JP2007317315A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device capable of properly recording and/or reproducing information in a different optical information recording medium while suppressing the thickness of an objective lens in an optical axis direction. <P>SOLUTION: A luminous flux reflected from a cholesteric liquid crystal CLQ is reflected on the information recording surface of a BD, and also reflected when it is made incident on the cholesteric liquid crystal CLQ again. The luminous flux passed through the cholesteric liquid crystal CLQ is reflected on the information recording surface of an HD, and also passed when it is made incident on the cholesteric liquid crystal CLQ again. Thus, it is unnecessary to dispose a photodetector PD on a side opposed to a first objective lens OBJ1 sandwiching the cholesteric liquid crystal CLQ, and it is unnecessary to arrange a λ/4 wavelength plate QWP between the cholesteric liquid crystal CLQ and the first objective lens OBJ1. As a photodetector PD is installed in a position away from the first and second objective lenses OBJ1 and OBJ2, it is moved away from tracking and focusing actuators. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup device, and more particularly to an optical pickup device capable of appropriately recording and / or reproducing information on different optical information recording media.

  In recent years, research and development of a high-density optical disk system capable of recording / reproducing information using a blue-violet semiconductor laser having a wavelength of about 400 nm is rapidly progressing. As an example, in an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4, 7 GB) Can record information of 20 to 30 GB per surface on an optical disc having a diameter of 12 cm, which is the same size as the above, and an optical disc that records and reproduces information with specifications of NA 0.65 and light source wavelength 405 nm, so-called With HD DVD (hereinafter referred to as HD), information of 15 to 20 GB per side can be recorded on an optical disk having a diameter of 12 cm. Hereinafter, such an optical disc is referred to as a “high density optical disc” in the present specification.

  By the way, it is preferable for the user if there is an optical pickup device that records and / or reproduces information in a manner compatible with BD and HD. However, in an optical pickup device that records and / or reproduces information in a manner compatible with BD and HD, BD has a protective layer thickness of about 0.1 mm, and HD has a protective layer thickness of 0.6 mm. Therefore, when the same objective lens is used, there is a problem that spherical aberration occurs due to different thicknesses of the protective layer. Therefore, in order to correct the spherical aberration due to the difference in thickness of the protective layer, some device is required for the condensing optical system of the optical pickup device. Here, if the wavelength of the light beam to be used is different, if a diffraction ring zone is provided on the objective lens, a diffraction effect is given to only one light beam, thereby correcting the spherical aberration due to the difference in the protective layer thickness. However, since both BD and HD use a light beam having a short wavelength of about 405 nm, there is a problem that diffraction cannot be used to correct spherical aberration due to a difference in protective layer thickness.

On the other hand, in Patent Document 1, although BD and HD are not compatible, when a common optical system and two objective lenses are provided and information is recorded and / or reproduced on different types of optical disks. A technique has been proposed in which the light path is switched by the light beam switching means so that the light beam that has passed through the common optical system is selectively incident on one of the objective lenses.
JP-A-9-212905

  According to this technique, when the incident light with respect to the polarization beam splitter becomes P-polarized light, it is mainly transmitted through the polarization beam splitter, reflected by the rear reflecting mirror, and incident on the corresponding objective lens. If the incident light to the polarization beam splitter is changed to S-polarized light, it is mainly reflected by the polarization beam splitter and incident on another objective lens. In this way, an objective lens used for recording / reproduction can be selected from two different objective lenses.

  If a λ / 4 wavelength plate is arranged between the polarizing beam splitter and each objective lens, the reflected light beam from the optical disk passes through it twice, so that the polarization plane of the light is rotated 90 degrees and the phase is λ / 2. It will shift. Accordingly, the light beam reflected by the polarizing beam splitter because it was P-polarized light at the time of incidence is changed to S-polarized light when it is reflected from the optical disk (for example, BD) and again enters the polarizing beam splitter. It will pass through the splitter. On the other hand, since it was S-polarized light at the time of incidence, the light beam transmitted through the polarizing beam splitter is changed to P-polarized light when it is reflected from the optical disk (for example, HD) and enters the polarizing beam splitter again. Reflected by the splitter. That is, if a photodetector is placed on the opposite side of the BD objective lens across the polarizing beam splitter, the light beam reflected from the BD and transmitted through the polarizing beam splitter, and the light beam reflected from the HD and reflected by the polarizing beam splitter The optical pickup device can be simplified.

  Here, when an optical pickup device is to be mounted on a device that is required to be thin, such as a notebook computer, the information recording surface of the optical disk is usually arranged so as to be parallel to the keyboard surface. However, in the optical pickup device disclosed in Patent Document 1, because of the configuration, the photodetector must be disposed on the opposite side of the BD objective lens with the polarization beam splitter interposed therebetween, so that the dimension in the thickness direction increases. There is a problem that it is not possible to secure the thinness of the mounted device. On the other hand, in order to ensure the thinness of the optical pickup device, an optical system such as a light source and a prism is arranged in a plane parallel to the optical disc, and another upright mirror is provided to vertically irradiate the optical disc with light. Although it is possible to do so, it is disadvantageous in terms of space and the number of parts.

  The present invention has been made in view of the problems of the related art, and can efficiently distribute the light quantity to a plurality of objective lenses, and can control different optical information while suppressing the thickness of the objective lens in the optical axis direction. An object of the present invention is to provide an optical pickup device capable of appropriately recording and / or reproducing information on a recording medium.

The optical pickup device according to claim 1,
A light source that emits a light beam in a first linear polarization state;
A polarization state setting means for selectively setting one of a circular polarization state around one direction and a circular polarization state around the other direction when a light beam emitted from the light source is incident;
In the light beam emitted by the polarization state setting means, when the circular polarization state around the one direction is selected, the light beam is reflected, and when the circular polarization state around the other direction is selected. Is a first light distribution element having circular dichroism that transmits the luminous flux;
A first objective lens that focuses the light beam reflected by the first light distribution element on the information recording surface of the first optical information recording medium;
A second objective lens that focuses the light beam transmitted through the first light distribution element on the information recording surface of the second optical information recording medium;
A light branching unit disposed between the light source and the polarization state setting unit, allowing a light beam in a first linear polarization state to pass therethrough and reflecting a light beam in a second line change state;
A photodetector for receiving a light beam from the light branching means,
The reflected light from the first optical information recording medium is reflected by the first light distribution element and enters the polarization state setting means, thereby entering a second linear polarization state and entering the light branching means. The reflected light from the second optical information recording medium passes through the first light distribution element and is incident on the polarization state setting means, thereby entering a second linearly polarized state and entering the light branching means. It is characterized by doing.

  According to the present invention, the light beam reflected from the first light distribution element is reflected by the information recording surface of the first optical information recording medium, and is also reflected when entering the first light distribution element again. Since the light beam that has passed through the first light distribution element is reflected by the information recording surface of the second optical information recording medium and is transmitted again when incident on the first light distribution element, the photodetector is There is no need to provide the first light distribution element on the opposite side of the first objective lens, and a λ / 4 wavelength plate need not be disposed between the first light distribution element and the objective lens. In combination with this, it is possible to suppress the dimension in the thickness direction of the optical pickup device in the optical axis direction of the first objective lens. Furthermore, since the photodetector can be installed at a position away from the first objective lens and the second objective lens, it can be separated from the tracking and focusing actuators, and the space can be used effectively.

  According to a second aspect of the present invention, in the optical pickup device according to the first aspect, the first light distribution unit is a cholesteric liquid crystal having circular dichroism. A member having circular dichroism such as a cholesteric liquid crystal has a property of reflecting a light beam in either a clockwise circular polarization state or a counterclockwise circular polarization state in a specific wavelength range (reference: Nitto Technical Report 39). Vol. 1 “PCF (Reflective Polarizing Polarizer) Pursuing Improvement of Light Utilization Efficiency”, Applied Physics Vol. 70 No. 9 “Creation of Solid Reflective Film Utilizing Self-Organization of Liquid Crystal Molecules”). That is, a cholesteric liquid crystal having circular dichroism is used as a mirror, and a light beam in a clockwise circular polarization state or a counterclockwise circular polarization state is selectively incident on the mirror, thereby condensing it on an optical information recording medium. The objective lens can be arbitrarily switched.

  In particular, a general optical information recording medium such as a CD or DVD is designed on the condition that a circularly polarized light beam is incident. Therefore, when a linearly polarized light beam is incident, There is a problem that it is difficult to obtain a suitable reproduction signal as compared with the case where a polarized light beam is incident. Furthermore, when the material of the rising mirror (liquid crystal) reflects a linearly polarized light beam with a certain direction component and transmits the other light beam, the light beam returned through the rising mirror is the same as the forward path. In order to maintain the linear polarization state of the direction, a polarization beam splitter cannot be used for separation to the photodetector, and a mirror with a large light loss such as a half mirror must be used, resulting in poor efficiency. There is. As in the present invention, by using a cholesteric liquid crystal to reflect or transmit a circularly polarized light beam so that it is condensed from the objective lens onto the optical information recording medium, such a problem can be solved or alleviated. it can.

  The optical pickup device according to a third aspect is the invention according to the first or second aspect, wherein the polarization state setting means is a λ / 4 wavelength plate whose rotational position can be switched. By rotating the λ / 4 wavelength plate, either a circular polarization state around one direction or a circular polarization state around the other direction can be mechanically selected.

  The optical pickup device according to a fourth aspect is the invention according to the first or second aspect, wherein the polarization state setting means is a liquid crystal element. Either the circular polarization state around and the circular polarization state around the other direction can be electrically selected.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the optical axis of the first objective lens and the optical axis of the second objective lens are arranged in parallel. The light beam transmitted through the first light distribution element is reflected by a reflecting means and is incident on the second objective lens.

  The optical pickup device according to a sixth aspect is characterized in that, in the invention according to the fifth aspect, the first light distribution element and the reflecting means are incorporated in an integral prism. A small and simple configuration can be provided.

  An optical pickup device according to a seventh aspect is the invention according to the fifth aspect, wherein the first light distribution element is attached to a parallel plate that transmits light, and is separate from the reflecting means. Since the light beam incident on the first light distribution element is an infinite parallel light beam, it is possible to provide an optical pickup device that can easily adjust the optical axis and has excellent aberration characteristics. In addition, a space is created below the side surface of the light source of the objective lens, which contributes to the thinning of the optical pickup device.

  According to an eighth aspect of the present invention, in the optical pickup device according to any one of the first to seventh aspects, the recording density of the first optical information recording medium is different from the recording density of the second optical information recording medium. It is characterized by that.

  According to a ninth aspect of the present invention, in the optical pickup device of the eighth aspect, one of the first optical information recording medium and the second optical information recording medium has a protective substrate thickness t1 of 0.1 mm. The other is characterized in that the protective substrate thickness t2 is 0.6 mm, so that BD and HD can be used interchangeably.

  According to a tenth aspect of the present invention, in the optical pickup device according to any one of the first to ninth aspects, the light source includes a light beam having a wavelength λ1 (350 nm ≦ λ1 ≦ 450 nm) and a wavelength λ2 (600 nm ≦ λ2 ≦ 700 nm). ) Can be selectively emitted, and the second objective lens condenses the light beam of wavelength λ1 on the information recording surface of the second optical information recording medium, and the light beam of wavelength λ2 Since the light is condensed on the information recording surface of the third optical information recording medium, for example, in addition to BD and HD, compatible use of DVD becomes possible.

  An optical pickup device according to an eleventh aspect is characterized in that, in the invention according to the tenth aspect, the second optical information recording medium and the third optical information recording medium have the same protective substrate thickness. The degree of freedom in designing the objective lens 2 is improved, the production yield is improved, and the cost can be reduced.

  An optical pickup device according to a twelfth aspect of the present invention is the optical pickup device according to any one of the first to ninth aspects, wherein the light source includes a light beam having a wavelength λ1 (350 nm ≦ λ1 ≦ 450 nm) and a wavelength λ2 (600 nm ≦ λ2 ≦ 700 nm). ) And a light beam having a wavelength λ3 (700 nm ≦ λ3 ≦ 800 nm) can be selectively emitted, and the second objective lens emits a light beam having a wavelength λ1 to information on the second optical information recording medium. The light is condensed on the recording surface, and the light beam having the wavelength λ2 is condensed on the information recording surface of the third optical information recording medium having the protective substrate thickness t3 of 0.6 mm. Since the light is focused on the information recording surface of the 2 mm fourth optical information recording medium, for example, in addition to BD and HD, DVD and CD can be used interchangeably.

According to a thirteenth aspect of the present invention, in the invention according to any one of the first to ninth aspects, the light source includes a light beam having a wavelength λ1 (350 nm ≦ λ1 ≦ 450 nm) and a wavelength λ2 (600 nm ≦ λ2 ≦ 700 nm). ) And / or a light beam having a wavelength λ3 (700 nm ≦ λ3 ≦ 800 nm) can be selectively emitted.
The light beam that has passed through the first light distribution element is incident on the second light distribution element, and the second light distribution element reflects a light beam having a wavelength λ1 (350 nm ≦ λ1 ≦ 450 nm) and a wavelength λ2 (600 nm ≦ λ2). ≦ 700 nm) and / or a light beam having a wavelength λ3 (700 nm ≦ λ3 ≦ 800 nm) is transmitted, and the light beam transmitted through the second light distribution element is incident on a third objective lens. Appropriate information can be recorded and / or reproduced using a dedicated objective lens for the recording medium.

The optical pickup device according to claim 14,
A light source that emits a light beam in a first linear polarization state;
A phase difference element that selectively sets a circular polarization state around one direction or a circular polarization state around the other direction when a light beam emitted from the light source is incident;
A light distribution element capable of switching the expression of circular dichroism;
A first objective lens that focuses the light beam reflected by the light distribution element on the information recording surface of the first optical information recording medium;
A second objective lens that focuses the light beam transmitted through the light distribution element on the information recording surface of the second optical information recording medium;
A light branching unit disposed between the light source and the phase difference element, allowing the first linearly polarized light beam to pass therethrough and reflecting the second linearly changed light beam;
A photodetector for receiving a light beam from the light branching means,
The reflected light from the first optical information recording medium is reflected by the light distribution element and enters the phase difference element, thereby entering a second linearly polarized state and entering the light branching unit. The reflected light from the two-optical information recording medium is transmitted through the light distribution element and incident on the phase difference element, thereby entering a second linearly polarized state and incident on the light branching means. .

  According to the present invention, since the light distribution element can switch the expression of circular dichroism, the light beam reflected from the light distribution element by switching the expression of circular dichroism is A light beam that is reflected by the information recording surface of the first optical information recording medium, reflected when it is incident again on the first light distribution element, and transmitted through the light distribution element by switching the expression of circular dichroism. Is reflected on the information recording surface of the second optical information recording medium and is transmitted again when it enters the light distribution element again. Therefore, the photodetector is placed across the light distribution element. The optical axis direction of the first objective lens is not required to be provided on the opposite side of the lens, and it is not necessary to arrange a λ / 4 wavelength plate between the first light distribution element and the objective lens. Dimension of the optical pickup device in the thickness direction It can be suppressed. Furthermore, since the photodetector can be installed at a position away from the first objective lens and the second objective lens, it can be separated from the tracking and focusing actuators, and the space can be used effectively.

  According to a fifteenth aspect of the present invention, in the optical pickup device according to the fourteenth aspect, the optical distribution element includes a cholesteric liquid crystal.

  An optical pickup device according to a sixteenth aspect is the invention according to the fourteenth or fifteenth aspect, wherein the expression of the circular dichroism can be switched by switching a voltage applied to the light distribution element. It is characterized by that.

  For example, as shown in FIG. 6A, in the state where no voltage is applied to the cholesteric liquid crystal CLQ, the molecules are arranged in different spirals in each layer. However, as shown in FIG. 6B, a predetermined value is applied to the cholesteric liquid crystal CLQ. Is applied, the molecular arrangement in each layer is aligned to form a linear array. Thereby, the expression of circular dichroism can be switched.

  According to a seventeenth aspect of the present invention, in the invention according to any one of the thirteenth to sixteenth aspects, the light source includes a light beam having a wavelength λ1 (350 nm ≦ λ1 ≦ 450 nm) and a wavelength λ2 (600 nm ≦ λ2 ≦ 700 nm). ) And a light beam having a wavelength λ1 and a light beam having a wavelength λ2 pass through the second objective lens. In addition to BD and HD, DVD And CD can be used interchangeably.

  An optical pickup device according to an eighteenth aspect is the optical pickup device according to any one of the thirteenth to sixteenth aspects, wherein the light source includes a light beam having a wavelength λ1 (350 nm ≦ λ1 ≦ 450 nm) and a wavelength λ2 (600 nm ≦ λ2 ≦ 700 nm). ) And a light beam having a wavelength λ3 (700 nm ≦ λ3 ≦ 800 nm) can be selectively emitted, and the second objective lens is made to have a light beam having a wavelength λ1, a light beam having a wavelength λ2, and a light beam having a wavelength λ3. In addition to BD and HD, DVD and CD can be used interchangeably.

  An optical pickup device according to a nineteenth aspect is the invention according to any one of the first to eighteenth aspects, wherein the circular polarization state includes an elliptical polarization state. For example, when elliptically polarized light is incident on a circular dichroic material that reflects right circularly polarized light, the reflectance is maximized when the right circularly polarized light is incident and minimized when the left circularly polarized light is incident. In elliptically polarized light (including linearly polarized light) that is an intermediate polarization state, the reflectance increases as the polarized light is closer to the right circularly polarized light. For example, in FIG. 1, when the angle θ between the direction of the polarization plane when the light beam emitted from the semiconductor laser LD passes through the polarization beam splitter PBS and the optical axis of the λ / 4 wave plate QWP is + 45 °, the right circle Polarized light, left circularly polarized at -45 °. If the rotation of the λ / 4 wavelength plate QWP is adjusted and θ is changed from + 45 ° to −45 °, the reflectivity of the cholesteric liquid crystal CLQ decreases and the transmittance increases accordingly. That is, it is possible to control the distribution of the amount of light by the cholesteric liquid crystal CLQ even if the light incident on the cholesteric liquid crystal CLQ is elliptically polarized and the state of the elliptically polarized light is changed. Such a configuration is, for example, when the rotation range of the λ / 4 wave plate QWP is mechanically limited and when θ cannot be changed from + 45 ° to -45 ° or when it is necessary to change the polarization state quickly. It is effective for.

  The light source that emits light beams having different wavelengths may have a plurality of light emitting points in the same package, or may be a separate light source.

  ADVANTAGE OF THE INVENTION According to this invention, the optical pick-up apparatus which can record and / or reproduce | regenerate information appropriately with respect to a different optical information recording medium can be provided, suppressing the thickness of the optical axis direction of an objective lens.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1A shows an optical pickup device according to a first embodiment capable of appropriately recording / reproducing information with respect to BD and HD which are optical information recording media (also referred to as optical discs) having different protective layer thicknesses. FIG. 1B is a side view schematically showing the configuration of FIG. The λ / 4 wavelength plate QWP, which is a polarization state setting means, is driven to rotate about the optical axis by an actuator (not shown), and is λ for the linearly polarized light beam emitted from the polarization beam splitter PBS. / 4 Wave plate QWP is rotated around the optical axis so that the angle between the optical axis and the plane of polarization is + 45 ° or -45 °. Or can be output after being converted into a light beam in a counterclockwise circularly polarized state. A cholesteric liquid crystal CLQ having circular dichroism is attached on a transparent parallel plate PP. The cholesteric liquid crystal CLQ reflects a light beam in a clockwise circular polarization state and transmits a light beam in a counterclockwise circular polarization state. Here, description will be made assuming that the reflectance and transmittance are about 100%. However, the present invention is not limited to this, and can be arbitrarily set within a range exceeding 50% according to the formation of the cholesteric liquid crystal CLQ.

  The cholesteric liquid crystal CLQ has a layered structure in which elongate liquid crystal molecules are arranged in a certain direction in a plane as shown in FIG. 5, which is a conceptual diagram thereof, and further overlapped in a direction perpendicular to the plane. . The direction in which this molecule faces is twisted slightly in each adjacent layer, forming a helical structure. The light incident on this has the property of reflecting the polarized light in the rotational direction of this helix. Therefore, if the spirals of the liquid crystal molecules are aligned to the right rotation, for example, the right-handed circularly polarized light is reflected and the left-handed circularly polarized light is transmitted (this is called circular dichroism). When light is incident parallel to the helical axis, the wavelength of the reflected light of the incident light is given by the center wavelength λ = nP and the wavelength width Δλ = PΔn, where P is the pitch of this helix ( n: average refractive index of liquid crystal, Δn: anisotropy of refractive index). When incident at an angle θ with respect to the helical axis, the central wavelength and wavelength width of the reflected light are cos θ times the above values. In addition, if the uniformity of the liquid crystal molecules in the direction of the helical axis is low, the circular dichroism as a cholesteric liquid crystal will decrease, so the intensity of the circular dichroism will be changed by the method of making the liquid crystal. be able to.

  The first objective lens OBJ1 is designed so that aberrations are optimally corrected for BD, and the second objective lens OBJ2 is designed so that aberrations are optimally corrected for HD. Has been. In addition, an actuator (not shown) is arranged around the first objective lens OBJ1 and the second objective lens OBJ2 whose optical axes are arranged in parallel to each other so as to be driven for tracking and focusing operations. It has become. The light beam emitted from the semiconductor laser LD is incident on the cholesteric liquid crystal CLQ as an infinite parallel light beam by passing through a collimator lens (not shown).

  Further, as shown in FIG. 1, a cholesteric liquid crystal CLQ having circular dichroism is provided on a parallel plate PP made of transparent glass or plastic, and is disposed in the vicinity of the first objective lens OBJ1, and Since the light beam transmitted through the cholesteric liquid crystal CLQ is incident on the second objective lens OBJ2 via a triangular prism-shaped rising mirror (also referred to as reflecting means) M, the reflective surface of the cholesteric liquid crystal CLQ is close to the air. Alternatively, since it is in contact, the optical surface of the first objective lens can be brought close to the surface of the cholesteric liquid crystal CLQ element, and as a result, the optical pickup device can be thinned. However, when the light beam transmitted through the cholesteric liquid crystal CLQ having circular dichroism is non-parallel, astigmatism occurs when the light beam passes through the cholesteric liquid crystal CLQ. It is desirable to use a lens designed with an infinite optical magnification.

  First, when recording and / or reproducing information with respect to a BD, the optical axis of the λ / 4 wavelength plate QWP is directed in a predetermined direction so that only a clockwise circularly polarized light beam can be emitted. In the optical pickup device of FIG. 1, a light beam in a P-polarized (first) linearly polarized state emitted from a semiconductor laser LD (light source) having a light source wavelength λ1 = 400 ± 50 nm is applied to a polarization beam splitter PBS which is an optical branching unit. Then, it passes through the λ / 4 wavelength plate QWP, enters a clockwise circular polarization state (light quantity A0), and enters the cholesteric liquid crystal CLQ that is the first light distribution element.

  Here, most of the light beam incident on the cholesteric liquid crystal CLQ is reflected (light amount R1> 0.5 × A0) and incident on the first objective lens OBJ1, from which the BD information recording surface (protective layer) (Thickness t1 = 0.1 mm).

  The reflected light beam modulated by the information pits on the information recording surface of the BD again passes through the first objective lens OBJ1, but the circularly polarized light beam reflected on the information recording surface of the BD has the spiral direction of the cholesteric liquid crystal CLQ. In the same direction, it is reflected again by the cholesteric liquid crystal CLQ, and enters the λ / 4 wavelength plate QWP. Here, the light beam incident on the λ / 4 wavelength plate QWP is again converted from the circularly polarized state to the linearly polarized state, but is shifted to the S-polarized (second linearly polarized) state by shifting the phase.

  The light beam that has passed through the λ / 4 wavelength plate QWP and has become P-polarized light is reflected by the polarization beam splitter PBS and condensed on the light receiving surface of the photodetector PD. A read signal of information recorded on the BD is obtained using the output signal of the photodetector PD.

  In addition, focus detection and track detection are performed by detecting spot shape change and light quantity change on the photodetector PD. Based on this detection, the first objective lens OBJ1 is formed so that the focusing actuator and tracking actuator (not shown) of the first objective lens OBJ1 appropriately form the light beam from the semiconductor laser LD on the information recording surface of the BD. Is supposed to move.

  Next, when recording and / or reproducing information with respect to the HD, the optical axis of the λ / 4 wave plate QWP is rotated by 90 degrees from a predetermined direction so that only a left-handed circularly polarized light beam can be emitted. To. In the optical pickup device of FIG. 1, a light beam in a P-polarized (first) linearly polarized state emitted from a semiconductor laser LD (light source) having a light source wavelength λ1 = 400 ± 50 nm is applied to a polarization beam splitter PBS which is an optical branching unit. Then, the light passes through the λ / 4 wavelength plate QWP, enters a counterclockwise circularly polarized state (light quantity A0), and enters the cholesteric liquid crystal CLQ that is the first light distribution element.

  Here, most of the light beam incident on the cholesteric liquid crystal CLQ (the amount of light T1> 0.5 × A0) is transmitted, passes through the parallel plate PP, is reflected by the rising mirror M, and the second objective lens. The light is incident on OBJ2 and is focused on the HD information recording surface (protective layer thickness t2 = 0.6 mm).

  The reflected light beam modulated by the information pits on the HD information recording surface again passes through the second objective lens OBJ2, is reflected by the rising mirror M, and passes through the parallel plate PP, but is reflected by the HD information recording surface. The circularly polarized light beam is in the direction opposite to the spiral direction of the cholesteric liquid crystal CLQ, passes through the cholesteric liquid crystal CLQ again, and enters the λ / 4 wavelength plate QWP. Here, the light beam incident on the λ / 4 wavelength plate QWP is again converted from the circularly polarized state to the linearly polarized state, but is shifted to the S-polarized (second linearly polarized) state by shifting the phase.

  The light beam that has passed through the λ / 4 wavelength plate QWP and has become P-polarized light is reflected by the polarization beam splitter PBS and condensed on the light receiving surface of the photodetector PD. Using the output signal of the photodetector PD, a read signal of information recorded in the HD is obtained.

  In addition, focus detection and track detection are performed by detecting spot shape change and light quantity change on the photodetector PD. Based on this detection, the second objective lens OBJ2 is configured so that the focusing actuator and tracking actuator (not shown) of the second objective lens OBJ2 appropriately image the light flux from the semiconductor laser LD on the information recording surface of the HD. Is supposed to move.

  According to the present embodiment, the light beam reflected from the cholesteric liquid crystal CLQ is reflected by the information recording surface of the BD, is reflected when it is incident on the cholesteric liquid crystal CLQ again, and the light beam transmitted through the cholesteric liquid crystal CLQ is HD Therefore, it is not necessary to provide the photodetector PD on the opposite side of the first objective lens OBJ1 with the cholesteric liquid crystal CLQ interposed therebetween, and also when the light is incident on the cholesteric liquid crystal CLQ again. Coupled with the fact that the λ / 4 wave plate QWP need not be disposed between the cholesteric liquid crystal CLQ and the first objective lens OBJ1, the dimension in the thickness direction of the optical pickup device in the optical axis direction of the first objective lens OBJ1. Can be suppressed. Further, since the photodetector PD can be installed at a position away from the first objective lens OBJ1 and the second objective lens OBJ2, it can be separated from the tracking and focusing actuators, and the space can be used effectively. .

  Next, a second embodiment will be described with reference to the drawings. FIG. 2 shows a second embodiment in which information can be appropriately recorded / reproduced with respect to BD, HD and DVD (or CD), which are optical information recording media (also referred to as optical discs) having different protective layer thicknesses. It is a side view which shows the structure of an optical pick-up apparatus roughly. The λ / 4 wavelength plate QWP, which is a polarization state setting means, is driven to rotate about the optical axis by an actuator (not shown), and is λ for the linearly polarized light beam emitted from the polarization beam splitter PBS. / 4 Wave plate QWP is rotated around the optical axis so that the angle between the optical axis and the plane of polarization is + 45 ° or -45 °. Or can be output after being converted into a light beam in a counterclockwise circularly polarized state. The first cholesteric liquid crystal CLQ1 having circular dichroism as the first light distribution means and the second cholesteric liquid crystal CLQ2 having circular dichroism as the second light distribution means are disposed in the prism PZ. Are integrally formed. The first cholesteric liquid crystal CLQ1 reflects a light beam in a clockwise circular polarization state and transmits a light beam in a counterclockwise circular polarization state. The second cholesteric liquid crystal CLQ2 reflects a light beam in a counterclockwise circularly polarized state and transmits a light beam having a wavelength of 700 nm or less. As in the present embodiment, if the first cholesteric liquid crystal CLQ1 and the second cholesteric liquid crystal CLQ2 are formed in an integral prism shape, the productivity is increased and the component cost can be reduced. The semiconductor laser LD is a so-called two-laser one package that can emit light beams having two different wavelengths (λ1, λ2).

  Furthermore, the first objective lens OBJ1 is designed so that aberrations are optimally corrected for BD, and the second objective lens OBJ2 is designed so that aberrations are optimally corrected for HD. The third objective lens OBJ3 is designed so that aberrations are optimally corrected with respect to DVD (or CD).

  First, when recording and / or reproducing information with respect to a BD, the optical axis of the λ / 4 wavelength plate QWP is directed in a predetermined direction so that only a clockwise circularly polarized light beam can be emitted. In the optical pickup device shown in FIG. 2, the P-polarized (first) linearly polarized light beam emitted from the semiconductor laser LD (light source) having the light source wavelength λ1 = 400 ± 50 nm is applied to the polarization beam splitter PBS, which is an optical branching unit. Passes through the λ / 4 wavelength plate QWP, enters a clockwise circular polarization state (light quantity A0), and enters the first cholesteric liquid crystal CLQ1 in the prism PZ.

  Here, most of the light beam incident on the first cholesteric liquid crystal CLQ1 is reflected (the amount of light R1> 0.5 × A0), and is emitted from the prism PZ and then incident on the first objective lens OBJ1. To BD information recording surface (protective layer thickness t1 = 0.1 mm).

  The reflected light beam modulated by the information pits on the information recording surface of the BD again passes through the first objective lens OBJ1, but the circularly polarized light beam reflected on the information recording surface of the BD does not spiral in the first cholesteric liquid crystal CLQ1. This is the same direction as that of the direction, is reflected again by the first cholesteric liquid crystal CLQ1 in the prism PZ, is emitted from the prism PZ, and then enters the λ / 4 wavelength plate QWP. Here, the light beam incident on the λ / 4 wavelength plate QWP is again converted from the circularly polarized state to the linearly polarized state, but is shifted to the S-polarized (second linearly polarized) state by shifting the phase.

  The light beam that has passed through the λ / 4 wavelength plate QWP and has become P-polarized light is reflected by the polarization beam splitter PBS and condensed on the light receiving surface of the photodetector PD. A read signal of information recorded on the BD is obtained using the output signal of the photodetector PD.

  In addition, focus detection and track detection are performed by detecting spot shape change and light quantity change on the photodetector PD. Based on this detection, the first objective lens OBJ1 is formed so that the focusing actuator and tracking actuator (not shown) of the first objective lens OBJ1 appropriately form the light beam from the semiconductor laser LD on the information recording surface of the BD. Is supposed to move.

  Next, when recording and / or reproducing information with respect to the HD, the optical axis of the λ / 4 wave plate QWP is rotated by 90 degrees from a predetermined direction so that only a left-handed circularly polarized light beam can be emitted. To. In the optical pickup device shown in FIG. 2, the P-polarized (first) linearly polarized light beam emitted from the semiconductor laser LD (light source) having the light source wavelength λ1 = 400 ± 50 nm is applied to the polarization beam splitter PBS, which is an optical branching unit. Then, the light passes through the λ / 4 wavelength plate QWP, enters a counterclockwise circularly polarized state (light quantity A0), and enters the first cholesteric liquid crystal CLQ1 in the prism PZ.

  Here, most of the light beam incident on the first cholesteric liquid crystal CLQ1 is transmitted (light quantity T1> 0.5 × A0), but is reflected by the second cholesteric liquid crystal CLQ2 and emitted from the prism PZ. Is incident on the objective lens OBJ2 and focused on the HD information recording surface (thickness t2 of the protective layer = 0.6 mm).

  The reflected light beam modulated by the information pits on the HD information recording surface again passes through the second objective lens OBJ2, but the circularly polarized light beam reflected on the HD information recording surface is spiraled by the second cholesteric liquid crystal CLQ2. Is reflected again by the second cholesteric liquid crystal CLQ2 in the prism PZ, passes through the first cholesteric liquid crystal CLQ1, and enters the λ / 4 wavelength plate QWP. Here, the light beam incident on the λ / 4 wavelength plate QWP is again converted from the circularly polarized state to the linearly polarized state, but is shifted to the S-polarized (second linearly polarized) state by shifting the phase.

  The light beam that has passed through the λ / 4 wavelength plate QWP and has become P-polarized light is reflected by the polarization beam splitter PBS and condensed on the light receiving surface of the photodetector PD. Using the output signal of the photodetector PD, a read signal of information recorded in the HD is obtained.

  In addition, focus detection and track detection are performed by detecting spot shape change and light quantity change on the photodetector PD. Based on this detection, the second objective lens OBJ2 is configured so that the focusing actuator and tracking actuator (not shown) of the second objective lens OBJ2 appropriately image the light flux from the semiconductor laser LD on the information recording surface of the HD. Is supposed to move.

  Furthermore, when recording and / or reproducing information on a DVD (or CD), the optical axis of the λ / 4 wave plate QWP is rotated 90 degrees from a predetermined direction so that only a light beam in a counterclockwise circular polarization state is obtained. It can be emitted. In the optical pickup device of FIG. 2, the light beam in the P-polarized (first) linearly polarized state emitted from the semiconductor laser LD (light source) having the light source wavelength λ2 = 650 ± 50 nm (or λ3 = 750 ± 50 nm) The light passes through the polarization beam splitter PBS, which is a means, and further passes through the λ / 4 wavelength plate QWP to enter a counterclockwise circularly polarized state (light quantity A0), and enters the first cholesteric liquid crystal CLQ1 in the prism PZ.

  Here, most of the light beam incident on the first cholesteric liquid crystal CLQ1 is transmitted (light amount T1 ′> 0.5 × A0), further transmitted through the second cholesteric liquid crystal CLQ2, and reflected by the reflecting surface RP of the prism PZ. After that, the light enters the third objective lens OBJ3 and is focused on the DVD (or CD) information recording surface (thickness of the protective layer t3 = 0.6 mm (or t4 = 1.2 mm)). .

  The reflected light beam modulated by the information pits on the information recording surface of the DVD (or CD) again passes through the third objective lens OBJ3, is reflected by the reflecting surface RP of the prism PZ, and then the second cholesteric liquid crystal in the prism PZ. The light passes through CLQ2, further passes through the first cholesteric liquid crystal CLQ1, and enters the λ / 4 wavelength plate QWP. Here, the light beam incident on the λ / 4 wavelength plate QWP is again converted from the circularly polarized state to the linearly polarized state, but is shifted to the S-polarized (second linearly polarized) state by shifting the phase.

  The light beam that has passed through the λ / 4 wavelength plate QWP and has become P-polarized light is reflected by the polarization beam splitter PBS and condensed on the light receiving surface of the photodetector PD. A read signal of information recorded on a DVD (or CD) is obtained using the output signal of the photodetector PD.

  In addition, focus detection and track detection are performed by detecting spot shape change and light quantity change on the photodetector PD. Based on this detection, the second actuator OBJ3 has a focusing actuator and a tracking actuator (not shown) that appropriately form a light beam from the semiconductor laser LD on the information recording surface of the DVD (or CD). The objective lens OBJ3 is moved.

  Next, a third embodiment will be described with reference to the drawings. FIG. 3 shows a third embodiment in which information can be recorded / reproduced appropriately for BD, HD and DVD (or CD) which are optical information recording media (also called optical discs) having different protective layer thicknesses. It is a side view which shows roughly the structure of the optical pick-up apparatus of a form. In this embodiment, the λ / 4 wave plate QWP, which is a phase difference element, is fixed, and a linearly polarized light beam can be converted into a clockwise circularly polarized light beam and emitted. Further, the cholesteric liquid crystal CLQ having circular dichroism that is a light distribution element has an external input terminal (not shown), and when a predetermined voltage is not applied through this (state of FIG. 6A), A light beam in a clockwise circular polarization state or a counterclockwise circular polarization state is reflected, but when a predetermined voltage is applied (the state shown in FIG. 6B), the light beam is transmitted, that is, circularly polarized dichroic. It is designed to switch the expression of sex. More specifically, the cholesteric liquid crystal CLQ to which a predetermined voltage is not applied enters a light beam with a light amount A0 and reflects a light beam with a light amount R1 (> 0.5 × A0), but a predetermined voltage is applied. The cholesteric liquid crystal CLQ receives a light beam having a light amount A0 and transmits a light beam having a light amount T1 (> 0.5 × A0). The semiconductor laser LD is a so-called two-laser one package that can emit light beams having two different wavelengths (λ1, λ2).

  Furthermore, the first objective lens OBJ1 is designed so that aberrations are optimally corrected for BD, and the second objective lens OBJ2 is optimal for HD and DVD (or CD). Designed to correct aberrations.

  First, when recording and / or reproducing information on a BD, a predetermined voltage is not applied to the cholesteric liquid crystal CLQ. In the optical pickup device shown in FIG. 3, a P-polarized (first) linearly polarized light beam emitted from a semiconductor laser LD (light source) having a light source wavelength λ1 = 400 ± 50 nm is applied to a polarization beam splitter PBS, which is an optical branching unit. Then, it passes through the λ / 4 wavelength plate QWP, enters a circularly polarized state (light quantity A0), and enters the cholesteric liquid crystal CLQ in the prism PZ.

  Here, most of the light beam incident on the cholesteric liquid crystal CLQ is reflected (light quantity R1> 0.5 × A0), is emitted from the prism PZ, and then enters the first objective lens OBJ1, from which BD The information recording surface (thickness t1 of the protective layer = 0.1 mm) is condensed.

  The reflected light beam modulated by the information pits on the information recording surface of the BD again passes through the first objective lens OBJ1, but the circularly polarized light beam reflected on the information recording surface of the BD is reflected on the cholesteric liquid crystal CLQ in the prism PZ. This is the same direction as the spiral direction, is reflected again by the cholesteric liquid crystal CLQ, is emitted from the prism PZ, and then enters the λ / 4 wavelength plate QWP. Here, the light beam incident on the λ / 4 wavelength plate QWP is again converted from the circularly polarized state to the linearly polarized state, but is shifted to the S-polarized (second linearly polarized) state by shifting the phase.

  The light beam that has passed through the λ / 4 wavelength plate QWP and has become P-polarized light is reflected by the polarization beam splitter PBS and condensed on the light receiving surface of the photodetector PD. A read signal of information recorded on the BD is obtained using the output signal of the photodetector PD.

  In addition, focus detection and track detection are performed by detecting spot shape change and light quantity change on the photodetector PD. Based on this detection, the first objective lens OBJ1 is formed so that the focusing actuator and tracking actuator (not shown) of the first objective lens OBJ1 appropriately form the light beam from the semiconductor laser LD on the information recording surface of the BD. Is supposed to move.

  Next, when recording and / or reproducing information with respect to HD (or DVD), a predetermined voltage is applied to cholesteric liquid crystal CLQ. In the optical pickup device of FIG. 3, the light beam in the P-polarized (first) linear polarization state emitted from the semiconductor laser LD (light source) having the light source wavelength λ1 = 400 ± 50 nm (or λ2 = 650 ± 50 nm) The light passes through the polarizing beam splitter PBS, which is a means, and further passes through the λ / 4 wavelength plate QWP to be in a circularly polarized state (light quantity A0), and enters the cholesteric liquid crystal CLQ in the prism PZ.

  Here, most of the light beam incident on the cholesteric liquid crystal CLQ is transmitted (light quantity T1> 0.5 × A0), reflected by the reflecting surface RP of the prism PZ, and emitted from the prism PZ, and then the second objective. The light enters the lens OBJ2 and is focused on the HD (or DVD) information recording surface (protective layer thickness t2 (or t3) = 0.6 mm).

  The reflected light beam modulated by the information pits on the HD (or DVD) information recording surface again passes through the second objective lens OBJ2 and is reflected by the reflecting surface RP of the prism PZ, but is reflected by the HD information recording surface. The circularly polarized light flux is in the direction opposite to the spiral direction of the cholesteric liquid crystal CLQ, passes through the cholesteric liquid crystal CLQ again, exits from the prism PZ, and then enters the λ / 4 wavelength plate QWP. Here, the light beam incident on the λ / 4 wavelength plate QWP is again converted from the circularly polarized state to the linearly polarized state, but is shifted to the S-polarized (second linearly polarized) state by shifting the phase.

  The light beam that has passed through the λ / 4 wavelength plate QWP and has become P-polarized light is reflected by the polarization beam splitter PBS and condensed on the light receiving surface of the photodetector PD. A read signal of information recorded on the HD (or DVD) is obtained using the output signal of the photodetector PD.

  In addition, focus detection and track detection are performed by detecting spot shape change and light quantity change on the photodetector PD. Based on this detection, the second objective lens OBJ2 has a focusing actuator and a tracking actuator (not shown) that appropriately form a light beam from the semiconductor laser LD on the information recording surface of the HD (or DVD). The objective lens OBJ2 is moved.

  Next, a fourth embodiment will be described with reference to the drawings. FIG. 4 shows a fourth embodiment in which information can be recorded / reproduced appropriately with respect to BD (or HD), DVD and CD, which are optical information recording media (also referred to as optical disks) having different protective layer thicknesses. It is a side view which shows the structure of an optical pick-up apparatus roughly. The λ / 4 wavelength plate QWP, which is a polarization state setting means, is fixed, and the light beam incident in the linear polarization state can be converted into a clockwise circular polarization state and emitted. The first cholesteric liquid crystal CLQ1 having circular dichroism as the first light distribution means and the second cholesteric liquid crystal CLQ2 having circular dichroism as the second light distribution means are disposed in the prism PZ. Are integrally formed. The first cholesteric liquid crystal CLQ1 is in a clockwise circular polarization state, reflects a light beam having a wavelength of 500 nm or less, and transmits other light beams. The second cholesteric liquid crystal CLQ2 is in a clockwise circular polarization state, reflects a light beam having a wavelength of 700 nm or less, and transmits other light beams. The semiconductor laser LD is a so-called three-laser one package that can emit light beams having three different wavelengths (λ1, λ2, λ3).

  Furthermore, the first objective lens OBJ1 is designed so that aberrations are optimally corrected for BD (or HD), and the second objective lens OBJ2 is optimally corrected for aberrations for DVD. The third objective lens OBJ3 is designed so that aberrations are optimally corrected with respect to the CD.

  First, when recording and / or reproducing information with respect to BD (or HD), in the optical pickup device of FIG. 4, P-polarized light (radiated from a semiconductor laser LD (light source) having a light source wavelength λ1 = 400 ± 50 nm The light beam in the first linearly polarized state passes through the polarization beam splitter PBS, which is a light branching means, and further passes through the λ / 4 wavelength plate QWP to become a clockwise circularly polarized state (light quantity A0), and the prism PZ And enters the first cholesteric liquid crystal CLQ1.

  Here, most of the light beam incident on the first cholesteric liquid crystal CLQ1 is reflected (the amount of light R1> 0.5 × A0), and is emitted from the prism PZ and then incident on the first objective lens OBJ1. To BD (or HD) information recording surface (protective layer thickness t1 = 0.1 (or 0.6) mm).

  The reflected light beam modulated by the information pits on the information recording surface of the BD (or HD) passes through the first objective lens OBJ1 again, but the circularly polarized light beam reflected by the information recording surface of the BD is in the prism PZ. The first cholesteric liquid crystal CLQ1 has the same spiral direction as that of the first cholesteric liquid crystal CLQ1, is reflected again by the first cholesteric liquid crystal CLQ1, is emitted from the prism PZ, and then enters the λ / 4 wavelength plate QWP. Here, the light beam incident on the λ / 4 wavelength plate QWP is again converted from the circularly polarized state to the linearly polarized state, but is shifted to the S-polarized (second linearly polarized) state by shifting the phase.

  The light beam that has passed through the λ / 4 wavelength plate QWP and has become P-polarized light is reflected by the polarization beam splitter PBS and condensed on the light receiving surface of the photodetector PD. A read signal of information recorded in the BD (or HD) is obtained using the output signal of the photodetector PD.

  In addition, focus detection and track detection are performed by detecting spot shape change and light quantity change on the photodetector PD. Based on this detection, the first and second focusing actuators and tracking actuators (not shown) of the first objective lens OBJ1 appropriately image the light flux from the semiconductor laser LD on the information recording surface of the BD (or HD). The objective lens OBJ1 is moved.

  Next, when recording and / or reproducing information on a DVD, the P-polarized light (first) emitted from the semiconductor laser LD (light source) having the light source wavelength λ2 = 650 ± 50 nm in the optical pickup device of FIG. The linearly polarized light beam passes through the polarization beam splitter PBS, which is an optical branching unit, and further passes through the λ / 4 wavelength plate QWP to become a clockwise circularly polarized state (light quantity A0). The light enters one cholesteric liquid crystal CLQ1.

  Here, most of the light beam incident on the first cholesteric liquid crystal CLQ1 is transmitted (light quantity T1> 0.5 × A0), but is reflected by the second cholesteric liquid crystal CLQ2 and emitted from the prism PZ. Is incident on the objective lens OBJ2 and focused on the information recording surface of the DVD (thickness t2 of the protective layer = 0.6 mm).

  The reflected light beam modulated by the information pits on the information recording surface of the DVD passes through the second objective lens OBJ2 again, but the circularly polarized light beam reflected by the HD information recording surface is the second cholesteric in the prism PZ. The direction is the same as the spiral direction of the liquid crystal CLQ2, is reflected again by the second cholesteric liquid crystal CLQ2, passes through the first cholesteric liquid crystal CLQ1, and enters the λ / 4 wavelength plate QWP. Here, the light beam incident on the λ / 4 wavelength plate QWP is again converted from the circularly polarized state to the linearly polarized state, but is shifted to the S-polarized (second linearly polarized) state by shifting the phase.

  The light beam that has passed through the λ / 4 wavelength plate QWP and has become P-polarized light is reflected by the polarization beam splitter PBS and condensed on the light receiving surface of the photodetector PD. Using the output signal of the photodetector PD, a read signal of information recorded on the DVD can be obtained.

  In addition, focus detection and track detection are performed by detecting spot shape change and light quantity change on the photodetector PD. Based on this detection, the second objective lens OBJ2 is formed so that the focusing actuator and tracking actuator (not shown) of the second objective lens OBJ2 appropriately image the light beam from the semiconductor laser LD on the information recording surface of the DVD. Is supposed to move.

  Furthermore, when recording and / or reproducing information on a CD, the P-polarized light (first) emitted from the semiconductor laser LD (light source) having a light source wavelength λ3 = 750 ± 50 nm in the optical pickup device of FIG. The light beam in the linearly polarized state passes through the polarization beam splitter PBS, which is a light branching unit, and further passes through the λ / 4 wavelength plate QWP to become a clockwise circularly polarized state (light quantity A0). The light enters the cholesteric liquid crystal CLQ1.

  Here, most of the light beam incident on the first cholesteric liquid crystal CLQ1 is transmitted (light amount T1 ′> 0.5 × A0), further transmitted through the second cholesteric liquid crystal CLQ2, and reflected by the reflecting surface RP of the prism PZ. After that, the light enters the third objective lens OBJ3 and is focused on the information recording surface of the CD (thickness of the protective layer t3 = 1.2 mm).

  The reflected light beam modulated by the information pits on the information recording surface of the CD again passes through the third objective lens OBJ3, is reflected by the reflecting surface RP of the prism PZ, and then passes through the second cholesteric liquid crystal CLQ2 in the prism PZ. Further, the light passes through the first cholesteric liquid crystal CLQ1 and enters the λ / 4 wavelength plate QWP. Here, the light beam incident on the λ / 4 wavelength plate QWP is again converted from the circularly polarized state to the linearly polarized state, but is shifted to the S-polarized (second linearly polarized) state by shifting the phase.

  The light beam that has passed through the λ / 4 wavelength plate QWP and has become P-polarized light is reflected by the polarization beam splitter PBS and condensed on the light receiving surface of the photodetector PD. Using the output signal of the photodetector PD, a read signal of information recorded on the CD can be obtained.

  In addition, focus detection and track detection are performed by detecting spot shape change and light quantity change on the photodetector PD. Based on this detection, the second objective lens OBJ3 so that the focusing actuator and the tracking actuator (not shown) of the third objective lens OBJ3 appropriately image the light beam from the semiconductor laser LD on the information recording surface of the CD. Is supposed to move.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. As the cholesteric liquid crystal, for example, a clockwise circularly polarized light beam is reflected and a counterclockwise circularly polarized light beam is transmitted with respect to 45 ° incident light of light beams having different wavelengths λ1, λ2, and λ3 (1 Or select three types of liquid crystal that reflect right circularly polarized light and transmit left circularly polarized light with respect to 45 ° incident light of light beams having wavelengths λ1, λ2, and λ3. You can do it. Further, as the polarization state setting means or the phase difference element, a voltage may be applied to the liquid crystal sandwiched between the transparent electrodes so as to give a phase difference to the passing light beam. The size can be reduced compared with the case where the plate is mechanically rotated.

It is a figure which shows schematically the structure of the optical pick-up apparatus of 1st Embodiment. It is a figure which shows schematically the structure of the optical pick-up apparatus of 2nd Embodiment. It is a figure which shows schematically the structure of the optical pick-up apparatus of 3rd Embodiment. It is a figure which shows schematically the structure of the optical pick-up apparatus of 4th Embodiment. It is a conceptual diagram of a cholesteric liquid crystal. It is a figure which shows the case where a predetermined voltage is not applied with respect to the cholesteric liquid crystal which has circular dichroism (a), and the case where a predetermined voltage is applied (b).

Explanation of symbols

CLQ cholesteric liquid crystal CLQ1 first cholesteric liquid crystal CLQ2 second cholesteric liquid crystal LD semiconductor laser M rising mirror OBJ1 first objective lens OBJ2 second objective lens OBJ3 third objective lens PBS polarizing beam splitter PD photodetector PP parallel Flat plate PZ Prism QWP λ / 4 wave plate RP Reflective surface

Claims (19)

A light source that emits a light beam in a first linear polarization state;
A polarization state setting means for selectively setting one of a circular polarization state around one direction and a circular polarization state around the other direction when a light beam emitted from the light source is incident;
In the light beam emitted by the polarization state setting means, when the circular polarization state around the one direction is selected, the light beam is reflected, and when the circular polarization state around the other direction is selected. Is a first light distribution element having circular dichroism that transmits the luminous flux;
A first objective lens that focuses the light beam reflected by the first light distribution element on the information recording surface of the first optical information recording medium;
A second objective lens that focuses the light beam transmitted through the first light distribution element on the information recording surface of the second optical information recording medium;
A light branching unit disposed between the light source and the polarization state setting unit, allowing a light beam in a first linear polarization state to pass therethrough and reflecting a light beam in a second line change state;
A photodetector for receiving a light beam from the light branching means,
The reflected light from the first optical information recording medium is reflected by the first light distribution element and enters the polarization state setting means, thereby entering a second linear polarization state and entering the light branching means. The reflected light from the second optical information recording medium passes through the first light distribution element and is incident on the polarization state setting means, thereby entering a second linearly polarized state and entering the light branching means. An optical pickup device.   2. The optical pickup device according to claim 1, wherein the first light distribution unit is a cholesteric liquid crystal.   The optical pickup device according to claim 1, wherein the polarization state setting unit is a λ / 4 wavelength plate whose rotation position can be switched.   The optical pickup apparatus according to claim 1, wherein the polarization state setting unit is a liquid crystal element.   The optical axis of the first objective lens and the optical axis of the second objective lens are arranged in parallel, and the light flux that has passed through the first light distribution element is reflected by a reflecting means and is reflected by the second objective lens. The optical pickup device according to claim 1, wherein the optical pickup device is incident on an objective lens.   6. The optical pickup device according to claim 5, wherein the first light distribution element and the reflection means are incorporated in an integral prism.   The first light distribution element is attached to a parallel plate that transmits light, is separate from the reflection means, and a light beam incident on the first light distribution element is an infinite parallel light beam. The optical pickup device according to claim 5.   8. The optical pickup device according to claim 1, wherein a recording density of the first optical information recording medium is different from a recording density of the second optical information recording medium.   One of the first optical information recording medium and the second optical information recording medium has a protective substrate thickness t1 of 0.1 mm, and the other has a protective substrate thickness t2 of 0.6 mm. 9. The optical pickup device according to 8.   The light source can selectively emit a light beam having a wavelength λ1 (350 nm ≦ λ1 ≦ 450 nm) and a light beam having a wavelength λ2 (600 nm ≦ λ2 ≦ 700 nm), and the second objective lens has a wavelength λ1. The light beam having the wavelength λ2 is condensed on the information recording surface of the third optical information recording medium, and the light beam having the wavelength λ2 is condensed on the information recording surface of the third optical information recording medium. The optical pick-up apparatus in any one.   The optical pickup device according to claim 10, wherein the second optical information recording medium and the third optical information recording medium have the same protective substrate thickness.   The light source can selectively emit a light beam having a wavelength λ1 (350 nm ≦ λ1 ≦ 450 nm), a light beam having a wavelength λ2 (600 nm ≦ λ2 ≦ 700 nm), and a light beam having a wavelength λ3 (700 nm ≦ λ3 ≦ 800 nm). The second objective lens condenses the light beam having the wavelength λ1 on the information recording surface of the second optical information recording medium, and the light beam having the wavelength λ2 is the third light having a protective substrate thickness t3 of 0.6 mm. 2. A light beam having a wavelength λ3 is condensed on an information recording surface of the information recording medium, and a light beam having a wavelength λ3 is condensed on an information recording surface of a fourth optical information recording medium having a protective substrate thickness t4 of 1.2 mm. 10. The optical pickup device according to any one of 9 above. The light source can selectively emit a light beam having a wavelength λ1 (350 nm ≦ λ1 ≦ 450 nm), a light beam having a wavelength λ2 (600 nm ≦ λ2 ≦ 700 nm) and / or a light beam having a wavelength λ3 (700 nm ≦ λ3 ≦ 800 nm). And
The light beam that has passed through the first light distribution element is incident on the second light distribution element, and the second light distribution element reflects a light beam having a wavelength λ1 (350 nm ≦ λ1 ≦ 450 nm) and a wavelength λ2 (600 nm ≦ λ2). ≦ 700 nm) and / or a light beam having a wavelength of λ3 (700 nm ≦ λ3 ≦ 800 nm) is transmitted, and the light beam transmitted through the second light distribution element is incident on a third objective lens. 10. The optical pickup device according to any one of 9 above. A light source that emits a light beam in a first linear polarization state;
A phase difference element that selectively sets a circular polarization state around one direction or a circular polarization state around the other direction when a light beam emitted from the light source is incident;
A light distribution element capable of switching the expression of circular dichroism;
A first objective lens that focuses the light beam reflected by the light distribution element on the information recording surface of the first optical information recording medium;
A second objective lens that focuses the light beam transmitted through the light distribution element on the information recording surface of the second optical information recording medium;
A light branching unit disposed between the light source and the phase difference element, allowing the first linearly polarized light beam to pass therethrough and reflecting the second linearly changed light beam;
A photodetector for receiving a light beam from the light branching means,
The reflected light from the first optical information recording medium is reflected by the light distribution element and enters the phase difference element, thereby entering a second linearly polarized state and entering the light branching unit. The reflected light from the two-optical information recording medium is transmitted through the light distribution element and incident on the phase difference element, thereby entering a second linearly polarized state and incident on the light branching means. Optical pickup device.   The optical pickup device according to claim 14, wherein the light distribution element includes a cholesteric liquid crystal.   The optical pickup device according to claim 14 or 15, wherein the expression of the circular dichroism can be switched by switching a voltage applied to the light distribution element.   The light source can selectively emit a light beam having a wavelength λ1 (350 nm ≦ λ1 ≦ 450 nm) and a light beam having a wavelength λ2 (600 nm ≦ λ2 ≦ 700 nm). The optical pickup device according to claim 13, wherein a light beam having a wavelength of λ2 and a light beam having a wavelength of λ2 pass therethrough.   The light source can selectively emit a light beam having a wavelength λ1 (350 nm ≦ λ1 ≦ 450 nm), a light beam having a wavelength λ2 (600 nm ≦ λ2 ≦ 700 nm), and a light beam having a wavelength λ3 (700 nm ≦ λ3 ≦ 800 nm). The optical pickup device according to any one of claims 13 to 16, wherein a light beam having a wavelength λ1, a light beam having a wavelength λ2, and a light beam having a wavelength λ3 pass through the second objective lens. The optical pickup device according to claim 1, wherein the circularly polarized state includes an elliptically polarized state.

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