JPH1139705A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the optical pickup device capable of recording and reproducing two kinds of optical recording media which are different in recording and reproducing wavelength, high utilizing efficiency of light with good shaping of a beam and also compactness in size. SOLUTION: This device has 1st and 2nd light sources 1 and 2 which are different in wavelength of light emission, a coupling lens for coupling light beams from the individual light sources l and 2, an objective lens 7, optical path separating optical means 4 and 5 for separating return light beams from projecting optical paths from the light sources 1 and 2 to the objective lens 7, detecting means 9, 10 and 11 for receiving the separated light beams and detecting information of the reflected light beams as common to these light beams and a control means for performing focusing control and tracking control based on the above detecting result. These individual light sources 1 and 2 are lit at the time of using the optical recording medium 8A of the 1st kind and the optical recording medium 8B of the 2nd kind respectively, and the coupling lens 3 is an anamorphic lens to substantially collimate the light beams from the light sources 1 and 2 respectively and also to shape these beams.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optical pickup device.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for optical recording media typified by optical disks to have "larger recording capacity". In order to increase the recording capacity without increasing the size of the optical recording medium itself, it is necessary to reduce the diameter of the light spot for recording and reproducing information. Since the light spot diameter is proportional to the light wavelength: λ, the recording capacity is inversely proportional to the square of the light wavelength: λ. For this reason, the “shortening of the wavelength of the light source used in the optical pickup device” has been pursued, and a conventional optical disc (CD-R) that performs recording / reproduction at a wavelength of 785 nm has been developed.
An optical disk (DVD) that performs recording and reproduction at a light source wavelength of 650 nm has been realized.

As an optical pickup device that can be used for any of different types of optical recording media having different recording / reproducing wavelengths, two types of semiconductor lasers having different emission wavelengths (hereinafter referred to as a light source LD in this specification). ) As a light source has been proposed (Japanese Patent Application Laid-Open No. 6-259804).

By the way, as is well known, the light source LD
Is divergent, the divergence angle is maximum in a direction perpendicular to the active layer and minimum in a direction parallel to the active layer, and the far-field pattern is elliptical.

The light spot converged on the optical recording medium is preferably “circular”, and as the light spot becomes “elliptical”, the recording / reproducing ability tends to decrease. In order to obtain a circular light spot, when coupling a light beam from the light source LD with a coupling lens, a part of the far field pattern in the long axis direction is shielded to obtain a circular light beam cross section. However, in this method, "a small portion of the light beam from the light source" is blocked from the optical recording medium, so that the efficiency of using the light energy used for recording / reproduction is low. When information is recorded on an optical recording medium by an optical pickup device, light energy that is 10 times or more that of information reproduction is required. part"
Must be taken into light spot formation.

At this time, simply taking in the light beam edge in the long axis direction of the far field pattern results in an elliptical light spot shape (the short axis direction of the far field pattern becomes the long axis direction of the light spot). Therefore, “beam shaping” is performed to capture the light flux to the peripheral portion in the long axis direction and to make the cross-sectional shape of the captured light flux “close to a circular shape”.

As a method of performing beam shaping, a method of combining two prisms and a method of using a cylindrical lens are known. However, the use of these methods has a problem that an optical pickup device becomes large.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an optical pickup device for recording / reproducing information on / from two types of optical recording media having different recording / reproducing wavelengths. It is an object of the present invention to reduce the size of the optical pickup device.

[0009]

An optical pickup device according to the present invention is an "optical pickup device which can be used for both first and second types of optical recording media having different recording / reproducing wavelengths". , A first and a second light source LD, a coupling lens, an objective lens, an optical path separating optical unit, a detecting unit, and a control unit. "First and second
Is a semiconductor laser light source that emits laser beams having different emission wavelengths from each other. The “coupling lens” is provided commonly to the first and second light sources LD, and couples the light flux from each light source LD to the subsequent optical system. The “objective lens” is provided in common for each light beam coupled by the coupling lens, and condenses each coupled light beam on the optical recording surface of the optical recording medium. The “optical recording medium” on which the light beam is collected by the objective lens differs for each light beam. The “optical path separating optical unit” is a unit that separates each light beam reflected by the optical recording medium and returned as a light beam through the objective lens from the “irradiation light path from the light source LD to the objective lens”. "Detection means" is information of each light flux separated by the optical path separation optical means, that is,
It is means for detecting reproduction information, focus error information, and track error information. The “control means” is means for performing focusing control and tracking control based on information detected by the detection means.

The features of the optical pickup device according to the first aspect of the present invention are as follows. That is, the first light source LD
Is "lit only when the first type optical recording medium is used"
Then, the second light source LD is turned on only when the second type of optical recording medium is used, and the coupling lens is turned on in the direction in which the divergence angle of the incident light beam, which is common to the respective light beams, becomes maximum and minimum. And has a function of substantially collimating the light beams from the first and second light sources LD and a function of beam shaping the anamorphic lens. “Beam shaping” refers to an optical action that enlarges the light beam diameter in the direction in which the divergence angle is the smallest to make the light beam cross-sectional shape of the coupled light beam “circular or similar”.

The first and second light sources LD may be provided with their respective light-emitting portions arranged close to each other. The axis and the optical axis of the light beam from the second light source LD may be made to coincide with each other with respect to the coupling lens. In this case, it is preferable that the optical axes aligned with each other match the optical axis of the coupling lens.

The optical axis alignment optical means may be various means such as a half mirror prism or the like, but it is desirable that effective light use efficiency can be realized. From the viewpoint of such light utilization efficiency, the optical axis alignment optical means may be “a prism element having a different transmittance or reflectance depending on the polarization of the light beam (Claim 3)” or “a prism element having different transmittance or reflectance depending on the polarization of the light beam. A prism element having different prism elements and a phase shifter for rotating the polarization plane of one light beam by 90 degrees (claim 4), a "prism element having different transmittance or reflectance depending on wavelength (claim 5)", "Prism elements having different polarization separation characteristics depending on the wavelength (claim 6)" and the like are preferable. An optical pickup device according to a seventh aspect of the present invention is the optical pickup device according to the second aspect, wherein the optical axis alignment optical means is configured to “deflect and separate the film having a different transmittance or reflectivity depending on the polarization of the light beam and the wavelength of the light beam. A prism element having a film with different characteristics), a “phaser” that acts as a quarter-wave plate for each light beam from each light source LD, and the return light beam is “a coupling lens, a phaser, Incident on the light receiving means of the detecting means via the prism element. " In such a configuration, the phaser and the prism element constitute an “optical path separating optical unit”, and the light receiving unit and the coupling lens constitute a “detecting unit”.

[0013] The first and second light sources LD can be arranged in the “same package”.

In the optical pickup device according to any one of the first to eighth aspects, it is possible to configure so that "the optical path separating optical means has a polarizing hologram" (claim 9).
The “polarizing hologram” is a “diffraction element that is transmitted or diffracted depending on the polarization state of light incident on the grating groove” and is known as a polarizing diffraction grating. Such a polarizing hologram is described in “Polarizing hologram optical element” on page 86 and below in O plus E, March 1991, and “Polymer using LiNmO ₃ as material”; Vol. 20 No. 8 (August 1991) 500
(36) A “diffraction grating with a narrow pitch of about の of the wavelength and a deep groove” described in “High-density dual grating for a magneto-optical head” on page 36 and below can be used.

According to a ninth aspect of the present invention, in the optical pickup device, the optical path separating optical means is constituted by integrating the polarizing hologram and the phaser, and the phaser has different wavelengths from the first and second light sources LD. Acts as a quarter-wave plate on the light beam "(claim 9). In other words, the phase of the light beam is changed to linearly polarized light and circularly polarized light by a phaser (having the same function as the phaser in the invention according to claim 7) acting as a quarter wave plate for each light beam from each light source LD. In addition to the conversion, the linear polarization states of the irradiation light beam and the return light beam are made orthogonal to each other, so that the diffraction effect of the polarization hologram acts on the return light beam. 10. The optical pickup device according to claim 8, wherein the optical path separating optical means is configured by integrating a retarder on both sides of the polarizing hologram, and one of the retarders has a polarization plane of only one light beam at 90 degrees. The other phase shifter has a function of acting as a quarter-wave plate for each light beam. "
0).

The above claim 4 or 7 or 10 or 1
The “phaser” used in the optical pickup device according to claim 1 can be formed as a “deposited film”.
2). Further, in the optical pickup device according to any one of claims 9 to 12, "the detecting means for receiving each light flux separated by the optical path separating optical means and detecting the information of the reflected light flux is provided by the first and second detecting means. (In the same package as the light source LD) (claim 13), and in this case, the optical path separating means having the polarization hologram is "housing the detection means and the first and second light sources LD." Integrated into the same package. "
4).

The optical pickup device according to any one of claims 1 to 14, wherein the first light source LD has a light emission wavelength of 785 nm and the second light source LD has a light emission wavelength of 650 nm. The first type of optical recording medium is a “low capacity optical disk with a substrate thickness of 1.2 mm”, and the second type of optical recording medium is a “large capacity optical disk with a substrate thickness of 0.6 mm”. (Claim 15).

Further, in the optical pickup device according to any one of claims 1 to 14, the first and second light sources L
One of D is "one that emits the TE mode light",
The other can be "the one that performs TM mode light emission" (claim 16).

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 (a), reference numeral 1 denotes a first light source LD, and reference numeral 2 denotes a second light source LD.
The light source LD1 is a semiconductor laser having an emission wavelength of 785 nm, and the light source LD2 is a semiconductor laser having an emission wavelength of 650 nm. Since the semiconductor laser has "wavelength variation for each laser individual" and "wavelength change due to temperature", the actual emission wavelength is in a wavelength range of about ± 20 nm with the above-mentioned wavelength as a substantially central value.

Reference numeral 8A denotes a first type optical recording medium.
Substrate thickness: indicates "low capacity optical disk" of 1.2 mm,
Reference numeral 8B denotes a substrate thickness as a second type optical recording medium:
This shows a "large capacity optical disk" of 0.6 mm. These are originally “separate bodies” and used separately, but are illustrated in a single form for convenience of explanation.

When recording or reproduction is performed on the low capacity optical disk 8A, the light source LD1 is turned on. The laser beam from the light source LD1 passes through the coupling lens 3, the polarizing beam splitter 4, and the phase shifter 5, is reflected by the deflecting prism 6 and is incident on the objective lens 7, and the objective lens 7
A light beam is condensed by the action of the light beam, passes through the substrate of the low capacity optical disk 8A, and is condensed as a light spot on the recording surface. The light reflected by the recording surface passes through the objective lens 7 to become a “return light beam”, is reflected by the deflecting prism 6, passes through the phase shifter 5, is reflected by the polarization beam splitter 4, and is condensed by the condensing lens 9 and the cylinder lens 10 and the light receiving means 11
Incident on.

When recording or reproduction is performed on the large-capacity optical disk 8B, the light source LD2 is turned on, and the emitted laser light flux passes through the coupling lens 3, the polarizing beam splitter 4, and the phase shifter 5, and the deflection prism. The reflected light is transmitted through the substrate of the large-capacity optical disk 8B through the objective lens 7, and is condensed as a light spot on the recording surface. The light reflected by the recording surface passes through the objective lens 7 to become a “return light beam”, is reflected by the deflecting prism 6, and is received by the phase shifter 5, the polarizing beam splitter 4, the condensing lens 9, and the cylindrical lens 10. It is incident on 11.

The laser beams emitted from the light sources LD1 and LD2 have a polarization direction parallel to the drawing, and
In the “irradiation optical path” from the optical disk to the optical disk, the light passes through the polarization beam splitter 4 as P-polarized light. The retarder 5 is formed by “forming a vapor-deposited film on transparent glass”, and this vapor-deposited film acts as a 波長 wavelength plate for each laser beam from the light sources LD1 and LD2. Accordingly, the light beam transmitted through the phaser 5 from the light source side has its polarization state “converted from a linearly polarized state to a circularly polarized state”. The return light flux reflected on the recording surface of the optical disk is in a circularly polarized state in which the direction of rotation of the polarization plane is opposite to the irradiation optical path, and when transmitted through the phaser 5, the return light flux "is a linear polarization state in which the polarization plane is orthogonal to the irradiation optical path. And reflected by the polarization beam splitter 4 as S-polarized light. That is, the polarizing beam splitter 4 and the phaser 5 are "optical path separating optical means".
Is configured.

When the returning light beam is reflected by the polarizing beam splitter 4, it is converged by the condenser lens 9, further given astigmatism by the cylindrical lens 10, and enters the light receiving means 11. The light receiving means 11 generates a focus error signal by a known astigmatism method and a track error signal by a phase difference method, and a control means (microcomputer, CPU, etc.) not shown based on these signals.
Performs focusing control and tracking control. The light receiving means 11 also outputs a "reproduction signal". That is, the condenser lens 9, the cylindrical lens 10, and the light receiving means 11 constitute "detection means". In addition, instead of the condenser lens 9 and the cylindrical lens 10, "one side is a convex spherical surface,
A single lens whose other surface is a convex cylinder surface "
Can also be used. The focus control may be another method such as a known knife edge method instead of the astigmatism method, and the tracking control may use a known appropriate method such as a push-pull method. The detection means can be appropriately configured according to the specific method. In the embodiment shown in FIG.
The light emitting portion of the light source LD2 is aligned with the optical axis of the optical system below the coupling lens 3, but the light emitting portion of the light source LD1 is slightly displaced from the optical axis. Depending on whether the return light beam is
Are slightly different from each other, so that "one set of light receiving units is provided for each return light beam" or "light source LD1,
2, the position of the light receiving means 11 is adjusted so that the return light beam is incident on an appropriate position of the light receiving means 11, or "the focus error signal / track error signal is previously determined. At the same time, an offset corresponding to the shift of the incident position of the return light beam "is required.

That is, the optical pickup device of the embodiment shown in FIG. 1A can be used for both the first and second types of optical recording media 8A and 8B having different recording / reproducing wavelengths. An optical pickup device, wherein first and second light sources LD1 and LD2 having different emission wavelengths are provided in common with the first and second light sources LD1 and LD2, and light beams from the respective light sources LD are coupled. The coupling lens 3 to be coupled and each coupled light beam are transmitted to an optical recording medium 8.
An objective lens 7 common to each of the above-mentioned light beams, which is condensed as an optical spot on the optical recording surfaces A and 8B, and each light beam reflected by the optical recording medium and returned as a light beam through the objective lens 7 is converted into a light source LD1. , 2 from the irradiation optical path leading to the objective lens 7, common optical path separating optical means 4, 5 for each of the light fluxes, and information of each light flux separated by the optical path separating optical means is detected. Common detection means 9, 1
0, 11 and control means (not shown) for performing focusing control and tracking control based on the detection result of the detection means, and the first light source LD1 is a first type optical recording medium 8A. The second light source LD2 is lit only when the second type optical recording medium 8B is used (claim 1).

The “collimating function and beam shaping function” of the coupling lens 3 will be described. In FIG. 1 (b),
The state of a laser beam emitted from the light source LD (the light source LD1 or the light source LD2) is shown. The luminous flux emitted from the light source LD is divergent, but the divergence angle of the luminous flux is maximum in the “y direction (long axis direction of the far field pattern (elliptical shape in the figure)) perpendicular to the active layer, and It is the smallest in the parallel “x direction (the short axis direction of the far field pattern)”, and the minimum divergence angle: the maximum divergence angle is about 1: 2 to 1: 4 and is determined according to the type of the light source LD. The coupling lens 3 has a collimating function of converting the light beams from the light sources LD1 and LD2 into “substantially parallel light beams”, and a beam for expanding the light beam diameter in the direction of the minimum divergence angle to “close” the light beam cross-sectional shape. The shaping function is formed to have a single lens.

That is, the coupling lens 3 has the above-mentioned x,
An anamorphic lens having different optical effects in two directions of y. FIG. 1C shows the “lens action in the y direction” of the coupling lens 3. Light source LD
Since the luminous flux from the light source LD2 (exemplifying the light source LD2) has a large divergence angle in the y direction, the coupling lens 3 simply collimates the incident divergent light beam in the y direction to obtain a light beam diameter: Dy (substantially). A) A parallel light flux. Fig. 1 (d)
Indicates the “lens action in the x direction” of the coupling lens 3. Since the luminous flux from the light source LD has a small divergence angle in the x direction, the coupling lens 3 first enlarges the divergence angle of the luminous flux by refraction of the incident side surface in the y direction, and the luminous flux diameter: Dx on the exit side surface. Collimates into a parallel beam. The light beam diameter: Dx of the light beam converted into a parallel light beam by the lens action in the x direction is equal to the light beam diameter in the y direction: D
to be close to y. That is, the coupled light flux is “beam-shaped” by satisfying Dx ≒ Dy. 1C and 1D illustrate the light source LD2 as the light source LD, but the same applies to the light source LD1.

That is, the coupling lens 3 includes the light source LD
An anamorphic lens having a different lens action between the direction in which the divergence angle of the incident light beam becomes maximum (y direction) and the direction in which the divergence angle of the incident light beam becomes minimum (x direction).
And a function of substantially collimating the light beams from the second light sources LD1 and LD2 and a function of beam shaping.

As described above, in the present invention, since the coupling lens 3 has a beam shaping function as well as a collimating function, it is not necessary to use a "optical element dedicated to beam shaping" such as a prism pair or a cylindrical lens, and the optical pickup device is not required. It is possible to effectively avoid an increase in the size of the device and make the device compact.

It should be noted that the chromatic aberration of the coupling lens 3 may be affected by the difference between the emission wavelengths of the light sources LD1 and LD2, but this is not an effect that causes a practical problem.
Of course, it is also possible to correct chromatic aberration by configuring the coupling lens 3 as a “joint lens” of two lenses having different Abbe numbers. In addition, each surface of the coupling lens 3 can have an “aspherical shape” so that the collimating function and the beam shaping function are optimized according to the emission wavelength of each light source LD.

In the embodiment shown in FIG. 1, the light source LD2
Is located on the optical axis of the optical system after the coupling lens 3 and the light emitting section of the light source LD1 is "off" from the optical axis, so that either of the light sources LD1 and LD2 is turned on as described above. Depending on the situation, it is necessary to provide an offset to the detection signal or to provide a light receiving unit for each return light beam. In order to avoid such trouble, as described in the second aspect of the present invention, "the coupling of the optical axis of the light beam from the first light source LD with the optical axis of the light beam from the second light source LD is performed. The optical axis alignment optical means for matching each other may be used.

FIG. 2 schematically shows an embodiment of the optical pickup device according to the third aspect of the present invention, in which only portions necessary for explanation are schematically shown. FIG. 2A shows an embodiment in which the prism element 12 is used as “optical axis alignment optical means”. The film 121 formed in the prism element 12 has optical characteristics of reflecting S-polarized light and transmitting P-polarized light. That is, the prism element 12 is a “prism element having a different transmittance or reflectance depending on the polarization of the light beam”. The light beam from the light source LD1 is emitted as P-polarized light and transmits through the film 121. The light beam from the light source LD2 is emitted as S-polarized light, and is reflected by the film 121. Both the light beam transmitted through the film 121 and the light beam reflected by the film 121 have the optical axes (divergence angle: 0) coincide with the optical axis of the coupling lens 3 so that the light sources LD1, LD2,.
The positional relationship between the prism element 12, the coupling lens 3, and the like is determined.

FIG. 2B shows an embodiment in which the prism element 13 is used as "optical axis alignment optical means". The film 132 formed in the prism element 13 reflects S-polarized light,
It has optical characteristics of transmitting P-polarized light. The slope portion is a reflection surface 131. Therefore, the prism element 13 is also a “prism element having a different transmittance or reflectance depending on the polarization of the light beam”. The light beam from the light source LD1 is emitted as P-polarized light, reflected by the reflection surface 131, and transmitted through the film 132. The light beam from the light source LD2 is emitted as S-polarized light, and is reflected by the film 132. The luminous flux transmitted through the film 132 is also
The positional relationship among the light sources LD 1 and LD 2, the prism element 13, the coupling lens 3, and the like is determined such that the optical axis of the light flux reflected by the light source 32 also matches the optical axis of the coupling lens 3.

In the embodiment shown in FIGS. 2A and 2B, it is assumed that two light beams incident on the film 121 or 132 have "polarization directions orthogonal to each other". The laser beam emitted from the semiconductor laser that is the light source LD is substantially linearly polarized light, and the polarization direction is generally “the direction parallel to the active layer (the x direction in FIG. 1B)”. In such laser oscillation, since the oscillation direction of the electric field E of the laser beam is parallel to the active layer, "TE mode emission" is performed.
Called. FIG. 2C shows that the light source LD1 is of “TE mode light emission”.

2A and 2B, the light source LD1
Must be adjusted so that the polarization direction of the emitted light beam becomes P-polarized light with respect to the films 121 and 132.
2A and 2B, a light source L is used as a light source LD2.
Assuming that the light source LD2 emits light in the "TE mode" as in the case of D1, the light source LD2 is arranged in the orientation shown in FIGS. 2A and 2B so that the polarization direction is S-polarized with respect to the films 121 and 132. Must be determined. However, in this case, the “long axes of the far field patterns are orthogonal to each other” of the light beam incident on the coupling lens 3 from each light source LD, and the coupling lens 3 is anamorphic. The function will not be the same for the two light beams. Therefore,
In this case, a "TM mode light emission" light source is used as the light source LD2 (claim 16).

FIG. 2D shows that the light source LD2 is of "TM mode light emission". TM mode emission is the polarization direction of the emitted laser beam (electric field: the oscillation direction of E)
Are parallel to the direction perpendicular to the active layer (the major axis direction of the far field pattern). At this time, the oscillation direction of the magnetic field in the emitted laser beam becomes parallel to the active layer, so that "TM
It is called “mode emission”. At present, as a light source LD for TM mode light emission, a light source having an emission wavelength of 635 nm is known. When this is used as the light source LD2, the second type optical recording medium is set according to the wavelength: 635 nm.

2A and 2B, if the light source LD1 is of "TE mode emission" and the light source LD2 is of "TM mode emission", the polarization directions of the laser beams are orthogonal to each other. And the major axis directions of the far field patterns can be made parallel to each other. Of course, the light source LD1 may be of "TM mode emission" and the light source LD2 may be of "TE mode emission" (claim 16).

The optical arrangement after the coupling lens 3 in FIGS. 2A and 2B is the same as that in FIG. 1A except that the light sources LD1 and LD2 are set to the optical axis of the coupling lens 3. On the other hand, since the optical axes are aligned, the light receiving portion arrangement of the light receiving means 11 is the same for each return light beam.

Using “a prism element having a different transmittance or reflectance depending on the polarization of a light beam” as an optical axis alignment optical means,
When both light sources LD1 and LD2 have the same emission mode, the long axes of the two far-field patterns are set to be parallel to each other, and the polarization plane of the light beam from one light source LD is rotated by 90 degrees. What is necessary is just to use a "phaser" (claim 4).

Such a phaser is a well-known "1/2"
Wave plate ". That is, for example, as shown in FIG. 3A, a half-wave plate 14a is provided as a “phaser” on the incident surface on the light source LD1 side of the prism element 12 in FIG. As shown in FIG. 2B), if the half-wave plate 14b is provided as a “phaser” on the incident surface of the light beam from the light source LD1 in the prism element 13 in FIG.
As both 1 and 2, “the same light emission mode” can be used.

In the embodiments of FIGS. 2 and 3 described above, "a prism element having a different transmittance or reflectance depending on the polarization of the light beam" is used as the optical axis alignment optical means.
Various types of optical axis alignment optical means other than those using polarized light are possible. As the prism elements 12 and 13 in FIG. 2, "prism elements having different transmittance or reflectance depending on the wavelength" can be used (claim 5). A well-known “dichroic filter” has optical characteristics of transmitting light in a specific wavelength range and reflecting light of a wavelength outside the above wavelength range. Therefore, FIG.
As shown in (a), the film 121 of the prism element 12 or the film 132 of the prism element 13 transmits a light beam (wavelength: 785 nm) from the light source LD1 and reflects a light beam (wavelength: 650 nm) from the light source LD2. If formed as a filter film, the light sources LD1, LD2
Both of them can be arranged so that the polarization direction of the light beam and the major axis direction of the far field pattern are parallel to each other. As the optical axis alignment optical means, a "prism element having different polarization separation characteristics depending on the wavelength" can be used. FIG. 4 (a)
The prism element 12 'in FIG. 4 and the prism element 13' in FIG. 4C are "prism elements having different polarization separation characteristics depending on the wavelength". Film 1 in prism element 12A '
Reference numeral 21 'denotes a filter having "wavelength polarization filter characteristics" as shown in FIG. 4B, and the transmittance of S-polarized light and P-polarized light changes as shown in the figure with the wavelength. Since the light beam from the light source LD1 has a wavelength of 785 nm, the light beam from the light source LD1 is reflected by the film 121 'regardless of whether the polarization state is P-polarized light or S-polarized light, whereas the light beam from the light source LD2 has a wavelength of 650 nm.
This light flux transmits through the film 121 ′ when it is P-polarized light. Therefore, two light sources LD having the same light emission mode
4 are both set to “P-polarized light with respect to the film 121 ′”.
By arranging as shown in (a), desired optical axis alignment can be performed.

The film 13 of the prism element 13 'shown in FIG.
2 ′ (reference numeral 131 ′ indicates a “reflection surface”) corresponds to FIG.
This is a filter having the “wavelength polarization filter characteristic” as shown in FIG. 4D, and the transmittance of S-polarized light and P-polarized light changes with wavelength as shown in the figure. The light beam from the light source LD1 has a wavelength of 785.
nm, the light beam from the light source LD1 has a polarization state of S
, The light is reflected by the film 132 ′, but the light beam from the light source LD2 has a wavelength of 650 nm, and the film 1
32 'is transmitted.

Accordingly, the two light sources LD1 and LD2 having the same light emission mode are brought into the S-polarized state with respect to the film 132 'and are arranged as shown in FIG. It can be performed. Note that a film having characteristics as shown in FIG. 4C can be used as the film 121 ′,
It is also possible to use a film having characteristics as shown in FIG.

FIG. 5 shows two embodiments of the optical pickup device according to the eighth aspect of the present invention, showing only the portions necessary for explanation. The optical pickup device of the invention according to claim 8 is characterized in that "the first and second light sources LD are arranged in the same package". FIG. 5A shows an example in which the light sources LD1 and LD2 are arranged in the same package PC. Although the optical system from the coupling lens 3 to the optical recording medium, the optical path separating optical means for the return light beam, the detecting means, and the like are not shown, they are the same as those shown in FIG. In the embodiment of FIG. 5B, the light sources LD1 and LD2 are arranged in the same package PC ′, and the prism element as “optical axis alignment means” described with reference to FIG. 12 is an example in which the light flux from each light source LD is aligned with the optical axis. The optical system after the coupling lens is the same as the optical system arrangement shown in FIG. However, since the luminous flux from each light source LD is aligned with the optical axis, the arrangement of the light receiving section in the light receiving means of the detecting means is the same for each return light.

As a modification of the embodiment shown in FIG.
It goes without saying that (C) and the other “optical axis alignment means” described with reference to FIGS. 3 and 4 can be appropriately used.

FIG. 6 shows only the parts necessary for explaining the first embodiment of the present invention. FIG.
In (a), two light sources LD1 and LD2, a prism element 50 as an optical axis aligning unit, a phase shifter 5A, and a light receiving unit 110 as a detecting unit are provided in the same package PK. The light source LD1 has an emission wavelength of 785 nm,
It is assumed that the light source LD2 has an emission wavelength of 650 nm, and both light sources emit "TE mode light". The prism element 50 has two films 51 and 52 inside. The film 51 reflects the S-polarized light and transmits the P-polarized light with the polarization reflection film. The membrane 52 is shown in FIG.
It has "wavelength polarization filter characteristics" as shown in FIG. From the light sources LD1 and LD2, S
A laser beam is emitted so as to be polarized. Light source LD2
Is turned on, the laser beam having a wavelength of 650 nm is S-polarized light, is reflected by the film 51, passes through the film 52, and enters the coupling lens 3 via the phase shifter 5A. When the light source LD1 is turned on, the emitted luminous flux having a wavelength of 785 nm is S-polarized, and is thus reflected by the film 52 and the phase shifter 5A.
And enters the coupling lens 3 via the. Phaser 5A
Has a function of converting the polarization state of each light beam from the light sources LD1 and LD2 from “linearly polarized light to circularly polarized light and from circularly polarized light to linearly polarized light”, that is, a function as a 波長 wavelength plate. This function is the same as the “function of the phase shifter 5” in the embodiment of FIG. In a single-beam type optical pickup device, since only one kind of light beam is used and “one wavelength”, a １ ／ wavelength plate used may be an ordinary one. However, in the optical pickup of the present invention, two types of light beams having different wavelengths are used for recording and reproduction, and therefore, the phase shifter 5A (or the phase shifter 5) having a function as a quarter-wave plate is composed of two types. It is necessary to function as a quarter-wave plate for any of the light having the wavelengths of.

Such a phase shifter can be realized as follows. The refractive index difference with respect to the ordinary ray and the extraordinary ray in the birefringent material forming the phase shifter 5A, wavelength: lambda relative ₁ (785 nm in the example in the description): N _1, wavelength: lambda ₂ (in the example in the description 650 nm), N ₂ and the mechanical thickness of the birefringent material as d, and the wavelength: λ ₁ , λ ₂ , the phase difference between the ordinary ray and the extraordinary ray when transmitted through the birefringent material Is a 1/4 wavelength assuming that k ₁ and k ₂ are integers, N ₁ · d = (k ₁ + ／) λ ₁ , N ₂ · d = (k ₂ + 1 /
4) λ _2. Therefore, "(k ₁ + ／) λ ₁ / N ₁ = (k ₂ +1
/ 4) By setting the integers: k ₁ and k ₂ so as to satisfy λ ₂ / N ₂ , the thickness d of the birefringent material can be determined,
The birefringent material having this thickness: d has the wavelength: λ ₁ ,
It becomes a “phaser” that functions as a １ ／ wavelength plate for both lights of λ ₂ . Such a retarder can be formed as a "deposited film" (claim 11).

Returning to FIG. 6, the light beam transmitted through the coupling lens 3 is condensed as a light spot on the recording surface of the optical recording medium by the objective lens (via a deflecting prism if necessary), and reflected by the recording surface. The transmitted light beam passes through the objective lens and becomes a return light beam, enters the phase shifter 5A via the coupling lens 3, and returns to linearly polarized light by passing through the phase shifter 5A. On the other hand, since the light becomes P-polarized light, the return light flux passes through the films 52 and 51 regardless of the wavelength and enters the light receiving means 110. The light receiving means 110
As shown in FIG. 6B, a four-division light receiving element (the vertical direction is parallel to the vertical direction in FIG. 6A) has a light receiving surface: α,
Light receiving signals: Sα, Sβ, Sγ, Sδ are output from β, γ, δ.

The light receiving means 110 is designed so that the returning light beam (when the tracking error is 0) is condensed at the intersection of the dividing lines dividing the light receiving surface. The coupling lens 3 is an “anamorphic lens” having a collimating action in the long axis direction of the light field from the light source LD in the long axis direction and a collimating action and beam shaping action in the short axis direction. If an error occurs between the light collecting part of the spot and the recording surface, "astigmatism" occurs. Accordingly, “focusing control by the astigmatism method” is performed with (Sα + Sγ) − (Sβ + Sδ) as the focus error signal.
, And “tracking control by the push-pull method or the phase difference method” using (Sβ−Sδ) as a tracking error signal can be performed. The playback signal is (Sα
+ Sγ + Sβ + Sδ).

That is, in the embodiment shown in FIG. 6, the optical axis of the light beam from the first light source LD1 and the optical axis of the light beam from the second light source LD2 coincide with each other with respect to the coupling lens 3. An optical pickup device having an optical axis aligning optical means (claim 2), wherein the optical axis aligning optical means has a film 51 having a different transmittance or reflectance depending on the polarization of a light beam.
And a film 52 having different polarization / separation characteristics depending on the wavelength of the light beam. The phase element 5A acts as a quarter-wave plate for each light beam from the light sources LD1 and LD2.
And the returning light beam is coupled to the coupling lens 3 and the phase shifter 5.
A and the light receiving means 1 of the detecting means via the prism element 50
10. The retarder 5A and the prism element 50 constitute "optical path separating optical means", and the light receiving means 110 and the coupling lens 3 constitute detecting means. Further, the first and second light sources LD1 and LD2 are arranged together with other optical elements in the same package PK (claim 8).

FIG. 7 shows a ninth embodiment of the present invention. This embodiment is different from the embodiment shown in FIG. 1A in that a polarizing hologram 40 is used as an optical path separating optical unit, and a coupling lens 3 and a light receiving unit 11A are used.
This is a mode in which the detection means is configured by the above. The polarizing hologram 40 is configured such that "when the polarization direction of the polarized light beam is parallel to the groove, the diffractive effect acts, and when the polarization direction of the polarized light beam is orthogonal to the groove, the diffractive effect does not act". When the light source LD1 or the light source LD2 is turned on, the emitted light flux is collimated and beam-shaped by the coupling lens 3, passes through the polarization hologram 40 without being subjected to the diffraction action, and is circularly polarized by the phase shifter 5. The light is converted into a state, enters the objective lens 7 via the deflection prism 6, and is condensed as a light spot on the recording surface of the optical disk 8A or 8B. The light reflected by the recording surface passes through the objective lens 7 to become a return light flux, is reflected by the deflecting prism 6, passes through the phase shifter 5, and becomes a linearly polarized state in a direction orthogonal to the initial direction. Then, the light enters the light receiving unit 11A via the coupling lens 3.

As shown in FIG. 11A, the polarizing hologram 40 has three hologram portions 4 having different diffraction effects.
01, 402, and 403, and the return light beam incident on the hologram portion 401 is incident on the two-divided light receiving portion 11A of the light receiving means 11A shown in FIG. The portions enter the light receiving portions 11A2 and 11A3, respectively. These incident light beams are converged toward the respective light receiving portions by the action of the coupling lens 3. The “linear boundary” between the hologram portion 401 and the hologram portions 402 and 403 of the polarizing hologram 40 functions as a “knife edge” for focusing control by the knife edge method, and a focus error for focusing control. The signal is configured as a difference between outputs from the respective light receiving units of the two-divided light receiving portion 11A1. Further, a tracking error signal for tracking control can be configured as a difference between outputs of the light receiving portions 11A2 and 11A3. Of course, the reproduced signal is transmitted to the light receiving portion 11.
A1, 11A2, and 11A3 are obtained as output sums. In the embodiment of FIG. 7, since the light sources LD1 and LD2 are not aligned, the incident positions of the three light spots on the light receiving unit 11A are slightly shifted depending on which light source LD is turned on. The signal is adjusted by giving an appropriate offset so that an appropriate signal is obtained according to each light source LD.

FIG. 8 shows a first embodiment of the present invention.
The form is shown. An optical pickup device according to a tenth aspect of the present invention is an optical pickup device comprising:
0 and the phase shifter 5A are integrated, and the phase shifter 5A acts as a quarter-wave plate with respect to the light beams having different wavelengths from the first and second light sources LD1 and LD2. " I do. The optical axis of each light beam from the light sources LD1 and LD2 is aligned with the optical axis of the coupling lens 3 by the prism element 13 'by the optical axis alignment based on the "wavelength polarization filter characteristic" described with reference to FIG. Then, the light enters the coupling lens 3 and is collimated and beam-shaped, passes through the polarization hologram 40, and transmits the phase shifter 5A (a vapor deposition film similar to that described with reference to FIG. The light is converted into a circularly polarized light by an optical recording medium (not shown) via a deflecting prism.

The return light beam from the optical recording medium is transmitted to the phase shifter 5A.
And returns to the linear polarization state, and the polarization hologram 40
The light is diffracted by the action of (1) and is incident on the light receiving means 11A via the coupling lens 3 so as to be condensed. The polarization hologram 40 and the light receiving means 11A are the same as those described with reference to FIG. 11, and the focus error signal, the track error signal, and the reproduction signal are obtained in the same manner as described above.

FIG. 9 shows a first embodiment of the present invention.
The form is shown. An optical pickup device according to an eleventh aspect of the present invention is the optical pickup device, wherein the optical path separating optical means is a polarization hologram 4
The phase shifters 5A and 14A are integrated on both surfaces of the light beam 0, and one phase shifter 14A has a polarization plane of only one light flux of 9
It has a function of turning by 0 degrees, and the other phase shifter 5A acts as a quarter-wave plate for each light beam. "

The light source LD1 is of "TE mode light emission", and the light source LD2 is of "TM mode light emission". The optical axis is adjusted using the prism element 13 described with reference to FIG. Is performed.

When the light source LD1 or the light source LD2 is turned on, the light beam is collimated by the coupling lens 3 and beam-shaped, and is incident on the phase shifter 14A. In this case, at the stage of entering the phase shifter 14A, the polarization directions of the light beam are orthogonal to each other between the light beam from the light source LD1 and the light beam from the light source LD2.

Therefore, the phase shifter 14A functions as a half-wave plate for only one light beam, rotates its polarization plane by 90 degrees, and acts to maintain the polarization direction for the other light beam. Such conditions that the retarder 14A should satisfy include the refractive index difference between the ordinary ray and the extraordinary ray in the birefringent material constituting the retarder 14A, for a wavelength: λ ₁ (785 nm in the example being described): N _1, wavelength: a N ₂ relative to (635 nm in the example in the description) lambda _2, if the mechanical thickness of the birefringent material is d, the wavelength to λ _1, λ _2, birefringence The condition that the phase difference between the ordinary ray and the extraordinary ray when transmitted through the material is 1 wavelength and 1/2 wavelength respectively is as follows: k ₁ and k ₂ are integers, and N ₁ · d = (k ₁ +1) λ ₁ , N ₂ · d = (k ₂ + ／)
It is λ _2. Therefore, “(k ₁ +1) λ ₁ / N ₁ = (k ₂ + 1 /
2) By setting the integers: k ₁ and k ₂ so as to satisfy λ ₂ / N ₂ ”, the thickness: d of the birefringent material can be determined. wavelength: lambda ₁ of ordinary transparent film to light, wavelength: functions as a half wavelength plate with respect to lambda ₂ light is "retarder". A birefringent material having such a thickness can be formed as a “deposited film”.

Thus, the light sources LD1 and LD2
Are transmitted through the polarizing hologram 40 without being diffracted by the polarizing hologram 40 and are converted into a circularly polarized state by the phase shifter 5A. Irradiated. The returned light flux returns to a linearly polarized state by the phase shifter 5A, is diffracted by the polarization hologram 40, passes through the phase shifter 14A, enters the light receiving unit 11A via the coupling lens 3, and generates various signals. Polarizing hologram 40,
The light receiving means 11 is the same as that described with reference to FIG. The retarders 5A and 14A can be configured as a “deposited film” as described above (claim 11), and the birefringent material forming the deposited film is magnesium fluoride (Mg).
F ₂ ) and the like can be suitably used.

FIG. 10 shows an embodiment of the optical pickup device according to the present invention. According to a thirteenth aspect of the present invention, the detecting means 11A 'for receiving each light beam separated by the optical path separating optical means and detecting the information of the reflected light beam has the same package as the first and second light sources LD1 and LD2. Placed in PK1 ".
The optical pickup device according to claim 14, wherein the optical path separating means 40 'and 5A' (a phase shifter acting as a quarter-wave plate for each light beam) having the polarizing hologram 40 'is connected to the detecting means 11A and the first And the second light sources LD1 and LD2 are integrated into the same package PK1.

As in this embodiment, the polarization hologram 40 ′ and the phase shifter 5 A ′ can be provided between the light source LD and the coupling lens 3. These polarizing hologram 40 'and light receiving means 11A' are the same as those described with reference to FIG. In the configuration as shown in FIG. 10, the light source, the optical path separating optical unit, and the detecting unit can be compactly integrated by the package PK1, so that the optical pickup device can be made compact.

Of course, as a modification of the embodiment of FIG. 10, the optical axes of the light beams from the light sources LD1 and LD2 can be aligned by the various methods described above. "A phaser that functions as a half-wave plate for only one light beam, rotates its polarization plane by 90 degrees, and acts to maintain the polarization direction for the other light beam" on the side surface. Or, of course, it can be deployed separately.

[0063]

As described above, according to the present invention, a novel optical pickup device can be realized. The optical pickup device of the present invention is an optical pickup device that can be used for both first and second types of optical recording media having different recording / reproducing wavelengths. A coupling lens, which is provided in common and couples light beams from the respective light sources LD, is configured to have a function of substantially collimating the light beams from the first and second light sources LD and a function of beam shaping. Because
There is no need to provide a dedicated beam shaping means in addition to the coupling lens, and the optical pickup device can be made compact. Also, beam shaping is performed by “enlarging the beam diameter in the direction of the minimum divergence angle of the laser beam”,
The light use efficiency of the light flux from the light source is good.

In the optical pickup device according to the second to eighth aspects of the present invention, since the optical axes of the light beams from the two light sources LD are aligned, the positional relationship between the return light beam and the detecting means becomes the same without being selected as the light source. The detection by the detecting means is simplified. In addition, since each light beam enters the coupling lens and the objective lens without having an angle of view, deterioration of the wavefront due to these lenses can be minimized, and a good light spot can be obtained.

According to the ninth to twelfth aspects of the present invention, since the optical path separating optical means has the polarizing hologram, it is possible to arrange the detecting means for detecting the return light beam on the same side as the light source, By using a hologram, an element for generating a servo signal (focus error signal / track error signal) such as a knife edge prism becomes unnecessary, so that the optical pickup device can be made more compact.

Further, by integrating the phase shifter with the polarizing hologram, the compactness of the optical pickup device is promoted, and the variation between the components is reduced, so that the optical pickup device is improved. Increases reliability. By configuring the retarder as a vapor-deposited film as in the twelfth aspect of the present invention, the retarder can be made thinner, and there is no need to use an expensive birefringent crystal as a material for the retarder, and the optical pickup device can be made smaller. And cost reduction.

Further, as in the invention according to claims 8 and 14, by integrating other elements together with the first and second light sources LD in the same package, the number of parts is reduced and integrated parts are provided. It is possible to improve the reliability by preventing the fluctuations between them.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of the invention described in claim 1;

FIG. 2 is a view for explaining an embodiment of the invention described in claims 2 and 3;

FIG. 3 is a diagram for explaining an embodiment of the invention described in claims 2 and 4;

FIG. 4 is a view for explaining an embodiment of the invention described in claims 2 and 6;

FIG. 5 is a diagram showing only the characteristic portion of the embodiment of the invention described in claim 8;

FIG. 6 is a diagram showing only the characteristic portions of the embodiment of the invention described in claims 2, 7, and 8;

FIG. 7 is a diagram showing an embodiment of the invention described in claim 9;

FIG. 8 is a diagram showing an embodiment of the invention according to claims 9 and 10;

FIG. 9 is a diagram showing only one characteristic portion of the first embodiment of the present invention.

FIG. 10 is a diagram showing only a characteristic portion of the embodiment of the invention described in claim 14;

FIG. 11 is a diagram for explaining a polarizing hologram and a light receiving means when using the same.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source LD 2 Light source LD 3 Coupling lens 4 Polarization beam splitter 5 1/4 wavelength plate 6 Deflection prism 7 Objective lens 8A Optical disk (optical recording medium) 8B Optical disk (optical recording medium) 9 Condensing lens 10 Cylindrical lens 11 Light receiving means

Claims (16)

[Claims] 1. An optical pickup device that can be used for both first and second types of optical recording media having different recording / reproducing wavelengths, wherein the first and second light sources have different emission wavelengths. An LD, a coupling lens which is provided in common for the first and second light sources LD, and couples a light beam from each light source LD; and outputs each coupled light beam to an optical recording surface of an optical recording medium. An objective lens common to each light beam to be condensed as a spot, and each light beam reflected by the optical recording medium and returned as a light beam through the objective lens, from an irradiation light path from the light source LD to the objective lens. An optical path separation optical unit common to the respective light beams to be separated; and a detection means common to the respective light beams to receive the respective light beams separated by the optical path separation optical unit and detect information on the reflected light beams. And control means for performing focusing control and tracking control based on the detection result of the detection means, wherein the first light source LD is turned on only when the first type optical recording medium is used, The second light source LD is turned on only when the second type of optical recording medium is used, and the coupling lens minimizes the direction in which the divergence angle of the incident light beam is common and common to each light beam. An anamorphic lens having a different lens action in different directions.
And an optical pickup device having a function of substantially collimating a light beam from the second light source LD and a function of beam shaping. 2. The optical pickup device according to claim 1, wherein the optical axis of the light beam from the first light source LD and the optical axis of the light beam from the second light source LD coincide with each other with respect to the coupling lens. An optical pickup device comprising an optical axis aligning optical unit for causing the optical axis to be adjusted. 3. The optical pickup device according to claim 2, wherein the optical axis aligning optical means is a prism element having a different transmittance or reflectance depending on the polarization of the light beam. 4. The optical pickup device according to claim 2, wherein the optical axis aligning optical means includes a prism element having different transmittance or reflectance depending on the polarization of the light beam, and a phase shifter for rotating the polarization plane of one light beam by 90 degrees. An optical pickup device comprising: 5. The optical pickup device according to claim 2, wherein the optical axis alignment optical means is a prism element having a different transmittance or reflectance depending on the wavelength of the light beam. 6. The optical pickup device according to claim 2, wherein the optical axis alignment optical means is a prism element having different polarization separation characteristics depending on the wavelength of the light beam. 7. The optical pickup device according to claim 2, wherein the optical axis alignment optical means has a film having different transmittance or reflectance depending on the polarization of the light beam, and a film having different deflection / separation characteristics depending on the wavelength of the light beam. A phase shifter that acts as a quarter-wave plate for each light beam from each light source LD, and a return light beam is transmitted to a detection unit via a coupling lens, the phase shifter, and the prism element. By being configured to be incident on the light receiving means, the phaser and the prism element constitute an optical path separating optical means, and the light receiving means and the coupling lens constitute a detecting means. Optical pickup device. 8. The optical pickup device according to claim 1, wherein the first and second light sources LD are arranged in the same package. 9. An optical pickup device according to claim 1, wherein the optical path separating optical means has a polarizing hologram. 10. An optical pickup device according to claim 9, wherein the optical path separating optical means integrally forms a polarizing hologram and a phaser, wherein the phaser is mutually separated from the first and second light sources LD. An optical pickup device which functions as a quarter-wave plate for light beams having different wavelengths. 11. An optical pickup device according to claim 9, wherein the optical path separating optical means is such that a phase shifter is integrated on both sides of the polarizing hologram, and one of the phase shifters comprises only one light flux. An optical pickup device having a function of rotating a polarization plane by 90 degrees, and the other retarder acting as a quarter-wave plate for each light beam. 12. The method according to claim 5, wherein
The optical pickup device according to claim 1, wherein the retarder is formed as a vapor-deposited film. (13) An eighth or ninth or tenth or eleventh aspect.
Or in the optical pickup device according to 12, receiving each light beam separated by the optical path separating optical unit,
The detecting means for detecting the information of the reflected light flux includes first and second information.
An optical pickup device disposed in the same package as the light source LD. 14. The optical pickup device according to claim 13, wherein the optical path separating means having the polarization hologram is integrated into the same package containing the detecting means and the first and second light sources LD. An optical pickup device characterized by the above-mentioned. 15. The optical pickup device according to claim 1, wherein the first light source LD has an emission wavelength of 785 nm, the second light source LD has an emission wavelength of 650 nm, and the first light source LD has a light emission wavelength of 650 nm. An optical pickup device characterized in that the optical recording medium is a low-capacity optical disk having a substrate thickness of 1.2 mm, and the second type of optical recording medium is a large-capacity optical disk having a substrate thickness of 0.6 mm. 16. An optical pickup device according to claim 1, wherein one of the light sources LD emits light in a TE mode, and the other light source LD emits light in a TM mode. Optical pickup device.