JPH10233025A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the optical pickup capable of adopting a short wave laser diode that is different in oscillation mode from a long wave laser diode by only addition of a simple structure. SOLUTION: This pickup is equipped with a laser diode 11, a 1/2 wavelength plate 12, a beam splitter 40 consisting of a polarizing film 41 and a shaping prism 42, a 1/4 wavelength plate 5 and a photodiode 8. The laser diode 11 has a wavelength <=660nm to output a light beam of a TM polarization mode. An incident light beam is converted into 90 degrees and is outputted to a beam splitter 40 by the 1/2 wavelength plate 12. The individual constituting members are so arranged that the light beam emitted from the laser diode 11 is guided via the 1/2 wavelength plate 12, the beam splitter 40 to an optical disk, and then the light beam reflected by this optical disk is reflected via the 1/4 wavelength plate 5 by the beam splitter 40 so as to be incident upon the photodiode 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical pickup for optically recording and reproducing desired information and an optical element constituting the optical pickup, and more particularly to a DV.
The present invention relates to a technical field of an optical pickup for recording and reproducing information on a high-density recording medium represented by a digital versatile disc (DR).

[0002]

2. Description of the Related Art As a medium capable of optically recording and reproducing a large amount of information, a CD-R (Compact Disc-Recordable) is known. A conventional optical pickup in a recording / reproducing apparatus for recording information on such a CD-R and reproducing the information will be described below with reference to FIG.

In the conventional optical pickup for a CD-R shown in FIG. 6, a laser diode 1 generally has a 780 nm diameter because the recording / reproducing characteristics of the CD-R depend on the wavelength.
One that emits a light beam having a wavelength near m is employed. The luminous flux emitted from the laser diode 1 is a luminous flux that is linearly polarized and oscillates in a so-called TE polarization mode, which is polarized in a direction horizontal to an active layer (not shown) on the resonator end face of the laser diode 1. In addition, the far field pattern (far-field image) of such a light beam has an elliptical shape in which the above-mentioned polarization direction is the short axis direction.

The laser beam of the TE polarization mode emitted from the laser diode 1 is converted into a parallel beam by a collimator lens 2, and further, by a grating 3, a main beam (0-order beam) and a sub beam (+ 1-order beam and − beam). (Primary light). Then, the main beam and the sub beam generated by the grating 3 are combined with the beam splitter 40.
Is irradiated.

The beam splitter 40 includes a polarizing film 41 having a property of transmitting P-polarized light and reflecting S-polarized light, and a short-axis direction component of an incident elliptical light beam (bidirectional arrow S in FIG. 6).
and a shaping prism 42 for shaping the image into a circular shape by enlarging a direction (horizontal to the paper surface indicated by ar) at a predetermined magnification.

Accordingly, a light beam, which is supplied from the laser diode 1 and supplied through the diffraction grating 3 and whose polarization direction is an elliptical short-axis direction, is directed to the polarizing film 41 in such a polarization direction. When incident so as to be P-polarized light,
From the beam splitter 40, a P-polarized light beam whose beam shape is shaped into a circle is emitted to the 波長 wavelength plate 5. 1 /
Each of the light beams incident on the four-wavelength plate 5 is converted into linearly-polarized light by operation of the quarter-wave plate, and is condensed on the recording surface of the disk 9 via the objective lens 6.

The main light beam among the main light beam and the sub light beam generated by the grating 3 is used for reading information recorded on the disk 9 or writing information on the disk 9. The sub light beam is used for tracking control of the main light beam on the disk 9. As the tracking control, methods such as a differential push-pull method and a three-beam method are well known.

Each light beam reflected on the recording surface of the disk 9 enters the beam splitter 40 via the objective lens 6 and the quarter-wave plate 5. Each light beam reflected by the disk 9 is
Due to the function of the 板 wavelength plate, the circularly polarized light is converted into linearly polarized light again. However, the linearly polarized light in this case is S-polarized light whose polarization direction is rotated by 90 degrees with respect to the light beam irradiated from the beam splitter 40 to the 波長 wavelength plate 5. That is, by passing through the quarter-wave plate 5 twice before entering the disk 9 and after being reflected by the disk 9,
What was P-polarized light is converted to S-polarized light. Therefore, the light beam reflected by the disk 9 is reflected by the polarizing film 41 constituting the beam splitter 40 and enters the photodiode 8 via the condenser lens 7. Focus control and tracking control are performed by the light beams of the main light beam and the sub light beam incident on the photodiode 8, and the recorded information is reproduced.

[0009]

By the way, the CD-
DVD-Rs capable of recording a large amount of information by dramatically increasing the recording density compared to Rs have been developed. In such a DVD-R, the wavelength of the laser beam needs to be 660 nm or less due to the necessity of high-density recording. That is, as the recording density increases, it is necessary to reduce the light beam diameter on the disk, and the wavelength of the light beam emitted from the laser diode is shortened (for example, the wavelength 6).
(About 35 nm). Therefore, D
When an optical pickup for use in a VD-R is configured, a laser diode having a shorter wavelength of an emitted light beam than the laser diode 1 (hereinafter, a short-wavelength laser diode if necessary) is used instead of the laser diode 1. ) Is used.

However, unlike the laser diode 1 (hereinafter, referred to as a long-wavelength laser diode as necessary), the short-wavelength laser diode emits a light beam of an active layer on the resonance end face of the laser diode. It is a light beam that is polarized in the vertical direction and becomes linearly polarized light and oscillates in a so-called TM polarization mode. The far-field pattern of the light beam has an elliptical shape whose major axis is the polarization direction. Therefore, if an optical pickup as shown in FIG. 6 is configured using a short-wavelength laser diode to be employed in a DVD-R or the like, the polarization direction is set to be the elliptical long-axis direction with respect to the beam splitter 40. When the incident light flux is incident on the polarizing film 41 such that the polarization direction becomes P-polarized light, the major axis direction of the elliptical shape is enlarged by the action of the shaping prism 42, and the shape cannot be circularly shaped. There is.

Conversely, when the polarization direction is incident on the polarizing film 41 so as to be S-polarized, giving priority to the shaping of the beam shape, the general characteristics of the polarizing film 41 cause the characteristics shown in FIG. As shown, S-polarized light does not have a reflectance of 0%.
There is a problem that utilization efficiency of a light beam emitted from the light source is deteriorated. That is, the light (S-polarized light) emitted from the light source does not become 100% transmitted light due to the action of the polarizing film 41.

FIG. 7 is a characteristic diagram showing the reflectance (equivalent transmittance) with respect to the incident angle of the incident light beam on the polarizing film 41. The incident angle of about 56 degrees is a so-called Brewster angle. The reflectance of P-polarized light is 0% (that is, the transmittance is 100%). The polarizing film 41 in FIG.
Is designed so that the light beam is incident at the above Brewster angle.

As shown in FIG. 5, it is also possible to employ a short-wavelength laser diode by devising the arrangement of each optical element constituting the optical pickup shown in FIG. That is, the polarization direction of the TM polarization mode light beam supplied from the short-wavelength laser diode 11 becomes S-polarized light with respect to the polarizing film 41 having the property of transmitting P-polarized light and reflecting S-polarized light. The short-axis direction of the elliptical shape of the light beam is arranged in the direction of the arrow Sar in FIG. 5, and the １ ／ wavelength plate 5 and the objective lens 6 are arranged in the reflection direction of the S-polarized light by the polarizing film 41. The light beam guided to the optical disk 9 by the light source, and the light beam reflected by the disk 9 passes through the quarter-wave plate 5 again, so that the light beam converted into P-polarized light passes through the polarizing film 41 and is condensed. The lens 7 and the photodiode 8 are arranged. The shaping prism 402 is a shaping prism that shapes an elliptical pattern into a circular shape, and has the same operation as the shaping prism 42.

According to the above configuration, since it can be composed only of the conventionally used optical element shown in FIG. 6, there is an advantage that it is not necessary to increase the number of parts.

However, the polarizing film 41 shown in FIG.
As is clear from the characteristics of (1), the transmittance of P-polarized light becomes almost 0% at an incident angle at which S-polarized light supplied from the light source is guided (reflected) to the disk 9 by almost 100%, and the light beam is not guided to the photodiode 8. This makes it impossible to read the recorded information on the disk 9. Conversely, at an incident angle at which the transmittance of P-polarized light increases, the reflectance of S-polarized light decreases. Therefore, a recording apparatus used particularly for recording information on a recordable medium such as a DVD-R. It cannot be adopted for optical pickups. That is, the configuration shown in FIG. 5 is inappropriate from the viewpoint of improving the utilization efficiency of the laser beam.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to add a simple configuration to a conventional optical pickup, and to reduce the use efficiency of a long-wavelength laser without reducing the use efficiency of a laser beam. An object of the present invention is to provide an optical pickup which can employ a short-wavelength laser diode having a different oscillation mode from a diode.

[0017]

According to an aspect of the present invention, there is provided an apparatus for recording information on a recording surface of a recording medium or reproducing information recorded on the recording surface of the recording medium. An optical pickup for performing the above, wherein the far field pattern is an elliptical shape, a light source that generates a linearly polarized light beam having the major axis direction of the elliptical shape as a polarization direction, and a polarization direction of the light beam. A half-wave plate that differs by 90 degrees, and a 90-wave plate supplied from the half-wave plate.
A shaping prism for shaping the far-field pattern of the light beam having a polarization direction that has been varied to a circular shape,
The luminous flux supplied from the half-wave plate and having a polarization direction deviated by 90 degrees is transmitted, and the luminous flux having a polarization direction deviated by 90 degrees from the polarization direction deviated by 90 degrees is reflected. The polarizing film to be transmitted, the luminous flux transmitted through the polarizing film is guided to the recording surface by passing the luminous flux transmitted through the polarizing film, and the luminous flux reflected by the recording surface is passed again by the luminous flux transmitted through the polarizing film. A quarter-wave plate that changes the polarization direction by 90 degrees from the polarization direction of the light beam transmitted through the polarizing film, and then guides the light to the polarizing film;
A light receiving element for receiving a light beam supplied from the wave plate and reflected by the polarizing film.

According to the operation of the first aspect of the present invention, T
Between a short-wavelength laser diode that oscillates in the M-polarization mode, a shaping prism that shapes the far-field pattern of the light beam, and a polarizing film that separates the P-polarized light and the S-polarized light, 、 Since the wavelength plate is provided, the beam splitter is rotated by 90 degrees in the polarization direction of the light flux, which is a long axis direction of the ellipse in which the far field pattern incident on the half-wave plate is elliptical and the polarization direction is applied. Will be supplied to Therefore, the beam splitter is supplied with a laser beam oscillated in the conventional TE polarization mode in which the far-field pattern is an elliptical shape and the polarization direction is the short axis direction of the ellipse, Even in an optical pickup using a short-wavelength laser diode, a beam splitter used for a long-wavelength laser diode can be adopted.

According to a second aspect of the present invention, there is provided an optical pickup according to the first aspect, wherein the half-wave plate has a plurality of grooves formed on one end surface thereof in parallel with each other. By forming, a function of a diffraction grating for separating a light beam incident on the recording medium into a main light beam and a sub light beam is additionally provided, and the main light beam and the sub light beam are respectively formed on the recording surface. When the angle between the line connecting the spot lights and the tangential direction of the track on the recording surface is θ, and the angle of rotation of the half-wave plate is γ, the direction in which the plurality of grooves are formed and the angle of rotation are γ. The angle δ between the crystal of the half-wave plate and the optical axis is set as δ = 45 ° −θ + (γ / 2) or δ = 45 ° −θ− (γ / 2).

According to the function of the invention described in claim 2, in addition to the function of the invention described in claim 1, the half-wave plate has a plurality of light-emitting elements each having a function as a diffraction grating on one end surface thereof. Are formed at an angle defined by the above δ, so that the diffraction grating necessary for separating the light beam incident on the recording medium into the main light beam and the sub light beam, and the 1 / 2
The wave plate and the wave plate can be integrally formed. In other words, since the plurality of grooves are formed in the direction defined by δ, the rotation adjustment for determining the diffraction direction of each light beam by the diffraction grating and the rotation adjustment of the half-wave plate are integrally performed. And the adjustment becomes easy.

According to a third aspect of the present invention, in the optical pickup according to the first aspect, the half-wave plate has a plurality of grooves parallel to each other on one end surface thereof. By forming the beam splitter, a function of a diffraction grating for separating a light beam incident on the recording medium into a main light beam and a sub light beam is added, and a shaping ratio for shaping the far field pattern in the beam splitter is adjusted. EX, and θ is an angle between a line connecting the spot light beams formed on the recording surface by the main light beam and the sub light beam, respectively, and a tangential direction of a track on the recording surface.
The angle δ between the direction in which the plurality of grooves are formed and the optical axis of the crystal of the 波長 wavelength plate is configured as δ = 45 ° −θ × EX or δ = 45 ° −θ / EX. .

According to the function of the invention described in claim 3, in addition to the function of the invention described in claim 1, the half-wave plate includes a plurality of light-emitting elements having a function as a diffraction grating on one end surface thereof. Are formed at an angle defined by the above δ, so that the diffraction grating necessary for separating the light beam incident on the recording medium into the main light beam and the sub light beam, and the 1 / 2
The wave plate and the wave plate can be integrally formed. In other words, since the plurality of grooves are formed in the direction defined by δ, the rotation adjustment for determining the diffraction direction of each light beam by the diffraction grating and the rotation adjustment of the half-wave plate are integrally performed. Can be.

[0023]

Next, preferred embodiments of the present invention will be described with reference to the drawings. In this embodiment, an optical pickup in a recording / reproducing apparatus for an optical disk which is a high-density information recording medium such as a DVD-R will be described.

In FIG. 1, the same components as those in FIG. 6 are denoted by the same reference numerals, and a specific description thereof will be omitted as appropriate.
As shown in FIG. 1, an optical pickup according to this embodiment includes a short-wavelength laser diode 11, which is a light source, a collimator lens 2, a half-wave plate 12, a diffraction grating 3,
It is configured by arranging a beam splitter 40, a quarter-wave plate 5, an objective lens 6, a condenser lens 7, and a photodiode 8 as a light receiving element as shown in the figure. That is, in the optical pickup for CD-R shown in FIG. 6, the laser diode 1 is replaced by the short-wavelength laser diode 11 and the short-wavelength laser diode 11
Between the beam splitter 40 and, more specifically, between the collimator lens 2 and the grating 3, the direction of polarization of the input linearly polarized light beam is rotated by 90 degrees to make it different by 1/90. It is configured by disposing the two-wavelength plate 12. Other configurations are the same as those shown in FIG.

The short-wavelength laser diode 11 has a wavelength of 635 nm, is a laser beam that is polarized in the vertical direction of the active layer on the resonance end face of the laser diode 11, and has a far-field pattern that changes the polarization direction. The laser beam that has an elliptical shape in the major axis direction is emitted. The laser beam is applied to the half-wave plate 12 via the collimator lens 2.

The half-wave plate 12 is made of, for example, a crystal exhibiting linear birefringence such as quartz or calcite, and converts the linearly polarized light incident at an angle of + α with respect to the high-speed axis of the crystal to the high-speed light. Output as linearly polarized light tilted by -α with respect to the axis. Accordingly, the half-wave plate 12 is arranged so that the linearly polarized light from the short-wavelength laser 11 irradiated through the collimator lens 2 is incident at an angle of, for example, 45 degrees with respect to the high-speed axis of the half-wave plate. If provided, the linearly-polarized light beam emitted from the short-wavelength laser diode 11 has its polarization direction rotated by 90 degrees, that is, an elliptical far-field pattern of the laser light beam emitted from the short-wavelength laser diode 11. Is a light beam of linearly polarized light whose polarization direction is the minor axis direction. The linearly polarized light beam is applied to the grating 3 to be separated into a main light beam and a sub light beam, and then supplied to the beam splitter 40.

As described above, the laser beam supplied from the half-wave plate 12 has its polarization direction changed by the beam splitter 4.
For the zero polarization film 41, the light becomes a P-polarized light beam. Accordingly, the P-polarized light flux whose beam shape is shaped circular is emitted from the beam splitter 40 toward the quarter-wave plate 5.

As described above, by interposing the half-wave plate 12 for converting the polarization direction between the laser diode 11 and the beam splitter 40, the other configuration is the same as that of the conventional optical pickup. It becomes possible to share.

Incidentally, the half-wave plate 12 is paraphrased so that the light beam supplied from the half-wave plate 12 to the beam splitter 40 becomes exactly P-polarized light when viewed from the polarizing film 41 of the beam splitter 40. Then, the optical axis of the half-wave plate 12 is adjusted so that the linearly polarized light emitted from the short-wavelength laser diode 11 is irradiated at an angle of exactly 45 degrees with respect to the high-speed axis of the half-wave plate 12. It is necessary to make fine adjustment of rotation around the center. As shown in FIG. 7, if the supplied light beam is exactly P-polarized light viewed from the polarizing film 41, the light beam is transmitted 100%, so that the amount of light received by the photodiode 8 is maximized. Therefore, in the rotation fine adjustment, while observing the output signal of the photodiode 8, the adjustment is performed so that the output signal is maximized.

On the other hand, in the grating 3, a line segment connecting the main light beam and the sub light beam generated by the grating 3 has a predetermined distance from a tangential direction of a recording track for recording information formed on the disk. It is necessary to adjust the rotation of the grating 3 about the optical axis so that the light is emitted with the following relationship. That is, the line connecting the spots of the main light beam (zero-order light) and the sub-light beam (± first-order light) formed on the recording surface of the optical disk shown in FIG. Is adjusted so as to be a predetermined angle defined by the tracking error generation method to be used, the beam interval between the main light beam and the sub light beam, and the like.

More specifically, first, a tracking error signal (in the case of the three-beam method, two sub-beams (+
While observing the difference signal of the amount of reflected light from each disk (the primary light and the −1st light), the grating 3 is rotated (that is, the above θ is changed) to search for a null point. Here, the null point means that the above θ is 0 degrees, that is,
This is the rotation position of the grating where the line connecting the spots of the main light beam and the sub light beam and the tangential direction of the track on the recording surface are parallel, and the amplitude of the envelope of the tracking error signal is minimized. Next, while rotating the grating around the null point, the grating position is adjusted to a rotation position at which the amplitude of the envelope of the tracking error signal is maximized.

However, there are a plurality of angles at which the amplitude of the envelope of the tracking error signal is minimized in addition to the null point. For example, when the main light beam is positioned on a certain track, and the two sub-light beams are positioned on a track other than the track on which the main light beam is positioned (for example, an adjacent track), the null point is set. Will take the same form. Similarly, since there are a plurality of angles at which the amplitude of the envelope of the tracking error signal is maximized, the search for the null point is not easy. As described above, since there are two optical elements for rotational adjustment, there is a problem that the adjustment operation becomes complicated.

Therefore, the optical member 12 shown in FIG. 2 having both the function of the half-wave plate 12 and the function of the grating 3 is provided.
0.

The optical member 120 will be described below with reference to FIGS. As shown in FIG.
0 is provided on one end surface 14 of the parallel plate 13 made of a biaxial birefringent crystal such as artificial quartz at a predetermined interval defined by the wavelength of the incident light beam, the focal length of the objective lens 6 and the collimator 2, and the like. By forming a plurality of rectangular grooves 15 parallel to each other, the half-wave plate 12 and the grating 3 are integrally formed.

The direction in which the rectangular grooves 15 are formed is defined by the following method. A line segment connecting each spot light formed on the recording surface of the disk by the main light beam (zero-order light) and the sub-light beam (± first-order light) generated by the rectangular groove 15, and the tangential direction of the track on the recording surface Is defined as θ (degrees), θ is defined as (45) based on one of the two axes (high-speed axis X and low-speed axis Y) of the birefringent crystal in the half-wave plate 120. The direction of the angle (゜ −θ) is the direction of v. The direction orthogonal to the direction of v is the rectangular groove 15.
Direction.

The half-wave plate 12 is inclined by the same absolute angle with respect to two orthogonal axes of the birefringent crystal, ie, both the high-speed axis X and the low-speed axis Y in FIG. 2B. Linearly polarized light, that is, linearly polarized light having an inclination of +45 degrees with respect to the x-axis and −45 degrees with respect to the y-axis and having a polarization direction parallel to the center line L in FIG. 2B is incident. Is output as linearly polarized light rotated by 90 degrees, the half-wave plate 12 has the above (45 ° −θ).
By forming a rectangular groove in a direction orthogonal to the direction v, the optimum rotation angle of the half-wave plate and the optimum rotation angle of the grating coincide.

Therefore, the tracking error signal obtained by the optical pickup having the optical member 120 is
As shown in FIG. 4, amplitude modulation is performed by an amplitude change due to the action of the half-wave plate, and the maximum amplitude position of the modulated signal is a position to be adjusted. In short, the adjustment simply involves searching for the position where the amplitude is maximum while observing the tracking error signal. By the way, FIG.
5 shows the amplitude level of the tracking error signal with respect to the angle θ. In the figure, an angle of 0 degree is a null point.

As described above, by forming the rectangular groove 15 so that the direction of an angle of (45 ° -θ) with respect to the crystal axis of the birefringent crystal constituting the half-wave plate becomes the above-mentioned perpendicular v. In addition, it is not only necessary to perform the rotation adjustment only once, but in particular, it is not necessary to detect the rotation angle corresponding to the null point, which is a problem in the rotation adjustment of the grating, so that the adjustment process is simplified.

If the birefringent crystal such as artificial quartz constituting the optical member 120 has optical rotation (a phenomenon in which the plane of polarization of linearly polarized light propagating in the direction of the optical axis is twisted with the progress of light), such a phenomenon occurs. Since the angle θ between the line connecting the main light beam and the sub-light beam and the track on the disk is rotated by the rotation angle generated by the optical rotation, the direction of the rectangular groove 15 is corrected by the rotation angle. There is a need. That is, if the optical rotation angle is γ, the plurality of rectangular grooves 1
The angle δ between the perpendicular v to 5 and one crystal axis of the crystal of the half-wave plate, that is, the high-speed axis X or the low-speed axis Y
To the following equation (1).

[0040]

## EQU1 ## δ = 45 ° −θ ± γ / 2

In the above equation, when the artificial crystal used is a right crystal (a state in which the atoms constituting the crystal are arranged clockwise in the optical axis direction), + γ / 2 is adopted, and the left crystal ( In the case where the above arrangement state is counterclockwise, -γ
/ 2 is adopted.

Further, the shaping action of the shaping prism 42 of the beam splitter 40 changes the angle θ between the line segment connecting the main light beam and the sub light beam on the recording surface and the tangential direction of the track. That is, the light beam irradiated on the recording surface expands in the radial direction of the disk (radiation direction about the rotation axis) with the shaping ratio EX (the ratio of the vertical and horizontal radiation angles of the laser beam in the laser diode). In this case, the angle θ on the recording surface is enlarged to EX times the angle when the shaping ratio is 1, that is, EX × θ. On the other hand, when the shape is expanded in the tangential direction of the disc (tangential direction of the track) with the shaping ratio EX, the angle θ is 1 / EX times the angle when the shaping ratio is 1, that is, θ.
/ EX is enlarged.

Therefore, in order to cancel the influence of the shaping, that is, the rotation of the angle θ due to the expansion by the shaping prism 42 in the radial direction at the shaping ratio EX, the perpendicular v to the plurality of rectangular grooves 15 is required.
And one crystal axis of the birefringent crystal, that is, the angle δ between the high-speed axis or the low-speed axis,

[0044]

Δ = 45 ° −θ / EX ± γ / 2

Assume that

Similarly, the shaping ratio E in the tangential direction
When expanding by X,

[0047]

Δ = 45 ° −θ × EX ± γ / 2

That is,

By forming the rectangular groove 15 in a direction perpendicular to the direction v rotated by an angle δ with respect to the crystal axis, the main light beam and the sub light beam due to the optical rotation of the shaping prism 42 and the half-wave plate 120 are formed. The rotation of the angle θ between the line connecting the light flux and the tangential direction of the track can be corrected.

The rectangular groove 15 is described as being formed so that the line connecting the main light beam and the sub light beam on the recording surface becomes -θ with respect to the tangential direction of the track. However, even when such a line segment is formed so as to be + θ, the above conditions remain unchanged.

[0051]

As described above, according to the first aspect of the present invention, the short-wavelength laser diode oscillating in the TM polarization mode, the shaping prism for shaping the far-field pattern of the light beam, and the P-polarized light. Between the S-polarized light and a beam splitter composed of a polarizing film that separates the S-polarized light.
Since the two-wavelength plate is provided, the far-field pattern incident on the half-wavelength plate has an elliptical shape, and the polarization direction of the light beam is the major axis direction of the ellipse.
After being rotated by 90 degrees, it is supplied to the beam splitter. Therefore, the beam splitter is supplied with a beam that is equal to the laser beam oscillated in the conventional TE polarization mode in which the far field pattern has an elliptical shape and the polarization direction is the minor axis direction of the ellipse. Even in an optical pickup using a short-wavelength laser diode, a beam splitter used for a long-wavelength laser diode can be used as it is without reducing the utilization efficiency of a laser beam.

According to the invention described in claim 2, according to claim 1
In addition to the effects of the invention described in the above, the half-wave plate,
A plurality of grooves having a function as a diffraction grating are formed on one end surface thereof at an angle defined by δ = 45 ° −θ + (γ / 2) or δ = 45 ° −θ− (γ / 2). In addition, a diffraction grating necessary for separating a light beam incident on a recording medium into a main light beam and a sub-light beam, and a half-wave plate rotating in a polarization direction can be integrally formed. That is, since the plurality of grooves are formed in the direction defined by δ, the rotation angle corresponding to the optimum position in the diffraction direction of each light beam by the diffraction grating and the straight line emitted by the half-wave plate Since the rotation angle corresponding to the optimum position in the polarization direction of the polarized light can be matched, the adjustment becomes easy.

According to the invention of claim 3, according to claim 1,
In addition to the effects of the invention described in the above, the half-wave plate,
A plurality of grooves having a function as a diffraction grating are formed on one end surface thereof at an angle defined by δ = 45 ° −θ × EX or δ = 45 ° −θ / EX, so that the light beam incident on the recording medium Can be integrally formed with a diffraction grating necessary for separating the light into a main light beam and a sub light beam, and a half-wave plate rotating the polarization direction. In other words, since the direction in which the plurality of grooves is formed is formed in the direction defined by the above δ, the rotation adjustment for determining the direction of diffraction of each light beam by the diffraction grating and １ ／
The rotation adjustment of the wave plate can be performed integrally.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical pickup according to an embodiment of the present invention.

2A and 2B are diagrams showing a specific configuration of an optical member 120, wherein FIG. 2A is a front view, FIG. 2B is a diagram showing directions of crystal axes X and Y in FIG. 2A, and FIG. It is AA sectional drawing of.

FIG. 3 is a diagram showing an arrangement relationship between a spot light applied to a disk 16 and a track.

FIG. 4 is a diagram showing an amplitude characteristic of a tracking error signal obtained from the photodiode 8 with respect to a rotation angle of the half-wave plate 120 when the optical member 120 is employed.

FIG. 5 is a diagram showing a configuration of a conventional optical pickup.

FIG. 6 is a diagram showing a configuration of another conventional optical pickup.

FIG. 7 is a diagram showing characteristics of reflectance of P-polarized light and S-polarized light with respect to an incident angle.

[Explanation of symbols]

 5 1/4 wavelength plate 8 Photodiode as light receiving element 11 Short wavelength laser diode 12 1/2 wavelength plate 120 Optical member 15 Groove forming diffraction grating 40 Beam splitter 41 Polarizing film 42 Shaping prism 400 Beam splitter 401 Polarizing film 402 Shaping prism

Claims (3)

[Claims] 1. An optical pickup for recording information on a recording surface of a recording medium or reproducing information recorded on the recording surface of the recording medium, wherein the far field pattern has an elliptical shape and the elliptical shape. A light source that generates a light beam that is linearly polarized light whose polarization direction is the major axis direction of the shape, a half-wave plate that changes the polarization direction of the light beam by 90 degrees, and the far-field pattern of the light beam is circular. A shaping prism for shaping, and a luminous flux having a polarization direction changed by 90 degrees supplied from the 波長 wavelength plate is transmitted, and the polarization direction is different from the polarization direction changed by 90 degrees. A light beam that differs by 90 degrees reflects a polarizing film, and a light beam that transmits the light beam transmitted through the polarizing film and guides the light beam to the recording surface, and a light beam transmitted through the polarizing film reflected by the recording surface. By passing again, after the polarization direction of the light beam polarization direction transmitted through the polarizing film of the light flux the reflected it was made different by 90 degrees, leading to the polarizing film 1 /
An optical pickup comprising: a four-wavelength plate; and a light-receiving element that receives a light beam supplied from the quarter-wavelength plate and reflected by the polarizing film. 2. The half-wave plate has one end face,
By forming a plurality of grooves parallel to each other, a function of a diffraction grating for separating a light beam incident on the recording medium into a main light beam and a sub light beam is additionally provided, and the main light beam and the sub light beam are When the angle between the line connecting the spot lights formed on the recording surface and the tangential direction of the track on the recording surface is θ, and the optical rotation angle of the half-wave plate is γ, Δ = 45 ° −θ + (γ / 2) or δ = 45 ° −, the angle δ between a line segment perpendicular to the direction in which the groove is formed and one crystal axis of the crystal of the 波長 wavelength plate is defined as The optical pickup according to claim 1, wherein θ− (γ / 2). 3. The half-wave plate has, on one end surface thereof,
By forming a plurality of grooves parallel to each other, a function of a diffraction grating for separating a light beam incident on the recording medium into a main light beam and a sub light beam is additionally provided, and the far field pattern in the beam splitter is provided. A shaping ratio for shaping is EX, a line connecting the spot light beams formed on the recording surface by the main light beam and the sub light beam, and
When the angle between the tangent direction of the track on the recording surface and θ is θ, the line segment perpendicular to the direction in which the plurality of grooves are formed and one crystal axis of the crystal of the half-wave plate are formed. The optical pickup according to claim 1, wherein the angle δ is set to δ = 45 ° −θ × EX or δ = 45 ° −θ / EX.