JP2002237080A - Integrated unit and optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an integrated unit and an optical pickup device capable of detecting a DPP signal controlling the occurrence of a track offset. SOLUTION: The unit and the device are provided with an LD chip 3 exiting a laser beam, a diffraction grating 7 dividing the exited laser beam into the plural, a hologram 6 in which an optical disk is irradiated with a plurality of laser beams and which guides light by diffracting reflected light from the optical disk, and a photodetector 4 which receives light diffracted by the hologram 6. Light quantities of ±1st order diffracted light diffracted by the diffraction grating 7 are unbalanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an integrated unit and an optical pickup device used for an optical disk device for optically recording and reproducing information on an information recording medium such as an optical disk.

[0002]

2. Description of the Related Art A push-pull method (hereinafter, abbreviated as a PP method) is known as a method of detecting a track error signal using one beam. In the PP method, a pit (information signal) or a groove (a signal) on a disk is used. This is a method of performing tracking control based on the intensity difference in the direction perpendicular to the track direction of the reflected diffracted light reflected from the guide groove). However, this PP
In general, the method has a large problem that a similar intensity difference occurs even when the objective lens is shifted according to tracking or the disk is inclined, and the reflected diffracted light cannot be distinguished. .

In order to solve such a problem, conventionally, a differential push-pull method (hereinafter, referred to as DPP) has been proposed.
Law). This DPP method is a three-beam method having a main beam and sub-beams before and after the main beam. In addition to detecting a PP signal of each of the three beams, a shift amount of an objective lens and a disk In this method, a pure track error signal is detected by detecting the amount of inclination and removing the amount from the PP signal of the main beam.

On the other hand, an optical pickup device using a hologram has been proposed as a means for realizing a small, thin, and highly reliable optical pickup device. In this regard, Japanese Patent Laid-Open No. 9-16 / 1994
The hologram disclosed in Japanese Patent No. 1282 is divided into two in the radial direction of the disk, and one of the two is further divided into two in the track direction. Then, the focus signal is detected by half of the reflected beam from the disk, the track error signal is detected by the other half, and the information signal is detected by the entire surface of the beam. Since the half-split beam is further split into two, the PP signal from the track can be detected.

[0005]

However, when the DPP method is applied to a pickup device having a hologram, the following problems occur. That is, each reflected light from the three-beam disk is incident on the hologram.
(See FIG. 11). As mentioned above, the hologram is 3
The signal is divided and the PP signal of each beam is detected based on the operation output of the area BC shown in FIG. However, since the front and rear sub-beams are shifted from the center of the hologram,
The ratio of the part for detecting the PP signal to all the beams is different. That is, a light amount difference occurs. Originally, there is no output difference between the PP signal of the front sub-beam and the PP signal of the rear sub-beam, but in the above case, a difference occurs in the output signal.

In such a case, when calculating the track error signal by the following equation, TES = MPP−α / 2 * (SPPf + SPPr) (1) MPP: PP SPPf of the main beam: PP SPPr of the front sub beam: PP α of rear sub beam: coefficient Track offset occurs. If only the DC offset component is considered, the DC offset component of the MPP: OFm The DC offset component of the sub beam on the front side: OFsf The DC offset component of the sub beam on the rear side: OFsr.

Here, as described above, if the light amount ratio due to the fact that the front and rear sub-beams are shifted from the center of the hologram = K, then OFsr / OFsf = K, so that the DC offset after the calculation of equation (1) is obtained. OF = OFm−α / 2 * (OFsf + OFsr) = OFm−α / 2 * OFsf * (1 + K) Here, if α = OFm / OFsf = 10, OF = OFm−5 * OFsf * (1 + K) = OFm−OFm * (1 + K) / 2 = OFm * (1−K) / 2, and when K ≠ 1, a residual offset occurs.

On the other hand, if the following arithmetic expression is used, TES = MPP−α / 2 * (SPPf + β * SPPr) (2) β = coefficient Here, α = 10 and β = 1 / K, OF = OFm−α / 2 * (OFsf + β * OFsr) OF = OFm−α * OFsf = OFm−10 * OFsf = 0, and by using the coefficient β, the light amount difference between the front and rear sub beams is eliminated. Therefore, occurrence of a track offset can be suppressed.

In order to perform such an operation, it is necessary to individually extract the PP signals of the front and rear sub beams. That is,
A total of four output terminals are required, two each for the front and rear subs. However, in order to reduce the size of the photodetector,
By connecting the front and rear subs in the photodetector, the output terminals need to be reduced as much as possible so that only two output terminals are required. In that case, instead of equation (2),
Since the calculation must be performed in (1), the track offset occurs as described above.

The present invention has been made in view of the above, and has as its object to provide an integrated unit and an optical pickup device capable of detecting a DPP signal in which occurrence of a track offset is suppressed.

[0011]

According to the present invention, in order to achieve the above object, a light emitting section for emitting laser light, a diffraction grating for dividing the emitted laser light into a plurality of light beams, A hologram for irradiating a laser beam onto a disc and diffracting the reflected light from the disc to guide the light, and a light receiving unit for receiving the light diffracted by the hologram; It is characterized in that the amount of ± first-order diffracted light is made unbalanced. The hologram can be divided into two in the track direction of the disk, and one of them can be further divided into two in the radial direction of the disk. Further, the diffraction grating can be blazed. Further, the cross-sectional shape of the blazed diffraction grating can be made substantially stepwise.

Further, in the photodetector according to the first aspect of the present invention, of the plurality of beams divided by the diffraction grating, the reflected light of the ± primary light from the disk is diffracted by the hologram and enters. In the unit, the photodetectors that pass through the same pattern of the hologram having the pattern of + and are incident ± primary light are connected within the unit, and the photodetectors that pass through and analyze the + primary light of another hologram pattern are analyzed. Can be connected within the unit.

Further, in order to achieve the above object, a light emitting section for emitting a laser beam;
A diffraction grating that divides the emitted laser light into a plurality of parts, a hologram that irradiates the disk with a plurality of laser lights, diffracts reflected light from the disk to guide the light, and receives light diffracted by the hologram. And a light detector in which, among the beams divided into a plurality of parts by the diffraction grating, the reflected light of the ± primary light from the disk is diffracted by the hologram and enters, and the + primary light is The present invention is characterized in that the gain at the time of voltage conversion between the incident photodetector and the photodetector into which the primary light is incident is made different.

Further, in the invention according to claim 7,
In order to achieve the above object, the present invention is characterized by comprising an integrated unit according to claim 1 and lens means for converging laser light emitted from the integrated unit on a disk. Furthermore, in the invention described in claim 8, in order to achieve the above object, the integrated unit according to claim 6 and a lens means for condensing the laser light emitted from the integrated unit on a disk are provided. It is characterized by comprising. Here, the substantially stepped shape in the claims includes a shape that is recognized as a substantially stepped shape in addition to the stepped shape. The components of the claims can be combined with each other as far as possible.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an integrated unit 1 according to the present embodiment. It comprises a mounted LD chip 3, a photodetector 4, and a diffraction element 5 shown in FIG. The diffraction element 5 is placed on the opposite surface (the upper surface in FIG.
Is formed, and the LD chip 3 side (FIG. 1)
A diffraction grating 7 is formed on (the lower surface of). The role of the hologram 6 is that light emitted from the integrated unit 1 is reflected by the optical disk 24 (in this regard, see FIG. 10), returned to the integrated unit 1 again, diffracted by the hologram 6, and Incident on the surface.

The diffraction element 5 is formed using a transparent body such as various kinds of glass and resin. When the transparent material is glass, for example, quartz or soda glass is used. On the other hand, when the material of the transparent body is a resin, for example, an acrylic resin or the like is used. The diffraction element 5 includes a hologram 6 and a diffraction grating 7 facing each other, and is formed by various methods such as etching and molding. Light emitted from the LD chip 3 that is a light emitting unit enters the diffraction grating 7 of the diffraction element 5 and is split into three beams b1, b2, and b3 in FIG. here,
The beams b2 and b3 are ± first-order diffracted lights generated by the diffraction grating 7, and the light quantity of the beam b2 (+ first order)> beam b3
There is a (-primary) light quantity relationship.

The hologram 6 is formed as shown in FIG. In the figure, X is the track direction of the optical disk 24,
Y indicates the radial direction of the optical disk 24, and Z indicates the optical axis direction.
As shown in FIG. 3, the hologram 6 is formed in a circular shape at the center of the square diffraction element 5, for example, and is divided into three regions. That is, the hologram 6 is divided into two with respect to the Y axis, and only one side thereof is divided into two with respect to the X axis. The reflected light from the optical disk 24 is incident on the hologram 6, is divided into three, and is incident on the photodetector 4, and detects the control signal of the optical pickup device and the information signal on the optical disk 24. The reflected light detects a focus error signal in a semicircle in the A area, a track error signal in each quarter circle in the BC area, and detects an information signal from the entire ABC area.

The diffraction grating 7 is formed as shown in FIGS. 4 (a) and 4 (b). The diffraction grating 7 is formed in a circular shape or a rectangular shape at the center of a square diffraction element 5, for example, as shown in FIG. In order to make the ± first-order diffracted light unbalanced, the cross-sectional shape of the diffraction grating 7 should
As shown in an enlarged manner in FIG. 7A, a blaze (inclination) is formed, in other words, a plurality of substantially saw-tooth shapes are arranged in a horizontal row. That is, the diffraction grating 7 has, as shown in FIG.
In the case of a rectangular cross section, ± first-order diffracted light is uniformly generated. However, as shown in FIG. To When it is difficult to form the blaze, the diffraction grating 7 is formed in a plurality of steps arranged in a horizontal row as shown in FIG. In this case, the same effect as that of FIG. 5A can be obtained.

FIG. 7 shows the relationship between the state of the disk reflected light incident on the hologram 6 and the photodetector 4. Hologram 6
On the top, three beams b1 · 3 divided by the diffraction grating 7
b2 and b3 enter. As is clear from FIG. 7, for example, the + first-order diffracted light as the beam b2 is shifted below the center of the hologram 6, and the −first-order diffracted light as the beam b3 is shifted upward.

The photodetector 4 corresponding to the hologram 6 divided into three parts is composed of eight elements as shown in FIG. Of the disk reflected light (main beam), which is the beam b1, the diffracted light in the area A of the hologram 6 enters the element, the diffracted light in the area B of the hologram 6 enters the element, and the diffracted light in the area C of the hologram 6 enters the element. Also, of the disc reflected light (front sub-beam), which is the beam b3, the diffracted light in the BC area of the hologram 6 is directed to the element, and the diffracted light in the A area is outside the element (upper in the figure).
Incident on. Further, the disk reflected light which is the beam b2
Of the (rear sub beam), the diffracted light in the BC area of the hologram 6 is incident on the element, and the diffracted light in the A area is incident on the outside of the element (below in the figure). FES from element
Signal (focus error signal)
An ES signal (track error signal) and an RF signal from the element are detected.

As shown in FIG. 8, when outputting signals from all the eight divided elements of the photodetector 4, eight output terminals are required. The external size of the conversion unit 1 increases. Since the integrated unit 1 is generally required to be reduced in size and thickness, it is preferable that the number of output terminals is small. Therefore, as shown in FIG. 7, in the photodetector 4, if the elements and the elements are connected, the number of output terminals can be reduced to six,
This makes it possible to reduce the size and thickness of the integrated unit 1.

Here, the disk reflected light which is the beam b2
(+ First order diffracted light) and the disk reflected light (−
As shown in FIGS. 5 (a) and 6, the light amount ratio of the first-order diffracted light is blazed, and if the light amount ratio is optimally set, the element of the photodetector 4 and the incident light amount to the element are made the same. Becomes possible. As a result, DPP = (−) − α / 2 × ((−) + β × (−
)), It is possible to make β ≒ 1, so that DPP = (−) − α / 2 × ((−) + (−)) = (−) − α / 2 × ((+ )-(+)), The offset component does not remain due to the objective lens shift or tilt.

Next, an embodiment of the optical pickup device according to the present invention using the integrated unit 1 is shown in FIG. In the figure, light emitted from the integrated unit 1 is converted into substantially parallel light by a condensing lens 21 positioned in the horizontal and horizontal direction, the optical axis is converted by 45 ° by an adjacent 45 ° mirror 22, and the upper objective is changed. The light enters the lens 23. The objective lens 23 condenses the light on the signal surface of the upper optical disk 24 and reads the information signal.
The light returns to the integrated unit 1 via the 5 ° mirror 22 and the condenser lens 21, is diffracted by the hologram 6, enters the photodetector 4 in the unit, and detects an information signal.

According to the above configuration, an optical pickup device for a DVD or the like is constituted by using the integrated unit 1 of the present embodiment. Therefore, the optical pickup device is constituted by using minimum necessary optical parts. And no adjustment of the signal detection system is required at all. Therefore, the size and thickness can be extremely easily reduced, the assemblability and reliability can be remarkably improved, and an optical pickup device free from unnecessary offset when detecting a DPP signal can be obtained.

In the above embodiment, the diffraction grating 7 is blazed.
The method shown in FIG. In FIG. 9, light incident on the photodetector 4 is current-converted, and current-voltage converted by an integrated circuit incorporated in the integrated unit 1 and output. Here, the amplification gain at the time of conversion is changed according to each element,
In other words, if the amplification gain of the element is made larger than the amplification gain of the element, an effect equivalent to changing the amount of light incident on each element by the blaze can be obtained.

In the above embodiment, the infinite optical system using the condenser lens 21 has been described as an example.
A finite optical system in which 1 is omitted may be used. Although the optical path is converted by the 45 ° mirror 22 to reduce the thickness of the pickup device, a vertical optical system in which the 45 ° mirror 22 is omitted may be used. Further, if the optical pickup device is configured by using the integrated unit 1, the optical pickup device can be configured to be equivalent to that of FIG. By doing so, it is possible to extremely easily reduce the size and thickness of the optical pickup device, and to remarkably improve the assemblability and reliability, and to obtain an optical pickup device that does not generate an unnecessary offset when detecting a DPP signal.

[0027]

As described above, according to the present invention, there is an effect that a DPP signal in which occurrence of a track offset is suppressed can be detected. In addition, it is possible to reduce the size and thickness of the integrated unit and the optical pickup device, and it is also possible to improve their mass productivity and reliability.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an embodiment of an integrated unit according to the present invention.

FIG. 2 is an explanatory diagram showing a diffraction element mounted on the integrated unit of FIG.

FIG. 3 is an explanatory view showing a hologram formed on one surface of the diffraction element of FIG. 2;

FIG. 4 is an explanatory view showing a diffraction grating formed on one surface of the diffraction element of FIG. 2;

FIG. 5 is an explanatory sectional view showing the diffraction grating of FIG. 4;

FIG. 6 is an explanatory sectional view showing another example of the sectional shape of the diffraction grating of FIG. 4;

FIG. 7 is an explanatory diagram showing a hologram and a photodetector in an embodiment of the integrated unit according to the present invention.

FIG. 8 is an explanatory view showing a photodetector in a conventional integrated unit.

FIG. 9 is an explanatory diagram showing a photodetector in the integrated unit in the embodiment of the integrated unit according to the present invention.

FIG. 10 is an explanatory diagram showing an optical pickup device equipped with an integrated unit according to the present invention.

FIG. 11 is an explanatory diagram showing a relationship between a hologram pattern mounted on a conventional integrated unit and reflected light from a disc.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Integrated unit 2 Stem 3 LD chip (light-emitting part) 4 Photodetector (light-receiving part) 5 Diffraction element 6 Hologram 7 Diffraction grating 21 Condensing lens 22 45-degree mirror 23 Objective lens 24 Optical disk (disk) b1 beam b2 beam b3 beam

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Miki Renzaburo 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Hiroshige Hirashima 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka (72) Inventor Noboru Fujita No. 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka F-term in Sharp Corporation (reference) 5D119 AA02 AA29 AA38 BA01 CA09 DA01 DA05 FA02 FA08 JA23 LB05

Claims (8)

[Claims] 1. A light emitting section for emitting laser light, a diffraction grating for dividing the emitted laser light into a plurality of parts, a plurality of laser lights irradiating a disk, and diffracted light reflected from the disk to convert the light. An integrated unit comprising a guiding hologram and a light receiving unit for receiving light diffracted by the hologram, wherein an amount of ± first-order diffracted light diffracted by a diffraction grating is imbalanced. And an integrated unit. 2. The integrated unit according to claim 1, wherein the hologram is divided into two in the track direction of the disk, and one of the two is further divided into two in the radial direction of the disk. 3. The integrated unit according to claim 1, wherein the diffraction grating is blazed. 4. The integrated unit according to claim 3, wherein the cross-sectional shape of the blazed diffraction grating is substantially stepped. 5. The photodetector according to claim 1, wherein, of the plurality of beams divided by the diffraction grating, reflected light of ± primary light from the disk is diffracted by the hologram and enters. In the unit, the photodetectors that pass through the same pattern of a hologram having a plurality of patterns and are incident ± primary light are connected to each other in the unit, and the light detection where the ± primary light that is analyzed by passing another hologram pattern is incident An integrated unit in which units are connected within the unit. 6. A light emitting section for emitting laser light, a diffraction grating for dividing the emitted laser light into a plurality of parts, and irradiating a disk with a plurality of laser lights and diffracting light reflected from the disk to convert the light. In an integrated unit that includes a hologram to be guided and a light receiving unit that receives light diffracted by the hologram, of the beams divided into a plurality of pieces by the diffraction grating, the reflected light of the ± primary light from the disk is reflected by the hologram. A photodetector diffracted and incident, wherein the amplification factor at the time of voltage conversion between a photodetector to which + primary light is incident and a photodetector to which-primary light is incident is made different. Integrated unit. 7. An optical pickup device comprising: the integrated unit according to claim 1; and lens means for converging laser light emitted from the integrated unit onto a disk. 8. An optical pickup device comprising: the integrated unit according to claim 6; and lens means for converging laser light emitted from the integrated unit onto a disk.