JP3471960B2 - Pickup device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pickup device used for recording or reproducing a video signal, an audio signal or the like on an optical recording medium such as an optical disk, and particularly reproducing different types of optical recording media. The present invention relates to improvement of a pickup device for use in a reproducing device.

[0002]

2. Description of the Related Art In recent years, high density recording optical discs have been developed. In order to read this high-density recorded optical disc, it is necessary to form a minute spot on the information recording surface of the optical disc, so a pickup device having an objective lens with a large numerical aperture is required. On the other hand, if an attempt is made to read a conventional optical disk with an objective lens having a large numerical aperture, the thickness of the substrate of the optical disk is different, so that the spot generated on the information recording surface spreads and the information cannot be read well. Therefore, a pickup device using a bifocal lens has been used to read a plurality of types of optical discs having different substrate thicknesses.

FIG. 7 shows a pickup device using a conventional bifocal lens. As shown in FIG. 7, in the conventional pickup device 200, the light beam emitted from the laser light source 101 is reflected by the beam splitter 102 and collimated by the collimator lens 103.
The objective lens 105 includes a holographic optical element 104.
Is stuck. Therefore, the holographic element 10
The light beam incident on the beam No. 4 is split into first-order light that is diffracted light and zero-order light that is non-diffracted light.

Since the 0th-order light is incident on the objective lens 105 as parallel rays, the spherical aberration becomes almost 0 for a disk having a thin substrate, and an ideal spot is formed on the information recording surface. The incident angle of the outermost ray (peripheral ray) of the primary light to the objective lens 105 exists at a predetermined angle. This predetermined angle is such that when the objective lens 105 focuses the primary light on a disc having a substrate thicker than the optical disc, an imaging point is formed at a distance different from that of the zero-order light. The angle is set so as to correct the spherical aberration at this image formation point. Therefore, the spherical aberration of the primary light focused by the objective lens 105 becomes almost zero.

With the above arrangement, the best focusing is obtained when the information recording surface of the optical disk exists at the 0-dimensional image forming point, and the information recording surface of the optical disk exists within the one-dimensional correction of spherical aberration. Also in the case of doing, a readable return light is obtained.

The 0th-order light beam or the 1st-order light beam is reflected on the information recording surface of the optical disc 106,
It is emitted as return light along the same optical axis as at the time of incidence. Then, it again enters the beam splitter 102 via the objective lens 105 and the holographic element 104. Since the beam splitter 102 transmits the return light from the optical disk, either the 0th order light or the 1st order light is detected by the photodetector 10.
Detected at 7.

[0007]

However, the above-mentioned conventional pickup device has the drawback that the intensity of the return light detected by the photodetector is low and the light utilization efficiency is low. The reason for this is that the light beam passes through the holographic element and the collimator lens twice before and after it is irradiated onto the optical disc, and the holographic element simultaneously transmits not only the first-order light but also higher-order diffracted light. The reason may be that it occurs. For example, when the light beam passes through the holographic element once, the amount of diffracted light after diffraction is reduced to about 30% of that at the time of incidence. According to the above conventional example, since the light beam passes through the holographic element twice in total, the final light amount (diffraction efficiency) of the obtained return light with respect to the incident light is significantly reduced to about 9%.

Further, in the conventional example, since the holographic element is fixed to the objective lens, there is a drawback that the actuator for driving the heavy objective lens becomes large. That is, in order to drive a heavy objective lens, not only the driving power of the servo circuit must be increased, but also the number of windings of magnets and coils in the pickup device must be increased in order to obtain a stronger driving force. .

Therefore, in view of the above-mentioned drawbacks, an object of the present invention is to enable recording / reproducing with high light utilization efficiency and driving on any of a plurality of types of optical recording media having different substrate thicknesses. An object of the present invention is to provide a pickup device that requires less load.

[0010]

According to a first aspect of the present invention, there is provided a pickup device for recording and / or reproducing information on a plurality of types of optical recording media having substrates having different thicknesses. Of the pickup device, which is supplied from the light source
A ray bundle having one polarization plane of the light beam
Different for a bundle of rays with a different plane of polarization
A polarization separation means for providing a stroke having an optical path length of
A beam splitter for changing the path of at least one of the light beam from the polarization splitting means and the return light from the condensing means, and each of the light beam bundles supplied through the beam splitter, are optically recorded. The light condensing means for condensing on the information recording surface of the medium and for returning the return light from the information recording surface caused by the condensing to the beam splitter again, is separated by the polarization separating means. Ray of light
Each of the bundles is adjusted so that the spherical aberration at the time of focusing on the information recording surface of the optical recording medium by the converging unit becomes substantially zero for any one of the plurality of types of optical recording media. ing.

The pickup device according to claim 2 is a contractor.
In the pickup device according to claim 1, the polarized component
Away means causes the transmission of the light beams having one polarization plane of the light beam supplied from the light source, the light emitted the light beam having a polarization plane different from the plane of polarization of the one along a predetermined optical axis A beam splitting means and a beam of light that has passed through the light beam splitting means are provided with a predetermined stroke from the position of passing through the light beam splitting means , and the light flux that has gone through the predetermined stroke is along the predetermined optical axis. And an optical path difference generating means for emitting the light.

The pickup device according to claim 3 is a contractor.
In the pickup device according to claim 1, the polarized component
The separating means is an optical element having a different refractive index with respect to the first polarization component in the optical axis of the light beam supplied from the light source and a second polarization component different from the polarization component.

The pickup device according to claim 4 is a contractor.
In the pickup device according to claim 1, the polarized component
The separating means transmits a part of a bundle of rays of the light traveling on the same optical axis as the optical axis of the light beam supplied from the light source , and reflects the rest of the bundle of rays along the optical axis. A separating means; a second separating means which is installed on the optical axis, transmits a part of the light flux of the light traveling on the optical axis, and reflects the remaining light flux along the optical axis; It is configured with.

The pickup device according to claim 5 is a contractor.
In the pickup device according to claim 4, at least one of the first separating unit and the second separating unit is
A polarization separation film that transmits a light beam having a first polarization plane and reflects a light beam having a different polarization plane on the optical axis between the first separation means and the second separation means. In the above, a phase adding means for interposing a predetermined amount of phase change with respect to the polarization component of the light beam passing therethrough is interposed.

According to a sixth aspect of the present invention, there is provided the pickup device according to any one of the first to fifth aspects, wherein the condensing means is one of a plurality of light beam bundles supplied from the beam splitter. A collimator lens for converting one light ray bundle into a substantially parallel light ray bundle, and an objective lens for condensing the plurality of light ray bundles including the parallel light ray bundle passing through the collimator lens on the information recording surface of the optical recording medium. , And are configured.

[0016]

[0017]

[0018]

According to the pickup device of the first aspect,
The polarized light separating means is one of the light beams supplied from the light source.
Of light having a plane of polarization of 2 and polarization different from the plane of 1 of polarization
A path with a different optical path length for a bundle of rays with a surface
give.

The beam splitter changes the path of at least one of the light flux from the polarization splitting means and the return light from the condensing means. That is, the traveling direction of the light flux from the polarized light separating means is changed, or the traveling direction of the return light is changed. Therefore, light flux transmitted through the single polarization separation means, there is no being transmitted through the polarization separation means again, not subject to loss of light.

The light collecting means collects each of the light fluxes supplied through the beam splitter on the information recording surface of the optical recording medium. Further, the return light from the information recording surface generated by this light collection is again supplied to the beam splitter. By the beam splitter, the returned light is supplied to, for example, a photodetector or the like without being supplied to the light beam splitting means again.

The light beam separated by the polarized light separating means
Each of the bundles is adjusted so that the spherical aberration at the time of condensing on the information recording surface of the optical recording medium by the condensing means becomes substantially zero with respect to any of the plurality of types of optical recording media (for example, A method of providing a difference in the optical path length between the light beam bundles, a method of changing the incident angle of the marginal ray when entering the light converging means, and the like). Therefore, good focusing is performed on the optical disk having the substrate thickness within the correctable range where the spherical aberration is substantially zero. That is, information can be read from each of the optical recording media having different substrate thicknesses.

The light source may be one that emits parallel light rays or one that gives gradually expanding light rays .

According to the pickup device of the second aspect , the light beam splitting means transmits the light beam bundle having one polarization plane of the light beam supplied from the light source, and transmits the polarization plane different from the one polarization plane. A light ray bundle having a is emitted along a predetermined optical axis. At this time, the light beam splitting means splits the light flux by the plane of polarization, so that the loss of the amount of light is small especially when the incident light is circularly polarized light. The optical path difference generating means is a light beam
A predetermined stroke is given to the light flux that has passed through the separation means from the position where the light beam split means has passed, and the light flux that has advanced the predetermined stroke is emitted along a predetermined optical axis. That is, although the two optical fluxes at the position emitted from the optical path difference generating means have the advancing optical axes coincident with each other, an optical path difference exists between them. Therefore, the light flux emitted from the light flux splitting means goes through different steps. By adjusting the difference in this process in accordance with the correction amount of the spherical aberration required by the light converging means, a good light condensing state can be obtained for the optical recording medium having the substrates having different thicknesses.

According to the pickup device of the third aspect , the polarization separation means has a refractive index for the first polarization component on the optical axis of the light beam and a second polarization component different from the first polarization component. Since the optical elements are different from each other in refractive index, the light beam transmitted through the polarization splitting means includes a plurality of ray bundles having substantially different strokes.

That is, the difference in the refractive index when the light beam is transmitted is the difference in the air-converted process on the assumption that the light beam travels in the air. Thus, for example, when the refractive index with respect to the first polarization component is higher than the refractive index with respect to the second polarized light component, the polarized light separating hands
The advanced travel of the ray bundle having the first polarization component transmitted through the step is greater than the advanced travel of the ray bundle having the second polarization component.

According to the pickup device of the fourth aspect , the first separating means transmits a part of the light flux of the light traveling on the same optical axis as the optical axis of the light beam supplied from the light source. , Reflect the rest of the bundle of rays along the optical axis. Also, the second
The separating means is installed on the same optical axis, transmits a part of the light flux of the light traveling on the optical axis, and reflects the remaining light flux along the optical axis. For example, a part of the light beam transmitted through the first separating means is reflected again by the second separating means and returns to the first separating means. In the first separating means, a part of the returned ray bundle is reflected again toward the second separating means.

Therefore, among the ray bundles which have passed through the second separating means, the ray bundle which has first directly passed through the second separating means and the ray bundle which has reciprocated between the second separating means and the first separating means. And are included. Since both ray bundles have an optical path difference with each other, this optical path difference is adjusted according to the correction amount of the spherical aberration required in the condensing means.

According to the pickup device of the fifth aspect, at least one of the first separating means and the second separating means transmits a light beam bundle having a first polarization plane and has a polarization plane different from this. It is a polarization separation film that reflects the bundle of rays of light. For example, assuming that the first separating means is a polarization separating film, the light flux transmitted through the first separating means and reflected by the second separating means is given a predetermined amount of phase by the phase adding means. The plane of polarization of the ray bundle when entering the first separating means again has a different plane of polarization than when the ray bundle was transmitted last time. Therefore, of this bundle of rays, the bundle of rays having a polarization component other than the first polarization plane is reflected. A part of the reflected ray bundle passes through the second separating means.

That is, by using the polarized light separating film and the phase adding means in combination, as in the invention according to claim 5,
It is possible to obtain a plurality of ray bundles having optical path differences with each other .

According to the sixth aspect of the present invention, one of the plurality of light ray bundles incident on the objective lens becomes a substantially parallel light ray bundle. That is, the spherical aberration on the pupil of the collimator lens differs for each ray bundle. For a bundle of rays that have become parallel rays, even if the position of the bundle may fluctuate along the optical axis due to the focus servo or other operation of the objective lens, the accuracy of the spherical aberration can be kept almost zero. Good light collection is possible. Therefore, if a spot having a higher recording density among a plurality of optical recording media is read by the spot obtained by the parallel light beam, accurate information can be read.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the apparatus of the present invention will be described with reference to the drawings. In particular, each embodiment relates to a pickup device having compatibility between a compact disc and a digital video disc. (I) pick-up device of the first embodiment of the first embodiment the present invention, claim
The inventions of claims 1 and 2 and claim 6 are applied. Configuration of Optical System FIG. 1 shows the overall configuration of an optical system in the pickup device of the present invention.

As shown in FIG. 1, the pickup device of the present invention has a structure in which a prism as a polarized light separating means is interposed in the optical system of an optical disc pickup device for reproducing an ordinary type of optical disc. Equipped with.

The laser light source 21 is a semiconductor laser that emits red laser light. It may be a blue laser having an optical non-linearity suitable for reading out information having a higher density. The prism 25a corresponds to the polarized light separating means described in the claims. The prism 25a splits one light beam into two ray bundles (S-polarized light and P-polarized light), and further gives one ray bundle a long optical path length. Details will be described later.

The beam splitter 22 has a prism 25a.
From the optical disc 26 to the optical disc 26. The collimator lens 23 refracts the gradually expanding light flux, and changes the emitting directions of the 0th-order light and the 1st-order light at a larger angle as the distance from the center of the optical axis increases. The collimator lens 23 includes a dielectric protective film 33 (see FIG. 2) of the prism 25a.
It is adjusted so that the bundle of rays with the longer optical path length that is emitted after passing through (see) will be parallel rays.

The objective lens 24 has a large numerical aperture in order to form a minute spot on an optical disc for high density recording. This objective lens is a collimator lens 2
When a parallel light beam enters from 3, an ideal spot with spherical aberration of 0 is formed.

As the optical disk 26, in this embodiment, a high density recording digital video disk with a thin substrate (= 0.6 mm) and a thicker substrate (= 0.6 mm) are used.
1.2 mm) Consider a compact disc. The optical disc 26 is formed by coating a substrate with a protective layer. Recording pits for carrying information are provided on the information recording surface of the substrate. When the optical disc 26 is a digital video disc, the protective layer is thick and the substrate is thin.
An information recording surface exists at the position of a. Also, the optical disc 2
When 6 is a digital video disc, the protective layer is thin and the substrate is thick, so that the information recording surface exists at the position 26b.

The bundle of rays (return light) reflected by the information recording surface of the optical disc 26 passes through the objective lens 24 and the collimator lens 23, passes through the beam splitter 22, and enters the photodetector 27.

The photodetector 27 photoelectrically converts the received return light and outputs it as a detection signal to a reproduction circuit (not shown).
In addition, in order to eliminate the influence of the unused polarization component and the like, a polarization separating means may be provided in front of the photodetector 27 to remove unnecessary polarization components.

Further, a variable polarization filter 28 (see the broken line in FIG. 1) such as a liquid crystal plate, which can freely change the polarization direction, may be interposed between the laser light source and the prism 25a to be used as a normal pickup device. . That is, because of the presence of the variable polarization filter, only one of the polarization components is selected, and the optical disc can be read using only this one light. Description of Polarization Separation Means FIG. 2 shows the structure of a prism 25a, which is a light beam splitting means used in this embodiment.

The present prism 25a is similar to a so-called penta prism (a pentagonal prism), but differs from a normal penta prism in that it has a light separating surface 33.
The incident surface 32 and the exit surface 36 transmit all the light beams regardless of the polarization direction of the light beam from the laser light source 21.

The dielectric multilayer film 33 is composed of a polarization separation film, and transmits only a light flux having a specific polarization component (for example, P polarization) of a light beam having a plurality of polarization planes and transmits other polarization components ( For example, it reflects a ray bundle having S-polarized light. The prism 25a is installed such that the surface of the polarization separation film forms an angle of 45 degrees with the optical axis from the laser light source. As the dielectric multilayer film 33, another structure (what is called a polarizer or the like) can be applied as long as it is an optical element having a function of splitting a specific polarized light.

The reflecting surfaces 34 and 35 act as reflecting prisms. By the two reflections of the reflecting surfaces 34 and 35,
The incident ray bundle changes its direction twice at right angles. The prism 25a has reflecting surfaces 33 and 34 configured to emit a bundle of rays reflected in a direction perpendicular to the optical axis when the bundle of rays is incident on the dielectric multilayer film 33 at an angle of 45 degrees. ing.

If the structure is for obtaining the required difference in optical path length, the shape of the prism and the number of reflections are not limited,
It is possible to select the optimum outer shape that is allowed for the pickup device. For example, as in the following modified example, a plurality of reflection mirrors may be combined instead of the prism to give an optical path difference. In this case, there is an advantage that the optical path can be finely adjusted at the position of the reflection mirror.

FIG. 3A shows a first modification of the polarized light separating means of the first embodiment. In FIG. 3A, reference numeral 40
Is a prism provided with a dielectric multilayer film, and reference numerals 41 to 41
Reference numeral 43 constitutes a reflection mirror. In the first modification as well, similar to the function of the prism 25a, the dielectric multilayer film transmits a specific polarization component (P-polarized light) and reflects another polarization component (S-polarized light). The reflection mirrors 41 to 43 give a predetermined optical path to P-polarized light.

FIG. 3B shows a second modification of the polarized light separating means of the first embodiment. In FIG. 3B, reference numerals 45 and 48 are beam splitters, and reference numerals 46 and 47 are reflection mirrors. Both the beam splitters 45 and 48 transmit only specific polarized light (P polarized light) and transmit other polarized light (S polarized light). Also in the second modification, the reflection mirror 4
6 and 47 give an optical path difference between both polarizations.

Although the light utilization efficiency decreases, the dielectric multilayer film 33, the prism 40, and the beam splitters 45 and 48 in the prism 25a may be composed of half mirrors.

Further, in the prism 25a, the angle formed by the plane of polarization of the light beam with respect to the film surface of the dielectric multilayer film 33 is set to 45 degrees, but it may be set to another angle.
In this case, the light quantity of the reflected light bundle (S-polarized light) and the light quantity of the transmitted light bundle (P-polarized light) are not equal. However, when it is necessary to adjust the light amount of one light beam bundle and the light amount of the other light beam bundle due to the influence of the optical path length and the optical element, the angle of the polarization plane of the light beam can be polarized and adjusted.

Further, a ray bundle having a longer optical path length may be generated from a ray bundle having an S-polarized light having a longer optical path length. For example, a part of the light flux having S-polarized light transmitted through the dielectric multilayer film 33 is divided by a beam splitter or the like.
Then, an optical path having a longer optical path length than that of the S-polarized light which has not been transmitted is further given to a part of the S-polarized light which has passed. Then, in the dielectric multilayer film 33, the light flux having a short optical path length previously split is emitted along the same optical axis. With this configuration, it is possible to obtain, from one light beam, three or more kinds of light beams having different optical path lengths. Operation of this Embodiment Next, the operation of the first embodiment will be described.

In FIG. 2, when the light beam output from the laser light source 21 passes through the dielectric multilayer film 33, the light beam having S polarization is reflected from the light beam, and only the light beam having P polarization is reflected. Incident on the inside of the prism.

The P-polarized light beam bundle entering the prism is reflected by the two reflecting surfaces 34 and 35 and returns to the dielectric protective layer 33 again at a predetermined distance (l ₁ + l ₂ + l).
Go on ₃ ). On the other hand, in the light beam, marginal rays located at the outer edge with respect to the optical axis gradually spread as the distance increases. Therefore, when a light beam bundle having P polarization and a light beam having S polarization having an optical path difference of a predetermined distance (l ₁ + l ₂ + l ₃ ) are supplied through the beam splitter 22, the collimator lens 23 respectively Gives different spherical aberrations to the ray bundle of. Specifically, the collimator lens 23 is
A ray bundle corresponding to P-polarized light is set as parallel rays, and a ray bundle corresponding to S-polarized light having an optical path length shorter than that of the ray bundle corresponding to P-polarized light is refracted differently from P-polarized light. For this reason, the respective bundles of rays that have passed through the collimator lens 23 enter the objective lens 24 at the same incident angle of the marginal rays while having the same optical axis. The objective lens 24 is corrected so that the spherical aberration of each incident light beam bundle becomes substantially zero.
Therefore, the objective lens 24 condenses each light beam bundle in a state where the spherical aberration is corrected.

Therefore, when the information recording surface exists within the range where spherical aberration is corrected by this optical system,
The information on the optical disk can be read. In particular, the bundle of rays incident from the collimator lens 23 is a parallel ray P
With respect to polarized light, even if the objective lens 24 moves the position in the optical axis direction due to a focusing operation or the like, spherical aberration does not change, and an ideal minute spot can always be obtained. Therefore, as in the present embodiment, it is preferable to adjust the optical system so that the information recording surface of the optical disc recorded with higher density is present at the image forming point of the bundle of rays having P polarization.

From the above, the optical path (l ₁ + l ₂ + l ₃ ) of the P-polarized light in the prism 25a is determined from the optical characteristics of the objective lens 24 and the collimator lens 23 based on the thickness of the substrate of the optical disc to be reproduced. It will be calculated by back calculation. For example, the thickness of the substrate is 0.6mm
For high-density recorded digital video discs of
A large numerical aperture (for example, 0.6) of the objective lens is selected to obtain the optimum focusing state, and the numerical aperture of the collimator lens 23 (0.
1) is obtained. Then, how much the optical path difference is required to correct the spherical aberration generated for the compact disc having the substrate thickness of 1.2 mm is calculated based on the numerical apertures of the objective lens 24 and the collimator lens 23 (for example, Under the above conditions, l ₁ + l ₂ + l ₃ = 7.7 mm
Becomes ). Then, a prism is manufactured so as to obtain this difference in optical path length.

According to the pickup device 100 designed as described above, it is possible to irradiate the best read light beam when reading information from the optical disk 26 having any thickness of the substrate. . Description of Effects As described above, according to the first embodiment, the configuration of the optical system capable of reproducing the compatible player can be designed due to the difference in the thickness of the substrate of the optical disk to be reproduced. In particular, when an optical element such as a dielectric multilayer film that has a small loss of light quantity is used for light separation, a sufficient amount of light beam can be emitted even with a small output laser beam. Also, when a half mirror is used for light separation , polarization separation is easier and cheaper.
Means can be provided. (II) Second Embodiment The second embodiment of the present invention is an application of the invention of claim 3 .

FIG. 4 is a block diagram of the polarized light separating means of the second embodiment. As shown in FIG. 4, the polarized light in the present embodiment.
Separation means 25b is calcite (Ca [CO3
])).

Next, the operation of this polarized light separating means will be described. Calcite has a sodium nitrate type structure.
structure) and has unique optical properties. That is, calcite separates a light beam incident from a particular direction of the crystal into two polarization components. The vibration of one of the waves occurs in the direction perpendicular to the optical axis. The vibration of the other wave includes the optical axis and occurs in a direction different from the polarization direction of the one wave.

Further, the calcites are separated at right angles to each other.
Different refractive indices inside the crystal for the separated polarization components
Have. For example, refraction for one particular polarization component
Rate n ₁= 1.6, refraction for the other polarization component
Rate n₂= 1.8 is given.

Therefore, since the two polarization components travel at equal distances in the medium having different refractive indices, the air conversion distances when the light is converted as traveling in the air having the refractive index n = 1 are different from each other. That is, it is equivalent to that the light beam bundle having one polarization component travels in the air longer than the light beam bundle having the other polarization component.

From the above fact, it is possible to easily set the length of the total length D of the light flux splitting means 25b by calcite. First, the optical path difference L required for the light beams corresponding to the two polarization components is obtained from the thickness difference d of the substrate of the optical disk as in the first embodiment. Next, by utilizing the difference L in the optical path and the difference in the refractive index in the air, D · (n ₁ −
The total length D of calcite is obtained from n ₂ ) = L. For example, based on the refractive index and the optical path difference of 7.7 mm obtained in the first example, the total length D of calcite is D = 7.7 / (1.8-1.
2) = 38.5 mm.

As described above, according to the second embodiment, if a birefringent material having a crystal structure for performing polarization separation and giving different refractive indexes to respective polarization components is used, it is the same as the first embodiment. Polarization that produces a bundle of rays with different optical path differences in
Separation means can be provided. (III) Third Embodiment A third embodiment of the present invention is an application of the inventions of claims 4 and 5 .

FIG. 5 shows the construction of the polarized light separating means of the third embodiment. As shown in FIG. 5, the polarization splitting means 25c of this embodiment constitutes a coaxial beam splitter.

Reference numeral 50 denotes a λ / 4 wavelength plate, and a beam splitter 50a for transmitting only the P-polarized component and reflecting the S-polarized component is provided on the laser light source 21 side. However, λ /
The four-wave plate 50 and the beam splitter 50a may be provided separately.

54 is the width T ₁ when connected to 50
And 56 is a glass plate having a width T ₂ when joined to 52. 52 is
It is the same λ / 4 wavelength plate as 50, and the half mirror film 52a is provided on the laser light source 21 side. However, the λ / 4 wavelength plate 50 and the beam splitter 50a may be provided separately.

Reference numeral 58 is a dielectric film that transmits the P-polarized component and reflects the S-polarized component. Instead of the half mirror 52a, a dielectric film that transmits the S-polarized component of the incident circularly polarized light O and reflects the remaining component may be provided. Further, the widths T ₁ and T ₂ may be the thickness itself of the λ / 4 wavelength plate without providing the glass plate.

Next, the operation will be described. First, the light beam emitted from the laser light source 21 passes through the dielectric film 50a,
Circularly polarized light (polarized light in which the S-polarized component and the P-polarized component are in the same direction) O is obtained by the λ / 4 wavelength plate 50. The bundle of rays that has become circularly polarized light O passes through the glass plate 54 and is reflected by the half mirror 52a with half the amount of light. The reflected circularly polarized light (indicated by a solid line) O passes through the λ / 4 wave plate 50 again and has an S-polarized component. The light flux having this S-polarized component is reflected by the dielectric film 50a, and this time the half mirror 52
After passing through a and the λ / 4 wave plate 52, it has a P-polarized component. Further, this bundle of rays passes through the glass plate 56 and the dielectric film 58 and is emitted to the outside as a bundle of rays P ₁ having the first P-polarized component.

Further, the remaining half of the bundle of rays (shown by a broken line) which has become circularly polarized light O by the λ / 4 wavelength plate 50 and has passed through the half mirror 52a has a P polarization component by the λ / 4 wavelength plate 52. For this reason, this light beam is reflected by the glass plate 5.
After passing through 6, the light is reflected by the dielectric film 58. The reflected light beam passes through the glass plate 56 again, is circularly polarized by the λ / 4 wavelength plate 52, and half is reflected by the half mirror 52a. The reflected ray bundle is rotated by the λ / 4 wavelength plate 52 again and has a P-polarized component. Therefore, after passing through the glass body 56, the light flux having the P polarization component passes through the dielectric film 58 and is emitted to the outside as the light flux P ₂ having the second P polarization component.

From the above, the optical path length L ₁ of the light beam having the first P-polarized component and the optical path length L ₂ of the light beam bundle having the second P-polarized component are L ₁ = 3T ₁ + T ₂ L ₂ = T It becomes ₁ + 3T ₂ . From this, the optical path difference L ₂ −L ₁ between the two ray bundles is obtained as L ₁ −L ₂ = 2 (T ₂ −T ₁ ), so that the required optical path obtained by the method of the first embodiment or the like is required. The length L may be applied to the above formula and the widths of the glass plates 54 and 56 may be adjusted.

The polarization separating means 25c of this embodiment is set to 1
If blocks are connected in the optical axis direction, it is possible to obtain twice or even four times as much light as in this embodiment. At that time, a strong laser light source is used in consideration of the loss of light quantity.

Further, in this embodiment, the half mirror 52a is used.
The circularly polarized light O reflected by is reciprocated once with respect to the dielectric film 50a and is emitted in the direction of the glass plate 56, but is further reciprocally reciprocated two times and three reciprocally to adjust so as to obtain different optical path lengths. You may. That is, a person skilled in the art can apply the technical idea of this embodiment and combine light separating means such as a dielectric film and a half mirror to generate light having two or more different optical path lengths. It's easy.

As described above, according to the third embodiment, it is possible to provide the polarized light separating means which can be adapted only by adjusting the width of the glass plate in order to match the type of the optical disk to be reproduced. (IV) Fourth Example A fourth example of the present invention is an embodiment of a pickup device.
Is.

FIG. 6 shows a pickup device according to the fourth embodiment. In FIG. 6, the pickup device 10 of the present embodiment
1, the same components as those of the pickup device 100 of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

Reference numeral 60 is a holographic element that can obtain the first-order diffracted light (first-order light) in addition to the zero-order light. In this embodiment, a grating collimator lens will be considered in particular. The holographic element represented by this grating collimator lens is used as a grating element and a diffraction grating. Normally, it is used to generate a sub-beam for the tracking error signal.

In this embodiment, the holographic element 60 is used.
Is used as a light separation element and is interposed between the laser light source 21 and the beam splitter 22. Next, the operation will be described.

The holographic element 60 receives a light beam and generates the first-order light in addition to the zero-order light by the diffraction effect. The 0th order light without diffraction is directly used for the collimator lens 2
3 makes a parallel light beam. Since the objective lens 24 is designed so that an ideal minute spot is formed on the information recording surface 26a of the optical disc 26 when a parallel light beam is incident, the optical disc having a thin substrate (digital video It is possible to read the data such as a disc.

The primary light is a light beam which gradually spreads from the collimator lens 23, like the light beam bundle having S-polarized light in the first embodiment. In the present embodiment, in the arrangement of the optical system that obtains an ideal image formation point by the 0th-order light, the spherical aberration that occurs when the 1st-order light is condensed by the objective lens 24 is corrected to almost zero. Get the light. In particular,
The diffraction amount of the holographic element 60 is adjusted so that the incident angle of the marginal ray of the primary light upon entering the collimator lens 23 becomes an angle capable of correcting the spherical aberration. Therefore, an optical disc (compact disc or the like) having a thick substrate can be read by the primary light.

In this embodiment, 1 is set as the diffracted light.
If secondary light or the like is used in addition to the next light, it is possible to further widen the width of the focal length capable of converging, that is, the correctable spherical aberration.

As described above, according to the pickup device of the fourth embodiment, desired diffracted light can be obtained relatively easily by the holographic element, so that information can be read from a plurality of types of optical disks having different substrate thicknesses. A light beam suitable for emitting can be generated.

[0077]

According to the pickup device of any one of claims 1 to 6 , the spherical aberration required for reading information from the optical recording medium having different substrate thicknesses is divided into ray bundles. Since the correction is performed by the means, information can be read out with high light utilization efficiency from any of the optical recording media that are different due to the difference in the thickness of the substrate. In particular, the present invention is preferable for use in so-called compatible players and the like.

Further, since the beam splitter does not allow the return light from the optical recording medium or the like to pass through the polarization splitting means again,
There is no light loss, and the light utilization efficiency is high. In particular, claim 1
And according to the pick-up device according to claim 5, polarization
Since the separating means is provided, the loss of light is small and the light utilization efficiency can be improved. Furthermore, the polarized light separating means is
Since it is provided separately from the light collecting means, the driving load can be reduced.

Further, according to the pickup device of the first to fifth aspects, the spherical aberration required in the light converging means can be corrected depending on the number of steps given to the light beam bundle.

Furthermore, according to the pickup device of the third aspect , the above object can be achieved with a simple structure without providing a mechanical structure .

According to the pickup device of the sixth aspect , the spot obtained by condensing the parallel light beam always forms the best condensing spot regardless of the movement of the position of the condensing means. Therefore, by reading an optical recording medium having a higher information density with a spot having the best condensing state, a pickup device capable of recording / reproducing on / from a plurality of types of optical recording media including an optical recording medium recorded at high density is provided. Can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system of a pickup device according to a first embodiment.

FIG. 2 is a configuration diagram of a polarized light separating means of the first embodiment.

FIG. 3 is a modification of the polarization splitting means of the first embodiment,
(A) is a 1st modification, (B) is a 2nd modification.

FIG. 4 is a configuration diagram of a polarized light separating unit according to a second embodiment.

FIG. 5 is a configuration diagram of a polarized light separating means according to a third embodiment.

FIG. 6 is a configuration diagram of an optical system of a pickup device according to a fourth embodiment.

FIG. 7 is a configuration diagram of an optical system of a conventional pickup device.

[Explanation of symbols]

21, 101 ... Laser light sources 22, 45, 48, 50a, 52a, 58, 102 ... Beam splitters 23, 104 ... Collimator lenses 24, 105 ... Objective lenses 25a ... Prisms 25b, 25c ... Polarization separation means 26 ... Optical disks 27, 107 Photodetector 33 ... Dielectric multilayer films 34, 35 ... Reflective surfaces 41-43, 46, 47 ... Reflective mirror 60 ... Grating collimator lens (holographic element) 50, 52 ... λ / 4 wave plates 54, 56 ... Glass Plates 100 to 102 ... Pickup device

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiro Tachibana 6-1, 1-1 Fujimi, Tsurugashima City, Saitama Pioneer Co., Ltd. Research Institute (56) Reference JP-A-7-65407 (JP, A) JP-A 7-98431 (JP, A) JP 5-6546 (JP, A) JP 5-217201 (JP, A) JP 8-249718 (JP, A) JP 8-241529 (JP, A) European Patent Application Publication 610055 (EP, A 1) (58) Fields searched (Int.Cl. ⁷ , DB name) G11B 7/09-7/135 G02B 5/00-5/32

Claims (6)

(57) [Claims] 1. A pickup device for recording and / or reproducing information on a plurality of types of optical recording media having substrates having different thicknesses, the light beam being supplied from a light source. Has one of the planes of polarization
A ray bundle and a ray bundle having a polarization plane different from the one polarization plane
Polarization splitting gives paths with different optical path lengths for and
Means, a beam splitter for changing the path of at least one of the light flux from the polarization splitting means and the return light from the condensing means, and each of the light fluxes supplied through the beam splitter to the optical recording. The light condensing means for condensing on the information recording surface of the medium and for returning the return light from the information recording surface caused by the condensing to the beam splitter again, is separated by the polarization separating means. Each of the light beam bundles is adjusted so that spherical aberration when focusing on any of the plurality of types of optical recording media on the information recording surface of the optical recording medium by the focusing means becomes substantially zero. Pickup device characterized by being. 2. The pickup device according to claim 1 , wherein the polarization separation means transmits a light beam bundle having one polarization plane of the light beam supplied from the light source , and is different from the one polarization plane. a light beam separating means for emitting along a light beam having a polarization plane in a predetermined optical axis, said optical beam separating hands
An optical path difference generating means for giving a predetermined stroke from a position where the light beam separating means has passed to the light beam that has passed through a step , and emitting a light flux that has advanced the predetermined step along the predetermined optical axis, A pickup device comprising: 3. The pickup device according to claim 1 , wherein the polarization splitting unit has a refractive index different from a first polarization component in the optical axis of the light beam supplied from the light source and the polarization component. A pickup device, which is an optical element having a refractive index different from that of a polarized light component of 2. 4. The pickup device according to claim 1 , wherein the polarization splitting means transmits a part of a light beam bundle of light traveling on the same optical axis as the optical axis of the light beam supplied from the light source. To reflect the rest of the bundle of rays along the optical axis
A separating means; a second separating means which is installed on the optical axis, transmits a part of the light flux of the light traveling on the optical axis, and reflects the remaining light flux along the optical axis; A pickup device comprising: 5. The pickup device according to claim 4, wherein at least one of the first separating means and said second separating means, a light beam having a first polarization plane passes, and different polarization A polarization separation film that reflects a light flux having a surface, and a predetermined amount with respect to a polarization component of a light flux that transmits itself on the optical axis between the first separation means and the second separation means. A pickup device characterized by interposing a phase adding means for changing the phase of the pickup. 6. The pickup device according to claim 1 , wherein the light converging unit converts one of the plurality of light beams supplied from the beam splitter into substantially parallel light beams. A collimator lens for converting the bundle of rays into a bundle, and an objective lens for condensing the plurality of bundles of rays including a bundle of parallel rays passing through the collimator lens onto an information recording surface of the optical recording medium. Pickup device to do.