JPH0413256A - Composite beam splitter element and optical head for magneto-optical disk using same - Google Patents

Abstract

PURPOSE:To reduce the size and weight of the optical head for magneto-optical disks by disposing a laser beam source, an optical system for separating optical paths and a signal detecting system in the space to be restricted by the focal length of a collimating lens. CONSTITUTION:The optical system for separating the optical paths, a magneto- optical signal detecting system and the servo-signal detecting system are provided in the space from a semiconductor laser 1 to a collimating lens 2 in order to commonly use the collimating lens 2 as the condenser lens of the optical system of the backward path. The size of the optical head for magneto- optical disks is, therefore, reduced. All of the composite beam splitter element 25, a double refractive crystal plate 31 and optical parallel flat plates 33 for correcting aberrations are formed of parallel flat plates. The need for polishing required for determining an angle of high accuracy like the prism of the optical system is eliminated in this way and the production with high accuracy is facilitated even if the size of the parts is reduced. Hermetic sealing of gas integrally in a hermetic housing is executed and the miniaturization is further promoted. The access time is thereby shortened.

Description

[Detailed description of the invention]

〔table of contents〕 overview\ Industrial applications Conventional technology (Figure 12) Conventional technology (Figure 13) Problems that the invention aims to solve Means to solve problems action Example Composition of composite element Explanation of steps for creating composite elements Optical head configuration First example Description of magneto-optical signal detection system Description of the first photodetector Second embodiment Third embodiment Fourth example Fifth embodiment Sixth example (Figure 1) (Figure 2) (Figure 3) (Figure 4) (Figure 5) (Figure 6) (Figure 7) (Figure 8) (Figure 9) (Figure 10) (Figure 1) 6 pages 7 pages 8 pages 12 pages 13 pages 14 pages 17 pages 17 pages 18 pages 20 pages 21 pages 23 pages 25 pages 28 pages 30 pages 30 pages page 31 page 31 page 31 Effect of the invention

[Brief explanation of drawings]

Page 32, page 33 [Summary] Regarding magneto-optical disk devices, particularly regarding miniaturized optical heads for magneto-optical disks, it is possible to combine and simplify optical elements while maintaining high light utilization efficiency and polarization state. The purpose of the present invention is to provide a composite beam splitter element, a miniaturized optical head using the element, and a hermetically sealed optical head for a magneto-optical disk. A multilayer beam splitter is integrated on one side of the transparent parallel plane substrate and a hologram beam splitter is integrated on the other side between the collimating lens that receives the divergent light beam and converts it into parallel light. A surface of the multilayer beam splitter of the composite beam splitter element formed in is provided at a position to reflect and relay the diverging light flux to the collimating lens, and converges the parallel light converted by the collimating lens onto the magneto-optical disk. An objective lens is provided, and the first-order diffracted light is reflected by the magneto-optical disk and travels backward through the outgoing optical system, and the returned light that has passed through the multilayer beam splitter and the parallel plane substrate is separated by the hologram beam splitter. The signal detection system is configured to use the zero-order transmitted light for the servo signal detection system. [Industrial Field of Application] The present invention relates to a magneto-optical disk device, and particularly to a miniaturized optical head for a magneto-optical disk. Magneto-optical disk devices are attracting attention as external storage devices for computers because they can rewrite extremely large amounts of information.
It is popular in the field of small computers. In order to use this magneto-optical disk device in a wider range of fields, it is desired to make the device smaller and thinner, and to improve cost performance (high-speed access, high-speed transfer, and lower cost). Smaller and lighter optical heads are essential for making devices smaller and thinner and improving cost and performance. This is because miniaturization of the optical head reduces the space occupied by the optical head within the device (including the access range), which facilitates miniaturization of the device. Further, the purpose of reducing the weight of the optical head is to reduce the energy required to move the optical head and enable high-speed access (movement). [Prior Art] FIG. 12 shows a basic configuration diagram of a conventional optical head for a magneto-optical disk. Optical heads for magneto-optical disks use the Kerr effect, a polarization characteristic of light, to read information recorded on the medium. preservation) is particularly important. The components are shown below. 1 is a semiconductor laser that serves as a light source, 2 is a collimating lens that converts the diverging laser beam with an elliptical pattern emitted from the light source into parallel laser beam, and 3 is a collimator lens that converts the elliptical parallel laser beam into circular parallel laser beam. 4 is a polarized beam that transmits or reflects incident parallel light at a certain rate depending on the difference in polarization plane, and separates the optical path of transmitted light and reflected light while maintaining the polarization state. A splitter 5 is an objective lens that focuses the laser beam transmitted through the polarizing beam splitter 4 onto the medium surface of a magneto-optical disk 6 (to be described later) close to the diffraction limit, and 6 is a magneto-optical recording medium that records and holds information in the direction of magnetization. The deposited magneto-optical disk, 7 is a photodetector for detecting the amount of parallel laser light emitted from the beam shaping prism 3 and guided to the side optical path by reflection at the polarizing beam splitter 4; An auto power controller (Auto power controller) is used to control the power of the semiconductor laser 1 to a predetermined value based on the value.
A power controller (hereinafter abbreviated as APC circuit 8), 9 is reflected by the magneto-optical disk 6, returns to the polarizing beam splitter 4 via the objective lens 5, and generates a focus error signal and a track from the separated light guided to the side optical path by reflection. This is a signal detection system that detects light spot control signals (hereinafter collectively referred to as servo signals) such as error signals, magneto-optical signals, and ID (preformat) signals. There are various methods for the signal detection system 9, but in this example, the astigmatism method is used to detect the focus error signal. A push-pull method is used to detect the track error signal, a method using a 1/2 wavelength plate and a polarizing beam splitter is used to detect the magneto-optical signal, and a method using the total amount of light incident on the signal detection system 9 is used to detect the ID signal. are doing. Since the principle of detection of each signal has no direct relation to the present invention, detailed explanation will be omitted. Next, the components 10-19 of the signal detection system 9 will be explained. 10 is a half-wave plate that rotates the polarization plane of the light incident on the signal detection system 9 by about 45 degrees; 1) is a polarizing beam splitter that separates the incident light according to its polarization state in order to detect a magneto-optical signal; 13 is a cylindrical lens for focusing error signal detection (astigmatism method); 14 is polarizing beam splitter 1; ) A split photodetector that detects a focus error signal, a track error signal, a magneto-optical signal, and a part of the ID signal using transmitted light (only the photodetector is shown in a plan view)
, 15 is a photodetector that detects a part of the magneto-optical signal and the ID signal by the reflected light from the polarizing beam splitter 1), and 16 is a servo signal generation circuit that generates from a combination of the difference signals of the outputs of the split photodetector 14. It is composed of a focus error signal generation circuit 16a and a track error signal generation circuit 16b. 18 is a magneto-optical signal generating circuit that generates a magneto-optical signal from each output signal of the 4-split photodetector 14 and the photodetector 15; 19 is a circuit that generates an ID signal from each output signal of the 4-split photodetector 14 and the photodetector 15; This is an ID signal generation circuit that generates an ID signal. Note that the APC circuit 8 and each signal generation circuit 16, 18,
Each of the 19 electronic circuits may not be included in the optical head and may be provided separately from the optical head. In the above explanation, the optical system existing in the optical path from the semiconductor laser 1 of the light source to the magneto-optical disk 6 is referred to as the outgoing optical system, and the optical system existing in the optical path of the reflected light reflected by the magneto-optical disk 6 is referred to as the incoming optical system. It is called a system. FIG. 13 shows a basic configuration diagram of a conventional read-only optical head for an optical disc. In the figure, this optical system includes a semiconductor laser 20 serving as a light source, and an objective lens 2 that focuses the light emitted from the semiconductor laser 20 onto a read-only medium 22.
1, a beam splitter 23 provided between the semiconductor laser 20 and the objective lens 21 to split the optical path, and a split photodetector that detects the signal light split by the beam splitter 23 using reflected light from the read-only medium 22. It consists of 24. With the configuration of such a read-only optical head for an 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 there is no need for a magneto-optical recording (erasing) operation that heats the read-only medium 22 above the Curie point temperature, the optical power irradiated to the read-only medium 22 may be small, and an optical system with extremely reduced optical efficiency can be used. It becomes. Furthermore, the polarization state of the light beam, which is essential for reproducing magneto-optical signals, does not need to be taken into consideration, so it can be configured with a very simple circuit that does not have the function of maintaining the polarization state or separating polarized light. . [Problems to be Solved by the Invention] An optical head for a conventional magneto-optical disk device is composed of many optical parts that share functions. Due to the large number of parts, parts management, one assembly, and adjustment man-hours and installation space are increased, resulting in high cost and large size. In particular, the increase in size is a cause of impediments to shortening the access time of the optical head. As a means of reducing the size of the optical head, it is conceivable to reduce the phase of the optical system as shown in the example of FIG. 12. However, although this method makes it possible to reduce the size and weight, it poses a problem in terms of cost. This is because, in general, reducing the dimensions of an optical component without reducing its precision requires stricter processing conditions and increases manufacturing costs. In addition, among the optical head components, each photodetector and other photoelectric conversion function elements are treated with an inert gas or dry nitrogen gas for each element in order to increase its environmental resistance and guarantee its function for a long period of time. Either hermetic sealing is carried out by air-tight sealing, or solid sealing is carried out by resin molding, and these sealing parts are a drawback that hinders the miniaturization of optical heads. Furthermore, the size of the circuit components required for the optical head is also an issue, and there is a method of directly mounting an IC bare chip inside the optical head for the purpose of miniaturization. Hermetic sealing is essential. The present invention was created in view of the above-mentioned drawbacks of the conventional technology.
The present invention aims to provide a composite beam splitter element that can be simplified, a miniaturized optical head using the element, and a hermetically sealed optical head for a magneto-optical disk. [Means for solving the problem] FIG. 1 is a block diagram of a composite beam splitter element of the present invention;
FIG. 3 is a block diagram of an optical head for a magneto-optical disk using the composite beam splitter element, and FIG. 4 and FIGS. 7 to 1) show first to sixth embodiments of the present invention, respectively. In the present invention, the structure is as simple as the conventional read-only optical head, and as a means of reducing the number of parts of the optical head in order to realize an optical head for magneto-optical recording and playback, the present invention has a high light utilization effect and a polarization state. Composite and simplify parts while maintaining First, we aim to make the lens system more complex. In optical heads for playback-only optical discs, the return optical system converges the reflected light (return light) from the optical disc using an objective lens, and uses this convergent light to detect servo signals and magneto-optical signals. In order to utilize this method in an optical head for a magneto-optical disk, the collimator lens 2 having a similar function in the forward optical system is used to form convergent light in the backward optical system, thereby constructing an optical head for a magneto-optical disk. Next, the magneto-optical signal detection system and the servo signal detection system are constructed from flat optical elements that are simple in shape and easy to implement. A multilayer beam splitter 27 and a hologram beam splitter 28 combine a beam splitter function for switching between forward and return paths and a signal light separation function for signal detection.
A composite beam splitter element 25 is used in which a plurality of beam splitters are formed on each surface of a single transparent parallel plane substrate 26. Also,
The parallel plane substrate 2 is connected to the hologram beam splitter 28.
The first-order diffracted light j that has been corrected and separated by the aberrations associated with the 6-transmission is used for detecting a magneto-optical signal, and the polarization separation for the detection is configured by a birefringent crystal plate 31 in the form of a parallel plate. Furthermore, the zero-order transmitted light that has passed through the hologram beam splitter 28 is used for detecting servo signals, and the optical parallel plate 3
3, convergence detection is performed while correcting aberrations. The optical head configured in this manner further includes a wavelength plate 35 that facilitates adjustment of the polarization direction of the emitted light f of the semiconductor laser 1. Alternatively, it is also possible to add a third photodetector 36, etc. used for power control of the emitted light of the semiconductor laser 1, and the combination and dual-purpose effect allows for miniaturization, and it can be integrated into the sealed casing 37. , an inert gas, etc. can be hermetically sealed. [Function] In order to use the collimating lens 2 as a condensing lens for the return optical system, 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 from the semiconductor laser l to the collimating lens 2. This makes it possible to dramatically reduce the size of the optical head for a magneto-optical disk. -This uses diverging and converging light fluxes, so the diameter of the light flux becomes smaller.
This is because the size of the optical components used becomes smaller. Since the composite beam splitter element 25, the birefringent crystal plate 31, and the optical parallel plate 33 for aberration correction are all made of parallel plates, there is no need for polishing that requires highly accurate angle adjustment as with prisms in conventional optical systems. Even if the component size is reduced, it is easy to manufacture while maintaining precision, and by integrally sealing the airtight housing 37 with gas, miniaturization is further promoted and the access time can be shortened. [Examples] Examples of the present invention will be described in detail below with reference to the drawings. Note that, in order to make the explanation of the configuration and operation easier to understand, the same parts are given the same reference numerals throughout all the figures, and repeated explanation thereof will be omitted. FIG. 1 shows a configuration diagram of a composite beam splitter element of the present invention. In the figure, 25 is the composite beam splitter element 2
5, a parallel plane substrate 26 that is transparent to the wavelength of light to be used, a multilayer beam splitter 27 formed on one of the two opposing surfaces of the parallel plane substrate 26, and a multilayer beam splitter 27 formed on the other side. The formed hologram beam splitter 28 has a three-layer structure. In this composite beam splitter element 25, the S-polarized component has a reflectance of 60 to 70% with respect to the incident light f (for example, the emitted light of a semiconductor laser) obliquely incident on the surface of the multilayer beam splitter 27. It is preferable to form it so that it has approximately 100% transmittance for the P-polarized component of incident light. Reflected light g and transmitted light m are generated at the above ratio in accordance with the polarization state of incident light f. The reflected light g is irradiated onto the magneto-optical disk through an objective lens (not shown), and the light wave (return light) h reflected by the magneto-optical disk is sent to the multilayer beam splitter 27 and the parallel plane substrate according to its polarization state. Almost 100% of the P-polarized light component and 40 to 30% of the S-polarized light component are transmitted diagonally through the hologram beam splitter 26 as incident light i. The incident light i to the hologram beam splitter 28 is
The light is separated into a first-order diffracted light j and a zero-order transmitted light according to its polarization state, but as a result of being transmitted obliquely through the parallel plane substrate 26, it has aberrations. Therefore, the hologram beam splitter 28 has a function (wavefront conversion function, essentially a lattice pattern distribution). Furthermore, the zero-order transmitted light that is transmitted through the hologram beam splitter 28 without being diffracted also has aberrations due to its transmission through the parallel plane substrate 26, but this can be corrected by the optical system described later. The composite beam splitter element 25 configured in this manner is similar to the polarizing beam splitter 4 of the conventional configuration shown in FIG.
It has most of the combined functions of the 1/2 wavelength plate 10 and the polarizing beam splitter 1), and is a complex and simplified element, and the first-order diffracted light j is sent to the magneto-optical signal detection system as described above. The zero-order transmitted light can be used in a servo signal detection system. FIG. 2 is a diagram showing an example of a procedure for manufacturing a composite beam splitter element of the present invention. Although holograms can be created either in the surface texture type or the volume type, in consideration of mass production, it is preferable to copy the surface texture type by stamping. As for the procedure for integrally forming the multilayer film on the same flat plate, first, in Step 2, a multilayer film beam splitter is placed on one side of the transparent parallel plane substrate 26 (for example, 1 m of optical glass BK/7 thickness 0.51). 27 to the required transmittance (nearly 100% for P polarization component: 4 for S polarization component)
titanium dioxide TiOz
A multilayer film of silicon dioxide, SiO□, etc. is alternately formed by vapor deposition means. In step (2), a protective film 27a is formed using photoresist or the like to prevent damage in subsequent processes. In step ■, the previously set aberration (
A hologram pattern with a lattice stripe distribution designed using a computer in order to correct the lattice pattern (including the allowance) is formed on the surface opposite to the multilayer beam splitter 27 by a photopolymer method, etc., and the protective film 27a is removed in step (2). to form a composite beam splitter. FIG. 3 is a block diagram of an optical head for a magneto-optical disk using the composite beam splitter element of the present invention. In the figure, between a semiconductor laser 1 serving as a light source and a collimating lens 2 that receives a diverging luminous flux emitted from the semiconductor laser 1 and converting it into parallel light, the diverging luminous flux is reflected to the collimating lens 2. A composite beam splitter element 25 having the surface of the multilayer beam splitter 27 set at the relay position is provided. With this arrangement, 60 to 70% of the S-polarized light component included in the diverging light beam is reflected, and after being converted into parallel light by the collimating lens 2, it is passed through the objective lens 5 to the magneto-optical disk 6.
The reflected light, which includes a polarized component due to Kerr rotation generated when reflecting on the magneto-optical disk 6, travels backward through the outgoing optical system and returns to the surface of the multilayer beam splitter 27. Depending on the polarization state of the light, the light passes obliquely through the multilayer beam splitter 27 and the parallel plane substrate 26 and reaches the surface of the hologram beam splitter 28 . Here, the returned light is polarized and separated into first-order diffracted light j and zero-order transmitted light in accordance with the polarization state of the returned light. In the process of obtaining the first-order diffracted light j and the zero-order transmitted light, the composite beam splitter element 25 is used to directly use the diverging light emitted from the semiconductor laser 1 and the convergent light converged by the collimating lens 2. As a result of the polarization separation, the collimator lens 2 can be used also as a condensing lens for the return path optical system, and the diameter of the light beam is reduced, which has the advantage that the size of the optical components used can be reduced. The returned light containing the polarization component due to the Kerr rotation has its Kerr rotation component enhanced by transmission through the multilayer beam splitter 27 (with polarization dependence), and the polarization direction of the incident light i is the main diffraction direction of the hologram beam splitter 28. It forms an angle with respect to the direction perpendicular to the plane (defined by the plane formed by the incident light i and the first-order diffracted light j). Therefore, the returned light has an S component and a P component for the hologram beam splitter 28. The hologram beam splitter 28 is S
. First-order diffracted light j is generated with appropriate efficiency for both P polarized light components, and is incident on the magneto-optical signal detection system 29. The zero-order transmitted light that is transmitted through the hologram beam splitter 28 without being diffracted can be incident on the servo signal detection system 30 to detect respective signals. Since each signal detection system uses convergent light as it is, the diameter of the light beam becomes small, which has the advantage that the size of the optical components used can be reduced. FIG. 4 shows a first embodiment of the invention. In the figure, the 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 a first photodetector that receives and detects the transmitted light that has passed through the birefringent crystal plate 31. Vessel 3
2, and the servo signal detection system 30 is composed of an optical parallel plate 33 that receives and transmits the zero-order transmitted light k, and a second photodetector 34 that detects the transmitted light of the optical parallel plate 33. There is. For example, if an axle crystal such as calcite or rutile is placed such that its optical axis (crystal axis) is at an angle of approximately 45″ to the direction of travel of the incident light beam, the plane of polarization will change to the polarization component (abnormal The direction of propagation in the crystal differs between the polarized light component (light component) and the polarized light component (ordinary light component) with a plane of polarization perpendicular to it, and the position of the focal point shifts.The birefringent crystal plate 31 utilizes this phenomenon. It is used for the purpose of polarization separation.
The reason why the parallel plate shape is adopted is to reduce the size of mounting within the optical head. The optical parallel plate 33 that receives and transmits the zero-order transmitted light k has a function of removing comatic aberration due to the oblique optical parallel plate placed in the optical path of the incident convergent light. It can be configured 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 when used with aberrations corrected, accurate detection can be achieved. As the material of the optical parallel plate 33, for example, porcelain K7, which is commonly used as optical glass, may be used. At the time of this aberration correction, astigmatism is left and the second photodetector 34 is constituted by a split photodetector to be used for focus detection. A push-pull method can be applied to detect the tracking error signal. FIG. 5 shows a perspective view of the magneto-optical signal detection system of 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, but more specifically, the polarization direction of the incident light i is the main diffraction surface (the incident The hologram beam splitter 2 forms an angle θ with respect to the direction perpendicular to
In the X, Y coordinate system (the y-axis is parallel to the hologram lattice fringes) taken on the hologram 8, it has an X-direction component (S-polarized light component) and a Y-direction component (P-polarized light component). What is produced by Kerr rotation is the P component. The appropriate diffraction efficiency of the hologram for S-polarized light is 50 to 80%, and P
The hologram is created so that the efficiency for polarized light is equal to or higher than that for S-polarized light. It is known that when the linearly polarized light of the first-order diffracted light j is made incident on the birefringent crystal plate 31, ordinary light and extraordinary light are separated. That is, by making convergent signal light from the magneto-optical disk incident on the birefringent crystal plate 31, the signal light can be separated into two orthogonal polarized components and spatially separated. A y-axis configured on the surface of the hologram beam splitter 28 and a Z-axis relative to the Y-axis are provided, and the hologram beam splitter 28 separates the incident light i that is incident on the coordinate origin within a plane including the Z-axis and the Y-axis. A birefringent crystal plate 31 having an origin of coordinates x and y and a first photodetector 32 are sequentially arranged on the way in the traveling direction of the first-order diffracted light j. It is assumed that the X and Y axes are set parallel to each other. The direction of the optical axis (crystal axis) of the birefringent crystal constituting the birefringent crystal plate 31 is 45° with respect to the x' and y' planes within the plane pqrs.
Take steps to achieve this. The birefringent crystal plate 31 is set so that its Although it is shown in a fixed shape, this is to make the explanation easier to understand, and the actual shape can be cut out into a shape that is easy to implement.The polarization direction of the signal light in the plane of the hologram beam splitter 28 is along the y-axis. The occurrence of θ is due to the Kerr rotation received during reflection on the magneto-optical disk surface, but it is increased by the transmission through the multilayer beam splitter (which has polarization dependence).Birefringence The y-direction component (ordinary light; polarized light perpendicular to the plane containing the crystal axis) of the signal light incident on the crystal plate 31 is transmitted through the birefringent crystal plate 31 according to the ordinary law of refraction, and is transmitted to the first photodetector 3.
2 (in this figure, the origin of coordinates x, y). However, in the X'' direction polarization component of the signal light (extraordinary light; polarized light parallel to the plane containing the crystal axis), an X'' direction propagation component occurs,
Separate from ordinary light. Since the light diffracted by the hologram beam splitter 28 toward the birefringent crystal plate 31 is convergent light, two light spots are connected on the surface of the first photodetector 32 as a result. A magneto-optical signal can be obtained by receiving these two light spots with different photodetectors (divided photodetectors) and extracting a difference signal between the detected values. The angle θ depends on the recording state (direction of magnetization) of the magneto-optical disk.
The direction in which the light is generated changes, and the differential output of the first photodetector 32 fluctuates between positive and negative. 2 on the surface of the first photodetector 32
The separation distance d between the two light spots is proportional to the thickness t of the birefringent crystal plate 31. When rutile is used as the material for the birefringent crystal plate 31, the relationship d=0°1t holds true. 2
A birefringent crystal plate 31 with a thickness of mm allows a spot separation of approximately 200 mm, which is sufficient for this purpose. Although the birefringent crystal plate 31 and the first photodetector 32 are shown separated from each other in this figure, it is preferable to use an adhesive structure when mounting them. Note that this polarization separation optical system can also utilize a combination of a conventional 1/2 wavelength plate and a polarization beam brick, but it has the disadvantage of being complicated. FIG. 6 is an explanatory diagram of the first photodetector used in the present invention, which will be explained with reference to FIGS. 1, 3 to 5. The oscillation wavelength of a semiconductor laser not only varies individually, but also varies depending on the driving current, the temperature of the resonator, etc. If the wavelength changes, the hologram beam splitter 28
Since the direction of diffraction of light changes due to
The light spot focused on 2 moves, and due to the occurrence of aberration, the spot diameter (the spot in the figure is a schematic diagram) also changes as shown in the figure. Hologram beam splitter 28
The distance between the surface and the first photodetector 32 is approximately 4 mm, and the beam diameter on the hologram beam splitter 28 is approximately 1 mm.
The composite beam splitter element 25 of the present invention is set to be inclined at 45 degrees with respect to the central optical axis of the returned light, so 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. Setting the conditions, the center wavelength of the semiconductor laser 1 is set to 790 nm.
, the wavelength fluctuation was mainly assumed to be 20n. The spot shapes shown in IV in the figure are 770, 780, 790, respectively.
It corresponds to wavelengths of 800 and 810 nm. The wavelength is 770. At 810 nmO, the spot diameter becomes a maximum of 40 mm in the X direction. The change in position is approximately 35 Jm in the y direction for a wavelength variation of 10 nm (movement in the positive direction of the y axis as the wavelength increases). Even if the beam diameter changes and position changes occur as described above, if the first photodetector 32 is provided as shown, the magneto-optical signal can be stably detected. The separation distance between the two spots is approximately 150
tm+, the dimensions of each photodetector are approximately 200-X 100-1
It is possible to ensure a spacing of 10- or more between each photodetector, and as described above, this separation distance is fully achievable. FIG. 7 is a diagram showing a second embodiment of the present invention, and is a diagram showing a fourth embodiment of the present invention.
The difference from the diagram is that the wavelength plate 35 (for example, 1/2
The point is that a two-wavelength plate) is provided. The effect of this wavelength plate 35 is that in a general semiconductor laser, a light beam with a small radiation angle has a polarized component, but the half-wave plate has the role of making the light beam incident on the composite beam splitter element 25 S-polarized within the plane of incidence. This has the effect of simplifying the design of the beam splitter. FIG. 8 is a diagram showing a third embodiment of the present invention, and a fourth embodiment of the present invention.
The difference from the previous example is that a third photodetector 36 is provided to detect the transmitted light that first passes through the composite beam splitter element 25 in the laser light emitted from the semiconductor laser 1 serving as the light source. 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 diagram showing a fourth embodiment of the present invention.
The difference from the figure is that the wave plate 35 shown in FIG. 7 and the third photodetector 36 shown in FIG. 8 are both provided. This simplifies the adjustment of the mounting position of the semiconductor laser 1 and allows signals for power control of the semiconductor laser 1 to be obtained within the same housing, thereby increasing the functionality of the optical head. In the 10th session, each component of the optical head shown in FIG. 9, except for the magneto-optical disk 6 and the objective lens 5, was assembled into the same sealed casing 37 with at least the collimating lens 2 as a window, as shown in the figure. The device is miniaturized by hermetically sealing it 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. 1) In FIG. 1, the components shown in FIG.
C circuit 8. An electronic circuit 39 consisting of an ID consisting of a servo signal generation circuit 16, a magneto-optical signal generation circuit 18, and an ID signal generation circuit 19, an optical signal generation circuit 39a, and a connection terminal 39b that connects the inside and outside of the sealed casing 37. In addition, instead of hermetically sealing each single component constituting each generation circuit, the entire generation circuit is hermetically sealed within an airtight housing 37 to achieve miniaturization. [Effects of the Invention] As is clear from the above description, according to the present invention, by arranging the laser light source, the optical path separation optical system, and the signal detection system in the space restricted by the focal length of the collimating lens, Optical heads for magneto-optical disks are dramatically smaller and lighter. As a result, it is possible to promote miniaturization of the apparatus, and it is also easy to perform tracking by moving only the objective lens, for example, and it is possible to significantly reduce the size of the space occupied by the movable part and to achieve high-speed access. In addition, when downsizing the optical components used, the lens is a small molded product, and the remaining optical components are flat plate components, which has the effect of reducing costs while maintaining processing accuracy. .

[Brief explanation of drawings]

Fig. 1 is a block diagram of the composite beam splitter element of the present invention, Fig. 2 is a diagram showing an example of the manufacturing procedure of the composite beam splitter element of the present invention, and Fig. 3 is a diagram showing the configuration of the composite beam splitter element of the present invention. 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 diagram of the first light beam used in the present invention. An explanatory diagram of the detector, FIG. 7 is the second embodiment of the present invention, FIG. 8 is the third embodiment of the present invention, FIG. 9 is the fourth embodiment of the present invention, and FIG. 10 is the present invention. The fifth embodiment of the invention, Figure 1) shows the sixth embodiment of the invention, Figure 12 is a basic configuration diagram of a conventional optical gutter for a magneto-optical disk, and Figure 13 shows a conventional reproduction-only The basic configuration diagram of an optical gutter for an optical disc is shown. In Figures 1, 3, 4, 7 to 1),
1 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 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, 34 is a second photodetector, 35 is a wavelength plate, 36 is a third photodetector, 37 is a sealed casing, 39 is an electronic circuit, i is a light wave (light incident on the hologram beam splitter), J is first-order diffracted light, and k is zero-order transmitted light. Eve 6th 1st day of OA Tunmei's beam Nupriarin No. 6・To base disadvantage 1 Figure 12 Figure 13

Claims (9)

[Claims] (1) A composite beam splitter element in which a multilayer beam splitter (27) is integrally formed on one of the opposing surfaces of a transparent parallel plane substrate (26), and a hologram beam splitter (28) is integrally formed on the other surface. 25), wherein the multilayer beam splitter (27) has a characteristic that the transmittance and reflectance depend on the polarization state of the incident light incident on the multilayer beam splitter, and the hologram beam splitter (28) , is formed so as to polarize and separate a light wave (i) obliquely incident from the multilayer beam splitter side into a first-order diffracted light (j) and a zero-order transmitted light (k) in accordance with the polarization state of the light wave. A composite beam splitter element characterized by: (2) The multilayer beam splitter (27) 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 60 to 70% for the P-polarized component of the incident light. A composite beam splitter element according to claim 1, characterized in that the beam splitter element has a transmittance of approximately 100%. (3) The composite beam splitter element (25
) between the semiconductor laser (1) serving as the light source and the collimating lens (2) that receives the diverging light beam emitted from the semiconductor laser and converts it into parallel light. and an objective lens (5) provided at a position to reflect and relay the diverging light flux to the collimating lens, and condensing the parallel light converted by the collimating lens (2) onto the magneto-optical disk (6). The return light that is reflected by the magneto-optical disk (6), travels backward through the outgoing optical system, and is transmitted through the multilayer beam splitter (27) and the parallel plane substrate (26) is sent to the hologram beam splitter (28). The first-order diffracted light (j) separated by the above is guided to a magneto-optical signal detection system (29), and the zero-order transmitted light (k) is guided to a servo signal detection system (30). Optical head for magnetic disks. (4) The magneto-optical signal detection system (29) includes a parallel plate-shaped birefringent crystal plate (31) that separates the primary diffracted light (j) into ordinary light and extraordinary light according to the polarization state; A first photodetector (32) that detects each transmitted light of the refractive crystal plate.
The servo signal detection system (30) includes an optical parallel plate (33) that corrects the aberration of the zero-order transmitted light (k), and a second photodetector that detects the transmitted light of the optical parallel plate. (
34) Claim 3 is characterized by comprising:
The optical head for the magneto-optical disk described above. (5) A wavelength plate (35) is inserted between the semiconductor laser (1) and the multilayer beam splitter (27) for controlling the polarization plane of the light emitted from the semiconductor laser. 5. The optical head for an optical disc device according to 3 or 4. (6) A third photodetector (36) is provided for receiving transmitted light in which the light emitted from the semiconductor laser (1) first passes through the composite beam splitter element (25). 6. The optical head for a magneto-optical disk according to 3, 4 or 5. (7) The magneto-optical disk (6) and the objective lens (5)
7. The magneto-optical disk according to claim 3, wherein each of the components except for the collimating lens (2) is incorporated in a sealed casing (37) with at least the collimating lens (2) as a window. optical head. (8) The optical head for a magneto-optical disk according to claim 7, wherein the inside of the sealed housing (37) is filled with an inert gas. (9) The semiconductor laser (
9. The optical head for a magneto-optical disk according to claim 7 or 8, further comprising the heat sink (38) of 1) and an electronic circuit (39) constituting a signal detection system of the optical head.