JPH10162403A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup device capable of performing stable photodetection even when an optical recording medium itself has birefringence. SOLUTION: In the optical pickup device 30 having a phase difference plate 33 for conversion of the polarization state of emitting light from a laser diode 31 and return light from an optical recording medium 32 and a polarization diffraction grating 10 for separating the return light from an optical axis from the laser diode 31 to the optical recording medium 32 and guiding it to a photodetector 35 by a difference between the emitting light and the return light in their polarization state, the phase difference plate 33 is disposed to be orientated in the radial direction of the optical recording medium 32, i.e., in the birefringent direction of the optical recording medium 32, and also a phase difference amt. of deviation from a 1/4 wavelength by an amt. equivalent to a birefringent amt. possessed by the optical recording medium 32 itself is used for the phase difference plate 33. The laser diode 31 is disposed with the polarizing direction of its emitting light at 45 deg. to the direction of the phase difference plate 33.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical pickup device for reproducing an optical recording medium. More specifically, the present invention relates to an optical system for separating outgoing light from a light source and return light from an optical recording medium.

[0002]

2. Description of the Related Art An optical pickup device for reproducing an optical recording medium such as a compact disk (CD) includes:
Polarization light that is configured so that the emitted light and the return light can be separated by passing the emitted light from the laser light source and the return light from the optical recording medium through a λ / 4 phase difference plate (1/4 wavelength plate). Pickup devices are known. For example, in the case where a polarizing beam splitter (polarizing optical element) and a λ / 4 retardation plate are arranged at an intermediate position in the optical path from the laser light source to the photodetector, the light emitted from the laser light source emits the polarizing beam splitter and the λ / After passing through the four phase difference plate, the recording surface of the optical recording medium is irradiated as a light spot, and the return light from the optical recording medium passes through the λ / 4 phase difference plate and the polarizing beam splitter again. . When the return light from the optical recording medium passes through the λ / 4 retardation plate, the return light is changed to a laser light having a polarization direction different from the polarization direction of the light emitted from the laser light source by 90 °. The light is guided to a photodetector installed in the camera. In some cases, a hologram element is disposed between the laser light source and the λ / 4 phase difference plate, and the hologram element guides return light from the optical recording medium to the photodetector.

FIGS. 7A and 7B schematically show an optical pickup device using a hologram element in any of these polarization system optical pickup devices, as a development view and a polarization state of light. The linearly polarized light emitted from the laser diode (laser light source) is converted into circularly polarized light by a λ / 4 phase difference plate, and the return light (circularly polarized light) from the optical recording medium is converted by the λ / 4 phase difference plate. It converts the linearly polarized light emitted from the laser light source into linearly polarized light having a polarization direction different from that of the laser light source by 90 °, and guides the light to a photodetector installed in a direction different from the laser light source. There is an advantage that the medium can be effectively irradiated, and return light from the optical recording medium can be guided to the photodetector with high efficiency.

[0004]

However, the above description is based on the assumption that the optical recording medium does not have birefringence and the amount of birefringence δ
Is 0, the effective light amount can be said to be 100%,
When the optical recording medium itself has birefringence, the birefringence also causes a change in the polarization state, so that there is a problem that the effective light amount is reduced. For example, FIG.
As shown in (C), when the optical recording medium itself has a birefringence amount δ equivalent to λ / 4 in a reciprocating manner, it becomes linearly polarized light when reflected by the optical recording medium. As a result, when the return light passes through the λ / 4 phase difference plate, it becomes circularly polarized light, and the effective light amount is reduced to 50%. Further, as shown in FIG. 7D, the optical recording medium reciprocates λ /
When the birefringence amount δ corresponds to 2, the return light is λ
When the light passes through the / 4 phase difference plate, the light is changed to linearly polarized light having the same polarization direction as the linearly polarized light emitted from the laser light source. As a result, it cannot be separated from the light emitted from the laser light source,
The effective amount of light reaching the photodetector is 0%.

[0005] The relationship between the birefringence amount δ of the optical recording medium and the detected light amount is expressed as a relationship indicated by “●” and a solid line LA in FIG. That is, when the amount of light detected by the photodetector when the amount of birefringence δ of the optical recording medium is 0, the amount of light detected decreases as the amount of birefringence δ of the optical recording medium increases. When the refraction amount δ is λ / 2, the detected light amount becomes 0. As described above, in the conventional optical pickup device, the birefringence δ of the optical recording medium is 0.28λ.
When the value exceeds, the detected light amount becomes 0.4 or less, and it becomes impossible to completely reproduce the optical recording medium.

[0006] In view of the above, an object of the present invention is to provide an optical pickup device capable of performing stable light detection even if the optical recording medium itself has birefringence. .

[0007]

According to the present invention, there is provided a phase difference plate for converting a polarization state of light emitted from a laser light source and return light from an optical recording medium, and comprising: A polarizing optical element that separates the return light from the optical axis toward the optical recording medium from the laser light source based on the polarization state of the return light and guides the return light to a photodetector; The phase difference plate is arranged so that the azimuth of the phase difference plate is oriented in the radial direction of the optical recording medium, and the phase difference amount deviates from １ ／ wavelength by an amount corresponding to the birefringence amount of the optical recording medium itself. Characterized in that the value is set to

In the present invention, first, when the base of the optical recording medium is manufactured by injection molding, the resin flows in the radial direction from the inner peripheral side, so that the optical recording medium has birefringence. Then, the birefringence has a radial birefringence. Therefore, the direction of the retardation plate is oriented in this direction, and the birefringence direction of the optical recording medium and the direction of the retardation plate are matched. The first feature is that the optical recording medium itself and the retardation plate are configured to function as one retardation plate in this manner. Next, the second characteristic point is that a retardation plate having a retardation amount shifted from a quarter wavelength by an amount corresponding to the birefringence amount of the optical recording medium itself is used. Have. Accordingly, since the phase difference plate and the optical recording medium themselves function as a λ / 4 phase difference plate, the light emitted from the laser light source is emitted even if the optical recording medium has birefringence. After the return light has passed through the retardation plate,
The light is changed to linearly polarized light having a polarization direction different from that of the linearly polarized light emitted from the laser light source by 90 °. Therefore, even if the optical recording medium has birefringence, the return light having a high effective light amount reaches the photodetector, so that the photodetector performs stable light detection.

According to the present invention, when the polarization state is converted by the birefringence of the optical recording medium itself and the phase difference plate, the laser light source is switched between linearly polarized light and circularly polarized light. And the azimuth of the phase difference plate makes an angle of 45 °. When the polarization direction of the light emitted from the laser light source and the direction of the phase difference plate form an angle of 45 °, for example, the laser light source is rotated by a predetermined angle around the emission optical axis. Let it be. Further, a half-wave plate through which the emitted light passes may be arranged in a predetermined direction with respect to the emitted light from the laser light source.

In the present invention, it is preferable that the laser light source, the polarization optical element, and the photodetector are integrated as an optical unit.

[0011]

Embodiments of the present invention will be described with reference to the drawings.

First Embodiment (Overall Configuration) FIG. 1 shows an example of an optical system of an optical pickup device to which the present invention is applied. In the optical system of the optical pickup device 30 shown in FIG.
1 (laser light source) to the recording surface 32a of the optical recording medium 32, a mirror 38, a polarizing diffraction grating 10 (a hologram element / a polarizing optical element having a birefringent diffraction grating structure) ), The phase difference plate 33 and the objective lens 34 are arranged in this order. The laser diode 31 is integrally formed on the same substrate as the photodetector 35, for example.

The polarizing diffraction grating 10 is a composite diffraction grating in which a first diffraction grating 11 is formed on one surface and a second diffraction grating 21 is formed on the other surface. This polarizing diffraction grating 10 is such that the first diffraction grating 11 is
3, and the second diffraction grating 21 faces the side of the laser diode 31. Here, the first
Diffraction grating 11 diffracts only ordinary light and passes extraordinary light as it is. Conversely, the second diffraction grating 21 diffracts only the extraordinary light and passes the ordinary light as it is. The grating patterns formed on these diffraction gratings 11 and 21 are shown in FIG.
And (C) are orthogonal.

As such a polarizing diffraction grating 10,
For example, a structure in which a first diffraction grating 11 is formed on the front surface of a lithium niobate crystal plate 2 which is a birefringent crystal substrate, and a second diffraction grating 21 is formed on the back surface can be used. In the first diffraction grating 11, FIG.
As shown in (1), on the surface of a lithium niobate crystal plate which is a birefringent crystal plate, proton ion exchange regions 3 are formed in a lattice shape with a constant width and depth. A non-proton ion exchange region 4 where proton exchange has not been performed remains between the adjacent proton ion exchange regions 3. A dielectric film having a constant thickness, for example, a SiO ₂ film is formed on the surface of the non-proton ion exchange region 4, and the surface of the proton ion exchange region 3 is exposed as it is. In the example shown here, a proton ion exchange region 3 is formed on the surface of a lithium niobate crystal plate as an x-plate in the z-axis direction.
And the non-proton ion exchange regions 4 are formed alternately (periodically). In the proton ion exchange region 3 of the crystal plate, the refractive index ne for extraordinary light increases by about 0.11 with respect to the non-proton ion exchange region 4, and conversely, the refractive index no for ordinary light decreases by about 0.04.

Here, in order to prevent the extraordinary light from being diffracted, a dielectric film having a predetermined thickness is formed on the surface of the non-proton ion exchange region 4, and the extraordinary light is transmitted to the proton ion exchange region 3. And the phase difference generated when passing through the non-proton ion exchange region 4 is canceled out. The phase of the ordinary light advances when passing through the proton ion exchange region 3. However, the non-proton ion exchange region 4
, The phase is relatively delayed, and the phase is further delayed by the dielectric film formed on the surface.
Therefore, when ordinary light passes through the polarizing diffraction grating 1, a phase difference is generated and the ordinary light is subjected to a diffraction effect. That is, when linearly polarized light is incident on the polarizing diffraction grating 1, the ordinary light component whose polarization direction is in the y-axis direction is converted into the proton ion exchange region 3 and the non-proton ion exchange region 4 in which the dielectric film 5 is formed on the surface. Since a phase difference occurs when passing through each of them, the light is diffracted in a direction orthogonal to the grating. On the other hand, the extraordinary light component whose polarization direction is the z-axis direction has the same phase change when passing through each of the regions 3 and 4, so that the extraordinary light component passes straight without undergoing the diffraction effect. .

As shown in FIG. 1C, the second diffraction grating 21 has a proton ion-exchange region 23 formed at a predetermined width and a predetermined depth on the back surface of a lithium niobate (LiNbO ₃ ) crystal plate at regular intervals. And a dielectric film having a constant thickness is formed only on the surface of the proton ion exchange region 23. The extraordinary light is reflected by the second diffraction grating 21
When incident on the surface, when passing through the proton ion exchange region 23 having a dielectric film formed on the surface, both of these portions (the proton ion exchange region 23 and the dielectric Phase lag occurs due to the presence of the body membrane). Therefore, the extraordinary light is diffracted by a diffraction effect. On the other hand, in the case of ordinary light incidence, the phase slightly advances when passing through the proton ion exchange region 23 as compared with when passing through other regions. However, when passing through the dielectric film formed on the surface, the phase is delayed. In the present example, by adjusting the depth of the proton ion exchange region 23 and the thickness of the dielectric film, there is no phase difference when passing ordinary light through any part. Therefore, ordinary light is not affected by diffraction,
The light goes straight on the diffraction grating 21 as it is.

(Structure of Retardation Plate) Referring again to FIG. 1A, when an optical recording medium 32 used in the optical pickup 30 having such a structure is manufactured by injection molding of a base, resin is applied from the inner peripheral side. It flows in the radial direction. Therefore, if the optical recording medium 32 has birefringence, it has birefringence in the radial direction. Therefore, in the present embodiment, the direction of the phase difference plate 33 is oriented in this direction, and the direction of the birefringence of the optical recording medium 32 and the direction of the phase difference plate 33 are matched. That is, in the present embodiment, as shown in FIG. 2A, the azimuth (indicated by arrow D) of the phase difference plate 33 is oriented in the radial direction of the optical recording medium 32 (indicated by arrow C), and optical recording is performed. By matching the birefringence direction of the medium 32 with the azimuth of the phase difference plate 33, the optical recording medium 32 itself and the phase difference plate 33 function as one phase difference plate.

Here, the optical recording medium 32 itself and the retarder 3
In order to reliably switch between linearly-polarized light and circularly-polarized light when 3 functions as a phase difference plate, the orientation of the phase difference plate 33 and the polarization orientation of the light emitted from the laser diode 31 are required. Must form an angle of 45 °. Therefore, in the present embodiment, as shown schematically in FIG.
1 is shifted by 45 ° with respect to the radial direction of the optical recording medium 32 (the direction of the phase difference plate 33), and the direction of the phase difference plate 33 and the polarization direction of the light emitted from the laser diode 31 (arrow E). Are shown) at an angle of 45 °. FIG. 2 (C) shows this portion in a direction perpendicular to the emission optical axis F of the laser diode 31 (FIG. 2 (B)).
(Direction from arrow A1 shown in FIG. 1) schematically shows the structure.

In the present embodiment, the phase difference amount of the phase difference plate 33 which is conventionally formed as a λ / 4 phase difference plate corresponds to the birefringence amount of the optical recording medium 32 itself. The phase difference amount is shifted from / 4 wavelength.

In other words, in the present embodiment, the following calculation results are based on the assumption that the optical recording medium 32 has a birefringence of 100 nm ± 20 nm in a reciprocating manner and the wavelength of the laser beam used is 650 nm. 100λ / 640 (reciprocating) = 50λ / 640 (one side) The phase difference plate 3 having a phase difference amount of 0.173λ based on the phase difference amount of the phase difference plate 33 = λ / 4−50λ / 640 = 0.173λ.
3 is used.

The optical recording medium 32 has a reciprocating distance of 100 nm.
When the wavelength of the laser beam used is 780 nm when the birefringence amount is ± 20 nm, the following calculation result: The birefringence amount of the optical recording medium 32 = 100λ / 780 (round trip) = 50λ / 780 ( One side) The phase difference plate 33 having a phase difference amount of 0.186λ based on the phase difference amount of the phase difference plate 33 = λ / 4−100λ / 780 = 0.186λ.
Will be used.

(Operation) In the optical pickup 30 having this configuration, the polarization direction of the laser light from the laser diode 31 is set so that it becomes ordinary light for each of the diffraction gratings 11 and 21 of the polarizing diffraction grating 10. Therefore, the emitted laser light passes through the second diffraction grating 21 as it is and passes through the first diffraction grating 11 on the opposite surface.
Due to the diffraction effect, the light is split into, for example, three beams. The three beams pass through the phase difference plate 33 and are irradiated onto the recording surface 32a of the recording medium by the objective lens 34 in a state where the linearly polarized light is switched to the elliptically polarized light. However, the elliptically polarized light is switched to circularly polarized light due to the birefringence of the optical recording medium 32 itself, and is condensed as a light spot on the recording surface 32a. The reflected light from the recording surface 32a changes its polarization state due to the birefringence of the optical recording medium 32 itself, passes through the objective lens 34 in an elliptically polarized light state, and then passes through the phase difference plate 33 again. Only then does the return light return to linearly polarized light. The return light that has passed through the phase difference plate 33 is
The polarization direction is a direction orthogonal to the polarization direction of the laser light on the emission side. Therefore, the return light from the recording medium 32 is
As extraordinary light, it reenters the polarizing diffraction grating 10.
As a result, the light passes through the first diffraction grating 11 as it is, but is diffracted by the diffraction effect when passing through the second diffraction grating 21. In this case, the direction of the grating is the first diffraction grating 1
Since the direction is orthogonal to 1, the light is diffracted into, for example, positive and negative first-order lights in a direction orthogonal to the diffraction direction of the three beams. Therefore, the diffracted light is transmitted to the laser diode 31
Is focused on the light receiving surfaces 35a and 35b of the photodetector 35 located at positions deviated in the diffraction direction of the second diffraction grating 21 with respect to the light.

(Effect of this embodiment) As described above, in this embodiment,
The azimuth of the phase difference plate 33 is aligned with the birefringence direction of the optical recording medium 32 so that the phase difference plate 33 and the optical recording medium 32 themselves function as one phase difference plate. The phase difference amount of 0.173λ whose phase difference amount deviates from １ ／ wavelength by an amount corresponding to a birefringence amount of 100 nm ± 20 nm (a birefringence amount of 0.154λ with respect to a laser beam having a wavelength of 650 nm). With the use of the retardation plate 33, the retardation plate 33 and the optical recording medium 32 themselves are configured to function as one λ / 4 retardation plate. Accordingly, the relationship between the amount of birefringence δ of the optical recording medium 32 and the detected light amount is represented by “」 ”and the solid line LB in FIG. If it has, the detected light amount is peak (detected light amount is 1)
Becomes That is, since the optical recording medium is configured to allow for the amount of birefringence δ, even if the optical recording medium 32 has birefringence, the return light having a high effective light amount can be detected by the photodetector 3.
5 arrives. In addition, as shown by “▲” and the solid line LB in FIG. 8, even when the optical recording medium 32 does not have birefringence (when the birefringence amount is 0), the detected light amount is 0.8, which is the effective light amount. Optical recording medium 32 such as a high return light reaching photodetector 35
Even if the amount of birefringence in the reciprocation varies within the range of 0λ to 0.42λ, the amount of light detected by the photodetector 35 is 0.4 or more, and the photodetector 35 performs stable light detection.

[Second Embodiment] The basic configuration of the present embodiment is the same as that of the first embodiment, and therefore, portions having common functions are denoted by the same reference numerals and description thereof will be omitted. In the present embodiment, when the polarization direction of the light emitted from the laser diode and the direction of the phase difference plate make an angle of 45 °, the laser diode 31 is rotated in a predetermined angular direction about the emission optical axis. Let me do it. That is, also in this embodiment, as shown in FIG. 3A, the radial direction of the optical recording medium 32 (the birefringence direction of the optical recording medium 32 / arrow C).
Indicated by ), The azimuth (indicated by an arrow D) of the phase difference plate 33 is oriented so that the optical recording medium 32 itself and the phase difference plate 33 act as one phase difference plate. Further, as schematically shown in FIG. 3B, the emission optical axis (indicated by an arrow F) of the laser diode 31 in a plan view is set in the radial direction of the optical recording medium 32 (the direction of the phase difference plate 33). When viewed from an extension of the optical axis of the laser diode 31 (direction from the arrow A2), FIG.
As schematically shown in (C), the laser diode 31 itself is rotated by 45 ° about the emission optical axis.

In this embodiment and in any of the embodiments described below, the retardation plate 33 has a position corresponding to the amount of birefringence of the optical recording medium 32 itself as described in the first embodiment. The phase difference amount is shifted from the quarter wavelength.

Even in the case of such a configuration, the phase difference plate 3
Since the azimuth 3 and the polarization azimuth of the light emitted from the laser diode 31 are at an angle of 45 °, the light emitted from the laser diode 31 is in one position by the optical recording medium 32 itself and the phase difference plate 33. The same effects as in the first embodiment are obtained, such as switching between linearly polarized light and circularly polarized light when acting as a phase difference plate.

Third Embodiment In each of the first and second embodiments, the polarization direction of the light emitted from the laser diode 31 and the direction of the phase difference plate 33 are 45 ° due to the mechanical arrangement of the laser diode 31. However, the polarization direction of the light emitted from the laser diode 33 may be optically rotated to satisfy the above condition.

Also in this embodiment, as shown in FIG. 4A, the azimuth (arrow D) of the phase difference plate 33 in the radial direction of the optical recording medium 32 (birefringence direction of the optical recording medium 32 / indicated by arrow C). ), And the optical recording medium 32 itself and the retardation plate 33 act as one retardation plate.
Further, as schematically shown in FIG. 4B, the emission optical axis (indicated by an arrow F) of the laser diode 31 is set to the optical recording medium 3.
2 in the radial direction (direction of the phase difference plate 33) in a plane,
FIG. 4 shows the structure when this part is viewed from the extension of the optical axis of the laser diode 31 (in the direction of arrow A3).
As schematically shown in (C), mechanically, the polarization direction (indicated by an arrow E) of the light emitted from the laser diode 31 and the direction of the phase difference plate 33 form an angle of 90 °. Looks like However, in the present embodiment, a half-wave plate 39 is arranged between the polarizing diffraction grating 10 and the retardation plate 33, and as shown in FIG. The direction (indicated by an arrow G) is inclined by 22.5 ° with respect to the polarization direction of the light emitted from the laser diode 31. That is, when the angle between the polarization direction of the light emitted from the laser diode 31 and the direction of the phase difference plate 33 is α °, only β ° obtained by the following equation β = (α−45) / 2 is used. , The half-wave plate 39 is inclined with respect to the optical axis of light emitted from the laser diode 31.

In such a configuration, when the light emitted from the laser diode 31 passes through the half-wave plate 39, the polarization direction is inclined by 45 °. Therefore, the emitted light from the laser diode 31 becomes return light while changing the polarization state between the linearly polarized light and the circularly polarized light with high efficiency, and is separated toward the photodetector 35.

[Modification of Third Embodiment] Also in this embodiment, as shown in FIG. 5A, in the radial direction of the optical recording medium 32 (indicated by the birefringence direction of the optical recording medium 32 / arrow C). The azimuth (indicated by arrow D) of the phase difference plate 33 is oriented. Also, as schematically shown in FIG. 5B, the emission optical axis (indicated by an arrow F) of the laser diode 31 in a plan view corresponds to the radial direction of the optical recording medium 32 (the direction of the phase difference plate 33). FIG. 5 is a vertical view and FIG. 5 shows the portion as viewed from an extension of the optical axis of the laser diode 31 (in the direction of arrow A4).
As schematically shown in (C), mechanically, the polarization direction of the light emitted from the laser diode 31 (indicated by an arrow E).
And the azimuth of the phase difference plate 33 appear to be parallel. However, also in the present embodiment, the half-wave plate 39 is arranged between the polarizing diffraction grating 10 and the retardation plate 33, and
As shown in (A), the azimuth of the half-wave plate 39 (indicated by an arrow G) is -22.5 with respect to the polarization azimuth of the light emitted from the laser diode 31 (the azimuth of the phase difference plate 33). °
It is tilted by a minute. That is, in the above equation, α is set to 0 °.

Even in such a configuration, when the light emitted from the laser diode 31 passes through the half-wave plate 39, the polarization direction is inclined by 45 °. Therefore, the emitted light from the laser diode 31 becomes return light while changing the polarization state between the linearly polarized light and the circularly polarized light with high efficiency, and is separated toward the photodetector 35.

[Other Embodiments] In each of the first to third embodiments, the hologram element (polarizing diffraction grating 10) having a birefringent diffraction grating structure is used. An optical pickup device of a type that guides the return light from the optical recording medium 32 to the photodetector 35 by passing the output light from the diode 31 and the return light from the optical recording medium 32 through the phase difference plate 33 The present invention can also be applied to the above type. For example, light of a type in which light emitted from a laser diode 31 and light returned from an optical recording medium 32 pass through a phase difference plate 33 and light returned from the optical recording medium 32 is guided to a photodetector 35 by a polarizing beam splitter. The present invention can be applied to a pickup device.

For example, as shown in FIG. 6A, the polarization beam splitter 41 (polarization optical element) and the light emitted from the laser diode 31 are diffracted from the laser diode 31 toward the optical recording medium 25. Optical recording medium 32
A non-diffracting hologram element 42, a phase difference plate 33, and an objective lens 34 are arranged in this order for return light from the optical recording medium 32, and return light from the optical recording medium 32 is used as a polarization beam splitter 41.
Accordingly, the present invention can be applied to a five-beam optical pickup device configured to condense the photodetector 35 installed in a direction different from that of the laser diode 31. In such an optical pickup device as well, the retardation plate 33
Are arranged so that the azimuth of the phase difference plate is oriented in the radial direction of the optical recording medium 32, and the phase difference amount is reduced from １ ／ wavelength by an amount corresponding to the birefringence amount of the optical recording medium 32 itself. Set to a shifted value. Also in this case, when the polarization direction of the light emitted from the laser diode 31 and the direction of the phase difference plate 33 form an angle of 45 °, as described in the first and second embodiments, Although the above condition may be satisfied by the mechanical arrangement structure of FIG. 31, as described in the third embodiment,
The half-wave plate 39 indicated by the dotted line may be arranged in a predetermined direction so as to satisfy the above conditions.

The polarization optical element for guiding the return light from the optical recording medium 32 to the photodetector 35 is shown in FIG.
As shown in FIGS. 6B and 6C, a polarizing optical element 50 having a rectangular cross section or a trapezoidal cross section can be used, but if the optical system shown in FIG.
As shown in (D), if the laser diode 31, the polarization beam splitter 41, and the photodetector 35 are integrally mounted on the substrate 44 as the optical unit 40, the productivity of the optical pickup device can be increased. .

[0035]

As described above, in the optical pickup device according to the present invention, the azimuth of the phase difference plate is oriented in the radial direction of the optical recording medium (the birefringence direction of the optical recording medium), and the optical recording medium itself is oriented. The phase difference plate is configured to act as one phase difference plate, and the phase difference amount of the phase difference plate is set to 1 by an amount corresponding to the birefringence amount of the optical recording medium itself.
It is characterized in that the value is shifted from / 4 wavelength.
Therefore, according to the present invention, since the retardation plate and the optical recording medium themselves function as one λ / 4 retardation plate,
Even if the optical recording medium has birefringence, return light reaches the photodetector with a high effective light amount. Therefore, the light detector performs stable light detection.

[Brief description of the drawings]

FIG. 1A is a configuration diagram of an optical system used in an optical pickup device, and FIGS. 1B and 1C are a first diffraction grating and a second diffraction grating configured as a polarizing diffraction grating, respectively. FIG.

FIG. 2A is a schematic plan view showing an arrangement relationship of a phase difference plate with respect to an optical recording medium in an optical pickup device according to Embodiment 1 of the present invention, and FIG. Schematic plan view showing the arrangement relationship of diodes,
(C) is a schematic arrow view when viewed from the direction indicated by the arrow A1 in (B).

FIG. 3A is a schematic plan view showing an arrangement relationship of a phase difference plate with respect to an optical recording medium in an optical pickup device according to a second embodiment of the present invention, and FIG. Schematic plan view showing the arrangement relationship of diodes,
(C) is a schematic arrow view when viewed from the direction indicated by arrow A2 in (B).

FIG. 4A is a schematic plan view showing an arrangement relationship of a phase difference plate with respect to an optical recording medium in an optical pickup device according to Embodiment 3 of the present invention, and FIG. Schematic plan view showing the arrangement relationship of diodes,
(C) is a schematic arrow view when viewed from the direction indicated by arrow A3 in (B).

FIG. 5A is a schematic plan view showing an arrangement relationship of a phase difference plate with respect to an optical recording medium in an optical pickup device according to Embodiment 4 of the present invention, and FIG. Schematic plan view showing the arrangement relationship of diodes,
(C) is a schematic arrow view when viewed from the direction indicated by arrow A4 in (B).

FIG. 6A is a configuration diagram of an optical pickup device using a polarization beam splitter as a polarization optical element, and FIG.
(C) is an explanatory view showing the shape of another polarizing optical element, and (D) is an explanatory view of an optical unit integrating a laser diode, a polarizing optical element, and a photodetector.

7A is a development view of an optical system configured in an optical pickup device using a hologram element, and FIGS. 7B to 7D are respectively a reciprocating birefringence amount and light polarization of an optical recording medium itself. It is explanatory drawing which shows a state typically.

FIG. 8 is a graph showing a relationship between a birefringence amount of reciprocation of an optical recording medium in an optical pickup device and a light amount detected by a photodetector.

[Explanation of symbols]

 Reference Signs List 10 polarizing diffraction grating (polarizing optical element) 11 first diffraction grating 21 second diffraction grating 30 optical pickup device 31 laser diode (laser light source) 32 optical recording medium 32a recording surface of optical recording medium 33 retardation plate 34 objective Lens 35 Photodetector 38 Mirror 39 λ / 2 wavelength plate 41 Polarizing beam splitter (Polarizing optical element) 42 Hologram element 40 Optical unit

Claims (5)

[Claims] 1. A phase difference plate for converting a polarization state of light emitted from a laser light source and return light from an optical recording medium, and optical recording from the laser light source based on polarization states of the emitted light and the return light. A polarizing optical element that separates the return light from the optical axis toward the medium and guides the return light to a photodetector, wherein the phase difference plate has an orientation of the phase difference plate in a radial direction of the optical recording medium. Wherein the phase difference is set to a value deviated from １ ／ wavelength by an amount corresponding to the amount of birefringence of the optical recording medium itself. . 2. The optical pickup device according to claim 1, wherein the polarization direction of the light emitted from the laser light source and the direction of the phase difference plate form an angle of 45 °. 3. The laser light source according to claim 2, wherein said laser light source is rotated about its emission optical axis when the polarization direction of light emitted from said laser light source and the direction of said phase difference plate form an angle of 45 °. An optical pickup device characterized in that the optical pickup device is rotated by a predetermined angle. 4. The method according to claim 2, wherein the polarization direction of the light emitted from the laser light source and the direction of the phase difference plate form an angle of 45 ° with respect to the light emitted from the laser light source. An optical pickup device, wherein a half-wave plate through which the emitted light is transmitted is arranged in a predetermined direction. 5. The method according to claim 1, wherein
The optical pickup device, wherein the laser light source, the polarization optical element, and the photodetector are integrated as an optical unit.