JPS62154337A - Optical head - Google Patents

Abstract

PURPOSE:To prevent positional deviation between an erasing light spot and a recording and reproducing light spot by converging parallel recording and reproducing light beam and non-parallel erasing light beam by the same converging lens and controlling to make an erasing light spot form an image on the same track with a recording and reproducing light spot. CONSTITUTION:The center of rotation of a parallel prism 41 supported rotatably is set at a position where the plane of incidence of an erasing light beam 37 becomes vertical, and optical axes of erasing light beams 37 and 40 are in conformity. When the parallel prism 41 is rotated by an angle theta. The optical axis of the erasing light beam 40 deviates from the optical axis of the erasing light beam 37 in the direction B by epsilon. As the erasing light beam 40 is made to non-parallel light beam to the degree to correct chromatic aberration, an image is formed on the same plane with the recording and reproducing beam 22. An erasing light spot 39 is adjusted to conform with a recording and reproducing spot in regard to the direction of tracking. Accordingly, the erasing light spot 39 moves from the recording and reproducing light spot 29 by DELTAS in the direction C, and the image is formed on the same disk recording face.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical head for an optical disk device for recording and reproducing information, and in particular, the present invention relates to an optical head for an optical disk device for recording and reproducing information. The invention relates to an optical head that separates and extracts.

Conventional technology In recent years, still image disk device 2 correspondence file device.

Optical disk devices are being actively developed and commercialized as large-capacity information recording devices such as data file devices. An optical disk device is a device that irradiates a high-speed rotating disk with a laser beam to record information bits on the recording medium, then lowers the power of the same laser and reads changes in reflectance of recorded pits.

Now, for example, when using a thin film made of tellurium oxide doped with germanium and soot as a recording medium, when recording information pits, a light spot with a high power density narrowed down to the diffraction limit (about 0, S μm in diameter) is irradiated. Then,
The recording medium is rapidly heated and cooled to transition to a state with low reflectance, and recording is completed. In addition, when erasing recorded bits, a low power density and elliptical shaped light spot (elliptical diameter of about 1 μm) is irradiated onto the recording pit, and the recording medium in this area is annealed to restore its original reflectance. Erasing is completed by transitioning to the pre-recording state with a high value. As described above, an optical head that emits a source spot that can be annealed in erasing recorded bits has been proposed as an optical head for an optical disk device having a rewriting function.

A conventional example of such an optical head will be described below with reference to the drawings.

FIG. 8 is a diagram showing a schematic configuration of a conventional optical head.
is a recording and reproducing semiconductor laser, which irradiates the disk with a laser beam having a wavelength of λ1 and a power of approximately 8 mW during recording and approximately 1 mW during reproducing. 2 is a semiconductor laser for erasing, which emits wavelengths λ2. Power approximately 20m
A laser beam of approximately W is irradiated. 3 and 4 are condenser lenses, each of which has a recording/reproducing semiconductor laser 1. 5. Focusing the light beam from the erasing semiconductor laser 2; A recording/reproducing light beam and an erasing light beam No. 6 are formed. A cylindrical lens 7 imparts astigmatism to the erasing light beam 6 in order to make the shape of the aperture light elliptical. A first polarizing beam splitter 8 reflects the S-polarized light beam and transmits the P-polarized light beam. Reference numeral 9 denotes a second polarizing beam splitter, which has characteristics as shown in FIG. 9, and reflects S-polarized light of wavelength λ2 and transmits S-polarized light of wavelength λ1. 10 is Z
In the wave plate, 11 and 12 are aperture lenses. 13 is a disk having a recording medium for recording and reproducing, and 14 is a cylindrical lens for detecting a focus control signal using an astigmatism method. Reference numeral 16 denotes a signal detector, which includes a plurality of light-receiving elements for detecting a reproduction signal, a focus control signal, and a tracking control signal.

Based on the focus control signal and tracking control signal obtained from the signal detector 15, the aperture lens 11 is subjected to focus control and tracking control. 16 disc 1
3, the recording and reproducing light spot is narrowed down to 3, the erasing light spot 17 is focused into an elliptical shape, and 18 is the recording bit string in the track.

Next, the operation of the conventional optical head configured as described above will be explained. First, when recording or playing,
A recording/reproducing semiconductor laser 1 emits a light beam with a predetermined power. This P-polarized recording and reproducing light beam 5 passes through the first polarizing beam splitter 8, passes through a two-wavelength plate 10, and is irradiated onto the disk 13 by an aperture lens 11 as a recording and reproducing light spot 1e. This recording/reproducing light spot 1
6 increases its power during recording, and rapidly heats and cools the recording medium of the disk 13 to change its state and change its reflectance. This forms recording bits.

In addition, during reproduction, the power of the light beam is lowered, and the recording and reproduction light spot 1 is
6. Next, the reflected light from the disk is condensed by an aperture lens 11 and returned to the first polarizing beam splitter 8. At this time, the returned recording/reproducing light beam 6 is 2
Since the P-polarized light is changed to S-polarized light by the wavelength plate 10, it is reflected by the first polarization splitter 8 and enters the second polarization beam splitter 9. Since the second polarizing beam splitter does not have a polarization splitting characteristic for the light beam having the wavelength λ1, the recording/reproducing light beam 6 having the wavelength λ1 is transmitted therethrough and focused by the aperture lens 12 onto the signal detector 16.

The cylindrical lens 14 imparts astigmatism to this aperture light to enable focus detection.

Next, in erasing, the erasing semiconductor laser 2 emits a light beam with a predetermined power. Since the second polarizing beam splitter 9 has polarization splitting characteristics at wavelength λ2, the erasing light beam 6 with wavelength λ2 incident as S-polarized light is reflected here.
The light is incident on the first polarizing beam splitter 8. The S-polarized erasing light beam 6 is also reflected by the first polarizing beam splitter 8, is combined with the recording/reproducing light beam 6, passes through the wavelength plate 10, and is produced as an erasing light spot 17 on the disk 13 by the aperture lens 11. Narrowed down. This erasing light spot 17 is given astigmatism by a cylindrical lens, and has an elliptical shape long in the track direction. That is, since the power density is low and the recording bit is irradiated for a long time, the recording bit is heated by the thermal energy and then slowly cooled to receive the annealing effect.

Therefore, the state of the recording medium in that area changes, and erasing is performed by returning to the reflectance before recording. Note that the reflected light from the disk 13 at the erasing light spot 17 is condensed by the aperture lens 11, passes through the wavelength plate 1° again, and enters the first polarizing beam splitter 8. At this time, since the erasing light beam 6 has changed from S-polarized light to P-polarized light, it passes through the first polarized beam sgritter 8 and escapes toward the recording/reproducing semiconductor laser 1 . By slightly shifting the optical axes of the erasing light beam and the recording/reproducing light beam, the escaped erasing light beam can be directed to the recording/reproducing semiconductor laser 1.
The structure is such that the light is not incident on the light emitting point of the light source.

Problems to be Solved by the Invention Problems in the conventional optical head having the above configuration will be explained below. As described above, the recording and reproducing light spot 16 and the erasing light spot 17 are controlled by moving the aperture lens 11 using the recording and reproducing light beam reflected from the disk 13. Therefore, the erasing light spot 17
If the recording/reproducing light spot 16 deviates in the tracking direction, the amount of deviation cannot be corrected.

The main reason why the recording/reproducing light spot 16 and the erasing light spot 17 are shifted is that the relative positions of the recording/reproducing semiconductor laser 1 and the erasing semiconductor laser 2 are shifted due to temperature changes. If the allowable value for the deviation between the recording and reproducing light spot 16 and the erasing light spot 17 is 0.1 μm, then the allowable deviation in the relative positions of the respective lasers is only about 0.2 μm. It is structurally difficult to maintain this level of accuracy against temperature changes.

Furthermore, if factors other than temperature, such as setting errors, are considered, the above-mentioned allowable value becomes even smaller. For this reason, erasing light spot 1
7 and the recording/reproducing light spot 16, it is necessary to detect the shift of the erasing light spot and control it so that it is on the same trunk as the recording/reproducing light spot.

Means for Solving the Problems The present invention solves the conventional problems as described above.
A parallel recording/reproducing light beam with a wavelength λ1 and a non-parallel erasing light beam with a wavelength λ2 are focused by the same aperture lens to form a main recording/reproducing light spot and an erasing light spot on the disk, and By rotating a parallel prism provided in the optical path of the erasing light beam so that its incident surface is substantially perpendicular, the erasing light spot is configured to move in a direction perpendicular to the track. A tracking error signal is detected and control is performed so that the extinction spot is focused on the same track as the recording/reproducing light spot.

Function: With the above-described configuration, the erasing light beam with the wavelength λ2 is imaged on the focal plane on which the parallel recording/reproducing light beam with the wavelength λ1 is focused, so that the erasing light beam is composed of non-parallel light beams. The beam enters the aperture lens. By shifting the incident position of this non-parallel erasing light beam onto the aperture lens in the direction perpendicular to the track, the erasing light spot moves in the opposite direction. On the other hand, the optical axis of a non-parallel erasing light beam can be shifted by rotating a parallel prism provided in its optical path, so by rotating this parallel prism, the erasing light spot can be shifted. It is possible to control the recording and reproducing light spot so that it is aligned with the same track.

Therefore, the erasing light spot can be stably aligned with the recording/reproducing light spot with high precision (0.1 μm or less), and the conventional problem of misalignment of the two spots can be solved.

Embodiment An embodiment of the present invention is shown in the accompanying drawings FIGS. 1 and 2. First, the configuration of the recording/reproducing optical system will be explained. 2o is a recording/reproducing semiconductor laser that generates a laser beam of wavelength λ1;
21 is a condensing lens that converts the laser beam into a parallel light beam;
22 is a converted recording/reproducing light beam. 23 is the first
This polarizing beam splitter has wavelength characteristics as shown in FIG. 3, and has polarization characteristics that transmit P-polarized light of wavelength λ1 and reflect P-polarized light of wavelength λ2, which will be described later.

The recording/reproducing semiconductor laser 20 is a polarizing beam splitter 2
3, the recording/reproducing light beam 22 passes through the first polarizing beam splitter 23 and enters the second polarizing beam splitter 24. The second polarized beam subrifter 24 has wavelength characteristics as shown in FIG.
It has polarization properties that reflect polarized light. Therefore, the recording/reproducing light beam 22 also passes through the second polarizing beam splitter 24, and its optical path is bent at right angles by the reflecting prism 25, resulting in a
Wave plate 26. Passing through the aperture lens 27, the disc recording surface 2
A minute recording/reproducing light spot 29 is formed at 8. After reflection on the disk recording surface 28, the aperture lens 27. Wavelength plate 26
Since the reflected light traveling through the nine reflecting prisms 26 is S-polarized, its optical path is bent at a right angle by the second polarizing beam splitter 24, and the reflected light passes through the third polarizing beam splitter 30.
leading to. As shown in FIG. 6, this third polarizing beam splitter 3o reflects the S-polarized light from the recording/reproducing light beam having the wavelength λ1, and reflects the S-polarized light from the erasing semiconductor laser 31 with the wavelength λ1.
S polarization for light beam 2.

It has a polarization characteristic of transmitting both P-polarized light.

That is, the reflected light of the recording and reproducing light beam 22 is reflected by the third polarizing beam splitter 30 and reaches the aperture lens 33. The recording/reproducing light beam 22 passing through the aperture lens 33 is given astigmatism by the cylindrical lens 34 and is received by the signal detector 35 . The signal detector 36 is composed of a plurality of light receiving elements as in the conventional example, and detects the reproduced signal, and
It is configured such that a focus control signal can be detected using a so-called astigmatism method, and a tracking control signal can be detected using a push-pull method. Further, the aperture lens 27 is subjected to focus control and tracking control based on the focus control signal and tracking control signal obtained from the signal detector 35.

Next, the configuration of the erasing optical system will be explained. The erasing semiconductor laser 31 has an S
The emitted laser light having a wavelength λ2 is turned into a slightly non-parallel erasing light beam 37 by a condensing lens 36 for erasing. What makes the erasing light beam 37 slightly non-parallel is the parallel recording/reproducing light beam 22 with wavelength λ1.
This is to form an image of the erasing light beam of wavelength λ2 on the focal plane on which the image is formed. For example, the recording/reproducing semiconductor laser 2
0 wavelength is 830 nm, the wavelength λ2 of the erasing semiconductor laser 31 is 780 nm, and the NA of the aperture lens 27 is 0.5. When each light beam is collimated with parallel light, the color beam 37 has a divergence angle sufficient to correct this. must have. The erasing light beam 37 passes through the erasing light beam forming means 38 and the parallel prism 41 to become the erasing light beam 40, whose optical path is bent at right angles by the reflecting prism 32, and enters the third polarizing beam splitter 3o. Note that the erasing beam forming means 38 is composed of a cylindrical lens or the like as in the conventional example. Further, the parallel prism 41 is held rotatably in the R direction. As described above, the third polarizing beam splitter 30 does not have polarization splitting characteristics for the S-polarized light having the wavelength λ2, so the erasing light beam 4o passes therethrough. The erase light beam 4o is then passed through a second polarizing beam splitter 24.degree. reflection prism 26. y4 wavelength plate 26. Aperture 9
The light reaches the disk recording surface 28 through the lens 27 and forms an erasing light spot 39. Therefore, as in the conventional example, this erasing light spot 39 is given an astigmatism by an erasing beam forming means 38 constituted by a cylindrical lens or the like, and has an elliptical shape long in the track direction. That is, since the power density is low and recording pits are irradiated for a long time, the recording bits are subjected to an annealing effect due to the thermal energy. Due to this effect, the state of the recording medium in that area changes, returning to the reflectance before recording and erasing is performed. On the other hand, like the recording and reproducing light beam 22, the reflected light of the erasing light beam 40 returns to the second polarizing beam splitter 24. At this time, it is P-polarized light, so it passes through this,
The light is incident on the first polarizing beam splitter 23. Since the first polarizing beam splitter 23 reflects the P-polarized light of wavelength λ2 as described above, this erasing light beam 40 is reflected and reaches the detector 42.

The detector 42 consists of two light receiving elements, and is configured to detect a tracking error of the erasing light spot 39 by a so-called push-pull method to obtain an erasing light tracking control signal.

In the above configuration, the operation of the present invention will be explained in the sixth section.
This will be explained with reference to FIG. FIG. 6 shows the image formation state of the recording/reproducing light beam 22 and the erasing light beam 4o when FIG. 2 is viewed from the entrance direction, and FIG. The relationship between the erasing light beam 37 and the emitted erasing light beam 4° is shown. The center of rotation of the parallel prism 41, which is rotatably supported in the R direction, is the erasing light beam 37.
The optical axis of the erasing light beams 37 and 40 coincide with each other, as shown in FIG. 7(,). Here, the parallel prism 41 is
When the angle θ is rotated as shown in the figure), the erasing light beam 40
The optical axis of is shifted in the B direction by ε with respect to the optical axis of the erasing light beam 37. On the other hand, since the erasing light beam 40 emitted in the state shown in FIG. The image is formed on the same plane as. Here, the erasing light spot 39 is adjusted to match the recording/reproducing light spot 29 in the tracking direction.

Next, since the optical axis of the erasing light beam 40 emitted in the state shown in FIG. 7(b) is shifted by ε, an image is formed as shown in FIG. 7(e) cb). That is, the erasing light spot 39 moves from the recording/reproducing light spot 29 by ΔS in the C direction and is imaged on the same disk recording surface. This amount of movement is about 1 μm, assuming that the thickness of the parallel prism is 3 mm and θ=100.

Therefore, the erasing light spot 39 is moved in the tracking direction by ΔS
If there is a deviation, the erase light spot 39 can be made to coincide with the recording/reproducing light spot 29 by detecting this deviation with the detector 42 and rotating the parallel prism 41 in a direction to absorb it. The parallel prism 41 is the detector 4
Such control is performed by the erasing light tracking control signal No. 2. Therefore, the erasing light spot 39 and the recording/reproducing light spot 29 follow the same trunk with high precision, and no deviation occurs as in the conventional example.

Effects of the Invention According to the configuration of the present invention, by rotating the parallel prism, the erasing light beam can be moved in parallel and the erasing light spot can be moved independently, so that tracking control of the erasing light spot has become possible. . This allows the recording/reproducing light spot and the erasing light spot to travel stably on the same track. Therefore, even if the position between the two semiconductor lasers changes due to a temperature change, stable performance can be maintained without deteriorating the erasing performance. Also, it is possible to prevent the above-mentioned two spots from shifting due to adjustment errors or changes over time.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of an optical head according to an embodiment of the present invention, Fig. 2 is a principle diagram of an optical head seen from a direction perpendicular to Fig. 1, and Figs. Characteristic diagrams of the polarizing beam splitter used in the optical head, Figures 6 and 7 are principle diagrams showing the operation of the parallel prism used in the present invention, and Figure 8 is a principle diagram of the optical head using a conventional light source. FIG. 9 is a characteristic diagram of a polarizing beam splitter of a conventional optical head. 2o... Semiconductor laser for recording and reproduction, 23...
...first polarizing beam splitter, 24...
2nd polarizing beam splitter, 29... Recording and reproducing light spot, 3o... Third polarizing beam splitter, 31... Semiconductor laser for erasing, 38.
...Erasing beam forming means, 39...Erasing light spot, 40...Erasing light beam, 41...
...Parallel prism, 42...Detector. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 (fix) Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] A parallel recording and reproducing light beam with a wavelength λ_1 and a non-parallel erasing light beam with a wavelength λ_2 are focused by the same aperture lens to form a recording and reproducing light spot and an erasing light spot on the disk, and the erasing light beam is By rotating a parallel prism provided in the optical path of the beam, the erasing light spot is configured to move in a direction perpendicular to the track, and a tracking error signal of the erasing light spot is detected, and the erasing light spot is moved in the direction perpendicular to the track. An optical head characterized in that the optical head is controlled to form an image on the same track as a recording/reproducing light spot.