CN100423106C - Method and unit for separating light, optical pickup device, and optical recording/reproducing device - Google Patents

Abstract

A method of splitting light comprising the steps of: splitting, by a focusing lens, light traveling towards a light receiver into at least two parts along its optical axis; and from each split part, separating For the light component at a specific position, this separation is achieved between the focus position closer to the focusing lens than the focus position of the light component from the specific position and the focus position of the light component from the specific position, by removing the focus position and The light components from the particular location are in focus closer to the focusing lens than the light components from the particular location, and/or at a focus location closer to the light receiver than the light components from the particular location are in focus between the focus positions of , by removing the light components whose focus position is closer to the light receiver than the focus position of the light component from a particular position.

Description

Method and unit for separating light, optical pickup device, and optical recording/reproducing device

technical field

The present invention relates to, for example, a method and unit of splitting light used in recording/reproduction of a multilayer optical recording medium, and also relates to an optical pickup and an optical recording/reproducing apparatus based on the method and unit of splitting light. In particular, the present invention relates to a method and unit for separating light of interest from light from an illuminated medium having a plurality of reflective surfaces by removing light entering the receiving light after reflection by surfaces other than the reflective surface of interest. The invention also relates to an optical pickup device and an optical recording/reproducing apparatus based on the method and unit of separating light.

Background technique

Optical recording media (including magneto-optical recording media) typified by compact discs (CDs) and digital versatile discs (DVDs) are widely used as media to store audio information, video information, data, programs, and the like. Larger-capacity optical recording media and optical recording/reproducing apparatuses for recording/reproducing such information have been required to store information with higher sound and image quality and higher capacity.

An optical recording and/or reproducing apparatus for recording and/or reproducing of these optical recording media includes, for example, a light source (such as a semiconductor laser), a light splitting element (such as a beam splitter), an objective lens, a focusing lens, and a light receiver (such as Photodetector). Light from the light source passes through the light splitting element and is focused onto the recording layer of the optical recording medium through the objective lens. Then, the light is reflected by the recording layer, split by the light splitting element, and collected on the light receiver through the focusing lens.

Multilayer optical technology media with multiple recording layers have been proposed to achieve higher capacities. With this type of recording medium, a specific recording layer is irradiated with light (such as laser light) as a spot for recording/reproducing. However, this light is also reflected by the adjacent recording layer and the interface between the outermost layer and air. Therefore, the light receiver undesirably receives unwanted light reflected from adjacent recording layers and interfaces.

Such unwanted light may cause problems such as degradation of radio frequency (RF) signals and offset of servo signals. Specifically, for an optical recording medium having a higher recording density and capacity than DVD, interference of light reflected by an adjacent recording layer may undesirably cause degradation of signal reproduction characteristics because the recording layers of such a medium are spaced at a narrower pitch stack. Therefore, there is a need for a method of removing this unwanted light.

For example, Japanese Unexamined Patent Application Publication No. 2005-63595 proposes a method of removing light reflected by adjacent recording layers of a multilayer recording medium using light shielding. Light-shielding light-shielding regions are arranged in smaller regions on the optical axis to selectively remove light reflected by recording layers other than the recording layer of interest. For example, a pinhole is placed at the focal point of light reflected by a recording layer of interest to remove unnecessary light, thereby reducing the influence of light reflected by other recording layers.

Contents of the invention

However, according to the method disclosed in the above publication, it is difficult to receive the light component reflected by the recording layer of interest and travel along the optical axis, and thus it is difficult to detect all the light signals of interest. For example, if a diffraction grating is used to provide side spots for servo tracking or address readout, it is difficult to selectively receive all light of interest using a light shield as described above. On the other hand, it is difficult to use pinholes to completely remove unwanted light.

Therefore, it is necessary to provide a method and a unit for allowing reliable reception of light reflected at a specific position of the illuminated medium, for example light reflected by a recording layer of interest of a multilayer optical recording medium, enabling This is done by removing unwanted light that reaches the light receiver after it has been reflected by recording layers other than the layer of interest. In addition, it is desirable to provide an optical pickup device and an optical recording/reproducing apparatus that use the method and unit for separating light to suppress interference of light reflected by other recording layers in recording/reproducing of a multilayer optical recording medium. Influence.

According to an embodiment of the present invention, there is provided a method of splitting light from an illuminated multilayer medium having multiple reflective surfaces to pass through a focusing lens to a light receiver. The method comprises the steps of: splitting light traveling through the focusing lens towards the light receiver into at least two parts along its optical axis; and separating from each split part of the light light from the A light component of a specific position of the illuminated medium, this separation is achieved at a focus position of the focusing lens closer to the focus position of the light component from the specific position than the focus position of the light component from the specific position between the focus positions of , by removing the light components whose focus position is closer to the focusing lens than the focus position of the light component from the specific position, and/or at the same focus position as the light component from the specific position Between the focus position of the light component closer to the light receiver than the focus position of the light component from the specific position, by removing the focus position closer to the light than the focus position of the light component from the specific position The light component of the receiver.

According to another embodiment of the present invention, there is provided a light splitting unit comprising a splitting portion for separating light from an illuminated medium having a plurality of reflective surfaces through a focusing lens to a light receiver. , between the focus position of the light component closer to the focusing lens than the focus position of the light component from the specific position of the illuminated medium and the focus position of the light component from the specific position, the focus position and the light component from the specific position are removed. the focus position of the light component from the specific position is closer to the focus lens than the light component of the focus lens, and/or the focus position of the light component from the specific position is closer to the light receiver and Among the focus positions of the light components from the specific position, the light components whose focus position is closer to the light receiver than the focus position of the light components from the specific position are removed.

According to another embodiment of the present invention, there is provided an optical pickup device including: a light source for emitting light; a light receiver; and an optical system. The optical system includes an objective lens, a focusing lens, a splitting section, and a light splitting unit. The objective lens is arranged opposite a multilayer optical recording medium having a plurality of reflective surfaces. Light emitted from the light source is guided to the objective lens and made incident on a predetermined position of the optical recording medium. The focusing lens collects light from the optical recording medium through the objective lens onto the light receiver. The splitting portion splits the light traveling toward the light receiver through the focusing lens into at least two parts along its optical axis. by being between a focus position closer to the focus lens than a focus position of the light component reflected from the recording layer of interest and a focus position of the light component reflected from the recording layer of interest, removing the light component whose focus position is closer to the focus lens than the focus position of the light component reflected from the recording layer of interest, and/or by The focus position of the component is closer to the focus position of the light receiver than the focus position of the light component reflected from the recording layer of interest, and the focus position and the reflection from the recording layer of interest are removed. The focus position of the light component is closer to the light receiver than the light component, the light splitting unit causes the light component reflected by the recording layer of interest of the optical recording medium to be split with each of the light part of the separation.

According to another embodiment of the present invention, there is provided an optical recording/reproducing apparatus including: a light source for emitting light; a light receiver; and an optical system for recording and/or reproducing. The optical system includes an objective lens, a focusing lens, a splitting section, and a light splitting unit. The objective lens is arranged opposite a multilayer optical recording medium having a plurality of reflective surfaces. Light emitted from the light source is guided to the objective lens and made incident on a predetermined position of the optical recording medium. The focusing lens collects light from the optical recording medium through the objective lens onto the light receiver. The splitting portion splits the light traveling toward the light receiver through the focusing lens into at least two parts along its optical axis. by being between a focus position closer to the focus lens than a focus position of the light component reflected from the recording layer of interest and a focus position of the light component reflected from the recording layer of interest, removing the light component whose focus position is closer to the focus lens than the focus position of the light component reflected from the recording layer of interest, and/or by The focus position of the component is closer to the focus position of the light receiver than the focus position of the light component reflected from the recording layer of interest, and the focus position and the reflection from the recording layer of interest are removed. The focus position of the light component is closer to the light receiver than the light component, the light splitting unit causes the light component reflected by the recording layer of interest of the optical recording medium to be split with each of the light part of the separation.

According to the above-described embodiments, based on the difference in focus position in the area between the focus lens and the light receiver, the light component from a predetermined position of the medium to be irradiated (such as a predetermined recording layer of an optical recording medium) is different from that from other recording layers (i.e. Light components from different depths) are separated. Thereby, the light receiver can reliably receive only light from the recording layer of interest.

In the above-described embodiments, the light passing through the focusing lens is split into at least two parts along its optical axis. Light components focused at locations other than the focus location of the light component of interest are then removed by, for example, blocking, reflection, refraction, or polarization based on the difference in focus location. This allows reliable removal of light components from positions along the optical axis that deviate from the position from which the light component of interest originates.

By partially blocking the light without splitting it, eg based on differences in beam size, or by simply splitting the light, it is difficult to receive all the light reflected by the layer of interest. Also, with these methods, it is difficult to completely remove unwanted light.

In contrast, by splitting light along its optical axis and separating the split light based on differences in focus position, embodiments of the present invention allow reliable reception of only light of interest.

As described above, the method and unit for splitting light according to embodiments of the present invention allow removing unnecessary light and reliably receiving light from a specific position of an irradiated multilayer medium having a plurality of reflective surfaces.

In the recording/reproducing of a multilayer optical recording medium having a plurality of reflective surfaces, the optical pickup device and the optical recording/reproducing apparatus according to the embodiments of the present invention can suppress reflections reflected by layers other than the recording layer of interest. The effect of light.

Description of drawings

1 is a schematic diagram of an example of an optical recording/reproducing apparatus including an optical pickup device according to an embodiment of the present invention;

2 is a schematic cross-sectional view of an example of an optical recording medium;

3A and 3B are schematic diagrams illustrating optical paths of unwanted light components reflected by an irradiated medium;

4A and 4B are schematic diagrams illustrating a method for splitting light according to one embodiment of the present invention;

5 is a schematic diagram of an optical system comprising a light separation unit according to one embodiment of the present invention;

6 is a schematic diagram of an optical system comprising a light separation unit according to another embodiment of the present invention;

7A and 7B are respectively a schematic diagram of an optical system based on a method of splitting light according to another embodiment of the present invention and a schematic diagram illustrating how light is split in the method of splitting light according to this embodiment;

8 is a schematic diagram of an optical system based on a method of splitting light according to another embodiment of the present invention;

9A, 9B and 9C are respectively a schematic diagram of an optical system based on a method of splitting light according to another embodiment of the present invention, another schematic diagram of an optical system, and a diagram illustrating how light is processed in a method of splitting light according to this embodiment. Schematic diagram of separation;

10 is a schematic diagram of an optical system based on a method of splitting light according to another embodiment of the present invention;

11 is a schematic diagram of an optical system based on a method of splitting light according to another embodiment of the present invention;

12 is a schematic diagram of an optical system based on a method of splitting light according to another embodiment of the present invention;

13A and 13B are respectively another schematic diagram of an optical system based on the method of splitting light according to this embodiment and a schematic diagram illustrating how light is split in the method of splitting light according to this embodiment;

14 is another schematic diagram illustrating how light is split in the method of splitting light according to this embodiment;

15 is a schematic diagram illustrating how light is split in a method of splitting light according to another embodiment of the present invention;

16 is a schematic diagram illustrating how light is split in a method of splitting light according to another embodiment of the present invention;

17 is a schematic diagram illustrating polarization direction change using a half-wave plate;

18A to 18C are schematic diagrams illustrating polarization directions in a method of splitting light according to this embodiment;

19 is a schematic diagram illustrating how light is split in a method of splitting light according to another embodiment of the present invention;

20 is a schematic diagram illustrating how light is split in a method of splitting light according to another embodiment of the present invention;

21A to 21C are schematic diagrams illustrating polarization directions in a method of splitting light according to this embodiment;

22 is a schematic diagram illustrating how light is split in a method of splitting light according to another embodiment of the present invention;

23A, 23B, and 23C are respectively a schematic diagram of an optical system based on a method for splitting light according to another embodiment of the present invention, another schematic diagram of the optical system, and a diagram illustrating how light is split in a method for splitting light according to this embodiment. schematic diagram.

Detailed ways

Preferred examples of the present invention will now be described, but the present invention is not limited to the following examples.

First, an example of an optical recording/reproducing apparatus including an optical pickup device based on a method and unit for splitting light according to an embodiment of the present invention will be described below with reference to FIG. 1 . Fig. 1 is a schematic diagram of an optical recording/reproducing apparatus.

In the example shown in FIG. 1 , information supplied from an information source 1 is recorded on a disc-shaped optical recording medium 100 . A light beam is emitted from a light source 3, which includes, for example, a laser diode (LD), and modulated according to an information signal supplied from an information source 1 . An automatic power controller (APC) 2 controls the output of the beam. The light beam is then collimated by the collimating lens 4 of the optical unit 41 to enter the head unit 42 via the beam splitter 6 and the mirror 7 . The drive unit 45 includes, for example, the actuators 17 for focusing and tracking. The head unit 42 includes an optical system, which is mounted on the actuator 17, and irradiates the optical recording medium 100 with a light beam. This optical system includes an objective lens 8 consisting of an aspheric lens or lens group. The head unit 42 allows light exiting the optical unit 41 to be irradiated on a specific recording layer of the optical recording medium 100 where information is to be recorded.

The moving mechanism 48 includes the rotation unit 15 that holds and rotates the optical recording medium 100 . A horizontal movement mechanism (not shown) moves the optical system of the head unit 42 along the recording surface of the optical recording medium 100, for example. The motion mechanism 48 scans, eg, a spiral or concentric recording channel, with light propagating through the head unit 42 along the surface of the optical recording medium 100 in cooperation with the horizontal motion mechanism.

The light reflected by the optical recording medium 100 passes through the head unit 42 and is reflected by the beam splitter 6 . The light then passes through the focusing lens 10 and is detected by a detection unit 43 including a light receiver 11 such as a photodetector.

In this embodiment, the optical recording/reproducing device further includes a splitting section 30 and a light splitting unit 50 arranged between the focusing lens 10 and the light receiver 11 . The splitting part 30 splits the light into at least two parts along its optical axis. The light separation unit 50 separates the light component reflected from the recording layer of interest of the optical recording medium 100 from each split portion of the light.

The detected light amount is input to the servo circuit 13 of the control unit 44, and converted into a focus control signal Sf based on, for example, a scattering method or a knife-edge method, and converted into a tracking control signal St based on, for example, a push-pull method. These control signals Sf and St are supplied to the actuator 17 of the drive unit 45 to correct focusing and tracking of the objective lens 8, for example. Therefore, a constant distance is maintained between the objective lens 8 and the optical recording medium 100 to enable successful recording on a predetermined track.

In reproduction or for a reproduction-only device, light emitted from the light source 3 is irradiated on the optical recording medium 100 through the same optical path. The light receiver 11 detects light reflected by the optical recording medium 100 to generate and output a reproduced signal through a circuit (not shown) that detects the reproduced signal.

The detected amount of light is also partly supplied to the servo circuit 13 of the drive unit 44 for focus control and tracking control.

For example a diffractive element may be arranged between the collimator lens 4 and the beam splitter 6 to split the light emitted from the light source 3 into at least two beams irradiated on the optical recording medium 100 . One of the two beams can be used for recording and/or reproduction, while the other beam can be used for focus control or tracking control.

The optical recording medium 100 for recording/reproducing using an optical recording/reproducing apparatus may be a multilayer recording medium such as a recording medium having three recording layers shown in FIG. 2 . This recording medium 100 includes a substrate 101 and first to third recording layers laminated thereon in the order that light passes through the recording layers. The first to third recording layers respectively have reflective surfaces RS1 to RS3 that reflect light. A transparent protective layer 102 is disposed on the reflective surface RS1 of the first recording layer. The surface of the protective layer 102 is an interface with air. That is, the optical recording medium 100 has a multilayer structure with three reflective surfaces RS1 to RS3. The term "reflective surface" herein also includes film surfaces having some transparency (eg, translucent films).

The optical recording/reproducing apparatus according to this embodiment can be applied to various types of optical recording media, including read-only media with pits, recordable media with dye layers, and rewritable media of magneto-optical type or phase-change type. medium. In addition, for example, a transparent interlayer adhesive film (not shown) may be disposed between the recording layers.

The optical recording/reproducing apparatus according to this embodiment can be applied not only to an optical recording medium having three recording layers, as shown in FIG. 2, but also to an optical recording medium having one, two or four or more recording layers. optical recording media. For an optical recording medium having a single recording layer, the light reflected by the recording layer can be separated from the light reflected by the surface of the protective layer.

The optical recording medium 100 may be irradiated with light from the substrate 101 side in addition to the light from the protective layer 102 side.

The focus position of the light reflected by the recording layer of the multilayer optical recording medium when the medium is irradiated will be described below with reference to FIGS. 3A and 3B .

Fig. 3A is a schematic cross-sectional view of an optical system for collecting light reflected by an optical recording medium onto a light receiver, taken along an optical axis C. In the example shown in FIG. 3A, the irradiated medium 200 has a multilayer structure similar to the optical recording medium 100, having a first reflective surface S1, a second reflective surface S2, and a third reflective surface S3. Light components reflected by the first reflective surface S1, the second reflective surface S2, and the third reflective surface S3 are indicated by a dotted line L1, a solid line L2, and a two-dot chain line L3, respectively. These light components L1 to L3 pass through the objective lens 8 to enter the focusing lens 10, which focuses the light components L1 to L3. In FIG. 2, the second recording layer of the multilayer optical recording medium 100 is assumed here as a recording layer for recording/reproduction, for example. The surface of the second recording layer of the multilayer optical recording medium 100 corresponds to the second reflective surface S2 of the irradiated medium 200 . The light component L2 reflected by the second reflective surface S2 is focused at the focus position F2. The photoreceiver 11 (not shown in FIG. 3A ) is arranged farther from the focus lens 11 than the focus position F2. The first reflective surface S1 is closer to the outer surface S0 than the second reflective surface S2. The light component L1 reflected by the first reflective surface S1 is focused at a focus position F1 farther from the focus lens 10 than the focus position F2 . The third reflective surface S3 is further away from the outer surface S0 than the second reflective surface S2. The light component L3 reflected by the third reflective surface S3 is focused at a focus position F3 closer to the focus lens 10 than the focus position F2 , that is, on the focus lens 10 side.

FIG. 3B illustrates light components L1 to L3 in a case where the light receiver 11 is arranged at the focus position F2. The light components L1 and L3 overlap the light component L2 on the light receiver 11 . Figure 3B illustrates that if the illuminated medium 200 is, for example, an optical recording medium, the overlapping light components L1 and L3 negatively affect the signal.

The method for splitting light according to this embodiment will be described below with reference to FIGS. 4A and 4B in which components corresponding to those in FIG. 3 are denoted by the same reference numerals to avoid redundant description. In FIG. 4A , the z axis represents the optical axis, the y axis represents the direction parallel to the cross section and perpendicular to the optical axis, and the x axis represents the direction parallel to the cross section and perpendicular to the y axis direction. In FIGS. 4A and 4B , the light is divided into upper and lower parts along the xz plane, and only the upper part of the light (on the positive side of the y-axis) is shown.

In the example shown in FIGS. 4A and 4B , a separation portion 51 is disposed between the focus position F2 and a focus position F3 that is closer to the focus lens 10 than the focus position F2, and another separation portion 52 is disposed between the focus position F2 and the focus position F3. The position F2 is further away from the focus position F1 of the focusing lens 10 . The separation parts 51 and 52 may use light shielding, for example. In this case, the separation portion 51 blocks light on the lower side of the xz plane, and the separation portion 52 blocks light on the upper side of the xz plane.

4B is a cross-sectional view of the light components L1 to L3 taken along the xy plane at different positions on the z-axis of FIG. 4A . The light components L1 to L3 overlap each other between the focus lens 10 and the focus position F3. The light component L3 passes through the xz plane between the focus positions F3 and F2 to reach the lower side of this plane. The light components L1 and L2 overlap each other on the xz plane upper side at the position where the separation portion 51 is arranged. The separation portion 51 blocks and removes the light component L3 passing through the xz plane to the lower side of the plane (shown as a shaded area in FIG. 4B ).

The light component L2 passes through the xz plane to the lower side of the plane between the focus positions F2 and F1, and only the light component L1 remains on the upper side of the xz plane. The separation portion 52 blocks and removes the light component L1, as shown by the shaded area in FIG. 4B. Therefore, the light receiver 11 receives only the light component L2 reflected by the recording layer of interest. The parts of the light component L2 split along the optical axis are thus all separated from the other light components L2 to L3 to reach the light receiver 11 without being affected by the separation parts 51 and 52 .

In the method of splitting light according to this embodiment, as described above, the splitting portions 51 and 52 are respectively arranged between the focus position F2 of the light component of interest L2 and the focus positions F1 and F3 of the unnecessary light components L1 and L3 between. These separation portions 51 and 52 can reliably remove the light components L1 and L3 without affecting the light component L2 to extract the light component L2 at the light receiving position.

In the example shown in Figs. 4A and 4B, the light is split into two parts along the xz plane, but the light may also be split into three or more parts. Furthermore, light does not have to be spatially split. That is, the light components of interest can be separated without spatially splitting the light, for example by controlling the polarization of the light using an optical rotator or wave plate, such as described in detail in the sixth embodiment below. After the light has passed through the optical rotator or the wave plate, the light components of interest can be separated by means of a light separation unit comprising, for example, a polarizing filter section. Therefore, the term "splitting" here includes not only the spatial separation of light, but also the division of light into regions with different optical properties.

The light components of interest can also be separated without using the separation section 52 . For example, the light receiver 11 may be arranged between the focus positions F2 and F1 instead of the split portion 52 in FIG. 4A . In this case, the light-receiving area of the light receiver 11 may be divided along the x-axis so that the light receiver 11 can reliably receive only light reflected at a specific position, for example, only the light produced by the optical recording medium 100 as described above. The light reflected by the second recording layer.

Furthermore, if the method of splitting light according to this embodiment is applied to an irradiated medium having two reflective surfaces (for example, an optical recording medium having two recording layers), the splitting portion 51 may not be used to split the light. In this case, the light reflected by the internal recording layer can be separated without removing the light reflected inside the internal reflection layer. Thereby the light component L2 can be reliably separated by inserting the separation part 52 only between the focus position F2 of the light component L2 of interest and the focus position F1 on one side of the light receiver 11, so that the light receiver 11 can receive the light component L2. Similarly, the method of separating light according to this embodiment can be applied to an optical recording medium having a single recording layer to separate the light reflected by the recording layer from the light reflected by the protective layer.

For the method and unit for separating light, the optical pickup device, and the optical recording/reproducing apparatus according to this embodiment, as described above, it is possible to separate only the light of interest by using the separation part 51 and/or the separation part 52. The components are directed to the light receiver 11 . The use of the separation part 51 and/or the separation part 52 depends on conditions such as the layer structure of the used irradiated medium (or the used optical recording medium) and which recording layer reflects the light component of interest.

Next, a light splitting unit based on the above-mentioned method of splitting light according to an embodiment of the present invention will be described.

first embodiment

5 is a schematic diagram of a light separation unit and an optical system including the unit according to a first embodiment of the present invention. In FIG. 5, components corresponding to those in FIG. 4 are denoted by the same reference numerals to avoid redundant description.

In this embodiment, the light separation unit 50 includes a separation portion 51 arranged between the focus position F3 of the light component L3 and the focus position F2 of the light component L2 of interest, and arranged between the focus position F2 of the light component L2 and the light component Another separation 52 between the focus position F1 of L1. The separation portion 51 has a non-transparent region 51A and a transparent region 51B. The separation portion 52 has a non-transparent region 52A and a transparent region 52B. The separation parts 51 and 52 may be separately arranged, supported by supports at predetermined intervals, or integrated with, for example, a transparent member (not shown) as shown by a dotted line A arranged therebetween.

The non-transparent area 51A of the separation portion 51 can block and remove the light component L3 because the light component L3 travels to the lower side of the xz plane through the focus position F3. The non-transparent area 52A of the separation portion 52 can block and remove the light component L1 because the light component L1 remains on the upper side of the xz plane before traveling through the focus position F1.

This structure allows only the light component reflected at a specific position of the irradiated medium (for example, the light component reflected only by the recording layer of interest of the optical recording medium) to pass through the light separation unit 50, while reliably removing light components other than those of interest. Components of light reflected by layers other than the recording layer. The light receiver 11 is thus able to reliably detect only the light components reflected by the recording layer of interest.

The non-transparent regions 51A and 52A of the separation parts 51 and 52 respectively may have any structure capable of preventing light from traveling in a straight line; for example they may also be reflective surfaces, refractive surfaces, scattering surfaces or diffractive surfaces.

It is also possible to separate the light component L1 reflected by the reflective surface S1 or the light component L3 reflected by the reflective surface S3. In this case, the light splitting unit 50 can be translated, for example, along the optical axis in the z-axis direction in FIG. 5 so that the splitting portions 51 and 52 are located at appropriate positions. For example, the light component L3 can be split by disposing the splitting portion 52 between the focus positions F3 and F2, and the light component L1 can be split by disposing the splitting portion 51 between the focus positions F1 and F2.

second embodiment

6 is a schematic diagram of a light separation unit and an optical system including the unit according to a second embodiment of the present invention. In FIG. 6, components corresponding to those in FIG. 4 are denoted by the same reference numerals to avoid redundant description.

In this embodiment, the light separation unit 50 is a prism-shaped integral unit. In FIG. 6, the light separation unit 50 has a reflective surface 53A located below the xz plane on the light entering side, a transparent surface 53B located above the xz plane on the light entering side, and a transparent surface 53B located above the xz plane on the light exit side. A reflective surface 54A, and on the light exit side has a transparent surface 54B below the xz plane. The reflective surface 53A reflects the light component L3. The reflective surface 54A deviates the optical path of the light component L1 from the optical axis. Reflective surface 53A and reflective surface 54A are inclined at a predetermined angle with respect to a plane perpendicular to the optical axis (ie, z-axis) to change the optical paths of unnecessary light components L1 and L3 into appropriate directions.

A prism-shaped light separation unit 50 is arranged between the focusing lens 10 and the light receiver 11 . This simple arrangement allows the light receiver 11 to reliably receive only light components reflected by the layer of interest, while reliably removing unwanted light components reflected by other layers (which in the related art may overlap the light component of interest). light component).

Further light receivers may be arranged on the optical paths of the light components L1 and L3 to receive them respectively. This arrangement allows, for example, reception of signals from the respective recording layers of a three-layer optical recording medium. Furthermore, as shown in the first embodiment, the light receiving unit 50 may be translated, for example, along the optical axis in the z-axis direction so that the light receiver 11 receives only the light component L1 or L3.

The prism shape of the light receiving unit 50 is not limited to the illustrated example, and various modifications are allowed. For example, the angles of transparent surfaces 53B and 54B can be adjusted such that light component L2 travels in a straight line, or the angles of reflective surfaces 53A and 54A can be tilted to change the direction of light travel, such as in the x-axis direction.

The light separation unit 50 may therefore be composed of a single optical element such as a prism, or may also be composed of a combination of optical elements such as a light shielding portion, a reflective surface, and a transparent member.

In the description of the first and second embodiments, the light passing through the focusing lens 10 is split into two parts along the xz plane, and the light component of interest is separated from the upper part of the light. In these embodiments, the light component of interest may also be separated from the lower part of the light on the split optical path, so that the light receiver 11 receives only the light component of interest. The light can for example be split by a prism placed with its ridges arranged along the xz plane. The prism can spatially split the light components L1 to L3 along the optical axis.

The split parts of the light component L2 may be separated and combined so that the light receiver 11 can receive only the light component L2. When applied to an optical pickup device or an optical recording/reproducing apparatus for recording/reproducing of a multilayer recording medium, the light separation unit 50 can reliably remove light components reflected by layers other than the recording layer of interest to A reduction in recording/reproducing characteristics is suppressed.

Next, an optical system including a combination of a splitting section that splits light along an optical axis and a light splitting unit according to an embodiment of the present invention will be described.

third embodiment

7A and 7B are schematic diagrams of a light separation unit and an optical system including the unit according to a third embodiment of the present invention. In FIGS. 7A and 7B , components corresponding to those in FIG. 4 are denoted by the same reference numerals to avoid redundant description.

In this embodiment, the prism 20 is arranged on the light exit side of the focusing lens 10 . This prism 20 has a transparent surface on the light entrance side and a refractive structure on the light exit side. The refraction structure splits the light along the xz plane, so that the optical axis of the split part of the light deviates from the z-axis toward the y-axis direction, as shown by the single-dashed lines C1 and C2.

In FIG. 7A, prism 20 splits light components L1, L2, and L3 into light components L1a and L1b, L2a and L2b, and L3a and L3b, respectively. The light components L1a to L3a have an optical axis C1 and the light components L1b to L3b have an optical axis C2. The light separation unit 50 is arranged in the same way as the above-described embodiment, that is, its light shielding portion 55A is arranged between focus positions F2 and F3, and its light shielding portions 55B and 55C are arranged between focus positions F2 and F1. The light shielding portion 55A blocks an area between the optical axes C1 and C2. The light shielding portions 55B and 55C block regions outside the optical axes C1 and C2, respectively.

The light shielding portion 55A of the separation portion 51 blocks the light components L3a and L3b reflected by the inside of the layer of interest. The light shielding portions 55B and 55C of the separation portion 52 respectively block the light components L1a and L1b reflected by the outside of the layer of interest. This arrangement can reliably remove unwanted light. The light receiver 11 is thus able to receive only the light components L2a and L2b reflected by the recording layer of interest.

Thereby, the light components L2a to L2b can be combined such that the light receiver 11 is able to detect all the light reflected by the layer of interest.

When applied to an optical pickup device or an optical recording/reproducing device for recording/reproducing of a multilayer recording medium, the simple optical system having the prism 20 and the light separation unit 50 can suppress degradation of recording/reproducing characteristics.

Fourth embodiment

8 is a schematic diagram of a light separation unit and an optical system including the unit according to a fourth embodiment of the present invention. In FIG. 8, components corresponding to those in FIGS. 7A and 7B are denoted by the same reference designations to avoid redundant description.

In this embodiment, instead of the prism 20 used in the third embodiment, a diffraction element 22 is used as the splitting portion 30 . The diffractive element 22 splits the light exiting from the focusing lens 10 such that the optical axis of the split portion of the light deviates from the z-axis toward the y-axis direction, as indicated by single-dashed lines C1 and C2. Thus, the diffractive element 22 splits the light components L1, L2 and L3 into the light components L1a and L1b, L2a and L2b, and L3a and L3b, respectively.

The light shielding portion 55A of the separation portion 51 blocks the light components L3a and L3b reflected by the inside of the layer of interest. The light shielding portions 55B and 55C of the separation portion 52 respectively block the light components L1a and L1b reflected by the outside of the layer of interest. This arrangement can reliably remove unwanted light. The light receiver 11 is thus able to receive only the light components L2a and L2b reflected by the recording layer of interest.

Thereby, the light components L2a to L2b can be combined such that the light receiver 11 is able to detect all the light reflected by the layer of interest.

When applied to an optical pickup device or an optical recording/reproducing device for recording/reproducing of a multilayer recording medium, the simple optical system having the diffraction element 22 and the light separation unit 50 can suppress degradation of recording/reproducing characteristics.

fifth embodiment

9A and 9B are schematic views of a light separation unit and an optical system including the unit according to a fifth embodiment of the present invention. FIG. 9A is a plan view of the yz plane in the x-axis direction. Fig. 9B is a plan view of the xz plane in the y-axis direction. In FIGS. 9A and 9B , components corresponding to those in FIG. 8 are denoted by the same reference designations to avoid redundant description.

In this embodiment, the diffraction element 22 serving as the splitting section 30 in the fourth embodiment is arranged to split light in the x-axis direction. In FIG. 9B , diffractive element 22 splits the light exiting from focusing lens 10 such that the optical axes C3 and C4 of the split portion of the light are shifted toward the x-axis direction toward the z-axis. Thus, the diffractive element 22 splits the light components L1, L2 and L3 into the light components L1c and L1d, L2c and L2d, and L3c and L3d, respectively.

9C, the diffraction element 22 has a diffraction region 22A and a diffraction region 22B, the diffraction region 22A diffracts light in the positive direction of the x-axis, that is, along the optical axis C3, and the diffraction region 22B diffracts light in the negative direction of the x-axis, that is, along the light Axis C4. The separation portion 51 includes light shielding portions 56A and 56B that block the light components L3d and L3c reflected by the inside of the layer of interest, respectively. The separation part includes light-shielding parts 56C and 56D which respectively block the light components L1c and L1d reflected by the outside of the layer of interest. This arrangement can reliably remove unwanted light. The light receiver 11 is thus able to receive only the light components L2c and L2d reflected by the recording layer of interest.

Thereby, the light components L2c to L2d can be combined such that the light receiver 11 is able to detect all the light reflected by the layer of interest.

When applied to an optical pickup device or an optical recording/reproducing device for recording/reproducing of a multilayer recording medium, the simple optical system having the diffraction element 22 and the light separation unit 50 can suppress degradation of recording/reproducing characteristics.

Sixth embodiment

Fig. 10 is a schematic diagram of a light separation unit and an optical system including the unit according to a sixth embodiment of the present invention. In FIG. 10, components corresponding to those in FIG. 8 are denoted by the same reference designations to avoid redundant description.

In this embodiment, the separation section 51 includes polarization filter sections 57A and 57B, and the separation section 52 includes polarization filter sections 58A and 58B. The splitting section 30 includes an optical rotator or wave plate, such as an optical rotator 31A, and a transparent section 31B. Incident light is selectively allowed to pass through the optical rotator 31A, which is a region that changes the polarization of the light. For example, the polarization direction of light passing through the optical rotator 31A is the direction shown by the arrow P along the x-axis, and the polarization direction of the light passing through the transparent portion 31B is the direction shown by the arrow s along the y-axis. . That is, the polarization direction of the light passing through the optical rotator 31A is perpendicular to the polarization direction of the light passing through the transparent portion 31B. The polarization filter sections 57A and 58A transmit light polarized in the direction indicated by arrow p, but do not transmit light polarized in the direction indicated by s. The polarization filter sections 57B and 58B transmit light polarized in the direction indicated by arrow s, but do not transmit light polarized in the direction indicated by p.

Therefore, the polarization filter portion 57A does not transmit the portion of the light component L3 above the xz plane, and the polarization filter portion 58A does not transmit the portion of the light component L1 above the xz plane. Therefore, the polarization filter sections 57A and 58A can reliably remove unnecessary light, and only the part of the light component L2 above the xz plane passes through the polarization filter sections 57B and 58B, and is received by the light receiver 11 .

On the other hand, the polarization filter portion 57B does not transmit the portion below the xz plane of the light component L3, and the polarization filter portion 58B does not transmit the portion below the xz plane of the light component L1. Therefore, the polarization filter sections 57B and 58B can reliably remove unnecessary light, and only the part of the light component L2 below the xz plane passes through the polarization filter sections 57A and 58A, and is received by the light receiver 11 .

Thereby, the light receiver 11 is able to detect all the light reflected by the layer of interest. When applied to an optical pickup device or an optical recording/reproducing device for recording/reproducing of a multilayer recording medium, the simple optical system having the splitting portion 30 and the light separation unit 50 can suppress degradation of recording/reproducing characteristics.

In this embodiment, the splitting part 30 and the light splitting unit 50 can also be integrated into a light splitting unit 60, as shown by the dotted line B. A simple optical system having the light splitting unit 60 (which also has a photo-splitting function) can suppress a reduction in recording/reproducing characteristics in recording/reproducing of a multilayer recording medium.

In this embodiment, light components reflected by the reflective surface of interest may be allowed to pass across the optical axis through split sections 51 and 52, ie polarization filter sections 57A and 58A or polarization filter sections 57B and 58B. As in the first and second embodiments, therefore, the light separating unit 50 can be translated along the optical axis in the z-axis direction so that the light receiver 11 can receive only the light component L1 or L3.

Fig. 11 is a schematic diagram of a photo-splitting unit integrated with a splitting part according to another embodiment of the present invention. In FIG. 11, components corresponding to those in FIG. 10 are denoted by the same reference numerals to avoid redundant description.

In this embodiment, the light splitting unit 60 having a light splitting function has a first diffractive lens portion 61 on the light entering side and a second diffractive lens portion 62 on the light exiting side. For example, these diffractive lens portions 61 and 62 have a focusing function to reduce the optical path length of light and thereby reduce the size of the light separation unit 60 , or adjust the distance between the light separation unit 60 and the light receiver 11 .

The transparent part 31B can be replaced by an optical rotator or a wave plate, depending on the polarization of the light passing through the focusing lens 10 . Also, in this case, only the splitting portion 30 and the light separation unit 50 may be integrally provided without the diffractive lens portions 61 and 62 .

Thereby, the light receiver 11 is able to detect all the light reflected by the layer of interest. When applied to an optical pickup device or an optical recording/reproducing device for recording/reproducing of a multilayer recording medium, the simple optical system with the light separation unit 60 can suppress degradation of recording/reproducing characteristics.

Seventh embodiment

12 is a schematic diagram of a light separation unit and an optical system including the unit according to a seventh embodiment of the present invention. In FIG. 12, components corresponding to those in FIGS. 10 and 11 are denoted by the same reference numerals to avoid redundant description.

In this embodiment, splitting section 51 includes a uniform polarization filter section 59 and splitting section 30 includes two optical rotators or wave plates, eg first optical rotator 32 and second optical rotator 33 . The first optical rotator 32 has a first optical rotation area 32A and a second optical rotation area 32B, and the second optical rotator 33 has a first optical rotation area 33A and a second optical rotation area 33B. The first optical rotation area 32A of the first optical rotator 32 and the second optical rotation area 33B of the second optical rotator 33 rotate the polarization direction of light by 45° in opposite directions. Similarly, the second optical rotation area 32B of the first optical rotator 32 and the first optical rotation area 33A of the second optical rotator 33 rotate the polarization direction of light by 45° in opposite directions.

The polarization direction of the light passing through the first optical rotation area 32A of the first optical rotator 32 and the second optical rotation area 33B of the second optical rotator 33 returns to the original polarization direction. The polarization direction of this light is rotated by 45° by the first optical rotator 32 and by the same amount of rotation by the second optical rotator 33 in the opposite direction. Similarly, the polarization direction of light passing through the second optical rotation region 32B of the first optical rotator 32 and the first optical rotation region 33A of the second optical rotator 33 returns to the original polarization direction. The polarization direction of this light is rotated by 45° by the first optical rotator 32 and by the same amount of rotation by the second optical rotator 33 in the opposite direction.

On the other hand, the rotation of the polarization direction of the light passing through the first optical rotation regions 32A and 33A and the light passing through the second optical rotation regions 32B and 33B is twice the amount of rotation caused in the respective optical rotation regions, that is to say , rotated to a direction perpendicular to the polarization direction of the incident light.

The polarization filter section 59 of the separation section 51 transmits only light polarized in the original polarization direction. This structure allows only the light component L2 to travel toward the light receiver 11 . For example, the light component L2 can reach the light receiver 11 through the lens 70, as indicated by the solid line Lo.

Figure 13A is a cross-sectional view of light taken along the yz plane in this embodiment. Figure 13B is a cross-sectional view of light taken at different positions on the z axis along the xy plane. 13A and 13B illustrate light passing through the focusing lens 10 only on the positive side of the y-axis. In FIGS. 13A and 13B, components corresponding to those in FIG. 12 are denoted by the same reference numerals to avoid redundant description.

In FIG. 13A, the first optical rotator 32 is arranged between the focus positions F3 and F2 of the light components L3 and L2, and the second optical rotator 33 is arranged between the focus positions F2 and F1 of the light components L2 and L1. The separation portion 51 is arranged on the light receiver 11 side.

The light components L1 and L2 pass through the part of the first optical rotator 32 located above the z-axis, that is, the second optical rotation region 32B, and the light component L3 passes through the part of the first optical rotator 32 located below the z-axis, namely the first Optical rotation area 32A. On the other hand, the light components L2 and L3 pass through the first optical rotation area 33A, and the light component L1 passes through the second optical rotation area 33B.

Therefore, for example, when the light component L3 passes through the first optical rotator 32, the polarization direction of the light component L3 rotates clockwise by 45°; Rotate a further 45° clockwise.

Similarly, for example, when the light component L1 passes through the first optical rotator 32, the polarization direction of the light component L1 rotates counterclockwise by 45°; At 59 o'clock, further rotate counterclockwise by 45°.

In contrast, only the light component L2 passes through the second optical rotation area 32B of the first optical rotator 32 and the first optical rotation area 33A of the second optical rotator 33, so that its rotated polarization direction returns to the original polarization direction.

Polarization filter section 51 reliably removes unnecessary light, ie, light components L1 and L3, and transmits only light polarized in the original polarization direction. The light receiver 11 thus only receives light reflected by the recording layer of interest.

13A and 13B only illustrate the part of the light located on the positive side of the y-axis, but the above-mentioned structure can also separate the part of the light located in the negative direction of the y-axis by rotating the polarization direction, so that the light receiver 11 only receives The light reflected by the layer of interest. Thereby, the light receiver 11 can detect all light reflected by the layer of interest.

14 and 15 are schematic cross-sectional views of examples of optical rotators 31 and 32 .

In the example shown in FIG. 14, the first optical rotation area 32A of the first optical rotator 32 and the first optical rotation area 33A of the second optical rotator 33 rotate the polarization direction by -45° (when viewed in the direction of light travel). 45° counterclockwise). The second optical rotation area 32B of the first optical rotator 32 and the second optical rotation area 33B of the second optical rotator 33 rotate the polarization direction by +45° (45° clockwise when viewed in the direction of light travel).

The light component Ld passes through the first optical rotation areas 32A and 33A of the optical rotators 32, 33, respectively, and the light component La passes through the second optical rotation areas 32B and 33B. Thereby, the polarization directions of the light components La and Ld are rotated by 90° from that of the incident light. The light component Lb passes through the second optical rotation area 32B of the first optical rotator 32 and the first optical rotation area 33A of the second optical rotator 33, and the light component Lc passes through the first optical rotation area 32A and the second optical rotation area 32A of the first optical rotator 32. The second optical rotation area 33B of the second optical rotator 33 . The polarization directions of the light components Lc and Lb are thereby returned to the original polarization directions because the first optical rotation areas 32A and 33A and the second optical rotation areas 32B and 33B rotate the polarization directions of the light in opposite directions.

In this case, a polarization filter or a polarization beam splitter may be arranged to separate the portion 51 to extract only light polarized in the polarization direction of the incident light. The separating portion 51 is thus able to separate only the light reflected by the layer of interest.

In the example shown in FIG. 15 , the first optical rotation region 32A of the first optical rotator 32 and the second optical rotation region 33B of the second optical rotator 33 rotate the polarization direction by −45°. The second optical rotation area 32B of the first optical rotator 32 and the first optical rotation area 33A of the second optical rotator 33 rotate the polarization direction by +45°.

The light component Ld passes through the first optical rotation areas 32A and 33A of the optical rotators 32, 33, respectively, and the light component La passes through the second optical rotation areas 32B and 33B. Thereby, the polarization directions of the light components La and Ld return to the polarization directions of the incident light. The light component Lb passes through the second optical rotation area 32B of the first optical rotator 32 and the first optical rotation area 33A of the second optical rotator 33, and the light component Lc passes through the first optical rotation area 32A and the second optical rotation area 32A of the first optical rotator 32. The second optical rotation area 33B of the second optical rotator 33 . The polarization directions of the light components Lc and Lb are thus rotated by 90° from the original polarization directions.

In this case, a polarizing filter or a polarizing beam splitter may be arranged to split the portion 51 to extract only light polarized in a polarization direction perpendicular to the incident light. The separating portion 51 is thus able to separate only the light reflected by the layer of interest.

FIG. 16 illustrates another example in which the splitting section 30 includes two wave plates. In this example, the first wave plate 34 and the second wave plate 35 are each divided into two regions along the xz plane. The first wave plate 34 includes a first region 34A introducing a -1/2 wavelength phase shift and a second region 34B introducing a +1/2 wavelength phase shift. The second wave plate 35 includes a first region 35A introducing a -1/2 wavelength phase shift and a second region 35B introducing a +1/2 wavelength phase shift. The conversion of the polarization direction of light using a half-wave plate will be described below with reference to FIG. 17 , where the symbol + in FIG. 17 indicates clockwise rotation, and the symbol - indicates counterclockwise rotation. In Figure 17, the half-wave plate converts the incident light P1 polarized in the direction of -θ1° to the optical crystal axis a _c of the wave plate into a direction of +θ1° to the optical crystal axis a _c of the wave plate Polarized incident light P2. The -θ1 and +θ1 directions are symmetrical with respect to the optical crystal axis a _c . The amount of change in the polarization direction is +2θ1.

In FIG. 18A, for example, the optical crystal axis _{ac1 of} the second region 34B of the first wave plate 34 shown in FIG. 2 is tilted at -22.5° with respect to the x-axis. Light polarized in the x-axis direction as shown by arrows P1 and P5 is polarized in a direction inclined at 45° with respect to the x-axis when passing through the second region 34B, and is polarized in a direction inclined at 45° with respect to the x-axis when passing through the first region 34A with respect to The x-axis is tilted to -45° in the direction of polarization.

18B illustrates a change in the direction of polarization when the light passing through the first region 34A of the first wave plate 34 passes through the first region 35A of the second wave plate 35, as shown by the arrow Ld in FIG. 16, And the change of the polarization direction in the case where the light passing through the second region 34B of the first wave plate 34 passes through the second region 35B of the second wave plate 35, as shown by the arrow La in FIG. 16 . The polarization direction of light passing through regions with optical crystal axes positioned in the same direction returns to the original polarization direction of light incident on the first wave plate 34, as shown by arrows P3 and P7 in FIG. 18B.

18C illustrates a change in the direction of polarization when the light passing through the first region 34A of the first wave plate 34 passes through the second region 35B of the second wave plate 35, as shown by the arrow Lc in FIG. 16, And the change of the polarization direction in the case where the light passing through the second region 34B of the first wave plate 34 passes through the first region 35A of the second wave plate 35, as shown by the arrow Lb in FIG. 16 . The polarization direction of light passing through regions with optical crystal axes positioned in different directions is perpendicular to the original polarization direction of light incident on the first wave plate 34, as indicated by arrows P4 and P8 in FIG. 18C.

In this case, light polarized in a polarization direction perpendicular to the incident light may be reflected or transmitted to the polarization filter portion 59 (not shown). The polarizing filter portion 59 is thereby able to separate only the light reflected at a specific position of the irradiated medium (eg, the optical recording medium), as in the embodiment shown in FIGS. 13A and 13B .

Referring to FIG. 19 , the light of interest can also be separated by changing the area of the wave plates 34 and 35 . In FIG. 19, components corresponding to those in FIG. 16 are denoted by the same reference numerals to avoid redundant description. In this example, the light indicated by the arrow La and the light indicated by the arrow Ld are polarized in a direction perpendicular to the polarization of the incident light when passing through the wave plates 34 and 35 . The light indicated by the arrow Lb and the light indicated by the arrow Lc return to the original polarization direction when passing through the wave plates 34 and 35 . In this case, the light polarized in the polarization direction of the incident light may be reflected or transmitted to the polarization filter portion 59 (not shown). The polarization filter portion 59 is thereby able to separate only the light reflected at a specific position of the irradiated medium (eg, the optical recording medium).

FIG. 20 illustrates another example in which the splitting section 30 includes two quarter-wave plates. In this example, the first wave plate 36 and the second wave plate 37 are each divided into two regions along the xz plane. The first wave plate 36 includes a first region 36A that introduces a -1/4 phase shift and a second region 36B that introduces a +1/4 phase shift. The second wave plate 37 includes a first region 37A introducing a -1/4 phase shift and a second region 37B introducing a +1/4 phase shift.

In FIG. 21A, for example, the optical crystal axis a _c 1 of the second region 36B of the first wave plate 36 is inclined +45° relative to the x-axis, while the optical crystal axis a _c 2 of the first region 36A is inclined relative to the x-axis -45°. Light polarized in the x-axis direction as indicated by arrows P11 and P15 is polarized circumferentially clockwise when passing through the second region 36B, and is polarized circumferentially counterclockwise when passing through the first region 36A.

FIG. 21B illustrates a change in the direction of polarization when the light passing through the first region 36A of the first wave plate 36 passes through the first region 37A of the second wave plate 37, as shown by the arrow Ld in FIG. 20, And the change of the polarization direction in the case where the light passing through the second region 36B of the first wave plate 36 passes through the second region 37B of the second wave plate 37, as shown by the arrow La in FIG. 20 . The polarization direction of light passing through regions with optical crystal axes positioned in the same direction is perpendicular to the original polarization direction of light incident on the first wave plate 36, as indicated by arrows P13 and P17 in FIG. 21B .

FIG. 21C illustrates a change in the polarization direction when the light passing through the first region 36A of the first wave plate 36 passes through the second region 37B of the second wave plate 37, as shown by the arrow Lc in FIG. 20, And the change of the polarization direction in the case where the light passing through the second region 36B of the first wave plate 36 passes through the first region 37A of the second wave plate 37, as shown by the arrow Lb in FIG. 20 . The polarization direction of light passing through regions with optical crystal axes positioned in different directions returns to the original polarization direction of light incident on the first wave plate 36, as indicated by arrows P14 and P18 in FIG. 21C.

In this case, the light polarized in the polarization direction of the incident light may be reflected or transmitted to the polarization filter portion 59 (not shown). The polarizing filter portion 59 is thereby able to separate only the light reflected at a specific position of the irradiated medium (eg, the optical recording medium), as in the embodiment shown in FIGS. 13A and 13B .

Referring to FIG. 22 , the light of interest can also be separated by changing the area of the wave plates 36 and 37 . In FIG. 22, components corresponding to those in FIG. 20 are denoted by the same reference numerals to avoid redundant description. In this example, the light indicated by the arrow La and the light indicated by the arrow Ld return to the polarization direction of the incident light when passing through the wave plates 36 and 37 . The light indicated by the arrow Lb and the light indicated by the arrow Lc are polarized perpendicular to the original polarization direction of the incident light when passing through the wave plates 36 and 37 . In this case, light polarized in a polarization direction perpendicular to the incident light may be reflected or transmitted to the polarization filter portion 59 (not shown). The polarization filter portion 59 is thereby able to separate only the light reflected at a specific position of the irradiated medium (eg, the optical recording medium).

Although two rotators or wave plates and a single polarizing filter are used for splitting section 30 and splitting section 51, respectively, in this embodiment any combination of rotators or wave plates that operate in a similar manner can be used, and polarizing Filter 59 may be replaced by a polarizing beam splitter, as described above.

In this embodiment, light components reflected by the reflective surface of interest may be allowed to pass through the rotator or waveplate across the optical axis. Therefore, as in the sixth embodiment, the light separating unit 50 can translate in the z-axis direction along the optical axis so that the light receiver 11 can receive only the light component L1 or L3.

It should be noted that waveplates are distinct from optical rotators, as described below. A wave plate refers to a birefringent plate that introduces a predetermined optical phase shift between linearly polarized light components vibrating in orthogonal directions as the light components pass through the plate.

On the other hand, when light passes through the optical rotator, the optical rotator operates by rotating the polarization plane of the light by a predetermined angle. An optical rotator differs from a wave plate in that an optical rotator introduces no optical phase shift (retardation) to the light passing through it, thus maintaining linear polarization when its polarization direction is rotated. That is, only the optical power of the optical rotator changes according to different wavelengths. Optical rotators have the advantage that for incident linearly polarized light, the front polarization direction can be oriented along any direction within the plane of the optical rotator, because unlike wave plates, optical rotators have no optical axis in their plane. Thus, the rotator advantageously eliminates the need to align its optical axes, facilitating assembly and production.

When applied to optical pickup devices or optical recording/reproducing equipment for recording/reproducing of multi-layer recording media, a simple optical system with two optical rotators or wave plates and a single polarization filter or polarization beam splitter can suppress Deterioration of recording/reproducing characteristics.

Furthermore, in this embodiment, the splitting section 51 splits the light components passing through the splitting section 30 based on the optical paths thereof. The separating section 51 is thus also able to similarly separate the light components L1 or L3.

Eighth embodiment

23A to 23C are schematic diagrams of a light separation unit and an optical system including the unit according to an eighth embodiment of the present invention. In FIGS. 23A to 23C , components corresponding to those in FIG. 10 are denoted by the same reference numerals to avoid redundant description.

In this embodiment, the second reflective surface S2 of the optical recording medium 100 is irradiated with three beams arranged along the x-axis including a main beam for recording/reproduction and two beams on both sides thereof. side beam. Two side beams are reflected and received for processing such as tracking and focusing.

In a section parallel to the optical axis, along the direction in which these light beams are distributed, ie, in the xz plane, the splitting portion 30 splits the light beams reflected by the second reflective surface S2. In the embodiment shown in FIG. 10, for example, the split part 30 includes an optical rotator and a transparent part. The polarization direction of light passing through the optical rotator is rotated by 90°, while the polarization direction of light passing through the transparent part is not rotated. 23A and 23B illustrate only the light component L21 of the main beam reflected by the second reflective surface S2 and the light components L22 and L23 of the two side beams reflected by the second reflective surface S2.

23C, the separation parts 51 and 52 of the light separation unit 50 reliably remove unwanted light components L11 to L13 reflected by the first reflective surface S1 and unnecessary light components L31 to L33 reflected by the third reflective surface S3 . Thus, the light receiver 11 detects only the light components L21 to L23 reflected by the second reflective surface S2.

When applied to an optical pickup device or an optical recording/reproducing device to realize recording/reproduction of a medium by irradiating a multilayer recording medium with at least two light beams, a simple optical system having a splitting portion 30 and a light separation unit 50 can suppress Deterioration of recording/reproducing characteristics. Similarly, when an optical recording medium having a single recording layer is irradiated with at least two light beams, the above-described optical system can reliably remove the reflections caused by surfaces other than the reflective surface of interest (such as the interface between the recording layer and the protective layer). Unnecessary light is reflected to suppress degradation of recording/reproducing characteristics.

According to the above-described embodiments, after the light is split, light from layers other than the layer of interest can be reliably removed based on the difference in focus position without affecting the light from the layer of interest.

Unwanted light can be easily removed eg by blocking light or changing its optical path by reflection or refraction. Furthermore, relatively simple optical elements such as prisms or diffractive elements can be used for splitting, or optical rotators or waveplates can be used to split light based on differences in polarization directions without splitting its optical axis. In addition, the splitting section and the light separation unit can be integrated into a single unit to easily and reliably remove unnecessary light components. These light components would otherwise overlap the light components of interest at the light receiver in the related art.

The present invention should not be construed as being limited by the above-described embodiments. For example, optical elements other than the above examples may also be used to split or remove light within the scope of the present invention. In addition, the method and unit for separating light according to the embodiment of the present invention are not limited to the application to the above-mentioned optical pickup device and optical recording/reproducing apparatus, but can be applied to other various types of optical pickup devices and optical recording/reproducing devices equipment. Furthermore, the method and unit for separating light according to the embodiments of the present invention can of course be applied to any optical system for unwanted light coming from a position deviated along the optical axis from the light to be detected the location from.

It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions may be made depending on design requirements and other factors so long as they are within the scope of the claims or the equivalents thereof.

The present application contains subject matter related to Japanese Patent Application JP2005-235456 filed in the Japan Patent Office on Aug. 15, 2005, the entire content of which is hereby incorporated by reference.

Claims (18)

1. A method of separating light from an illuminated multilayer medium with multiple reflective surfaces, through a focusing lens to a light receiver, the method comprising the steps of: splitting light traveling through the focusing lens towards the light receiver into at least two parts along its optical axis; and A light component from a specific location of the illuminated medium is separated from each split portion of the light by being closer to the focal position of the light component from the specific location than between the focus position of the focus lens and the focus position of the light components from the specific position, by removing the light components whose focus position is closer to the focus lens than the focus position of the light components from the specific position, and/or between the focus position closer to the light receiver than the focus position of the light component from the specific position and the focus position of the light component from the specific position, by removing the focus position and the light component from the specific position The focus position of the light component at the specific position is closer to the light receiver than the light component. 2. The method of splitting light according to claim 1 , wherein the light traveling through the focusing lens towards the light receiver is split into at least two parts along its optical axis by means of a prism. 3. The method of splitting light according to claim 1 , wherein the light traveling through the focusing lens towards the light receiver is split into at least two parts along its optical axis by means of a diffractive element. 4. The method of splitting light according to claim 1, wherein, said light is split into at least two parts along its optical axis by selectively allowing said light traveling through said focusing lens towards said light receiver to pass through a region of altered polarization; and A light component from a specific position of the illuminated medium is separated from each split portion of the light by means of a polarizing filter portion, this separation being achieved by focusing with the light component from the specific position position closer to the focus position of the focusing lens and the focus position of the light component from the specific position, by removing the focus position closer to the focus position than the focus position of the light component from the specific position The light component of the lens, and/or between the focus position closer to the light receiver than the focus position of the light component from the specific position and the focus position of the light component from the specific position, by removing The focus position is closer to the light component of the light receiver than the focus position of the light component from the specific position. 5. The method of splitting light according to claim 4, wherein, said light passing through at least two optical rotators or waveplates as said regions of changing polarization; By changing the polarization direction of a light component from a specific position or a light component from a position other than the specific position, and then returning the changed polarization direction to the original polarization direction while changing the unaltered polarization direction to In a direction perpendicular to the original polarization direction, the light component from a specific position is separated from light components from positions other than the specific position using a polarization filter section. 6. The method of splitting light according to claim 1, wherein, The light traveling through the focusing lens towards the light receiver comprises at least two light beams, each of which is split into at least two parts by a plane parallel to the optical axis, and the alignment direction of the at least two light beams lies in the plane; and A light component from a specific position is separated from each split portion of the light beam, this separation being achieved at a focus position closer to the focus lens than the focus position of the light component from the specific position and the focus position of the light components from the specific position, by removing the light components whose focus position is closer to the focusing lens than the focus position of the light components from the specific position, and/or between the light components from the specific position Between the focus position of the light component at the specific position and the focus position of the light component from the specific position closer to the light receiver than the focus position of the light component from the specific position, by removing the focus position and the light component from the specific position The focus position is closer to the light component than the light receiver. 7. A light splitting unit comprising a splitting portion for passing light from an irradiated medium having a plurality of reflective surfaces to a light receiver through a focusing lens, in combination with light from the irradiated medium The focus position of the light component at a specific position is between the focus position of the light component closer to the focusing lens and the focus position of the light component from the specific position, and the difference between the focus position and the focus position of the light component from the specific position is removed. focusing of light components from said specific position at a focus position closer to said light receiver than the focus position of light components from said specific position than closer to said focusing lens Between the positions, light components whose focus position is closer to the light receiver than the focus position of the light component from the particular position are removed. 8. The light splitting unit according to claim 7 , further comprising a splitting portion for splitting the light traveling toward the light receiver through the focusing lens into at least two parts along its optical axis . 9. The light separation unit according to claim 7, wherein the separation portion includes a light shielding portion. 10. The light splitting unit according to claim 7, wherein the splitting portion comprises a reflective surface. 11. The light splitting unit according to claim 7, wherein the splitting portion comprises a refractive surface. 12. The light splitting unit according to claim 7, wherein the splitting portion comprises a polarizing filter portion. 13. The light splitting unit according to claim 12 , further comprising a splitting portion for splitting light passing through the focusing lens to the light receiver along the optical axis, the splitting portion including at least A rotator or wave plate. 14. The light splitting unit according to claim 13, wherein the splitting part comprises at least two optical rotators or wave plates to change the light component from the specific position or from a position other than the specific position The polarization direction of the light component, and then the changed polarization direction is returned to the original polarization direction, while the unchanged polarization direction is changed to a direction perpendicular to the original polarization direction. 15. An optical pick-up device, comprising: a light source for emitting light; light receivers; and An optical system, the optical system comprising: an objective lens disposed opposite to a multilayer optical recording medium having a plurality of reflective surfaces, light emitted from the light source is guided to the objective lens and made incident on a predetermined position of the optical recording medium, a focusing lens for converging light from the optical recording medium through the objective lens onto the light receiver, a splitting section for splitting the light traveling through the focusing lens towards the light receiver into at least two parts along its optical axis, and a light separation unit for separating the light component reflected by the recording layer of interest of the optical recording medium from each split portion of the light, this separation is achieved in conjunction with the The focus position of the light component reflected by the recording layer is closer to the focus position of the focusing lens than the focus position of the light component reflected from the recording layer of interest, by removing the focus position and the focus position from the sensor The light component reflected by the recording layer of interest is focused closer to the focusing lens than the light component and/or is closer to the focus than the light component reflected from the recording layer of interest. between the focus position of the light receiver and the focus position of the light component reflected from the recording layer of interest by removing the focus position compared with the focus position of the light component reflected from the recording layer of interest The light component closer to the light receiver. 16. The optical pickup device according to claim 15, wherein the splitting part comprises at least two optical rotators or wave plates, to remove the interesting recording by changing the light component reflected by the recording layer of interest or from the recording layer of interest. The polarization direction of the light component at a position other than the layer, and then return the changed polarization direction to the original polarization direction while changing the unaltered polarization direction to a direction perpendicular to the original polarization direction, along the light An axis splits the light that reaches the light receiver through the focusing lens. 17. An optical recording/reproducing device comprising: a light source for emitting light; light receivers; and Optical system for recording and/or reproducing, said optical system comprising: an objective lens disposed opposite to a multilayer optical recording medium having a plurality of reflective surfaces, light emitted from the light source is guided to the objective lens and made incident on a predetermined position of the optical recording medium, a focusing lens for converging light from the optical recording medium through the objective lens onto the light receiver, a splitting section for splitting the light traveling through the focusing lens towards the light receiver into at least two parts along its optical axis, and a light separation unit for separating the light component reflected by the recording layer of interest of the optical recording medium from each split portion of the light, this separation is achieved in conjunction with the The focus position of the light component reflected by the recording layer is closer to the focus position of the focusing lens than the focus position of the light component reflected from the recording layer of interest, by removing the focus position and the focus position from the sensor The light component reflected by the recording layer of interest is focused closer to the focusing lens than the light component and/or is closer to the focus than the light component reflected from the recording layer of interest. between the focus position of the light receiver and the focus position of the light component reflected from the recording layer of interest by removing the focus position compared with the focus position of the light component reflected from the recording layer of interest The light component closer to the light receiver. 18. The optical recording/reproducing apparatus according to claim 17, wherein said splitting section comprises at least two optical rotators or wave plates to desensitize by changing the light component reflected by the recording layer of interest or by desensitizing the polarization direction of the light component at a position other than the recording layer of interest, and then returning the changed polarization direction to the original polarization direction while changing the unaltered polarization direction to a direction perpendicular to the original polarization direction, Light passing through the focusing lens to the light receiver is split along an optical axis.

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