JPH05128577A - Optical pickup - Google Patents

Abstract

PURPOSE:To provide an optical pickup for three beams which can be thin with a small number of parts and inexpensive. CONSTITUTION:The light emitted from a light source 22 is separated to one main beam and two sub beams by a grating 26a of an optical element 26. The beams are reflected in a direction approximately parallel to a recording medium 29 by a reflecting surface 26c of the optical element 26. Thereafter, the beams are reflected approximately in a direction of normal line of the recording medium 29 by a reflecting member 27 and condensed on the recording medium 29 by a converging optical system 28. The returning light reflected by the recording medium 29 is, through the converging optical system 28 and the reflecting member 27, diffracted by a hologram surface 26b formed in the optical element 26. The + or - first-order diffracted light is detected by photodetecting parts 23, 24 on a same substrate 21 as the light source 22 through the reflecting surface 26c of the optical element 26.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used in a recording / reproducing apparatus for recording / reproducing information on / from an optical information recording medium such as an optical disc.

[0002]

2. Description of the Related Art As a conventional optical pickup, for example, the one shown in FIG. 4 has been proposed in Japanese Patent Application Laid-Open No. 2-141936. In this optical pickup, a package 2 on which a light emitting and receiving composite element 1 having a semiconductor laser and a photodetector is mounted is provided on a lens bobbin 3, and a light beam from the semiconductor laser is provided on the lens bobbin 3. The optical disk 7 is irradiated with the objective lens 6 held by the lens bobbin 3 through the mirrors 4 and 5 of the optical axis, and the reflected light thereof passes through the objective lens 6, the second and first mirrors 5 and 4 and By receiving light with a photodetector,
An information signal, a focus error signal, and a tracking error signal are obtained with one light beam.

In the optical pickup shown in FIG. 4, the light emitting and receiving composite element 1 is arranged on a surface substantially parallel to the optical disk 7, and the first and second mirrors are provided between the light emitting and receiving composite element 1 and the objective lens 6. Since they are optically coupled via 4 and 5, there is an advantage that the entire structure can be made thin.

[0004]

On the other hand, the present applicant has proposed an optical pickup using three beams as shown in FIG. 5 in Japanese Patent Application No. 3-21492. In this optical pickup, as shown in the plan view and the sectional view in FIGS. 6A and 6B, the semiconductor laser 1 is mounted on the semiconductor substrate 11.
2 is mounted, and the photodetectors 13 and 14 are provided on both sides of the optical path of the emitted light from the semiconductor laser 12 as a boundary.
Is formed. Light is emitted from the semiconductor laser 12 in a direction parallel to the substrate 11, and is reflected by a rising mirror 15 provided on the substrate 11, and then a hologram element 16 is provided.
And irradiate the recording medium 18 through the objective lens 17, and the reflected light (return light) is made incident on the hologram element 16 through the objective lens 17 to generate ± first-order diffracted lights that generate powers in opposite directions, These ± first-order diffracted lights are received by the photodetectors 13 and 14.

In the hologram element 16, a grating is formed on the surface facing the semiconductor substrate 11, and a hologram is formed on the other surface. The hologram element 16 is emitted from the semiconductor laser 12, passes through the raising mirror 15, and is a hologram element. The light incident on 16 is separated into three beams of one main beam and two sub-beams for tracking error detection by the grating, and the hologram of these three beams is transmitted as 0th-order light. The beam is projected onto the recording medium 18 by the objective lens 17. Of the return light from the recording medium 18, the three beams incident on the hologram generate ± first-order diffracted lights that generate powers in mutually opposite directions, and the + first-order diffracted lights thereof are Each of the first-order diffracted lights is received by the photodetector 14.

The photo-detecting section 13 has three photo-detectors 13a, 13b, 1 so as to receive the + first-order diffracted light of the three beams.
The photodetector 13b configured to have the main beam in the center is constituted by 3c, and the photodetector 13b is divided into three light receiving regions 13d, 13 having a dividing line in the diffraction direction of the hologram element 16.
e, 13f. Similarly, the light detector 14
Is composed of three photodetectors 14a, 14b, and 14c so as to receive each -1st-order diffracted light of three beams, and the photodetector 14b which receives the central main beam is
The hologram element 16 is composed of three divided light receiving regions 14d, 14e and 14f having a dividing line in the diffraction direction.

In this way, the light receiving regions 13d, 13 of the photodetector 13b for receiving the + 1st order diffracted light of the main beam.
The focus error signal is detected by the beam size method based on the outputs of e and 13f and the outputs of the light receiving regions 14d, 14e, and 14f of the photodetector 14b that receives the −1st-order diffracted light. A tracking error signal is obtained based on the outputs of the photodetectors 13a and 13c that receive the + 1st-order diffracted light and the outputs of the photodetectors 14a and 14c that receive the -1st-order diffracted light.

According to such an optical pickup, when the wavelength of the light emitted from the semiconductor laser 12 changes, the diffraction angle of the ± first-order diffracted light in the hologram pattern region 16b changes, and the light on the photodetectors 13b and 14b is changed. Although the spot moves, its moving direction is parallel to the dividing line of the photodetectors 13b and 14b, so that the focus error signal is less susceptible to the wavelength change. Further, even if the spots on the photodetectors 13b and 14b are deviated due to component processing error or assembly error, etc., the ± 1st order diffracted light causes the same deviation, so that the + 1st order diffracted light obtained from the photodetector 13b is focused. By taking the difference between the error signal and the focus error signal of the −first-order diffracted light obtained from the photodetector 14b, the offset of each focus error signal can be canceled, and an accurate focus error signal can be obtained. There is.

However, as shown in FIG. 5, in the structure in which the substrate 11 is arranged in parallel with the recording medium 18 and the laser beam is applied to the recording medium 18 through the hologram element 16 and the objective lens 17, the optical The pickup cannot be thin. In order to make this thin, as shown in FIG. 7, the semiconductor substrate 11 is arranged on a plane (xy plane) parallel to the optical axis of the objective lens 17, and the light beam from the semiconductor laser 12 is launched. The mirror 15 reflects the light in the horizontal direction (z direction), and the folding mirror 19 is arranged between the hologram element 16 and the objective lens 17, whereby the light beam is reflected in the x direction and passes through the objective lens 17 and the recording medium. 18
It is conceivable to have a configuration of projecting on.

However, in this optical pickup, four wires for detecting the focus error signal, two wires for detecting the tracking error signal, and three wires for driving the semiconductor laser 12 are required for a total of nine wires. It is necessary to form the land portion on the substrate 11. Therefore, there is a problem that the area occupied by the land and the like becomes large and the substrate 11 becomes large in the x and y directions, which hinders the thinning and downsizing of the optical pickup.

As a method for solving this problem, as in FIG. 4, the substrate 11 is arranged on a plane substantially parallel to the recording medium 18, and the substrate 11 and the objective lens 17 are optically coupled via two folding mirrors. Coupled to the substrate 11
In the optical path between the objective lens 17 and the hologram element 16
It is conceivable that the arrangement of However, with such a configuration, since the two folding mirrors and the hologram element 16 are arranged between the substrate 11 and the objective lens 17, the number of parts increases and the cost increases, and the hologram element also occurs. When 16 is arranged between the substrate 11 and the first folding mirror, there arises a problem that the two interfere with each other and the effect of thinning cannot be obtained.

The present invention has been made in view of the above-mentioned various problems, and an object thereof is to provide an optical pickup for three beams which is thin, has a small number of parts, and is appropriately configured so as to be inexpensive. To do.

[0013]

In order to achieve the above object, according to the present invention, a substrate having a light source and a light detecting portion and arranged on a plane substantially parallel to a recording medium, and the light from the light source are recorded. An optical element having a grating for separating one main beam for reading information on the medium and two sub-beams for detecting a track deviation of the recording medium, and an optical element formed on this optical element and separated by the grating. A reflecting surface that reflects the three beams in a direction substantially parallel to the recording medium, a reflecting member that reflects the beam reflected by the reflecting surface in a direction substantially normal to the recording medium, and a reflecting member that reflects the beam. A converging optical system that condenses a beam on a recording medium, and diffracts return light from the recording medium that is formed on the optical element and that enters through the converging optical system and a reflecting member, and 1 next time diffracted light through the reflecting surface provided with the hologram surface to be incident on the light detecting unit.

[0014]

In the above structure, the light emitted from the light source is
After being separated into one main beam and two sub beams by the grating of the optical element, the light is reflected in a direction substantially parallel to the recording medium by the reflecting surface formed on the optical element. After that, the light is reflected by the reflecting member substantially in the normal direction of the recording medium, and is converged on the recording medium by the converging optical system. Further, the return light reflected by the recording medium passes through the converging optical system and the reflecting member, is diffracted by the hologram surface formed on the optical element, and the ± first-order diffracted light passes through the reflecting surface formed on the optical element, The light is received by the photodetector on the same substrate as the light source.

[0015]

1 shows an embodiment of the present invention. In this embodiment, a semiconductor laser 22 is mounted on a semiconductor substrate 21 as shown in a plan view and a cross-sectional view in FIGS. 2A and 2B, and light is emitted on both sides of an optical path of light emitted from the semiconductor laser 22 as a boundary. A rising mirror 25 provided on the substrate 21 for forming the detectors 23 and 24 and emitting light emitted from the semiconductor laser 22 in a direction parallel to the substrate 21.
After being reflected by the recording medium 2 through the optical element 26, the folding mirror 27 and the objective lens 28 as shown in FIG.
Project to 9. Further, the reflected light from the recording medium 29 passes through the objective lens 28 and the folding mirror 27, and the optical element 2
6 and make the powers in the opposite directions ±
First-order diffracted light is generated, and the ± first-order diffracted lights are received by the photodetectors 23 and 24.

The semiconductor substrate 21 is mounted on the plane of the pickup that is substantially parallel to the recording medium 29, and the semiconductor laser 22 is attached.
The emitted light from the mirror is reflected by the rising mirror 25 in a direction substantially normal to the recording medium 29 and is incident on the optical element 26. As shown in FIG. 3A, the optical element 26 has a grating 26 a on the semiconductor substrate 21 side and a folding mirror 27.
On the side, as shown in FIG. 3B, the hologram pattern area 26
b is formed respectively, and a mirror surface 26c is formed between the grating 26a and the hologram pattern area 26b.

In this way, the light emitted from the semiconductor laser 22, incident on the optical element 26 through the raising mirror 25, is recorded by the grating 26a as one main beam for recording / reproducing and focus detection and tracking. It is separated into three beams of two sub beams for error detection, and these three beams are reflected by the mirror surface 26c in a direction substantially parallel to the recording medium 29 so that the hologram pattern region 2
6b to make the hologram pattern region 26b 0.
The three beams transmitted as the next light are reflected by the folding mirror 27 in a direction substantially normal to the recording medium 29, and the objective lens 28
And then projected onto the recording medium 29. Further, the three beams of return light reflected by the recording medium 29 and incident on the optical element 26 via the objective lens 28 and the folding mirror 27 generate ± first-order diffracted lights having mutually opposite powers in the hologram pattern region 26b. , Mirror them 26c
After that, the + 1st-order diffracted light is received by the photodetector 23, and the -1st-order diffracted light is received by the photodetector 24.

As shown in FIG. 2A, the photodetector 23
Are three photodetectors 23a, so as to receive each + first-order diffracted light by the three-beam hologram pattern area 26b.
The photodetector 23b for receiving the central main beam is constituted by three light receiving regions 23d, 23e, 23f having a dividing line in the diffraction direction in the hologram pattern region 26b. Similarly, the photodetection section 24 is configured with three photodetectors 24a, 24b, and 24c so as to receive each −1st-order diffracted light by the three-beam hologram pattern area 26b, and at the same time, the light that receives the central main beam is received. Detector 24b
Is a light receiving region 24d, 24e, 24f divided into three having a dividing line in the diffraction direction in the hologram pattern region 26b.
Configure with.

In this way, in this embodiment, the outputs of the light receiving regions 23d, 23e, 23f of the photodetector 23b for receiving the + 1st order diffracted light of the main beam are set to A1, A2, A.
When the outputs of the light receiving regions 24d, 24e, and 24f of the photodetector 24b receiving the 3rd and -1st order diffracted light are A4, A5, and A6, the focus error signal FE is

## EQU1 ## FE = (A1 + A3 + A5)-(A2 + A4 + A6) In addition, the tracking error signal TE of the irradiation beam with respect to the track of the recording medium 29 is the photodetector 23a that receives the + 1st order diffracted light of the two sub-beams.
Let B1 and B2 be the outputs of 23c and B3 and B4 be the outputs of photodetectors 24a and 24c that receive the −1st order diffracted light.

[Equation 2] TE = (B1 + B3) − (B2 + B4)

In the above embodiment, the semiconductor substrate 2
Although 1 and the optical element 26 are provided separately, they may be provided integrally via a spacer.

[0021]

As described above, according to the present invention, in addition to the reflecting member disposed under the converging optical system, the optical element having the grating, the hologram surface and the reflecting surface formed between them is used for the pickup. Since this is configured, an inexpensive and thin optical pickup having a small number of parts can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an arrangement of the semiconductor laser and a photodetector shown in FIG.

3 is a diagram showing a structure of a grating and a hologram pattern region of the optical element shown in FIG.

FIG. 4 is a diagram for explaining a conventional technique.

FIG. 5 is a diagram showing a configuration of an optical pickup previously developed by the present applicant.

FIG. 6 is a diagram showing the arrangement of the semiconductor laser and photodetector shown in FIG.

FIG. 7 is a diagram showing a configuration example when the optical pickup shown in FIG. 5 is thinned.

[Explanation of symbols]

21 Semiconductor Substrate 22 Semiconductor Laser 23, 24 Photodetector 23a, 23b, 23c, 24a, 24b, 24c Photodetector 23d, 23e, 23f, 24d, 24e, 24f Photoreceptive Area 25 Raising Mirror 26 Optical Element 26a Grating 26b Hologram pattern area 26c Mirror surface 27 Folding mirror 28 Objective lens 29 Recording medium

Claims (1)

[Claims] 1. A substrate having a light source and a light detection unit and arranged on a surface substantially parallel to a recording medium, and light from the light source,
An optical element having a grating for separating one main beam for reading information on the recording medium and two sub-beams for detecting track deviation of the recording medium, and an optical element formed on this optical element and separated by the grating A reflecting surface that reflects the three reflected beams in a direction substantially parallel to the recording medium, a reflecting member that reflects the beam reflected by the reflecting surface in a direction substantially normal to the recording medium, and a reflecting member that reflects the beam. A convergent optical system for converging the beam on a recording medium and the return light from the recording medium which is formed in the optical element and which enters through the converging optical system and the reflecting member, and diffracts the ± first-order diffracted light. An optical pickup comprising: a hologram surface that is incident on the photodetection unit via the reflection surface.