JPH10233032A - Optical head device and optical recording and reproducing device equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the optical head device capable of reading and writing whichever an optical disk is a compact disk(CD) or a digital video disk(DVD) by utilizing different polarizing directions of a light beam for these two kinds of disks. SOLUTION: A light beam LB emitted from a light projecting part is transmitted through an annular polarizing filter 10. Since an S-polarizing component out of the light beam LB transmitted through the polarizing filter 10 is transmitted through the polarizing filter 10, while a P-polarizing component is intercepted by the polarizing filter 10, light of the S-polarizing component is transmitted through the polarizing filter 10 and is converged by an objective lens 6 as the light of a large numerical aperture so as to be converged on the DVD. Then, light of the P-polarizing component is transmitted through the polarizing filter 10 and is converged by the objective lens 6 as the light of a small numerical aperture so as to be converged on the CD. The light beam LB reflected by the DVD is transmitted through a polarizing beam splitter 11 and is received by a photodiode 7 for the DVD, while the light beam reflected by the CD is reflected by the polarizing beam splitter 11 and is received by a photodiode 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical head device and an optical recording / reproducing device provided with the optical head device. In particular, the present invention relates to an optical head device for recording and reproducing different types of optical disk recording media such as CDs and DVDs, and an optical recording / reproducing device including the optical head device.

[0002]

2. Description of the Related Art Several types of optical disk recording media have been developed, and a typical type is a DVD.
(Digital video disk) and CD (compact disk) are known. The CD and the DVD have the same thickness and the appearance of the disk is similar, but the CD has a recording layer formed by evaporating aluminum on the back surface of a resin layer having a thickness of 1.2 mm. A resin layer having a thickness of 0.6 mm is laminated, and a recording layer is formed between the resin layers. Therefore, when setting in the optical disk cartridge of the optical disk device,
The recording layer of the DVD is located closer to the objective lens of the optical head device than the recording layer of the CD, and the light beam condensing position is different.
Also, DVDs have smaller pits than CDs,
In the optical head device for D, it is necessary to narrow the focused spot more than in the optical head device for CD.

[0003] As described above, the fine structure of the CD differs from that of the DVD.
Unlike the optical disk device for D, the optical disk device for CD cannot record and reproduce DVD. However, in consideration of product needs, it is preferable that the same optical disk device can record and reproduce both CDs and DVDs.

[0004] Therefore, the same optical disk device can be used for CDs as well.
Various methods for recording and reproducing VD have been studied. For example, in FIGS. 20A and 20B, a monochrome liquid crystal shutter 102 is disposed so as to face the objective lens 101, and the numerical aperture (NA) of the light beam LB is changed by turning the liquid crystal shutter 102 on and off. It is D by changing
This allows both VD and CD to be read.

That is, when reading a DVD, the liquid crystal shutter 102 is turned off so that the light beam LB passes through the entire surface of the liquid crystal shutter 102. In this case, the entire light beam LB passes through the liquid crystal shutter 102,
The light beam LB having a large numerical aperture is focused on a small light spot by the objective lens 101, and the light beam LB focused on the small spot is focused on the recording layer T _DVD of the _DVD . On the other hand, when reading a CD, the liquid crystal shutter 102
Is turned on, the outer peripheral portion 102a (shaded area) of the liquid crystal shutter 102 is made opaque, the peripheral light of the light beam LB is blocked, and the light beam LB having a small numerical aperture is narrowed down by the objective lens 101 to the recording layer T _CD of the _CD . Collect light.

Accordingly, in a state where the liquid crystal shutter 102 is turned off, the numerical aperture becomes large, so that the light beam LB can be narrowed down, and a light spot having a large beam power can be focused on the DVD pit. On the other hand, when the liquid crystal shutter 102 is turned on, the peripheral light having a large aberration can be cut, so that the central light of the light beam LB can be focused on the pit of the CD.

[0007]

However, in the above optical head device, the liquid crystal shutter is turned on,
Since the numerical aperture of the projection beam is changed by turning off, a special liquid crystal panel which is not generally available is required. Further, even if such a special liquid crystal panel can be obtained, there is a problem that it is very expensive.

Further, since the liquid crystal shutter is used, a liquid crystal driving circuit and a power supply for driving the liquid crystal shutter are required, which causes a problem that the configuration becomes complicated and the cost increases. Furthermore, the portable optical disk device has a drawback that the battery life is shortened due to the power consumption of the liquid crystal shutter.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and has as its object the purpose of
It is an object of the present invention to provide an optical head device capable of reading different types of optical disks such as D, and which are inexpensive and consume less power, and an optical recording / reproducing device using the optical head device.

[0010]

An optical head device according to claim 1, wherein a light projecting unit for emitting a light beam, a light condensing element for irradiating a recording medium with the light beam emitted from the light projecting unit, and the light projecting unit Numerical aperture control for converting light polarized in a predetermined direction into a light flux with a large numerical aperture and converting light polarized in a different direction into a light flux with a small numerical aperture among light beams emitted from the unit and irradiated on a recording medium Means.

The optical head device according to the first aspect of the present invention can separate a light beam having a large numerical aperture and a light beam having a small numerical aperture by means of a numerical aperture control means utilizing the difference in the polarization direction of light.
Therefore, on a recording medium such as a DVD or DVD-R, a light beam having a large numerical aperture can be converged on a recording layer by narrowing the light beam to a minimum with a condensing element. CD, CD-
For a recording medium such as R, a light beam with a small numerical aperture that cuts light passing through the outer periphery of the light-collecting element, which is a cause of aberrations caused by differences in recording media, is focused on a light spot that can be read. Light can be collected on the recording layer. Therefore, in this optical head device, light having different polarization directions can be focused on the recording layers of different recording media.

In this optical head device, the light beams are condensed on a plurality of recording media by utilizing the difference in the polarization direction of the light beams emitted from the light projecting unit. Compared with the method of condensing light on a medium, a special component such as a liquid crystal shutter is not required, so that it can be easily manufactured and the cost can be reduced. In addition, since a driving circuit and a power supply are not required unlike the liquid crystal shutter, power consumption can be reduced, and the battery can be used for a long time when used in a portable device.

According to a second aspect of the present invention, in the optical head device according to the first aspect, the numerical aperture control means is formed around a region through which a light beam is transmitted irrespective of a polarization direction, and around the region. It is characterized by comprising a region that transmits only light of a predetermined polarization direction.

For example, by using a polarizing filter or the like, only light in a predetermined polarization direction is transmitted at the peripheral portion, and a light beam is transmitted at the center portion regardless of the polarization direction.
Light having a predetermined polarization direction is transmitted through both the central part and the peripheral part of the numerical aperture control means, and is converted into a light flux having a large numerical aperture. On the other hand, light in the polarization direction that does not pass through the peripheral portion passes through only the central portion, and is converted into a light beam having a small numerical aperture.

According to a third aspect of the present invention, in the optical head device of the second aspect, a polarizing filter as the numerical aperture control means and a light beam emitted from the light projecting unit are coaxial with a light receiving optical system. With a half mirror to make
The polarizing filter and the half mirror are integrated.

In this embodiment, since the polarizing filter is integrated with the half mirror for coaxializing the light beam from the light projecting unit with the light receiving optical system, a member for fixing the polarizing filter is omitted. Cost can be reduced. In addition, the labor for mounting the half mirror and the polarizing filter is reduced, and the assemblability is improved. Furthermore, since the arrangement space is reduced, the size of the optical head device can be reduced.

According to a fourth aspect of the present invention, in the optical head device according to the second aspect, there is provided a polarizing filter as the numerical aperture control means, and a lens as the light-collecting element.
The polarizing filter and the lens are integrated.

In this embodiment, since the polarizing filter is integrated with the lens serving as the light collecting element, a member for fixing the polarizing filter can be omitted, and the cost can be reduced. In addition, the time and effort required to mount the lens and the polarizing filter are reduced, and the ease of assembly is improved. Furthermore, since the arrangement space is reduced, the size of the optical head device can be reduced.

According to a fifth aspect of the present invention, there is provided the optical head device according to the second aspect, wherein the numerical aperture control means has an optical path length of light passing through a region through which a light beam is transmitted regardless of a polarization direction; It is characterized in that the difference from the optical path length of light that has passed through a region that transmits only light of a predetermined polarization direction is an integral multiple of the wavelength of light.

In this embodiment, the phase of the light passing through the region where the light is polarized and the light passing through the region where the light is not polarized in the numerical aperture control means coincide with each other.
The coherence of the light beam that has passed through both regions is not reduced, and the spread of the focused spot on the recording medium can be prevented.

According to a sixth aspect of the present invention, in the optical head device, a light projecting section for emitting a light beam, a condensing element for irradiating the recording medium with the light beam emitted from the light projecting section, and a polarization of transmitted light are provided. An element made of a material having a different refractive index depending on the direction; and an element made of a material having a different refractive index depending on the polarization direction is provided between the light-collecting element and a recording medium setting position.

In the optical head device according to the sixth aspect, since an element made of a material having a different refractive index depending on the polarization direction is disposed between the light-collecting element and the recording medium, the element passes through the element depending on the polarization direction. In this case, the optical path lengths are different, so that lights having different polarization directions are condensed at different points.
Therefore, by appropriately adjusting the thickness, the refractive index, and the like of the element, light beams can be focused on the recording layers of the two types of recording media.

In this optical head device, the light beams are converged on a plurality of recording media by utilizing the difference in the polarization direction of the light beams emitted from the light projecting unit. Compared to the method of condensing light on a medium, special components such as a liquid crystal shutter are not required, so that it can be easily manufactured and the cost can be reduced. In addition, since a driving circuit and a power supply are not required unlike the liquid crystal shutter, power consumption can be reduced, and the battery can be used for a long time when used in a portable device.

According to a seventh aspect of the present invention, in the optical head device according to the first or sixth aspect, there is provided one or more light receiving elements for receiving a light beam reflected by the recording medium,
The light receiving element receives light having different polarization directions as signal light according to the type of the recording medium.

More specifically, a polarization separating means is arranged in a light receiving optical path which does not overlap with the light projecting optical path, and separates the light having the two polarization directions reflected by the recording medium. The two light receiving elements receive the light of each polarization direction separated by the polarization separation means.

Alternatively, as described in claim 9, the polarization separating means is disposed in a light receiving optical path which does not overlap with the light projecting optical path, and any one of the two polarization directions of light reflected by the recording medium. Light of one polarization direction is selectively transmitted, so that the light receiving element receives light of the polarization direction transmitted through the polarization separation means, and the polarization direction of the light beam transmitted by the polarization separation means can be changed. It was done.

Alternatively, the polarization direction of the light beam emitted from the light projecting unit may be rotatable.

In the optical head device according to the embodiments of the present invention, light having different polarization directions is focused on the recording layer of the recording medium according to the type of the recording medium. When the light in the polarization direction reflected by the recording layer has two light receiving elements that receive light in different polarization directions, the light is received by one of the light receiving elements, and the recording on the recording medium is read. Also, in the case of a light receiving element that receives light in one polarization direction, if the polarization direction is set in advance by a polarization separation unit or a light emitting unit according to the type of recording medium,
The record on the recording medium is read.

The embodiment according to claim 11 is the same as the embodiment 8.
In the optical head device described above, the focus error signal is received by only one of the light receiving elements.

In this embodiment, regardless of which light receiving element receives the signal light, one of the light receiving elements receives the focus error signal and detects the focus error. There is no need to use a special light receiving element for focus error detection,
Cost can be reduced.

According to a twelfth aspect of the present invention, there is provided an optical recording / reproducing apparatus, comprising: an optical head device according to the first to eleventh aspects; a means for converting recording information read from a recording medium by the optical head device into reproduction data; Means for modulating the light beam based on the embedded data and irradiating the recording medium from the light projecting unit.

According to this optical recording / reproducing apparatus, since the optical head device of the present invention is used, the type of recording medium which can be read / written by utilizing the difference in the polarization direction of light without using a liquid crystal shutter is switched. be able to.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 is a view showing an optical head device 1 according to an embodiment of the present invention. In this optical head device 1, C which is an optical disk recording medium of two different standards is used.
D and DVD are to be read, and the light beam LB projected from the semiconductor laser element (LD) 2 is focused on the recording layer T _{DVD of DVD} or the recording layer T _{CD of} CD and is recorded on the recording layer T _DVD or T _CD . The individual light receiving elements 7 and 8 receive the reflected light from the minute pits.
For this reason, a polarization filter 10 (numerical aperture control means) for separating the light beam LB into light of a polarization component having a large numerical aperture and light of a polarization component having a small numerical aperture and receiving the light by the individual light receiving elements 7 and 8; A polarization beam splitter 11 (polarization separation means) is provided. Hereinafter, this embodiment will be described in detail.

In the optical head device 1, an objective lens 6 for both light transmission and reception, a polarizing filter 10, a half mirror 5, a polarization mirror, and an optical axis (optical axis of an objective lens) 3 are arranged in this order from the optical disk setting side. Beam splitter (PB
S) 11 is arranged, the semiconductor laser element 2 is arranged beside the half mirror 5, and the DVD light receiving elements 7 are arranged on the transmission side and the reflection side of the polarization beam splitter 11, respectively.
And a light receiving element 8 for CD. The light projecting optical system includes a semiconductor laser element 2, a polarizing filter 10, and an objective lens 6, and the light receiving optical system includes an objective lens 6, a polarizing beam splitter 11, a DVD light receiving element 7, and a CD.
And a light receiving element 8 for use.

The half mirror 5 is arranged obliquely with respect to the optical axis 3, and the semiconductor laser element 2 is arranged so as to emit a light beam LB toward the half mirror 5 from a direction perpendicular to the optical axis 3. The light beam LB emitted from the semiconductor laser element 2 is coaxial with the light receiving optical system by being reflected by the half mirror 5, and is incident on the polarization filter 10.

As shown in FIG. 2, the polarizing filter 10
The outer diameter is larger than the diameter of the light beam LB, and the inner diameter is smaller than the diameter of the light beam LB and the objective lens 6. In addition, the polarizing filter 1
Numeral 0 is arranged so that its polarization plane is oriented in a direction parallel to the plane of FIG. In the annular polarizing filter 10 shown in FIG. 2, the through hole 10a is opened at the center, but the center may be an optically transparent body such as a glass plate or a transparent plastic plate. .

Here, since the light beam LB emitted from the semiconductor laser element 2 is linearly polarized, the polarization direction of the light beam LB incident on the polarization filter 10 is at an angle of 45 degrees with respect to the polarization plane of the polarization filter 10. The angle of the emission surface of the semiconductor laser element 2 is adjusted so that However, the polarization direction of the light beam LB is not limited to 45 degrees with respect to the polarization plane of the polarization filter 10, and need not be parallel or perpendicular to the polarization plane of the polarization filter 10.

Therefore, when the light beam LB is incident on the polarizing filter 10, the surrounding light of the light beam LB passing through the polarizing filter 10 is polarized in a direction parallel to the polarization plane of the polarizing filter 10 (hereinafter referred to as an S-polarized component). ) Is transmitted. On the other hand, the through hole 10 of the polarizing filter 10
The center light of the light beam LB passing through the a
A polarized light component in a direction orthogonal to the polarized light component (hereinafter, referred to as a P-polarized light component) is also transmitted. That is, the S-polarized light component of the light beam LB forms a projected light beam having a large numerical aperture, and the P-polarized light component forms a projected light beam having a small numerical aperture.

The objective lens 6 is used for both light emission and light reception.
The light beam LB that has passed through the polarizing filter 10 is collected by the objective lens 6. Here, since the objective lens 6 has a spherical aberration, the peripheral light has a focal point closer to the center light. That is, the focal point of the central light is located on the recording layer TCD of the _CD set in the optical disc cartridge,
The dimensions of the objective lens 6 and the position of the semiconductor laser element 2 are designed such that the focal point of the ambient light is located on the recording layer T _DVD of the DVD set in the optical disk cartridge.

The polarizing beam splitter 11 is oriented so as to transmit S-polarized component light parallel to the polarization plane of the polarization filter 10 and reflect P-polarized component light perpendicular to the polarization plane of the polarization filter 10. It is arranged obliquely with respect to the optical axis 3.

A photodiode or the like is used as the light receiving element 7 for DVD, and the polarization beam splitter 11
Is disposed at or near the focal point of the light beam LB.

The light receiving element 8 for CD also uses a photodiode or the like, and is arranged on the reflection side of the polarization beam splitter 11 at or near the converging point of the light beam LB.

The light beam LB emitted from the semiconductor laser element 2 enters the half mirror 5 and the light beam LB reflected by the half mirror 5 is
0 and the objective lens 6, and the recording layer T _{DVD of the DVD}
Alternatively, the light is focused on the recording layer T _CD of the _CD . DVD recording layer T
_DVD or optical beam LB reflected by the recording layer T _CD of the CD passes through the objective lens 6 and polarizing filter 10 again enters the polarizing beam splitter 11. In the polarization beam splitter 11, the S-polarized light component is transmitted through the polarization beam splitter 11 to form an image on the DVD light receiving element 7 due to the difference in the polarization direction. The light of the P-polarized component is reflected by the polarization beam splitter 11 and is imaged on the light receiving element 8 for CD.

According to the optical head device 1 having the above-described configuration, the S-polarized light component parallel to the polarization plane of the polarization filter 10 is used to emit the light beam L having a large numerical aperture in the light projection optical system.
The light is condensed as B at the position of the recording layer T _DVD of the DVD, and is received by the light receiving element 7 for DVD as a signal for DVD in the light receiving optical system. On the other hand, the light of the P polarization component is D
Even if the light is reflected by the VD, the light is reflected by the polarization beam splitter 11 and is not received by the light receiving element 7 for DVD. Therefore, when the DVD is set at the optical disc setting position, the light beam LB having a large numerical aperture is converged on the recording layer T _{DVD of the} DVD by the objective lens 6 so that the light beam is read from the DVD. Can be performed.

On the other hand, the light of the P polarization component orthogonal to the polarization plane of the polarization filter 10 is condensed in the projection optical system as a light beam LB having a small numerical aperture at the position of the recording layer T _CD of the _CD. In the light receiving optical system, the light is received by the light receiving element 8 for CD as a signal for CD. On the other hand, the S-polarized light component is transmitted through the polarization beam splitter 11 even if reflected by the CD, and is not received by the light receiving element 8 for CD. Therefore, when a CD is set at the optical disc setting position, the light beam LB having a small numerical aperture, which is a light source that cuts off the light passing through the outer peripheral portion of the objective lens 6, which is a cause of aberration caused by the difference between the discs, is transmitted to the objective lens 6.
Thus, the light can be focused on the recording layer T _{CD of the} CD by narrowing it to a light spot that can be read, and the CD can be read.

Accordingly, any optical disk can be read according to the DVD or CD set at the optical disk setting position.

The light beam LB (DVD signal) on the transmission side of the polarization beam splitter is also used as a focus error signal and a tracking error signal for reading DVDs and CDs. For this reason, a diffraction grating 9 for generating a tracking signal is arranged between the semiconductor laser element 2 and the half mirror 5, and a focus error is detected between the polarization beam splitter 11 and the light receiving element 7 for DVD. A cylindrical lens 4 for generating an application signal is arranged. However, the diffraction grating 9 may be placed anywhere as long as it is in the light projection optical path. In response to this, the DVD light receiving element 7 has a structure for detecting a focus error signal or a tracking error signal, and as shown in FIG. It has a surface 12a and a light receiving surface 12b for detecting side spots.

The 0th-order diffracted light (main spot, which is a signal light) emitted from the diffraction grating 9 is divided into four light receiving surfaces 12a.
, And ± 1st-order diffracted light (side spot) emitted from the diffraction grating 9 is received by the light receiving surface 12b. Then, a tracking error is detected when the side spot deviates from the light receiving surface 12b. In addition, since the main spot changes its light spot shape along the optical axis near the focal position by passing through the cylindrical lens 4, the focus error is detected by detecting the main spot at the four-divided light receiving surface 12a.

As described above, even when reading a CD, D
Since the tracking error and the focusing error are detected by the light receiving element 7 for DVD even at the time of VD reading, an inexpensive light receiving element such as a normal photodiode can be used as the light receiving element 8 for CD. Only one lens 4 is required, and the cost of the optical head device 1 can be reduced. The detection of the tracking error or the focus error may be performed by the light receiving element 8 for CD.

The S-polarized light component of the light beam LB passes through the half mirror 5 and then also passes through the polarizing beam splitter 11, and the half mirror 5 and the polarizing beam splitter 1
Since both aberrations 1 are added, it is not necessary to use a thick half mirror 5 to increase the aberration amount when detecting a focus error signal. Therefore, the size of the optical head device 1 can be reduced.

In the optical head device 1 according to the present invention, the light beam having a large numerical aperture and the light beam having a small numerical aperture are separated by the polarizing filter 10 and the polarizing beam splitter 11 and guided to different light receiving elements 7 and 8. Therefore, a special black-and-white liquid crystal shutter is not required unlike the method using the liquid crystal shutter, and a driving circuit and a driving power supply are not required unlike the liquid crystal shutter. Further, the annular polarizing filter 10 is a simple component as compared with a liquid crystal shutter or the like, and a commercially available product can be used, so that the cost is reduced.

In FIG. 1, the polarizing filter 10 is arranged on the optical axis 3 between the objective lens 6 and the half mirror 5, but as is clear from the above description, the semiconductor laser element 2 and the half It may be arranged between the mirrors 5.

Further, a collimating lens is arranged in front of the semiconductor laser element 2 so that the collimated light is
And into the objective lens 6, the light receiving element 7,
A collimating light may be arranged on the light receiving elements 7 and 8 by disposing a condenser lens before 8.

Although the center of the polarizing filter 10 is desirably a through hole or the like, another polarizing filter 10 having a different polarization plane from the polarizing filter 10 may be provided at the center of the polarizing filter 10.

For example, due to the shape of the objective lens, D
When the focus of VD or CD becomes insufficient, focus servo for finely adjusting the position of the objective lens 6, for example, by the offset amount of the focus position, in consideration of the shift of the minimum spot position between the P-polarized component and the S-polarized component in advance. A mechanism may be provided.

For detecting a focus error, the aberration generated by a half mirror or a polarizing beam splitter may be used without using the cylindrical lens 4.
Therefore, in the following embodiments, a cylindrical lens is not shown.

(Second Embodiment) FIG. 4 is a view showing an optical head device 20 according to another embodiment of the present invention. In this optical head device 20, a hollow polarization beam splitter 21 is used as a numerical aperture control means. Also,
A diffraction grating 9 for generating a tracking signal is provided between the hollow polarization beam splitter 21 and the objective lens 6. The other configuration, operation and effect are the same as those of the above embodiment, and the same members are denoted by the same reference numerals. In this embodiment, the polarization direction of the light passing through the polarization beam splitter 21 is referred to as an S polarization direction, and a direction orthogonal to the S polarization direction is referred to as a P polarization direction.

FIG. 5 is a perspective view showing the structure of the hollow polarization beam splitter 21 and how the light beam LB passes through the hollow polarization beam splitter 21. The hollow polarizing beam splitter 21 is formed by forming a vapor deposition film 22b in a region other than the center of the surface of a rectangular glass plate 22a, and is disposed obliquely with respect to the optical axis 3 of the objective lens 6. Therefore, as shown in FIG. 5, when the light beam LB enters the hollow polarization beam splitter 21 from below, the light beam LB
Is transmitted through the region where the S-polarized component is formed on the vapor deposition film 22b, and is reflected out of the optical axis 3 by the region where the P-polarized component is formed on the vapor deposition film 22b. On the other hand, the center light of the light beam LB has the S-polarized light component and the P-polarized light component both in the vapor deposition film 22b of the polarization beam splitter 21.
Transmits through the opening 22c.

Therefore, also in this embodiment, of the light beam LB emitted from the semiconductor laser element 2 and reflected by the half mirror 5, the S-polarized light component passes through the polarization beam splitter 21 and has a large numerical aperture. The light beam LB is focused on the _DVD recording layer TDVD. In contrast, P
Polarized component, since the peripheral portion is reflected to the outside of the optical axis by the polarization beam splitter 21, it is focused on the recording layer T _CD of the CD as a small light beam LB numerical aperture.

(Third Embodiment) FIG. 6 is a view showing an optical head device 25 according to still another embodiment of the present invention.
In this optical head device 25, a Wollaston prism 26 is used as polarization separation means, and a light receiving element 7 for DVD and a light receiving element 8 for CD are arranged to face the Wollaston prism 26.

The Wollaston prism 26 splits the S-polarized light component and the P-polarized light component in slightly different directions.
The light receiving element 7 for VD and the light receiving element 8 for CD can be arranged close to each other, so that the optical head device 25 can be reduced in size and space can be saved.

(Fourth Embodiment) FIG. 7 is a view showing an optical head device 30 according to still another embodiment of the present invention.
In the optical head device 30, an analysis filter 31 is disposed between the half mirror 5 and the light receiving element 32 as polarization separation means. The light receiving element 32 serves both as a light receiving element for DVD and a light receiving element for CD. The analyzing filter 31 is rotated by 90 ° between an angle at which the S-polarized component passes and the P-polarized component is blocked and an angle at which the P-polarized component is passed and the S-polarized component is blocked. In addition,
The other configuration and operation and effect are the same as those of the first embodiment, and the same members are denoted by the same reference numerals.

When the DVD is loaded at the optical disk setting position, the angle of the analyzing filter 31 is set so that the S-polarized light component is transmitted. In this state, light having a large numerical aperture is focused on the recording layer T _DVD of the DVD, and the S-polarized light reflected by the DVD is transmitted through the analysis filter 31 and received by the light receiving element 32. On the other hand, P
Even if the light of the polarization component is reflected by the DVD,
1, the light is not received by the light receiving element 32.

Also, the CD is set at the optical disc setting position.
Is mounted, the angle of the analyzing filter 31 is set so as to transmit the P-polarized component. In this state, the light is focused on the recording layer T _CD of the CD with a small numerical aperture,
The light of the P-polarized component reflected by is transmitted through the analysis filter 31 and received by the light receiving element 32. On the other hand, the light of the S-polarized component is not received by the light receiving element 32 because it is blocked by the analysis filter 31 even if it is reflected by the CD.

In this embodiment, the rotation of the analyzing filter 31 as described above allows the
Can be switched for D. The analysis filter 31 may be rotated manually, or may be rotated by an actuator such as a motor. In this embodiment, since only one light receiving element is required, the space efficiency during mounting is high, and the cost is low.

(Fifth Embodiment) FIG. 8 is a view showing an optical head device 35 according to still another embodiment of the present invention.
In this optical head device 35, a semiconductor laser element 36 that emits laser light having a random polarization component is used, and a rotary polarization filter 37 is provided on an optical path between the semiconductor laser element 36 and the half mirror 5. The rotating polarization filter 37 is rotatable around the optical axis. The transmittance of the central portion of the polarizing filter 10 is reduced to about 50% so that the transmittance of S-polarized light becomes uniform.

When a DVD is mounted at the optical disk setting position, the rotation polarization filter 3
When the polarized light transmitted through 7 enters the polarizing filter 10, S
The angle of the rotation polarization filter 37 is set so as to be polarized light. In this state, only the S-polarized component light is projected,
The light passes through the polarizing filter 10 with a large numerical aperture, is focused on the recording layer T _DVD of the _DVD, and the light of the S-polarized component reflected by the DVD is received by the light receiving element 32.

Also, the CD is set at the optical disc setting position.
Is mounted, the angle of the rotating polarizing filter 37 is set so that the polarized light transmitted through the rotating polarizing filter 37 becomes the P-polarized light when entering the polarizing filter 10.
In this state, only light of the P-polarized component is projected, passes through the polarizing filter 10 with a small numerical aperture, and is recorded on the recording layer T _{CD of the CD.}
The P-polarized light reflected by the CD is received by the light receiving element 32.

Also in this embodiment, since one light receiving element can be used, the optical head device 35 can be made compact, and the space for mounting can be reduced. Also, the cost can be reduced.

(Sixth Embodiment) FIG. 9 is a view showing an optical head device 38 according to still another embodiment of the present invention.
In this optical head device 38, the linearly polarized semiconductor laser element 2 is rotatably mounted. Thus, if the semiconductor laser element 2 can be rotated, the light beam LB emitted from the semiconductor laser element 2
Can be rotated, so that the same operation and effect as the optical head device 35 according to the fifth embodiment using the rotating polarization filter 37 can be realized without using the rotating polarization filter 37. Therefore, the cost can be further reduced.

(Seventh Embodiment) FIG. 10 is a view showing an optical head device 40 according to still another embodiment of the present invention. In this optical head device 40, as shown in FIG.
Is used, and the composite component 41 is used to be integrated with the optical axis 3. Thus, the light beam LB emitted from the semiconductor laser element 2 is transmitted from the polarizing filter 10 to the composite component 4.
At the center, both the S-polarized light component and the P-polarized light component are reflected by the half mirror at the center and travel toward the objective lens 6. On the other hand, in the peripheral light beam LB, only the S-polarized light passes through the polarizing filter, is reflected by the half mirror on the back surface, passes through the polarizing filter 21 again, and only the light of the S-polarized component travels to the objective lens 6. As a result, the light of the S-polarized component is collected as a light beam with a large numerical aperture, and the light of the P-polarized component is collected as a light beam with a small numerical aperture.

In this embodiment, since the half mirror 5 and the polarizing filter 10 are bonded and integrated,
A member for fixing the polarizing filter 10 is not required, the cost is reduced, the arrangement space is small, and the optical head device can be downsized.

(Eighth Embodiment) For example, if a through hole 10a is opened at the center as in the polarization filter 10 used in the optical head device 1 of FIG. A phase shift occurs between the light and the light passing through the through-hole. In an optical system that focuses coherent light to the diffraction limit, phase disturbances cause spot spread,
Such a phase shift causes an increase in spot diameter when the light beam LB is focused on the DVD.

This embodiment solves such a problem, and the difference in the optical path length between the light passing through the polarizing filter 10 and the light passing through the through hole 10a is an integral multiple of the wavelength of the light. Like that. FIG. 12 is an enlarged sectional view showing a part of such a polarizing filter 10. In the this polarization filter 10, the refractive index n _1, when the t ₁ thickness, the wavelength of the light beam _{LB λ, n 1 t 1 -t} 1 = kλ (k: integer) so as to , The refractive index n ₁ or the thickness t ₁ of the polarizing filter 10 is adjusted. As a result, the polarization filter 10
And the light beam LB passing through the through hole 10a has the same phase.

Therefore, the polarization filter 1 according to the present embodiment is
0 can polarize only a part (peripheral light) of the light beam LB without deteriorating the coherence of the light beam LB. The spread of the light spot can be prevented.

(Ninth Embodiment) FIGS. 13A and 13B show a light beam LB passing through an annular polarizing filter 10 and a light beam LB passing through the center of the polarizing filter 10.
It is the perspective view and sectional drawing which show another method for preventing the phase shift of B. In this polarization filter 10,
By filling the transparent member 42 having the refractive index n ₂ with the thickness t ₂ in the through hole 10a, the difference in the optical path length between the light beam LB passing through the polarizing filter 10 and the light beam LB passing through the transparent member 42 is reduced. It is set to be an integral multiple of the wavelength of light. That is, the refractive index n ₂ and the thickness t ₂ of the transparent member are adjusted so that n ₁ t ₁ −n ₂ t ₂ = kλ (k: integer). The polarizing filter 1 is formed by the transparent member 42.
The light transmittance of the zero through-hole 10a may also be adjusted.

(Tenth Embodiment) FIG. 14 shows an optical head device 1 having the structure shown in FIG. 1, for example, in which an objective lens 6 and a polarizing filter 10 are integrated. That is, the leg 6a provided on the objective lens 6
Is bonded to the polarizing filter 10. With such a structure, a member for fixing the polarizing filter 10 is not required, and assembly is simplified.

(Eleventh Embodiment) FIG. 15 is a perspective view showing the structure of an optical head device 60 according to still another embodiment of the present invention, and FIG. 16 is an explanatory diagram of its operation. The optical head device 60 has a configuration similar to a general CD pickup.

In this embodiment, along the optical axis of the objective lens 6, the objective lens 6, the annular polarizing filter 10,
A diffraction grating 9, a half mirror 5 having a triangular prism shape, an analysis filter 61, and a light receiving element 8 for CD are arranged. The polarization plane of the analysis filter 61 is oriented in a direction orthogonal to the polarization plane of the polarization filter 10. The half mirror 5 is arranged obliquely with respect to the optical axis, and another half mirror 62 is arranged in the lateral direction of the half mirror 5 at an angle of approximately 45 degrees. Behind the half mirror 62 (in the transmission direction), the light receiving element 7 for DVD is arranged.
The semiconductor laser element 2 is arranged in the horizontal direction, and the light receiving optical path of the light receiving element 7 for DVD and the light projecting optical path of the semiconductor laser element 2 are coaxial.

The light beam LB emitted from the semiconductor laser device 2 is reflected by the half mirror 62 and enters the half mirror 5. The light beam LB reflected by the half mirror 5 passes through the diffraction grating 9 and the polarizing filter 10, and is then collected by the objective lens 6. At this time, the S-polarized component light is focused on the _DVD recording layer T _DVD as a large numerical aperture light beam LB, and the P-polarized component light is focused on the _CD recording layer T _CD as a small numerical aperture light beam LB. Is done. The light beam LB reflected by the DVD or CD passes through the objective lens 6, the polarizing filter 10, and the diffraction grating 9 again and enters the half mirror 5. The light beam LB reflected by the half mirror 5 passes through the half mirror 62 and
The light enters the light receiving element 7 for D. In the light beam LB transmitted through the half mirror 5, only the P-polarized light is transmitted by the analyzing filter and received by the light receiving element 8 for CD.

A polarizing filter for transmitting only the S-polarized light component may be provided between the DVD light receiving element 7 and the half mirror 61.

(Twelfth Embodiment) FIG. 17 is a view showing an optical head device 70 according to still another embodiment of the present invention, in which an optical path length conversion element 71 is provided between an objective lens 6 and an optical disk setting position. It is characterized by the arrangement points. In this embodiment, a collimating lens 72 is arranged in front of the semiconductor laser element 2 so that the light receiving elements 7 and 8 can be used.
The condensing lenses 73 and 74 are arranged in opposition to each other so as to form a collimating optical system.
3, 74 is not required.

The light beam LB emitted from the semiconductor laser device 2 is converted into collimated light by the collimating lens 72, and the collimated light beam L
B enters the half mirror 5. The light beam LB that has entered the half mirror 5 is reflected by the half mirror 5, passes through the objective lens 6, passes through the optical path length conversion element 71, and is collected at the front. The optical path length conversion element 71 is an element made of a material having a different refractive index depending on the polarization direction of the light beam LB, and examples of such an optical material include lithium niobate. If the directions of the linearly polarized light polarized in the electrical principal axis direction of the optical path length converting element 71 are defined as the S-polarized direction and the P-polarized direction, and the linearly polarized light having the larger refractive index is defined as the S-polarized light, Refractive index n for the component
Due to the difference in the refractive index n _P for the _S and P polarization components (n _S > n _P ), the light of the S polarization component is focused on the _DVD recording layer T _DVD and the P polarization component light is condensed on the CD recording layer T Focused on _CD .

When the optical path length conversion element 71 made of a material having a different refractive index depending on the polarization direction is inserted into the optical path of the light projecting system, the amount of aberration differs depending on the polarization direction due to the difference in the optical path length. Recording layer T _DVD and C
The recording layer T _{CD of} D can be irradiated with the smallest focused light spot.

The S-polarized light reflected by the recording layer T _DVD of the _DVD passes through the polarization beam splitter 11 and passes through the DV.
The light of the P-polarized light component received by the light receiving element 7 for D and reflected by the recording layer T _CD of the _CD is reflected by the polarization beam splitter 11 and received by the light receiving element 8 for CD.

FIG. 18A shows the optical path length conversion element 71.
FIG. 18B is a view for explaining the action of condensing the light of the S-polarized component on the recording layer T _DVD of the _DVD , and FIG.
FIG. 4 is a diagram for explaining an operation of condensing light on a recording layer T _{CD of} D. Now, it is assumed that the refractive index of the optical path length conversion element 71 for the S-polarized light component is n _S , the refractive index for the P-polarized light component is n _P , and the thickness is d. The focal length of the objective lens 6 is F,
The distance from to the recording layer T _DVD of the DVD to L _DVD, the distance to the recording layer T _CD of CD and L _CD. The depth from the resin layer surface to the DVD recording layer T _DVD is d _DVD (= 0.6 m).
m), the depth from the resin layer surface to the CD recording layer T _CD is d
The refractive index of the resin layer of _CD (= 1.2 mm), DVD and CD is n ₀ . At this time, the following relationship is satisfied: F = L _DVD + (n _S −1) d + (n ₀ −1) d _DVD ... F = L _CD + (n _P −1) d + (n ₀ −1) d _CD . If an optical system is designed, the light of the S-polarized component is focused on the recording layer T _DVD of the _DVD, and the light of the P-polarized component is focused on the recording layer T _CD of the _CD . From the above equation and the equation, L _CD −L _DVD (= 1.2 mm) = (n _S −n _P ) d + (n ₀
-1) (d _DVD -d _CD ), and to realize such an optical system, d = [(L _CD -L _DVD )-(n ₀ -1) (d _DVD -d _CD ) _{] / (n S -n P)} ... may it can be seen that by using the optical path length conversion device thickness d, represented by. Further, since L _CD -L _DVD = d _CD -d _DVD , the above expression is expressed as follows. d = n ₀ (d _CD −d _DVD ) / (n _S −n _P )

According to the optical head device 70, when a DVD is set at the optical disk setting position,
The DVD can be read by the light receiving element 7 for DVD, and when the CD is set, the CD can be read by the light receiving element 8 for CD. Alternatively, in order to switch so that only one of the optical discs can be read, for example, a polarizing filter is provided rotatably by 90 degrees in front of the semiconductor laser element 2 and the S-polarized light or the P-polarized light is rotated by rotating the polarizing filter. By emitting
Switching between DVD and CD may be possible.

(Thirteenth Embodiment) FIG. 19 is a diagram showing a schematic configuration of an optical recording / reproducing apparatus 80 using an optical head device according to the present invention, which is, for example, a specification for a personal computer. As the optical head device 81,
For example, although the same one as shown in FIG. 1 is shown, it is not limited to such an optical head device.

In this optical recording / reproducing device 80,
An optical disk such as a DVD or a CD is set in a setter 82 for positioning and holding the optical disk at a predetermined position and rotating the optical disk at a constant rotation speed. When the CD is set in the setter 82 and the power is turned on, the setter drive circuit 83 causes the setter 82 to operate.
Is rotated at a constant speed, and DVD
Or the CD rotates.

In this state, when a reproduction command is input to the control circuit 84, the semiconductor laser element driving circuit 85 causes the semiconductor laser element 2 to emit a pulse to cause the DVD or CD to emit light.
Is irradiated with the light beam LB, and the light beam LB reflected by the DVD or CD is received by the light receiving elements 7 and 8 for DVD or CD. When the optical disk is a DVD, the light is received by the light receiving element 7 for DVD.
Is output to the DVD reading circuit 86,
The DVD reading circuit 86 outputs reproduction data in a predetermined format. Similarly, if the optical disc is a CD, C
Since the light is received by the light receiving element 8 for D, the photocurrent output from the light receiving element 8 for CD is sent to the CD reading circuit 87,
Reproduced data in a predetermined format is output from the CD reading circuit 87.

When a write command is input to the control circuit 84, the semiconductor laser device drive circuit 85 drives the semiconductor laser device 2 to emit the light beam LB output for writing. On the other hand, when the write circuit 88 receives the write data, the write circuit 88 outputs the light beam LB output from the semiconductor laser element 2 according to the write data via the semiconductor laser element driving circuit 85. The modulated light is emitted, the modulated light beam LB is applied to the DVD or CD, and write data is recorded on the DVD or CD.

[Brief description of the drawings]

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

FIG. 2A is a plan view of a polarizing filter according to the first embodiment;
(B) is a sectional view thereof.

FIG. 3 is a diagram showing a structure of a light receiving element for DVD.

FIG. 4 is a diagram showing an optical head device according to another embodiment of the present invention.

FIG. 5 is a diagram illustrating an optical function when a light beam passes through a hollow polarization beam splitter.

FIG. 6 is a diagram showing an optical head device according to still another embodiment of the present invention.

FIG. 7 is a diagram showing an optical head device according to still another embodiment of the present invention.

FIG. 8 is a diagram showing an optical head device according to still another embodiment of the present invention.

FIG. 9 is a diagram showing an optical head device according to still another embodiment of the present invention.

FIG. 10 is a diagram showing an optical head device according to still another embodiment of the present invention.

FIG. 11 is still another embodiment of the present invention, and is a view for explaining an optical action that a light beam receives by a polarizing filter attached to a half mirror.

FIG. 12 is a view showing a phase of a light beam passing through a polarizing filter and a phase of a light beam passing through a central through hole according to still another embodiment of the present invention.

FIG. 13 is yet another embodiment of the present invention,
(A) is a perspective view showing a polarizing filter in which a transparent member is filled in a central hole, and (b) shows a phase of a light beam passing through the polarizing filter and a phase of a light beam passing through the transparent member in the through hole. FIG.

FIG. 14 is still another embodiment of the present invention, showing a polarizing filter integrated with an objective lens.

FIG. 15 is a perspective view showing a configuration of an optical head device according to still another embodiment of the present invention.

FIG. 16 is a diagram illustrating the operation of the optical head device.

FIG. 17 is a diagram showing a configuration of an optical head device according to still another embodiment of the present invention.

FIGS. 18A and 18B are diagrams illustrating how the optical path length changing element changes the light beam condensing position according to the type of the optical disc recording medium in the optical head device of the above.

FIG. 19 is a diagram showing a configuration of an optical recording / reproducing device according to still another embodiment of the present invention.

FIGS. 20A and 20B are explanatory diagrams illustrating the principle of an optical disk device according to a conventional example.

[Explanation of symbols]

2, 36 Semiconductor laser element 3 Optical axis of objective lens 5 Half mirror 6 Objective lens 7 Light receiving element for DVD 8 Light receiving element for CD 10 Polarizing filter 11 Polarizing beam splitter 21 Hollow polarizing beam splitter 26 Wollaston prism 71 Optical path length conversion Element LB Light beam T _DVD DVD recording layer T _CD CD recording layer

Claims (12)

[Claims] A light emitting unit that emits a light beam; a light-collecting element that emits a light beam emitted from the light emitting unit to a recording medium; and a light emitting unit that emits the light beam from the light emitting unit and irradiates the recording medium. Numerical aperture control means for converting light polarized in a predetermined direction of the light beam into a light flux having a large numerical aperture, and converting light polarized in a different direction into a light flux having a small numerical aperture. Optical head device. 2. The apparatus according to claim 1, wherein the numerical aperture control means includes a region through which the light beam is transmitted irrespective of the polarization direction, and a region formed around the region, which transmits only light having a predetermined polarization direction. The optical head device according to claim 1, wherein 3. A polarizing filter as the numerical aperture control means, and a half mirror for coaxializing a light beam emitted from the light projecting unit with a light receiving optical system, wherein the polarizing filter and the half mirror are integrated. The optical head device according to claim 2, wherein the optical head device is formed. 4. The apparatus according to claim 2, further comprising: a polarizing filter serving as the numerical aperture control means; and a lens serving as the light collecting element, wherein the polarizing filter and the lens are integrated. Optical head device. 5. An optical path length of light passing through a region through which a light beam is transmitted irrespective of a polarization direction of the numerical aperture control means, and an optical path length of light passing through a region through which only light of a predetermined polarization direction is transmitted. 3. The optical head device according to claim 2, wherein the difference from the optical head is an integral multiple of the wavelength of light. 6. A light projecting unit for emitting a light beam, a light condensing element for irradiating a recording medium with the light beam emitted from the light projecting unit, and a material having a different refractive index depending on the polarization direction of transmitted light. An optical head device, comprising: an element made of a material having a different refractive index depending on the polarization direction, disposed between the light-collecting element and a recording medium setting position. 7. One or more light receiving elements for receiving a light beam reflected by a recording medium, the light receiving elements receiving linearly polarized light having different polarization directions as signal light according to the type of the recording medium. 7. The method according to claim 1, wherein:
An optical head device according to item 1. 8. A polarization separating unit disposed in a light receiving optical path which does not overlap with the light projecting optical path, for separating the light of the two polarization directions reflected by the recording medium, and for each of the polarization directions separated by the polarization separating unit. The optical head device according to claim 7, further comprising: two light receiving elements that receive light. 9. A polarization separating means which is disposed in a light receiving optical path which does not overlap with the light projecting optical path and selectively transmits light in one of the two polarization directions reflected by the recording medium. A light receiving element for receiving light in a polarization direction transmitted through the polarization separation means, wherein a polarization direction of a light beam transmitted by the polarization separation means can be changed. The optical head device as described in the above. 10. The apparatus according to claim 7, wherein the polarization direction of the light beam emitted from said light projecting unit is rotatable.
An optical head device according to item 1. 11. The optical head device according to claim 8, wherein only one of the light receiving elements receives the focus error signal. 12. An optical head device according to claim 1, further comprising: means for converting recording information read from a recording medium by the optical head device into reproduction data; and modulating a light beam based on the write data. Means for irradiating a recording medium from a light projecting unit.