JPH11250485A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical pickup capable of surely holding interchangeability of two kinds of optical disks having respectively different substrate thickness without deteriorating recorded and reproduced signals. SOLUTION: The optical pickup device for reproducing an information signal by projecting luminous flux from a semiconductor laser and forming fine optical spots on two kinds of optical disks 52, 53 having respectively different substrate thickness through an objective lens 51 is provided with at least one polarized beam splitter 43. First and second reflectors 46, 49 are constituted so that exit beam from the laser is divided into a 1st beam to be transmitted through a polarized light separating film 44 in the splitter 43 and a 2nd beam to be reflected by the film 44 and the 2nd beam is transmitted through a 1st 1/4 wavelength plate 45, reflected by the 1st reflector 46, transmitted through the plate 45 again, transmitted through the film 44, transmitted through a 2nd 1/4 wavelength plate 47, reflected by the 2nd reflector 49, transmitted through the plate 47, and then reflected by the film 44 so as to be transmitted on the same optical path as the 1st beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical pickup device for writing / reading information signals to / from an optical disk as an information recording medium.

[0002]

2. Description of the Related Art FIG. 7 shows the configuration of an optical pickup device conventionally used in an optical information recording / reproducing apparatus of the type which detects information recorded on an optical disk as a change in reflectance. The optical pickup includes a laser diode 31, which is a light source, a collimator lens 33, a polarizing beam splitter 32, a quarter-wave plate 34, an objective lens 35, a condenser lens 37, and a photodiode 38, which is a photodetector.

[0003] A linearly-polarized diffused and emitted light beam emitted by a laser diode 31 passes through a collimator lens 33 to become a parallel light beam, passes through a polarizing beam splitter 32, and enters a quarter-wave plate 34. Thereafter, the light is converted into circularly polarized light by the quarter-wave plate 34, enters the objective lens 35, and is condensed on the optical disk 36 by the objective lens 35. afterwards,
This condensed light undergoes intensity modulation on the optical disc 36,
The light is reflected, passes through the objective lens 35 and the quarter-wave plate 34 again, becomes linearly polarized light, and is reflected at right angles by the polarization beam splitter 32. After that, the light passes through the condenser lens 37 and
The light enters a photodiode 38, which is a photodetector divided into six, and the information of the incident light is converted into an electric signal in the photodiode 38, and is converted into an information signal, a focus error signal, and a tracking error signal.

[0004]

In recent years, higher-density recording on an optical disk as a recording medium for a computer or a package medium for music, image information, and the like has been researched and developed. As one method for increasing the density of an optical disc, there is a technique (higher NA) in which the numerical aperture (NA) of an objective lens is made larger than that of a conventional one. However, when the numerical aperture (NA) of the objective lens is increased, coma aberration proportional to the product of the skew amount θ and the substrate thickness t of the optical disk increases.
Even if the numerical aperture (NA) is increased, a system in which the substrate thickness t of the optical disk is reduced to obtain a high-quality reproduction signal without narrowing the allowable range of the tilt of the optical disk with respect to the objective lens has been considered. For example, a compact disk uses a substrate having a thickness of 1.2 mm, while a DVD uses a substrate having a thickness of 0.6 mm.

In an optical pickup apparatus using a lens optimized for an optical disk having a thin substrate, when reproducing an existing optical disk, for example, a compact disk or a write-once optical disk, a difference in the thickness of the disk occurs. As a result, aberrations such as spherical aberration occur, and a problem arises in that a high-quality reproduced signal cannot be obtained. That is,
In the optical pickup device as shown in FIG. 7, it is difficult to read information from two types of optical disks having different thicknesses of disk substrates.

The present invention has been proposed in view of the above problems, and has as its object to provide an optical disk system that does not deteriorate recording and reproduction signals for optical disks having different substrate thicknesses.

[0007]

In order to achieve the above object, an optical pickup device according to claim 1 of the present invention comprises:
In an optical pickup device for forming a minute light spot on two types of optical disks having different thicknesses of disk substrates through an objective lens using a light beam from a semiconductor laser and reproducing an information signal, at least one polarization beam splitter is provided. Wherein the laser output light is divided into a first light flux passing through the polarization splitting film of the polarization beam splitter and a second light flux reflecting the polarization splitting film, and the second light flux is divided into a first quarter.
Transmitted through the wave plate, reflected by the first reflector,
After passing through the 1/4 wavelength plate and passing through the polarization splitting film of the polarization beam splitter, it passes through the second 1/4 wavelength plate, is reflected by the second reflection plate, and is again returned to the second 1/4 wavelength plate. A first reflection plate and a second reflection plate are configured to transmit through a four-wavelength plate, reflect the polarization splitting film of the polarization beam splitter, and have the same optical path as the first light flux.

Further, in the optical pickup device according to a second aspect of the present invention, the first light beam and the second light beam are separated by the polarization splitting film of the polarization beam splitter, and then the first light beam is split into the first light beam and the second light beam. Between the light flux and the second light flux, a light restricting means for restricting the aperture of the second light flux is provided.

The optical pickup device according to a third aspect of the present invention is characterized in that at least one of the first and second reflectors has a curved shape.

According to a fourth aspect of the present invention, in the optical pickup device, a quarter-wave plate and a reflector are joined or formed in this order on at least one pair of opposing surfaces of the polarizing beam splitter. Features.

Further, the optical pickup device according to claim 5 of the present invention irradiates a light beam from a semiconductor laser onto two types of optical disks having different thicknesses of disk substrates,
An optical pickup device for detecting the reflected light and reproducing the information recorded on the optical disk includes a polarizing beam splitter between the semiconductor laser and the optical path of the optical disk, and a first beam splitter on one side of the polarizing beam splitter. /
A four-wavelength plate and a first reflector, and a second 1 /
It is characterized by comprising a four-wave plate and a second reflector.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Three specific embodiments to which the present invention is applied will be described below with reference to the drawings.

(Embodiment 1) As shown in FIG. 1, an optical pickup device according to Embodiment 1 includes a laser diode 41 as a light source, a hologram 42, and a collimator lens 5.
6. Polarizing beam splitter 43, quarter-wave plate 45, reflector 46, quarter-wave plate 47, aperture 48 for limiting aperture, reflector 49, quarter-wave plate 50, objective lens 5.
1 and a light receiving element 54 composed of a photodiode and a phototransistor. The light splitting surface (polarization splitting film) 44 of the polarization beam splitter 43 has a characteristic of reflecting S-polarized light and transmitting P-polarized light. The reflection plate 49 is formed by depositing a total reflection film for totally reflecting the incident light beam on the concave surface of the plano-concave lens, and using the inside thereof. Further, in the present invention, the laser diode 41 is rotated around the optical axis, and adjustment is performed so that the laser output light beam includes both the S-polarized light beam perpendicular to the paper surface and the P-polarized light beam parallel to the paper surface. Do. In this embodiment, it is assumed that the objective lens 51 is optimally designed so that the amount of spherical aberration generated in the apparatus when the first optical disk 52 is used is substantially zero. Here, the first optical disk 52 has a smaller substrate thickness than the second optical disk 53.

The divergent emitted light beam from the laser diode 41 is converted into a substantially parallel light beam by a collimator lens 56,
The light enters the polarization beam splitter 43, and the P component light is transmitted and the S component light is reflected by the light splitting surface 44 formed in the direction of 45 degrees from the optical axis. The light beam transmitted at this time is referred to as a light beam 1 and the reflected light beam is referred to as a light beam 2, which will be described below. The light beam 1 transmitted through the light splitting surface 44 passes through a quarter-wave plate 50, is converted into circularly polarized light, and then passes through an objective lens 51.
A minute light spot is formed on the first optical disc 52,
Records, reproduces, and deletes information.

The reflected light of the minute light spot irradiated on the first optical disk 52 passes through the objective lens 51 and is divided into 1/4.
After passing through the wave plate 50, the vibration direction becomes S-polarized light perpendicular to the paper surface, is reflected at a right angle by the light splitting surface 44 of the polarizing beam splitter, passes through the 波長 wave plate 47 and the aperture 48, and then passes through the reflecting plate 49. Reflected and again the aperture 48, 1 /
The light passes through the four-wavelength plate 47. At this time, since the light beam 1 passes through the quarter-wave plate 47 twice, the vibration direction is P
It is polarized. Therefore, this light beam 1 is transmitted through the light splitting surface 44.
, Passes through the quarter-wave plate 45, is reflected by the reflection plate 46, and passes through the quarter-wave plate 45 again. At this time, since the light beam 1 passes through the quarter-wave plate 45 twice, the vibration direction is S-polarized light perpendicular to the paper surface. Thereafter, the light beam 1 is reflected by the light splitting surface 44, passes through the collimator lens 56, is diffracted by the hologram 42, and
It is led to. The light receiving element 54 is divided into four to six parts,
The information of the incident light is converted into an electric signal, and arithmetic processing of a sum signal and a difference signal is performed, thereby forming an information signal, a focus error signal, and a tracking error signal.

The light beam 2 reflected from the light dividing surface 44 is 1/4
The light passes through the wavelength plate 45, is reflected by the reflection plate 46, and is again 1 /
The light passes through the four-wavelength plate 45. At this time, since the light beam 2 passes through the 波長 wavelength plate 45 twice, the vibration direction is P
It is polarized. Thereafter, the light beam 2 passes through the light splitting surface 44, passes through the 波長 wavelength plate 47 and the aperture 48, is reflected by the reflection plate 49, and passes through the aperture 48 and the 波長 wavelength plate 47 again. At this time, the luminous flux 2 is applied to the 波長 wavelength plate 47.
Is transmitted twice, so that the vibration direction is S-polarized light perpendicular to the paper surface. Here, by providing an aperture 48 for restricting the aperture of the light beam 2, the second optical disk 53 is provided.
The numerical aperture of the light beam converging on the optical disk can be changed, and the numerical aperture suitable for the optical disk can be obtained. For example, in the case of a DVD having a substrate thickness of 0.6 mm, an objective lens having an NA of 0.6 and light of 650 nm are used. In order to correspond to a compact disk having a substrate thickness of 1.2 mm using this objective lens and light, it is necessary to set the NA to 0.38. Therefore, the size of the aperture is such that the luminous flux incident on the objective lens is 0.38 / 0.6 = 0.63 of the objective lens diameter.
It is decided to double. Further, in order to compensate for aberrations due to the difference in the substrate thickness of the optical disk, the convex shape of the reflector, that is, the concave shape of the plano-concave lens, is used to connect a minute light spot to the second optical disk 53 via the objective lens 51.
The optimal design for aberration compensation is performed. Further, since the s-polarized light beam is reflected by the above-described light splitting surface 44, the light beam 2 has the same optical path as the light beam 1 at this time. Thereafter, the light beam 2 becomes circularly polarized light by the quarter-wave plate 50, and forms a minute light spot on the second optical disk 53 via the objective lens 51, thereby recording, reproducing, and erasing information.

This reflected light passes through an objective lens 51 and
After passing through the 波長 wavelength plate 50, the vibration direction becomes P-polarized light parallel to the paper surface, passes through the light splitting surface 44 of the polarizing beam splitter, passes through the collimator lens 56, and is diffracted by the hologram 42 to the light receiving element 54. Be guided. The information of the light incident on the light receiving element 54 is converted into an electric signal,
An information signal, a focus error signal, and a tracking error signal are used.

As described above, the optical pickup device of the present invention can similarly form a minute optical spot on the first optical disk 52 and the second optical disk, and can record the compatibility of the optical disks. The reproduced signal can be reliably maintained without deterioration. Moreover, using a hologram,
By using the diffraction effect to form the laser diode 41 and the light receiving element 54 on the same stem, the size of the pickup can be reduced.

(Embodiment 2) Next, a quarter-wave plate 45, a reflection plate 46 and a quarter-wave plate 4
7, an example in which the aperture 48 and the reflection plate 49 are joined by, for example, pasting or the like will be described.

As shown in FIG. 2, the optical pickup device according to the second embodiment has a laser diode 4 as a light source.
1, a hologram 42, a collimator lens 56, a polarization beam splitter 43, a 波長 wavelength plate 45, a reflection plate 46,
It comprises a quarter-wave plate 47, an aperture 48 for limiting the aperture, a reflection plate 49, a quarter-wave plate 50, an objective lens 51, and a light-receiving element 54, and the polarization beam splitter 43 has a quarter-wave plate 45. , Reflector 46, 1/4 wavelength plate 4
7, the aperture 48 and the reflection plate 49 are joined or formed. The light splitting surface (polarization splitting film) 44 of the polarization beam splitter 43 has a characteristic of reflecting S-polarized light and transmitting P-polarized light. The reflection plate 49 is formed by depositing a total reflection film for totally reflecting the incident light beam on the concave surface of the plano-concave lens, and using the inside thereof. Further, in the present invention, by rotating the laser diode 41 about the optical axis of the emitted light beam, the laser emitted light beam is configured to include both the S-polarized light beam perpendicular to the paper surface and the P-polarized light beam parallel to the paper surface. . In this embodiment, it is assumed that the objective lens 51 is optimally designed so that the amount of spherical aberration generated in the apparatus when the first optical disk 52 is used is substantially zero. Here, the first optical disk 52 is the second optical disk 5
The thickness of the substrate is smaller than that of No. 3.

The divergent light beam emitted from the laser diode 41 is converted into a substantially parallel light beam by the collimator lens 56.
The light enters the polarization beam splitter 43, and the P component light is transmitted and the S component light is reflected by the light splitting surface 44 formed in the direction of 45 degrees from the optical axis. At this time, the transmitted light beam is referred to as a light beam 1, and the reflected light beam is referred to as a light beam 2. The light beam 1 transmitted through the light splitting surface 44 passes through the quarter-wave plate 50, is converted into circularly polarized light, and then forms a minute light spot on the first optical disk 52 via the objective lens 51; Records, reproduces, and deletes information.

The reflected light of the minute light spot applied to the first optical disc 52 passes through the objective lens 51, and
After passing through the wave plate 50, the vibration direction becomes S-polarized light perpendicular to the paper surface, is reflected at a right angle by the light splitting surface 44 of the polarizing beam splitter, passes through the 波長 wave plate 47 and the aperture 48, and then passes through the reflecting plate 49. Reflected and again the aperture 48, 1 /
The light passes through the four-wavelength plate 47. At this time, since the light beam 1 passes through the quarter-wave plate 47 twice, the vibration direction is P
It is polarized. Therefore, this light beam 1 is transmitted through the light splitting surface 44.
, Passes through the quarter-wave plate 45, is reflected by the reflection plate 46, and passes through the quarter-wave plate 45 again. At this time, since the light beam 1 passes through the quarter-wave plate 45 twice, the vibration direction is S-polarized light perpendicular to the paper surface. Thereafter, the light beam 1 is reflected by the light splitting surface 44, passes through the collimator lens 56, is diffracted by the hologram 42, and
It is led to. The light receiving element 54 is divided into four to six parts,
The information of the incident light is converted into an electric signal, and arithmetic processing of a sum signal and a difference signal is performed, thereby forming an information signal, a focus error signal, and a tracking error signal.

The light beam 2 reflected from the light splitting surface 44 is １ ／
The light passes through the wavelength plate 45, is reflected by the reflection plate 46, and is again 1 /
The light passes through the four-wavelength plate 45. At this time, since the light beam 2 passes through the 波長 wavelength plate 45 twice, the vibration direction is P
It is polarized. Thereafter, the light beam 2 passes through the light splitting surface 44, passes through the 波長 wavelength plate 47 and the aperture 48, is reflected by the reflection plate 49, and passes through the aperture 48 and the 波長 wavelength plate 47 again. At this time, the luminous flux 2 is applied to the 波長 wavelength plate 47.
Is transmitted twice, so that the vibration direction is S-polarized light perpendicular to the paper surface. Here, by providing an aperture 48 for restricting the aperture of the light beam 2, the second optical disk 53 is provided.
The numerical aperture of the light beam converging on the optical disk can be changed, and the numerical aperture suitable for the optical disk can be obtained. Further, in order to compensate for aberrations due to the difference in the substrate thickness of the optical disk, the convex shape of the reflector, that is, the concave shape of the plano-concave lens is changed so as to connect a minute light spot to the second optical disk 53 via the objective lens 51. The optimal design of compensation is performed. Further S
Since the polarized light beam is reflected by the above-described light dividing surface 44, the light beam 2 has the same optical path as the light beam 1 at this point. Thereafter, the light beam 2 is converted into circularly polarized light by the quarter-wave plate 50, and a minute light spot is formed on the second optical disk 53 via the objective lens 51 to record, reproduce, and erase information.

This reflected light passes through the objective lens 51 and
After passing through the 波長 wavelength plate 50, the vibration direction becomes P-polarized light parallel to the paper surface, passes through the light splitting surface 44 of the polarizing beam splitter, passes through the collimator lens 56, is diffracted by the hologram 42, and is transmitted to the light receiving element 54. Be guided. The information of the light incident on the light receiving element 54 is converted into an electric signal,
An information signal, a focus error signal, and a tracking error signal are used.

As described above, the optical pickup device of the present invention can similarly form a minute optical spot on the first optical disk 52 and the second optical disk, and can record the compatibility of the optical disks. The reproduced signal can be reliably maintained without deterioration. Moreover, using a hologram,
By using the diffraction effect to form the laser diode 41 and the light receiving element 54 on the same stem, the size of the pickup can be reduced.

(Embodiment 3) As shown in FIG. 3, an optical pickup device according to Embodiment 3 includes a laser diode 41 as a light source, a collimator lens 56, a half mirror 10
0, polarization beam splitter 43, quarter-wave plate 45, reflection plate 46, quarter-wave plate 47, aperture 48 for limiting aperture, reflection plate 49, quarter-wave plate 50, objective lens 5
1. It is composed of a condenser lens 57 and a light receiving element 54. The half mirror 100 transmits 90% of the light beam, and
It has a characteristic of reflecting 0%.

In this embodiment, the light splitting surface (polarization splitting film) 44 of the polarization beam splitter 43 has a characteristic of reflecting S-polarized light and transmitting P-polarized light. The reflection plate 49 is formed by depositing a total reflection film for totally reflecting the incident light beam on the concave surface of the plano-concave lens, and using the inside thereof. In the present invention, by rotating the laser diode 41 about the optical axis of the emitted light beam, the laser emitted light beam is converted into an S-polarized light beam perpendicular to the paper surface and a P-polarized light beam parallel to the paper surface.
The configuration includes both polarized light beams. In this embodiment, it is assumed that the objective lens 51 is optimally designed so that the amount of spherical aberration generated in the apparatus when the first optical disk 52 is used is substantially zero. Here, the first optical disk 52 is
The thickness of the substrate is smaller than that of the optical disk 53. The divergent emitted light beam from the laser diode 41 is
After being made into a substantially parallel light beam by the collimator lens 56, the light beam enters the beam splitter 100, and 90% of the light passes through the light splitting surface 101 formed in the direction of 45 degrees with respect to the optical axis, and then enters the polarization beam splitter 43. The P-component light is transmitted and the S-component light is reflected by the light splitting surface 44 formed in the direction of 45 degrees with respect to the optical axis. At this time, the transmitted light beam is referred to as a light beam 1, and the reflected light beam is referred to as a light beam 2.

The light beam 1 transmitted through the light splitting surface 44 is １ ／
After passing through the wave plate 50 and being converted into circularly polarized light, a minute light spot is formed on the first optical disk 52 via the objective lens 51, and information is recorded / reproduced / erased.

The reflected light of the minute light spot applied to the first optical disk 52 passes through the objective lens 51 and is reduced to 1/4.
After passing through the wave plate 50, the vibration direction becomes S-polarized light perpendicular to the paper surface, is reflected at a right angle by the light splitting surface 44 of the polarizing beam splitter, passes through the 波長 wave plate 47 and the aperture 48, and then passes through the reflecting plate 49. Reflected and again the aperture 48, 1 /
The light passes through the four-wavelength plate 47. At this time, since the light beam 1 passes through the quarter-wave plate 47 twice, the vibration direction is P
It is polarized. Therefore, this light beam 1 is transmitted through the light splitting surface 44.
, Passes through the quarter-wave plate 45, is reflected by the reflection plate 46, and passes through the quarter-wave plate 45 again. At this time, since the light beam 1 passes through the quarter-wave plate 45 twice, the vibration direction is S-polarized light perpendicular to the paper surface. Thereafter, the light beam 1 is reflected by the light splitting surface 44, and the light beam reflected by the half mirror 100 is guided to the light receiving element 54 via the condenser lens 57. The light receiving element 54 is divided into four to six parts. The information of the incident light is converted into an electric signal, and a calculation processing of a sum signal and a difference signal is performed to be an information signal, a focus error signal, and a tracking error signal.

The light beam 2 reflected from the light splitting surface 44 is １ ／
The light passes through the wavelength plate 45, is reflected by the reflection plate 46, and is again 1 /
The light passes through the four-wavelength plate 45. At this time, since the light beam 2 passes through the 波長 wavelength plate 45 twice, the vibration direction is P
It is polarized. Thereafter, the light beam 2 passes through the light splitting surface 44, passes through the 波長 wavelength plate 47 and the aperture 48, is reflected by the reflection plate 49, and passes through the aperture 48 and the 波長 wavelength plate 47 again. At this time, the luminous flux 2 is applied to the 波長 wavelength plate 47.
Is transmitted twice, so that the vibration direction is S-polarized light perpendicular to the paper surface. Here, by providing an aperture 48 for restricting the aperture of the light beam 2, the second optical disk 53 is provided.
The numerical aperture of the light beam converging on the optical disk can be changed, and the numerical aperture suitable for the optical disk can be obtained. In order to compensate for aberrations caused by differences in the substrate thickness of the optical disk, the convex shape of the reflector, that is, the concave shape of the plano-concave lens is optimized so as to connect a small light spot to the second optical disk 53 via the objective lens 51. Is becoming Further, since the s-polarized light beam is reflected by the above-described light splitting surface 44, the light beam 2 has the same optical path as the light beam 1 at this time. After that, the luminous flux 2 becomes 1/4
The light is converted into circularly polarized light by the wave plate 50, and a minute light spot is formed on the second optical disk 53 via the objective lens 51, thereby recording, reproducing, and erasing information.

This reflected light passes through the objective lens 51 and
After passing through the 波長 wavelength plate 50, the light beam becomes P-polarized light whose vibration direction is parallel to the paper surface, passes through the light splitting surface 44 of the polarizing beam splitter, and is reflected by the half mirror 100. Guided to 54. The information of the light incident on the light receiving element 54 is converted into an electric signal, and is converted into an information signal, a focus error signal, and a tracking error signal.

As described above, the optical pickup device of the present invention can form a minute light spot on the first optical disk 52 and the second optical disk 53 at the same time. The reproduced signal can be reliably maintained without deterioration. In addition, the optical pickup device having the configuration as in this embodiment can reduce the size of the components of the optical system and can be assembled in a small size, so that the space is reduced, which is advantageous for miniaturization of the device. Further, the number of parts is reduced, which is advantageous in terms of cost.

(Other Embodiments) In the embodiments shown in Embodiments 1 and 2, reflected light from two types of optical disks having different substrate thicknesses is received by one light receiving element.
As shown in (2), the + 1st order light and the -1st order light of the hologram 42 may be used, and the two light receiving elements 54 and 80 may receive the reflected light from the two types of optical disks.

In the first to third embodiments, the reflecting plate is formed by applying a reflecting film to the concave surface of the concave lens.
As shown in FIG. 5, one having a reflective surface formed on a convex surface can also be used. An aperture 48 for limiting the aperture is provided between the quarter-wave plate 47 and the reflection plate 49. The position of the aperture is between the polarization beam splitter 43 and the quarter-wave plate 47 and the polarization beam splitter. 43 and 1
It may be between the 波長 wavelength plate 45 or between the 波長 wavelength plate 45 and the reflection plate 46. As shown in FIG. 4, the reflector 49 has a convex mirror in the center and a concave mirror in the periphery to compensate for aberrations in the center and to obtain an aperture effect by kicking a light beam off the optical axis in the periphery. Can be. Further, in addition to providing the reflecting plate 49 with a curved surface shape for aberration compensation, the reflecting plate 46 may be formed with a curved surface shape for aberration compensation. Further, the light beam emitted from the laser diode 41 and incident on the polarization beam splitter 43 has a P-polarized
Although it is assumed that the light is linearly polarized light having both polarization components, when the emitted light of the laser diode is one of the linearly polarized light, a half-wave plate is provided between the laser diode 41 and the polarization beam splitter 43. Is arranged, and 1/2
The P-polarized light component and the S-polarized light component of the light beam that has passed through the wavelength plate may be set to desired values. Furthermore, although the objective lens and the polarizing beam splitter are shown separately, if the lens and the optical axis center are moved together with the objective lens using a cylindrical holder or the like and driven together by the same actuator, the deviation will occur. As a result, the compatibility of the optical disk can be maintained more reliably without deteriorating the recording and reproduction signals.

[0035]

According to the optical pickup device of the first aspect of the present invention, a light beam from a semiconductor laser is formed through an objective lens to form a minute light spot on two types of optical disks having different thicknesses of disk substrates. An optical pickup device for reproducing an information signal, comprising at least one polarization beam splitter, wherein the laser emission light is divided into a light flux 1 transmitting through the polarization splitting film of the polarization beam splitter and a light flux 2 reflecting the polarization splitting film, The second light beam is a first light beam.
After passing through the ４ wavelength plate, reflected by the first reflecting plate, again passing through the first ４ wavelength plate, and passing through the polarization splitting film of the polarizing beam splitter, the second 波長 wavelength The light passes through the plate, is reflected by the second reflector, passes through the second quarter-wave plate again, reflects the polarization splitting film of the polarization beam splitter, and has the same optical path as the first light flux. It constitutes a first reflector and a second reflector. According to this configuration, it is possible to form at least two types of light beams from the laser diode. As a result, the compatibility of the optical disk can be maintained without deterioration of the reproduction signal, and the reliability of the optical disk system can be greatly improved.

In the optical pickup device according to a second aspect of the present invention, the light beam 1 and the light beam 2 are separated by the polarization splitting film of the polarization beam splitter.
Between the light flux 1 and the light flux 2 being on the same optical path, a light restricting means for restricting the aperture of the light flux 2 is provided. Therefore, the NA for the light beam 2 in the objective lens can be set to a desired value, which is advantageous in maintaining the compatibility of the optical disk without deterioration of the reproduction signal.

According to a third aspect of the present invention, at least one of the reflection plates has a curved shape. According to this configuration, the radiation angle of the light beam reflected by the curved reflecting plate can be controlled by controlling the curvature, and the compatibility of the optical disk can be reliably maintained without deterioration of the reproduction signal.

In the optical pickup device according to a fourth aspect of the present invention, a quarter-wave plate and a reflector are joined or formed in this order on at least one pair of opposing surfaces of the polarizing beam splitter. According to such a configuration, at least two light beams having the same optical axis can be obtained, and compatibility of the optical disk can be maintained without deterioration of a reproduction signal.
The reliability of the optical disk system can be greatly improved.

In the optical pickup device according to a fifth aspect of the present invention, a light beam from a semiconductor laser is irradiated onto two types of optical disks having different thicknesses of disk substrates, and the reflected light is detected and recorded on the optical disk. An optical pickup device for reproducing the obtained information, comprising a polarizing beam splitter between the optical path of the semiconductor laser and the optical disk, and a first quarter-wave plate and a first reflecting plate on one side of the polarizing beam splitter. And a second quarter-wave plate and a second reflector on the other side. For this reason, compatibility between two types of optical disks having different substrate thicknesses can be maintained without deterioration of the reproduction signal.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating a configuration of an optical pickup device according to a first embodiment of the present invention.

FIG. 2 is a diagram schematically illustrating a configuration of an optical pickup device according to a second embodiment of the present invention.

FIG. 3 is a diagram schematically illustrating a configuration of an optical pickup device according to a third embodiment of the present invention.

FIG. 4 is a diagram schematically showing a configuration of another embodiment of the optical pickup device of the present invention.

FIG. 5 is a diagram showing a configuration of another embodiment of the reflector used in the optical pickup device of the present invention.

FIG. 6 is a diagram schematically showing the configuration of another embodiment of the optical pickup device of the present invention.

FIG. 7 is a diagram schematically showing a configuration of a conventional optical pickup device.

[Explanation of symbols]

 41 Laser Diode 42 Hologram 43 Polarizing Beam Splitter 44 Light Dividing Surface 45 Quarter Wave Plate 46 Reflector 47 Quarter Wave Plate 48 Aperture 49 Reflector 50 Quarter Wave Plate 51 Objective Lens 52 First Optical Disk 53 Second Optical disk 54 light receiving element 56 collimator lens

Continued on the front page (72) Inventor Takeshi Yamaguchi 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation

Claims (5)

[Claims] 1. An optical pickup device for forming a minute light spot on two types of optical disks having different thicknesses of disk substrates through an objective lens using a light beam from a semiconductor laser and reproducing an information signal. Laser beam splitting into a first light beam passing through the polarization splitting film of the polarizing beam splitter and a second light beam reflecting the polarization splitting film, and the second light beam is a first light beam. After passing through the quarter-wave plate, reflected by the first reflector, again passing through the first quarter-wave plate, and passing through the polarization splitting film of the polarizing beam splitter, the second quarter
Transmitted through the wave plate, reflected by the second reflector,
The first reflector and the second reflector are configured to transmit through the 1/4 wavelength plate, reflect the polarization splitting film of the polarization beam splitter, and have the same optical path as the first light flux. Optical pickup device. 2. The method according to claim 1, wherein the polarization beam splitter of the polarization beam splitter separates the first light flux and the second light flux from each other until the first light flux and the second light flux are converted into a first light flux and a second light flux. 2. The optical pickup device according to claim 1, further comprising a light restricting means for restricting an aperture of the two light beams. 3. The apparatus according to claim 1, wherein at least one of the first and second reflectors has a curved shape.
An optical pickup device according to item 1. 4. The optical pickup device according to claim 1, wherein a quarter-wave plate and a reflector are joined or formed in this order on at least one pair of opposing surfaces of the polarizing beam splitter. 5. An optical pickup device for irradiating a light beam from a semiconductor laser onto two types of optical disks having different thicknesses of a disk substrate to record / reproduce / erase the optical disk, wherein an optical path between the semiconductor laser and the optical disk is provided. A polarizing beam splitter, a first quarter-wave plate and a first reflector on one side of the polarizing beam splitter, and a second quarter-wave plate and a second reflector on the other side. An optical pickup device comprising a plate.