JP3213651B2 - Optical pickup - Google Patents

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 and / or reproducing information on an optical recording medium such as an optical disk.

[0002]

2. Description of the Related Art As conventional optical pickups, for example, those shown in FIGS. 8 and 9 have been proposed. In this optical pickup, the divergent beam from the semiconductor laser 61 is collimated by a collimator lens 64,
The objective lens 65 is transmitted through the polarization beam splitter 71.
Converges on the magneto-optical recording medium 66. The return light reflected by the magneto-optical recording medium 66 is reflected by the objective lens 65.
After being reflected by the polarization beam splitter 71 through
The polarization direction is rotated by 45 degrees by the two-wavelength plate 76, and the trapezoidal prism 73 having a polarization separation function is passed through the condenser lens 72.
And the polarization separation surface 73 of the trapezoidal prism 73
The S-polarized light component reflected by a is received by the three-segment photodetector 75b on the substrate 74, and the P-polarized component transmitted through the polarization splitting surface 73a is received by the three-segment photodetector 75a on the substrate 74. I have. Thus, the photodetectors 75a, 75
Based on the output of b, a magneto-optical signal is detected from the difference between them, and a focus error signal is obtained by a beam size method.

As an optical pickup, the present applicant also
For example, Japanese Patent Application No. Hei 4-110022 proposes the one shown in FIGS. In this optical pickup, a semiconductor laser, a photodetector, and a hologram are unitized, and light emitted from this unit
In addition, the recording medium 84 is irradiated through the objective lens 83, and the return light reflected by the recording medium 84 follows the reverse path and enters the unit 81.

As shown in a sectional view of FIG. 11, a unit 81 is provided with a semiconductor substrate 86 provided on a substrate 85 and a hologram optical element 88 provided with a spacer 87 interposed therebetween. As shown in the plan view of FIG. 12, a semiconductor laser 89 is mounted on the semiconductor substrate 86, and three photodetectors 91, 3 are arranged on both sides of the semiconductor laser 89 in the x direction in the y direction. 92, 93 and 9
4, 95, 96 are formed, and the light detectors 92 and 95 at the center are respectively divided into three light receiving areas 92 in the y direction.
a, 92b, 92c and 95a, 95b, 95c. Further, the semiconductor laser 89 is provided as shown in FIG.
As shown in the partial cross-sectional view, the semiconductor laser 86 is mounted on a concave portion 86a formed by etching the semiconductor substrate 86, and the inclined surface 86b formed by etching the concave portion 86a is used as a mirror surface in a direction parallel to the plane of the semiconductor substrate 86. Are reflected by the mirror surface 86b in a direction substantially normal to the semiconductor substrate 86.

Further, as shown in FIG. 11, the hologram optical element 88 has a grating on its surface on the side of the semiconductor substrate 86 for separating the light beam from the semiconductor laser 89 into three light beams of 0-order light and ± 1st-order diffracted light. A hologram pattern 88b is formed on the opposite surface to diffract the return light from the recording medium 84 and to give the ± 1st order diffracted lights focal powers in opposite directions.

[0006] In this manner, the light emitted from the semiconductor laser 89 is reflected by the mirror surface 86b, and then separated by the grating 88a into three beams, one main beam and two sub beams. The light is radiated on a recording medium 84 via a stop 82 and an objective lens 83. Also,
The return lights of the three light beams applied to the recording medium 84 are respectively diffracted by the hologram pattern 88b along the reverse paths, and the ± 1st-order diffracted lights of the main beam are respectively detected by the central photodetectors 92 and 95. Received, and the ± 1st-order diffracted light of one of the sub-beams is detected, for example, by photodetectors 91 and 94.
Then, the ± 1st-order diffracted light of the other sub-beam is
And 96, respectively, to obtain a focus error signal by the beam size method based on the outputs of the photodetectors 92 and 95, and to track by the three beam method based on the outputs of the photodetectors 91, 93, 94 and 96. An error signal is obtained.

[0007]

However, in the optical pickup shown in FIGS. 8 and 9, the return light is reflected by the polarizing beam splitter 71 substantially 90 ° and received by the photodetectors 75a and 75b. Therefore, there is a problem that the optical path protrudes in a direction perpendicular to the optical path from the semiconductor laser 61 to the objective lens 65, and it is difficult to reduce the size of the device. Further, the semiconductor laser 61 and the photodetector 75
Since a and 75b are separate from each other, there is a problem in that relative displacement due to a change with time and a change in temperature is likely to occur, which makes it difficult to obtain high reliability.

Further, in the optical pickup previously proposed by the present applicant shown in FIGS. 10 to 13, a semiconductor laser 89, photodetectors 91, 92, 93, 94, 95, 96,
Since the hologram optical element 88 is integrated as a unit, the apparatus can be downsized and high reliability can be obtained.However, a specific configuration for obtaining a magneto-optical signal is mentioned. Not.

SUMMARY OF THE INVENTION The present invention has been made in view of the various problems described above. An optical pickup which is small in size, has high reliability, and is appropriately configured to stably detect a magneto-optical signal. The purpose is to provide.

[0010]

In order to achieve the above object, in an optical pickup according to the present invention, a semiconductor substrate having a semiconductor laser and a plurality of photodetectors is provided, and light from the semiconductor laser is magneto-optically recorded. An objective lens that converges on a medium, a hologram that is arranged as a unit integrated with the semiconductor substrate, diffracts return light that is reflected by the magneto-optical recording medium and enters through the objective lens, and divides a pupil of the hologram. As
An optical block having a polarization splitting surface provided substantially parallel to the optical axis of the 0th-order light of the hologram, wherein return light diffracted by the hologram and separated by the polarization splitting surface is reflected by the plurality of photodetectors. It is configured to receive light and detect a magneto-optical signal.

[0011]

An embodiment of the present invention will be described below with reference to the drawings. 1 to 7 show an embodiment of the present invention. This optical pickup includes a unit 1 having a semiconductor laser, a photodetector, a hologram, and a polarization splitting surface, and an objective lens 2. The unit 1 emits a linearly polarized beam, and the objective lens 2 uses the magneto-optical recording medium. 3, the return light reflected by the magneto-optical recording medium 3 is made to enter the unit 1 via the objective lens 2. In this embodiment, the direction parallel to the information track of the magneto-optical recording medium 3 is the y direction, the tracking direction orthogonal thereto is the x direction, and the direction of the linearly polarized light emitted from the unit 1 is the x direction. Be parallel.

The unit 1 is, as shown in FIG.
In addition, a semiconductor substrate 5 is provided, and an optical block 7 is provided via a spacer 6. The optical block 7 joins two triangular prism-shaped blocks 7a and 7b, forms a polarization separation surface formed by coating a dielectric multilayer film on the joint surface 7c, and forms the polarization separation surface on the objective lens 2 side of the blocks 7a and 7b. The return light from the magneto-optical recording medium 3 is diffracted on the surface so that the pupil is divided by the polarization splitting surface 7c as shown in FIG. Holograms 8a and 8b having a lens function of giving focal powers in the opposite directions to the next-order diffracted light are formed by etching or
It is formed by a P method or the like. Note that the polarization separation surface 7c is formed substantially parallel to the optical axis of the zero-order light of the holograms 8a and 8b and inclined at approximately 45 ° with respect to the polarization direction (x direction) of the beam emitted from the unit 1. Form the diffraction angle larger than the diffraction angle of the hologram 8a.

On the other hand, as shown in the plan view of FIG. 4, a concave portion is formed in the semiconductor substrate 5 by etching or the like, and a semiconductor laser 11 is mounted in the concave portion. The light flux emitted in the direction parallel to the vertical direction is reflected by the mirror 12 in a direction substantially normal to the semiconductor substrate 5 by raising the slope by etching the concave portion or the like. The semiconductor substrate 5 has a light receiving unit 1 for receiving ± first-order diffracted lights by the holograms 8a and 8b.
3, 14, 15 and 16 are provided. The light receiving sections 13 and 14 are divided into six light receiving areas 13a, 13b,
13c, 13d, 13e, 13f and 14a, 14
b, 14c, 14d, 14e, 14f,
Each of the light receiving units 15 and 16 has one light receiving area.

The operation of this embodiment will now be described with reference to the cross-sectional views taken along line BB of FIG. 3 shown in FIGS. 5 and 6 and the cross-sectional view taken along line CC of FIG. 3 shown in FIG. In this embodiment, light emitted from the semiconductor laser 11 mounted on the semiconductor substrate 5 is
After the light is reflected by the rising mirror 12 in a direction perpendicular to the semiconductor substrate 5, the light is transmitted through the holograms 8 a and 8 b, converged by the objective lens 2 on the magneto-optical recording medium 3, and returned by the magneto-optical recording medium 3. Light enters the holograms 8a and 8b via the objective lens 2.

The return light incident on the hologram 8a is diffracted by the hologram 8a, and as shown in FIGS.
The + 1st-order diffracted light is made incident on the light receiving areas 13d, 13e, and 13f, and the -1st-order diffracted light is made incident on the polarization splitting surface 7c.
The return light reflected by the polarization splitting surface 7c is incident on the light receiving unit 15 at d, 14e, and 14f, respectively. The return light incident on the hologram 8b is diffracted by the hologram 8b, and as shown in FIGS. 4, 6, and 7, the -1st-order diffracted light is incident on the light receiving regions 14a, 14b, and 14c, and the + 1st-order diffracted light Is incident on the polarization separation surface 7c, and the polarization separation surface 7c
Return light passing through the light receiving regions 13a, 13b, 13c
Then, the return light reflected by the polarization splitting surface 7c is incident on the light receiving unit 16 respectively.

Here, the diffraction angle of the hologram 8b is set larger than the diffraction angle of the hologram 8a.
The light receiving portions 13 of the holograms 8a and 8b for diffracted light,
The spot position on 14 is such that the diffracted light of the hologram 8 b is farther from the semiconductor laser 11. Also, since the holograms 8a and 8b have a pattern that gives the ± 1st-order diffracted lights focal powers in directions opposite to each other,
Light receiving areas 13a, 13b, 13c, 13d, 13e, 1
3f and 14a, 14b, 14c, 14d, 14e,
The size of the spot on 14f is equal when the recording surface of the magneto-optical recording medium 3 is in focus, and changes in opposite directions when the focus is shifted back and forth. Therefore, the light receiving areas 13a, 13b, 13c, 13d, 13
e, 13f and 14a, 14b, 14c, 14d, 1
4e and 14f are output to A1, A2, A3, A4, A
5, A6 and A7, A8, A9, A10, A11, A
When the focus error signal FES is 12, the focus error signal FES is

FES = (A1 + A4 + A8 + A9 + A11 + A12) − (A2 + A3 + A5 + A6 + A7 + A10)

In FIG. 1, since the track direction is perpendicular to the plane of the drawing, the light quantity distribution in the x-direction becomes asymmetric in the off-track state. Therefore, a push-pull signal can be obtained by taking the difference in the intensity of the diffracted light of the holograms 8a and 8b that divide the pupil. If the outputs of the light receiving units 15 and 16 are B1 and B2, the tracking error signal TES Is

TES = B1-B2 TES = (A4 + A5 + A6)-(A7 + A8 + A9)

On the other hand, in FIG. 1, the light emitted from the semiconductor laser 11 is linearly polarized light parallel to the x direction.
Further, since the polarization separation surface 7c is inclined by approximately 45 ° with respect to the polarization direction of the emitted light, as described above, the -1st-order diffraction light on the hologram 8a and the + 1st-order diffraction light on the hologram 8b are Is separated into transmitted light and reflected light. Therefore, the magneto-optical signal MOS calculates the difference between the transmitted light and the reflected light at the polarization separation surface 7c,

MOS = (A1 + A2 + A3 + A10 + A11 + A12)-(B1 + B2)

It should be noted that the present invention is not limited to the above-described embodiment, and that various modifications and changes are possible. For example, (A4 + A8 + A9), (A5 + A6 +
A7), (A1 + A11 + A12), (A2 + A3 +
A10) is set to a constant G so that the focus error signal FES is equal to the focus error signal FES.

FES = (A4 + A8 + A9) + G × (A1 + A11 + A12) − (A5 + A6 + A7) + G × (A2 + A3 + A10) In this case, the light passes through the polarization separation surface 7c and is received by the light receiving regions 13a, 13b, 13c, and 14
d, 14e, and 14f and the light receiving regions 13d, 13e, 13f, and 1 without passing through the polarization separation surface 7c.
4a, 14b, and 14c, the light amount difference between the light and the incident light can be adjusted, and the focus error signal FE is more stable.
S can be obtained.

The present invention is not limited to the finite optical system described above, but may be an infinite optical system, for example, by disposing a collimator lens between the unit 1 and the objective lens 2.

[0021]

As described above, according to the present invention, a semiconductor substrate having a semiconductor laser and a plurality of photodetectors,
Since the magneto-optical signal is obtained as a unit in which the hologram and the optical block on which the polarization separation surface is formed are integrated, it is possible to realize a small and high reliability and to stably detect the magneto-optical signal.

[Brief description of the drawings]

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

FIG. 2 is a perspective view showing the unit of FIG.

FIG. 3 is a view taken in the direction of arrow A in FIG. 2;

FIG. 4 is a plan view of the semiconductor substrate shown in FIG. 3;

FIG. 5 is a diagram for explaining the operation of the embodiment shown in FIG. 1;
It is B sectional drawing.

FIG. 6 is a sectional view taken along line BB of FIG. 3;

FIG. 7 is a sectional view taken along the line CC of FIG. 3;

FIG. 8 is a diagram illustrating an example of a conventional optical pickup.

FIG. 9 is a plan view of the substrate shown in FIG. 8;

FIG. 10 is a view showing an optical pickup proposed earlier by the present applicant.

FIG. 11 is a sectional view of the unit shown in FIG. 10;

FIG. 12 is a plan view of the semiconductor substrate shown in FIG. 11;

FIG. 13 is a partial sectional view of the same.

[Explanation of symbols]

Reference Signs List 1 unit 2 objective lens 3 magneto-optical recording medium 4 substrate 5 semiconductor substrate 6 spacer 7 optical block 7a, 7b block 7c polarization separation surface 8a, 8b hologram 11 semiconductor laser 12 rising mirror 13, 14, 15, 16 light receiving unit 13a, 13b, 13c, 13d, 13e, 13f and 14a, 14b, 14c, 14d, 14e, 14f
Light receiving area

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 5-28569 (JP, A) JP 5-28570 (JP, A) JP 4-372750 (JP, A) JP 4-A 295648 (JP, A) JP-A-4-255924 (JP, A) JP-A-3-178064 (JP, A) JP-A-3-150744 (JP, A) JP-A-6-309722 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B 11/00-13/08

Claims (2)

(57) [Claims] A semiconductor substrate having a semiconductor laser and a plurality of photodetectors, an objective lens for converging light from the semiconductor laser on a magneto-optical recording medium, and a unit integrated with the semiconductor substrate;
A hologram for diffracting return light reflected by the magneto-optical recording medium and entering through the objective lens, and polarized light provided substantially parallel to the optical axis of the zero-order light of the hologram so as to divide the pupil of the hologram. An optical block having a separation surface, wherein the return light diffracted by the hologram and separated by the polarization separation surface is received by the plurality of photodetectors to detect a magneto-optical signal. Optical pickup. 2. The optical pickup according to claim 1, wherein the hologram has a different pattern with the polarization splitting surface as a boundary.