JPH10340471A - Optical pickup - Google Patents

Abstract

[PROBLEMS] To provide an optical pickup capable of effectively reducing the incidence of unwanted return light to a semiconductor laser and sufficiently improving the C / N of a read signal. SOLUTION: In an optical pickup in which light emitted from a semiconductor laser 2 is applied to an optical recording medium 9 through an objective lens 8 and reflected light is received by a photodetector 11,
In an optical path between the semiconductor laser 2 and the objective lens 8, a wave plate 71 formed by bonding two birefringent crystal plates 71 a and 71 b so that their crystal axes are orthogonal to each other is placed in an azimuthal direction of the crystal axes. At an angle of about 45 ° with respect to the optical axis of the objective lens 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used for reproducing information recorded on an optical recording medium such as an optical disk and a magneto-optical disk.

[0002]

2. Description of the Related Art As a conventional optical pickup, for example,
There is one as shown in FIG. This optical pickup
Japanese Patent Application Laid-Open No. 6-251414 discloses a method in which light emitted from a semiconductor laser 2 having a high-frequency module 1 is converted into a parallel light beam by a collimator lens 3 and then incident on a beam splitter 5 via a diffraction grating 4. The beam transmitted through the beam splitter 5 is reflected by a mirror 6 and irradiates a spot on an optical disc 9 by an objective lens 8 via a quarter-wave plate 7. The return light reflected by the optical disk 9 follows the same optical path as the outward path and is incident on the beam splitter 5, and the return light reflected here is received by the photodetector 11 through the condenser lens 10, and The information recorded on the optical disk 9 is read based on the output.

That is, in the optical pickup shown in FIG. 9, a quarter-wave plate 7 is arranged between a mirror 6 and an objective lens 8 so that linearly polarized light from the semiconductor laser 2 is converted into circularly polarized light on the outward path. The laser beam is radiated onto the optical disc 9 and converted into circularly polarized light reflected on the optical disc 9 on the return path into linearly polarized light orthogonal to the linearly polarized light on the forward path, so that return light transmitted through the beam splitter 5 is incident on the semiconductor laser 2. Thus, fluctuation of the light emission is prevented, thereby improving the C / N of the read signal.

[0004]

However, according to various experiments conducted by the present inventors, in the conventional optical pickup shown in FIG. 9, the diffraction grating 4, the beam splitter 5, the quarter-wave plate 7, etc. Even if an antireflection coat is applied to the surface of the optical component, the outgoing light from the semiconductor laser 2 is slightly reflected on the surface of the optical component on the outward path, and is converted into linearly polarized light in the same direction as the linearly polarized light of the emitted light. 2, the light emission fluctuates, or the reflected light on the optical component surface enters the photodetector 11 as stray light, causing an offset or noise in the output, thereby reducing the C / N of the read signal. It turned out that there was a problem that it could not be improved sufficiently.

A first object of the present invention is to pay attention to the above-mentioned conventional problems, and it is possible to effectively reduce the incidence of undesired return light on a semiconductor laser and to reduce the incidence on a photodetector. Stray light incidence can be effectively prevented, and the read signal C
It is an object of the present invention to provide an optical pickup appropriately configured to sufficiently improve / N.

A second object of the present invention is to provide a C / N
It is an object of the present invention to provide an optical pickup appropriately configured to detect a good magneto-optical signal.

[0007]

In order to achieve the first object, according to the present invention, light emitted from a semiconductor laser is applied to an optical recording medium via an objective lens, and the reflected light is received by a photodetector. In the optical pickup, a wavelength plate formed by bonding two birefringent crystal plates so that their crystal axes are orthogonal to each other is provided in the optical path between the semiconductor laser and the objective lens. The optical system is characterized in that it is arranged at an angle of about 45 ° with respect to the azimuthal direction of the axis and inclined with respect to the optical axis of the objective lens.

In one embodiment of the present invention, light emitted from the semiconductor laser is guided to the optical recording medium through the objective lens in an optical path between the semiconductor laser and the objective lens, and the optical recording is performed. Beam separating means for guiding the light reflected by the medium through the objective lens to the photodetector is arranged, and the wave plate is arranged in an optical path between the beam separating means and the objective lens. With this configuration, it is possible to simplify the configuration of the optical system, to prevent the occurrence of undesired phase shift on the wave plate, and to further reduce unwanted return light to the semiconductor laser due to reflection on the wave plate surface. And the occurrence of offset and noise in the photodetector output can be effectively prevented, so that the C / N of the photodetector output can be sufficiently improved.

Further, in order to achieve the second object,
The present invention irradiates an optical recording medium with light emitted from a semiconductor laser through an objective lens, separates the reflected light into polarization components orthogonal to each other by an analyzing means, and receives the separated light components with a photodetector. In an optical pickup adapted to detect a magneto-optical signal based on the output of the device, disposed in an optical path between the semiconductor laser and the objective lens,
Beam splitting means for guiding light emitted from the semiconductor laser through the objective lens to the optical recording medium and guiding reflected light from the optical recording medium to the light analyzing means; In the optical path between the means, a wave plate formed by bonding two birefringent crystal plates so that their crystal axes are orthogonal to each other, in a direction substantially at 45 ° to the azimuthal direction of the crystal axes. , And are arranged to be inclined with respect to the optical axis.

[0010] In one embodiment of the present invention, in each of the above optical pickups, at least the semiconductor laser and the photodetector are arranged adjacent to each other in one unit. This makes it possible to make the optical pickup compact.

[0011]

FIG. 1 shows a first embodiment of an optical pickup according to the present invention. In this embodiment, in the configuration of the conventional optical pickup shown in FIG. 9, the diffraction grating 4 and the beam splitter 5 are arranged at an angle to the optical axis. As shown in the perspective view of FIG. 2, the quarter-wave plate 71 is formed by bonding two birefringent crystal plates 71a and 71b made of artificial quartz such that their crystal axes are orthogonal to each other. And the 1/4 wavelength plate 7
1 is arranged at an angle of approximately 45 ° with respect to the azimuthal direction of the crystal axes of the birefringent crystal plates 71a and 71b and at an angle of, for example, 3 ° with respect to the optical axis of the objective lens 8. Other configurations and operations are the same as those in FIG. 9, and thus detailed description is omitted.

With this configuration, unwanted reflection in the optical axis direction on the surfaces of the diffraction grating 4, the beam splitter 5, and the quarter-wave plate 71 can be effectively prevented, and the quarter-wave plate can be effectively prevented. The occurrence of a phase shift due to the inclination of 71 can also be effectively prevented. Accordingly, the incidence of unwanted return light on the semiconductor laser 2 can be effectively reduced, and the incidence of stray light on the photodetector 11 can also be effectively prevented, so that a sufficiently satisfactory C / N can be obtained.

That is, in the configuration shown in FIG.
The four-wavelength plate 71 is formed such that the direction parallel to the incident linearly polarized light emitted from the semiconductor laser 2 is the y axis, the optical axis direction of the objective lens 8 is the z axis, and the direction orthogonal to the y axis and the z axis is the x axis. In the dimensional coordinate system, for example, as shown in FIG. 3, the azimuth direction in which θ is ± 45 ° with respect to the x-axis on the xy-axis plane, that is, the azimuth of one of the crystal axes of the birefringent crystal plates 71a and 71b. If the tilted angle φ between the normal z ′ and the z-axis is set to be equal to, for example, 3 ° in the same direction, the diffraction grating 4,
Although undesired reflection in the optical axis direction on the surfaces of the beam splitter 5 and the quarter-wave plate 71 can be prevented, a sufficiently satisfactory C / N cannot be obtained.

According to various experimental studies by the present inventors, when the quarter-wave plate 71 is tilted as shown in FIG. 3, a phase shift occurs due to its thickness, and the quarter-wave plate 71 The return light transmitted through the beam splitter 71 is not completely linearly polarized light.
It has been found that the same polarization component as the polarization component of the light emitted from the semiconductor laser 2 is incident on the semiconductor laser 2 and the C / N cannot be sufficiently improved.

The phase shift caused by the quarter wavelength plate 71 will be described in more detail. Two birefringent crystal plates 71
a, the refractive index of the ordinary light is no, and the refractive index of the extraordinary light is n.
The phase is calculated from the optical path difference by using e and each thickness as d. Here, the thickness d is a substantial thickness passing through each birefringent crystal plate, and strictly speaking, no and ne
However, the description is not affected, so it is the same for simplicity.

First, the thickness of one birefringent crystal plate 71a is d, and the thickness of the other birefringent crystal plate 71b is d + Δd.
As shown in FIG. 4A, the birefringent crystal plate 71a has a refractive index ellipsoid 71an, and the birefringent crystal plate 71b has a refractive index ellipsoid 71bn. Here, when the incident light is incident on the birefringent crystal plate, the major axis of the ellipsoidal plane, which is a cut line obtained by cutting the refractive index ellipsoid with a plane including the center of the refractive index ellipsoid with the incident light as the normal, is extraordinary light. The refractive index and the minor axis become the ordinary light refractive index, and the incident linearly polarized light splits into components having a vibrating surface in these two directions and travels in the birefringent crystal plate. Also, the ordinary light refractive index does not change regardless of the direction from which light rays enter, but the extraordinary light refractive index changes. The index ellipsoids 71an and 71bn are at 90 ° to each other, and the ordinary light polarization direction of the birefringent crystal plate 71a and the extraordinary light polarization direction of the birefringent crystal plate 71b match. The polarization in this direction will be referred to as p-polarization for the sake of explanation, and the polarization in the direction orthogonal thereto will be referred to as s-polarization.

As shown in FIGS. 3 and 4 (a), when the azimuth θ of the incident light is θ = 45 °, a general p-polarized light component (including the incident light and the normal to the incident plane) is included. A polarization component having an in-plane vibration direction) and the above-mentioned p-polarized light coincide with each other, and the s-polarized light component and the above-mentioned s-polarized light coincide with each other. Therefore, the optical path length p (nd) for the p polarization and the optical path length s for the s polarization
(Nd), for p-polarized light, the incident light is
As shown in FIG. 4B, since the incident light is incident at an angle φ with respect to the optical axis, the refractive index of the extraordinary light is ne ′, and the major axis of the refractive index ellipsoid 71an is indicated by a broken line in FIG. Therefore, the optical path length p (nd) of the p-polarized light is
The optical path length at a is ne ′ · d, and the birefringent crystal plate 7
The optical path length at 1b is no · (d + Δd), and p (nd) = ne ′ · d + no · (d + Δd) (1) The optical path length s (nd) of the s-polarized light is such that the optical path length at the birefringent crystal plate 71a is no · d, and the optical path length at the birefringent crystal plate 71b is ne · (d + Δd). Therefore, s (nd) = no · d + ne · (d + Δd) (2)

Therefore, from the above equations (1) and (2), the phase difference between the p wave and the s wave in the quarter wave plate
2π / λ ｛ps (Δnd)｝ is 2π / λ ｛ps (Δnd)｝ = 2π / λ ｛p (nd) -s (nd)｝ = 2π / λ ｛d (ne′−ne ) + Δd (no−ne)｝ (3)

As is apparent from the above equation (3), 1/4
If the wave plate 71 is tilted in a direction coincident with the direction of one of the crystal axes of the birefringent crystal plates 71a and 71b, the phase becomes 90 °.
In addition to the term Δd (no−ne) that gives
−ne), which results in a phase shift from 90 °.
This phase shift occurs when the thickness d is very small (d = 0).
For example, in the case of 19 μm (Δd = 19 μm: 1/4 of the 0th order)
Wavelength plate) is hardly generated, but in practice, it takes 1 mm or more (d ≧ 0.5) to prevent the occurrence of distortion during manufacturing and cracking due to handling. .

Then, the present inventors set the tilt angle φ to 3 ° for the 波長 wavelength plate 71 having the configuration shown in FIG. 2, and set its tilting azimuth direction, that is, the angle θ from the x axis in the xy plane. Was used as a parameter, and a deviation from a phase of 90 ° when light was transmitted back and forth through the quarter-wave plate 71 was measured. FIG. 5 shows the measurement results, and the solid line indicates the thickness d.
= 0.5 mm, and the broken line indicates the thickness d = 0 (Δd = 19 μm: 0)
(The next ４ wavelength plate).

As is clear from FIG. 5, when θ = 45 °, a phase shift of about 6 ° occurs at a thickness d of 0.5 mm level, so that linearly polarized light is incident on the 波長 wavelength plate 71 on the outward path. However, it can be seen that perfect linearly polarized light is not obtained on the return path. On the other hand, if θ = 90 °, that is, ± 45 ° with respect to the azimuthal direction of the crystal axes of the birefringent crystal plates 71a and 71b, it is understood that basically no phase shift occurs. This is because, in the above equation (3), the term d (ne'-ne) becomes d (ne "-ne").
= 0. In addition, ne ″ indicates the refractive index of the extraordinary light of the refractive index ellipsoid formed by the light rays incident from the azimuth x or y axis direction.

The first embodiment is based on the above experimental results, whereby the occurrence of a phase shift due to the tilting of the quarter-wave plate 71 can be prevented, and therefore the return to the semiconductor laser 2 can be prevented. Since the light can be made almost perfect linearly polarized light orthogonal to the linearly polarized light emitted from the semiconductor laser 2, it is possible to effectively prevent the incidence of unwanted return light. In addition, by inclining the quarter-wave plate 71, it is possible to effectively prevent reflected light on the surface from entering the photodetector 11 as stray light, so that generation of offset and noise due to stray light can also be effectively prevented. Therefore, a sufficiently satisfactory C / N can be obtained.

FIGS. 6 and 7 show a second embodiment of the present invention. This optical pickup reads information recorded on a magneto-optical disk 31, and includes a semiconductor laser 21, a prism 22 made of lithium niobate as a uniaxial birefringent crystal, a diffraction element 23, a collimator lens 24, 1/2. It has a wavelength plate 81, an objective lens 25, parallel prisms 26-1, 26-2, and a semiconductor substrate 27 on which a plurality of photodetectors are formed. In FIG. 7, illustration of the parallel prisms 26-1 and 26-2 is omitted. The semiconductor laser 21 is provided on a base 29 via a base 28 made of metal, semiconductor, or insulator. A semiconductor substrate 27 is also provided on the base 29, and the semiconductor laser 21 emits linearly polarized laser light in a horizontal direction with respect to the semiconductor substrate 27. The semiconductor laser 21
The direction of polarization of the linearly polarized light from is set to the y-axis direction orthogonal to the x-axis direction parallel to the information track direction of the magneto-optical disk 31.

The prism 22 and the parallel prism 26
-1, 26-2 are provided on the semiconductor substrate 27 by bonding. The prism 22 has a first surface (slope) 22a
A polarizing film 30 having a characteristic that the reflectance of the S-polarized component is 50% or more and the transmittance of the P-polarized component is 80% or more;
The light emitted from the semiconductor laser 21 is applied to the polarizing film 30.
Light that is incident at an incident angle of approximately 45 ° and is reflected in a direction substantially normal to the semiconductor substrate 27 (z-axis direction), and light that is transmitted through the polarizing film 30 and refracted and transmitted through the first surface 22 a of the prism 22. And separated into The polarizing film 30 is formed of the semiconductor laser 2
Since divergent light is incident from 1, the configuration is such that the incident angle dependence is reduced.

Light from the semiconductor laser 21 reflected by the polarizing film 30 in the z direction is incident on the diffraction element 23. In addition, the light passes through the polarizing film 30 and passes through the first surface 22 of the prism 22.
The light from the semiconductor laser 21 that refracts and transmits through a is totally reflected by the second surface 22 b of the prism 22,
2c is transmitted and received by a predetermined photodetector formed on the semiconductor substrate 27. For this reason, in this embodiment, the prism 22 is formed such that the apex angle between the first surface 22a and the second surface 22b is 90 °.

By forming the prism 22 in this way, the refractive index of lithium niobate is 2.24 and the critical angle is 26.
Since it is 5 °, the central ray (principal ray) of the light beam incident on the first surface 22a at an incident angle of 45 ° is incident on the second surface 22b at an incident angle of approximately 71.6 ° and is totally reflected. Is done. In addition, a light beam incident on the second surface 22b at a critical angle of 26.5 ° becomes a light beam incident on the first surface 22a at an incident angle of approximately 88.2 °, and thus has a spread from the semiconductor laser 21. All of the divergent light beams are totally reflected by the second surface 22b. Therefore, the light from the semiconductor laser 21 that is refracted and transmitted through the first surface 22a can be received by the predetermined photodetector without causing a loss of light amount.

The diffraction element 23 is pupil-divided on the surface of the transparent substrate 23a opposite to the prism 22 by a division line parallel to the information track direction of the magneto-optical disk 31, that is, the x-axis direction. , 23c.
The hologram region 23b is formed in a concentric pattern so as to give different focal powers to the ± first-order diffracted lights, and the hologram region 23c is formed in a linear pattern.

The polarized light 3 emitted from the semiconductor laser 21
0, the hologram area 23b of the diffraction element 23,
The light that has entered the light source 23c is converted into a parallel light beam by the collimator lens 24, and the polarization direction is rotated by 90 ° by the half-wave plate 81, and spotted on the magneto-optical disk 31 by the objective lens 25. Irradiate in a shape.

The half-wave plate 81 is formed by bonding two birefringent crystal plates 81a and 81b such that their crystal axes are orthogonal to each other, as in the first embodiment.
This half-wave plate 81 is made of birefringent crystal plates 81a and 81b.
And at an angle of, for example, 3 ° with respect to the optical axis of the objective lens 25 in a direction substantially 45 ° with respect to the azimuthal direction of the crystal axis.

The return light reflected by the magneto-optical disk 31 passes through the objective lens 25, is again rotated by 90 ° in the polarization direction by the half-wave plate 81, and is incident on the diffraction element 23 through the collimator lens 24. Hologram area 23b
Are given different focal powers to the ± 1st-order diffracted light, and these ± 1st-order diffracted lights are received by a predetermined photodetector formed on the semiconductor substrate 27 via the parallel prisms 26-1 and 26-2. Also, the hologram area 23
Similarly, the ± first-order diffracted light diffracted by c is received by a predetermined photodetector formed on the semiconductor substrate 27 via the parallel prisms 26-1 and 26-2. Here, the parallel prisms 26-1 and 26-2 have, for example, respective thicknesses (heights).
Is d, and the refractive index is n.

Also, of the return light from the magneto-optical disk 31, each of the zeros in the hologram regions 23b and 23c is
The next light is incident on the polarizing film 30, and the return light transmitted through the polarizing film 30 is refracted and transmitted through the first surface 22a of the prism 22 to be separated into ordinary light and extraordinary light. The light is received by a predetermined photodetector formed on the semiconductor substrate 27 via the bottom surface 22c of the prism 22. The prism 2
The direction of the optical axis 22d of the uniaxial birefringent crystal constituting 2 is a direction substantially inclined by 45 ° with respect to the S-polarized light in a plane perpendicular to the optical axis of the return light. Further, the bottom surface 22c of the prism 22 is coated with an antireflection film in consideration of the refractive index of the adhesive used for joining the prism 22 and the semiconductor substrate 27, thereby preventing reflection on the bottom surface 22c of the prism 22. To do.

FIG. 8 is a plan view of the semiconductor substrate 27. This semiconductor substrate 27 has a semiconductor laser 21
Out of the polarizing film 30,
2, a photodetector 35 that receives light that is refracted and transmitted through the first surface 22a, totally reflected by the second surface 22b, and transmitted through the bottom surface 22c; The ± 1st-order diffracted light diffracted by the hologram area 23b of the diffraction element 23 is converted into parallel prisms 26-1 and 26-2.
, Photodetectors 36-1 and 36-2 that receive light through
The ± first-order diffracted light diffracted by the hologram region 23c is transmitted through the parallel prisms 26-1 and 26-2 to the photodetectors 37-1 and 37-2 and the hologram regions 23b and 23c by the 0-order light. Then, a photodetector 38 that receives the light that passes through the polarizing film 30 and is separated into ordinary light and extraordinary light by the prism 22 is formed. Further, in this embodiment, for example, stray light such as high-order diffracted light other than ± 1st-order diffracted light on the holograms 23b and 23c is transmitted to the photodetector 35
In order to prevent leakage to the outputs of 36-1, 36-2, 37-1, 37-2 and 38, a photodetector 39 is formed on almost the entire surface of the semiconductor substrate 27 other than the region where these detectors are formed. .

Here, the photodetector 35 is constituted by three light receiving areas 35a, 35b and 35c divided in the y-axis direction orthogonal to the information tracks of the magneto-optical disk 31. The photodetectors 36-1 and 36-2 are respectively divided into three divided light receiving areas 36a, 36b, and 3 divided by a dividing line in the y-axis direction.
6c; 36d, 36e, and 36f. Further, the photodetector 38 separates and receives the ordinary light and the extraordinary light by the prism 22, and thus receives the two light receiving regions 38a, 38a.
38b. Note that this photodetector 38 is
It is formed on the semiconductor substrate 27 so as to be located near the focal line position of astigmatism generated by the refraction of ordinary light and extraordinary light by the prism 22.

In this embodiment, of the return light from the magneto-optical disk 31, the + 1st-order diffracted light diffracted by the hologram area 23b is made incident on the photodetector 36-1, and the -1st-order diffracted light is incident on the photodetector 36-. 2 and its +1
The first-order diffracted light has a focal position before the photodetector 36-1, and the -1st-order diffracted light has a focal position behind the photodetector 36-2. Further, the + 1st-order diffracted light diffracted by the second hologram area 23c is made incident on the photodetector 37-1, and -1
The next-order diffracted light is made incident on the photodetector 37-2.

Further, in this embodiment, as shown in FIG. 6, a base 29 is fixed on a stem 41, and a set of components provided on the base 29, that is, a prism provided with a semiconductor laser 21 and a polarizing film 30 is provided. A cap 42 is provided on the stem 41 so as to cover a unit including the semiconductor substrate 27 on which the parallel prisms 26-1, 26-2, various photodetectors are formed, and the base 28.
After injecting nitrogen gas into the space surrounded by the cap 42 in 1, the upper part of the cap 42 is sealed with a sealing cover glass 43. The diffractive element 23 is provided with a sealing cover glass 4.
3. Mount on top.

The operation of this embodiment will be described below. In this embodiment, the linearly polarized light from the semiconductor laser 21 is
The first surface 22a of the prism 22 provided with the polarizing film 30 has S
Inject with polarized light. As described above, when the light is incident with S-polarized light, the polarizing film 20 has a reflectance of the S-polarized component of 50% or more,
Since the transmittance of the polarized light component is 80% or more, 50% or more of the light is reflected and enters the hologram regions 23b and 23c of the diffraction element 23 through the sealing cover glass 43. These hologram areas 23b, 23
The outgoing light from the semiconductor laser 21 that has entered the c.
The above is transmitted as the 0th-order light, and the 0th-order light is converted into parallel light by the collimator lens 24, and then the polarization direction is rotated by 90 ° by the half-wave plate 81, and the objective lens 25 rotates the light on the magneto-optical disk 31. Is irradiated as a spot.

The light from the semiconductor laser 21 transmitted through the polarizing film 30 passes through the prism 22 and is received by the photodetector 35 so that the output power of the semiconductor laser 21 becomes a desired power based on the output. Controlled. In this embodiment, the light receiving regions 35a, which are located on both sides from the peak position of the intensity distribution of the incident light incident on the photodetector 35,
The power of the light emitted from the semiconductor laser 21 is controlled by adding the outputs of 35c.

The return light reflected by the magneto-optical disk 31 is condensed again by the objective lens 25, and is returned to the half-wave plate 81.
The polarization direction is again rotated by 90 °, and the hologram areas 23b and 23 of the diffraction element 23 pass through the collimator lens 24.
c, 70% or more of the light is transmitted by the 0th-order light, and the remaining part becomes ± 1st-order diffracted light. Here, the hologram area 2
The + 1st-order diffracted light at 3b is reflected on the parallel prism 26-1 provided on the sealing cover glass 43 and the semiconductor substrate 27.
And focuses on the zero-order light in front of the photodetector 36-1 with an optical path difference of d × (n−1), and enters the light receiving regions 36a to 36c. The -1st-order diffracted light is
Similarly, the photodetector 36 transmits through the parallel prism 26-2 provided on the sealing cover glass 43 and the semiconductor substrate 27 and has an optical path difference of d × (n−1) with respect to the zero-order light.
Focusing on the back of -2, the light enters the light receiving regions 36d to 36f.

Similarly, the + 1st-order diffracted light in the hologram area 23c passes through the sealing cover glass 43 and the parallel prism 26-1, and is d × (n−) with respect to the 0th-order light.
The light enters the photodetector 37-1 with the optical path difference of 1), and -1
The second-order diffracted light passes through the sealing cover glass 43 and the parallel prism 26-2, and is d × (n−
The light enters the photodetector 37-2 with the optical path difference of 1).

Therefore, the focus error signal FES
Output the respective outputs of the light receiving areas 36a to 36f from Ia to
If 1f, the beam size method can be used to obtain FES = (Ia + 1e + 1c)-(1d + Ib + 1f). Assuming that the outputs of the photodetectors 37-1 and 37-2 are I1 and I2, the tracking error signal TES is TES = (Ia + Ib + 1c + 1d + 1e + 1f)-by the push-pull method.
(I1 + I2).

The hologram areas 23b and 23c are set to 0
The return light from the magneto-optical disk 31 transmitted by the next light enters the polarizing film 30 again through the sealing cover glass 43. Here, since information is recorded on the magneto-optical disk 31 as the direction of magnetization, the polarization direction of the return light reflected by the magneto-optical disk 31 slightly rotates in the opposite direction according to the direction of magnetization. It will be. Therefore, the return light from the magneto-optical disk 31 incident on the polarizing film 30 again contains a P-polarized component. Due to the action of the polarizing film 30, less than 50% of the S-polarized light component is refracted and transmitted through the first surface 22a of the prism 22, and 80% or more of the P-polarized light component of the return light from the magneto-optical disk 31 is reflected by the prism 22. The light is refracted and transmitted through the first surface 22a, is separated into ordinary light and extraordinary light by the action of the uniaxial birefringent crystal, and is emitted from the bottom surface 22c of the prism 22.

The ordinary light and the extraordinary light emitted from the bottom surface 22c of the prism 22 are refracted and transmitted through the first surface 22a of the prism 22, thereby generating astigmatism and coma. Light receiving area 3 of photodetector 38 arranged near the position where abnormal light forms an image in the form of a focal line
8a and the light receiving region 38b. Here, the optical axis 22d of the uniaxial birefringent crystal constituting the prism 22 is substantially 45 ° inclined with respect to the S polarization direction in a plane perpendicular to the optical axis of the return light from the magneto-optical disk 31. Therefore, the polarization direction of the return light changes its angle with respect to the optical axis 22d, and the intensity of the ordinary light and the extraordinary light changes. Therefore, this intensity change is reflected in the light receiving regions 38a,
If detected at 38b, a magneto-optical signal corresponding to the information recorded on the magneto-optical disk 31 can be obtained. That is, assuming that outputs of the light receiving areas 38a and 38b of the photodetector 38 are Ja and Jb, the magneto-optical signal S can be obtained by S = Ja-Jb.

According to this embodiment, a half-wave plate 81 is formed by bonding two birefringent crystal plates 81a and 81b such that their crystal axes are orthogonal to each other.
The two-wavelength plate 81 is set at an angle of approximately 45 ° with respect to the azimuthal direction of the crystal axes of the birefringent crystal plates 81a and 81b, and the objective lens 25 is
波長 wavelength plate 81
Can be effectively prevented from entering the semiconductor laser 21 and various photodetectors disposed in the vicinity thereof as stray light, and the phase reflected by the half-wave plate 81 can be effectively prevented. Deviation can be effectively prevented. Therefore, it is possible to effectively prevent the occurrence of offset or noise due to stray light in the signal to be detected, and also to effectively prevent the deterioration of the magneto-optical signal due to the phase shift, thereby obtaining a magneto-optical signal having a high C / N. Can be.

Furthermore, in this embodiment, the half-wave plate 81 changes the polarization direction of the linearly polarized light from the semiconductor laser 21 to 90 degrees so that the polarization direction is parallel to the information track of the magneto-optical disk 31. Rotate °° magneto-optical disk 3
In this case, the tracking error signal having a modulation degree twice or more as compared with the case where the polarization direction is set to the direction orthogonal to the information track can be detected. Therefore, high-accuracy tracking servo becomes possible.

It should be noted that the present invention is not limited only to the above-described embodiment, and various modifications or changes can be made. For example, in the first embodiment, the diffraction grating 4
The beam splitter 5 and the beam splitter 5 are also arranged to be inclined with respect to the optical axis. However, only the quarter-wave plate 71 can be inclined with respect to the optical axis as described above. Even in this case, the C / N can be sufficiently improved. Further, in the first embodiment, the beam splitter 5 can be a polarization beam splitter. This makes it possible to further reduce the incidence of unwanted return light on the semiconductor laser 2.

Further, the configuration shown in FIG.
Similarly to the second embodiment, an optical pickup that reads a magneto-optical signal from a magneto-optical recording medium can be configured. That is, in FIG. 1, the quarter-wave plate 71 is omitted, and the return light reflected by the beam splitter 5 passes through the half-wave plate and is incident on, for example, a light analyzing means composed of, for example, a polarizing beam splitter to be orthogonal. The light is separated into polarized light components, each of the polarized light components is received by a photodetector, and a magneto-optical signal is obtained based on a difference between the output signals. Here, 1/2
The wave plate is formed by bonding two birefringent crystal plates so that their crystal axes are orthogonal to each other, as in the embodiment described above, and has a direction substantially 45 ° with respect to the azimuthal direction of the crystal axes. Then, it is disposed at an angle of, for example, 3 ° with respect to the optical axis. Further, in order to control the output power of the semiconductor laser 2, the photodetector is tilted with respect to the optical axis so as to receive a part of the output beam from the semiconductor laser 2 reflected by the beam splitter 5 on the outward path. Place. With this configuration, it is possible to effectively prevent an undesired reflected light beam reflected on the surface of the half-wave plate from entering the photodetector for controlling the output power of the semiconductor laser 2 via the beam splitter 5. The output power of the semiconductor laser 2 can be stably controlled to a desired value, and the occurrence of a phase shift in the half-wave plate can be prevented.
A good magneto-optical signal can be obtained.

Further, the present invention relates to, for example,
As disclosed in Japanese Unexamined Patent Application Publication No. 6534, in the configuration described in the above modification, a 板 wavelength plate is used instead of the 波長 wavelength plate, thereby detecting a change in the elliptically polarized state of the return light. The present invention can be effectively applied to an optical pickup for obtaining a magneto-optical signal. Also in this case, the quarter-wave plate is formed by bonding two birefringent crystal plates so that their crystal axes are orthogonal to each other as in the above-described embodiment, and the azimuthal direction of the crystal axes is set. The same effect can be obtained by arranging at an angle of about 45 ° to the optical axis with respect to the optical axis.

Furthermore, in the above-described embodiments and modifications, the birefringent crystal plate constituting the wave plate is not limited to quartz, but may be made of lithium niobate, rutile, calcite, or the like.

In the first embodiment and the above-mentioned modified examples, the beam separating means is not limited to a beam splitter formed by bonding prisms, but may be a parallel plate having a dielectric multi-layer film provided on one surface or a hologram. It can also be configured with a diffractive optical element including the same. Further, in the first embodiment and the above-described modified examples, the semiconductor laser and the photodetector may be arranged adjacent to each other by appropriately reflecting the return light separated by the beam separating means. it can.

[0050]

According to the first aspect of the present invention, a wave plate is formed by bonding two birefringent crystal plates so that their crystal axes are orthogonal to each other. In the optical path between the objective lens and the azimuth direction of the crystal axis, it is arranged at an angle of approximately 45 ° to the optical axis of the objective lens. Undesired return light and stray light incident on the photodetector can be effectively prevented, and undesired phase shift in the wave plate can be effectively prevented.
A read signal with a high C / N can be obtained.

According to the third aspect of the present invention, a wave plate is formed by bonding two birefringent crystal plates so that their crystal axes are orthogonal to each other. The return light from the laser beam is separated into polarization components orthogonal to each other, and the light is guided to the photodetector, and the light emitted from the semiconductor laser is guided to the optical recording medium via the objective lens, and the reflected light from the optical recording medium is reflected. In the optical path between the beam splitter leading to the analyzing means and in the direction substantially 45 ° with respect to the azimuthal direction of the crystal axis, it is arranged at an angle to the optical axis. While effectively preventing the occurrence of displacement,
On the outward path, when a part of the output beam from the semiconductor laser reflected by the beam splitter is received by the photodetector to control the output power of the semiconductor laser, an undesired reflected light beam reflected on the surface of the wave plate Can be effectively prevented from being incident on the photodetector for controlling the output power. Therefore, a magneto-optical signal having a high C / N can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a perspective view showing a configuration of a quarter wavelength plate shown in FIG.

FIG. 3 is a diagram for explaining the occurrence of a phase shift due to a quarter-wave plate.

FIG. 4 is also a diagram for explaining the occurrence of a phase shift.

FIG. 5 is a view showing an experimental result of a phase shift.

FIG. 6 is a perspective view showing a second embodiment of the present invention.

FIG. 7 is a partial side view of FIG. 6;

8 is a plan view of the semiconductor substrate shown in FIG.

FIG. 9 is a diagram for explaining a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 High frequency module 2 Semiconductor laser 3 Collimator lens 4 Diffraction grating 5 Beam splitter 6 Mirror 8 Objective lens 9 Optical disk 10 Condensing lens 11 Photodetector 21 Semiconductor laser 22 Prism 23 Diffraction element 23b, 23c Hologram area 24 Collimator lens 25 Objective lens 26 -1,26-2 Parallel prism 27 Semiconductor substrate 28 units 29 Base 30 Polarizing film 31 Magneto-optical disk 35,36-1,36-2,37-1,37-2,3
8, 39 Photodetector 41 Stem 42 Cap 43 Sealing cover glass 71 1/4 wavelength plate 71a, 71b Birefringent crystal plate 81 1/2 wavelength plate 81a, 81b Birefringent crystal plate

Claims (4)

[Claims] 1. An optical pickup in which light emitted from a semiconductor laser is applied to an optical recording medium via an objective lens and reflected light is received by a photodetector. In the optical path, a wave plate formed by bonding two birefringent crystal plates so that their crystal axes are orthogonal to each other is provided at a direction of approximately 45 ° with respect to the azimuthal direction of the crystal axes. An optical pickup characterized by being arranged at an angle to an optical axis. 2. The optical pickup according to claim 1, wherein the optical pickup is disposed in an optical path between the semiconductor laser and the objective lens, and guides light emitted from the semiconductor laser to the optical recording medium via the objective lens. A beam separating unit that guides reflected light from the optical recording medium to the photodetector through the objective lens, and the wavelength plate is disposed in an optical path between the beam separating unit and the objective lens. An optical pickup characterized in that: 3. A light emitted from a semiconductor laser is applied to an optical recording medium through an objective lens, and the reflected light is separated into polarization components orthogonal to each other by a light detecting means and received by a photodetector. In an optical pickup configured to detect a magneto-optical signal based on an output of a detector, the optical pickup is disposed in an optical path between the semiconductor laser and the objective lens, and emits light from the semiconductor laser through the objective lens. It has a beam separating means for guiding the optical recording medium to the light reflected by the optical recording medium to the light detecting means, and in a light path between the beam separating means and the light detecting means,
A wave plate formed by bonding two birefringent crystal plates so that their crystal axes are orthogonal to each other is disposed at an angle of approximately 45 ° with respect to the azimuthal direction of the crystal axes and inclined with respect to the optical axis. An optical pickup characterized by the following. 4. The optical pickup according to claim 1, wherein at least the semiconductor laser and the photodetector are arranged adjacent to each other in one unit.