JPH0528570A - Magneto-optical pickup - Google Patents

Abstract

PURPOSE:To prevent a light receiving element in a compact and lightweight magneto-optical pickup from the deterioration of light receiving efficiency. CONSTITUTION:A semiconductor laser 50 exciting a laser beam toward an optical recording medium 16 and a wave-guide 30 having a polarization separating function are integrated into one body. Reflected light from the optical recording medium 16 is diffracted by a hologram optical element 12 and is made incident to the end face of the wave-guide 30. Then, the laser beam passes through the wave-guide 30 and the beam excited therefrom is detected by a light receiving part 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical pickup for recording a signal on an optical recording medium and / or reproducing the recorded signal, and more particularly to a compact and lightweight magneto-optical pickup.

[0002]

2. Description of the Related Art In general, a pickup for magneto-optical recording must detect a slight rotation of a polarization plane, unlike a read-only type such as a compact disc, and a prism for separating polarization, such as PBS ( A polarizing beam splitter) is required. As a result, the number of parts is increased, and the magneto-optical pickup itself is large and heavy.

In order to eliminate such drawbacks, a technique has been proposed in which a hologram element is used instead of a prism, and a light receiving element and a light emitting element are unitized to achieve a compact and lightweight magneto-optical pickup. ing.
For example, in Japanese Patent Laid-Open No. 1-229437, FIGS.
A thin-film magneto-optical pickup as shown in 1 is disclosed. Hereinafter, the configuration of the conventional magneto-optical pickup will be described with reference to these drawings.

In the semiconductor laser used in this magneto-optical pickup, a light receiving element and a light emitting element are integrally formed on a semiconductor substrate. That is, as shown in FIG. 11, two light receiving elements 2a to 2d are formed on both sides of the central portion of the active layer 1 which emits a laser beam.

Then, as shown in FIG. 10, the laser beam emitted from the active layer 1 in the central portion of the semiconductor laser is
The light is focused on the track of the optical disk 7 via the hologram diffraction grating 3 and the condenser lens 5. Then, the reflected light from the optical disk 7 enters the hologram diffraction grating 3 via the condenser lens 5. The hologram diffraction grating 3 is configured to generate an astigmatic difference, and the reflected light incident on the hologram diffraction grating 3 is the light receiving elements 2a to 2d.
It is diffracted to project a light spot on. The light receiving elements 2a to 2d detect the reflected light from the optical disk. As described above, since the hologram element is used and the light receiving element and the light emitting element are integrally formed, it is advantageous in terms of size and weight compared to the magneto-optical pickups used so far.

[0006]

As described above, by integrally providing the light receiving element and the light emitting element on the semiconductor substrate, the magneto-optical pickup can be made quite small and lightweight. However, since the reflected light from the optical disk is received by the active layer portion of the semiconductor laser structure, the following problems are raised. Generally, the active layer of a semiconductor laser is
Due to the mode control, it cannot be made too thick, and is usually about 0.07 μm. On the other hand, the spot diameter of the reflected light from the optical disk in the light receiving element is several μm or more even if the light is narrowed down by the hologram optical element.
That is, since the area of the light receiving surface is extremely small with respect to the spot size, the light receiving efficiency is poor and most of the reflected light cannot be received. Further, along with this, the S / N ratio also deteriorates, which makes it difficult to detect a signal when the reflected light is received. Therefore, in the above conventional example, it is very difficult to obtain practical performance as a magneto-optical pickup.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a compact and lightweight magneto-optical pickup which does not cause a decrease in light receiving efficiency and S / N ratio. And

[0008]

In order to solve the above-mentioned problems, the magneto-optical pickup of the present invention has a laser light source for emitting a laser beam toward an optical recording medium and a light guide having a polarization separation function. An element integrating a wave layer, an optical element that allows reflected light from the optical recording medium to enter the waveguide layer, and a light detection unit that detects light emitted from the waveguide layer. Is characterized by.

[0009]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a diagram showing the outline of the present invention.
The main components of the magneto-optical pickup according to the present invention are an element 20 in which a semiconductor laser 50 and a polarization separation function waveguide 30 (hereinafter referred to as a waveguide or a waveguide layer) are integrated, and a hologram. Optical element 12 and objective lens 1
4 and the light receiving unit 10. And the semiconductor laser 5
The laser light emitted from 0 is the hologram optical element 1
2. The light is condensed on the track 17 of the optical recording medium 16 via the objective lens 14, and the reflected light therefrom is detected by the light receiving unit 10 via the objective lens 14, the hologram optical element 12, and the waveguide 30. It is like this. These components will be described in detail below.

FIG. 2 shows the structure of a prototype semiconductor laser 50. The wavelength was designed at 790 nm. A Si-doped n-Al _0.45 Ga _0.55 As layer 52 was epitaxially grown to a thickness of 1.5 μm on a 350 μm thick gallium arsenide substrate 51 by MOCVD. An Al _0.15 Ga _0.85 As layer 53 was grown thereon to a thickness of 0.07 μm. In addition, Zn-doped p
An -Al _0.45 Ga _0.55 As layer 54 and a p-GaAs layer 55 were grown to a thickness of 1.5 μm and 0.5 μm, respectively.
Then, p-Al _0.45 Ga _0.55 A is left, leaving a width of 5 μm.
The s layer 54 was partially etched. At this time, p-A
The l _0.45 Ga _0.55 As layer 54 has a convex cross section,
The p-GaAs layer 55 was formed on the protruding portion. A Si-doped n-GaAs layer 56 was grown on both of the protruding sides so that the heights were equal to each other to form a current blocking layer. And p-GaAs
On the layer 55 and the n-GaAs layer 56, Ti, Pt,
Au was sequentially deposited to form a Ti layer, a Pt layer, and an Au layer, and then heated at 450 ° C. to be alloyed to form an electrode. Then, this laser diode portion was removed by etching up to the gallium arsenide substrate 51, leaving a width of 300 μm, to manufacture a semiconductor laser 50.

A waveguide 30 is provided on both sides of the semiconductor laser 50 so as to extract components in polarization directions orthogonal to each other.
Are formed by using a sputtering method, a CVD method or the like.
FIG. 3 is a diagram showing the concept of the waveguide used in this embodiment. A second waveguide 44 in which both TE and TM modes propagate is formed on the substrate with the cladding layer 46 sandwiched therebetween. On the second waveguide 44, the TE layer with the cladding layer 42 sandwiched is formed.
A first waveguide 40 in which only modes propagate is formed. All the return light from the hologram optical element once enters the first waveguide 40, but only the TE mode light propagates and the TM mode light does not proceed in the first waveguide 40 and escapes to the lower side. And propagates in the second waveguide 44.

FIG. 4A shows a concrete structure of the waveguide 30 formed on the gallium arsenide 51. This has a seven-layer structure except for the gallium arsenide substrate 51. The uppermost SiO ₂ layer 37 having a thickness of 5.3 μm and the glass layer 32 having a thickness of 1 μm are the first waveguide 37 and the first waveguide 37, respectively. The two waveguides 32 are configured. All the return light from the hologram optical element is once incident on the SiO ₂ layer 37. Then, the incident light, the thickness of each formed in a 0.1 [mu] m, and functions as a cladding layer, TiO ₂ layer 36, S
It is confined by the iO ₂ layer 35 and the TiO ₂ layer 34. However, this can guide only a limited guided mode, in the case of this structure, only the TE mode, and the light in the TM mode cannot be guided but leaks downward. The light leaked downward passes through the SiO ₂ layer 33 having a thickness of 2.5 μm and has a thickness of 1.
It is trapped in the glass layer 32 formed on the 5 μm SiO ₂ layer 31. The lights thus separated propagate in the waveguide layers 37 and 32, respectively, and are emitted from the end faces of the waveguide layers.

A waveguide in which two types of layers having different refractive indexes are multilayered also exhibits birefringence, and the TE and TM modes have significantly different refractive indexes when propagating. Utilizing this property,
If a waveguide having the same effective refractive index as the TM mode is provided under these multilayer waveguides, only the TM mode light is coupled with the lower waveguide and guided.

FIG. 4B shows a concrete structure of the waveguide layer for obtaining such an effect. 2μ thick on substrate 51
An m ₂ SiO ₂ layer 52 is formed, a Si ₃ N ₄ layer 53 having a refractive index of 2.0 is formed as a second waveguide layer with a thickness of 600 nm, and a core layer is formed thereon. 1 μm SiO
_Two layers 54 are formed. Then, on the SiO ₂ layer 54, a TiO ₂ layer 56 having a refractive index of 2.49 and a SiO ₂ layer 58 having a refractive index of 1.47 are alternately arranged in 26 layers (total thickness 1.3 μm). ) Laminate to form the first waveguide layer 60. In the waveguide having such a configuration, when the return light from the optical recording medium is incident on the first waveguide layer 60, only the TE mode light is emitted from the first waveguide layer 60 to the second waveguide layer 60.
Only the TM mode light can be extracted from the waveguide layer 53.

FIG. 5 specifically shows the structure of the light receiving portion 10. The reflected light from the optical recording medium that has entered the hologram optical element is diffracted so as to enter the end face of the first waveguide layer 37 (60) of the left and right polarization separation function waveguides 30 as shown in the figure. It As described above, the light incident on the first waveguide layer 37 (60) is separated into TE and TM modes, and the first waveguide layer 37 (60) and the second waveguide layer 32 (53) are separated. Eject from the rear end face. Then, the emitted light is detected by the light receiving unit 10 to obtain a magneto-optical signal, a focus error signal, and a track error signal.

A method of detecting each of the above signals will be described with reference to FIGS. 5 and 6. The light receiving unit 10 is divided into three photodetectors PD1 to PD3 and PD4 to PD6 that detect TE mode light, and two photodetectors PD8a, PD8b and PD9 that are divided into two to detect TM mode light.
a, PD9b. The magneto-optical signal is
It is detected by taking the difference between the combined signal of the left and right TE mode members and the combined signal of the left and right TM mode members. The focus error signal is detected by receiving the spread of light in the left and right TE modes after passing the waveguide by the beam size method and taking the difference. The track error signal is detected by the push-pull method by taking the difference between the sum of the signals on the outside and the sum of the signals on the inside of the photodetector divided into two parts on the left and right sides. In addition,
The track of the optical recording medium is set to be perpendicular to the straight line connecting the waveguides on both sides of the semiconductor laser 50. The PD7 shown in the figure is
This is for monitoring the emitted light of the semiconductor laser.

With reference to FIG. 7, the positional relationship between the above-mentioned components and the operation thereof will be described. The gallium arsenide substrate prepared by the above method is polished and thinned to facilitate cleavage from the substrate side. Then, the end faces of the semiconductor laser and the waveguide are exposed by the cleavage. A hologram optical element 12 is arranged in front of the element 20 in which the semiconductor laser and the polarization separation function waveguide are integrated. Further in front of it, an objective lens 14 having a tracking coil 15a and a focusing coil 15b is arranged.

When reproducing information, the linearly polarized light emitted from the semiconductor laser is returned by the rotation of the plane of polarization of the optical recording medium 16. This reflected light is diffracted by the hologram optical element 12 and is condensed on the end faces of the waveguides formed on the left and right of the semiconductor laser. Since the waveguide has the same thickness as the spot diameter of the diffracted light by the hologram optical element 12, the light is not wasted. A 1 / 2λ plate is attached to each end face of the waveguide, and the optical axis of the wave plate is set so as to rotate the polarization plane by 45 degrees. The light whose polarization plane is rotated by 45 degrees is generated in the waveguide by the TE mode, TM
It is divided into modes and detected by the light receiving unit 10. Then, the amount of light received by each photodetector is converted into an electrical signal, and based on these signals, the coils 15a,
A control current is passed through 15b. As a result, the convergent light from the objective lens 14 is always reflected on the track 17 of the optical recording medium 16.
The recording domain 18 is controlled to be in focus, and at the same time, information recording / reproduction is performed.

Information is erased and new writing is performed on the optical recording medium by applying a laser beam while applying a magnetic field from the outside with a coil, a permanent magnet or the like, as in the conventional general magneto-optical pickup. The reversal of the magnetization of the medium recording layer by increasing the power is used.

FIG. 8 shows a modification of the element 20 in which the semiconductor laser 50 and the waveguide 30 are integrated. In the above-described embodiment, the ½λ plate is placed before the diffracted light from the hologram optical element 12 is incident on the end face of the waveguide 30, and the polarization plane is rotated by 45 degrees. In this modification, 1
The / 2λ plate 30a is arranged in front of the semiconductor laser 50, and the polarization plane is inclined by 45 degrees before reaching the optical recording medium. Other configurations are similar to those of the above-described embodiment.

In the device 20, for example, as shown in FIG. 9, a device in which a waveguide 30a is formed on the left and right sides of a Si substrate 51a and a semiconductor laser 50a are manufactured separately, and then the semiconductor laser 50a is manufactured by Si. It may be configured by being attached to the substrate 51a.

[0023]

As described above, according to the present invention, it is possible to obtain a compact and lightweight magneto-optical pickup having a small number of parts and a high S / N ratio of a magneto-optical signal.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a magneto-optical pickup according to the present invention.

2 is a schematic diagram of the magneto-optical pickup shown in FIG.
It is a figure which shows the structure of a semiconductor laser.

FIG. 3 is a diagram showing an outline of a waveguide having a polarization separation function.

4A is a diagram showing a structure of a waveguide having a polarization separation function in the magneto-optical pickup shown in FIG. 1, and FIG. 4B is a diagram showing a modified example thereof.

5 is a schematic diagram of the magneto-optical pickup shown in FIG.
It is a figure which shows the structure of the element which integrated the semiconductor laser and the waveguide provided with the polarization separation function, and the light-receiving part.

6A and 6B are diagrams showing a method of detecting a signal in a light receiving unit, FIG. 6A is a magneto-optical signal, FIG. 6B is a focus error signal, and FIG. 6C is a diagram showing a track error signal.

FIG. 7 is a diagram showing a configuration of a magneto-optical pickup according to the present invention.

FIG. 8 is a view showing a modified example of an element in which a semiconductor laser and a waveguide having a polarization separation function are integrated.

FIG. 9 is a diagram showing yet another modified example of an element in which a semiconductor laser and a waveguide having a polarization separation function are integrated.

FIG. 10 is a diagram showing a configuration of a conventional magneto-optical pickup.

11 is a diagram showing a configuration of a light emitting / receiving unit in the magneto-optical pickup shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Light receiving part, 12 ... Hologram optical element, 16 ... Optical recording medium, 20 ... Element which integrated semiconductor laser and polarization separation function waveguide, 30 ... Polarization separation function waveguide, 50
… Semiconductor laser.

Claims (1)

Claim: What is claimed is: 1. An element integrating a laser light source for emitting a laser beam toward an optical recording medium and a waveguide layer having a polarization separation function, and reflection from the optical recording medium. A magneto-optical pickup comprising: an optical element that causes light to enter the waveguide layer; and a photodetection unit that detects light emitted from the waveguide layer.