JP2008033990A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device in which noise can be eliminated effectively when recording and/or reproducing of information is performed for an optical information recording medium provided with an information recording surface of a multi-layer. <P>SOLUTION: In luminous flux passed through a first waveform plate OE1 and a second wavelength plate OE2, since reflected light from the information recording plane other than an information recording plane in which recording and/or reproducing of information is intended to perform is a noise component and a polarization direction is not changed, and as the reflected light is transmitted through a second polarization beam splitter BS2, it does not reach to a photodetector PD, thereby, causing an error can be suppressed. Also, since the optical path of the luminous flux forward the photodetector is bent by a mirror M, constitution of the optical pickup device PU1 can be made compact. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup device that is preferably used when an optical disc having multiple information recording layers is used.

  An optical disc represented by a DVD can record a large amount of information signals at a high density, and therefore is being used in many fields such as audio, video, and computer. Recently, in order to meet the demand for further increase in recording capacity, optical discs having multiple information recording surfaces have been developed and are already on the market.

By the way, when the distance between the recording / reproducing surfaces in the optical disk having the information recording surface provided in multiple layers is small, when the recording / reproducing light beam is condensed on one recording / reproducing surface, the recording / reproducing is performed. The reflected light from the surface is affected by the reflected light from the adjacent recording / reproducing surface, and may be recognized as noise. On the other hand, an optical pickup device is known that suppresses noise by combining two wave plates having two regions having different polarization characteristics (see Non-Patent Document 1).
Lecture material of the 6th optical disc round-table conference "Detection of interlayer separation of multilayer discs using photonic crystals" by Tetsuya Kosugi, March 17, 2006

  Here, in the optical pickup device disclosed in Non-Patent Document 1, the light beam reflected from the information recording surface of the optical disk passes through the first wave plate, and then the first wave plate and the second wave plate. , The noise component is removed when passing through the second wave plate and passing through the polarization beam splitter, and only the regular signal is incident on the photodetector. . However, in the optical pickup device of Non-Patent Document 1, at least two wavelength plates and a polarizing beam splitter must be arranged between the objective lens and the photodetector, and the optical path length becomes long, There is a problem that the configuration of the pickup device is increased.

  The present invention has been made in view of the problems of the prior art, and is effective in noise when recording and / or reproducing information on an optical information recording medium having a multilayer information recording surface. An object of the present invention is to provide an optical pickup device that can be removed easily.

The optical pickup device according to claim 1 is an optical pickup device that records and / or reproduces information with respect to an optical information recording medium having a multilayer information recording surface.
A first optical element comprising a first optical region and a second optical region across the optical axis;
A second optical element comprising a third optical region and a fourth optical region across the optical axis;
A reflective optical element disposed in an optical path between the first optical element and the second optical element;
A condensing element for condensing a light beam condensed and reflected on the information recording surface of the optical information recording medium between the first optical element and the second optical element;
A polarization splitting element;
A photodetector,
The main light beam that has passed through the first optical region and the fourth optical region, and the main light beam that has passed through the second optical region and the third optical region have a polarization direction in the first direction. Yes,
The sub-light beam that has passed through the first optical region and the third optical region and the sub-light beam that has passed through the second optical region and the fourth optical region have a polarization direction in the first direction. Is a second direction different from
The light beam reflected from the information recording surface of the optical information recording medium passes through the condensing optical element, the first optical element, the reflective optical element, and the second optical element, and then the main light beam is polarized light splitting means. Is branched from the sub-beam and enters the photodetector. In the present specification, the “optical axis” refers to the optical axis of the objective lens.

  The principle of the present invention will be described with reference to FIG. 1, the first optical element OE1 has a first optical region A above the optical axis X and a second optical region B below the optical axis. Further, the second optical element OE2 that is separated from the first optical element OE1 by a predetermined distance along the optical axis has a third optical region C above the optical axis X, and a fourth optical element below the optical axis. It has an optical region D. Each of the optical regions A to D has a function of generating a phase difference of λ / 4 in the light beam passing therethrough, but the directions of the optical regions A and B and C and D are different from each other. Also, the optical regions A and C, and B and D facing each other have different directions. As a specific example, a phase difference of + λ / 4 is generated in the light beam that has passed through the first optical region A, a phase difference of −λ / 4 is generated in the light beam that has passed through the second optical region B, It is conceivable that a phase difference of −λ / 4 is generated in the light beam that has passed through the third optical region C, and a phase difference of + λ / 4 is generated in the light beam that has passed through the fourth optical region D. Further, a phase difference of + λ / 2 is generated in the light beam that has passed through the first optical region A, and the light beam that has passed through the second optical region B has passed through the third optical region C without causing a phase difference. A phase difference of + λ / 2 may be generated in the light beam, and the light beam that has passed through the fourth optical region D may not cause a phase difference.

  Here, it is assumed that reflected light in a linearly polarized state is emitted from the information recording surface of the optical information recording medium from the left side of FIG. In an optical information recording medium having a multilayer information recording surface, the marginal ray α in the reflected light from the target information recording surface for recording and / or reproducing information is indicated by a solid line, and from the information recording surface deeper than that. The marginal ray β in the reflected light is indicated by a dotted line, and the marginal ray γ in the reflected light from the information recording surface shallower than the target information recording surface is indicated by a one-dot chain line. That is, here, the light ray α is a regular information recording light, and the light rays β and γ are noise components.

  Since light is condensed at a position having a conjugate relationship with the reflected information recording surface, the light ray α is at a position X in the optical axis direction between the first optical element OE1 and the second optical element OE2. In the case of being condensed, the light beam β is condensed at a position Y closer to the optical information recording medium (left side in FIG. 1) than the position X, and the light beam γ is closer to the light detector side (see FIG. The light is condensed at a position Z 1).

  However, the portion of the light ray α that passes through the first optical region A necessarily passes through the fourth optical region D, and the portion that passes through the second optical region B always passes through the third optical region D. It will pass through region C. Therefore, the polarization direction of the light beam α after being emitted from the second optical element OE2 is 90 degrees different from the light beam α before being incident on the first optical element OE1 (first polarization direction).

  On the other hand, the portion of the light beam β that passes through the first optical region A passes through the third optical region C, and the portion that passes through the second optical region B further passes through the fourth optical region C. It will pass through region D. Therefore, the polarization direction of the light beam β after exiting from the second optical element OE2 is invariable with respect to the light beam β before entering the first optical element OE1 (a second direction different from the first polarization direction). Polarization direction).

  Similarly, the portion of the light ray γ that passes through the first optical region A passes through the third optical region C, and the portion that passes through the second optical region B further passes through the fourth optical region. D will be passed. Accordingly, the polarization direction of the light beam γ after exiting from the second optical element OE2 is invariable with respect to the light beam γ before entering the first optical element OE1 (a second direction different from the first polarization direction). Polarization direction).

  As described above, since the normal information recording light (also referred to as a main light beam) and the noise component light (also referred to as a sub light beam) have different polarization directions, for example, by 90 degrees, the light emitted from the second optical element OE1 is By passing through a polarization branching unit such as a polarization beam splitter, for example, regular information recording light can be reflected and light of noise components can be transmitted, and thereby noise components can be removed. In addition, the regular information recording light may be transmitted and guided to the photodetector, and the noise component light may be reflected. The polarization splitting means is not limited to the polarization beam splitter, and a linear polarizing plate that allows only regular information recording light in a predetermined polarization state to pass therethrough may be used. Furthermore, the first optical element, the second optical element, and the third optical element may be integrated.

  Further, according to the present invention, it is possible to provide a compact optical pickup device by bending the optical path by reflecting the light beam that passes through the second optical element and travels toward the polarization branching unit by the reflecting element. When the reflected light from the reflecting element passes through the same optical element, the first optical element and the second optical element can be made common.

  According to a second aspect of the present invention, there is provided the optical pickup device according to the first aspect, wherein the first optical element and the second optical element have a structural birefringence structure.

Here, structural birefringence will be described. Structural birefringence refers to birefringence generated by the direction of fine structure. For example, flat plates with different refractive indexes that do not have birefringence characteristics are arranged in parallel with a period sufficiently smaller than the wavelength of light (<λ / 2). In addition, it is known that a fine periodic structure (so-called line and space structure) generates birefringence characteristics (see Principle of Optics, Max Born and Emi Wolf, PERGAMON PRESS LTD.). The refractive index n _{p of the} light whose polarization direction is parallel to the groove and the refractive index n _v of the perpendicular light are respectively
n _p = (tn ₁ ² + (1−t) n ₂ ² ) ^1/2 (1)
n _v = 1 / (t / n ₁ ² + (1−t) / n ₂ ² ) ^1/2 (2)
It becomes. n ₁ and n ₂ are the refractive index of the material (line) in which the fine periodic structure is formed and the refractive index of the material (space) filling the groove, respectively, and t is the duty ratio of the fine periodic structure. If the width of the space is w ₁ and the width of the space is w ₂ ,
t = w ₁ / (w ₁ + w ₂ ) (3)
It is.

The birefringence characteristics of quartz and calcite are unique to the substance and can hardly be changed. On the other hand, the birefringence of fine periodic structures can be changed by changing the material and shape. Can be easily controlled. Further, the phase difference (delay amount) Re between the light whose polarization direction is parallel to the groove and the light perpendicular to the groove is d, where the birefringence height (groove depth) of the fine periodic structure is d.
Re = (n _p −n _v ) d (4)
It becomes. From these equations, the phase difference (delay amount) Re can be changed by making the birefringence duty ratio t of the fine periodic structure and the birefringence height (groove depth) d of the fine periodic structure variable. I understand.

  For example, when trying to form a λ / 4 wavelength plate for 400 nm laser light as an optical element, a resin material having a refractive index of about 1.5 at room temperature is used, the line width is 100 nm, and the space width is Is 90 nm, the fine structure height d needs to be 1200 nm. That is, the aspect ratio is about 12. According to the fine periodic structure, it is easy to integrally manufacture wave plates having the same phase difference but different optical axis orientations, and the loss area generated at the boundary between the wave plates can be reduced to several μm or less. Light loss can be reduced and unnecessary light blocking performance can be improved.

  According to a third aspect of the present invention, there is provided the optical pickup device according to the first or second aspect, wherein the reflective optical element has a light beam such that the incident light beam has an optical axis different from the optical axis of the incident light beam. Since the optical axis is bent toward the light output side, the light beam that has passed through the polarization branching means is prevented from returning to the information recording surface side of the optical information recording medium, and the generation of error signals is suppressed. it can. Note that “the optical axis of the incident light beam is different from the optical axis of the outgoing light beam” means that the two optical axes do not match, and the two optical axes are parallel and angled. Including both.

  According to a fourth aspect of the present invention, there is provided the optical pickup device according to the third aspect, wherein the optical axis of the light beam incident on the first optical element and the optical axis of the light beam emitted from the second optical element are Is characterized by being angled.

  According to a fifth aspect of the present invention, in the invention of the third aspect, the optical axis of the light beam incident on the first optical element, and the optical axis of the light beam emitted from the second optical element, Are parallel.

An optical pickup device according to claim 6 is an optical pickup device that records and / or reproduces information on an optical information recording medium having a multilayer information recording surface.
An optical element comprising a first optical region and a second optical region across the optical axis;
A reflective element comprising a third optical region and a fourth optical region across the optical axis;
A condensing element for condensing the light beam collected and reflected on the information recording surface of the optical information recording medium between the optical element and the reflecting element;
A polarization splitting element;
A photodetector,
The main light beam that has passed through the first optical region and the fourth optical region, and the main light beam that has passed through the second optical region and the third optical region have a polarization direction in the first direction. Yes,
The sub-light beam that has passed through the first optical region and the third optical region and the sub-light beam that has passed through the second optical region and the fourth optical region have a polarization direction in the first direction. Is a second direction different from
After the light beam reflected from the information recording surface of the optical information recording medium passes through the optical element and the reflecting element, the main light beam is branched from the sub-light beam by the polarization branching means and is incident on the photodetector. Features.

  According to the present invention, the light beam reflected from the information recording surface of the optical information recording medium is condensed between the optical element and the reflecting element, so that the information recording surface for recording and reproducing information is used. The reflected light (regular signal) and the other reflected light (noise component) are made to have different polarization directions by, for example, 90 degrees. By utilizing this, for example, the light flux relating to the noise component is transmitted through the polarization branching means, while the light flux relating to the normal signal is reflected by the polarization branching means and detected by the photodetector, so that the noise component Separation can be performed effectively. Also, a compact optical pickup device can be provided by bending the optical path by reflecting the light beam reflected from the information recording surface of the optical information recording medium by the reflecting element.

  According to a seventh aspect of the present invention, in the invention according to the sixth aspect, the reflective element and the optical element have a structural birefringence structure.

  An optical pickup device according to an eighth aspect of the present invention is the optical pickup apparatus according to the sixth or seventh aspect, wherein the reflecting element is configured to cause the incident light beam to have an optical axis different from the optical axis of the incident light beam. The optical axis is bent toward the exit side.

  In the optical pickup device according to claim 9, in the invention according to claim 8, the optical axis of the light beam incident on the optical element and the optical axis of the light beam reflected by the reflecting element are angled. It is characterized by.

  An optical pickup device according to a tenth aspect is the invention according to the eighth aspect, wherein the optical axis of the light beam incident on the optical element is parallel to the optical axis of the light beam reflected by the reflecting element. And

An optical pickup device according to claim 11 is an optical pickup device that records and / or reproduces information on an optical information recording medium having a multilayer information recording surface.
An optical element that gives a phase difference of λ / 2 to a passing light beam;
A reflective element;
A condensing element for condensing the light beam collected and reflected on the information recording surface of the optical information recording medium between the optical element and the reflecting element;
A polarization splitting element;
A photodetector,
Of the luminous flux condensed and reflected on the information recording surface of the optical information recording medium, the first luminous flux passes through the optical element with the optical axis in between, and the remaining second half passes air. Further, it is reflected by the reflecting element, the first half passes through the air, the second half passes through the optical element, and is directed to the polarization branching means,
Of the luminous flux collected and reflected on the information recording surface of the optical information recording medium, the secondary luminous flux passes through the optical element, is reflected by the reflective element, passes again through the optical element, or passes through air. And is reflected by the reflecting element and passes through the air again toward the polarization splitting means.
The main light beam is branched from the sub-light beam by a polarization branching unit and is incident on the photodetector.

  According to the present invention, the light beam reflected from the information recording surface of the optical information recording medium is condensed between the optical element and the reflecting element, so that the information recording surface for recording and reproducing information is used. For the reflected light (regular signal), the polarization direction changes by 90 degrees, and the other reflected light (noise component) is emitted with the polarization direction unchanged. By utilizing this, for example, the light flux relating to the noise component is transmitted through the polarization branching means, while the light flux relating to the normal signal is reflected by the polarization branching means and detected by the photodetector, so that the noise component Separation can be performed effectively. Also, a compact optical pickup device can be provided by bending the optical path by reflecting the light beam reflected from the information recording surface of the optical information recording medium by the reflecting element.

  According to a twelfth aspect of the present invention, there is provided the optical pickup device according to the eleventh aspect, wherein the optical element has a structural birefringence structure.

  According to a thirteenth aspect of the present invention, in the optical pickup device according to the eleventh or twelfth aspect of the present invention, the reflecting element is configured so that the incident light beam has an optical axis different from the optical axis of the incident light beam. The optical axis is bent toward the exit side.

  According to a fourteenth aspect of the present invention, in the optical pickup device of the thirteenth aspect, the optical axis of the light beam incident on the optical element and the optical axis of the light beam reflected by the reflecting element are angled. It is characterized by.

  An optical pickup device according to a fifteenth aspect is characterized in that, in the invention according to the thirteenth aspect, an optical axis of a light beam incident on the optical element is parallel to an optical axis of a light beam reflected by the reflecting element. And

The optical pickup device according to claim 16 is an optical pickup device for recording and / or reproducing information with respect to an optical information recording medium having a multilayer information recording surface.
A first reflective element;
A first optical element comprising a first optical region and a second optical region across the optical axis;
A second optical element comprising a third optical region and a fourth optical region across the optical axis;
A second reflecting element that reflects the light beam that has passed through the first optical element and the second optical element;
A condensing element for condensing a light beam condensed and reflected on the information recording surface of the optical information recording medium between the first optical element and the second optical element;
A polarization splitting element;
A photodetector,
The main light beam that has passed through the first optical region and the fourth optical region, and the main light beam that has passed through the second optical region and the third optical region have a polarization direction in the first direction. Yes,
The sub-light beam that has passed through the first optical region and the third optical region and the sub-light beam that has passed through the second optical region and the fourth optical region have a polarization direction in the first direction. Is a second direction different from
The light beam reflected from the information recording surface of the optical information recording medium passes through the first reflecting element, the first optical element, the second optical element, and the second reflecting element, and then the main light beam is The light beam is branched from the auxiliary light beam by a polarization branching unit and is incident on the photodetector.

  According to the present invention, the light beam reflected from the information recording surface of the optical information recording medium is condensed between the first optical element and the second optical element, thereby recording and reproducing information. For example, the reflected light (normal signal) from the information recording surface and the other reflected light (noise component) are made to have different polarization directions by, for example, 90 degrees. By utilizing this, for example, the light flux relating to the noise component is transmitted through the polarization branching means, while the light flux relating to the normal signal is reflected by the polarization branching means and detected by the photodetector, so that the noise component Separation can be performed effectively. Further, a compact optical pickup device can be provided by bending the optical path by reflecting the light beam reflected from the information recording surface of the optical information recording medium by the first reflecting element and the second reflecting element.

  An optical pickup device according to a seventeenth aspect is the invention according to the sixteenth aspect, wherein the first optical element and the second optical element have a structural birefringence structure.

  An optical pickup device according to an eighteenth aspect is the optical pickup device according to the sixteenth or seventeenth aspect, wherein an optical axis of a light beam incident on the first reflecting element and an optical axis of a light beam emitted from the second reflecting element. Are angled, so that the polarization branching unit can be made compact, and the light beam that has passed through the polarization branching unit is prevented from returning to the information recording surface side of the optical information recording medium, resulting in an error. Signal generation can be suppressed.

  An optical pickup device according to a nineteenth aspect is the optical pickup device according to the sixteenth or seventeenth aspect, wherein an optical axis of a light beam incident on the first reflecting element and an optical axis of a light beam emitted from the second reflecting element. And are angled.

  ADVANTAGE OF THE INVENTION According to this invention, when recording and / or reproducing | regenerating information with respect to the optical information recording medium provided with the multilayer information recording surface, the optical pick-up apparatus which can remove a noise effectively can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 schematically shows the configuration of the optical pickup apparatus PU1 of the present embodiment that can appropriately record / reproduce information with respect to a DVD that is an optical information recording medium (also referred to as an optical disk) having a multilayer information recording surface. FIG. Needless to say, the present invention can be applied to BD (Blu-ray Disc), HD DVD, and other multilayer optical disks.

  FIG. 3 is a perspective view showing a first wave plate OE1 that is a first optical element and a second wave plate OE2 that is a second optical element. In FIG. 2, a first optical region A and a second optical region B are formed on the optical surface of the thin plate-shaped first wave plate OE1 with an optical axis (not shown) interposed therebetween. In the first optical region A, a plurality of fine walls WA are arranged at equal intervals. In the second optical region B, a plurality of fine walls WB are arranged at equal intervals, but the end portions are joined with each wall WB and the wall WA being orthogonal to each other. A structural birefringence structure is formed by the walls WA and WB.

  Similarly, a third optical region C and a fourth optical region D are formed on the optical surface of the thin plate-like second wavelength plate OE2 with an optical axis (not shown) interposed therebetween. In the third optical region C, a plurality of fine walls WC are arranged at equal intervals, but are orthogonal to the wall WA facing the optical axis direction when viewed in the optical axis direction. A plurality of fine walls WD are arranged at equal intervals in the fourth optical region D, but are orthogonal to the walls WB facing the optical axis direction when viewed in the optical axis direction. Each wall WC and wall WD are joined to each other in an orthogonal state, and a structural birefringence structure is formed by the walls WC and WD.

  Among the light beams that have passed through the first wave plate OE1 and the second wave plate OE2, the light beams that have passed through the first optical region A and the fourth optical region D, and the second optical region B and the third optical region C. And the second optical region B and the fourth optical region D. The light beams that have passed through the first optical region A and the third optical region C, and the second optical region B and the fourth optical region D. The direction of polarization of the light beam that has passed through is unchanged.

  In FIG. 2, the first wave plate OE1 and the second wave plate OE2 are a first optical region A, a second optical region B, a third optical region C, and a fourth optical device in a direction perpendicular to the paper surface with the optical axis in between. The optical region D is arranged side by side. In the optical pickup device PU1, when recording / reproducing information with respect to a DVD, the semiconductor laser LD1 is caused to emit light. The divergent light beam emitted from the semiconductor laser LD1 passes through the coupling lens CL and is converted into a parallel light beam as depicted by the solid line in FIG. 2, and is then reflected by the first polarization beam splitter BS1. After passing through the expander lens EXP including the convex lens L1 and the concave lens L2, and further passing through the λ / 4 wavelength plate QWP, the light beam diameter is regulated by a diaphragm (not shown), and information is recorded and / or reproduced by the objective lens OBJ. This is a spot formed on the information recording surface RL1 of the DVD to be performed. The objective lens OBJ performs focusing and tracking by a biaxial actuator (not shown) arranged around the objective lens OBJ.

  The reflected light beam modulated by the information pits on the information recording surface RL1 passes through the objective lens OBJ, the λ / 4 wavelength plate QWP, and the expander lens EXP again, and then passes through the first polarizing beam splitter BS1. The light beam emitted from the first polarization beam splitter BS1 is converted into a convergent light beam by the lens L3, which is a condensing element, passes through the first wave plate OE1, is reflected by the mirror M, which is a reflective optical element, and further has a second wavelength. Passes through the plate OE2. At this time, the light beam is condensed between the first wave plate OE1 and the second wave plate OE2. The light beam that has passed through the second wave plate OE2 passes through the lens L3, passes through the λ / 2 wave plate HWP, and enters the second polarizing beam splitter BS2.

  As described above, in the light beam that has passed through the first wave plate OE1 and the second wave plate OE2, the reflected light (main light beam) from the information recording surface to record and / or reproduce information has a polarization direction of 90. Therefore, the light beam is reflected by the second polarization beam splitter BS2 that is a polarization branching unit, condensed by the lens L5, added with astigmatism by the sensor lens SEN, and converged on the light receiving surface of the photodetector PD. . And the information recorded on DVD can be read using the output signal of photodetector PD. When recording and / or reproducing information on another information recording layer, the condensing position is changed by moving the lens L2 of the expander lens EXP in the optical axis direction.

  According to the present embodiment, the reflected light (sub-light from the information recording surface other than the information recording surface on which information is recorded and / or reproduced) in the light flux that has passed through the first wave plate OE1 and the second wave plate OE2. Since the light beam) is a noise component and the polarization direction is unchanged, it passes through the second polarization beam splitter BS2 and therefore does not reach the photodetector PD, thereby suppressing the occurrence of errors and the like. In addition, since the optical path of the light beam toward the photodetector PD is bent by the mirror M, the configuration of the optical pickup device PU1 can be made compact.

  FIG. 4 is a schematic configuration diagram of an optical pickup device PU2 according to the second embodiment. In the embodiment shown in FIG. 4, the second structural birefringent structure OE2 ′ having the function of a second wave plate including a plurality of fine walls (see FIG. 3) on the mirror M as a reflective element, that is, A third optical region C and a fourth optical region D are formed side by side in the direction perpendicular to the paper surface. The light beam reflected from the DVD and emitted from the first polarizing beam splitter BS1 becomes a converged light beam by the lens L3 that is a condensing element, passes through the first wave plate OE1, and is condensed before the mirror M that is the reflecting element. Then, the light passes through the second wave plate OE2, is reflected from the mirror M as a reflection element, is converted into a parallel light beam by the same lens L3, and is incident on the second polarization beam splitter BS2. Since other configurations are the same as those of the above-described embodiment, the description thereof is omitted. The lens that allows the incident light beam to the first wave plate OE1 and the lens that allows the outgoing light beam from the mirror M to pass may be separated.

  FIG. 12 is a diagram illustrating a modification of the present embodiment. In the present embodiment, an optical element OE having a structural birefringence that gives a phase difference of λ / 2 to a light beam that has passed and a mirror M that is a simple reflecting element are provided. Referring to FIG. 4, the light beam reflected from the DVD and emitted from the first polarization beam splitter BS1 becomes a converged light beam by the lens L3, which is a condensing element, and is irradiated onto the optical element OE1.

  Here, the regular information recording light, which is the main light beam, passes through the optical element OE through the optical element OE across the optical axis, and the remaining second half LB2 passes through the air. Reflected, this time, the first half LB1 passes through the air, and the second half LB2 passes through the optical element OE and goes to the polarization beam splitter. On the other hand, all of the noise light that is a sub-light beam passes through the optical element OE and is reflected by the mirror M, and then passes again through the optical element OE, or passes through the air and is reflected by the mirror M, and is again air. Through the polarization beam splitter. That is, since the polarization direction of the main light beam changes by 90 degrees, the polarization direction of the noise light does not change, so that the main light beam and the noise light can be branched by the polarization beam splitter.

  FIG. 5 is a schematic configuration diagram of an optical pickup device PU3 according to the third embodiment. FIG. 6 is a perspective view of the prism PS used in the present embodiment. In FIG. 6, one surface of the prism PS is an entrance surface IP and an exit surface OP, and the other two surfaces are reflection surfaces R1 and R2. A first structural birefringent structure OE1 ′ having a function of a first wave plate including a first region A and a second region B formed of a plurality of fine walls (see FIG. 3) is formed on the incident surface IP. In addition, the emission surface OP has a function of a second wavelength plate having a function of a first wavelength plate including a third region C and a fourth region D each including a plurality of fine walls (see FIG. 3). A two-structure birefringent structure OE2 ′ is formed.

  In FIG. 5, the light beam reflected from the DVD and passed through the expander lens EXP passes through the polarization beam splitter BS, becomes a converged light beam by the lens L3 that is a condensing element, and is formed on the incident surface IP of the prism PS. The second structural birefringence formed on the exit surface OP after passing through the one structural birefringent structure OE1 ′, being reflected after being reflected by the reflective surface R1, and further reflected by the second reflective surface R2. It passes through the structure OE2 ′, exits from the prism PS, is converted into a parallel light beam by the same lens L3, and is incident on the same polarization beam splitter BS, from the information recording surface RL1 to record and / or reproduce information. Only the reflected light is directed to the photodetector PD. At this time, the optical axis of the light beam traveling from the lens L3 to the polarizing beam splitter BS is inclined by the angle θ with respect to the optical axis of the bundle traveling from the polarizing beam splitter BS to the lens L3. In this way, by angling the incident light beam with respect to the outgoing light beam of the polarizing beam splitter BS, it is possible to suppress the noise light transmitted through the polarizing beam splitter BS from returning directly to the information recording surface of the DVD and becoming stray light. it can. In addition, good signal detection is possible because the position where the information recording light is incident on the light receiving surface of the photodetector PD is different from the position where the light beam that leaks and passes through the polarization beam splitter BS of the light emitted from the semiconductor laser LD. In addition, it becomes possible to detect the power monitor light of the semiconductor laser LD with the same photodetector. Since other configurations are the same as those in the above-described embodiment, description thereof is omitted. The lens that allows the incident light beam to the first structural birefringent structure OE1 'and the lens that allows the light beam emitted from the second structural birefringent structure OE2' to pass may be separated. The optical axis of the light beam traveling from the polarization beam splitter BS to the lens L3 and the optical axis of the light beam traveling from the lens L3 to the polarization beam splitter BS may be shifted in parallel. In such a case, the distance between the optical axes may be as long as the incident and outgoing light beams can be separated.

  7 and 8 are perspective views of a prism according to a modified example. The prisms shown in FIG. 6 are different in the extending direction of fine walls, but include optical regions A to D having the above-described functions. Yes. In such a case, the optical axis of the incident light beam to the prism may coincide with the optical axis of the outgoing light beam, but the regions passing when the light beam condensed between the two wave plates is incident are the first and second optical regions. Suppose that the regions that pass at the time of emission are the third and fourth regions. The prism is not limited to the above example and can take various forms. For example, instead of providing a structural birefringence structure on the entrance surface IP and the exit surface OP, a first structural birefringence structure OE1 ′ having optical regions A and B is formed on the reflective surface R1, and the optical surface is formed on the reflective surface R1. A second structural birefringent structure OE2 ′ having regions C and D may be formed.

  FIG. 9A is a schematic configuration diagram of an optical pickup device PU4 according to the fourth embodiment. FIG. 9B is an enlarged view of a configuration in which the first prism PS1, the second prism PS2, and the parallel plate PP are integrally formed. In FIG. 9, the first prism PS1 has an entrance surface IP1, a reflection surface R1, and an exit surface OP1, and the exit surface OP1 is a first composed of a plurality of fine walls (see FIG. 3). The first structural birefringence structure OE1 ′ including the region A and the second region B is formed. The second prism PS2 has an entrance surface IP2, a reflection surface R2, and an exit surface OP2. The entrance surface IP1 has a third region composed of a plurality of fine walls (see FIG. 3). A second structural birefringent structure OE2 ′ including C and the fourth region D is formed. A parallel plate PP is closely disposed between the first prism PS1 and the second prism PS2.

  In FIG. 9, the light beam reflected from the DVD and passed through the expander lens EXP passes through the polarization beam splitter BS, becomes a convergent light beam by the lens L3 that is a condensing element, and passes through the incident surface IP1 of the first prism PS1. Then, after being reflected by the reflecting surface R1 and passing through the first structural birefringent structure OE1 ′ formed on the exit surface OP1, the light is condensed in the parallel plate PP and further incident on the incident surface IP2 of the second prism PS2. The light passes through the formed second birefringent structure OE2 ′, is reflected by the reflecting surface R2, is emitted from the exit surface OP2S, is converted into a parallel light beam by the lens L4, and is incident on the same polarization beam splitter BS. Only reflected light from the information recording surface RL1 to be recorded and / or reproduced is directed to the photodetector PD. Other configurations are the same as those in the embodiment shown in FIG. The lens L3 may be a plurality of lenses.

  In the above-described embodiment, it is preferable to use a thick meniscus lens as shown in FIG. 10 as the lens L3 because the focal position can be made closer and the size can be reduced. Further, as shown in FIG. 11, a structural birefringence structure OE is formed on the reflecting surface R1, and the light beam incident from the incident / exiting surface IOP is reflected by the reflecting surface R1, then reflected by the reflecting surface R2, and reflected again. The prism PS that can be output from the incident / exit surface IOP after being reflected by the surface R1 can also be used in the above-described embodiment.

  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. In the above embodiment, it is preferable that the optical axis of the outgoing light from the polarizing beam splitter to the reflecting element side and the optical axis of the incident light from the reflecting element side are angled or shifted in parallel.

It is a figure for demonstrating the principle of this invention. 1 is a diagram schematically showing a configuration of an optical pickup apparatus PU1 of the present embodiment that can appropriately record / reproduce information with respect to a DVD that is an optical information recording medium (also referred to as an optical disc) having a multilayer information recording surface. FIG. . It is a perspective view which shows 1st wavelength plate OE1 which is a 1st optical element, and 2nd wavelength plate OE2 which is a 2nd optical element. It is a schematic block diagram of optical pick-up apparatus PU2 concerning 2nd Embodiment. It is a schematic block diagram of optical pick-up apparatus PU3 concerning 3rd Embodiment. It is a perspective view of prism PS used in this embodiment. It is a perspective view of the prism concerning a modification. It is a perspective view of the prism concerning a modification. It is a schematic block diagram of optical pick-up apparatus PU4 concerning 4th Embodiment. It is sectional drawing of lens L3 concerning a modification. It is sectional drawing of the prism PS concerning a modification. It is a partial perspective view of the pick-up apparatus concerning a modification.

Explanation of symbols

A to D Optical region BS Polarizing beam splitter BS1 First polarizing beam splitter BS2 Second polarizing beam splitter CL Coupling lens EXP Expander lens IP Incident surface IP1 Incident surface IP2 Incident surface L1 Convex lens L2 Concave lens L3 Lens L4 Lens L5 Lens LD1 Semiconductor laser M Mirror OBJ Objective lens OE1 First optical element OE1 ′ First structural birefringence structure OE1 First wave plate OE2 First optical element OE2 ′ Second structural birefringence structure OE2 Second wave plate OP exit surface OP1 exit surface OP2 exit surface PD photodetector PS prism PS1 first prism PS2 second prism PU1 optical pickup device PU2 optical pickup device PU3 optical pickup device PU4 optical pickup device PU5 optical pickup device QWP λ / 4 wavelength Board R1 reflecting surface R2 reflecting surface RL1 information recording surface SEN sensor lens WA wall WB wall WC wall WD wall

Claims (19)

In an optical pickup device for recording and / or reproducing information with respect to an optical information recording medium having a multilayer information recording surface,
A first optical element comprising a first optical region and a second optical region across the optical axis;
A second optical element comprising a third optical region and a fourth optical region across the optical axis;
A reflective optical element disposed in an optical path between the first optical element and the second optical element;
A condensing element for condensing a light beam condensed and reflected on the information recording surface of the optical information recording medium between the first optical element and the second optical element;
A polarization splitting element;
A photodetector,
The main light beam that has passed through the first optical region and the fourth optical region, and the main light beam that has passed through the second optical region and the third optical region have a polarization direction in the first direction. Yes,
The sub-light beam that has passed through the first optical region and the third optical region and the sub-light beam that has passed through the second optical region and the fourth optical region have a polarization direction in the first direction. Is a second direction different from
The light beam reflected from the information recording surface of the optical information recording medium passes through the condensing optical element, the first optical element, the reflective optical element, and the second optical element, and then the main light beam is polarized light splitting means. The optical pickup device is branched from the sub-beam and incident on the photodetector.   The optical pickup device according to claim 1, wherein the first optical element and the second optical element have a structural birefringence structure.   3. The reflective optical element according to claim 1 or 2, wherein the reflection optical element bends the optical axis toward the side from which the light beam exits so that the optical axis is different from the optical axis of the incident light beam. The optical pickup device described.   4. The optical pickup device according to claim 3, wherein the optical axis of the light beam incident on the first optical element and the optical axis of the light beam emitted from the second optical element are angled. .   4. The optical pickup device according to claim 3, wherein an optical axis of a light beam incident on the first optical element is parallel to an optical axis of a light beam emitted from the second optical element. In an optical pickup device for recording and / or reproducing information with respect to an optical information recording medium having a multilayer information recording surface,
An optical element comprising a first optical region and a second optical region across the optical axis;
A reflective element comprising a third optical region and a fourth optical region across the optical axis;
A condensing element for condensing the light beam collected and reflected on the information recording surface of the optical information recording medium between the optical element and the reflecting element;
A polarization splitting element;
A photodetector,
The main light beam that has passed through the first optical region and the fourth optical region, and the main light beam that has passed through the second optical region and the third optical region have a polarization direction in the first direction. Yes,
The sub-light beam that has passed through the first optical region and the third optical region and the sub-light beam that has passed through the second optical region and the fourth optical region have a polarization direction in the first direction. Is a second direction different from
After the light beam reflected from the information recording surface of the optical information recording medium passes through the optical element and the reflecting element, the main light beam is branched from the sub-light beam by the polarization branching means and is incident on the photodetector. A characteristic optical pickup device.   The optical pickup device according to claim 6, wherein the reflective element and the optical element have a structural birefringence structure.   8. The reflection element according to claim 6 or 7, wherein the reflection element bends the optical axis toward the side from which the light beam exits so that the incident light beam has an optical axis different from the optical axis of the incident light beam. Optical pickup device.   9. The optical pickup device according to claim 8, wherein the optical axis of the light beam incident on the optical element is angled with the optical axis of the light beam reflected by the reflecting element.   9. The optical pickup device according to claim 8, wherein the optical axis of the light beam incident on the optical element is parallel to the optical axis of the light beam reflected by the reflecting element. In an optical pickup device for recording and / or reproducing information with respect to an optical information recording medium having a multilayer information recording surface,
An optical element that gives a phase difference of λ / 2 to a passing light beam;
A reflective element;
A condensing element for condensing the light beam collected and reflected on the information recording surface of the optical information recording medium between the optical element and the reflecting element;
A polarization splitting element;
A photodetector,
Of the luminous flux condensed and reflected on the information recording surface of the optical information recording medium, the first luminous flux passes through the optical element with the optical axis in between, and the remaining second half passes air. Further, it is reflected by the reflecting element, the first half passes through the air, the second half passes through the optical element, and is directed to the polarization branching means,
Of the luminous flux collected and reflected on the information recording surface of the optical information recording medium, the secondary luminous flux passes through the optical element, is reflected by the reflective element, passes again through the optical element, or passes through air. And is reflected by the reflecting element and passes through the air again toward the polarization splitting means.
The optical pickup device according to claim 1, wherein the main light beam is branched from the sub-light beam by a polarization branching unit and is incident on the photodetector.   The optical pickup device according to claim 11, wherein the optical element has a structural birefringence structure.   13. The reflection element according to claim 11 or 12, wherein the reflecting element bends the optical axis toward the light beam exit side so that the incident light beam has an optical axis different from the optical axis of the incident light beam. Optical pickup device.   14. The optical pickup device according to claim 13, wherein the optical axis of the light beam incident on the optical element is angled with the optical axis of the light beam reflected by the reflecting element.   14. The optical pickup device according to claim 13, wherein the optical axis of the light beam incident on the optical element is parallel to the optical axis of the light beam reflected by the reflecting element. In an optical pickup device for recording and / or reproducing information with respect to an optical information recording medium having a multilayer information recording surface,
A first reflective element;
A first optical element comprising a first optical region and a second optical region across the optical axis;
A second optical element comprising a third optical region and a fourth optical region across the optical axis;
A second reflecting element that reflects the light beam that has passed through the first optical element and the second optical element;
A condensing element for condensing a light beam condensed and reflected on the information recording surface of the optical information recording medium between the first optical element and the second optical element;
A polarization splitting element;
A photodetector,
The main light beam that has passed through the first optical region and the fourth optical region, and the main light beam that has passed through the second optical region and the third optical region have a polarization direction in the first direction. Yes,
The sub-light beam that has passed through the first optical region and the third optical region and the sub-light beam that has passed through the second optical region and the fourth optical region have a polarization direction in the first direction. Is a second direction different from
The light beam reflected from the information recording surface of the optical information recording medium passes through the first reflecting element, the first optical element, the second optical element, and the second reflecting element, and then the main light beam is An optical pickup device, which is branched from the sub-light beam by a polarization branching means and enters the photodetector.   The optical pickup device according to claim 16, wherein the first optical element and the second optical element have a structural birefringence structure.   The optical pickup device according to claim 16 or 178, wherein an optical axis of a light beam incident on the first reflecting element and an optical axis of a light beam emitted from the second reflecting element are angled. . 18. The optical pickup device according to claim 16, wherein an optical axis of a light beam incident on the first reflective element is angled with an optical axis of a light beam emitted from the second reflective element. .