KR101189125B1 - Optical pick-up - Google Patents

Abstract

The present invention relates to an optical pickup. In one embodiment of the present invention, the 0th order beam is generated by a first pattern that does not include an area corresponding to the +/− 1st order beam when reflected from the disk in a branched state into the 0th order and +/− 1st order beams. A sub-beam is formed by diffraction, and a second pattern is formed in the first pattern so that the beam reflected by the other layer is not diffracted by the sub-beam PD receiving the sub-beam by the first pattern. At this time, the PD for the sub-beam should be located outside the effective radius of the beam reflected from the other layer and pass through the first pattern and the second pattern as it is, for this purpose, the diffraction angle of the first pattern is adjusted. Therefore, the beam reflected from the other layer does not enter the sub beam, thereby obtaining a stable tracking error signal and improving reproduction or recording performance.

DPP, MPP, SPP, grating, tracking error signal, interlayer interference, diffraction

Description

Optical pick-up {Optical pick-up}

1 illustrates the principle of detecting a tracking error signal by the DPP method,

FIG. 2 shows an example in which one objective lens is stockpiled away from the center axis of the disc when two objective lenses mounted on one actuator are arranged in the track direction,

3 illustrates a state in which noise light reflected from another layer flows into a photo detector,

4 illustrates an example in which a tracking error signal is distorted by interlayer interference,

FIG. 5 illustrates a phenomenon in which the offset of the DPP signal is increased at the recording / unrecorded boundary and the section in which the offset occurs is long when the objective lens is non-stocked and the DPP method using the three beams is applied.

6 shows the configuration of an optical pickup to which the 1 beam DPP method is applied.

7 exemplarily shows a form in which a beam incident on a recording disc is branched;

8 exemplarily illustrates a baseball pattern formed by branching beams incident on a recording disk;

9 schematically illustrates the principle of obtaining a sub beam from which an ac component has been removed from a beam reflected and branched from a disk,

FIG. 10 illustrates various embodiments of a diffraction grating for obtaining a sub beam from which an ac component has been removed.

FIG. 11 illustrates the result of removing only the dc component and the ac component from the push-pull signal of the sub-beam by the diffraction grating of FIG. 10.

12 illustrates the distribution of beams in a diffraction grating and PD in accordance with the present invention for eliminating interlayer interference,

FIG. 13 illustrates positions of a main beam cell and a sub beam cell of a light receiving device according to an embodiment of the present invention for removing interlayer interference;

FIG. 14 illustrates an example in which a shape of a sub beam of a layer different from that of a current layer is different among beams diffracted by the diffraction grating of FIG. 12,

Fig. 15 shows another embodiment of the optical pickup configuration to which the present invention is applied.

<Description of the symbols for the main parts of the drawings>

100, 200: optical pickup 110, 210: light source

120, 220: collimator lens 130, 230: beam splitter

140, 240: diffraction grating 150: 1/4 wave plate

160, 260: objective lens 170, 270: sensor lens

180, 280: light detection means

TECHNICAL FIELD The present invention relates to an optical pickup, and more particularly, to an optical pickup that can suppress noise from entering a servo signal from another layer.

Since the launch of the Compact Disc (CD), an optical storage medium capable of storing 74 minutes of music and approximately 650 Mbytes of data, a DVD (Digital Versatile) that can hold 2 hours of standard definition (SD) movies Disc is widely commercialized, and a BD (Blu-ray Disc) or HD-DVD, which can store a high definition (HD) class movie, will soon appear in the market.

Optical storage media such as CD, DVD, BD, and the like are disc-type media for storing data using optical characteristics, and record data on or reproduce recorded data on the disc through optical pickup. On an optical storage medium, recording discs for playback in which data is already stored, and CD-R / RW, DVD-R / + R / -RW / + RW / RAM, BD-R / -RE, etc. that can be recorded or rewritten There is a disk.

The optical pickup writes data to or reads data from the disk, with the laser beam correctly focused on tracks in the disk rotating at high speed.

It is possible to obtain a servo signal such as a focusing error signal and a tracking error signal corresponding to a position error of an optical spot formed on the disk, and to correct a position error of the optical spot based on the servo signal, that is, to perform a servo operation. The optical pickup includes an optical lens such as an objective lens, a beam splitter, an instrument part such as an actuator, a base, a laser diode, a photo detector, and the like. And electrical components are arranged.

In general, astigmatism is used to detect a focusing error signal irrespective of the type of disc and the disc for recording / playback. Regarding the detection of the tracking error signal, a 3-beam method or a differential phase detection (DPD) method is used for a disc for playback, and a differential push-pull (DPP) method is used for a disc for recording. It is typically used.

1 illustrates the principle of detecting a tracking error signal by the DPP method.

The DPP method is an improvement on the conventional one-beam push-pull method. The DPP method can detect a stable tracking error signal by eliminating offset caused by movement in the radial direction of the objective lens or tilt of the disk. That's how it is.

In the DPP method, a laser beam output from a light source through a diffractive element called grating is divided into three, such as 0th-order diffraction light and +/- 1st diffraction light, and the main beam, which is the 0th-order diffraction light, is formed in the groove of the disc track. When placed in a groove, the sub-beams of the +/- 1st diffraction light are arranged in a land adjacent to the groove in which the main beam is placed (the sub beam is placed 1/2 track pitch away from the main beam). The grating is adjusted, and a tracking error signal is detected based on the difference signal on the left and right of each beam with respect to the radial direction.

The main beam reflected from the disk is received by a 4-divided (a, b, c, d) main photodetector to the push-pull signal, Main Push-Pull (MPA) ((A + D)-(B + C)). Each sub-beam detected and reflected from the disk is received by a sub-photo detector divided into two (E1, E2) (F1, F2) in the radial direction, and the sub push-pull ((E1-E2) + (F1) -F2)) is detected. If the main beam and the sub beam are spaced apart by 1/2 track pitch, the phases of the MPP and SPP are reversed.

Since both the MPP and the SPP generate offset components in the same direction as the tilt or the objective lens moves in the radial direction, a calculation is performed according to DPP = MPP-kxSPP (k is a proportional constant) to obtain a push-pull signal with the offset component removed. do. In addition, by subtracting the SPP that is out of phase from the MPP, a larger amplitude push-pull signal can be obtained.

In general, in the DPP method, the ratio of light quantity between the main beam used for the MPP signal and the sub beam used for the SPP signal is about 1: 5: 1 to 1: 20: 1, so that the sub beam is 1/5 to 1 / Make it as small as 20 In the equation for DPP, the offset is adjusted by adjusting the proportional constant k (for example, 5 when the light ratio is 1: 10: 1).

As described above, in order to use the DPP method, it is necessary to adjust the angle of the sub-beam, which is +/- 1 order diffracted light while rotating the grating. However, the characteristics of the signal are affected by the degree of adjustment.

That is, if the main beam is in the groove (or land), the sub-beam should be in the land (or groove). Since the track pitch may be different for each type of disc, the sub beam cannot be applied simultaneously to discs having different track pitches.

With the advent of BD or HD-DVD, there is an increasing demand for an optical disc recording / reproducing apparatus capable of playing or recording all CDs, DVDs, and BDs (or HD-DVDs). However, since the numerical aperture of the objective lens for recording / reproducing CD, DVD, and BD varies greatly, it is almost impossible to reproduce all three types of discs with only one objective lens.

In response to this demand, optical pickups have recently been developed in which an actuator is equipped with two objective lenses, an objective lens for CD / DVD, and an objective lens for BD or HD-DVD. The two objective lenses may be arranged in the track direction or the inner and outer circumferential direction of the disc. When arranged in the inner and outer circumferential direction, the optical pickup mainly having two objective lenses arranged in the track direction is difficult because the innermost circumference of the disk is not easy to access. Is being developed.

2 shows an example in which one objective lens is stockpiled away from the central axis of the disc when two objective lenses mounted on one actuator are arranged in the track direction.

When two objective lenses are arranged in the track direction as shown in FIG. 2, at least one of the two objective lenses deviates from the axis connecting the inner and outer circumferences (the axis passing through the center of the disk). In an optical system using an objective lens positioned off the central axis of the disc, the relative position (angle of the sub beam) in the tracks of the main beam and the sub beam for DPP detection changes as the optical pickup moves from the inner circumference to the outer circumference, The angle adjustment of the sub beams becomes meaningless.

Meanwhile, a multi-layer structure in which two or more recording layers are formed to increase storage capacity has been adopted in the DVD and BD standards, and a multi-layer structure is expected to be generalized in the case of high density discs to be developed in the future. .

In order to increase the density of the disk, the wavelength of the laser beam is shortened and the numerical aperture (NA) of the objective lens is increasing. The laser diode and the objective lens of 780nm, NA = 0.45 for CD, 650nm for NA, 0.6 = NA, 405nm for BD, NA = 0.85 are adopted.

In multi-layer discs, the spacing between recording layers is determined approximately in proportion to the depth of focus of the light spot, which is proportional to the wavelength of the laser beam and inversely proportional to the square of the numerical aperture of the objective lens. The gap between them should also be narrow.

When performing a recording or reproducing operation for a multi-layer disc having a narrow gap between layers, as shown in FIG. 3, a beam reflected from a layer adjacent to the current recording layer, that is, noise light of another layer, is transferred to the photo detector. It is easily introduced.

The noise light of the other layer also flows into the main photo detector for receiving the main beam and the sub photo detector for receiving the sub beam, and affects not only the reproduction signal but also the servo signal. In particular, it has a greater influence on the servo signal obtained by using a sub beam having a relatively small amount of light. Therefore, as shown in FIG. 4, the SPP signal is severely distorted by the noise light from another layer, and a problem arises in that the DPP, that is, the tracking error signal calculated based on the SPP signal, is degraded.

Accordingly, the present invention has been made to solve the above problems, and an object of the present invention is to reduce interlayer interference in a multilayer disk to obtain a stable servo signal and to improve playback or recording performance.

Optical pickup according to an embodiment of the present invention for achieving the above object, the light source for emitting a beam of a predetermined wavelength; An objective lens for condensing a beam emitted from the light source on an optical storage medium; A beam splitter that transmits or reflects a beam emitted from the light source or a beam reflected from the optical storage medium; A beam that diffracts a portion of the beam passing through the first region of the beam reflected in the branched state from the optical storage medium and diffracts a portion of the beam passing through the second region in the first region by the first region A diffraction grating diffracted to a position different from this conjunctive position; A sensor lens for generating a boiling point on the beam reflected from the optical storage medium; And a light detecting means including main detecting means for receiving a beam passing through the diffraction grating as it is and two first sub detecting means for receiving a beam diffracted by the first region. It is done.

In one embodiment, the first sub-detection means is located outside the effective radius of the beam passing through the diffraction grating as it is from a beam reflected from a layer other than the current layer of the optical storage medium in which recording or reproduction is in progress. It is done.

Further, in one embodiment, the second region corresponds to a region where the beam to be reflected on the first sub-detection means of the beam reflected by the other layer and diffracted by the first region passes through the diffraction grating. It is characterized by.

Further, in one embodiment, the first region is characterized in that the beam diffracted by the optical storage medium does not include a region passing through the diffraction grating among the beams reflected from the optical storage medium.

In this case, the first region may have a rectangular shape bordering an area where a beam diffracted by the optical storage medium passes through the diffraction grating among the beams reflected by the optical storage medium. In addition, the diffraction grating includes a third region in a region other than the first region and the second region, and a part of the beam passing through the third region is diffracted to form the main detection means and the first sub detection means. The lattice pattern of the third region is formed so as not to.

Further, in one embodiment, the optical pickup may further comprise second detection means for conventional DPP detection, wherein the distance between the first sub detection means and the main detection means is equal to the second sub detection means and the main detection means. It is characterized by being at least five times farther than the distance between the detection means.

Further, in one embodiment, the tracking error signal is detected by Mpp-k (Spp1 + Spp2), where k is calculated using the offset change of Mpp and the offset change of Spp1 and Spp2 according to the radial shift of the objective lens. It is characterized by.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the case of DPP using 3 beams, the sub beams are formed on the disc with a half track pitch deviating from the main beams. In the general case where the objective lens is located on the center axis of the disc, the relative position of the main beam and the sub beam does not change regardless of the inner and outer circumferences.

However, in the case of the non-axis arrangement in which the objective lens operates off the center axis of the disc, relative positions of the main beam and the sub beam in the track vary according to the inner and outer circumferences. In this case, as shown in FIG. 5, the offset of the DPP signal increases at the recorded / unrecorded boundary of the disk, and the length of the section in which the offset occurs increases.

The difference between the recorded and unrecorded areas is represented by the difference in reflectance. When the objective lens travels through the recorded and unrecorded areas in the DPP method using 3 beams, the level difference of the DPP signal appears in each area.

The offset of the DPP signal at this recorded / unrecorded boundary is caused by the time difference entering the recorded / unrecorded area when using 3 beams. In order to solve this problem, only one beam is incident on the disk, and a main diffraction grating generates a main beam and a sub beam from a beam reflected and branched by the track structure of the disk, and the main beam is used by using the sub beam. A method for removing an offset from a push-pull signal of A, a 1 beam DPP method has been proposed in another application by the applicant of the present invention, it will be described.

The main purpose of using a sub beam in DPP is to remove offsets generated in the main beam by radial shift of an objective lens, and the increase of the level of the DPP signal due to the ac component generated in the push-pull signal of the sub beam is secondary. Effect.

In the method proposed by the applicant of the present invention, the beam reflected and branched by the track structure of the disc (land / groove of the track serves as a diffraction grating) is passed through the diffraction grating as it is to become a main beam, and a predetermined shape in the diffraction grating. The beam diffracted by the pattern of becomes a sub beam.

The main beam that passes through the diffraction grating as it contains both the ac component reflecting the position of the beam on the disk and the dc component reflecting the radial shift of the objective lens. All ingredients appear.

The pattern in the diffraction grating is shaped to diffract only the beam corresponding to the dc component (offset) except for the beam corresponding to the ac component among the beams reflected and branched by the track structure of the disk. Therefore, only the dc component appears in the push-pull signal of the sub-beam diffracted and generated by the pattern.

Therefore, the offset corresponding to the radial shift of the objective lens appearing in the push-pull signal of the main beam passing through the diffraction grating as it is, can be effectively removed using the push-pull signal of the sub-beam.

6 shows a configuration of an optical pickup to which the method is applied.

The optical pickup 100 of FIG. 6 includes a light source 110, a collimator lens 120, a beam splitter 130, a diffraction grating 140, and a quarter wave plate (QWP). Wave plate 150, the objective lens 160, the sensor (Sensor) lens 170, and the light detecting means 180 is configured to include. The disk is mounted on the side where the objective lens 160 is focused.

The light source 110 emits a laser beam, and the collimator lens 120 converts the beam emitted from the light source into parallel light. The beam splitter 130, which is an optical splitter, transmits the incident beam to the diffraction grating according to the polarization direction of the beam incident from the collimator lens 120, and reflects the beam reflected from the disk to the sensor lens 170.

The quarter wave plate 150, which rotates the polarization of the beam, converts a beam of linearly polarized light emitted from the light source 110, for example, a beam of p-polarized light into a beam of circularly polarized light, and also another circularly polarized light on the disk. Is converted into another linearly polarized beam, for example a beam of s polarized light.

The beam focused on the disk through the objective lens 160 is reflected and diffracted by the disk having a land / groove structure to become a zeroth order beam and a + 1st order beam, and then directed to the objective lens 160. The beam of circularly polarized light reflected from the disk is converted into a parallel beam through the objective lens 160 and is converted into linearly polarized light while passing through the quarter wave plate 150. The sensor lens 160 reflects off the disk and generates a boiling point for the incident beam as the path is changed in the beam splitter 130 and transmits the boiling point to the light detecting means 180.

The diffraction grating 140 is a sub-pattern of the light detecting means 180 in the circular pattern region of the first-order beam and the circular pattern of the zero-order beam in the circular pattern of the diffraction beams generated while being reflected and branched to the disk. The grating pattern is formed so that it is not received by the PD cell for the beam.

That is, the beam reflected and branched from the disk becomes a main beam and a sub beam through the diffraction grating 140. The main beam passing through the diffraction grating 140 as it is is the light detecting means 180, that is, the main cell of the light receiving element. Two sub-beams received by the main cell to form an MPP signal and diffracted by a pattern of a predetermined shape in the diffraction grating 140 are received by the sub-cells of the light detecting means 180 to be connected to the first SPP signal. It becomes a 2nd SPP signal.

In order to detect the MPP signal and the SPP signal, the main cell of the light detecting means 180 is divided into at least two parts in a direction corresponding to the radial direction and the tangential direction, and the subcells of the light detecting means 180 are At least two divisions are made in a direction corresponding to the radial direction.

7 exemplarily shows a form in which a beam incident on a recording disk is branched.

When the beam incident through the objective lens and incident on the recording disk is viewed at the focal length of the objective lens, as shown in FIG. 7, the beam is divided into a + 1st order beam, a 0th order beam, and a -1st order beam. This is due to the track (land / groove) structure of the recording disc having a predetermined track pitch TP, which is because lands and grooves of the recording disc have an irregular shape in cross section, which produces an effect such as a diffraction grating.

The 0th order beam (b2), the + 1st order beam (b1), and the -1st order beam (b3) reflected and branched from the disk form a circular pattern and directed to the objective lens, and the size of the circular pattern formed by the beams is the objective lens. It has the same value as the EPD (Entrance Pupil Diameter). If the objective lens is focused f and the numerical aperture is NA, the EPD is 2xfxNA.

Further, the + 1st order beam b1 and the -1st order beam b3 move left and right as shown in FIG. 7, and the amount of movement becomes fxλxTp when the track pitch of the disk is Tp and the wavelength of the laser beam is λ.

The circular pattern P2 of the center 0th order beam is partially overlapped with the circular pattern P1 by the + 1st order beam moving left and right by the track structure of the disk and the circular pattern P3 by the -1st order beam. It forms the same pattern as the one, which is called the baseball pattern because it resembles the shape of a baseball.

At this time, the size and the degree of overlap of the circular patterns (P1, P2, P3) are different depending on the type of disc. In the case of BD or DVD-RW, the overlapping degree is relatively small because of the large amount of movement. . In the push-pull signal (MPP and SPP signal in the case of 3-beam DPP), the ac component is generated by the overlapping portion of the 0th order beam and the +/- 1st order beam in the baseball pattern of FIG.

9 schematically illustrates the principle of obtaining a sub beam from which an ac component has been removed from a beam reflected and branched from a disk.

The beam incident on the disk is diffracted into three beams by the disk track structure, wherein the center beam of the three diffracted beams is the 0th order beam, and the beams formed at the left and right sides of the 0th order beam are +/- 1. Is defined as the secondary beam. The three beams (0th order beam and +/- 1st order beam) formed separately from the beam incident on the disk form a baseball pattern as shown in FIG. 8 by overlapping some regions P7.

In this case, the diffraction grating illustrated as an embodiment in FIG. 9 diffracts only the 0th order beam P5 except for the portion where the 0th order beam and the +/- 1st order beam overlap in the baseball pattern, and receives the photodetector for the subbeam. And the pattern is designed such that the +/- 1st beams P4, P6, P7, including the portion where the 0th and +/- 1st beams overlap, are not received by the photo detector for the subbeam. .

However, the main beam passing through the diffraction grating as it is reflects the baseball pattern regardless of the pattern of the diffraction grating, so that both the ac component and the dc component (offset) appear in the push-pull signal (MPP) of the main beam.

Since the 0th order beam P5 except for the portion where the 0th order beam and the +/- 1st order beam overlap in the baseball pattern is diffracted by the pattern of the hatched area of the diffraction grating, it is received by the photo detector for the subbeam. The ac component does not appear in the push-pull signal SPP, but only the offset of the main beam.

Accordingly, by subtracting the push-pull signal SPP of the sub-beam from which ac has been removed from the push-pull signal MPP of the main beam, the tracking error signal having the offset removed without using the three-beams connecting the three-beams to the disk can be obtained. You can get it.

10 illustrates various embodiments of a diffraction grating for obtaining a sub beam from which an ac component has been removed. The diffraction grating may be formed in various patterns.

As described above, the main beam passing through the diffraction grating of FIG. 10 as it is reflects all of the bassball pattern, and both the ac component and the offset appear in the MPP. However, the beam reflected and branched from the disk is only partially diffracted by the first patterns A1, A3, and A5 corresponding to the use region of the diffraction grating to form a sub beam.

The diffraction grating of FIG. 10 (a) has a first pattern A1 formed in the form of vertically oriented gears ("I") when the X axis is radial and the Y axis is tangential. And a second pattern A2 formed in the remaining areas except for the first pattern.

The first pattern A1 is formed of the circular pattern regions P1 and P3 of the first-order beams b1 and b3 and the circular pattern region P2 of the zero-order beam b2 and the first-order beams b1 and b3. The circular pattern regions P1 and P3 are formed in the region P5 except for the overlapping region P7.

In addition, the upper / lower end of the first pattern A1 (the rectangular portion except for the middle circular recessed portion) has a diffraction grating within the extent that it does not involve the circular pattern regions P4 and P6 of the primary beams b1 and b3. It may have a form extending to both sides of the.

The diffraction grating of FIG. 10 (b) includes a first pattern A3 having a vertically long rectangular shape and a second pattern A4 formed on both of the first patterns A3 in the center portion. Here, the position and width of the first pattern (A3) is an important factor, the first pattern (A3) is a rectangular shape so that the circular pattern (P1, P3) of the first beam (b1, b3) is not included. That is, it is preferable that the position and width of the first pattern A3 in the x-direction are determined so as to contact the ends of the circular patterns P1 and P3 of the first-order beam lying in the circular pattern P2 of the zero-order beam. Do.

The diffraction grating of FIG. 10 (c) includes a first rectangular pattern A5 long in the center and a second pattern A6 formed above and below the first pattern A5. Here, among the four points where the boundary between the circular pattern P2 of the zeroth order beam b2 and the circular patterns P1 and P3 of the first order beams b1 and b3 meet, It is preferable that the position and width | variety of the y direction of 1st pattern A5 are determined by a line.

FIG. 11 shows the result of removing only the dc component and the ac component from the sub-pump push-pull signal of the sub-beam by the diffraction grating of FIG. 10. FIG. On the other hand, the ac component of the push-pull (SPP) signal of the sub-beam can be confirmed through FIG. 11.

Here, the dc level (offset) of the SPP signal is closely related to the amount of movement of the objective lens, that is, the amount of radial shift indicating the movement of the objective lens from the center of the actuator to the inner and outer circumferential directions.

In general, since the offset (dc level) of the MPP signal and the SPP signal increases in proportion to the amount of radial shift of the objective lens, the offset of the push-pull signal is linear in proportion to the amount of radial shift of the objective lens. I can do it.

Therefore, at DPP = MPP-kx (SPP1 + SPP2), when the slope of the dc level of the MPP signal with respect to the radial shift amount of the objective lens is a, and the slope of the dc level of the SPP signal with respect to the radial shift amount of the objective lens is b. By setting the proportional constant k = 1 / 2b, the offset of the MPP signal generated by the movement of the objective lens can be eliminated.

12 shows the distribution of beams in a diffraction grating and PD in accordance with the present invention for removing interlayer interference. The diffraction grating of FIG. 12A according to the present invention can be applied to the diffraction grating 140 of the optical pickup of FIG. 6.

The grating direction (lattice direction) of the phase management areas A11 and A13 in the pattern of the diffraction grating is set to 90 degrees with that of the use area A12. In FIG. 12, grating is formed in the horizontal direction in A12, and grating is formed in the vertical direction in A11 and A13. Thus, the +/- 1st beam diffracted by A12 is arranged above and below the 0th order beam, and the +/- 1st beam diffracted by A11 and A13 is arranged to the left and right of the 0th order beam.

The diffraction grating of FIG. 12 (a) is similar to the diffraction grating of 10 (b) except that the A13 pattern is formed in the A12 pattern. As described with reference to Figs. 9 and 10, A11 (A4 in Fig. 10 (b)) and A12 (A3 in Fig. 10 (b)) are offset by the main beam offset (radial shift of the objective lens) in the one-beam DPP method. Is a combination of patterns to generate a sub-beam to remove), which is designed such that no ac component is included in the sub-beam.

To this end, the A12 pattern is a circular pattern P1 of the primary beams b1 and b3 in the baseball pattern formed by three beams (zeroth order beam and +/- 1st order beam) generated when reflected from the disk. It is configured in a rectangular shape so that P3) is not included in the sub beam. The sub-beam diffracted by the A12 pattern is formed on the sub-beam PD (sub-cell of the light receiving element) for receiving the sub-beam.

Of course, the main beam passing through the diffraction grating of FIG. 12A as it is is connected to the main beam PD (main cell of the light receiving element) for receiving the main beam, and used for the RF signal, the focus signal, and the push-pull signal. do. The main and sub beams differ in the amount of light due to the outer shape of the A12 pattern and the shape of the valleys and floors forming the A12 pattern.

The beam reflected from a layer other than the current layer in which recording or reproduction is in progress passes through the diffraction grating of FIG. 12A as it is, and forms a beam on the PD for the main beam, and is diffracted by the A12 pattern of FIG. Also attached to the PD for a sub beam. Beams reflected from other layers further influence the sub-beams with a relatively small amount of light, which greatly affects the tracking error signal using the sub-beams.

In the present invention, the beam reflected by the other layer does not enter the sub-beam PD so that the tracking error signal is not degraded by interlayer interference. In the first case of deteriorating the tracking error signal, the beam of another layer passing through the interlayer interlayer diffraction grating as it is is incident on the PD for sub-beam, and in the second case diffraction by A12 in FIG. 12 (a). The beam of another layer is incident on the PD for sub-beams.

As a way to solve the problem of the first case, the present invention provides that the subbeam of the current layer diffracted by A12 is located outside the effective radius of the beam of the other layer passing through the diffraction grating of 12 (a) as it is. Adjust the concave-convex shape (determining the diffraction angle) and the position of the PD for the sub beam.

To this end, as shown in FIG. 13, the PD for the sub-beams is disposed farther than the PD for detecting the sub-beams of the conventional DPP. That is, the distance between the main beam PD cell and the sub beam PD cell is increased. For example, the distance D between the subbeam PD cell and the main beam PD cell according to the present invention is set to be five times or more the distance d between the subbeam PD cell and the main beam PD cell of the conventional DPP. The light receiving element may be arranged as shown in FIG. 13 (b) to include both the conventional DPP detection and the PD for the one-beam DPP detection according to the present invention.

As a method for solving the problem in the second case, the present invention provides that the subbeams of another layer diffracted by A12 are not condensed into the PD for subbeams designed to receive the subbeams of the current layer diffracted by A12. A13 with different grating directions is formed in A12.

The A13 pattern is used in a region where the beam passing through the diffraction grating of 12 (a), which can affect the region where the sub-beam PD is to be placed (region B2 in FIG. 12 (b)), among the beams of another layer diffracted by A12. Correspondingly, the outline shape is designed.

The beam reflected from the other layer passes through the diffraction grating of FIG. 12 (a) as it is and forms the main beam PD in the shape of B0.

In addition, the beam of another layer is diffracted by A12 in FIG. 12 (a) to form the shape of B1 above and below the main beam. In this case, since the grating direction of A13 in A12 is different from A12, the PD for the sub-beam (FIG. 12 In (b) region B2), no beam of another layer enters.

In addition, among the beams reflected from other layers, some are diffracted by A11 in FIG. 12 (a) to form the shape of B4 on the left and right sides of the main beam, and others are diffracted by A13 in FIG. 12 (a). The left and right sides of the main beam bear in the shape of B5. In Fig. 12 (b), the empty area between B4 and B5 is an area generated because the beam reflected from another layer is bound to B1 by A12.

The tracking error signal can be obtained through DPP = MPP-kx (SPP1 + SPP2) using the MPP, which is the push-pull signal obtained from the PD for the main beam, and SPP1 and SPP2, which are the push-pull signals obtained from the PD for the sub-beam.

As described above, assuming that the offset of the MPP signal and the SPP signal has a linear property proportional to the amount of radial shift of the objective lens, the slope of the dc level of the MPP signal relative to the amount of radial shift of the objective lens is a, the objective lens When the slope of the dc level of the SPP signal with respect to the amount of radial shift of b is b, the proportionality constant can be calculated as k = 1 / 2b.

Meanwhile, in FIG. 12 (b), among the beams diffracted by A12, the shape of the sub-beams reflecting in the current layer (elongated in the left-right direction) and the shape of the beam B1 reflecting in the other layer ( Up and down) is different.

In general, the sensor lens 170 that generates astigmatism to obtain a focus error signal uses a cylindrical lens to focus the focal position of two axes, for example, the x-axis and the y-axis, with respect to the incident beam. Alternatively, make the focusing point the intermediate position of the focal point on the x and y axes.

The lens that generates astigmatism serves to rotate the shape (light distribution) of the beam by 90 degrees while maintaining the geometric position of the beam with respect to the incident beam so as to focus between two focal points. It does not rotate the shape of the beam with respect to the incident beam so that it focuses outside the focal point of the two axes.

That is, the beam reflected from the current layer focused for recording or playback passes through the sensor lens 170, and the light quantity distribution is rotated 90 degrees, and the beam reflected from another layer out of focus causes the sensor lens 170 to rotate. Even if it passes, the light quantity distribution is maintained as it is.

Therefore, among the beams of FIG. 14 (a) shape (up-and-down elongated shape) passing through A12 in a form in which a part of the left and right are cut by A11, the beam reflected in the current layer passes through the lens generating astigmatism, and FIG. As shown in (b), the beam is changed into an elongated shape to the left and right, and the beam reflected from the other layer maintains the elongated shape as shown in FIG. 14 (c) even after passing through the lens generating the astigmatism.

Similarly, the beam reflected from the other layer among the beams passing through A11 in a form in which the center is cut off by A12 and only a part of the left and right remains in the original shape as shown by B4 in FIG. 12 (b) even after passing through the lens causing the astigmatism. They remain in place away from the PD for the main beam and the PD for the sub beam while maintaining the same.

In another embodiment of the present invention, A11 and A12 need not necessarily be perpendicular to the grating direction. The grating direction and the concave-convex shape of A11 may be designed so that the beam diffracted by A11 among the beams reflected by the other layer does not form on the main beam PD and the sub-beam PD.

Therefore, even if the grating directions of A11 and A12 coincide with each other, the diffraction angle of A11 is increased to prevent the beam diffracted by A11 from forming on the main beam PD and the subbeam PD.

The same is true of the grating direction and irregularities of A13. In addition, A11 and A13 do not need to have the same grating direction and uneven shape (pitch, depth, inclination of floor and valley, etc.).

In addition, by combining the pitch, depth and the like of the unevenness forming the A12 pattern, it is possible to adjust the position, the diffraction angle and the like to form the sub-beam.

Further, in the diffraction grating according to the present invention, except that the A13 pattern is formed in the A12 pattern, the A11 and A12 pattern shapes may be designed similar to the A1 and A2 pattern shapes of the diffraction grating of FIG. 10 (a).

The diffraction grating of FIG. 12A according to the present invention may be applied to the diffraction grating 140 of the optical pickup 100 of FIG. 6, in which the diffraction grating of FIG. 12A is one-quarter of the beam splitter 130. When located between the wave plates 150, it is preferable for light efficiency to use a polarization diffraction grating so that only the light reflected from the disk can be diffracted without diffracting the beam incident on the disk. Non-polarized diffraction gratings can also be used if they accept light loss.

In the optical pickup 100 of FIG. 6 to which the present invention is applied, the diffraction grating 140 according to the present invention is driven like the objective lens 160, that is, supports the objective lens 160 and focuses and / or tracks it. It is advantageous to mount it with an objective lens 160 to an actuator that performs a servo. The diffraction grating 140 according to the present invention may be mounted to the base of the optical pickup 100 without being mounted to the actuator.

In addition, the diffraction grating according to the present invention can be applied to the optical pickup configured as shown in FIG.

The optical pickup 200 of FIG. 15 to which the present invention is applied includes a light source 210, a collimator lens 220, a beam splitter 230, a diffraction grating 240 according to the present invention, an objective lens 260, and a sensor lens. 270, and the optical detection means 280, and a disk is mounted on the side in which the objective lens 260 is in focus.

The optical pickup 200 of FIG. 15 is similar in configuration to the optical pickup 100 of FIG. 6 described above, but is not provided with a quarter wave plate 150 of the optical pickup 100 of FIG. The location of the grating 240 is different between the beam splitter 230 and the sensor lens 270. In the optical pickup 200 of FIG. 15, since the diffraction grating 240 does not lie in the path from the light source 210 to the disk, the polarization diffraction grating does not need to be used.

Except for this difference, the configuration and operation of the optical pickup 200 of FIG. 15 are the same as those of the optical pickup 100 of FIG. 6.

The optical pickup 100 of FIG. 6 to which the diffraction grating according to the present invention is applied and the optical pickup 200 of FIG. 15 are optical recording media for recording having a plurality of recording layers, for example, DVD-RAM, DVD-RW. , DVD + RW, DVD-R, DVD + R, BD-R, BD-RE and the like are advantageous for recording and playback.

In addition, the optical pickup 100 of FIG. 6 and the optical pickup 200 of FIG. 15 to which the diffraction grating according to the present invention is applied are applied to a part of the optical pickup capable of recording and / or playing all CDs, DVDs, and BDs. Can be applied.

For example, when the optical system for the CD and DVD and the optical system for the BD are implemented in one pickup, as shown in FIG. 2, two objective lenses should be mounted on one actuator, and the objective of the BD optical system is mainly used. The lens is stockpiled.

Thus, the optical pickup 100 of FIG. 6 and the optical pickup 200 of FIG. 15, in which the diffraction grating according to the present invention is used, are applied to the optical system for BD, so that the three beam DPP may be generated by the stockpile arrangement of the objective lens. Can solve the problem.

Preferred embodiments of the present invention described above have been disclosed for the purpose of illustration, and those skilled in the art will improve, change, and substitute various other embodiments within the technical spirit and the technical scope of the present invention disclosed in the appended claims below. Or addition may be possible.

In the optical pickup device according to the present invention, a beam reflected from another layer does not enter the sub-beam, thereby obtaining a stable tracking error signal, thereby improving reproduction or recording performance.

Claims (17)

A light source emitting a beam of a predetermined wavelength; An objective lens for condensing a beam emitted from the light source on an optical storage medium; A beam splitter that transmits or reflects a beam emitted from the light source or a beam reflected from the optical storage medium; A beam that diffracts a portion of the beam passing through the first region of the beam reflected in the branched state from the optical storage medium and diffracts a portion of the beam passing through the second region in the first region by the first region A diffraction grating diffracted to a position different from this conjunctive position; A sensor lens for generating a boiling point on the beam reflected from the optical storage medium; And And a main detecting means for receiving a beam passing through the diffraction grating as it is, and a light detecting means comprising two first sub detecting means for receiving a beam diffracted by the first region. And the first sub-detection means is located outside the effective radius of the beam passing through the diffraction grating as it is from a beam reflected from a layer other than the current layer of the optical storage medium in which recording or reproduction is in progress. delete The method of claim 1, And the second region corresponds to a region in which a beam to be reflected to the first sub-detection means passes through the diffraction grating among the beams reflected by the other layer and diffracted by the first region. The method of claim 1, And wherein the first region does not include a region in which the beam diffracted by the optical storage medium passes through the diffraction grating among the beams reflected by the optical storage medium. 5. The method of claim 4, And wherein the first area has a rectangular shape bordering an area where a beam diffracted by the optical storage medium passes through the diffraction grating among the beams reflected by the optical storage medium. 5. The method of claim 4, The diffraction grating includes a third region in a region other than the first region and the second region, and the portion of the beam passing through the third region is diffracted so as not to be formed in the main detecting means and the first sub detecting means. An optical pickup, wherein the grid pattern of the third region is formed. The method according to claim 6, And the grating direction of the first region and the third region is 90 degrees. The method according to claim 6, And a lattice direction between the second region and the third region is parallel. The method according to claim 6, And the grating directions of the second area and the third area are not parallel to each other. The method of claim 1, The diffraction grating is located between the beam splitter and the objective lens, And a quarter wave plate is further placed between the diffraction grating and the objective lens to rotate the polarization of the beam. The method of claim 10, And the diffraction grating diffracts only the beam reflected from the optical storage medium without diffracting the beam emitted from the light source. The method of claim 1, And the diffraction grating is located between the beam splitter and the sensor lens. The method of claim 1, And grating for diffracting the beam emitted from the light source into a 0th order beam and a +/- 1st order beam to form an optical storage medium, Wherein the optical detection means further comprises two second sub-detection means for receiving the +/- primary beam reflected from the optical storage medium. 14. The method of claim 13, And the distance between the first sub detection means and the main detection means is at least five times farther than the distance between the second sub detection means and the main detection means. The method of claim 1, The main detecting means is divided into at least two parts in a direction corresponding to a radial direction and a tangential direction, and the first sub detecting means is divided into at least two parts in a direction corresponding to a radial direction, When the push-pull signal detected by the main detecting means is Mpp and the two push-pull signals detected by the first sub detecting means are Spp1 and Spp2, the tracking error signal is determined by Mpp-k (Spp1 + Spp2). And k is calculated using an offset change of Mpp and an offset change of Spp1 and Spp2 according to the radial shift of the objective lens. The method of claim 1, The optical storage medium is at least one of CD, DVD-RAM, DVD-RW, DVD + RW, DVD-R, DVD + R, BD-R, and BD-RE. The method of claim 1, And the light source emits a beam of blue wavelengths and the objective lens is off the central axis of the optical storage medium.

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