JPH10143908A - Optical pickup device - Google Patents

Abstract

(57) [Problem] In an optical pickup device using two types of light sources, even if the two types of light sources are housed in the same unit, the light emitting points of the respective light sources cannot be matched, and the light emission of each light source cannot be achieved. There is a problem that the point shift is reflected on the light receiving position of the photodetector. SOLUTION: When a first light source 2 and a second light source 3 are arranged side by side, a first beam splitter 4 for separating an optical path in which the first light source 2 and the photodetector 11 are arranged is provided from the first light source 2. A second beam splitter 6 for separating an optical path in which the second light source 3 and the photodetector 11 are arranged is constituted by a first filter surface 5 having wavelength selectivity of the light beam of
Is constituted by a second filter surface 7 having wavelength selectivity of the light beam from the second light source 3, and the first filter surface 5 and the second filter surface 7 are formed by the first light source 2 and the second light source 3. In order to correct the deviation of the light emitting points, they are arranged on the same optical path so as to be parallel to each other with an appropriate interval.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for reading signals from both a normal density recording medium and a high density recording medium having different recording densities, and more particularly, to a first light source for emitting light beams having different wavelengths from each other. And an optical pickup device in which the second light sources are arranged side by side.

[0002]

2. Description of the Related Art As an optical disk in which a signal is optically read using a light beam such as a laser beam,
CDs (Compact Disks) have become widespread, but in response to the need for even larger capacities, the same disk diameter as CDs has been used to ensure mechanical compatibility, and higher density recording has been achieved by using higher density recording than CDs. A standardized high-density disk (DVD) has been proposed for the purpose of illustration.

This high-density disk uses a short-wavelength semiconductor laser to read a recording signal by using an optical pickup device having a high-resolution optical system.
By the way, in order to make the optical pickup device compatible with signal reading of both a CD and a high-density disk, a laser diode for emitting a light beam having a wavelength suitable for a normal density recording medium and a light beam having a wavelength suitable for a high-density recording medium are usually used. Two types of light sources having different wavelengths of laser diodes that emit light are prepared, and the type of light source used is switched according to the recording density of the recording medium from which a signal is read, so that two types of recording densities different with a single optical pickup are used. There is a method of enabling a signal to be read from a recording medium.

In an optical pickup device using these two types of light sources, a signal can be read by a light beam of an appropriate wavelength even on a recording medium whose recording film has a wavelength dependency. It is possible to prevent a situation in which the recording signal cannot be read due to a significant decrease in the intensity level.

[0005]

However, in an optical pickup device using two types of light sources, two types of light sources, for example, in the case of a laser diode, two types of laser chips emitting different wavelengths are housed in the same unit. However, the light emitting points of the respective light sources cannot be matched. Therefore, the shift of the light emitting point of each light source is reflected on the light receiving position of the light beam from each light source in the light detector of the optical pickup device, and the light detector forms two light receiving area patterns corresponding to each light source. I needed to.

In the case where the shift of the light emitting point of each light source is very small, the light receiving position of the light beam from each light source in the photodetector is intentionally separated by an optical element, and the two light receiving positions corresponding to each light source are separated. It was necessary to prevent the area patterns from overlapping.

On the contrary, there is a method in which the light beam from each light source in the photodetector can be shared by a single light receiving area pattern. However, this method complicates the optical system, and furthermore, the light receiving area pattern is increased. It is necessary to devise the shape of this, and it is difficult to achieve it.

[0008]

SUMMARY OF THE INVENTION The present invention provides a first light source and a second light source which emit light beams having different wavelengths for reading signals between a normal density recording medium and a high density recording medium having different recording densities. In a configuration in which the first light source and the second light source are arranged side by side, a first beam splitter for separating an optical path in which the first light source and the photodetector are arranged is provided. A second beam splitter formed by a first filter surface having wavelength selectivity of a light beam from one light source, and for separating an optical path in which a second light source and a photodetector are arranged, a light beam from the second light source; And a second filter surface having wavelength selectivity, and the first filter surface and the second filter surface are separated from each other by a distance between light emitting points of the first light source and the second light source. Are arranged so as to be parallel to each other at an appropriate interval on the same optical path so as to correct the optical axis, and the optical axis at the time when both light beams from the first light source and the second light source are irradiated on the photodetector. Try to match.

[0009]

FIG. 1 is an arrangement diagram showing an optical system of an optical pickup device according to an embodiment of the present invention, in which main parts are enlarged and displayed. The optical pickup device shown in FIG.
It is configured to be able to read signals from a normal density recording disc of the D family and a high density recording disc such as a DVD (digital video disc).

In FIG. 1, reference numeral 1 designates a first laser chip 2 for emitting a laser beam having a wavelength suitable for a normal density recording disk, for example, 780 nm, in the same package, and a wavelength suitable for a high density recording disk, for example, 6
This is a semiconductor laser unit including a second laser chip 3 that emits a 35 nm laser beam.

Reference numeral 4 denotes a first beam splitter which is formed by providing a first filter surface 5 of a dichroic filter having wavelength selectivity of a laser beam emitted from the first laser chip 2 on a triangular prism. The surface 5 is a half mirror that reflects a half of the laser beam having the wavelength of the first laser chip 2 and transmits half of the laser beam. Reference numeral 6 denotes a second beam splitter which is configured by providing a triangular prism with a second filter surface 7 of a dichroic filter having wavelength selectivity of a laser beam emitted from the second laser chip 3, and the second filter surface 7 This is a half mirror that reflects half of the laser beam of the second laser chip 3 and transmits half of it.

Then, the first beam splitter 4
The laser beam reflected from the filter surface 5 from the first laser chip 2 and the second laser beam from the second beam splitter 6
The laser beam from the second laser chip 3 reflected by the filter surface 7 is converted into collimated light by the collimator lens 8, and after being reflected by the reflection mirror 9, the luminous flux incident on the objective lens 11 by the diaphragm 10 is restricted. Incident on the objective lens 11 and is converged on the signal surface of the disk D by the objective lens 11.

The laser beam modulated and reflected by the signal surface of the disk D returns to the objective lens 11,
0, the first through the reflection mirror 9 and the collimator lens 8
The light is returned to the beam splitter 4 and the second beam splitter 6. Then, the laser beam transmitted through the first filter surface 5 and the second filter surface 7 is received by the photodetector 12. In this case, the first filter surface 5 functions as a half mirror for the laser beam emitted from the first laser chip 2, while the second filter surface 7 functions as a mere transmission surface, while the second filter surface 7 functions as a half-mirror. The second filter surface 7 functions as a half mirror for the laser beam emitted from the laser chip 3, while the first filter surface 5 functions as a mere transmission surface.

Incidentally, the diameter of the light spot converged on the signal surface of the disc and the depth of focus are determined by the NA value of the objective lens 11 and the wavelength of the laser beam. Therefore, when a laser beam emitted from the first laser chip 2 is used, the NA value of the objective lens 11 determined by the diameter of the aperture 10 and the wavelength of the laser beam emitted from the first laser chip 2 Thus, the diameter of the light spot converged on the signal surface of the disc and the depth of focus are determined. Therefore, by appropriately setting the wavelength of the laser beam emitted from the first laser chip 2 and the diameter of the stop 10, the light spot for reading the recording signal of the disk can be changed to a light spot diameter suitable for a normal density recording disk. It can be the depth of focus.

On the other hand, when the laser beam emitted from the second laser chip 3 is used, the NA value of the objective lens 11 determined by the diameter of the stop 10 and the laser beam emitted from the second laser chip 3 The wavelength determines the diameter of the light spot converged on the signal surface of the disk and the depth of focus. Therefore, the second laser chip 3
By appropriately setting the wavelength of the laser beam emitted from the optical disk and the diameter of the stop 10, the light spot for reading the recording signal of the disk can be made to have a light spot diameter and a depth of focus suitable for a high-density recording disk.

Meanwhile, the first filter surface 5 and the second filter surface 7 are arranged on the same optical path so as to be parallel to each other, and the first laser chip 2 and the second laser chip 3 and the first filter surface shown in FIG. As shown in the enlarged view of the surface 5 and the second filter surface 7, the reflection position at which the laser beam from the first laser chip 2 is reflected on the first filter surface 5 and the reflection position from the second laser chip 3 on the second filter surface 7. The first beam splitter 4 and the second beam splitter 6 are so arranged that the distance L1 from the reflection position at which the laser beam is reflected is equal to the distance L0 at which the light emitting points of the first laser chip 2 and the second laser chip 3 are shifted from each other. Are disposed, that is, the distance between the first filter surface 5 and the second filter surface 7 is the first distance.
The laser chip 2 and the second laser chip 3 are set so as to correct a distance between the light emitting points of the laser chip 2 and the second laser chip 3. Therefore, the first laser chip 2 and the second laser chip 3
After being reflected by the first filter surface 5 and the second filter surface 7, respectively, the laser beams emitted from the laser beam travel on the same optical axis whose optical axes coincide with each other.

Therefore, the respective laser beams from the first laser chip 2 and the second laser chip 3 reach the photodetector 12 through the same optical axis.
Although only a single light receiving area pattern is formed on the photodetector 12, the light receiving area pattern can be used for each laser beam.

In the configuration shown in FIG. 1, the first laser chip 2 is disposed on the reflection surface side of the first filter surface 5 and the second laser chip 3 is disposed on the reflection surface side of the second filter surface 7. And the optical axes of the laser beams respectively emitted from the first laser chip 2 and the second laser chip 3 are aligned on the optical path toward the disk. Thus, the arrangement of each optical element can be adjusted optimally, the quality of each laser beam can be kept good, and the tracking control system in the objective lens driving mechanism (not shown) does not occur with each laser beam.

FIGS. 3 and 4 show examples in which the first beam splitter and the second beam splitter in the present invention adopt a configuration different from that of FIG. In FIG. 3, the first beam splitter and the second beam splitter are formed by a single parallel plate 13, and one surface of the parallel plate 13 has wavelength selectivity of a laser beam from the first laser chip 2. The first filter surface 14 of the half mirror is formed, and the second surface of the half mirror having the wavelength selectivity of the laser beam from the second laser chip 3 is formed on the other surface.

In such a configuration, the laser beam from the first laser chip 2 enters the optical path toward the disk due to the internal reflection of the parallel plate 13, while the laser beam from the second laser chip 3 passes through the parallel plate 13. Enters the optical path toward the disk due to the external reflection of the laser beam, and the optical axes of the laser beams coincide with each other on the optical path.

In the case of the configuration shown in FIG. 3, the laser beam reaches the photodetector 12 through the inclined parallel flat plate 13 and is affected by astigmatism. And the second beam splitter can be constituted by a single parallel plate optical element, the structure is simple, and the interval between the first filter surface 14 and the second filter surface 15 is determined by the thickness of the parallel plate 13. A reflection position on the first filter surface 14 where the laser beam from the first laser chip 2 is reflected, and a second laser chip 3 on the second filter surface 15.
It is easy to set the distance from the reflection position where the laser beam is reflected from the first laser chip 2 and the second laser chip 3 such that the distance between the light emitting points of the first laser chip 2 and the second laser chip 3 is shifted.

In FIG. 4, the first beam splitter and the second beam splitter are configured by fixing two triangular prisms 17, 18 with a parallel plate 16 interposed therebetween.
One of the joining surfaces of the triangular prism 17 and the parallel flat plate 16 is formed with a first filter surface 19 of a half mirror having wavelength selectivity of the laser beam from the first laser chip 2. A second filter surface 20 of a half mirror having wavelength selectivity of the laser beam from the second laser chip 3 is formed on one of the 16 bonding surfaces.

With this configuration, the cost of the optical components is higher than that of the configuration shown in FIG. 3, but the influence of astigmatism can be prevented, and each optical component constituting the first and second beam splitters can be prevented. Since the elements are integrally fixed, similarly to the configuration of FIG. 3, the first filter surface 19 and the second filter chip 19 are used to correct the distance between the light emitting points of the first laser chip 2 and the second laser chip 3 that are shifted from each other. The setting of the distance between the two filter surfaces 20 is easy.

[0024]

As described above, according to the present invention, the light beams emitted from the first light source and the second light source reach the photodetector with their optical axes coincident with each other. The first light source and the second light source can also be used as the light receiving area pattern to be used, the number of light receiving elements constituting the light receiving area pattern can be reduced, and the configuration of the photodetector itself is, of course, simple. The connection with the light receiving elements is easy, and the circuit for arithmetically processing the light receiving signal obtained from each light receiving element can be simplified.

Further, if the first filter surface and the second filter surface are formed on the same optical element, or if the first beam splitter and the second beam splitter are integrally fixed, the first filter surface and the second filter surface are formed. It is easy to set the interval between the two filter surfaces so as to correct the distance between the light emitting points of the first light source and the second light source that are shifted.

Further, since the respective light beams respectively emitted from the first light source and the second light source are made to coincide on the optical path of the light beam toward the recording medium, the arrangement of each optical element with respect to each light beam Can be adjusted optimally, and each light beam can maintain good quality.

[Brief description of the drawings]

FIG. 1 is an arrangement diagram showing an optical system of an optical pickup device according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a first laser chip 2 and a second laser chip 3 and a first filter surface 5 and a second filter surface 7 in FIG.

FIG. 3 is a diagram illustrating an example of a first beam splitter and a second beam splitter different from FIG.

FIG. 4 is a diagram illustrating an example of a first beam splitter and a second beam splitter different from those of FIGS. 1 and 3;

[Explanation of symbols]

 2 1st laser chip 3 2nd laser chip 4 1st beam splitter 5 1st filter surface 6 2nd beam splitter 7 2nd filter surface 12 photodetector 13 parallel plate 14, 19 1st filter surface 15, 20 2nd filter surface

Claims (4)

[Claims] A first light source and a second light source that emit light beams having different wavelengths from each other, and a light source to be used is switched to perform signal reading between a normal density recording medium and a high density recording medium having different recording densities. An optical pickup device, wherein the first light source and the second light source are arranged side by side, and the light beam modulated by a recording signal of a recording medium and the light beam from the first light source and the recording signal of the recording medium are modulated. A photodetector that receives the light beam from the second light source together is arranged in a different optical path from the first light source and the second light source, and an optical path in which the first light source and the photodetector are arranged is separated. And a second beam splitter for separating an optical path in which the second light source and the photodetector are arranged.
The beam splitter includes a first filter surface having wavelength selectivity of a light beam emitted from the first light source, and the second beam splitter includes the second filter.
Second wavelength selective light beam emitted from the light source
A first filter surface and the second filter surface are arranged on the same optical path so as to be parallel to each other, and the first light source and the second light source are displaced from each other by a distance shifted from each other. An optical pickup device, wherein a distance between the first filter surface and the second filter surface is set so as to correct the following. 2. The optical pickup device according to claim 1, wherein said first filter surface and said second filter surface are formed on the same optical element. 3. The optical pickup device according to claim 1, wherein said first beam splitter and said second beam splitter are integrally fixed. 4. The first light source and the second light source are arranged on a reflection surface side of the first filter surface, and the second light source is arranged on a reflection surface side of the second filter surface. 2. The optical pickup device according to claim 1, wherein the optical axes of the respective light beams respectively emitted from the light sources are matched on the optical path of the light beam toward the recording medium.