JPH09212910A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup compatible with multiple kinds of optical disks including the magneto-optical disk, capable of leading an optical beam in high efficiency to an objective lens corresponding to an optical disk in use, and of obtaining a sufficient C/N in the case of detecting a magneto-optical signal. SOLUTION: A lens holder 6 is loaded with two objective lenses 4, 5. A polarizing beam splitter 22 is set to have different reflectances and transmittances according to p polarization or s polarization. A laser beam transmitted through the polarizing beam splitter 22 is entered into the objective lens 4 to focus on a magneto-optical disk, and a laser beam reflecting on the polarizing beam splitter 22 is entered into the objective lens 5 to focus on an optical disk other than the magneto-optical disk.

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 in an optical disc device, and more particularly to an optical pickup used in a plurality of types of optical discs having different substrate thicknesses.

[0002]

2. Description of the Related Art In recent years, optical disk devices are often used as large-capacity recording / reproducing devices. This optical disk device usually includes a light source that emits a light beam, an objective lens that converges the light beam and emits the light beam to an optical disc that is an optical recording medium, an optical system that guides the light beam to the objective lens, and a recording surface of the optical disc. The optical pickup is equipped with an objective lens drive mechanism that moves the objective lens in a direction perpendicular to the direction (hereinafter referred to as the focusing direction) and a radial direction of the optical disk (hereinafter referred to as the tracking direction).

FIG. 20 is a perspective view showing the structure of a conventional optical pickup, particularly an optical pickup applied to a magneto-optical recording medium. Examples of the magneto-optical recording medium include a mini disk (MD). The conventional optical pickup shown in FIG. 20 includes a light source 115 such as a semiconductor laser that emits a light beam, an objective lens 102 that focuses the light beam on an optical disc, and an optical system that guides the light beam from the light source 115 to the objective lens 102. Have

In the conventional optical pickup, as shown in FIG. 20, one objective lens 102 is a lens holder 103.
And is moved in the focusing direction and the tracking direction by the objective lens driving device 101. Substrates 104 are attached to both side surfaces of the lens holder 103, and the lens holder 103 is mounted on the substrate 104.
One end 108 a of an elastic body 108 that supports the base 107 so as to be movable in the focusing direction and the tracking direction with respect to the base 107 is fixed by a solder 109. The other end 108b of the elastic body 108 is fixed to the substrate 110 fixed to the base 107 with solder 111. The objective lens driving device 101 is provided with a focusing coil 105, a tracking coil 106, and a permanent magnet 113, which are fixed to a hole in the center of the lens holder 103, and a current can be passed through the coils 105 and / or 106. Thus, the objective lens 102 is moved in the focusing direction and / or the tracking direction by the interaction between the magnetic field and the electric current.

The objective lens driving device 101 further includes an objective lens 102 in the focusing direction and / or
Alternatively, a damper material 112 that suppresses resonance that may occur when moving in the tracking direction and a stopper 114 are provided.

As the light source 115, for example, one having a semiconductor laser and a photodetector (not shown) for detecting a servo signal therein may be used. The movement of the objective lens 102 in the focusing direction and the tracking direction is controlled based on the servo signal detected by the photodetector.

As described above, one objective lens 102 is mounted on the lens holder 103 of this optical pickup, and a standing beam for bending the light beam P from the light source 115 toward the objective lens 102 is provided below the objective lens 102. Lifting mirror 11
There is only one 6 placed. On the optical path from the light source 115 to the raising mirror 116, as shown in FIG. 20, a collimating lens 117 for making the light beam P parallel light, and a part thereof depending on the polarization of the incident light. Polarization beam splitter 118 that transmits and reflects the rest
And are arranged. In this example, the polarization beam splitter 118 is set to transmit about 80% of p-polarized light and reflect about 100% of s-polarized light. The light reflected by the polarization beam splitter 118 enters the monitoring photodetector 119, and the output of the light source 115 is monitored based on the signal detected here.

Next, the principle of detecting a magneto-optical signal using the optical pickup shown in FIG. 20 will be described with reference to FIG.

The semiconductor laser in the light source 115 emits a linearly polarized light beam P, here p polarized light. When the light beam P enters the polarization beam splitter 118, about 20% of the light beam P is reflected and enters the photodetector 119 for monitoring, and the remaining about 80% is transmitted through the polarization beam splitter 118 and passes through the rising mirror 116. It is incident on an optical disc (not shown) via the optical disc. Here, the optical disk is a magneto-optical recording medium.

The light beam reflected by the optical disk returns to the polarization beam splitter 118 with its polarization direction slightly rotated by the Kerr effect (that is, with a slight s-polarization included). At this time, the rotation angle of the polarization direction corresponds to the signal recorded at the position on the optical disc where the light beam is incident.

Since the reflectance of the polarization beam splitter 118 for p-polarized light is about 20% and the reflectance for s-polarized light is almost 100%, only the p-polarized component is reduced in the light beam reflected by the polarization beam splitter 118. As a result, the rotation angle of the polarization direction increases. The light beam with the increased rotation angle in the polarization direction is incident on the Wollaston prism 120, and is split into two light beams according to the polarization direction. The two light beams from the Wollaston prism 120 enter the photodetector 124 via the reflection mirror 121, the spot lens 122, and the reflection mirror 123.
Using these two light beams, a magneto-optical signal, that is, a signal recorded at the position where the light beam is incident, is detected.

By the way, the optical disc can be reproduced only as typified by a compact disc (CD), the write once type can be recorded only once, the magneto-optical system and the phase change system. There are various types such as those that can be recorded and erased any number of times. Further, in these optical discs, recently, there is a demand for higher capacity and higher density. In order to satisfy these requirements, the spot diameter may be reduced by shortening the wavelength of the light source and increasing the numerical aperture NA of the objective lens. When the NA is increased, the thickness of the disk substrate may be reduced so that the influence of the disk skew on the crosstalk and the tracking servo is reduced.

However, the optical pickup shown in FIG. 20 is designed to be used for an optical disc having a certain substrate thickness and a certain refractive index. In particular, the optical characteristics such as the focal length of the objective lens are designed in consideration of the thickness and the refractive index of the substrate of the optical disc. Therefore, if any of these changes from the values at the time of design, it will cause aberration. However, it becomes impossible to focus the light beam on the optical disk in an appropriate focus state (including the size of the light spot). Therefore, the optical pickup as shown in FIG. 20 cannot be used except for the optical disc having the substrate thickness and the refractive index which were taken into consideration when designing the objective lens.

In order to solve this problem, a method is known in which two objective lenses are mounted on the movable portion of the objective lens driving device, and the objective lenses are selectively used according to the type of the disk (Japanese Patent Laid-Open No. 6-333255). Hereinafter, referred to as a first conventional example). In this example, a beam separation mirror having two mirror surfaces is arranged below the two objective lenses, a mirror surface on the side closer to the light source is a half mirror, and the other is a reflection mirror. As a result, the light beam that has entered the beam separation mirror enters the two objective lenses.

An optical pickup for detecting a magneto-optical signal having two objective lenses is also known (Japanese Patent Publication No. 63-
No. 60451, hereinafter referred to as a second conventional example). In this example, the polarization direction of the light beam entering the polarization beam splitter is switched by inserting / removing the ½ wavelength plate into / from the optical path, and the magneto-optical signal is detected using the light beam reflected by the polarization beam splitter. A signal can be recorded on a magneto-optical disk by using a light beam that passes through a polarization beam splitter.

[0016]

However, in the first conventional example, no reference is made to the detection of the magneto-optical signal. When the first conventional example is applied to the magneto-optical disk, since the half mirror is used as the beam separating means, there is a problem that the effect of increasing the Kerr rotation angle cannot be obtained and a sufficient C / N cannot be obtained. Further, since the half mirror is used, the loss of the light amount in the reciprocating optical path becomes large.

In the second conventional example, detection of a magneto-optical signal is described, and the polarization direction is switched by inserting / removing the ½ wavelength plate into / from the optical path. for that reason,
Although there is no loss in the amount of light on the outward path, the two light beams separated correspond to the same magneto-optical disk. It is not possible to use different types of discs, for example discs with different substrate thickness or refractive index. Further, the light beam for detecting the magneto-optical signal is not reflected by the disc and then returns to the polarization beam splitter to detect the signal. Instead, a half mirror is arranged in the middle of the optical path to separate the light beam. The part is divided, and a signal is detected by the divided light beam. Therefore, there is a problem that the number of parts is increased and the effect of increasing the car rotation angle is not obtained.

The present invention has been made to solve the above-mentioned problems, and its object is to support a plurality of types of optical discs including a magneto-optical disc, and to provide a highly efficient objective lens suitable for the optical disc to be used. Can guide the light beam and is sufficient for detecting a magneto-optical signal.
It is to provide an optical pickup capable of obtaining / N.

[0019]

An optical pickup according to the present invention is an optical pickup for irradiating a first recording medium and a second recording medium with light, the first recording medium and the second recording medium. At least one of the thickness and the refractive index of the substrate is different in the medium, and the optical pickup receives the light and the light source that emits the light, and the optical pickup receives the light according to the polarization direction of the light. A polarization beam splitter that reflects at least a part of the light and transmits the remaining light, a first objective lens that converges the light reflected by the polarization beam splitter, and a first objective lens that converges the light transmitted by the polarization beam splitter. And two objective lenses, the first
The objective lens is designed according to the first recording medium, and the second objective lens is designed according to the second recording medium, thereby achieving the above object.

Preferably, the polarization beam splitter has different reflectances and transmittances for the first linearly polarized light and the second linearly polarized light, and the polarization direction of the first linearly polarized light and the first linearly polarized light are different from each other. The polarization directions of the two linearly polarized lights are orthogonal to each other.

More preferably, the light emitted from the light source is first linearly polarized light, and the transmittance of the polarization beam splitter for the first linearly polarized light is 60%.
It is 80% or less, and the reflectance of the polarization beam splitter with respect to the second linearly polarized light that is polarized in the direction orthogonal to the first linearly polarized light is 95% or more.

At least one of the first recording medium and the second recording medium may be a recording medium other than the magneto-optical recording medium.

One of the first recording medium and the second recording medium may be a magneto-optical recording medium.

In one embodiment, the first objective lens and the second objective lens are arranged substantially in the radial direction of the first recording medium or the second recording medium.

In another embodiment, the optical pickup receives light reflected by the first recording medium or the second recording medium, and outputs a signal according to the reflected light. And a first optical element arranged between the light source and the polarization beam splitter to change the polarization direction of the light, wherein the light reflected by the recording medium is the polarization beam splitter. Is incident on the photodetector via. The first optical element is 1/2
It may be a wave plate. Alternatively, the first optical element may be a liquid crystal panel having a twisted nematic liquid crystal layer.

In still another embodiment, the optical pickup further includes a second optical element that changes the polarization state of the light, the second optical element including the polarization beam splitter and the first optical element. Or the second objective lens, or between the polarizing beam splitter and the second objective lens. Preferably, the polarization beam splitter has different transmittances and reflectances for the first linearly polarized light and the second linearly polarized light whose polarization directions are orthogonal to each other, and the second optical element is 1 / It is a four-wave plate,
The crystal axis direction of the quarter-wave plate is set at 45 ° with respect to the first linearly polarized light and the second linearly polarized light.

In still another embodiment, the optical pickup further includes a second optical element that changes the polarization state of the light, the second optical element including the polarization beam splitter and the first optical element. It is arranged between the objective lens or between the polarization beam splitter and the second objective lens. Preferably, the polarization beam splitter has different transmittances and reflectances for the first linearly polarized light and the second linearly polarized light whose polarization directions are orthogonal to each other, and the second optical element is 1 / It is a four-wave plate, and the crystal axis direction of the quarter-wave plate is set at 45 ° with respect to the first linearly polarized light and the second linearly polarized light.

[0028] In still another embodiment, the reflectance of the polarization beam splitter for the first linearly polarized light is smaller than the reflectance for the second linearly polarized light, and the second optical element is It is movably disposed between the splitter and the second objective lens on which the light reflected by the polarization beam splitter is incident, and when the second linearly polarized light is incident on the polarization beam splitter, The second optical element is removed from the optical path between the polarization beam splitter and the second objective lens. More preferably, the polarization beam splitter has different transmittances and reflectances for the first linearly polarized light and the second linearly polarized light whose polarization directions are orthogonal to each other, and the first optical element is 1 1/2 wavelength plate, the second optical element is a 1/4 wavelength plate, and the crystal axis direction of the 1/4 wavelength plate is relative to the first linearly polarized light and the second linearly polarized light. The direction is set to 45 °, and the first optical element and the second optical element are mechanically movable by the same drive source.

In still another embodiment, the optical pickup receives the light reflected by the first recording medium and the light reflected by the second recording medium, and a signal corresponding to the reflected light. Is provided on the optical path between the first objective lens and the polarization beam splitter, or on the optical path between the second objective lens and the polarization beam splitter, And an optical element that converts the polarization direction of the light reflected by the first recording medium or the light reflected by the second recording medium, the optical element being a quarter-wave plate. , Its crystal axis direction is the amount of light when the light reflected by the first recording medium enters the photodetector, and the light beam reflected by the second recording medium enters the photodetector. and when As the amount of light and are substantially equal, are set.

Preferably, the light reflected by the first recording medium and the light reflected by the second recording medium are guided to the photodetector via the polarization beam splitter, and the photodetector is introduced. Has a first photodetector section for receiving a part of the reflected light reflected by the polarization beam splitter, and a second photodetector section for receiving a part of the reflected light transmitted through the polarization beam splitter. The amount of light received by the first photodetector is substantially the same when the light reflected by the first recording medium is incident and when the light reflected by the second recording medium is incident. Are equal to each other, and the light amounts of the portions received by the second photodetector are when the light reflected by the first recording medium is incident and when the light reflected by the second recording medium is incident. And substantially To be equal, the direction of the crystal axis of the quarter-wave plate is set.

In still another embodiment, the optical pickup further comprises a levitation type magnetic head for applying a magnetic field to the magneto-optical recording medium, the magnetic head having a core portion for generating the magnetic field, And a slider part that supports the core part and that is levitated by an airflow generated by the rotation of the magneto-optical recording medium, and the first objective lens and the second objective lens are the first objective lens and the second objective lens. The one of the first objective lens and the second objective lens, which corresponds to the magneto-optical recording medium, is arranged substantially in the tangential direction of the recording medium or the second recording medium. The center and the center of the core of the magnetic head are arranged so as to substantially coincide with each other, and the other lens is provided with respect to the objective lens corresponding to the magneto-optical recording medium.
It is located upstream of the air flow.

The operation will be described below.

A polarizing beam splitter for increasing the Kerr rotation angle and a prism for splitting and splitting a light beam into two objective lenses are also used, and the number of parts is small.
It can be applied to a plurality of types of optical discs including magneto-optical discs, and a sufficient C / N can be obtained in the case of magneto-optical signal detection.

Using the objective lens for the magneto-optical disk,
Since it can be applied to recording media having the same substrate thickness and refractive index other than the magneto-optical disk, it can be applied to three or more types of optical disks.

The polarization beam splitter has a p-polarized light transmittance of 60 to 80% and an s-polarized light reflectance of 95%.
Since it is set to ~ 100%, the Kerr rotation angle can be increased when detecting a magneto-optical signal, and
The incident light quantity of the light beam on the second objective lens applied to an optical recording medium other than the magneto-optical disk can be set to an appropriate value. Further, in this case, since the first objective lens arranged at the end of the optical pickup is used for the magneto-optical disk, it is difficult to increase the density as compared with the read-only type optical disk. On the other hand, there is a possibility that it can be used on the inner side.

Since the polarization direction conversion element is provided between the light source and the polarization beam splitter, when the light beam is incident on the objective lens which is applied to the optical recording medium other than the magneto-optical disk, the light beam By switching the polarization direction of, it is possible to eliminate the loss of light quantity.

Or remove the half-wave plate from the optical path,
By rotating the light beam by a predetermined angle, the polarization direction of the light beam incident on the polarization beam splitter can be switched, and the light beam can be efficiently incident on the objective lens applied to the optical recording medium other than the magneto-optical disk. be able to.

Since the polarization direction of the light beam is switched using the liquid crystal panel having the TN liquid crystal layer, a drive mechanism for switching is not required.

Since the polarization state conversion element is arranged between the polarization beam splitter and the objective lens applied to the optical recording medium other than the magneto-optical disk, the first objective lens records and reproduces data on the magneto-optical disk. , An unnecessary light beam which is incident on the second objective lens applied to an optical recording medium other than the magneto-optical disk when erasing is reflected by the disk and returned to the magneto-optical signal detection system. Can be prevented.

Since the quarter-wave plate is used as the polarization state conversion element, a driving mechanism or the like is not required to convert the polarization state, and the polarization direction is converted by passing back and forth through the quarter-wave plate. Therefore, it is possible to prevent the reflected light from the unnecessary disc, which has passed through the objective lens, which is applied to the optical recording medium other than the magneto-optical disc, from returning to the magneto-optical signal detection system.

Since the polarization direction conversion element and the polarization state conversion element are controlled in conjunction with each other, it is possible to prevent an unnecessary light beam from returning to the magneto-optical signal detection system, and to apply it to an optical recording medium other than the magneto-optical disk. The light beam can be efficiently incident on the objective lens to which it is applied.

When the first objective lens is used, since the polarization state conversion element is put in the optical path, it is possible to prevent an unnecessary light beam from returning to the magneto-optical signal detection system and to use the second objective lens. In this case, since the polarization conversion element is removed from the optical path, the reflected light from the disc can be efficiently returned to the hologram laser. Further, since the polarization state conversion element is arranged between the second objective lens and the polarization beam splitter, the polarization direction conversion element is arranged more than when it is arranged between the first objective lens and the polarization beam splitter. The distance between and becomes shorter, and the interlocking drive becomes easier.

A half-wave plate which is a polarization direction conversion element,
Since the polarization state conversion element and the polarization state conversion element are driven by the same drive source, the drive mechanism is simplified.

Since the quarter-wave plate is used as the polarization state conversion element, a driving mechanism or the like is not required to convert the polarization state, and the number of parts can be reduced. Also,
Since the crystal axis direction of the quarter-wave plate is set so that the light beams reflected by the two types of recording media are incident on the photodetector with substantially the same light amount, the crystal axis direction of the two types of recording media is Even when recording, reproducing, or erasing is performed by using the same method, it is not necessary to switch the laser power or the gain of the photodetector.

Further, the crystal axis direction of the quarter-wave plate is set so that the light beams reflected by the two types of recording media are incident on the two types of photodetectors with substantially the same light amount. It is not necessary to switch the laser power when recording, reproducing or erasing any of the two types of recording media, and it is not necessary to switch the gain for either photodetector.

The optical pickup of the present invention is equipped with a magnetic head having a slider portion capable of flying. A taper part is provided on the slider part, and this taper part is
By arranging it between the two objective lenses and near the line passing through the center of the disc, stable levitation is possible.

[0047]

DETAILED DESCRIPTION OF THE INVENTION An optical pickup of the present invention will be described below with reference to the drawings. Throughout the drawings, the same components are designated by the same reference numerals.

The optical pickup of the present invention comprises two objective lenses and a polarizing beam splitter having a reflectance and a transmittance which differ depending on the polarization direction. The two objective lenses are composed of a substrate thickness and a refractive index. It is designed for two types of optical discs, at least one of which is different. At least one of the two types of optical disks may be a disk other than the magneto-optical disk, and the other may be a magneto-optical disk or another optical disk. In each of the embodiments described below, one objective lens is designed corresponding to a magneto-optical disk having a substrate thickness of 1.2 mm and a refractive index of 1.55, and the other objective lens is a substrate. An example designed for an optical disc having a thickness of 0.6 mm and a refractive index of 1.55 will be described.

(First Embodiment) FIG. 1 is an exploded perspective view showing a structure of a first embodiment of an optical pickup according to the present invention. FIG. 2 is a plan view showing the structure of the objective lens driving device in FIG. FIG. 3 is a cross-sectional view taken along the line AA of FIG. 2, and also shows a prism corresponding to each objective lens arranged below the objective lens.

The optical pickup 1 comprises an objective lens driving device 2 and an optical system 3, which are mounted in a housing (not shown). Objective lens driving device 2
Is provided with two objective lenses 4 and 5 for converging the light beam and irradiating the recording medium with the converged light.
The two objective lenses 4 and 5 are designed to support different types of optical disks as described above,
The specifications are different. Here, the objective lens 4 is used for a magneto-optical disk, and the objective lens 5 is used for an optical disk other than the magneto-optical disk. Here, the “specification” of the objective lens means a numerical aperture (NA), a focal length, a corresponding cover glass thickness, and the like. Further, the "substrate" of the optical disk refers to a material through which a writing / reading light beam passes.
Therefore, the "substrate thickness" means the distance from the surface of the optical disc on the objective lens side to the recording film.

The movable portion of the objective lens driving device 2 includes objective lenses 4 and 5, a lens holder 6 for holding the objective lenses 4 and 5, a substrate 7 attached to both side surfaces of the lens holder 6, and a lens holder 6. The focusing coil 8 and the tracking coil 9 are fixed to the recesses at both ends of the. Elastic bodies 11 for movably supporting the lens holder 6 with respect to the base 10 in the focusing direction and the tracking direction are arranged above and below the side surface of the substrate 7. One end 11a of the elastic body 11 is
It is fixed to the substrate 7 by the solder 12, and the other end 11 b of the elastic body 11 is fixed to the substrate 14 by the solder 13. A damper material 15 is fixed to a root portion of the elastic body 11 near one end 11b thereof, which serves to suppress resonance of the elastic body 11.

A substantially U-shaped yoke 1 is provided on the base 10.
6 is placed, and the permanent magnet 1 is attached to one wall surface of the yoke 16.
7 is fixed. The substrate 14 is fixed via the spacer 18 to the standing portion 10a from the base 10 with the fixing screw 1
9. A part of the focusing coil 8 and the tracking coil 9 is a magnetic gap 20 of a magnetic circuit 20 formed by a yoke 16 and a permanent magnet 17.
The terminals of the focusing coil 8 and the tracking coil 9 which are arranged in a.
It is electrically connected to the substrate 14.

In the objective lens driving device 1 having such a structure, when a current is applied to the focusing coil 8 and the tracking coil 9, the focusing direction (that is, the direction parallel to the optical axis of the light beam) and the tracking direction (that is, the direction). The movable part can be driven independently in the radial direction of the optical disk.

The optical system 3 includes a reflection mirror 21, a polarization beam splitter 22, a hologram laser 23, a collimator lens 24, a Wollaston prism 25, and a reflection mirror 2.
6, a spot lens 27, a reflection mirror 28, and a photodetector 29. The reflection mirror 21 and the polarization beam splitter 22 are arranged below the objective lenses 4 and 5, respectively.

FIG. 4 is a perspective view showing the structure of the hologram laser 23.

As shown in FIG. 4, the hologram laser 23 comprises a semiconductor laser 30 and a photodiode 31 housed in one package 32. A glass substrate 35 having a hologram element 33 and a diffraction grating 34 formed on both surfaces is fixed to the upper surface of the package 32. The light beam emitted from the semiconductor laser 30 is
The diffraction grating 34 divides the main beam and two sub-beams into a total of three beams. The three beams enter the hologram element 33 and are transmitted as zero-order light.
The light beam thus emitted from the hologram laser 23 passes through the other optical elements of the optical system 3 and is applied to the optical disc. Further, a part of the light beam reflected by the optical disk returns to the hologram element 33 through the same route and is diffracted. Photodiode 3 having a detection surface in which one of the first-order diffracted lights of the diffracted lights is divided into five
1 and the servo signal including the focus error signal and the tracking error signal is detected based on this.

FIG. 5 is a diagram showing the relationship between the shape of the diffraction region of the hologram element 33 and the arrangement of the detection surface of the photodiode 31.

The hologram element 33 has two diffraction areas 36 and 37 having different grating periods. Of the reflected light of the main beam, the light incident on one area 36 is focused on the dividing line between the photodetectors D ₂ and D ₃ , and the light incident on the other area 37 is focused on the photodetector D _4. . In addition, the reflected light of the sub-beams is condensed on the photodetectors D ₁ and D ₅ , respectively. Here, the photodetector D of the five-division photodiode 31
_When the outputs from _{1 to} D ₅ are S _{1 to} S ₅ , respectively, the focus error signal FES is given by FES = S ₂ −S ₃ (1). The tracking error signal TES is detected by the so-called three-beam method, and is given by TES = S ₁ -S ₅ (2). By using these focus error signal FES and tracking error signal TES, the position control of the objective lens in the focusing direction and the position control of the objective lens in the tracking direction can be performed.

If the output from the photodiode 31 is used, it is also possible to obtain a reproduction signal of an optical disc (that is, an optical disc other than the magneto-optical disc) of the type that detects the intensity of reflected light. In this case, the reproduction signal RF is given by RF = S ₂ + S ₃ + S ₄ (3)

FIG. 6 is a side view showing a split state of the light beam. With reference to FIG. 6, the operation of causing the light beam to enter the two objective lenses 4 and 5 and the detection of the magneto-optical signal will be described.

The p-polarized light beam emitted from the hologram laser 23 is converted into parallel light by the collimator lens 24 and enters the polarization beam splitter 22. The polarization beam splitter 22 is designed to have a transmittance of about 80% for p-polarized light and a reflectance of about 100% for s-polarized light. Therefore, about 80% of the p-polarized light beam that is collimated by the collimator lens 24 passes through the polarization beam splitter 22, is reflected by the reflection mirror 21, and enters the objective lens 4. on the other hand,
About 20% of the p-polarized light beam entering the polarization beam splitter 22 enters the objective lens 5.

When the optical disk 41 is a magneto-optical disk, the lens designed accordingly, that is, the objective lens 4 is used. The light beam applied to the recording surface of the magneto-optical disc 41 by the objective lens 4 undergoes the Kerr effect and its polarization direction changes slightly (that is, with a slight s-polarized component), and the polarization beam splitter 22 Come back to. At this time, the reflectance of the p-polarized component in the polarization beam splitter 22 is about 20%, and s
The reflectance of the polarized component is about 100%. Therefore, in the light beam reflected by the polarization beam splitter 22, the p-polarized component is reduced and the s-polarized component is hardly reduced.
The rotation angle of the polarization direction increases.

The Wollaston prism 25 converts the light beam with the increased rotation angle into four beams for p-polarized light and s-polarized light.
It is divided into two light beams having an angle component of 5 °. 2
The light beam of the book is reflected by the reflection mirror 26 and the spot lens 27.
Then, the light enters the photodetector 29 through the reflection mirror 28. The photodetector 29 outputs a magneto-optical signal corresponding to the incident light beam.

Of the light beam reflected by the disk 41, the light transmitted through the polarization beam splitter 22 (p-polarized light)
Returns to the hologram laser 23, and the hologram element 33
Is guided to the built-in photodiode 31.
The photodiode 31 receives the incident light beam,
The servo signal (that is, the focus error signal FES and the tracking error signal TES) is detected.

At the same time that the light beam is incident on the objective lens 4, 20% of the light beam incident on the polarization beam splitter 22, which is the rest of the light beam incident on the objective lens 4 is also incident on the objective lens 5. The beam is incident, and the light beam reflected by the optical disc 41 is incident on the photodetector 29 for detecting a magneto-optical signal and the photodiode 31 built in the hologramr 23. However, the objective lens 5
Has a different specification from the objective lens 4, so
It cannot be focused so as to form a light spot of an appropriate size on the surface of the optical disc 41. as a result,
The light beams in the photodetector 29 and the photodiode 31 are in a blurred state (a state in which they are not sufficiently converged), and there is almost no adverse effect on recording, reproduction, and erasing using the objective lens 4.

In the above description, the case where the optical disc 41 is a magneto-optical disc having a substrate thickness of 1.2 mm and a refractive index of 1.55 has been described. However, even for optical discs other than the magneto-optical disc, the same objective lens 4 may be used if the substrate has the same thickness and refractive index. In this case, the photodetector 29 for detecting the magneto-optical signal is not used, and the photodiode 31 built in the hologram laser 23 allows the above-described formulas (1) to (3).
Both the servo signal and the reproduction signal RF can be detected based on

Next, the operation when an optical disk corresponding to the objective lens 5, here an optical disk having a substrate thickness of 0.6 mm and a refractive index of 1.55 is used will be described. For this optical disc, the objective lens 4 cannot sufficiently focus the light beam.

The p-polarized beam emitted from the hologram laser 23 enters the polarizing beam splitter 22, where about 20% of it is reflected and enters the objective lens 5. The light condensed on the optical disc 41 by the objective lens 5 is reflected by the optical disc 41 and returns to the polarization beam splitter 22 through the objective lens 5 while keeping the polarization direction. This is because the optical disc 41 is not a magneto-optical disc. The polarization beam splitter 22 reflects 20% of the returned light beam and makes it enter the hologram laser 23. The hologram laser 23 outputs a servo signal and a reproduction signal RF according to the incident light beam.
On the other hand, the remaining 80% after passing through the polarization beam splitter 22
The light beam of is incident on the photodetector 29. Therefore,
The detection signal output from the photodetector 29 may be used to detect the servo signal and the RF signal. The light beam is incident on the objective lens 5 and at the same time, the light beam is incident on the objective lens 4. However, as described above, since the objective lens 4 cannot sufficiently collect the light beam, the light beam from the objective lens 4 is recorded, reproduced,
It has almost no effect on erasure.

The transmittance and the reflectance of p-polarized light in the polarization beam splitter 22 are 80% and 20%, respectively.
It is not limited to. However, the effect of increasing the Kerr rotation angle in the detection of the magneto-optical signal is large, and the light beam assigned to the objective lens 5 can be appropriately secured.
It is preferably about 80%. The reflectance of s-polarized light is
It is desirable to be as close to 100% as possible. However, since it is difficult to make the reflectance 100% in the manufacture of parts,
The specification is preferably 95% or more. In addition,
When the objective lens 5 is used, in the polarization beam splitter 22, the light beam is split twice during the reciprocation, so that the loss becomes large. However, since a high output laser for a magneto-optical disk is used as the laser, the power of the light beam necessary for reproducing can be secured even if there is a loss.

In the above description, the polarization beam splitter 2
In Example 2, the transmittance of p-polarized light is set to about 60 to 80% and the reflectance of s-polarized light is set to about 95 to 100%. However, the reverse combination of setting the reflectance of s-polarized light to about 60 to 80% and the transmittance of p-polarized light to about 95 to 100% may be used. In this case, when one objective lens is used for the magneto-optical disk, the s-polarized light is made incident on the polarization beam splitter 22, and the polarization beam splitter 2
The light beam reflected at 2 will be used. That is, the objective lens located above the polarization beam splitter 22 is used for the magneto-optical disk. Therefore, it is necessary to switch the positions of the objective lenses 4 and 5 from the arrangements shown in FIGS.

Usually, an optical disk such as a magneto-optical disk for recording and reproducing has a lower recording density than other read-only optical disks. Therefore, in order to increase the recording capacity, there is a demand to use the inner peripheral portion of the optical disc. In order to satisfy this, particularly when two objective lenses are arranged in the radial direction of the optical disc, a recording / reproducing optical disc objective lens such as a magneto-optical disc should be arranged at the end of the optical pickup as much as possible. preferable. However, if the reflectance of s-polarized light is set to about 60 to 80% and the transmittance of p-polarized light is set to about 95 to 100%, the objective lens for the magneto-optical disk is arranged above the polarization beam splitter as described above. Since the need arises, the objective lens for the magneto-optical disk is not located at the end of the optical pickup. Therefore, in this case, the transmittance of p-polarized light is about 60 to 80%, and the reflectance of s-polarized light is 95%.
It is preferable to set to about 100% and perform recording, reproduction, and erasing of the magneto-optical disk by using the light beam transmitted through the polarization beam splitter 22.

(Second Embodiment) FIG. 7 is an exploded perspective view showing the structure of the second embodiment of the optical pickup according to the present invention. Since the objective lens driving device 2 has the same configuration as that of the first embodiment, its description is omitted. Optical system 3
Is a collimator lens 24 and a polarization beam splitter 22.
Except that the polarization direction conversion element 38 is arranged between
It has the same configuration as that of the first embodiment.

In general, the polarization state is determined by the amplitudes of two orthogonal linearly polarized lights and the phase difference between them, and is usually elliptically polarized light, but as a special case, the amplitudes are the same and the phase is only π / 2. Circularly polarized light when there is a deviation and linearly polarized light when there is no phase difference. In this specification, switching between circularly polarized light or elliptically polarized light and linearly polarized light is referred to as "changing the polarization state". Further, changing substantially only the polarization direction of linearly polarized light is referred to as “changing the polarization direction” here.

As described in the first embodiment, when the objective lens 5 is used, the polarization beam splitter 22 splits the light beam back and forth twice, resulting in a large loss of light quantity. In order to reduce this loss, the second embodiment has a collimator lens 24 and a polarization beam splitter 22.
A polarization direction conversion element 38 is provided between and.

FIG. 8 is a side view showing a split state of the light beam. Referring to FIG. 8, as a polarization direction conversion element 1
When a 1/2 wavelength plate is adopted and the polarization direction of the light beam emitted from the hologram laser 23 is p-polarized,
explain.

The half-wave plate 38 is arranged so that the angle between the crystal axis direction and the polarization direction of the incident beam is 45 °. Therefore, when the half-wave plate 38 is in the optical path, the light beam passes through the half-wave plate 38, whereby the polarization direction of the light beam is rotated by 90 ° and becomes s-polarized light. Since the reflectance of the polarization beam splitter 22 with respect to s-polarized light is set to almost 100%, almost all of the light is reflected and enters the objective lens 5. Therefore, the loss as described above is eliminated. You can

On the other hand, when the half-wave plate 38 is removed from the optical path, the p-polarized light beam is incident on the polarization beam splitter 22 and functions as in the first embodiment.
That is, by inserting / removing the half-wave plate 38 into / from the optical path, the polarization direction of the light beam incident on the polarization beam splitter 22 can be changed, and the light utilization efficiency when using the objective lens 5 is improved. be able to.
To insert / remove the half-wave plate, for example, the half-wave plate may be fixed to a slide table, the motor may move the slide table, or the plate holding the half-wave plate may be rotated. However, the method is not limited to these methods.

Further, instead of inserting / removing the ½ wavelength plate, a method of rotating the ½ wavelength plate by 45 ° around the optical axis of the light beam can be considered. If the crystal axis direction of the half-wave plate and the polarization direction of the incident light beam are the same, the polarization direction of the light beam does not change (remains p-polarized), and if rotated by 45 °, the The polarization direction of the beam is rotated by 90 ° (it becomes s-polarized light). To rotate the half-wave plate, for example, 1 /
The two-wave plate may be driven, but is not limited to this.

As the polarization direction conversion element 38, instead of using a half-wave plate, a twisted 90 ° twisted
Twisted nematic liquid crystal layer (hereinafter TN
A liquid crystal panel having a liquid crystal layer) may be used. T
The N liquid crystal layer rotates the polarization direction of the incident light beam by 90 ° when no voltage is applied. On the other hand, when the voltage is applied, the polarization direction of the incident light beam is not changed. Therefore, depending on whether or not a voltage is applied to the TN liquid crystal layer, the polarization direction of the light beam incident on the polarization beam splitter 22 can be changed between p-polarized light and s-polarized light. Other operations are the same as in the case of using the above-mentioned half-wave plate. When a liquid crystal panel having a TN liquid crystal layer is used, the polarization direction can be changed by applying a voltage, so that a mechanical driving mechanism is unnecessary. As a result, the structure is simplified and the number of parts can be reduced.

(Third Embodiment) FIG. 9 is an exploded perspective view showing a structure of an optical pickup according to a third embodiment of the present invention. FIG. 10 is a side view showing a split state of the light beam. Since the objective lens driving device 2 has the same configuration as that of the first embodiment, its description is omitted. Optical system 3
The configuration is the same as that of the first embodiment except that the polarization state conversion element 39 is arranged between the second objective lens 5 and the polarization beam splitter 22.

As described in the first embodiment,
At the same time that the light beam is incident on the objective lens 4, the remaining 20% of the light beam is incident on the objective lens 5 and the light beam reflected by the optical disk is the photodetector 2 for detecting the magneto-optical signal.
9 and the photodiode 31 built in the hologram laser 23, the objective lens 5 has a specification different from that of the objective lens 4, so that the light beam is not sufficiently condensed on the recording surface and the photodetector is not detected. It will be blurred even on the top and will have little effect. However, particularly in the detection of the magneto-optical signal, since a slight change in the polarization direction is detected, the p-direction component reflected by the magneto-optical disk through the objective lens 5 is incident on the photo-detector 29 which detects the magneto-optical signal. Then, noise is generated. Therefore, an unnecessary light beam is detected by the photodetector 29.
It is desirable not to let the light enter.

In the third embodiment, a polarization state conversion element is arranged between the objective lens 5 and the polarization beam splitter 22 in order to prevent an unnecessary light beam from entering the photodetector 29. . The polarization state conversion element is, for example, 1 /
It is a four-wave plate. The quarter-wave plate has a crystal axis direction of p
It is set at a direction of 45 ° with respect to the polarized light and the s-polarized light, and the polarization state of the incident linearly polarized light beam is converted and emitted as a circularly polarized light beam.

The p-polarized light beam emitted from the hologram laser 23 is converted into parallel light by the collimator lens 24 and enters the polarization beam splitter 22. First
Similar to the embodiment of
80% of the incident p-polarized light beam is transmitted and 20% is reflected. The light beam that has passed through the polarization beam splitter 22 enters the first objective lens 4 and is used for recording, reproduction, and erasing of the magneto-optical disk.

On the other hand, the 20% light beam reflected by the polarization beam splitter 22 is converted into circularly polarized light when passing through the quarter-wave plate 39, is incident on the second objective lens 5, and is incident on the magneto-optical disk 41. Is reflected. The rotation direction of circularly polarized light of the light beam reflected by the magneto-optical disk 41 is reversed. When it passes through the quarter-wave plate again, it becomes linearly polarized light (s-polarized light) rotated by 90 ° from the polarization direction of the outward path, and returns to the polarization beam splitter 22. Therefore, the polarization beam splitter 22 reflects almost all of the returned s-polarized light beam. As a result, it is possible to prevent a light beam unnecessary for the detection of the magneto-optical signal from entering the photodetector 29 that detects the magneto-optical signal.

As described above, by inserting the quarter-wave plate between the second objective lens 5 and the polarization beam splitter 22, the light utilization efficiency when the second objective lens 5 is used is also improved. can do. That is, 20% of the p-polarized component reflected by the polarization beam splitter 22 is the second
However, in the first embodiment, since it returns as p-polarized light as it is, it is split by the polarization beam splitter 22 again, and the hologram laser 2
The amount of light returning to the photodiode 31 built in 3 decreases. However, in the third embodiment, the p-polarized light beam returned from the quarter-wave plate is changed to s-polarized light. Therefore, all the s-polarized light beams are reflected by the polarization beam splitter 22 and enter the hologram laser 23.

(Fourth Embodiment) FIG. 11 is an exploded perspective view showing the structure of the fourth embodiment of the optical pickup of the present invention. Since the objective lens driving device 2 has the same configuration as that of the first embodiment, its description is omitted. Optical system 3
Is a collimator lens 24 and a polarization beam splitter 22.
A point where the polarization direction conversion element 38 is disposed between
The configuration is the same as that of the first embodiment except that the polarization state conversion element 39 is arranged between the second objective lens 5 and the polarization beam splitter 22. The fourth embodiment corresponds to a combination of the second embodiment and the third embodiment. That is, a ½ wavelength plate is arranged as an element for changing the polarization direction, and a ¼ wavelength plate is arranged as an element for changing the polarization state so that the crystal axis direction forms 45 ° with respect to p-polarized light and s-polarized light. A plate is added to the configuration of the first embodiment.

A case where the first objective lens 4 is used to irradiate the magneto-optical disk with a light beam will be described. First
When using the objective lens 4 of
The 1/4 wavelength plate 39 is arranged on the optical path without being arranged on the optical path. Similarly to the first embodiment, the hologram laser 23
The p-polarized light beam emitted from is converted into parallel light by the collimator lens 24, and enters the polarization beam splitter 22 as p-polarized light. 80% of the light beam passes through the polarization beam splitter 22 and enters the first objective lens 4 to be used for the magneto-optical disk.

2 reflected by the polarization beam splitter 22
The 0% light beam is incident on the second objective lens 5,
At this time, since the light passes through the quarter-wave plate twice in the round-trip optical path, it is converted into s-polarized light and the polarization beam splitter 2
Return to 2. As in the third embodiment, the polarization beam splitter 22 reflects the s-polarized light beam, so that the unnecessary light beam does not enter the photodetector 29 that detects the magneto-optical signal.

When irradiating the optical beam other than the magneto-optical disk with the light beam using the first objective lens 4, the ½ wavelength plate 38 and the ¼ wavelength plate 39 are used as described above. That is, the servo beam and the reproduction signal RF are detected by the photodiode 31 built in the hologram laser 23 using the light beam reflected by the polarization beam splitter 22 and returning to the hologram laser 23. Further, the servo signal and the reproduction signal RF may be detected by a photo detector that detects a magneto-optical signal.

FIG. 12 is a side view showing a split state of the light beam. With reference to FIG. 12, a case where the second objective lens 5 is used to irradiate a light beam on an optical disk other than the magneto-optical disk will be described. Half-wave plate 38 having a crystal axis direction of 45 ° with respect to the polarization direction of the incident light beam
Is inserted in the optical path, and the quarter-wave plate 39 is removed from the optical path. The p-polarized light beam emitted from the hologram laser 23 is converted into parallel light by the collimator lens 24 and is incident on the ½ wavelength plate 38. 1/2 wave plate 3
Reference numeral 8 converts the incident p-polarized light beam into an s-polarized light beam. The light beam converted into s-polarized light enters the polarization beam splitter 22. Polarization beam splitter 22
Reflects almost 100% of the incident light beam and makes it enter the second objective lens 5.

The light beam reflected by the optical disc 41 is
Since the quarter-wave plate 39 is removed from the optical path, its polarization direction is not converted. Therefore, the s-polarized light beam that has not passed through the quarter-wave plate returns to the polarization beam splitter 22. The polarization beam splitter 22 is
Since almost 100% of the polarized light beam is reflected, the incident light beam efficiently reaches the photodiode 31 built in the hologram laser 23.

As described above, by controlling the polarization direction conversion element 38 and the polarization state conversion element 39 in conjunction with each other, the utilization efficiency of the light beam can be improved and the photodetector 29 for detecting the magneto-optical signal can be improved. It is also possible to prevent an unnecessary light beam from entering.

When the polarization direction conversion element 38 is a half-wave plate, some kind of mechanical driving mechanism such as inserting / removing from the optical path for rotating the polarization direction or rotating it by a predetermined angle is required. Therefore, the polarization direction conversion element 3
The structure can be simplified by using a common drive mechanism for the polarization conversion element 8 and the polarization state conversion element 39. Further, as described in the first embodiment, the s-polarized reflectance of the polarization beam splitter is set to about 60 to 80%, and the p-polarized transmittance of the polarizing beam splitter is set to about 95 to 100%. 4 and 5
A configuration in which the positions of and are exchanged is also conceivable, but in this case, since the quarter wavelength plate is arranged on the side of the objective lens that is far from the light source, the distance to the half wavelength plate becomes large. I will end up. If the half-wave plate and the quarter-wave plate are interlocked, the distance between them becomes short.
Is preferable.

In the conventional optical pickup shown in FIG. 20, the photodetector 1 placed at the position shown in FIG.
19 was used to monitor the laser power. However, like the optical pickup of the present invention, the optical beam separated by the polarization beam splitter is recorded on another optical disc,
In an optical pickup having the purpose of being used for reproduction or erasing, a photodetector for monitoring laser power cannot be arranged at the position shown in FIG. Therefore, in the optical pickup of the present invention, the laser monitor pin is used to monitor the laser power, or as shown in FIG. 13, a member (aperture) 40 for limiting the opening of the collimator lens 24 is used as a photodetector. Used as. The opening limiting member 40 has an opening (aperture) at the center.
And a numerical aperture NA of the collimator lens 24 is set to a predetermined value by this opening. The peripheral portion of the opening serves as a light detecting portion, and the opening limiting member 40
Since a signal for power monitoring can be obtained by an unnecessary light beam limited by, the power of the light beam is not lost due to the power monitoring.

(Fifth Embodiment) FIG. 14 is an exploded perspective view showing the structure of an optical pickup according to a fifth embodiment of the present invention. In the present embodiment, the objective lens driving device 2 has the same configuration as that of the first embodiment, so the description thereof will be omitted.

The first difference between this embodiment and the first to fourth embodiments is the Wollaston prism 25,
The reflection mirrors 26 and 28, the spot lens 27, and the photodetector 29 are arranged in the same horizontal plane as the other optical elements forming the optical system 3, and the polarization beam splitter 22 is further arranged so that the reflected light is a polarized beam. That is, it is arranged not to be above the splitter 22 but to be emitted in a direction parallel to the horizontal plane in which the optical system 3 is arranged. With this arrangement, the polarization beam splitter 2
In order to make the light from 2 incident on the objective lenses 4 and 5, respectively, it is necessary to add the raising mirrors 41 and 42 directly below the objective lenses 4 and 5. However, since all the optical elements forming the optical system 3 are arranged on the same horizontal plane, it is possible to reduce the thickness of the optical pickup as a whole.

The second difference is that the mirror 21 arranged at a position capable of receiving the transmitted light from the polarization beam splitter 22 is not a total reflection mirror but a half mirror which transmits a part of the light. That is, the photodetector 43 for power monitor of the laser is arranged at a position where the light transmitted through the mirror 21 can be received. The half mirror 21 transmits part of the incident light regardless of the polarization direction, reflects the remaining part, and makes it enter the rising mirror 42. In this embodiment, as the half mirror 21, a mirror that transmits about 10% of the incident light and reflects the remaining about 90% is used.

As shown in FIG. 13, the collimator lens 24
When the member 40 for limiting the opening of is used as a photodetector for a laser power monitor, although light loss is small,
Since the portion functioning as a photodetector is arranged outside the opening, the member 40 becomes large in size, which leads to an increase in size of the entire optical pickup. Further, since it has to function also as an aperture limiting member, a commercially available photodetector cannot be used, and it becomes necessary to provide a special photodetector. However, with the configuration of this embodiment, a commercially available photodetector can be used as the photodetector 43 for the laser power monitor, and the photodetector 43 is also an optical detector such as the polarization beam splitter 22. Since it is arranged on the same horizontal plane as the other constituent elements of the system 3, it does not lead to an increase in size of the optical pickup.

The third difference between this embodiment and the first to fourth embodiments is that the light beam emitted from the hologram laser 23 is s-polarized. In this case, the reflectance and the transmittance of the polarization beam splitter 22 are 60 to 80% for s-polarized light and 95 to 90% for p-polarized light as described in the first embodiment. 1
The objective lens 4 corresponding to the magneto-optical disk is set on the side on which the reflected light from the polarization beam splitter 22 is incident. Such an arrangement of the objective lens 4 is disadvantageous in terms of recording capacity of the magneto-optical disk. However, when the outgoing light from the hologram laser 23 is the s-polarized light, if the p-polarized light is made to enter the polarization beam splitter 22, the polarization direction conversion element as described in the second embodiment must be provided. Occurs. The addition of such a polarization direction conversion element is performed by the optical system 3
This complicates the position adjustment of the optical elements constituting the optical disk and also increases the cost. However, the arrangement according to the fifth embodiment can prevent such a problem from occurring.

The fourth difference between this embodiment and the first to fourth embodiments is that a quarter wavelength plate is used as a polarization conversion element as shown in the third embodiment. However, the purpose is different from that of the third embodiment. In the third embodiment, when recording, reproducing, or erasing a magneto-optical disc corresponding to one objective lens 4, a light beam from the other objective lens 5 designed for another optical disc is A quarter-wave plate is used to prevent the light from being reflected by the magneto-optical disk and entering the photodetector 29 that detects the magneto-optical signal. On the other hand, in the present embodiment, recording, reproduction and erasing using the objective lens 4 and recording, reproduction and erasing using the objective lens 5 are performed.
For the purpose of making the light amount of the light beam incident on the photodetector 29 substantially the same as that of the erasing, and making the light amount of the light beam incident on the photodiode 31 incorporated in the hologram laser 23 substantially the same. 1/4 to change
A wave plate is used. Therefore, the direction of the crystal axis of the quarter-wave plate is set to achieve this purpose.

The arrangement of the quarter-wave plate 39 will be described below with reference to FIGS. 14 and 15.

In the optical pickup having the structure shown in FIG. 14, the reflectance and the transmittance of the s-polarized light in the polarization beam splitter 22 are set to 75% and 23%, respectively, and the transmittance of the p-polarized light is set to 96%. Further, the reflectance of the half mirror 21 is 90%, the transmittance of the quarter-wave plate 39 is 98%,
The effective area ratio between the objective lens 4 and the objective lens 5 is 0.85.
(Objective lens 5 / Objective lens 4), the reflectance of the magneto-optical disk corresponding to the objective lens 4 is 15%, and the reflectance of the optical disk corresponding to the objective lens 5 is 70%. further,
Almost 100% reflectance of the rising mirrors 41 and 42
And When the light amount of the s-polarized beam incident on the polarization beam splitter 22 is 100%, it is condensed on the magneto-optical disk through the objective lens 4 and then reflected by the magneto-optical disk before returning to the polarization beam splitter 22. come light quantity P ₄ of the light beams are focused on the optical disc other than the magneto-optical disk through the objective lens 5, the ratio of the light quantity P ₅ of the light beam returning to the polarizing beam splitter 22 after being reflected , P ₄ / P ₅ = (0.75 × 0.15) /
(0.23 x 0.9 x 0.98 x 0.85 x 0.7 x 0.98 x 0.9) ≈ 1. That is, as described above, when the transmittance and the reflectance of each optical element are set, substantially the same amount of light returns to the polarization beam splitter 22 when the objective lens 4 is used and when the objective lens 5 is used. Come on. Objective lens 4
In the case of using, the reflected light from the magneto-optical disk, about 23% of the amount of light returning to the polarization beam splitter 22, passes through the polarization beam splitter 22, and goes to the photodetector 29. About 75% is reflected by the polarization beam splitter 22 and goes to the photodiode 31 built in the hologram laser 23. Therefore, even when the objective lens 5 is used, the light directed to the photodetector 29 and the light directed to the photodiode 31 are reflected from the optical disk and are incident on the polarization beam splitter 22 so that the light has the same ratio. The polarization state of the light to be converted may be converted. In order to realize this, in the fifth embodiment, 1
A quarter wave plate 39 is used.

FIG. 15 is a diagram for explaining the function of the quarter-wave plate 39. Now, it is assumed that the quarter-wave plate 39 is arranged so that its crystal axis forms an angle of 28.4 ° with respect to the s-polarized light. FIG. 15A shows the polarization state of the light beam before entering the quarter-wave plate 39. As shown in this figure, before entering the quarter-wave plate 39, the light beam remains in the polarized state emitted from the hologram laser 23, that is, in the s-polarized state. Normally, linearly polarized light that vibrates in a plane including the transmission / reflection directions of a polarization beam splitter is defined as p-polarized light, and linearly polarized light that vibrates in a plane orthogonal to that is defined as s-polarized light. Also adopts these definitions. The light beam transmitted through the polarization beam splitter 22 has its polarization state converted by passing through the quarter-wave plate 39,
As shown in FIG. 15B, 28.4 ° for s-polarized light.
The objective lens 5 becomes elliptically polarized light having an axis in the inclined direction.
Incident on.

The light beam focused on the optical disc by the objective lens 5 is reflected by the optical disc to become elliptically polarized light which rotates in the opposite direction, and again passes through the objective lens 5 and passes through the quarter-wave plate 39. pass. FIG.
In (c), the light beam reflected by the optical disk is 1
The polarization state after passing through the quarter wave plate 39 is shown. As shown in this figure, by passing through the quarter-wave plate 39, the polarization direction of the light beam is further rotated by 28.4 °,
It becomes a linearly polarized light having a polarization plane forming 56.8 ° with respect to the polarization plane of the s-polarized light. At this time, the amplitude ratio between the s-polarized light and the p-polarized light is s-polarized light: p-polarized light = 0.65: 1, and the light amount ratio is 0.42: 1 when squared. That is, a light beam having a light amount of 30% for the s-polarized component and 70% for the p-polarized component returns to the polarization beam splitter 22.

Therefore, when the optical beam other than the magneto-optical disk is irradiated with the objective lens 5, the light beam returned to the polarization beam splitter 22 is reflected by the polarization beam splitter 22, and the photodetector 29 is used. The amount of light traveling toward is 0.3 × 0.75≈0.23. On the other hand, the amount of light transmitted through the polarization beam splitter 22 and directed to the photodiode 31 incorporated in the hologram laser 23 is 0.7 × 0.96 + 0.3 × 0.23≈0.75. Therefore, the ratio of the light beams incident on the photodetector 29 and the photodiode 31 is the same as when using the magneto-optical disk.

As described above, the amount of light incident on each photodetector is determined depending on whether the objective lens 4 is used to irradiate the magneto-optical disk with a light beam or the objective lens 5 is used to irradiate the optical disk with a light beam. Can be about the same.
Therefore, it is not necessary to change the conditions such as switching the laser power or switching the gain of the photodetector depending on the type of the optical disc.

In the above description, the direction of the crystal axis of the quarter-wave plate 39 is 28.4 ° with respect to s-polarized light.
Since an error due to variations in the optical elements forming the optical system 3 may be considered, the crystal axis direction may be adjustable on the optical pickup. Further, the ratio of the amount of light incident on the photodetector 29 and the photodiode 31 is the same in the case of the magneto-optical disk and the case of the optical disk,
If the specification (reflectance or transmittance) of any one optical element changes, this ratio also changes. In this case, for example, the reflectance of the half mirror 21 may be changed. Alternatively, if it is not possible to set the same ratio, the amount of light incident on one of the photodetector 29 and the photodiode 31 is set to be 1/4 in the case of the magneto-optical disk and the case of the optical disk. The crystal axis direction of the wave plate 39 can also be set. Then, gain switching is unnecessary for at least the photodetector.

As can be seen from the above description, in the fifth embodiment, not only the case where the objective lens 4 is used to irradiate the magneto-optical disk with the light beam, but also the objective lens 5 is used.
Even when an optical disk other than the magneto-optical disk is irradiated with the light beam by using, the light beam is incident on the photodetector 29. The light incident on the photodetector 29 is used for detecting the RF signal.

In the third embodiment, when the objective lens 5 is used to irradiate a light beam of an optical disk other than the magneto-optical disk, the light beam is prevented from entering the photodetector 29, and the RF signal is This is detected by the photodiode 31 built in the hologram laser 23. However, in this case, since the light beam incident on the hologram laser 23 is guided to the photodiode 31 by the diffraction of the hologram element 33, light loss occurs. In order to eliminate this loss, in the fifth embodiment, the photodetector 29 is used for detecting the RF signal.

Further, considering the above-mentioned light loss, the focus error signal FES and the tracking error signal TE.
It is also conceivable to detect the servo signal including S by the photodetector 29. However, if the servo signal is detected by the photodetector 29, the focus error signal FES
It is necessary to change the arrangement of optical elements and / or add optical elements depending on the method of detecting the. For example, in order to use the astigmatism method, a cylindrical lens must be added. Therefore, in the fifth embodiment, the RF signal is detected by the photodetector 29 and the servo signal is detected by the photodiode 31.

(Sixth Embodiment) FIG. 16 is a plan view showing the configuration of the sixth embodiment of the optical pickup of the present invention. In the first to fifth embodiments, the objective lens driving device 2 has been described as having a structure in which two objective lenses are arranged in the tracking direction, but the present invention is not limited to this. 2
One objective lens may be arranged in the tangential direction (that is, the tangential direction of the track of the optical disc) perpendicular to the tracking direction. In this case, if the configuration is such that the tracking drive is performed by rotating the two objective lenses around the middle position between the two objective lenses, the balance of the drive system is good. Further, by arranging the two objective lenses in the tangential direction in this manner, it is not necessary to consider the problem of which lens is to be arranged on the inner peripheral side in order to increase the recording capacity. As described in the fifth embodiment, it is effective when the light beam emitted from the hologram laser is s-polarized light. In the sixth embodiment, an example in which two objective lenses are arranged in the tangential direction will be described.

Since the optical system 3 is the same as that of the above-mentioned fifth embodiment, its explanation is omitted. The configuration of the objective lens driving device 2 will be briefly described with reference to FIG. The objective lens driving device 2 includes two objective lenses 4 and 5, a lens holder 6 that holds the objective lenses 4 and 5, a substrate 7 attached to the upper and lower surfaces of the lens holder 6, and the lens holder 6.
It has a movable portion constituted by a focusing coil 8 and a tracking coil 9 fixed to the concave portions on both side surfaces of the. Two elastic bodies 11 for movably supporting the lens holder 6 with respect to the base 10 in the focusing direction and the tracking direction are arranged above and below the substrate 7, and these elastic bodies 11 are provided near the center of gravity of the movable portion. They are arranged in a substantially V shape as an intersection on the extension line. Both ends of the elastic body 11 are fixed to the substrate 7 and the substrate 14, respectively. A part of the focusing coil 8 and the tracking coil 9 is arranged in the gap of the magnetic circuit formed by the yoke 16 and the permanent magnet 17,
The terminals of the focusing coil 8 and the tracking coil 9 are electrically connected to the substrate 14 via the substrate 7 and the elastic body 7.

In the above-mentioned structure, when the focusing coil 8 is supplied with current, the two objective lenses 4 and 5 can be driven in the focusing direction, and when the tracking coil 9 is supplied with current, the objectives 4 and 5 can be driven in the tracking direction. The lenses 4 and 5 can be driven.

(Seventh Embodiment) Hereinafter, FIG. 17 to FIG.
A seventh embodiment of the present invention will be described with reference to FIG. FIG. 17 is a side view showing the positional relationship between the optical pickup and the magnetic head according to the present embodiment.
(A) And (b) is a top view which shows the positional relationship of a magnetic head and two objective lenses. FIG. 19 is a side view showing the positional relationship between the slider part of the magnetic head and the two objective lenses.

Since the structure of the objective lens driving device 2 is the same as that of the sixth embodiment, its explanation is omitted. As can be seen from FIGS. 17 to 19, also in the seventh embodiment, the objective lenses 4 and 5 are arranged side by side in the tangential direction.

The magnetic head 44 has a slider portion 45, a spring portion 46, a support portion 47, and a core portion 48. As shown in FIG. 17, the slider portion 45 floats by the airflow generated by the rotation of the optical disc 41,
As a result, a constant space is maintained between the optical disc 41 and the slider portion 45. The support portion 47 is usually connected to the optical pickup 1, and the magnetic head 44 is provided so as to be movable integrally with the optical pickup 1 in the radial direction of the optical disc 41.

A coil for generating a magnetic field is wound around the core portion 48 of the magnetic head 44. As shown in FIG. 18, the core portion 48 is provided in the slider portion 45, and the center of the core portion 48 and recording / reproducing of the magneto-optical disk are performed.
It is arranged so that the optical axis center of the objective lens 4 used for erasing substantially coincides. FIG. 18 shows an optical disc 41
Shows an example in which the magnetic head 44 rotates clockwise as viewed from the surface of the magnetic head 44. In this case, the airflow generated by the rotation of the optical disc 41 is in the direction of A in the figure (that is,
Flows along the practice direction of the optical disc 41). FIG.
18A shows an example in which the objective lens 4 of the two objective lenses 4 and 5 used for the magneto-optical disk is located on the downstream side of the air flow, and FIG. It shows an example of being located on the upstream side of the air flow.

As shown in FIG. 19, a taper portion 49 is provided on the upstream side of the slider portion 45 in the air flow.
This contributes to the floating of the slider portion 45 due to the air flow.
In order to stabilize the floating, it is preferable that the airflow enter as perpendicular as possible to the end surface of the taper portion 49 on the airflow inflow side. However, in the arrangement in which the objective lens 4 is located on the upstream side of the air flow with respect to the objective lens 5, FIG.
As shown in (4), the air flow will obliquely flow into the end surface of the tapered portion 49 on the air flow inflow side. On the other hand, in the arrangement shown in FIG. 18A, the tapered portion 49 is seen from the center of the core portion 48 and the optical axis center of the objective lens 4.
Since the other objective lens 5 and the other objective lens 5 are in the same direction, the position of the taper portion 49 can be arranged closer to the middle of the two objective lenses and on the straight line passing through the center of the optical disc 41.

The positional relationship between the taper portion 49 and the core portion 48 is not limited to the positional relationship in the seventh embodiment. However, when the core portion 48 is provided in the tapered portion 49, the flying of the slider portion 45 becomes unstable, so that the tapered portion 49 and the core portion 48 are arranged with a certain distance. Therefore, the positions of the taper portion 49, the core portion 48, and the objective lenses 4 and 5 can be set so that the taper portion 49 is as close as possible to the straight line passing through the center of the optical disc 41 and between the two objective lenses. Is.

In each of the above-described embodiments, the case where two objective lenses each designed for an optical disk having at least one of the substrate thickness and the refractive index different are used. However, if two objective lenses are used for a disc having the same substrate thickness and the same refractive index,
The present invention can be applied even when A is designed to be different.

[0121]

In the optical pickup according to the present invention, the polarizing beam splitter for increasing the Kerr rotation angle and the prism for separating and splitting the light beam into the two objective lenses are used in combination, and the number of parts is small. It can be applied to a plurality of types of optical discs including magneto-optical discs, and a sufficient C / N can be obtained in the case of magneto-optical signal detection.

The optical pickup according to the present invention can be applied to recording media having the same substrate thickness and refractive index other than the magneto-optical disk by using the objective lens for the magneto-optical disk. can do.

In the optical pickup according to the present invention, the transmittance of the polarization beam splitter for p-polarized light is 60-80.
%, And the reflectance for s-polarized light is set to 95 to 100%, the Kerr rotation angle can be increased when detecting a magneto-optical signal, and it is applied to an optical recording medium other than a magneto-optical disk. The incident light amount of the light beam on the second objective lens can be set to an appropriate value.

In the optical pickup according to the present invention, since the polarization direction conversion element is provided between the light source and the polarization beam splitter, the light beam is incident on the objective lens which is applied to the optical recording medium other than the magneto-optical disk. If you want to
By switching the polarization direction of the light beam, it is possible to eliminate the loss of light quantity.

In the optical pickup according to the present invention, 1/2
A method for efficiently applying to optical recording media other than the magneto-optical disk, because the polarization direction of the light beam incident on the polarization beam splitter can be switched by inserting / removing the wave plate from the optical path or rotating it by a predetermined angle. The light beam can be made incident on the objective lens.

In the optical pickup according to the present invention, since the polarization direction of the light beam is switched by using the TN liquid crystal panel, a drive mechanism for switching is unnecessary.

In the optical pickup according to the present invention, since the polarization state conversion element is arranged between the polarization beam splitter and the second objective lens applied to the optical recording medium other than the magneto-optical disk, the first embodiment When recording, reproducing, or erasing the magneto-optical disc with the objective lens, an unnecessary light beam that is incident on the second objective lens applied to the optical recording medium other than the magneto-optical disc is reflected by the disc. ,
It is possible to prevent the return to the magneto-optical signal detection system. Alternatively, when recording, reproducing or erasing either of the two types of recording media, the light beam reflected by the recording medium is
Since it can be made to enter the photodetector with almost the same amount of light,
It is not necessary to switch the laser power or the gain of the photodetector according to the optical recording medium.

In the optical pickup according to the present invention, since the quarter-wave plate whose crystal axis direction forms an angle of 45 ° with respect to the p-polarized light and the s-polarized light is used as the polarization state conversion element, the polarization state is changed. Since a polarization mechanism can be converted by reciprocating through a quarter-wave plate without requiring a driving mechanism or the like to convert the light, the objective lens applied to an optical recording medium other than the magneto-optical disk. It is possible to prevent the reflected light from the unnecessary disk that has passed through the optical disk from returning to the magneto-optical signal detection system.

In the optical pickup according to the present invention, since the polarization direction conversion element and the polarization state conversion element are controlled in conjunction with each other, it is possible to prevent an unnecessary light beam from returning to the magneto-optical signal detection system, and at the same time, to detect the magneto-optical signal The light beam can be efficiently incident on the objective lens applied to the optical recording medium other than the disc.

In the optical pickup according to the present invention, when the first objective lens is used, the polarization state conversion element is placed in the optical path, so that an unnecessary light beam is prevented from returning to the magneto-optical signal detection system, and When the second objective lens is used, the polarization conversion element is removed from the optical path, so that the reflected light from the disk can be efficiently returned to the hologram laser. Further, since the polarization state conversion element is arranged between the second objective lens and the polarization beam splitter, the polarization direction conversion element is arranged more than when it is arranged between the first objective lens and the polarization beam splitter. The distance between and becomes shorter, and the interlocking drive becomes easier.

In the optical pickup according to the present invention, the half-wave plate which is the polarization direction conversion element and the polarization state conversion element are driven by the same drive source, so that the drive mechanism is simplified.

In the optical pickup according to the present invention, since the quarter-wave plate is used as the polarization state conversion element, no mechanical driving mechanism or the like is required to convert the polarization state.
The number of parts can be reduced. Further, since the crystal axis directions of the quarter-wave plate are set so that the light beams reflected by the two types of recording media are incident on the photodetector with substantially the same amount of light, the two types of recording media It is not necessary to switch the laser power or the gain of the photodetector when recording, reproducing, or erasing any of these.

Further, the crystal axis direction of the quarter-wave plate is set so that the light beams reflected by the two types of recording media are incident on the two types of photodetectors with substantially the same light quantity. When performing recording / reproducing / erasing on either of the two types of recording media, it is not necessary to switch the laser power, and it is not necessary to switch the gain for either photodetector.

The optical pickup of the present invention is equipped with a magnetic head having a slider portion capable of flying. A taper part is provided on the slider part, and this taper part is
By arranging it between the two objective lenses and near the line passing through the center of the disc, stable levitation is possible.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a structure of an optical pickup according to a first embodiment.

FIG. 2 is a plan view showing the structure of the objective lens driving device of FIG.

3 is a diagram in which a part of a prism is added to the AA cross-sectional view of FIG.

FIG. 4 is a perspective view showing the structure of a hologram laser.

FIG. 5 is a diagram illustrating a positional relationship between a hologram and a photodiode.

FIG. 6 is a side view showing a split state of a light beam according to the first embodiment.

FIG. 7 is an exploded perspective view showing the structure of the optical pickup of the second embodiment.

FIG. 8 is a side view showing a split state of a light beam according to a second embodiment.

FIG. 9 is an exploded perspective view showing a structure of an optical pickup according to a third embodiment.

FIG. 10 is a side view showing a split state of a light beam according to a third embodiment.

FIG. 11 is an exploded perspective view showing a structure of an optical pickup according to a fourth embodiment.

FIG. 12 is a side view showing a split state of a light beam according to a fourth embodiment.

FIG. 13 is a side view showing an example of an arrangement method of a photodetector for laser power monitor.

FIG. 14 is an exploded perspective view showing the structure of the optical pickup of the fifth embodiment.

15A and 15B are views for explaining the function of the quarter-wave plate, FIG. 15A shows the polarization state of the light beam before entering the quarter-wave plate, and FIG. FIG. 3C shows the polarization state of the light beam after passing through the / 4 wavelength plate, and FIG. 3C shows the polarization state of the light beam after passing through the ¼ wavelength plate after being reflected by the optical disc.

FIG. 16 is a plan view showing the structure of the optical pickup of the sixth embodiment.

FIG. 17 is a side view showing a positional relationship between a magnetic head and an optical pickup according to a seventh embodiment.

FIG. 18 is a plan view showing a positional relationship between a magnetic head and two objective lenses according to a seventh embodiment.

FIG. 19 is a side view showing a positional relationship between a slider section of a magnetic head and two objective lenses in a seventh embodiment.

FIG. 20 is a perspective view showing a structure of a main part of a conventional optical pickup.

FIG. 21 is a side view for explaining the principle of detecting a magneto-optical signal.

[Explanation of symbols]

 1 Optical Pickup 2 Objective Lens Driving Device 3 Optical System 4, 5 Objective Lens 21 Reflecting Mirror 22 Polarizing Beam Splitter 23 Hologram Laser 24 Collimating Lens 25 Wollaston Prism 26 Reflecting Mirror 27 Spot Lens 28 Reflecting Mirror 29 Photodetector 44 Magnetic Head

Front page continuation (72) Inventor Tomoyuki Miyake 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (18)

[Claims] 1. An optical pickup for irradiating light onto a first recording medium and a second recording medium, wherein the first recording medium and the second recording medium have a thickness of a substrate and a refractive index. At least one of them is different, the optical pickup receives the light, receives the light, reflects at least a part of the light according to a polarization direction of the light, and leaves the rest. A polarization beam splitter that transmits the light; a first objective lens that converges the light reflected by the polarization beam splitter; and a second objective lens that converges the light transmitted by the polarization beam splitter, The optical pickup according to claim 1, wherein the first objective lens is designed according to the first recording medium, and the second objective lens is designed according to the second recording medium. 2. The polarization beam splitter has different reflectance and transmittance for the first linearly polarized light and the second linearly polarized light, and the polarization direction of the first linearly polarized light and the second linearly polarized light are different from each other. 2. The optical pickup according to claim 1, wherein the polarization directions of the linearly polarized light are orthogonal to each other. 3. The light emitted from the light source is first
Linearly polarized light of the first
Is 60% or more and 80% or less, and the polarization beam splitter has a reflectance of 95% or more with respect to the second linearly polarized light that is polarized in the direction orthogonal to the first linearly polarized light. The optical pickup according to claim 1. 4. The optical pickup according to claim 3, wherein at least one of the first recording medium and the second recording medium is a recording medium other than a magneto-optical recording medium. 5. The optical pickup according to claim 4, wherein one of the first recording medium and the second recording medium is a magneto-optical recording medium. 6. The light according to claim 5, wherein the first objective lens and the second objective lens are arranged in a substantially radial direction of the first recording medium or the second recording medium. pick up. 7. The photodetector, which receives the light reflected by the first recording medium or the second recording medium, and outputs a signal corresponding to the reflected light, and the light source. And a first optical element for changing the polarization direction of the light, the light being reflected by the recording medium, the first optical element being disposed between the polarization beam splitter and the polarization beam splitter. The optical pickup according to claim 1, which is incident on a photodetector. 8. The optical pickup according to claim 7, wherein the first optical element is a half-wave plate. 9. The first optical element is a twisted optical element.
The optical pickup according to claim 7, which is a liquid crystal panel having a nematic liquid crystal layer. 10. The optical pickup further comprises a second optical element for changing the polarization state of the light, the second optical element being disposed between the polarization beam splitter and the first objective lens. Alternatively, the optical pickup according to claim 1, wherein the optical pickup is arranged between the polarization beam splitter and the second objective lens. 11. The polarization beam splitter has different transmittances and reflectances for the first linearly polarized light and the second linearly polarized light, and the first linearly polarized light and the second linearly polarized light. And the polarization directions are orthogonal to each other, the second optical element is a quarter-wave plate, and the crystal axis direction of the quarter-wave plate is the first linearly polarized light and the second linearly polarized light. The optical pickup according to claim 10, wherein the optical pickup is set at a direction of 45 ° with respect to linearly polarized light. 12. The optical pickup further comprises a second optical element for changing a polarization state of the light, the second optical element being provided between the polarization beam splitter and the first objective lens. The optical pickup according to claim 7, wherein the optical pickup is arranged between the polarization beam splitter and the second objective lens. 13. The polarization beam splitter has different transmissivities and reflectivities for a first linearly polarized light and a second linearly polarized light, and the first linearly polarized light and the second linearly polarized light. And the polarization directions are orthogonal to each other, the second optical element is a quarter-wave plate, and the crystal axis direction of the quarter-wave plate is the first linearly polarized light and the second linearly polarized light. The optical pickup according to claim 12, wherein the optical pickup is set in a direction of 45 ° with respect to linearly polarized light. 14. The first of the polarization beam splitters.
Of the first linearly polarized light is smaller than the reflectance of the second linearly polarized light, and the second optical element includes the polarization beam splitter and the second beam on which the light reflected by the polarization beam splitter is incident. Is movably disposed between the polarization beam splitter and the second objective lens, when the second linearly polarized light is incident on the polarization beam splitter. Removed from the optical path between the lens,
The optical pickup according to claim 13. 15. The polarization beam splitter has different transmittances and reflectances for the first linearly polarized light and the second linearly polarized light, and the first linearly polarized light and the second linearly polarized light. The polarization directions are orthogonal to each other, the first optical element is a half-wave plate, the second optical element is a quarter-wave plate, and the crystal of the quarter-wave plate is The axial direction is set at a direction of 45 ° with respect to the first linearly polarized light and the second linearly polarized light, and the first optical element and the second optical element are the same drive source. 13. The optical pickup according to claim 12, wherein the optical pickup is provided so as to be movable mechanically. 16. The optical detection, wherein the optical pickup receives the light reflected by the first recording medium and the light reflected by the second recording medium, and outputs a signal according to the reflected light. And an optical path between the first objective lens and the polarization beam splitter, or an optical path between the second objective lens and the polarization beam splitter.
An optical element for converting the polarization direction of the light reflected by the recording medium or the light reflected by the second recording medium, the optical element being a quarter-wave plate, and a crystal thereof. The axial direction is
The amount of light when the light reflected by the first recording medium enters the photodetector and the amount of light when the light beam reflected by the second recording medium enters the photodetector are substantially Are set to be equal to each other.
An optical pickup according to claim 1. 17. The light reflected by the first recording medium and the light reflected by the second recording medium are guided to the photodetector through the polarization beam splitter, and the photodetector A first photodetector unit for receiving a portion of the reflected light reflected by the polarization beam splitter, and a second photodetector unit for receiving a portion of the reflected light transmitted through the polarization beam splitter. The amount of light received by the first photodetector is substantially the same when the light reflected by the first recording medium is incident and when the light reflected by the second recording medium is incident. And the amount of light in the portion received by the second photodetector is when the light reflected by the first recording medium is incident and when the light reflected by the second recording medium is incident. Is substantially equal to In so that the direction of the crystal axis of the quarter-wave plate is set, the optical pickup according to claim 16. 18. The optical pickup further comprises a levitation type magnetic head for applying a magnetic field to the magneto-optical recording medium, wherein the magnetic head includes a core section for generating the magnetic field and the core section. The first objective lens and the second objective lens are supported, and have a slider part that is levitated by an airflow generated by the rotation of the magneto-optical recording medium.
The first objective lens and the second objective lens corresponding to the magneto-optical recording medium are arranged substantially in the tangential direction of the first recording medium or the second recording medium, and , The optical axis center and the center of the core of the magnetic head are substantially aligned with each other, and the other lens is provided with respect to the objective lens corresponding to the magneto-optical recording medium. The optical pickup according to claim 5, wherein the optical pickup is located upstream of the air flow.