. 7 is a second embodiment of the present invention, FIG. 8 is a third embodiment of the present invention, FIG. 9 is a fourth embodiment of the present invention, and FIG. Fifth Embodiment of the Invention, FIG. 11 is a sixth embodiment of the present invention, FIG. 12 is a basic configuration diagram of a conventional optical head for a magneto-optical disk, and FIG. 13 is a conventional optical disk for a read-only optical disk. FIG. 2 shows a basic configuration diagram of a head. In FIG. 1, FIG. 3, FIG. 4, FIG. 7 to FIG.
Is a semiconductor laser, 2 is a collimating lens, 5 is an objective lens, 6 is a magneto-optical disk, 25 is a composite beam splitter element, 26 is a parallel plane substrate, 27 is a multilayer beam splitter,
28 is a hologram beam splitter, 29 is a magneto-optical signal detection system, 30 is a servo signal detection system, 31 is a birefringent crystal plate, 32 is a first photodetector, 33 is an optical parallel plate, and 34 is a second photodetector , 35 is a wave plate, 36 is a third photodetector, 37 is a sealed housing,
39 denotes an electronic circuit, i denotes a light wave (light incident on the hologram beam splitter), j denotes first-order diffracted light, and k denotes zero-order transmitted light.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayuki Kato 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (56) References JP-A 1-184639 (JP, A) JP-A 1-250905 (JP, A) JP-A-2-21835 (JP, A) JP-A-2-96629 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 11/10

Claims (3)

(57) [Claims] 1. A composite beam splitter device comprising a transparent parallel plane substrate and a hologram beam splitter integrally formed on one surface of the front and back surfaces of a transparent parallel plane substrate and a hologram beam splitter on the other surface, respectively. The splitter has a reflectance of 60 to 70% for the S-polarized component of the incident light to the multilayer beam splitter, and has a reflectance of approximately 10% for the P-polarized component of the incident light.
The hologram beam splitter is formed so as to have a transmittance of 0%, and the hologram beam splitter converts incident light obliquely incident from the multilayer film beam splitter side into first-order diffracted light and zero-order transmitted light in accordance with the polarization state of the incident light. A composite beam splitter element formed to be separated from light. 2. A semiconductor laser as a light source and a collimator for receiving a divergent light beam emitted from the semiconductor laser and converting the light into a parallel light on a surface of the multilayer beam splitter of the composite beam splitter element according to claim 1. An objective lens is provided between the lens and the position where the divergent light beam is reflected and relayed to the collimating lens, and the light converted into parallel light by the collimating lens is collected on a magneto-optical disk, The first-order diffracted light reflected by the magneto-optical disk and traveling backward through the forward optical system, and the return light transmitted through the multilayer film splitter and the parallel plane substrate is separated by the hologram beam splitter into a magneto-optical signal detection system. An optical head for a magneto-optical disk, wherein the zero-order transmitted light is guided to a servo signal detection system. 3. A magneto-optical disk drive according to claim 2, wherein a wave plate for controlling a polarization plane of light emitted from said semiconductor laser is inserted between said semiconductor laser and said multilayer beam splitter. Optical head.