JP3108976B2 - Optical head tracking error detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking error detecting device for an optical head used in an optical recording device and a reproducing device.

[0002]

2. Description of the Related Art In recent years, as shown in JP-A-64-35737, an optical head in which a light source and a photodetector are integrated has been proposed. 14 and 15 show a perspective view of the optical head and a conceptual diagram of the optical system. As shown in FIG. 14, the optical head device 1a has first and second regions having five regions on a first semiconductor substrate 2 and a second semiconductor substrate 8.
Are formed, and the second semiconductor substrate 8 is mounted on the first semiconductor substrate 2. A semiconductor laser element (hereinafter, referred to as a semiconductor laser chip) 5 is mounted on the second semiconductor substrate 8, and a light receiving element 4 for monitoring is formed.

A prism is provided on the first semiconductor substrate 2.
11 are installed. The prism 11 has a substantially trapezoidal cross section, the inclined surface 11a serves as a mirror, and the vertical surface 11b faces the emission surface of the semiconductor laser chip 5 mounted on the second semiconductor substrate 8. The upper surface 11c of the prism 11 is the first diffraction grating 1
It is two. Above the first diffraction grating 12, a second diffraction grating 13 is arranged.

The operation of the semiconductor laser chip 5 shown in FIG. 14 will now be described. A beam emitted from the semiconductor laser chip 5 is reflected by a slope 11a of a prism 11 and is incident on a first diffraction grating 12.
The beam is divided into a zero-order beam for reading information and ± first-order beams for detecting a tracking error signal.
Next, the light is transmitted and focused on the disk 19 by the objective lens 18 shown in FIG. 0th order and ± 1
The next beam is reflected by the disk 19, passes through the objective lens 18, enters the second diffraction grating 13, is divided into ± first-order lights, and is guided to the first and second light receiving elements 9 and 10.

Here, the first and second light receiving elements 9, 10
As shown in the cross-sectional view of the optical head in Fig. 16, the light head is located before and after the light-collecting position, and utilizes the fact that the spot sizes on the light-receiving element change with each other as the focal point of the disk changes. Then, focus error detection is performed by the beam size method. The tracking error is detected by a three-beam method using ± first-order beams for detecting a tracking error signal generated in the first diffraction grating 12.

In the optical head in which the above-mentioned light source and photodetector are integrated, if the semiconductor laser chip 5 and the prism 11 are arranged close to each other, the disk 19
One of the ± first-order beams for detecting the tracking error signal reflected at the second order passes through the second diffraction grating 13 in the 0th order, is incident on the surface of the semiconductor laser chip 5 facing the second diffraction grating 13 and is reflected. You will return to the disk again. As described above, when the ± primary beam for detecting the tracking error signal reflected by the disk enters the vicinity of the light emitting element and is reflected there and returns to the disk again, the beam and the ± primary beam for detecting the tracking error signal are detected. It is known that the primary beam causes interference and the tangential skew of the disk causes an offset in the tracking error signal.
61-24031. Also, JP-A-61-240
In Japanese Patent Publication No. 31 proposes a method of providing a light shield for scattering or absorbing light on the emission end face of the semiconductor laser element as a measure against this.

[0007]

As mentioned above, the light source,
When an optical head having an integrated photodetector is miniaturized, an offset occurs in a tracking error signal due to tangential skew of a disk. In addition, JP-A-61-24
No. 031 discloses a method of providing a light shield for scattering or absorbing light on the emission end face of the semiconductor laser element, but in a small optical head in which the above-described light source and photodetector are integrated, a disk is used. One of the reflected ± first-order beams for detecting a tracking error signal passes through the second diffraction grating 13 in the 0th order, and sandwiches the surface of the semiconductor laser chip 5 facing the second diffraction grating 13 and / or the mirror. Therefore, since the light is incident on the surface opposite to the diffraction grating on the side opposite to the semiconductor laser chip 5, the light shielding body that scatters or absorbs light is provided on the emission end surface of the semiconductor laser chip as described above, thereby preventing interference. Can not get.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a tracking error detecting device for an optical head which integrates a light source and a photodetector and obtains a small and stable tracking error signal. I do.

[0009]

According to the present invention, there is provided a light beam reflected by a mirror which is close to a semiconductor laser element and reflects a laser beam emitted from the semiconductor laser element to deflect an optical path. Has a diffraction grating made incident thereon, and converges the 0th-order and ± 1st-order light beams of the diffraction grating emitted from the deflecting optical element, through which the 0th-order ± 1st-order light beams emitted from the diffraction grating are passed, to an optical recording medium. An objective lens, and the 0th-order and ± 1st-order light beams of the diffraction grating reflected by the optical recording medium pass through the objective lens, enter the deflection optical element, and are deflected by the deflection optical element. A photodetector for receiving the light beam, obtaining an optical output corresponding to the ± primary light beam from the photodetector, and obtaining a tracking error signal based on a difference between outputs corresponding to the ± primary light beams. In the tracking error detecting device for an optical head, at least one of the ± first-order light beams reflected by the optical recording medium and passing through the objective lens, the deflecting optical element, and the diffraction grating is the same as described above. Without passing through a mirror, the light is incident on the surface of the semiconductor laser device facing the diffraction grating and / or on the surface facing the diffraction grating on the side opposite to the semiconductor laser device with the mirror interposed therebetween. Are configured to scatter or absorb light.

[0010]

According to the tracking error detecting device for an optical head of the present invention, the sub-beam generated by the diffraction grating 36a of FIG. 3 is reflected by the disk 38, passes through the objective lens 37, and passes through the hologram 36b and the diffraction grating 36a in the 0th order. The light passes through and enters the surface of the semiconductor laser chip 32 facing the transmission optical element 36. By making the incident area scatter or absorb light, interference can be prevented, and therefore, occurrence of an offset in the tracking error signal due to the tangential skew of the disk can be eliminated.

[0011]

【Example】

(Embodiment 1) FIG. 1 is a front view showing an arrangement of a semiconductor laser chip and a photodetector of an optical head according to a first embodiment of the present invention. FIG. It is -A sectional drawing.

As shown in FIGS. 1 and 2, a semiconductor substrate
On the photodetector 31, photodetectors 33 and 34 each composed of five regions are provided.
Then, an etching mirror 35 formed by chemically anisotropic etching of the semiconductor substrate 31 is formed, and the semiconductor laser chip 32 is mounted near the etching mirror 35.

A feature of this embodiment is that a wire 39 is bonded to an electrode surface 40 of the semiconductor laser chip 32 to form a wire bonding portion 41.

Next, the operation will be described with reference to the schematic diagrams of the optical head tracking error detecting device shown in FIGS. 1, 2 and 3, and the diffraction grating and hologram of the optical head shown in FIG.

The beam emitted from the semiconductor laser chip 32 is reflected by an etching mirror 35 as shown by an arrow in FIG. 2, and a diffraction grating formed on the lower surface of the transmission optical element 36 shown in FIGS. The hologram 36b is incident on the lens 36a and diffracted, and is divided into a main beam for reading information and two sub-beams for tracking error detection. Converged to 38. The converged light is reflected by the disk 38, passes through the objective lens 37, enters the hologram 36b, is diffracted, is divided into ± first-order lights, and is guided to the photodetectors 33 and 34.

The tracking error signal is transmitted to the disk 38.
The sub-beams generated by the diffraction grating 36a reflected by are detected by the photodetectors 33a, 33c, 34a and 34c shown in FIG.
By taking the difference in intensity between the sub beams, the so-called three-beam method is used. Therefore, the photodetectors 33a, 33c, 34
Assuming that the outputs of a and 34c are G, H, I, and J, the tracking error signal TE can be obtained by TE = (G + I)-(H + J).

In FIG. 1 to FIG.
The incident light flux 42a of one of the sub-beams generated by the diffraction grating 36a passes through the objective lens 37, passes through the hologram 36b and the diffraction grating 36a at the 0th order, and passes through the transmission type optical element 36 of the semiconductor laser chip 32. The light enters the opposing electrode surface 40. The wire 39 for supplying power to the semiconductor laser chip 32 is bonded to the incident area of the electrode surface 40 which is the P or N-type electrode surface of the semiconductor laser chip 32 as described above. The wire 39 may be bonded anywhere on the electrode surface 40, considering only the function of power supply.

Usually, bonding is performed near the center. However, in the case of the present embodiment, as shown in FIG. 2, by aligning the wire bonding portion 41 with the region where the incident light beam 42a is incident, the incident light beam 42a is reflected in the dome shape of the wire bonding portion 41 and the scattered light 43a is reflected. Becomes

The scattered light 43 is larger than the incident light flux 42a.
Since the divergence angle is very large, the amount of scattered light 43 passing through the objective lens 37 and returning to the disk 38 again becomes almost zero. Therefore, the incident light beam 42a is reflected by the electrode surface 40 of the semiconductor laser chip 32 facing the transmission optical element 36, and the amount of light returning to the disk 38 is very small, thereby preventing the interference which has been a problem in the conventional example. be able to.

In the tracking error detecting device, when the focus error is detected, the hologram 36b
Is configured to give irregular lens power to the ± 1st order light, respectively, the spots incident on the photodetectors 33 and 34 have focal positions before and after the photodetectors 33 and 34, and the disc is defocused. Focus error detection is performed using the fact that the sizes of the spots on the photodetector at this time change in opposite directions. Therefore, the photodetectors 33d, 33e, 33
The outputs of f, 34d, 34e, 34f are A, B, C, D,
Assuming that E and F, the focus error signal FE can be obtained by FE = (A + C + E)-(B + D + F).

In the present embodiment, as described above, the sub-beam which causes interference to be incident on the semiconductor laser chip 32 is scattered by wire bonding. However, the means for scattering or absorbing the incident light is not limited to this. The same effect can be obtained by such means.

(1) As shown in the cross-sectional view of FIG. 5, a non-reflective coating portion 101a is formed on the incident surface of the sub-beam on the semiconductor laser chip 32 to prevent reflection.

(2) As shown in the sectional view of FIG. 6, a dome-shaped convex portion 102a is formed on the incident surface of the sub-beam on the semiconductor laser chip 32, and the incident light is scattered or absorbed in the convex portion. As a means for realizing such a structure, it can be constituted by potting a resin or performing wire bonding separately from power supply.

(3) As shown in the sectional view of FIG. 7, a prism-shaped convex portion 103a is formed on the incident surface of the sub-beam on the semiconductor laser chip 32 to scatter incident light (reflect in a direction without influence). Alternatively, it is absorbed in the convex portion. As means for realizing such a structure, it can be constituted by bonding a fine prism on the semiconductor laser chip 32 or etching the semiconductor laser chip 32 itself.

(4) As shown in the cross-sectional view of FIG. 8, a lattice-like uneven portion 104a (A is an enlarged view) is formed on the incident surface of the sub-beam on the semiconductor laser chip 32, and the incident light is diffracted and scattered. Let it. As a means for realizing such a structure, the semiconductor laser chip 32 can be configured by fixing a plate on which a lattice-shaped uneven portion has been formed in advance on the semiconductor laser chip 32 or by etching the semiconductor laser chip 32 itself in a lattice.

(5) As shown in the sectional view of FIG. 9, the semiconductor laser chip 32 is tilted and fixed to form an inclined portion 105a.
The incident light is scattered (reflected in an unaffected direction). As a means for realizing such a structure, when the semiconductor laser chip 32 is fixed, the solder layer is melted and solidified while the semiconductor laser chip 32 is tilted, or the semiconductor laser chip is interposed via a triangular spacer 106. It can be configured by fixing 32.

(6) As shown in the cross-sectional view of FIG. 10, the incident light is scattered by forming a ground glass-like rough surface portion 107a on the incident surface of the sub-beam on the semiconductor laser chip 32. As a means for realizing such a structure, a plate having a rough surface formed in advance is
Fixed on the top, apply a rough coating to the semiconductor laser chip 32 itself, or
It is configured by etching itself (for example, a gold thin film is roughened by etching with an iodine solution).

(Embodiment 2) FIG. 11 is a front view showing an arrangement of a semiconductor laser chip and a photodetector of an optical head according to a second embodiment of the present invention, and FIG. 12 is a semiconductor laser chip of the optical head shown in FIG. It is AA sectional drawing of a mount part.

The feature of this embodiment is that, as shown in FIGS. 11 and 12, an anti-reflection coating portion 51 is provided immediately above a semiconductor laser chip 32 mounted on a semiconductor substrate 31. In addition, etching mirror 35, 4
The photodetectors 33 and 34 composed of three regions are the same as those in the first embodiment.

The operation based on the above configuration will be described. The beam emitted from the semiconductor laser chip 32 is reflected by the disk 38 shown in FIG. 3, enters the hologram 36b through the objective lens 37, is diffracted, and ± 1 order light Photodetector 3
3, 34, and the tracking error signal T
The operation for obtaining E is the same as in the first embodiment.

In the present embodiment, one incident light beam 42b of the sub-beam generated by the diffraction grating 36a reflected by the disk 38 (the sub-beam on the side opposite to the first embodiment).
Passes through the objective lens 37 and passes through the hologram 36b and the diffraction grating 36a.
Through the zeroth order, and a transmission optical element 36 on the opposite side of the etching mirror 35 from the semiconductor laser chip 32.
Is incident on the surface 50 facing the. Since the anti-reflection coating portion 51 is applied to the incident area of the incident light beam 42b as shown in FIGS. 11 and 12, the incident light beam 42b is absorbed by the semiconductor substrate 31, so that the light is reflected. Thus, the amount of light returning to the disk 38 through the objective lens 37 is substantially zero. Therefore, the incident light beam 42b faces the transmission optical element 36 on the side opposite to the semiconductor laser chip 32 with the etching mirror 35 interposed therebetween.
And the amount of light reflected back to the disk 38 is very small, so that interference which has been a problem in the conventional example can be prevented.

Further, a focus error signal FE for detecting a focus error in the tracking error detection device.
The operation by the photodetector for obtaining the same is the same as in the first embodiment.

In this embodiment, as described above, the semiconductor substrate 31
Although the sub-beam causing the interference incident on the sub-beam is absorbed by the non-reflection coating portion 51, the means for scattering or absorbing the incident light is not limited to this, and the same effect can be obtained by the following means.

(1) As shown in the sectional view of FIG. 13, a wire bonding portion is
41 is formed, and the light incident in the dome shape of the wire bonding portion 41 is diffracted and scattered.

(2) As shown in the sectional view of FIG. 5, the anti-reflection coating 10
Construct 1b so that it does not reflect.

(3) As shown in the sectional view of FIG. 6, a dome-shaped convex portion 102b is formed on the incident surface of the sub-beam on the semiconductor substrate 31, and the incident light is scattered or absorbed in the convex portion.
As a means for realizing such a structure, it can be constituted by potting a resin or performing wire bonding separately from power supply.

(4) As shown in the sectional view of FIG. 7, a prism-shaped convex portion 103b is attached to the incident surface of the sub-beam on the semiconductor substrate 31 to scatter incident light (reflect in a direction having no influence) or Absorb in the convex part. As means for realizing such a structure, it can be configured by bonding a fine prism on the semiconductor substrate 31 or etching the semiconductor substrate 31 itself.

(5) As shown in the cross-sectional view of FIG. 8, a lattice-shaped uneven portion 104b (A
Is an enlarged view) and diffracts and scatters the incident light.
As a means for realizing such a structure, it can be configured by fixing a plate on which a lattice-shaped uneven portion is formed in advance on the semiconductor substrate 31 or by etching the semiconductor substrate 31 itself in a lattice.

(6) As shown in the sectional view of FIG. 9, an inclined portion 105b is formed on the sub beam incident surface itself on the semiconductor substrate 31,
The incident light is scattered (reflected in an unaffected direction). As a means for realizing such a structure, it can be configured by etching the semiconductor substrate 31 itself.

(7) As shown in the cross-sectional view of FIG. 10, the incident light is scattered by forming a ground glass-like rough surface portion 107b on the incident surface on the semiconductor substrate 31. As a means for realizing such a structure, a plate having a rough surface formed in advance is fixed on the semiconductor substrate 31, a rough coating is applied to the semiconductor substrate 31 itself, or the semiconductor substrate 31 itself is etched (for example, gold). The thin film is roughened by etching with an iodine solution).

In this embodiment, the semiconductor substrate is used as the mirror. However, the same effect can be obtained when the mirror is made of another material (glass, metal, ceramic, etc.).

[0042]

As described above, the tracking error detecting device for an optical head according to the present invention is an optical head having a light source and a photodetector integrated and miniaturized in the following two light beams: (1) The sub-beam generated by the diffraction grating is reflected by the disc, passes through the objective lens, passes through the hologram and the diffraction grating in the 0th order, and is incident on the surface of the semiconductor laser chip facing the transmission optical element. (2) Diffraction grating The sub-beam generated in step (1) is reflected by the disk, passes through the objective lens, passes through the hologram and diffraction grating at the 0th order, and is incident on the surface opposite to the transmission type optical element opposite to the semiconductor laser chip with the etching mirror interposed therebetween. These lights prevent the conventional problem of interference by causing the light to scatter or absorb in the incident area where they enter, thus reducing the disc Eliminate the occurrence of the offset of the emission tangential skew by the tracking error signal, it is possible to obtain a stable tracking error signal.

[Brief description of the drawings]

FIG. 1 is a front view showing an arrangement of a semiconductor laser chip and a photodetector of an optical head according to a first embodiment of the present invention.

FIG. 2 is a sectional view of the semiconductor laser chip mount portion of the optical head of FIG. 1 taken along the line AA.

FIG. 3 is a schematic diagram of the tracking error detection device for the optical head shown in FIG. 1;

FIG. 4 is a diagram showing a diffraction grating and a hologram of the optical head shown in FIG.

FIG. 5 is a sectional view showing a configuration of a semiconductor laser chip and a photodetector of an optical head according to first and second embodiments of the present invention.

FIG. 6 is a cross-sectional view showing a configuration around a semiconductor laser chip of the optical head according to the first and second embodiments of the present invention.

FIG. 7 is a sectional view showing a configuration around a semiconductor laser chip of the optical head according to the first and second embodiments of the present invention.

FIG. 8 is a sectional view showing a configuration around a semiconductor laser chip of an optical head according to the first and second embodiments of the present invention.

FIG. 9 is a sectional view showing a configuration around a semiconductor laser chip of the optical head according to the first and second embodiments of the present invention.

FIG. 10 is a sectional view showing a configuration around a semiconductor laser chip of the optical head according to the first and second embodiments of the present invention.

FIG. 11 is a front view showing an arrangement of a semiconductor laser chip and a photodetector of an optical head according to a second embodiment of the present invention.

12 is a sectional view of the semiconductor laser chip mount portion of the optical head shown in FIG. 11 taken along line AA.

FIG. 13 is a cross-sectional view showing a configuration around a semiconductor laser chip of an optical head according to a second embodiment of the present invention.

FIG. 14 is a perspective view of a conventional optical head.

FIG. 15 is a conceptual view of a conventional entire optical system.

FIG. 16 is a cross-sectional view of the optical head of FIG.

[Explanation of symbols]

31 ... Semiconductor substrate, 32 ... Semiconductor laser chip, 33,
34 photodetector 35 etching mirror 36 transmission optical element 36a diffraction grating 36b hologram 37
… Objective lens, 38… Disc, 39… Wire, 40
... electrode surface, 41 ... wire bonding part, 42a, 42b
… Light flux, 43… scattered light, 50… facing surface, 51, 101a, 101b
... non-reflective coating part, 102a, 102b ... dome-shaped convex part, 103a, 103b ... prism-shaped convex part, 104a, 104b ... lattice-shaped irregular part, 105a, 105b ... inclined part, 106 ... spacer such as solder layer, 107a, 107b: Rough surface.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akio Yoshikawa 1-1, Sachimachi, Takatsuki City, Osaka Prefecture Inside Matsushita Electronics Corporation (56) References JP-A-61-24031 (JP, A) JP-A Sho 64-35737 (JP, A) JP-A-5-307760 (JP, A) JP-A-59-171039 (JP, A) JP-A-5-90619 (JP, U) (58) Fields investigated (Int. G11B ^7/ 09-7/095 G11B 7/135

Claims (16)

(57) [Claims] A diffraction grating is provided near a semiconductor laser element, and a light beam reflected by a mirror for reflecting a laser light beam emitted from the semiconductor laser element and deflecting an optical path is made incident thereon, and emitted from the diffraction grating. An objective lens that converges the 0th-order and ± 1st-order light beams of the diffraction grating emitted from the deflecting optical element through which the 0th-order ± 1st-order light beams can pass, to the optical recording medium, and is reflected by the optical recording medium. And a light detector for receiving light beams deflected by the deflecting optical element through the objective lens, wherein the 0th-order and ± 1st-order light beams of the diffraction grating pass through an objective lens. A tracking error detection device for an optical head for obtaining an optical output corresponding to the ± primary light flux and obtaining a tracking error signal based on a difference between outputs corresponding to the ± primary light fluxes; In at least one of the ± first-order light beams reflected by the optical recording medium and passing through the objective lens, the deflection optical element, and the diffraction grating does not pass through the mirror, and A tracking error detecting device for an optical head, which is incident on a surface facing a diffraction grating and the incident region is a region that scatters or absorbs light. 2. An optical head tracking error detecting device according to claim 1, wherein said scattering or absorbing region is constituted by a wire bonding portion for supplying power to said semiconductor laser device. 3. The optical head tracking error detecting device according to claim 1, wherein said scattering or absorbing region is constituted by an anti-reflection coating portion provided on said semiconductor laser device. 4. The tracking error detecting device for an optical head according to claim 1, wherein said scattering or absorbing region is constituted by a dome-shaped convex portion provided on said semiconductor laser device. 5. An optical head tracking error detecting device according to claim 1, wherein said scattering or absorbing region is constituted by a prism-shaped convex portion provided on said semiconductor laser device. 6. The tracking error detecting device for an optical head according to claim 1, wherein said scattering or absorption region is constituted by a lattice-shaped uneven portion provided on said semiconductor laser device. 7. The semiconductor laser device according to claim 1, wherein the scattering region is formed by an inclined portion of the semiconductor laser device itself.
An optical head tracking error detection device according to any one of the preceding claims. 8. The tracking error detecting device for an optical head according to claim 1, wherein said scattering or absorption region is constituted by a rough surface portion provided on said semiconductor laser device. 9. A diffraction grating which is close to the semiconductor laser element and receives a light beam reflected by a mirror which reflects a laser light beam emitted from the semiconductor laser element and deflects an optical path, and emits the light beam from the diffraction grating. An objective lens that converges the 0th-order and ± 1st-order light beams of the diffraction grating emitted from the deflecting optical element through which the 0th-order ± 1st-order light beams can pass, to the optical recording medium, and is reflected by the optical recording medium. And a light detector for receiving light beams deflected by the deflecting optical element through the objective lens, wherein the 0th-order and ± 1st-order light beams of the diffraction grating pass through an objective lens. A tracking error detection device for an optical head for obtaining an optical output corresponding to the ± primary light flux and obtaining a tracking error signal based on a difference between outputs corresponding to the ± primary light fluxes; Wherein at least one of the ± first-order light beams reflected by the optical recording medium and passing through the objective lens, the deflection optical element, and the diffraction grating does not pass through the mirror but sandwiches the mirror. A tracking error detecting device for an optical head, wherein the light is incident on a surface opposite to the diffraction grating on a side opposite to the semiconductor laser element, and the incident region is a region that scatters or absorbs light. 10. The tracking error detecting device for an optical head according to claim 9, wherein said scattering or absorbing region is constituted by a wire bonding portion to said incident region. 11. The tracking error detecting device for an optical head according to claim 9, wherein said scattering or absorption region is constituted by an anti-reflection coating portion applied to said incident region. 12. The tracking error detecting device for an optical head according to claim 9, wherein said scattering or absorbing region is constituted by a dome-shaped convex portion provided on said incident region. 13. An optical head tracking error detecting device according to claim 9, wherein said scattering or absorbing region is constituted by a prism-shaped convex portion provided on said incident region. 14. An optical head tracking error detecting device according to claim 9, wherein said scattering or absorbing region is constituted by a lattice-shaped uneven portion provided on said incident region. 15. The optical head tracking error detecting device according to claim 9, wherein the scattering region is constituted by an inclined portion of the incident region itself. 16. The scattered or absorbed region is constituted by a rough surface portion applied to the incident region.
An optical head tracking error detection device according to any one of the preceding claims.