JPH03116546A - Information recording and reproducing device - Google Patents

Abstract

PURPOSE:To miniaturize an optical head, to simplify assembly and adjustment and to stably detect a light beam by setting the plane of polarization of the light beam from a light source so that it makes a specified angle against a reference axis on the light source with respect to the polarizing direction of the light beam separated by a separation means. CONSTITUTION:A non-polarizing light beam split surface (m) is used as the separation means for the light beam generated from a semiconductor laser element 2 and the plane of polarization of the light beam generated from the laser element 2 is rotated by about 45 deg., for example, against the reference axis included in a plane parallel with a direction where the light beam is transmitted on the polarizing light beam split surface for separating the light beam and making it incident on photodetectors 26 and 28, that is, a Y-axis. Therefore, a 1/2lambda plate for making the transmittivity of the P polarization component of the light beam and the reflectance of the S polarization component constant and a rotation adjusting mechanism for adjusting the rotation with respect to the optical axis of the light beam can be eliminated. Thus, the device has simple constitution and stable characteristic, it is miniaturized and the easy assembly and adjustment of the device are accomplished.

Description

[Detailed Description of the Invention] [Purpose of the Invention (Industrial Field of Application) The present invention relates to an optical head incorporated in an optical information recording/reproducing device such as an optical disk device, and particularly relates to an optical head incorporated in an optical information recording/reproducing device such as an optical disk device. The present invention relates to an optical head for recording, reproducing, or erasing information on an optical head.

(Prior Art) In an optical information recording and reproducing device, for example, an optical disk device, information is recorded on an optical recording medium, that is, an optical disk, and an optical head is used to reproduce the information from the optical disk. .

In such an optical head, a light beam generated from a semiconductor laser element as a light source is focused onto an optical disk by an objective lens inside the optical head, and a light beam reflected from the optical disk is guided to a photodetector. The light beam is detected and converted into a reproduced signal. When reproducing and recording information on an optical disk, the objective lens is maintained in a focused state so that the beam waist of the light beam, that is, the minimum beam spot is formed on the optical disk, and the objective lens is maintained in a focused track state. Tracks formed on the optical disc are tracked by a light beam to accurately record and reproduce information on the optical disc. As optical heads used in the above-mentioned optical disk devices, optical heads for write-once optical disks, optical heads for magneto-optical optical disks, and the like are known.

In a magneto-optical optical disk head, information is recorded, reproduced, and erased using a light beam irradiated onto the recording surface of an optical disk and a magneto-optical effect. This optical head includes a focusing means that focuses a light beam generated from a semiconductor laser element as a light source onto the information recording surface of an optical disk, and a light beam that directs reflected light from the optical disk to a photodetector that is a signal detection means. It consists of a beam separating means and a photodetector for detecting the separated light beam and using it as a focusing control signal, a tracking control signal, and an information reproduction signal. In this magneto-optical optical disk optical head, light emitted from a semiconductor laser has a polarization plane in a direction perpendicular to an optical axis parallel to the recording surface of an information recording medium, that is, an optical disk, and has an elliptical cross-sectional shape. The beam is focused onto an optical disk via an ellipse correcting refractor, a separating means or prism, and an objective lens.

This light beam is generated with a constant intensity when reproducing information, and is generated with intensity modulated according to the information when recording.

Furthermore, during erasing, the signal is generated at a constant intensity that is greater than during reproduction. When recording information on an optical disk, a magnetic field is applied from a magnet placed on the side of the optical disk facing the optical head, and the direction of magnetization of the area irradiated with the light beam is changed to record information. When erasing information, a magnetic field is applied in the same manner as during recording, and the direction of magnetization of the region irradiated with the light beam is changed again (returned to its original state). When reproducing information, the light beam is changed depending on the information recorded on the optical disc. That is, when no information is recorded on the optical disc, the light beam is reflected as is, and when information is recorded, the polarization plane of the light beam is slightly rotated. The light beam reflected from the optical disk is returned to parallel light by the objective lens, and is separated from the destination beam traveling from the light source to the information recording medium via the separating means. This separated light beam is separated into two light beams by a focus detection light beam separation means, one of which is guided to a focus detection photodetector, and the other beam is guided to a focus detection photodetector, and the other beam has a polarization plane of 45. The plane of polarization is rotated by 45'' through the rotating 1/2λ plate, and guided to the polarizing beam splitter, where the P polarized light component passes through the beam splitter and the S reflected by the beam splitter.
It is further separated into polarized components. This further separated P
Each of the polarized light component and the S-polarized light component is detected by two photodetectors, and the information recorded on the optical disc is reproduced. When reproducing information, normally when there is no recorded information, the P polarization component and the S polarization component are
The /2λ plate is rotated and adjusted, and when a difference occurs between the outputs of the two photodetectors, it is output as an information signal and the information is reproduced.

Therefore, in such an optical head, with respect to the rotation of the polarization plane of the light beam around the optical axis of the light beam,
1/2 wavelength plate for increasing the stability of reproduced signals and a rotation adjustment machine configuration or semiconductor that adjusts the rotation of the light beam of the 1/2 wavelength plate with respect to the optical axis in response to the difference in the polarization plane of each semiconductor laser. Additional devices such as a rotation mechanism for rotating the laser element 2 are provided.

(Problems to be Solved by the Invention) In the optical head described above, as described above, there is a method for increasing the stability of the reproduced signal with respect to rotation of the polarization plane of the light beam around the optical axis of the light beam. Additional devices such as a rotation adjustment mechanism for adjusting the rotation of the light beam of the 1/2 wavelength plate with respect to the optical axis due to the difference in the polarization plane of the 1/2 wavelength plate and the individual semiconductor lasers are required to form the optical head. The number of parts for the optical member increases. In such an optical head, the increase in the number of optical members complicates the assembly and adjustment of the device, making the device larger and heavier, reducing the stability in detecting and reproducing information signals, and reducing the durability of the device. There is a problem in that not only does it cause deterioration, but it also increases cost.

An object of the present invention is to provide an optical head that can prevent a decrease in the S/N ratio of a reproduced signal, reduce the size of the optical head, simplify assembly and adjustment, and stably detect a light beam. shall be.

[Structure of the Invention] (Means for Solving the Problems) The present invention has been made based on the above-mentioned problems, and includes a light source that generates a light beam having a plane of polarization, and a system that uses information about the light beam generated from the light source. a focusing means for focusing the light beam from the information recording medium onto the recording medium;
In an information recording/reproducing apparatus, the polarization plane of the light beam from the light source is set relative to a reference axis on the light source with respect to the polarization direction of the light beam separated by the separation means. The present invention provides an information recording/reproducing device characterized by forming a predetermined angle.

(Function) According to the optical head of the present invention, a non-polarizing beam splitting surface is used as a means for separating the light beam generated from the semiconductor laser probe.

Therefore, the polarization plane of the light beam generated from the semiconductor laser element is the reference axis included in the plane parallel to the direction in which the light beam is transmitted on the polarizing beam split surface that separates the light beam and makes it incident on the photodetector. i.e. approximately 45 to the Y axis
``It is possible to remove the 1/2 λ plate that is rotated to make the transmittance of the P-polarized light component and the reflectance of the S-polarized light component of the light beam constant, and the rotation adjustment mechanism that adjusts the rotation of the light beam with respect to the optical axis. It is possible to provide an optical head that has a simple structure, stable characteristics, is miniaturized, and can be easily assembled and adjusted during manufacturing.

(Embodiment) FIGS. 1A and 1B show an optical head that is incorporated into an erasable magneto-optical optical disc device that is an embodiment of the present invention. FIG. 1A schematically shows the arrangement of the components of the optical head, and FIG. 1B shows the optical head shown in FIG. 1A in a plan view.

In this optical system, it is assumed that a light source that generates a light beam having a polarization plane, that is, the semiconductor laser element 2, has an elliptical cross-sectional shape and that the polarization plane is image-formed on the reference axis, that is, the reference axis is projected. A light beam is generated that is rotated approximately 45'' with respect to the reference axis or Y axis of the separation means, which is polarized along the corresponding direction so that the shadow is displaced. A non-polarizing beam splitter is used as the beam splitter 6 that transmits or reflects the beam, and a non-polarizing mirror is used as the reflecting mirror m formed on one surface of the joined prism 18.

Conventionally used polarizing beam splitters and polarizing mirrors transmit the linearly polarized light component (P polarized light component) on the plane parallel to the polarizer on the beam splitting surface, and transmit the linearly polarized light component (S polarized light component) on the plane perpendicular to the polarizer. In contrast, the non-polarizing beam splitter and non-polarizing mirror do not have a polarizer and reflect almost all the P-polarized light components and S-polarized light components of the light beam generated from the semiconductor laser element 2. Transmit or reflect an equal amount. A light beam with an elliptical cross section generated from the semiconductor laser element 2 is converted into parallel light by a collimator lens 4, and is converted into a substantially circular cross-sectional shape equal to the short axis diameter of the ellipse by an incident light limiting means, which will be described later. The beam is restricted and incident on the first beam splitter 6. The light beam transmitted through the beam splitter 6 is reflected by the reflecting surface m, which is a non-polarizing beam split surface formed on one surface of the prism 18 joined to the beam splitter 6 via the beam splitter surface 8, and is reflected by the objective lens. Guided by 20. The light beam guided to the objective lens 2o is directed to a track of an optical disk 12, which has a recording layer made of an amorphous magnetic alloy or the like, and has concentric or spiral tracks 14 formed in a concave or convex shape. 14
focused on the top. The track 14 is pre-formatted with preliminary information such as a track address and a sector address. Information is recorded on the track 14, and information is reproduced and erased from the track 14 by a method of changing the intensity of the light beam, which will be described later. The light beam reflected from the optical disk 12 is again directed to the objective lens 2.
0, is returned to the beam splitter 6 via the reflective surface m of the prism 18. This light beam is beam musblitter 6
The beam is reflected by the beam splitting surface 8 and is incident on the second beam splitter 70 . The light beam is split into two beams by the polarization beam splitting surface of the beam splitter 70, and one beam is guided to the first photodetector 26 via the TTP 22 as a focus detection light beam.

The other light beam is separated into an S-polarized light component and a P-polarized light component by a polarizing beam splitter 90, and each light beam is guided to second and third photodetectors 27 and 28, where they are detected and electrically generated. information is reproduced.

In the optical head shown in FIGS. 1A and 1B, when there is no information recorded on the optical disc 12, the light beams detected by the two photodetectors 27 and 28 need to be made equal; In conventional optical heads, a 1/2 wavelength plate is used for the rotation of the polarization plane of the light beam around the optical axis of the light beam, and a 1/2 wavelength plate is used for the difference in the polarization planes of individual semiconductor lasers. Additional equipment was required to separate the P and S polarization components in equal proportions, such as a rotation adjustment mechanism to adjust the rotation of the light beam relative to the optical axis. In this embodiment, since a non-polarizing beam splitter and a non-polarizing mirror are used as the beam splitter and the reflecting surface, the polarization plane of the light beam from the semiconductor laser element 2 is
By rotating the polarizing beam split surface, which separates the light beam and enters the photodetector, by approximately 45'' with respect to the reference axis, that is, the Y axis, included in a plane parallel to the direction in which the light beam is transmitted, the P-polarized light component can be detected. Additional devices such as a 1/2 λ plate for separating the and S-polarized components in equal proportions and a rotation adjustment mechanism for adjusting the rotation of the light beam with respect to the optical axis are removed, making the device more compact and easier to assemble. and adjustment is simplified.

Recording, reproduction, and erasure of information on the tracks 14 of the optical disc 12 will be explained. When recording information on the optical disk 12, a magnetic field is generated from a magnet M provided on the side of the optical disk 14 facing the optical head, and the intensity is modulated according to the information to be recorded at a predetermined position on the track 14 on the recording surface. By being irradiated with a light beam, the material is rapidly heated, the direction of magnetization is reversed, a bit p is formed, and information is recorded. Therefore, when no information is recorded on the optical disk 12, the direction of magnetization in the track 14 is aligned in a fixed direction. When erasing the information recorded on the optical disk 12, a magnetic field is generated from the magnet M, and a beam having a constant intensity greater than that during information reproduction is irradiated onto the track 14, and a beam is formed on the track 14. Pit p is heated slowly and returned to the same state as when there was no information (inverted again)
.

When information recorded on the optical disk 12 is read out, a light beam of a certain intensity (weaker than the intensity at the time of erasing) is irradiated from the semiconductor laser element 4 onto the track 14 of the optical disk 12, and the light beam is emitted depending on the presence or absence of pits. The plane of polarization of the beam is rotated and reflected, and the beam is detected by a photodetector, which will be described later, and the information is reproduced. The light beam reflected from the optical disk 12 passes through the objective lens 20 again, is reflected by the reflective surface m of the prism 18, and is returned to the beam splitting surface 8 of the first beam splitter 6. The light beam is reflected at the beam splitting surface 8. Depending on the mounting direction of the semiconductor laser element 2, the light beam whose polarization plane is rotated by approximately 45'' with respect to the Y axis is guided to the second polarizing beam splitter 70.Polarizing beam splitter 7
0 is a combination of two right angle prisms, the joined surface of which is formed as a second beam splitting surface 74, and a second collimating lens 72 is provided on the side into which the light beam is incident. . The polarizing beam splitter 70 separates the light beam into two beams, and one beam is guided to the first photodetector 26 via the TTP 22 as a focus detection light beam. The other light beam is separated into an S-polarization component and a P-polarization component by a polarizing beam splitter 90, and the S-polarization component is reflected by a third beam splitter 90 and guided to a photodetector 28, where the light beam is divided into an S-polarization component and a P-polarization component. The P-polarized light component is passed through the beam splitter 90 and guided to the photodetector 27. By each photodetector,
The S-polarized component and the P-polarized component of the light beam are detected and subjected to predetermined processing by a signal processing circuit 30, which will be described later, to reproduce information recorded on the track 14 of the optical disc 12.

At the same time, a focus error signal FE and a tracking error signal TE are generated, and a focus control signal FC and a tracking control signal TC based on these FE and TE are supplied to the voice coils 32 and 34. 20, or the entire optical head is driven to maintain focusing and tracking.

FIG. 2 shows a modification of the optical head incorporated into a magneto-optical optical disk device. In this example, the first
The first beam splitter that separates the light beam directed from the light source toward the optical disk and the light beam reflected from the optical disk in the embodiment shown in Figures A and 1B and the prism having a non-polarizing reflective surface m are integrated. A formed example is shown.

According to this embodiment, the beam splitter 62 has a reflective surface 6
4, the size of the optical head itself is reduced. Moreover, it becomes possible to arrange the semiconductor laser element 2 and the collimating lens 4 below the optical disk 12, and a more compact optical head is provided. Note that in this embodiment as well, the reflecting surface 64 is formed of a non-polarizing beam split surface, as in the examples shown in FIGS. 1A and 1B, and the polarization plane of the light beam generated from the semiconductor laser element 2 is has already been rotated by approximately 45@ with respect to the Y axis, as already explained.

According to this embodiment, the light beam generated from the semiconductor laser element 2 is incident on the objective lens 20 via the polarization plane 64 of the beam splitter 62, is focused by the objective lens 20 on the track 14 of the optical disk 12, and is focused on the track 14 of the optical disk 12. The polarization plane of the light beam is slightly rotated according to the information recorded in the light beam 14 and is reflected back to the objective lens.

The light beam returned to the objective lens 20 is reflected by the beam splitting surface 64 and guided to a second beam splitter 70 to which a second collimating lens 72 is joined. The light beam given convergence by the second collimating lens 72 is separated into two beams by the second beam splitting surface 74, and one beam is used as a focus detection light beam to pass through the TTP 22 to the first light beam. guided to a detector 26. The other light beam is transmitted through a polarizing beam splitter 90
The light beams are separated into S-polarized light components and P-polarized light components, and the respective light beams are guided to second and third photodetectors 27 and 28. The light beams detected by the photodetectors 26, 27 and 28 are used for focusing and tracking by a signal processing circuit (not shown), as in the embodiment shown in FIGS. 1A and 1B above. Information recorded on track 14 is reproduced.

3A to 3D show means for converting the cross-sectional shape of the light beam generated from the semiconductor laser device 2 shown in FIGS. 1A and 1B from an ellipse to a circle. In the example shown in FIG. 3A, the outer periphery of the collimating lens 4 is covered with a light shielding film or reflective film 80 formed in a circular shape.

The light beam generated from the semiconductor laser element 2 is blocked or reflected by this light shielding film or reflective film 80, and is converted into a circular light beam having a diameter equal to the short axis of the ellipse. FIG. 3B shows an aperture 8 having a predetermined diameter between the collimating lens 4 and the semiconductor laser element 2.
2 is shown. In this example,
A light beam having an elliptical cross-sectional shape generated from the semiconductor laser element 2 is incident-limited by the aperture 82 and converted into a circular light beam having a size equal to the opening of the aperture 82 . This aperture may be formed integrally with the collimating lens 4 as shown in Figure 3D. FIG. 3C shows an example in which the cross-sectional shape of the tip beam is converted into a circular shape using only the collimating lens 4 and the semiconductor laser probe 2. As is clear from the drawing, by arranging the collimating lens 4 close to the semiconductor laser element 2, the part of the light beam with large divergence, that is, the part that is wider than the short axis diameter of the elliptical light beam. is not incident on the lens 4, and only the light beam limited by the diameter of the lens 4 is collimated. Naturally, the light beam directed to the outside of the lens 4 is blocked by a lens support member (not shown), so that it does not become disturbance light.

Next, signal processing of the light beam detected by the photodetector will be explained. FIGS. 4A to 4C show 1A to 4C.
The detection surface used in the optical head shown in FIG. 1B and FIG. The relationship between the projected beam spot and the objective lens 20 when it is in focus and out of focus is shown.

When the objective lens 20 is in focus on the front disk 12, spots Sa and sb as shown in FIG. 4B are projected onto the detection surface divided into eight sections of the photodetector 26. . The light beam that has passed through one glass plate of TTP22 is projected as a semicircular image onto the photodetection area ar')+g+h, and the light beam that has passed through the other glass plate is projected onto the photodetection area C9d, e, f. is projected as a semicircular image in the opposite direction. Parting lines α and β are arranged approximately at the center of each image so that images with equal amounts of light are projected onto the left and right photodetection areas. Therefore, the dividing line α
, β is the focusing error signal FE at the time of focusing, when the outputs of the photodetection areas a - h are ■ to ■. (■＋■＋■＋■)−(■＋■＋■＋■)
) 0.

When the objective lens 20 moves away from the in-focus position with respect to the optical disc 12, smaller images Sa and Sb are projected onto the detection surface of the photodetector than when in focus, as shown in FIG. 4A. , the focusing error signal FE satisfies FE>0.

Furthermore, when the objective lens 20 approaches the in-focus position with respect to the optical disc 12, larger images Sa and Sb than when in focus appear on the detection surface of the photodetector, as shown in FIG. 4C. The focusing error signal FE becomes FE<0.

5A to 5C, the detection surface used in the optical head shown in FIGS. 1A, 1B, and 2 is shown in a first photodetector 26 divided into eight sections. The relationship between the projected beam spot and the objective lens 20 when they are on track and when they are not on track is shown. When the objective lens 20 is in focus on the front disk 12, spots Sa and sb as shown in FIG. 5B are projected onto the detection surface divided into eight sections of the photodetector 26. . Parting lines u, v, and w are arranged approximately at the center of each image so that images of equal light intensity are projected onto the upper and lower photodetection regions. Therefore, the dividing line U.

When the output of the photodetection area a-h is from ■ to ■, the tracking error signal TE on the combined track is −E −+(■+■+■+■)−(■+■+■ +■))
− It is arranged so that the condition of 〇 is satisfied.

When the objective lens 20 moves away from the in-track position with respect to the optical disc 12, smaller images Sa and Sb are projected onto the detection surface of the photodetector than when in focus, as shown in FIG. 5A. , the focusing error signal TE satisfies TE>0.

Furthermore, when the objective lens 20 approaches the in-track position with respect to the optical disc 12, the image Sa becomes larger than when in focus, as shown in FIG. 5C.

sb is projected onto the detection surface of the photodetector, and the focusing error signal TE becomes TE<0.

FIG. 6 shows a signal processing circuit for focusing and tracking of the objective lens 20 in the optical head of the present invention, and for reproducing recorded information. Objective lens 2
Focusing and tracking of 0 is controlled by processing a light beam detected by a first photodetector 26 whose detection surface is divided into eight detection areas and driving a voice coil. The outputs of detection areas a and f are added together by an adder circuit 40, and the outputs of detection areas d and g are added together by an adder circuit 42. These adder circuits 40 and 42
The output of is input to a differential amplifier 44 to generate a focusing error signal FE.

Further, the outputs of the detection areas c and h are added together by an adder circuit 50, and the outputs of the detection areas s and e are added together by an adder circuit 52. The outputs of the adder circuits 50 and 52 are input to a differential amplifier 54 to generate a tracking error signal TE.

The focusing error signal FE and tracking error signal TE are transmitted to the voice coil drive circuit 46, respectively.
and 56. Based on the focusing error signal FE and tracking error signal TE input to the drive circuits 46 and 56, the drive circuit 46 sends a signal to the voice coil 32 that controls the position of the objective lens 20 in the optical axis direction.
A focusing control signal FC and a tracking control signal TC are sent from the drive circuit 56 to the voice coil 34 that controls the position of the objective lens 20 in a direction perpendicular to the optical axis.
is supplied.

The focusing control signal FC and tracking control signal TC cause the respective voice coils 46 and 56 to
is driven, the objective lens 20 is maintained in the focused state and the focused track state, and the information recorded on the optical disc 12 is accurately reproduced.

Furthermore, reproduction of the recorded information is performed using the second and third photodetectors 27.
．． The light beam detected by 28 is processed and displayed on a display device or the like. The outputs from the photodetectors 27 and 28 are input to an adder 60, the output of which is the output when the objective lens 20 is tracked in focus and on track by the first photodetector 26. is processed by a reproduction signal processing circuit, and the information is reproduced by a display device or the like.

(Effects) According to the present invention, a 1/2 λ plate is used to keep the transmittance of the P-polarized component and the reflectance of the S-polarized component of the light beam constant, and a rotation adjustment mechanism that adjusts the rotation of the light beam with respect to the optical axis. The present invention provides an optical head that can be removed, provides stable detection characteristics with a simple configuration, and can be easily assembled in manufacturing. Furthermore, since it is possible to reduce the number of special parts for correcting the ellipse of the light beam, the number of parts forming the optical head is reduced, and an optical head that can be incorporated into a small and compact optical disk device is provided. .

[Brief explanation of drawings]

FIG. 1A is a schematic diagram showing the arrangement of components of an optical head incorporated in a magneto-optical optical disk device, FIG. 1B is a plan view of the optical head shown in FIG. 1A, and FIG. 2 is a diagram showing the present invention. FIGS. 3A to 3D are schematic diagrams showing modified examples of the optical head incorporated in the magneto-optical optical disk device of FIG.
FIGS. 4A to 4C are schematic diagrams showing a method of converting the cross-sectional shape of the light beam generated from the semiconductor laser device 2 from an ellipse to a circular shape shown in FIGS.
A schematic diagram showing the relationship between the beam spot projected on the first photodetector 26 used in the optical head shown in FIG. A and FIG. 1B and the objective lens 20 when in focus and out of focus; FIGS. 5A to 5C show the first photodetector 2 used in the optical head shown in FIGS. 1A and 1B.
6 is a schematic diagram showing the relationship between the beam spot projected on the optical head 6 and the objective lens 20 during on-track and non-on-track. FIG. 20 is a block diagram showing a signal processing circuit for focusing, tracking, and reproduction of recorded information in No. 20. FIG. 2... Semiconductor laser element, 4... Collimating lens, 6... Beam splitter, 8.10... Beam splitting surface, 12... Optical disk, 14... Track, 16... Collimating lens , 18... Reflection prism, 20... Objective lens, 22... TTP (2
parallel flat glass), 24... Naifetsuji, 26
, 28.66... Photodetector, 32.34... Voice coil, 70... Second beam splitter, 72...
・Collimating lens, 74...beam split surface,
80... Reflective surface, 82... Aperture, 90...
polarizing beam splitter

Claims (1)

[Claims] A light source that generates a light beam having a plane of polarization, a focusing means that focuses the light beam generated from the light source onto an information recording medium, and a means that separates the light beam from the information recording medium into at least two light beams. an information recording/reproducing device comprising: a polarization plane of the light beam from the light source forming a predetermined angle with respect to a reference axis on the light source with respect to a polarization direction of the light beam separated by the separation means; Information recording and reproducing device.