JP2559011B2 - Optical head - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head in an optical disk device for optically recording or reproducing a signal on an information medium such as an optical disk.

[0002]

2. Description of the Related Art As an optical head used for a semiconductor laser,
A general one is shown in FIG. 11, the light beam was I De from the semiconductor laser 42 is a portion at the half mirror 43 is reflected. The reflected light beam 42 is bent at a right angle by a reflection mirror 44 and is condensed by a condenser lens 45 so as to become a substantially parallel light beam. The substantially parallel light flux 42 is narrowed down by the objective lens 46 and forms a light spot 48 on the recording surface of the information medium 47. Next, the light flux 49 reflected by the information medium 47 passes through the objective lens 46, the condenser lens 45, and the reflection mirror 44 again, and enters the half mirror 43. A part of the light beam 49 obliquely passes through the half mirror 43 to become a light beam having astigmatism, converges through the concave lens 50, and is received by the photodetector 51. Photodetector 51
Is configured to detect a reproduction signal, a focus control signal by a so-called astigmatism method, and a tracking control signal by a push-pull method.

The objective lens 46 used in the optical head having such a structure is designed in consideration of the thickness of the information medium 47, and spherical aberration occurs in an information medium having a thickness different from the designed value. The imaging performance deteriorates, and recording / reproduction cannot be performed. Conventionally, compact disc (C
The thickness of the substrate of the information medium used in D), the video disk, the magneto-optical disk device for data, etc. was 1.2 mm, which were all the same. Therefore, it is possible to record / reproduce different types of information media (CD, video disc, magneto-optical disc, etc.) with one optical head.

On the other hand, in recent years, in order to achieve higher density,
Increasing the numerical aperture of the objective lens has been studied. When the numerical aperture of the objective lens is increased, the optical resolution is improved and the frequency band for recording / reproducing can be widened, but there is a problem that the aberration of the converged light spot 48 is increased. The information medium 47 and the objective lens 46 are tilted due to the surface wobbling of the information medium 47 and the surface wobbling of the turntable to which the information medium is attached. Due to this inclination , coma aberration occurs in the light spot 48, and the convergence performance does not improve even if the numerical aperture is increased. Therefore, an attempt has been made to use a thin information medium so that the coma aberration does not increase even if the numerical aperture of the objective lens is increased.
Frame collection due to tilt of the information medium 47 and the objective lens 46
The difference is improved as shown in FIG. 12 when the substrate thickness of the information medium is reduced. The horizontal axis of FIG. 12 represents the thickness of the information medium, and the vertical axis represents the numerical aperture. The information medium and the objective lens are 0.2 °.
This is a calculation of the point at which the deterioration of the central light intensity of the light spot 48 becomes equal when tilted. From the figure, the numerical aperture is 0.
It can be seen that the deterioration of the central light intensity is almost the same when the thickness of the information medium is 1.2 mm at 5 ° and when the numerical aperture is 0.62 and the thickness of the information medium is 0.6 mm. Therefore, when the numerical aperture is increased, the thickness of the information medium is reduced so that the coma generated by the inclination of the information medium is reduced.
Aberration can be suppressed as much as conventional. However, when the thickness of the information medium is reduced, the objective lens for recording / reproducing the information medium cannot record / reproduce the conventional information medium and cannot maintain compatibility with the conventional information medium. . Therefore, it is necessary to use two optical heads to record and reproduce a thin information medium and an information medium having a substrate thickness of 1.2 mm by separate optical heads.

[0005]

In such a conventional optical head, one optical head cannot record / reproduce information media having different thicknesses. Therefore, in order to increase the numerical aperture of the objective lens to achieve high density, there is a problem that compatibility with conventional information media must be sacrificed. In order to solve such a problem, the present invention provides two objective lens convergence points to accommodate two information media having different thicknesses, thereby achieving both conventional information media and thin information media for high density. In contrast, an optical head capable of recording and reproducing is provided.

[0006]

In order to solve the above problems, the present invention is directed to a light source and a collector for collecting a part of light emitted from the light source with an optical path length L1 and a part with an optical path length L2. An optical optics means, and an objective lens that converges the condensed light flux on an information medium,
A light detector for detecting reflected light from the information medium is used. As a method of forming the optical path length L1 and the optical path length L2, a light beam emitted from a light source and a light beam reflected by a polarization separation film are transmitted. Is provided with a separating means for separating the luminous flux into
The reflected light flux is condensed as an optical path length L1, and the transmitted light flux is reflected at least twice to be condensed as an optical path length L2.

Further, in order to change the numerical aperture of the luminous flux radiated according to the information medium, a light source, a light limiting means for limiting the emitted light of the light source, and a luminous flux for reflecting the limited luminous flux by the polarization separation film. Separation means for separating the transmitted light beam 2, a prism configured so that the light beam 2 is reflected at least twice and transmitted through the polarization separation film again, and has substantially the same optical path as the light beam 1, and the light beam 1 and the light beam 2 are condensed. For the condensing lens and the information medium having the thickness t1, the light flux 1 is converged and the thickness t2 is obtained.
For the information medium, the objective lens for converging the light flux 2 and a photodetector for detecting the reflected light from the information medium having the thickness t1 or t2 are configured.

Further, in order to solve the above-mentioned problems, a light source, a mirror for reflecting a part of the emitted light of the light source, a hologram for reflecting a part of the emitted light, and each reflected light are used as an information medium. It is composed of an objective lens that converges and a photodetector that detects reflected light from the information medium.

As still another method, a light source, a condenser lens for condensing the light emitted from the light source into a substantially parallel light beam, and the condensed light beam is separated into a light beam 1 reflected by a polarization separation film and a light beam 2 transmitted therethrough. Separating means, a hologram for allowing the light beam 2 to pass through the polarization separation film again and to be reflected so as to have a substantially same optical path as the light beam 1, and for an information medium having a thickness t1, the light beam 2 is converged and an information medium having a thickness t2. On the other hand, it is composed of an objective lens which converges the light flux 1 and a photodetector which detects the reflected light from the information medium having the thickness t1 or t2.

[0010]

As described above, two light spots can be formed by converging the divided light beams with different optical path lengths. By selecting and irradiating one of the light spots, recording and reproduction can be performed on information media having different substrate thicknesses (t1 and t2). Further, by reflecting one of the divided light fluxes by the mirror and the other by the hologram, two light spots can be similarly formed, and two types of information media having different thicknesses can be recorded and reproduced. By blazing the hologram, the light amount of the + 1st order diffracted light can be increased, and the light utilization efficiency can be increased.

Since the optical head of the present invention can be realized by adding one prism or hologram to the conventional optical head, it is possible to use two different types of information media with one optical head while maintaining a small size and low cost. It can be recorded and played back. Further, it is possible to cope with an optical disk device that requires a large numerical aperture and an optical disk device that has a numerical aperture as small as a CD, and it is possible to achieve high density without sacrificing compatibility.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. 1, 2 and 3. In FIG. 1, a light beam 2 emitted from a semiconductor laser is reflected by a half mirror 3 and enters a prism 4. A polarization separation film 5 is formed between the prisms 4 and 6, and the light incident on this polarization separation film 5 propagates.
The component whose surface is perpendicular to the incident surface (S-polarized light) is reflected, and the parallel component (P-polarized light) is transmitted. The light beam 2 is set so as to be incident on the incident surface of the polarization separation film 5 at a constant angle, and is separated into a light beam 2a reflected by the polarization separation film 5 and a light beam 2b transmitted therethrough. Light flux 2a reflected by the polarization separation film 5
Is condensed by the condenser lens 7 and becomes a non-parallel luminous flux. The light beam 2b that has passed through the polarization splitting film 5 is reflected by the reflecting surfaces 6a and 6b of the prism 6, passes through the polarization splitting film 5 again, and is condensed by the condenser lens 7 to become a substantially parallel light beam. The light beams 2a and 2b enter the objective lens 8, the non-parallel light beam 2a is narrowed down to a convergence point p1 to form a light spot 9a, and the substantially parallel light beam 2b is narrowed down to a convergence point p2 to form a light spot 9b. To do. The light spot 9a is for recording and reproducing the information medium 10a on the disc having the thickness t1.
The light spot 9b is for recording / reproducing information medium 10b having a thickness t2. 2 shows a state in which the light spot 9a is formed on the recording surface of the information medium 10a, and FIG. 3 shows a state in which the light spot 9b is formed on the recording surface of the information medium 10b. When recording / reproducing an information medium having a thickness of t1, the light spot 9a is formed on the recording surface of the information medium 10a. The S-polarized light beam 11a (FIGS. 1 and 2) reflected by the information medium 10a is the objective lens 8 and the condenser lens 7.
The light enters the prism 4 through the light and is reflected by the polarization separation film 5 to become a light beam 11. On the other hand, when recording / reproducing an information medium having a thickness t2, the light spot 9b is formed on the recording surface of the information medium 10b. The P-polarized light beam 11b (FIG. 3) reflected by the information medium 10b passes through the objective lens 8 and the condenser lens 7, enters the prism 4, and passes through the polarization separation film 5. Further, the light beam 11b is reflected by the reflecting surfaces 6b and 6a of the prism 6, passes through the polarization separation film 5 again, is emitted from the prism 4, and becomes the light beam 11 like the light beam 11a. A part of the light flux 11 has astigmatism by obliquely passing through the half mirror 3, and is converged on the photodetector 13 through the concave lens 12. The concave lens 12 is for making the focus sensitivity and the beam diameter of the light beam 11 converged on the photodetector 13 practical. The photodetector 13 is for detecting a reproduction signal as in the conventional example. Similarly to the conventional example, the photodetector 13 is configured to detect a reproduction signal, a focus control signal due to astigmatism, and a tracking control signal due to a push bull or phase difference method.

When the information medium 10a is recorded / reproduced by the light spot 9a, the light beam 2 converged by the objective lens 8 is used.
b is diffused on the recording surface of the information medium 10a, and when the information medium 10b is recorded / reproduced by the light spot 9b, the light beam 2a converged by the objective lens 8 is diffused on the recording medium surface of the information medium 9b. Therefore, they are not detected as signals.

Therefore, the convergence point p depends on the thickness of the information medium.
By switching between 1 and p2, it becomes possible to record / reproduce information media having different thicknesses. Specifically, the thickness is 1.2m
When recording / reproducing a CD, a video disc, a magneto-optical disc, or the like of m, the light spot 9a is used, and when recording / reproducing a thin information medium having a thickness of 0.6 mm,
The light spot 9b is used. As an example, when the focal length of the condenser lens 7 is 23.5 mm, the focal length of the objective lens 8 is 3.3 mm, and the difference in optical path length between the light beam 2a and the light beam 2b is about 10.6 mm, the convergence points p1 and p2 Difference of 0.4
It will be about mm. Under such optical conditions, the light can be narrowed down to the diffraction limit for both the information medium having a thickness of 0.6 mm and the information medium having a thickness of 1.2 mm.

Further, by providing the opening 14 as shown in FIG. 1, it is possible to provide a difference in numerical aperture between the light beam 2a and the light beam 2b which enter the objective lens 8. In the above example, assuming that the numerical aperture of the substantially parallel light beam 2b incident on the objective lens 8 is 0.6 and the distance between the objective lens 8 and the condenser lens 7 is 7 mm, the light beam 2a incident on the objective lens 8 is The numerical aperture is about 0.47, which is suitable for reproducing compact discs. Furthermore, by limiting the aperture 14 only in the track direction of the information medium, it is possible to reduce the numerical aperture of the light beam 2a in the track direction and not limit the movement of the objective lens 8 by the tracking control.

Another embodiment is shown in FIG. In FIG.
The same numbers as in FIG. 1 perform the same operation. In this embodiment, the light beam 2b that has passed through the polarization splitting film 5 is reflected by the reflecting surfaces 15a, 15b, 15c of the prism 15, passes through the polarization splitting film 5 again, and is collected by the condenser lens 7 into a substantially parallel light beam. Glow. This light beam 2b and the light beam 2a reflected by the polarization splitting film 5 and condensed non-parallel by the condenser lens 7 enter the objective lens 8, and the light beam 2a is narrowed down to the convergence point p1 to form a light spot 9a. The light beam 2b is focused on the convergence point p2 to form a light spot 9b. When recording and reproducing the information medium 10a having the thickness t1 as in the above embodiment, the light spot 9a is formed on the recording surface of the information medium 10a, and the thickness t2.
When recording / reproducing the information medium 10b of
By forming b on the recording surface of the information medium 10b, it is possible to record / reproduce information mediums having different thicknesses with one objective lens.

In another embodiment shown in FIGS. 5 to 9, the light beam 22 emitted from the semiconductor laser 21 is
The light is reflected by the half mirror 23 and enters the prism 24. The light beam 22 set so as to be incident on the incident surface of the polarization separation film 25 at a constant angle is separated into a light beam 22b reflected by the polarization separation film 25 and a light beam 22a that is transmitted therethrough, as shown in FIG. Light flux 2 reflected by the polarization separation film 25
2b is condensed by a condenser lens 27 so as to be a substantially parallel light beam. The light beam 22a that has passed through the polarization separation film 25 is reflected by the hologram 26 having a reflective film formed on its surface. The + 1st order diffracted light reflected by the hologram 26 receives the same action as the convex lens, and diffuses the light beam 22 as shown in FIG . This diffused light again passes through the polarization separation film 25 and is condensed by the condenser lens 27 so as to become a non-parallel light flux. These light beams 22a and 22b are converged by the objective lens 28, and the non-parallel light beam 22a is converged on the converging point p3 by the light spot 29.
a, a substantially parallel light beam 22b is projected onto the convergence point p4 at the light spot 2
9b is formed. The light spot 29a is for recording and reproducing the information medium 30a having the thickness t1.
b is for recording / reproducing information medium 30b having a thickness t2. As shown in FIG. 7, the hologram 26 may have a blazed cross section or a stepped shape to enhance the efficiency of the + 1st order diffracted light. Further, by limiting the reflection area of the hologram 26 as shown in FIG.
The numerical aperture of the light beam 22a incident on the objective lens 28 is set to the light beam 2
It can be set smaller than the numerical aperture of 2b. Therefore, the thickness t
The numerical aperture can be 0.45 or the like for an information medium such as a CD, and the numerical aperture can be 0.6 or the like for a thin and high-density information medium having a thickness t2. The light beam 22a that enters the area other than the reflection area of the hologram does not converge on the information medium by passing through the hologram. FIG. 8 shows a state in which the light spot 29a is formed on the recording surface of the information medium 30a, and FIG. 9 shows a state in which the light spot 29b is formed on the recording surface of the information medium 30b. When recording and reproducing the information medium having the thickness t1, the light spot 2
9a is formed on the recording surface of the information medium 30a. The p-polarized light beam 31a (FIGS. 5 and 8) reflected by the recording medium 30a passes through the objective lens 28 and the condenser lens 27 and then the prism 24.
Incident on. Further, after passing through the polarization splitting film 25 , it is reflected by the hologram 26 and again passes through the polarization splitting film 25 to form a light beam 31. On the other hand, when recording / reproducing an information medium having a thickness of t2, the light spot 29b is formed on the recording surface of the information medium 30b. The S-polarized light beam 31b (FIG. 9) reflected by the information medium 30b is the objective lens 28 and the condenser lens 2
The light enters the prism 24 through 7 and is reflected by the polarization separation film 25 to become a light beam 31 like the light beam 31a. The light flux 31 passes through the half mirror 23 and the concave lens 32, and the photodetector 33.
Converge to. With the configuration described above, by switching the converging points p3 and p4 according to the thickness of the information medium, it is possible to record / reproduce information media having different thicknesses with one objective lens.

Another embodiment is shown in FIG. In FIG. 10, those having the same numbers as those in FIG. 5 perform the same operation. In this embodiment, the light beam 22 condensed by the condenser lens 34 enters the polarization separation film 25. This is because even if the light flux 22 condensed in substantially parallel does not enter the mirror 35 obliquely, no astigmatism occurs, so that an inexpensive configuration can be achieved without using a prism. The light beam 22 has a polarization separation film 25.
The light beam 22b reflected by is separated into a light beam 22a which is transmitted. The light beam 22a is reflected by the hologram 36, diffused, and transmitted through the polarization separation film 25 again to become a non-parallel light beam 22b. At this time, the non-parallel +1 reflected by the hologram 36
Since the next-order diffracted light passes through the mirror 35, astigmatism occurs, but this aberration can be corrected by the hologram 36. Next, the light beams 22a and 22b are incident on the objective lens 28 and are converged on the convergence points p3 and p4, respectively, and the light spot 29 is generated.
a and 29b are formed. Then, the information medium 30a having the thickness t1 is recorded / reproduced by the light spot 29a, and the light spot 29b is recorded.
By recording / reproducing the information medium 30b having the thickness t2, it is possible to record / reproduce two types of information medium having different thicknesses with one objective lens.

[0019]

As is clear from the above description,
According to the present invention, the following effects can be obtained.

First, two light spots can be formed by condensing the divided light beams with different optical path lengths. By selecting one of the light spots and irradiating it on the information medium, information media having different thicknesses (t1 and t2) can be recorded and reproduced. Further, by reflecting one of the divided light beams by the hologram and diffusing the diffracted light, two light spots can be formed, and similarly, two types of information media having different thicknesses can be recorded and reproduced. By blazing the hologram +1
The amount of the second-order diffracted light can be increased, and an optical head with high light utilization efficiency can be realized by using the hologram.

The optical head of the present invention can be realized by adding a prism or a hologram to the conventional optical head, and it is an optical head having a small number of parts and low cost, but an information medium having different thickness can be formed by one optical head. It can be recorded and played back. Further, by limiting the aperture of the light beam incident on the prism or by limiting the reflection area of the hologram, the numerical aperture of the light beam converged on the information medium having the thickness t1 and the information medium having the thickness t2 can be changed.
The numerical aperture suitable for the information medium can be set. As a result, the numerical aperture is relatively low (0.45-0.52) and the thick C of the substrate
It is possible to record and reproduce data on both D and video discs and thin optical discs whose numerical aperture is increased to achieve high density. Therefore, the optical head of the present invention makes it possible to manufacture a high-density optical disk device compatible with conventional information media.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an optical head configuration of a first embodiment of the present invention.

FIG. 2 is an explanatory view showing a state in which the light flux of the first embodiment is converged on an information medium.

FIG. 3 is an explanatory view showing a state in which the light flux of the first embodiment is converged on an information medium.

FIG. 4 is a configuration diagram showing an optical head configuration of a second embodiment of the present invention.

FIG. 5 is a configuration diagram showing an optical head configuration of a third embodiment of the present invention.

FIG. 6 is a side view showing a hologram and a polarization splitting film of a third embodiment.

FIG. 7 is a partially enlarged side view showing a hologram cross section of a third embodiment.

FIG. 8 is an explanatory diagram showing a state in which the light flux of the third embodiment is converged on an information medium.

FIG. 9 is an explanatory diagram showing a state in which the light flux of the third embodiment is converged on an information medium.

FIG. 10 is a configuration diagram showing an optical head configuration of a fourth embodiment of the present invention.

FIG. 11 is a configuration diagram showing a configuration of a conventional optical head.

FIG. 12 is an explanatory diagram of optical disc thickness and imaging performance.

[Explanation of symbols]

 1 semiconductor laser 2 light flux 4 prism 5 polarization separation film 6 prism 7 condenser lens 8 objective lens 9a, 9b light spot 10a, 10b information medium 11a, 11b light flux 14 aperture 15 prism 25 polarization separation film 26 hologram 35 mirror 36 hologram

Claims (12)

(57) [Claims] 1. A semiconductor laser light source and light emitted from the semiconductor laser light source have different optical path lengths.
It splits into two light beams that go to the two optical paths that it has
One of the reflected light beams is made parallel light and the other light beam is made diffuse light.
Then, enter the objective lens so that the optical axes of the two light beams match.
Focusing hand that forms two image points, far and near, by shooting
And one of the imaging points depending on the thickness of the information medium used
Before focusing on the information recording surface of the information medium used
The control means for controlling the position of the objective lens and the reflected light from the information recording surface of the used information medium are detected.
And a control means for detecting when a thick information medium is used.
Note Of the two image points, the one farther from the objective lens is focused.
Control when thin information media are used.
Note Of the two image points, the one closer to the objective lens is focused
An optical head characterized by being controlled so that 2. A semiconductor laser light source and light emitted from the semiconductor laser light source are provided with different optical path lengths.
It splits into two light beams that go to the two optical paths that it has
One of the reflected light beams is made parallel light and the other light beam is made diffuse light.
Then, enter the objective lens so that the optical axes of the two light beams match.
Focusing hand that forms two image points, far and near, by shooting
Step and one of the imaging points depending on the thickness of the optical disc used
To focus on the information recording surface of the optical disc used
And a control means for controlling the position of the objective lens,
To detect the light reflected from the information recording surface of the optical disc
A thick optical disk is used as the control means.
From the objective lens of the above two image formation points
Control so that the far side is in focus and use a thin optical disc.
When used, the objective lens is one of the two image points
It is characterized by controlling so that the closer one is focused
An optical disk device equipped with an optical head. 3. The light-collecting means is one of the separated ones.
The other light separated by the light flux being reflected at least twice
Equipped with a prism configured to have the same optical path as the bundle
The optical head according to claim 1, wherein: 4. The condensing means comprises one of the separated ones.
The other light separated by the light flux being reflected at least twice
Equipped with a prism configured to have the same optical path as the bundle
The optical disk device according to claim 2, wherein: 5. The semiconductor laser light source as the condensing means.
And a pre-polarization separation film that separates the emitted light of the
4. The optical system according to claim 3, wherein the optical system is integrated with the optical system.
head. 6. The semiconductor laser light source as the condensing means.
And a pre-polarization separation film that separates the emitted light of the
5. The optical device according to claim 4, wherein the optical device is integrated with the optical system.
Disk device. 7. The semiconductor laser light source as the condensing means.
The polarized light separating film that reflects a part of the emitted light as parallel light and the part other than the part that reflects the emitted light as parallel light.
And a hologram that reflects as diffused light.
The optical head according to claim 1. 8. The condensing means is the semiconductor laser light source.
The polarized light separating film that reflects a part of the emitted light as parallel light and the part other than the part that reflects the emitted light as parallel light.
And a hologram that reflects as diffused light.
The optical disc device according to claim 2. 9. The hologram is a phase type diffraction element.
And its cross-sectional shape is a blazed shape.
The optical head according to claim 7. 10. The hologram is a phase type diffractive element.
Yes, and its cross-sectional shape is blazed
The optical disk device according to claim 8. 11. The hologram is a phase type diffraction element.
Contracts characterized by a stepped cross-section
The optical head according to claim 7. 12. The hologram is a phase type diffractive element.
Contracts characterized by a stepped cross-section
The optical disk device according to claim 8.