JPH06103632A - Optical pickup device - Google Patents

Abstract

PURPOSE:To enable further miniaturization and to improve environmental resistance. CONSTITUTION:An optical wave guide element 7 being a detection means for detecting magneto-optical signals and signals for error control is constituted into an integral structure and thus the number of parts is reduced. Also, since at least the optical wave guide element 7, a light source 1 and a hologram 3 are fixed to a same package 8, the device can be miniaturized and made light in weight and also the positional relation of the respective parts 1, 3 and 7, etc., is stably maintained.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art As an optical pickup device for a magneto-optical disk, the one shown in FIG. 8 has been known at the beginning ("Optical disk system" edited by the Japan Society of Applied Physics and the Optical Conference (198
9) Chapter 10, 2.2). This optical pickup device has a semiconductor laser 206, and the multimode laser light emitted from the semiconductor laser 206 passes through a collimator lens 205 and a beam shaping prism 204, a polarizing beam splitter 203, and is reflected by a mirror 202 to be an objective. It is focused on the magneto-optical disk by the lens 201.

The reflected light from the magneto-optical disk is again the objective lens 201, the mirror 202 and the polarization beam splitter 203.
After passing through, the second polarization beam splitter 207 splits the light into magneto-optical signal detection light and control signal detection light. The former magneto-optical signal detection light further passes through the half-wave plate 211 and the lens 212, and is split into two orthogonal linearly polarized lights by the polarization beam splitter 213.
4, 215, where the magneto-optical signal recorded on the magneto-optical disk is detected. On the other hand, the latter control signal detection light is captured by the photodiode array 210 via the lens 208 and the cylindrical lens 209, and the signal obtained by the photodiode array 210 is used for tracking error detection and focus error detection.

Since the optical pickup device configured as described above is large and heavy, it is required to be compact and lightweight.

As an optical pickup device for a magneto-optical disk, which is obtained by further reducing the size and weight of the optical pickup device shown in FIG. 8, the one shown in FIG. 9 is known (Sharp Technical Report No. 50).
Issue (1991) P. 20). This optical pickup device is configured as follows.

That is, the light emitted from the semiconductor laser 61 as the light source passes through the hologram 62, the collimator lens 63, the shaping prism 64 and the polarization beam splitter 65,
The direction is changed by the mirror 66, and the light is focused on the magneto-optical disk 68 by the objective lens 67. The light reflected by the magneto-optical disk 68 passes through the objective lens 67 and the mirror 66 and is incident on the polarization beam splitter 65, where it is split into control signal detection light and magneto-optical signal detection light.

The control signal detection light is a polarization beam splitter.
65 and shaping prism 64 and collimator lens 63
The light is condensed by the hologram, then enters the hologram 62, and is diffracted there. The light diffracted by the hologram 62 is
It is divided into three parts by the difference in the grating period and is guided to the four photodiodes 69. These photodiodes
The signal detected at 69 is used for tracking error detection and focus error detection. On the other hand, the magneto-optical signal detection light is guided to the magneto-optical signal detector 72 through the Wollaston prism 70 and the spot lens 71, where the magneto-optical signal is detected. A part of the light that has entered the shaping prism 64 is given to the monitor detector 73.

In the optical pickup device having such various optical systems, the semiconductor laser 61 and the signal detecting photodiode 69 are mounted on a common stem and housed in one package 74, and the hologram 62 is The semiconductor laser 61, the photodiode 69, and the hologram 62 are integrated with each other by being adhesively fixed to the upper surface of the package 74. Therefore, this optical pickup device is made compact and lightweight by the above-mentioned integration, and the positional relationship of each optical system is stable irrespective of the use environment, so that the environmental resistance performance is improved.

Further, as an optical pickup device which has been made smaller and lighter, an optical pickup device for a magneto-optical disk utilizing an optical waveguide has been proposed in addition to FIG. 9 (Japanese Patent Laid-Open No. 63-188844). This optical pickup device is shown in FIG.
As shown in FIG. 11, the functions of the beam splitter, the lens, the prism, the photodiode, the half mirror, and the like are obtained by one optical waveguide element having a condensing diffraction grating. Specifically, a light source 116 that irradiates a surface 114 of a magneto-optical disk 113 with a linearly polarized light beam, and a lens 115 that collimates the light beam.
, An objective lens 118 for focusing on the surface 114 of the magneto-optical disk 113, and an optical waveguide element arranged in such a direction that the reflected beam reflected by the magneto-optical disk 113 is received on one surface.
122 and.

At the reflected beam irradiation position on the surface of the optical waveguide device 122, first, second, and third converging diffraction gratings 131, 132, 133 on which the reflected beam is respectively incident are arranged in parallel. ing. The first and second converging diffraction gratings 131 and 132
Are arranged along an axis that passes through substantially the center of the reflected beam with which the optical waveguide element 122 is irradiated and that extends on the surface at a substantially right angle to the tracking direction, and each of the waveguides is either TE or TM. It is formed so as to excite the modes and focus the reflected beams guided in the optical waveguide element 122 in the same waveguide mode at positions separated from each other with the axis interposed therebetween. On the other hand, the third converging diffraction grating 133 has the first
And a guided mode different from the guided mode by the second converging diffraction gratings 131 and 132 to cause the reflected beam to enter the optical waveguide element 122, and to reflect inside the optical waveguide element 122. It is formed so as to focus the beam within the optical waveguide element 122.

Further, on the surface or the end face of the optical waveguide element 122, a first detecting beam for each of the reflected beams focused by the first, second and third converging diffraction gratings 131, 132, 133 is detected. , Second and third photodetectors 124, 125,
126 is installed. Further, an amplifier group 137 for inputting output signals from the first and second photodetectors 124, 125, and tracking error control for controlling tracking error and focus error based on the output from the amplifier group 137, respectively. A system 135 and a focus error control system 136, and a reading system 134 for reproducing recorded information based on the difference between the output from the amplifier group 137 and the output from the third photodetector 126 are provided.

In the optical pickup device shown in FIGS. 10 and 11, the optical waveguide element 122, which is the main part of the optical pickup device, has a substrate 123.
Since it is a planar type that is provided on the same surface, it can be mass-produced easily and the cost can be significantly reduced.

[0013]

However, the optical pickup device shown in FIG. 9 and the optical pickup device shown in FIGS. 10 and 11 have the following problems.

That is, in the optical pickup device shown in FIG. 9, a servo error signal detecting photodiode is used.
By arranging 69 in the same package 74 as the semiconductor laser 61, the size and weight are reduced, but this is because the reflected light from the magneto-optical disk is divided into two by the polarization beam splitter 65 and travels in different optical paths. It is a fundamental obstacle to miniaturization.

On the other hand, in the optical pickup device shown in FIGS. 10 and 11, the optical waveguide element 122 is used for miniaturization, but the optical waveguide element 122 is arranged obliquely, so that it is structurally structured. It will be large, and the need for position adjustment will come out. Further, since the light source 116 is separated from the photodetectors 124, 125, 126, and the light source 116 is considerably separated from the optical waveguide 122, they are not fully integrated and the environmental resistance is poor.

As described above, in the two conventional optical pickup devices, there is still room for downsizing.

The present invention has been made to solve the problems of the prior art, and an object thereof is to provide an optical pickup device which is further miniaturized and which is excellent in environmental resistance.

[0018]

An optical pickup device according to the present invention records a light source and a beam from the light source into a plurality of beams, which are condensed on a recording medium having a magneto-optical signal recorded thereon. An optical system that transmits a plurality of reflected lights from a medium, a diffractive element that is provided on the optical path of the optical system that a plurality of reflected light passes, and diffracts each reflected light, and a plurality of reflections diffracted by the diffractive element It is arranged in a state that light is incident, and forms an integrated structure having an optical waveguide including a portion that polarizes and separates one of a plurality of incident reflected lights into two, and a portion that guides the remaining reflected light as it is, A detecting means for detecting the magneto-optical signal based on the two lights polarized and separated by the optical waveguide and detecting an error control signal based on the remaining reflected light;
At least the detection means, the light source, and the diffractive element are fixed in the same package, whereby the above-mentioned object is achieved.

[0019]

According to the present invention, the detecting means for detecting the magneto-optical signal and the error controlling signal are constructed as an integral structure, and therefore the number of parts is reduced. Further, since at least the detecting means, the light source and the diffractive element are fixed in the same package, the size and weight can be reduced, and the positional relationship among the detecting means, the light source and the diffractive element can be kept stable.

[0020]

EXAMPLES Examples of the present invention will be specifically described below.

(Embodiment 1) FIG. 1 shows the configuration of an optical pickup device of this embodiment. The basic structure of this device is the hologram laser unit (Op
tical Storage and Scanning Tecnology Proc. SPIE 13
9, p. P161-168 (1989)), which incorporates a miniaturized magneto-optical signal detection system using an optical waveguide. Specifically, it is as follows.

That is, laser light emitted from a light source 1 made of a semiconductor laser is divided into three by a diffraction grating 2, passes through a hologram 3 as a diffraction element, a collimator lens 4 and an objective lens 5 and is condensed on a magneto-optical disk 6. To be done. The reflected light from the magneto-optical disk 6 passes through the objective lens 5 and the collimator lens 4 again, is diffracted by the hologram 3, and is incident on the optical waveguide element 7 as a detecting means. At this time, the three divided incident lights are guided to the grating couplers 11, 12, and 13 of the optical waveguide device 7 configured as shown in FIG. 2, and thereafter, pass through the optical waveguide and the photodiode on the optical waveguide. The light is focused toward the 14a, 14b, 14c, 14d, 14e, 14f side.

The optical waveguide element 7 is fixed inside the package 8 via a fixture not shown, and the light source 1 is fixed inside the package 8. In addition, a support member 9 made of a transparent material is provided in the upper opening of the package 8.
Is attached, the diffraction grating 2 is attached to the lower surface of the support 9, and the hologram 3 is attached to the upper surface.

The optical waveguide element 7 is integrated and formed on one substrate, and has the optical waveguide on the substrate. Further, the light emitted from the grating couplers 11, 12, 13 is guided through the optical waveguide, and the photodiodes 14a,
It is designed to be captured by 14b, 14c, 14d, 14e and 14f. The three grating couplers 11, 12 and 13 are formed at positions on the optical waveguide element 7 corresponding to the divided three beams. The central grating coupler 11 is for the main beam, and the grating couplers 12 and 13 at both ends are sub-beams. It is for.

The grating coupler 11 at the center has a polarization separating function, which is different from the grating couplers 12 and 13 at both ends. Specifically, the grating coupler 11
Are two regions I and II with different grating pitches
It is divided into Also, the grating coupler 11
In one of the regions I and II excites TE light and the other in TM light, and excites the light excited in the region I into the photodiodes 14a and 14a.
It is designed to collect light in the gap between the photodiodes b and b and collect the light excited in the region II in the gap between the photodiodes 14c and 14d. Further, the grating couplers 12 and 13 at both ends are designed to be focused on the photodiodes 14e and 14f at both ends, respectively.
The track error signal is detected by the 3-beam method. The focus error signal is detected by the Foucault method using the four photodiodes 14a, 14b, 14c and 14d in the center.

Here, each photodiode 14a, 14b,
If the detection outputs of 14c, 14d, 14e, and 14f are A to F,
The track error signal RES is obtained by the following equation 1, the focus error signal FES is obtained by the equation 2, and the magneto-optical signal RF is obtained by the equation 3.

RES = EF (1) FES = (A + D)-(B + C) (2) RF = (A + B)-(C + D) (3) It should be noted that FIG. FIG. 3 shows a state in which the magneto-optical disk is far from the focal point,
FIG. 4 shows a condensed state when the magneto-optical disk is closer than the focal point.

In the optical pickup device of this embodiment having the above-described structure, the optical waveguide element 7 serving as the detecting means including the magneto-optical signal detecting system and the error signal detecting system uses the optical waveguide to form the same substrate. Since it is formed by being integrated on the top, the number of parts is reduced. Further, since at least the optical waveguide element 7, the light source 1 and the hologram 3 which is a diffraction element are fixed in the same package 8, further size reduction and weight reduction can be achieved, and the positional relationship among the respective components 1, 3, 7, etc. By being kept stable, the environmental resistance performance is improved.

(Embodiment 2) FIG. 5 is a plan view of an optical waveguide device as a detecting means provided in an optical pickup device according to another embodiment of the present invention. The optical pickup device of this embodiment has the same configuration as that of the first embodiment, except for the optical members other than the optical waveguide device. The optical waveguide device has three grating couplers 51, 52, 53, eight photodiodes 54a to 54h, and a mode splitter 55. The grating couplers 52 and 53 at both ends are connected to the photodiodes 54 without passing through the mode splitter 55.
Guide light to e and 54f. Further, in the central grating coupler 51, after the light emitted from this is split into two TE light and two TM light by the mode splitter 55, each light is guided to the photodiodes 54a to 54d, 54g, 54h. Is configured.

The mode splitter 55 can be realized by using, for example, a tapered waveguide (Kihara et al., H3 Autumn Response Proceedings 10p-ZN-9, magneto-optical signal detecting element for optical integrated pickup). Mode splitter 55 in this embodiment
As shown in FIG. 6 (cross-sectional view), is formed on a substrate (or a buffer layer on the substrate) 83 serving as a base of the optical waveguide device in a state where the waveguide layer 82 has a taper 82a at an end, Furthermore, another waveguide layer 81 is formed on the waveguide layer 82,
A via the taper joint C along the taper 82a
The region 84 and the B region 85 are combined.

In this structure, the inclination of the taper coupling portion C, that is, the thickness t of the waveguide layer 82 / the length L of the taper 82a in the direction along the substrate (or buffer layer) 83 is about 1/10.
If the following is very gentle, the light wave will not be partially reflected or mode-converted at the boundary of the tapered coupling portion C. Further, for example, when light of a guided mode having an equivalent refractive index of NA in the A region 84 and B in the B region 85 enters the taper coupling portion C from the A region 84 at an incident angle θ, the light is critical. Total reflection or total transmission is performed with the angle θc {θc = sin ⁻¹ (NB / NA)} as a boundary. At this time, if the critical angle of the TE _O mode is θ _CE , the critical angle of the TM _O mode is θ _CM , and the incident angle θ is θ _CE <θ <θ _CM , the optical waveguide element is TE at the boundary portion. It becomes a TE / TM mode splitter in which the _O mode is totally reflected and the TM _O mode is totally transmitted.

For the above reason, in the mode splitter 55 of this embodiment, the inclination of the taper coupling portion C is set so that the incident angle θ satisfies θ _CE <θ <θ _CM . Therefore, when the light guided from the central grating coupler 51 to the waveguide layer 82 is guided to the tapered coupling portion C, the TE light is reflected by the mode splitter 55 due to the difference in critical angle, as shown in FIG. TM light is transmitted through the waveguide layer 82 and propagates to the waveguide layer 81. At this time, the mode splitter 55 has two line segments 55a and 55b and is bent, and its corner exists within the width of the light guided from the grating coupler 51 to the waveguide layer 82. Therefore, one line segment 55a has T
E light and TM light are formed, and TE on the other line segment 55b.
Light and TM light are formed. One of the two TM lights formed is condensed between the photodiodes 54a and 54b,
The other TM light is condensed between the photodiodes 54c and 54d. In addition, the two TE lights formed are 54
It is focused on g and 54h. The waveguide layer 82 made of SiN is formed on the substrate (or buffer layer) 83 made of SiO _2.
And the waveguide layer 81 made of SiON, the extinction ratio of the TE _O mode is −26.2d.
B, a value of -24.8dB is obtained for the extinction ratio of the TM _O mode.

The focus error signal is detected by the Foucault method using the detection outputs of the photodiodes 54a to 54d. The photodiodes 54e and 54f detect the track error signal by the 3-beam method.

Here, the photodiodes 54a to 54d, 54
Assuming that the detection outputs of g and 54h are A ′ to D ′, G ′, and H ′, the track error signal RES is obtained by the following 4 equations, the focus error signal FES is obtained by 5 equations, and the magneto-optical signal RF is obtained by 6 equations. .

RES = E′−F ′ (4) FES = (A ′ + D ′) − (B ′ + C ′) (5) RF = (A ′ + B ′ + C ′ + D ′) − (G ′ + H Therefore, even in the optical pickup device of this embodiment, the detection means including the magneto-optical signal detection system and the error signal detection system is formed integrally on the same substrate by using the optical waveguide. Therefore, the number of parts is reduced. Although not shown in the present embodiment, since at least the optical waveguide element, the light source and the hologram are fixed in the same package, further miniaturization and weight reduction can be achieved, and each component, that is, the above-mentioned optical waveguide. Environmental resistance is improved by maintaining stable positional relationship among the waveguide element, the light source, the hologram, and the like.

[0036]

As described in detail above, according to the present invention, the number of parts can be reduced, the size and weight can be reduced, and the positional relationship between the parts can be stably maintained. It has the effect of improving the environmental performance.

[Brief description of drawings]

FIG. 1 is a front view (partial cross section) showing an optical pickup device of Example 1. FIG.

FIG. 2 is a plan view showing an optical waveguide device provided in the optical pickup device of FIG.

FIG. 3 is a plan view showing a condensed state in the optical waveguide device of FIG.

FIG. 4 is a plan view showing a condensed state in the optical waveguide device of FIG.

FIG. 5 is a plan view showing an optical waveguide device provided in the optical pickup device of Example 2.

6 is a cross-sectional view near a mode splitter provided in the optical waveguide device of FIG.

FIG. 7 is a plan view of the vicinity of a mode splitter provided in the optical waveguide device of FIG.

FIG. 8 is a schematic diagram showing an optical pickup device at the beginning of the related art.

FIG. 9 is a schematic diagram showing a conventional optical pickup device.

FIG. 10 is a front view schematically showing another conventional optical pickup device.

11 is a plan view showing an optical waveguide device provided in the optical pickup device of FIG. 10 together with an electric circuit.

[Explanation of symbols]

 1 Light source (semiconductor laser) 2 Diffraction grating 3 Hologram 4 Collimator lens 5 Objective lens 6 Magneto-optical disk 7 Optical waveguide element 8 Package 11-13 Grating coupler 14a-14f Photodiode 51-53 Grating coupler 54a-54h Photodiode 55 Mode splitter 61 Semiconductor laser 62 Hologram 63 Collimator lens 64 Shaping prism 65 Polarizing beam splitter 66 Mirror 67 Objective lens 68 Magneto-optical disk 69 Photodiode 70 Wollaston prism 71 Spot lens 72 Magneto-optical signal detector 73 Monitor detector 74 Package 81, 82 Waveguide layer 83 Substrate (or buffer layer) 113 Magneto-optical disk 115 Lens 116 Light source 117 Collimator lens 118 Objective lens 122 Optical waveguide element 123 Substrate 124 First photodetector 125 Second photodetector 126 Third photodetection Vessel 131 No. Condensing diffractive element 132 Second condensing diffractive element 133 Third condensing diffractive element 201 Objective lens 202 Mirrors 203, 207, 213 Polarizing beam splitter 204 Beam shaping prism 205 Collimator lens 206 Semiconductor laser 208, 212 Lens 209 Cylindrical lens 210 Photodiode array 211 Half-wave plate 214, 215 Photodiode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Renzaburo Miki 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation

Claims (1)

[Claims] 1. A light source, and an optical system that splits light from the light source into a plurality of lights, focuses the light on a recording medium on which a magneto-optical signal is recorded, and transmits a plurality of reflected lights from the recording medium. , A diffraction element that is provided on the optical path of the optical system through which a plurality of reflected lights pass and that diffracts each reflected light, and a plurality of reflected lights diffracted by the diffractive element are arranged to enter An integrated structure having an optical waveguide including a part for splitting and splitting one of the reflected light into two and a part for guiding the remaining reflected light as it is, is formed into two lights polarized and separated by the optical waveguide. And a detection means for detecting the magneto-optical signal based on the remaining reflected light and an error control signal based on the remaining reflected light, and at least the detection means, the light source and the diffractive element are fixed in the same package. Optical pickup device.