JPS63229634A - Optical head - Google Patents

Abstract

PURPOSE:To confirm the deviation between an erasing light spot and a recording and reproducing light spot by using the s-polarized light to form a first light spot and using the p-polarized light to form a second light spot and detecting an address signal with the first light spot. CONSTITUTION:A reflected light 73 of an erasing light spot 72 reflected on a disk 52 passes an objective lens 51, a quarter-wave plate 50, a triangular prism 49, and a prism 47 and is transmitted through a first polarization beam splitter 48. Thereafter, this light is reflected on a wavelength selecting filter 56 and is emitted from a prism 55 and has the optical path bent by an erasing beam forming means 69 and is made incident on a second polarization beam splitter 68. Since a reflected light 63 is an s-polarized light by the action of the quarter-wave plate 50, a reflected light 63 is reflected on the beam splitter 68 and reaches a photodetector 74. Thus, the track deviation of the erasing light spot 72 is detected and the address signal is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to an optical head for a phase-change optical disc device that erases recorded bits of an optical disc by annealing them.

2. Description of the Related Art In recent years, optical disk devices have been actively developed as large-capacity information storage devices such as document file devices and data file devices. An optical disk device is a device that irradiates a high-speed rotating disk with a laser beam to record information on a recording medium, and then lowers the power of the same laser to read changes in the reflectance of recorded bits. When using a phase change recording medium, during recording, a light spot with high power density narrowed down to the diffraction limit is irradiated, and the medium is rapidly heated and cooled, transitioning to a state with low reflectance. . In addition, when erasing recorded bits, a light spot with low power density and shaped into an ellipse is irradiated onto the recorded bits.
This portion of the medium is annealed (slowly cooled) and transferred to its original pre-recording state with high reflectance, and erasing is performed.

As described above, an optical head that emits a light spot that can be annealed in erasing recorded bits has been proposed as an optical head for an optical disk device having an erasing/rewriting function.

A conventional example of such an optical head has a configuration as shown in FIG. First, an optical system related to a light beam of wavelength λ1 used for recording and reproduction will be explained. 1 is the wavelength λ
A first semiconductor laser that emits one laser beam outputs a recording/reproducing light beam 2.

The recording and reproducing light beam 2 is turned into parallel light by a condenser lens 3, and is beam-shaped by a prism 4. At this time, on the enlarged surface 6,
A polarizing beam splitter 6 is formed, through which the recording/reproducing light beam 2 incident as a P-polarized wave is transmitted. Next, the light enters the prism 7 , is reflected by the total reflection surface 8 , and then enters the wavelength selection filter 9 . As shown in FIG. 12, the wavelength selection filter 9 has a characteristic of transmitting both P-polarized light and S-polarized light with a wavelength λ1, so the recording and reproducing light beam 2 passes through it, and the triangular prism 1o and the 174-wave plate 11
A recording/reproducing light spot 14 is formed on the disk 13 through the objective lens 12. On the other hand, the reflected light 16 reflected from the disk 13 is transmitted through the objective lens 12 + 'A wavelength plate 11
．． Triangular prism 10. Wavelength selection filter 9. Total reflection surface 8
After that, the S-polarized light wave is transmitted to the first polarized beam splitter 6.
It is incident on and reflected here. After the reflected light 16 enters the prism 16, it is reflected by the prism surface 17, and the reflected light 16 is reflected by the prism surface 17.
The beam enters a beam splitter 19 provided at 8. Here, the reflected light 16 is amplitude-divided into a detection light 151L that is reflected by the beam splitter 19 and directed toward the optical system for focus detection, and a detection light 15b that is transmitted through the beam splitter 19 and directed toward the optical system for tracking detection. The light 16& is the detection lens 20. Via a triangular prism 21, it reaches a photodetector 22 for obtaining a seven-occasion signal in a known manner. On the other hand, the detection light 15b passes through a sub-angle prism 23 and reaches a photodetector 24 for obtaining a tracking signal using a known method. These signals are used to control the recording/reproducing light spot 14 to follow the tracks of the disk 13.

Next, the optical path of the erasing light beam 27 emitted from the second semiconductor laser 26 and having a wavelength of λ2 will be explained. This erasing light beam 27 is narrowed in the track direction on the disk 13 and is used for erasing information signals.

The erasing light beam 27 becomes parallel light at the condensing lens 28,
After passing through an erasing beam forming means 30 for forming an erasing light spot as shown in Japanese Patent Application No. 60-40407, it becomes an erasing light beam 40 and enters an enlarged surface 32 of a prism 31. A second polarized beam splitter 33 is formed on the enlarged surface 32, and the erasing light beam 40 incident as a P-polarized wave is beam-shaped as it passes through the second polarized beam splitter 33. The shaped erasing light beam 40 is reflected by the total reflection surface 34, exits the prism 31, and then enters the wavelength selection filter 9.

The wavelength selection filter 9 has a characteristic of reflecting both P-polarized light wave and S-polarized light wave of wavelength λ2, and the erasing light beam 40 is reflected and passes through the triangular prism 10°'' A wavelength plate 1.
1. A second light spot 36 is formed through the objective lens 12 . On the other hand, the reflected light 37 reflected by the disk 13 is
Objective lens 12, 174 wavelength plate 11. triangular prism 10
．． The light passes through the total reflection surface 34 of the wavelength selection filter 9, becomes an S-polarized light wave, enters the second polarization beam splitter, and is reflected there. Thereafter, the reflected light 37 passes through a triangular prism 38 and reaches a photodetector 39, and is transmitted to the second photodetector by a known method.
The track deviation of the optical spot 35 is detected.

When track deviation is detected, measures such as stopping the operation are taken.

Problems to be Solved by the Invention In the above configuration, the problems will be explained below. The erasing beam forming means 30 disclosed in Japanese Patent Application Laid-Open No. 60-40407 is constructed as shown in FIGS. 10 and 11. That is, the surface 30G is parallel to the first surface 30D of the erasing beam forming means 30, and the second surface 30B is slightly inclined.

When the erasing light beam 27 is incident on the erasing beam forming means 30, the light beam that has passed through the surfaces 30m and 30B is affected by the prism and its path is deflected in the direction of the thickness of the prism, resulting in 40 erasing beams.

40B is formed, and the 30 erasing light beams that have passed through the 30 surfaces with larger prism apex angles are polarized to a greater extent. Erasing light beams 40M, 40B,
When the 40G light enters the objective lens 12Vc and is focused onto the disk 13, the images are formed at different positions because the angle of incidence is different. As a result, the erasing light spot 36 is the first light spot 3 which has a high peak and is relatively steep, as shown in FIG.
A second light spot 5esB, which is wide in the track direction and has a low peak, is formed by the erasing light beam 40G.
is formed by the erasing light beam 40B. This method of erasing light spot 36 is adopted because it is more efficient for erasing to have a steep first light spot 35 followed by a second light spot 35B for gradual cooling. . However, since the wavefront of the erasing light beam 27i is divided to form the erasing light beam 40G for rapid heating, the width of the light beam increases.

Then, the width of the first light spot narrowed down in the track direction becomes large. Generally, the half width of the recording/reproducing light spot 14 is 0.8 to 1.0.
The width at half maximum of the first 36 light spots is 1.5 to 2.5 μm. Therefore, the first optical spot 35A cannot detect the bit-shaped address signal of about 1 μm, which is formed in advance on the disk 13.

Therefore, only a tracking error signal is obtained from the photodetector 39, and if the erasing light spot 36 deviates from the recording/reproducing light spot 14 by more than the track pitch A,
Since it is not possible to check the deviation, there is a problem that the system may malfunction because it assumes that it is following the same track, and necessary data is erased.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention forms an optical film that is flat on one surface and has polarization splitting characteristics, and the other surface is made up of a plurality of tapered parts or arcuate parts. The prism on which the reflective film is formed reflects the S-polarized light wave of the light beam incident on the flat part, and also reflects the P-polarized light wave on the tapered part or the arcuate part, so that the peak is high and the width is high using the S-polarized light wave. A second light spot having a low peak and a wide width is formed using a P-polarized light wave from a narrow first light spot, and an address signal is detected using the first light spot.

Effect According to the above configuration, since the S-polarized light wave is created by amplitude division, the width of the light beam is larger than the width of the light beam created by conventional wavefront division.
The width of the optical spot becomes small and becomes comparable to the optical spot width for recording and reproduction.

Therefore, the address signal can be detected from the first optical spot of the erasing optical spot, and it can be confirmed whether the erasing optical spot and the recording/reproducing optical spot are on the same track even if the track pitch is shifted due to force. be able to.

Example Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention, where (&) is a plan view seen from the disk side, and (b) is a front view. Further, FIGS. 2, 3, and 4 are detailed views of the erasing beam forming means used in the present invention. In the figure, 41 is the first light source.
A recording/reproducing light beam 42 having a wavelength of λ1 is emitted by a semiconductor laser. The recording/reproducing light beam 42 is converged into a substantially circular shape on the disk, for example, for recording/reproducing and focusing information signals.

Used for servo signal detection for tracking control, etc. This recording/reproducing light beam 42 is converted into a parallel beam by a condensing lens 43 and enters an enlarged surface 45 of a prism 44 . At this time, the recording/reproducing light beam 42 having an elliptical light intensity distribution
The beam width is expanded only in the short axis direction of the ellipse, and the beam is shaped into a substantially circular light beam. The approximately circular recording/reproducing light beam 42 passes through the A wavelength plate 46 and is converted from P-polarized light to S-polarized light, and enters the first polarizing beam splitter 48 of the prism 47 . As shown in FIG. 6, the first polarizing beam splitter 48 has a characteristic of transmitting a P polarized light wave with a wavelength λ1 and reflecting an S polarized light wave, so that the recording and reproducing light beam 42 is reflected there, and the triangular prism 49r'/i wave plate 60. A substantially circular recording/reproducing light spot 53 is formed on the disk 62 through the objective lens 61. On the other hand, disk 6
The reflected light 64 of the recording and reproducing light spot 53 from the objective lens 61% wavelength plate 50. After passing through triangular prism 49,
Due to the action of the A wavelength plate 50, the light becomes P-polarized light, enters the first polarization beam splitter 48, and is transmitted therethrough.

Thereafter, the reflected light 64 passes through a prism 65. The light is incident on the wavelength selection filter 6e. As shown in FIG. 7, the wavelength selection filter 66 converts the light beam of wavelength λ into P-polarized light.

Since it has the characteristic of transmitting both S-polarized light, the reflected light 64
passes through this and enters the prism 6a.

Next, the reflected light 54 is totally reflected by the prism surface 57L and reaches a beam splitter 68 provided at the end of the prism surface 6. Since this beam sinter 68 has the characteristic of transmitting the light beam of wavelength λ1 at a certain rate, the reflected light 64
The detection light 54a that passes through the beam splitter 68 and goes to the optical system for focus detection, and the beam splitter 58
Detection light 5 reflected by and directed toward the optical system for tracking detection
The amplitude is divided into 4b. At this time, the optical path of the detection light 54b is deflected by the prism surface 67b, so when it enters the prism 5a again, it does not satisfy the conditions for total reflection and passes through the triangular prism 59 using a known method. and reaches a photodetector 6o for obtaining a tracking signal. On the other hand, the detection light 54a passes through the beam splitter 68 and then passes through the detection lens 61. The light passes through a triangular prism 62 and reaches a photodetector 63 for obtaining a focus signal using a known method. The tracking and focusing control signals obtained by the two photodetectors 60 and 63 are transmitted to an actuator 64 that holds the objective lens 61 and can control its displacement in two directions: the direction of its optical axis and the direction perpendicular to the optical axis. is fed back to perform the above control.

Next, the optical path of the erasing light beam 66, which is emitted from the second semiconductor laser 66 serving as the second light source and has a wavelength of λ2, will be explained. The second semiconductor laser 65 enters the second polarization beam splitter 68 as P-polarized light, and enters the polarization splitting film 70 provided in the erase beam forming means 69 so that the plane of incidence and the plane of polarization are constant. It is arranged at an angle. On the other hand, as shown in FIG. 8, the second polarizing beam splitter 68 is configured to transmit P-polarized light with a wavelength λ2 and reflect S-polarized light, and forms an erased light beam that is parallelized by the condenser lens 67. Since the light 66 enters as P-polarized light, it passes through this and reaches the erasing beam forming means 69.

As shown in FIG. 2, the erasing beam forming means has a plane e9D formed on the incident side of the erasing light beam 66, and an optical multilayer film is formed on the surface of the plane e9D. A polarization splitting film 70m having such characteristics is formed. Also, surfaces 69M, 69B, 6 on the reflective surface side
90 has a slight inclination with respect to the plane 69D,
A reflective film 70B is formed on its surface. Although this example shows a configuration consisting of three surfaces, 69 people, 69B, and 690, the number of surfaces may be arbitrary. When the erasing light beam θ6 is incident on the erasing beam forming means 69, the polarization splitting film 70
In the erasing light beam 66 whose polarization plane has a fixed angle with respect to the plane of incidence of the beam, only the S-polarized light wave is reflected at the plane 69D to become the erasing light beam 71D, while the P-polarized light wave is transmitted and becomes the erase light beam 71D. 69
Person, 69B.

It reaches esc and is reflected here. The reflected P-polarized light wave passes through the plane 69Di again, but through the plane 69M.

According to the inclination of 69B and 69G, the erasing light beam 71D
The course is slightly deflected. As a result, erasing light beams 71A, 71B, and 71G are formed, and the erasing light beam 71 reflected by the surface 69A having a larger inclination is deflected to a greater extent. Erasing light beam 71 thus formed
People, 71B, 71G.

When the light 1D enters the objective lens 61 and is focused onto the disk 52, the images are formed at different positions due to the different angles of incidence, resulting in a steep first light spot 72 as shown in FIG. is formed by the erasing light beam 71DK, and the second light spot 72B for slow cooling, which is wide in the track direction, is the erasing light beam 71DK.

71G.

To further explain the optical path of the erasing optical system, the erasing light beam 71 emitted from the erasing beam forming means is incident on the enlarged surface 55a of the prism 56. At this time, the erasing light beam 71 has an elliptical light intensity distribution similar to the recording and reproducing light beam 42, and is refracted at the magnifying surface 65&, and the beam width is expanded only in the short axis direction of the ellipse, resulting in a substantially circular light beam. It will be formatted like this. The shaped erasing light beam 71 passes through the prism 56 and enters the wavelength selection filter 56 . Wavelength selection filter 5
Since θ has the characteristic of reflecting both P-polarized light and S-polarized light with wavelength λ2, the erasing light beam 71 is reflected, passes through the prism 55 again, and is sent to the first polarizing beam splitter 4.
8. The first polarizing beam splitter 48
As shown in the figure, since the light beam with the wavelength λ2 passes through both P-polarized light and S-polarized light, the erasing light beam 71 passes through the prism 4A, triangular prism '9y'A wavelength plate 50. An erasing light spot 72 is formed on the disk 62 through the objective lens 61 . This erasing light spot 72 is imaged at a position close to the recording/reproducing light spot 64 on the same track and is used for erasing the information signal. Next disk 5
The erase light spot 720 reflected light 73 reflected by the objective lens 51. V4 wave plate 50. Triangular prism 49.
After passing through the prism 4, the first polarizing beam splitter 48
Transmit. Thereafter, the light is reflected by the wavelength selection filter 56, exits the prism 56, has its optical path bent by the erasure beam forming means 69, and enters the second polarizing beam splitter 68. Since the reflected light 63 has become S-polarized light due to the action of the demon wave plate 6o, it is reflected here and reaches the photodetector 74.
The track deviation of the erasing light spot 72 is detected by a known method, and an address signal is also detected.

Since the erasing light beam 71D is formed by amplitude division, it has a wider light beam width than the conventional example, and has a wider width than the recording/reproducing light beam 42.
It will be about the same as. Therefore, the half-value width of the spot of the first optical spora) 71A created by incorporating this is O,S~1.0 as shown in FIG. Address signals of about 1 μm or more that can be detected by the recording/reproducing light spot 53 can be similarly detected.

Furthermore, the configuration shown in FIG. 4 as the erasing beam forming means 69 is also conceivable. In the figure, the arc portion 69E is formed by a cylindrical lens. Similarly, the S-polarized wave of the erasing light beam 66 becomes the erasing light beam 71D, forming a steep first light spot 72 on the disk 52, and the P-polarized wave reflected by the arc portion 69 has astigmatism. Then, a slight optical path polarization is given to the erasing light beam 71, and an elliptical spot long in the track direction is formed at a position different from the first light spot 72. In this configuration as well, the half-width of the first optical spot 72 can be made small as in the configuration shown in FIG. 2, and the address signal can be detected.

With the above configuration, if the address signal of the erasing light beam detected by the photodetector 74 and the address signal of the recording/reproduction source beam detected by the photodetector 60 are different, the recording light spot 53, Since the erasing light spot 72 does not follow the same track, measures are taken such as returning the erasing light spot 72 to the same track using means (not shown) for driving only the erasing light spot 72 or stopping the recording and erasing operations.

Detailed Description of the Invention According to the configuration of the present invention, it is possible to detect an address signal using an erasing light beam, and it is possible to detect whether the recording/reproducing light spot and the erasing light spot are following the same designated track. What can be confirmed.

If the position of the erase light spot is confirmed by detecting only the tracking deviation with the erase light beam as in the conventional example, even if the erase light spot is shifted by one track, it will be detected as tracking the same track as the recording/reproduction light spot, resulting in erroneous erasure. However, according to the present invention, it is possible to detect even if the erasing light spot deviates significantly, so that the problem unlike the conventional method does not occur.

Therefore, reliability, which is an important issue for an optical disc device that records and erases information, can be ensured.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an optical head in an embodiment of the present invention;
2, 3, and 4 are detailed views of the erasing beam forming means used in the present invention, and FIG. 6 is an explanatory diagram of the erasing light spot formed by the optical head of the present invention. 7 and 8 are characteristic diagrams of a polarizing beam splitter used in the optical head of the present invention, FIG. 9 is a configuration diagram of a conventional optical head, and FIG.
FIG. 1 is a detailed diagram of the erasing beam forming means used in the conventional optical head, and FIG. 12 is a characteristic diagram of the polarizing beam splitter used in the conventional optical head. 41...First semiconductor laser, 42...
- Recording and reproducing light beam, 48...first polarizing beam splitter, 52...disc, 63...
...Recording/reproduction light spot, 66...Wavelength selection filter, 6B...Second semiconductor laser, 66
...Erasing light beam, 68...Second polarization beam sliver, 69...Erasing beam forming means, 70M...Polarization splitting film, 7QB・・・・・・
... Reflection film, 71 ... Erasing light beam, 74 ... Photodetector. Name of agent: Patent attorney Toshio Nakao (1st person)
Fig. 2 Fig. <9A Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 8 Polarized light Figure 11 Figure 12

Claims (2)

[Claims] (1) A prism in which one surface is flat and has an optical film having a polarization splitting property, and the other surface is composed of a plurality of tapered parts and a reflective film is formed, makes the S-polarized light beam incident on the flat part While reflecting the waves, the taper part
Reflecting the polarized light waves, forming a first light spot with a high peak and narrow width using the S polarized light wave and a second light spot with a low peak and wide width using the P polarized light waves, Second
An optical head that performs erasing by irradiating a light spot onto the recording surface of an optical disc. (2) A prism in which one surface is a flat surface and an optical film having polarization splitting characteristics is formed, and the other surface is an arcuate portion and a reflective film is formed on the prism, the S of the light beam incident on the flat surface is formed.
While reflecting the polarized light wave, the arc portion reflects the P polarized light wave, and the S polarized light wave is used to create a first light spot with a high peak and a narrow width, and the P polarized light wave is used to create a second light spot with a low peak and a wide width. An optical head that forms a light spot and performs erasing by irradiating the first and second light spots onto a recording surface of an optical disc.